Temporal changes in field calibration relationships for Aeroqual S500 O3 and NO2 sensor-based monitors Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-18 Nicola Masey, Jonathan Gillespie, Eliani Ezani, Chun Lin, Hao Wu, Neil S. Ferguson, Scott Hamilton, Mathew R. Heal, Iain J. Beverland
Sensor-based monitors are increasingly used to measure air pollutant concentrations, but require calibration under field conditions. We made intermittent comparisons (6 times over 6-month period) between ozone and nitrogen dioxide concentrations measured by Aeroqual gas-sensitive semiconductor (O3) and electrochemical (NO2) sensors (two of each) and reference analysers in the UK Automatic Urban and Rural Network. Each deployment period was split into equal (n = 48 h) training and test datasets, to derive and test calibration equations respectively. We observed significant bivariate linear relationships between Aeroqual O3 and Reference O3 concentrations, and significant multiple linear relationships between Aeroqual NO2 and both Reference NO2 and Aeroqual O3 concentrations. Changes in monitor responses over time (including apparent baseline drift in O3 sensor output, and discrepancies between the 2 Aeroqual NO2 sensors) resulted in relatively inaccurate concentrations estimates (cf. reference concentrations) from calibration equations derived in the first training period and applied to subsequent test deployments (e.g. NO2 RMSE = 47.2 μg m-3 (n = 286) for a dataset of all test periods combined, for one of the two monitor pairs). Substantial improvements in accuracy of estimated concentrations were achieved by combination of repeated intermittent training data into a single calibration dataset (NO2 RMSE = 8.5 μg m-3 for same test dataset described above). This latter approach to field calibration is recommended.
Synchronous Synthesis and Sensing Performance of α-Fe2O3/SnO2 Nanofiber Heterostructures for Conductometric C2H5OH Detection Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-17 Shuang Yan, Qingsheng Wu
A synthesis procedure based on single-capillary electrospinning and hard-template method was provided to synthesize hierarchical α-Fe2O3/SnO2 nanofibers. The samples exhibit unique microstructure where α-Fe2O3 nanoparticles were evenly decorated on three-dimensional SnO2 fibrous scaffold. During preparation, the α-Fe2O3 nanoparticles and SnO2 nanofibers were formed synchronously. Within the composite nanomaterials, the Fe/Sn content ratio can be adjusted by changing the diameter of SnO2 nanofibers backbone. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy and nitrogen adsorption-desorption analysis were used to characterize the structure of the synthesized products. By loading α-Fe2O3 nanoparticles, the grain growth of SnO2 was effectively restrained during heat treatment in air. The optimum Fe/Sn content ratio of α-Fe2O3/SnO2 heterostructures with the highest sensitivity was obtained through ethanol sensing measurements. Compared to pure α-Fe2O3 and SnO2 nanofibers, the binary composite nanofibers exhibits not only enhanced ethanol sensing response, but also higher dependence of response to the change of ethanol concentration. The remarkable improvement of sensing performance can be attributed to the synergetic effect of the component phases. The influences of heterojunctions on the gas sensing properties of α-Fe2O3/SnO2 nanofibers were discussed.
pH assisted selective detection of Hg(II) and Ag(I) based on nitrogen-rich carbon dots Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-17 Liang Luo, Pei Wang, Yuanhao Wang, Fu Wang
Novel nitrogen rich carbon dots were synthesized via a hydrothermal method by using with 2,4,6-triaminopyrimidine as the precursor. X-ray photoelectron spectroscopy showed that the carbon dots contained 41 at.% nitrogen; this is significantly higher than previously reported values for similar materials. When exposed to ultraviolet light, the carbon dots in solution emitted bright blue fluorescence, with a maximum quantum yield of 74.9%. The fluorescence was selectively quenched by Hg(II) at pH 6 and Ag(I) at pH 11, with detection limits of 11.4 and 10.3 nM, respectively. Analysis of the fluorescence lifetimes of the carbon dots showed that the fluorescence-quenching mechanism for Hg(II) differed from that for Ag(I). In analysis of lake water, the nitrogen-rich carbon dots were highly sensitive, and gave a wide linear range and satisfactory recovery. These results suggest that the carbon dots are suitable for use as novel metal ion probes for the selective detection of different ions at different pH values.
A dual-mode probe for colorimetric and fluorometric detection of cysteine based on phosphorus/nitrogen co-doped CQDs and gold nanorods Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-17 Yanying Wang, Ruoxuan Liang, Wei Liu, Qingbiao Zhao, Xiaoyan Zhu, Li Yang, Ping Zou, Xianxiang Wang, Fang Ding, Hanbing Rao
In this study a novel method was developed for the fluorescent and colorimetric determination of cysteine (Cys). The fluorescent determination was designed based on surface plasmon-enhanced energy transfer (SPEET), and phosphorus/nitrogen co-doped CQDs (PNCQDs) were employed as the donor, of which the fluorescence was quenched by gold nanorods (AuNRs) (acceptor). For the colorimetric assay, under the catalytic effect of Fe3+, AuNRs were effectively etched by OH· that was generated by the Fenton reaction. The etch of the AuNRs lead to the decrease in the absorbance intensity, the blue shift of longitudinal surface plasmon resonance (LSPR) absorption peak of AuNRs as well as the fluorescence of PNCQDs recovery. However, Cys can suppress this etching reaction by coordination effect between hydrosulfide group (-SH) in Cys and Fe3+, leading to red shift of the LSPR absorption peak. Similarly, the fluorescence will change with the absorbance. The peak shift and the fluorescence change can be applied to monitor of Cys. Under the optimal operation conditions, highly sensitive determination of Cys was achieved, with the fluorescent detection limit of 1.2 nM and the colorimetric detection limit of 0.9 nM. The linearity of the system towards Cys was in the range of 0.005-25 μM. The highly sensitive determination of Cys in urine samples demonstrates that this method possesses high potential for on-site and visual detection of urine Cys.
Glutathione Detection Based on Peroxidase-Like Activity of Co3O4–Montmorillonite Nanocomposites Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-17 Yan Gao, Kaili Wu, Hongyu Li, Wei Chen, Min Fu, Kang Yue, Xixi Zhu, Qingyun Liu
Co3O4 nanoparticles homogeneously anchored on montmorillonite (MMT) were synthesized via a facile hydrothermal method. Co3O4-MMT were demonstrated to possess intrinsic peroxidase- and weak oxidase-like activity, and employed as peroxidase mimics for the first time. The efficient catalytic activity of the Co3O4-MMT NCs may originate from the electron transfer among catalyst, TMB (3,3’,5,5’-tetramethylbenzidine) and H2O2. Furthermore, a sensitive colorimetric sensor for glutathione based on the peroxidase activity of Co3O4-MMT is proposed with a low detection limit of 0.088 µM. And the proposed method had been successfully applied in detecting GSH in human serum and reduced glutathione for injection solutions.
Facile Synthesis of Controllable TiO2 Composite Nanotubes via Templating Route: Highly Sensitive Detection of Toluene by Double Driving from Pt@ZnO NPs Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-17 Wei Liu, Lin Xu, Kuang Sheng, Xiangyu Zhou, Xinran Zhang, Cong Chen, Biao Dong, Xue Bai, Lu Geyu, Hongwei Song
Electrospinning is an effective way to fabricate ultralong nanotubes with a large surface area. However, the nanotubes synthesized through this way suffer from difficult controlling of structural parameters. A facile strategy for constructing highly controllable Pt@ZnO nanoparticles (NPs) drive TiO2 nanotubes (NTs) (Pt@ZnO-TiO2 NTs) was developed in this work. First, the polystyrene electrospun nanofibers (~490 nm) containing Pt@zeolitic imidazolate framework-8 (ZIF-8) was fabricated as a self-sacrificial template and then was decorated by a thinner tetrabutyl orthotitanate layer through soaking. After annealing, the Pt@ZnO NPs were obtained due to the decomposition of Pt@ZIF-8 during calcination. The involving of ZIF-8 can effectively prevent the aggregation of Pt during heat treatment (~3 nm, monodispersed), and thus highly improves its catalyst property. When Pt@ZnO-TiO2 NTs were evaluated as a sensing material for toluene detection, the obtained sensors exhibited an enhanced sensing response (11.1 to 1 ppm toluene), faster response/recovery times (7.5 and 20.1 s) and a lower detection limit (23 parts per billion) during dynamic measurement, when compared to the pristine TiO2 and directly mixed Pt-TiO2 NTs. This was mainly attributed to the improved oxygen vacancy concentration in the NT composite and resistance modulation effect induced by the unique NT structure, as well as the well-dispersed and small-sized Pt catalyst.
An aqueous methylated chromenoquinoline-based fluorescent probe for instantaneous sensing of thiophenol with a red emission and a large Stokes shift Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-17 Yani Geng, Huihui Tian, Liu Yang, Xingjiang Liu, Xiangzhi Song
A sensitive and selective fluorescent probe, MCQ-O-DNB, for the detection of thiophenol in aqueous media has been developed based on a methylated chromenoquinoline chromophore. This probe can instantaneously respond to thiophenol and reach to a balance within 2 min. In the detection process, this probe exhibited a large Stokes shift (108 nm) and a low detection limit (8.1 nM, based on S/N = 3). Importantly, practical application experiments demonstrated that this probe was able to detect thiophenol in real water samples and living cells.
Curcumin-based electrochemical sensor of amyloid-β oligomer for the early detection of Alzheimer’s disease Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-17 Jieling Qin, Jin Su Park, Dong Gyu Jo, Misuk Cho, Youngkwan Lee
Amyloid β oligomer (AβO) is a promising biomarker with potential to diagnose the Alzheimer’s disease (AD). To detect the low level of AβO is highly desirable for the early diagnosis of AD. Here we describe the fabrication and sensing performance of curcumin based AβO sensor. Curcumin-Ni was electropolymerized on Ni foam substrate, and the surface resistance change of the poly(curcumin-Ni) electrode depending on AβO concentration was confirmed by electrochemical impedance spectroscopy. The impedance response of the curcumin based sensor showed a proportional relationship with the concentrations of AβO in the range from 0.001 to 5 nM. The feasibility of the sensor was verified by the detection of AβO in artificial cerebrospinal fluid. The proposed AβO sensor presents valuable information related to early diagnosis of AD.
Nano-molar to milli-molar level Ag (I) determination using absorption of light by ZnS QDs without organic ligand Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-17 Rabindra Nath Juine, S. Amirthapandian, S. Dhara, A. Das
Despite of useful applications of Ag, it is hazardous to health and environment and hence early detection is required. Crystal defects influencing optical property is less likely utilized for Ag detection using prevalent UV-Vis technique. Quantum dots (QDs) ZnS prepared by soft chemical route are exploited for the detection of Ag+ in aqueous solution for nM to mM concentrations. UV-Vis and photoluminescence (PL) measurements reveal quantum confinement effect and presence of defects in ZnS nanoparticles (NPs). Controlled synthesis of ZnS NPs allows appearance of defects related peak at 400–550 nm in UV-Vis spectra. A plausible mechanism is presented and elucidated by XRD and PL studies for chemical interaction between ZnS with Ag+. The interaction affects prominently the defects related absorption of ZnS NPs and allows single step Ag+ detection in aqueous medium. This absorption method is extended to other ions (Na+, K+, Mg+, Ca+, Ba+) including ‘S’ prone heavy and toxic ions like Pb, Hg, and Cd. Among them, Ag+ shows the best response with ZnS NPs. This demonstration using a portable and cost effective technique with no organic component opens up possibility for other inorganic materials.
Fluorescent Cellulose Nanocrystals with Responsiveness to Solvent Polarity and Ionic Strength Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-17 Weibing Wu, Ruyuan Song, Zhaoyang Xu, Yi Jing, Hongqi Dai, Guigan Fang
Fluorescent and stimuli-responsive cellulose nanocrystals (CNC) were prepared via covalent conjugation of a 1, 8-naphthalimide dye onto TEMPO-oxided CNC. The structural and morphological integrity of CNC were essentially not affected by the functionalizaiton, in spite of their relatively high dye content of 0.1±0.01 mmol g-1. The dye-labeled CNC show much higher fluorescence sensitivity to solvent permittivity and ion concentration compared to pure dye. The fluorescence emission of dye-labeled CNC is greatly enhanced when reducing solvent permittivity or increasing ionic strength. The magnified fluorescence responsiveness is attributed to the effect of aggregation-enhanced emission (AEE) based on the sensitive colloidal stability of CNC to medium conditions. Under high ionic strength and low solvent permittivity, the compressed double layers of CNC lead to space restriction and steric hindrance of dye groups, which limit the process of nonradiative transition. The aggregation of CNC triggered by the change of ion concentration was supported by dynamic light scattering (DLS) particle sizes and Zeta potential values. Owing to the special AEE effect, the fluorescent CNC are promising sensing nanomaterials for wide applications.
Anomalous gas sensing behaviors to reducing agents of hydrothermally grown α-Fe2O3 nanorods Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-10 M. Donarelli, R. Milan, F. Rigoni, G. Drera, L. Sangaletti, A. Ponzoni, C. Baratto, G. Sberveglieri, E. Comini
α-Fe2O3 nanorods have been grown by hydrothermal method, dispersed in ethanol and drop casted on a pre-patterned alumina substrate with Pt electrodes. Their morphology, crystalline and electronic properties have been investigated by Scanning Electron Microscopy, Raman and X-ray Photoelectron Spectroscopies and X-ray Diffraction. The so-fabricated devices have been used for hydrogen gas sensing, showing their ability to detect H2 at operating temperatures > 200 °C, at relative humidity values comprised from 0% to 50%. The sensing behavior of α-Fe2O3 nanorods is compatible with an n to p conductivity transition when the operating temperature is increased up to 300 °C. Outstanding p-type hydrogen sensing performances of α-Fe2O3 have been observed and reported. Besides H2 detection, the α-Fe2O3 nanorods-based device is a good humidity sensor, at room temperature (n-type) and at 400 °C (p-type). CO and ethanol sensing performances have been investigated at different operating temperatures and relative humidity values. CO and ethanol anomalous acceptor-like behaviors at 200 °C in humid air has been explained by the interactions of these target gases with the water molecules adsorbed on the metal oxide surfaces. An explanation of the n-p behavior transition at T > 200 °C in terms of band bending is reported. ________________________________________________________________________________
Selective detection of methanol by zeolite/Pd-WO3 gas sensors Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-10 Yan Zeng, Zhongqiu Hua, Xuemin Tian, Xian Li, Zhilei Qiu, Chensheng Zhang, Mengjun Wang, Er-ping Li
In the present study, gas sensors based on Pd-loaded WO3 sensor layers were prepared and coated with zeolite films to improve the selectivity. The sensing behavior of such sensors was characterized using different single gases and mixtures to assess their selectivity. We observed that the selectivity of sensors based on Pd-WO3 can be significantly tailored towards specific target gases by adding a printed zeolite film. The use of an HZSM-5 zeolite film made the Pd-loaded WO3 sensor highly sensitive to CO, with a response of around 10 at 100 ppm CO. When Pt-modified HZSM-5 zeolite film was used, same sensor became sensitive to methanol, with a detection limit of 0.5 ppm even in the presence of high concentration of CO. Interestingly, the Pt-modified HZSM-5 film caused the catalytic conversion of CO, which resulted in a p-type response to CO. In addition, in the presence of methanol such a p-type response to CO was also observed in neat WO3 sensor. Based on the power-law response to oxygen, it is proposed that the resistive responses of all tested sensors were highly dependent on the oxygen content, indicating that oxygen adsorbates on the surface were involved in the fundamental sensing mechanism, which is the same process as conventional gas sensors. The present study showed that the configuration Pd-WO3 sensing layers coated with zeolite films is viable for tailoring the selectivity of gas sensors.
Enhanced sensitivity of lateral flow immunoassays by using water-soluble nanofibers and silver-enhancement reactions Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-11 Wuseok Kim, Sanghee Lee, Sangmin Jeon
We developed a facile method for enhancing the sensitivity of lateral flow immunoassays (LFIAs) using core–shell hybrid nanofibers comprising a water-soluble polymer in the shell and silver-reducing reagents in the core. These nanofibers were produced using a coaxial electrospinning method and directly deposited in front of the test line on a nitrocellulose (NC) membrane. When a human serum spiked with various concentrations of Troponin I (TnI), a cardiac biomarker, was dropped on the absorption pad, a color change was induced by the binding of TnI–gold nanoparticle complexes to the antibodies at the test line. The silver-reducing reagents were subsequently released from the nanofibers via dissolution, which reduced silver ions to metallic silver around the gold nanoparticles and darkened the color of the test line. The hybrid nanofibers enhanced the detection limit of a commercial LFIA by up to 10 times when viewed with the naked eye while maintaining the assay time and convenience characteristics of this analysis.
CMUT-based resonant gas sensor array for VOC detection with low operating voltage Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-11 Sangjun Park, Inug Yoon, Sungwoo Lee, Hyojung Kim, Ji-Won Seo, Yoonyoung Chung, Alexander Unger, Mario Kupnik, Hyunjoo J. Lee
With the anticipation for a more connected world through the Internet of Things, there is still a strong demand for miniaturized chemical sensors. Here, we report on a miniaturized resonant chemical sensor based on a Capacitive Micromachined Ultrasonic Transducer (CMUT) with a low operating voltage suitable for portable gas sensor applications. Previously reported CMUT chemical sensors required a DC operating voltage (16~50 V) higher than the supply voltages of common circuits (e.g., 1.8 ~ 5 V). Thus, additional circuitry such as a charge pump circuit often was required as a part of the sensor interface circuits to supply the DC voltage to CMUT. This resulted in additional power consumption and a larger footprint. In this work, the vacuum gap of the CMUT which determines the operating voltage was reduced to 50 nm through the development of a double oxidation process with a high wafer-level yield. We achieved a significantly smaller pull-in voltage (<10 V) for a 500-nm-thick CMUT resonant sensor. The CMUT was operated at approximately 80% of the pull-in voltage (~8 V) which does not require additional voltage supply to that of the real-time read-out circuitry. Based on the resonant frequency of 6.7 MHz, the theoretical sensitivity of the fabricated CMUT resonant sensor was 0.8 Hz/fg. By coating four different chemically-sensitive polymer layers, we confirmed the operation of the CMUT with low operating voltage as a chemical sensor. Frequency shifts due to the chemical reaction of volatile organic compounds were observed and analyzed through principal component analysis. This work demonstrates the potential of the developed CMUT with low bias voltage as a key component of a portable chemical sensor system.
Resonant enhancement of plasmonic nanostructured fiber optic sensors Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-11 P. Malara, A. Crescitelli, V. Di Meo, A. Giorgini, S. Avino, E. Esposito, A. Ricciardi, A. Cusano, I. Rendina, P. De Natale, G. Gagliardi
Improving the sensing capabilities of miniaturized probes nanofabricated on the tip of optical fibers is crucial for a large number of sensing applications in remote and harsh environ-ments. While most research efforts are directed towards developing improved fabrications techniques or more sensitive structures, we show that the performance of these sensors can be significantly en-hanced by designing an appropriate interrogation strategy. In our scheme, a nanostructured plasmonic fiber probe is included in an optical fiber resonator and interrogated with a single-mode laser. Any wavelength shift of the plasmonic resonance generates a mismatch of the resonator optical impedance, which is monitored and actively compensated by an optoelectronic gain element. We characterize the technique using samples with different refractive index and compare its performance to a conventional sensing scheme. Our cavity-enhanced configuration leads to a 50-fold improvement of the plasmonic probe’s refractive index resolution (corresponding to a detection limit of 10-5 RIU, the lowest reported so far for this type of sensors). The demonstrated measurement scheme can be devised with any fiber-optic sensor that responds with a resonance shift or with an attenuation of the transmitte/reflected.
Highly selective detection of epidermal growth factor receptor by multifunctional gold-nanoparticle-based resonance Rayleigh scattering method Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-11 Junbo Li, Jinghua Wang, Xinxin Zhang, Honghong Chang, Wenlong Wei
Gold nanoparticles (AuNPs) were modified by anti-epidermal growth factor receptor (EGFR) antibody (Ab) and EGFR aptamer (Apt) to obtain multifunctional Apt-AuNP-Ab nanoconjugate immunoprobe. The probe is specifically combined with EGFR to form large volume binding products that exhibited a remarkable enhancement of the resonance Rayleigh scattering (RRS) intensity, and to appear characteristic RRS peak at 312 nm. The scattering enhancement (ΔI) is linear to the EGFR concentration in the range of 20~100 ng•mL-1 with limit of detection of 0.1 ng•mL-1. The immunoassay was successfully tested and validated by using esophageal squamous cell carcinoma (ESCC) cell Eca109 cell lysates, as well as human serum samples. The mechanism of selectivity and the reasons for RRS enhancement have been discussed. The experimental results reported in this article opened a new possibility of simple, rapid, selective and reliable determination of EGFR by measuring RRS intensity from multifuncition gold nanosystems.
Application of ruthenium oxide pH sensitive electrode to samples with high redox interference Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-09 W. Lonsdale, S. Paul Shylendra, S. Brouwer, M. Wajrak, K. Alameh
In this work, the E* value of a sputter deposited RuO2 pH sensitive electrode is shown to shift in the presence of oxidising and reducing agents, whilst maintaining a Nernstian response slope from pH 2 to 12. This finding is used to develop a sample-equilibration calibration protocol that allows for the measurement of pH in samples with strong redox agents, such as fresh citrus juice, which could not be measured previously. Additionally, the RuO2 sputter deposition parameters (plasma gas pressure, argon/oxygen gas ratio and material thickness) are investigated for manufacture of a durable solid-state RuO2 pH electrode.
Performance optimisation of porous silicon rugate filter biosensor for the detection of insulin Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-09 Rinku Chhasatia, Martin J. Sweetman, Beatriz Prieto-Simon, Nicolas H. Voelcker
A porous silicon rugate filter (pSiRF) insulin biosensor has been constructed and systematically optimised by investigating the effects of specific experimental parameters. The pSiRF biosensor is based on an optical sensing platform using interferometric reflectance spectroscopy (IRS) to monitor insulin binding to a surface-anchored insulin binding aptamer (IBA) within the pores. The aim of this study was to determine the optimal fabrication to elicit the maximum sensor response, lowest limit of detection (LOD) and fastest response time. Thermal hydrosilylation with undecylenic acid was used as a base surface modification, with IBA attached through formation of an amide bond. The following pSiRF fabrication conditions were investigated; porous film thickness and IBA concentration in the conjugation solution. The effect of solution flow speed over the pSiRF during insulin biosensing was also investigated in an effort to improve the performance. The optimised pSiRF biosensor was successfully applied for the detection of insulin secreted from human islets on stimulation with glucose. Finally, as a proof of concept, insulin sensing in the presence of human islets on the pSiRF surface was performed to demonstrate the robust performance of the biosensor and the potential for in-situ insulin biosensing.
Electrodeposited Pt@Molecularly Imprinted Polymer Core-Shell nanostructure: Enhanced sensing platform for sensitive and selective detection of bisphenol A Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-09 Weihua Zheng, Zhili Xiong, Haifeng Li, Shangmin Yu, Gengen Li, Liting Niu, Weilu Liu
A novel electrochemical sensor based on Pt@molecularly imprinted polymer (MIP) core-shell nanostructure was developed using a facile electrodeposition method. This unique core-shell nanostructure offered the advantages of large electrode surface area, regular morphology, high selectivity and sensitivity. The poly(3, 6-diamino-9-ethylcarbazole) based MIP shell acted as the recognition element, while the inner Pt nanoparticles acted as a catalytic center. The morphology of the core-shell nanostructure was observed by scanning electron microscopy and the electrochemical property was evaluated using cyclic voltammetry. The sensing performance of the Pt@MIP sensor was investigated using the analyte of bisphenol A (BPA). Influence of the polymerization conditions on the performance of the Pt@MIP sensor was investigated. Under the optimized condition, a wide linear range (0.007 μM ~ 70 μM), a low detection limit (0.0032 μM) and a good selectivity were obtained for the detection of BPA. Finally, the sensor was applied to the detection of BPA in serum and drinking bottle samples with satisfying results.
The biomimic oxidase activity of layered V2O5 nanozyme for rapid and sensitive nanomolar detection of glutathione Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-09 Akhilesh Babu Ganganboina, Ruey-an Doong
The development of efficient sensing element for rapid and sensitive measurement of glutathione is important on early detection of human diseases. Herein, we introduce the V2O5 nanosheets (NS) as a novel nanozyme to biomimic the oxidase activity toward the rapid detection of glutathione. The 5 – 6 layered V2O5 NS with 300 – 600 nm in size is successfully fabricated by ultra-sonication assisted exfoliation of bulk V2O5 using N, N-dimethyl formamide as the intercalation reagent. The sensing mechanism involves the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by V2O5 NS with the concomitant increase in absorption intensity. Upon introduction of glutathione, the oxidized TMB is converted back to its original form and results in the simultaneous decrease in peak intensity at 650 nm. The sensor exhibits a good linear response to glutathione in the range of 10 – 500 nM with a limit of detection of 2.4 nM. Moreover, the V2O5-TMB sensor exhibits a good selectivity and high speciﬁcity, which makes the detection of glutathione applicable in diluted human serum samples. Since no functionalization of the V2O5 NS is required, this sensing system can open a new avenue to serve as an efficiently biomimic oxidase for glutathione detection in biological fluid samples.
Fluorescent carbon dots for probing the effect of thiram on the membrane of fungal cell and its quantitative detection in aqueous solution Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-05 Yan Zhang, Jianru Zhao, Xiaobo Sun, Wei Pan, Guifeng Yu, Jinping Wang
It is of great significance to probe the effect of fungicides on living fungal cell using fluorescent sensors, which can provide visual evidence for their fungicidal mechanism. In this work, the effect of thiram (0.0–80.0 µM) on the membrane of fungal cell was investigated by monitoring the influxes of amine terminated carbon dots (CDs–NH2), carboxylate group coated carbon dots (CDs–COO-) and Cu2+ into cells via fluorescent imaging. Results showed that the internalizations of the positively charged CDs–NH2 and Cu2+ into fungal cells were promoted by thiram at the concentration from 0.0 to 60.0 (40.0 for Cu2+) µM, but their internalizations decreased with a further increase in thiram concentration from 60.0 (40.0 for Cu2+) to 80.0 µM. On the other hand, the internalization of the passively charged CDs–COO- was not affected by thiram. Therefore, it can be deduced that the effect of thiram on the membrane of fungal cell probed by the fluorescent carbon dots is stimulating the non-selective cation channel up to a certain point in a dose dependent manner. Additionally, an approach was built for the detection of thiram with high sensitivity and selectivity in the presence of excessive Cu2+.
Spectrophotometric and Digital Colour Colourimetric (DCC) analysis of Colour-based Indicators Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-05 Dilidaer Yusufu, Andrew Mills
Seven simulated absorption spectra that span the visible spectrum, are used to probe the degree of linear correlation that exists between real absorbance, Ao, at λmax, and three well-established colour-based parameters, based on the standard Red, Green and Blue scale, sRGB, namely: (i) apparent absorbance, A(sRGB), (ii) apparent fraction of absorbed light, 1-T(sRGB), where T is the apparent transmittance and (iii) colour difference, ΔE. In all cases the colour-based parameter, A(sRGB), linearly correlates best with Ao. This predicted correlation is tested using three different, actual colour-based indicators, using UV/Vis absorption spectroscopy to monitor the change in actual absorbance of each of the indicators and digital photography to monitor simultaneously the change in the values of sRGB, and so A(sRGB). The three different indicators used were: a CO2 indicator, a photocatalytic activity indicator and an oxygen indicator. In all three cases the apparent absorbance parameter, A(sR), derived from sRGB analysis of the digital images, is proportional to the real absorbance, as measured using UV/Vis spectrophotometry, and able to yield the same key analytical information. The increasing use of sRGB analysis of digital photographic images, i.e. digital colour colourimetry, DCC, is discussed briefly.
A fluorescence resonance energy transfer biosensor based on carbon dots and gold nanoparticles for the detection of trypsin Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-05 Shaomei Xu, Fangmei Zhang, Longbin Xu, Xin Liu, Pinyi Ma, Ying Sun, Xinghua Wang, Daqian Song
Herein we propose a fluorescence turn-on strategy for the sensitive and selective detection of trypsin based on fluorescence resonance energy transfer (FRET) between gold nanoparticles (AuNPs) and amino-functionalized carbon dots (C-dots). In this assay, C-dots were treated as fluorometric reporter, while AuNPs were treated as fluorescence quencher. A specially designed negatively charged short peptide chain with one functioned cysteine group as the substrate for trypsin. The sensor works as follows: the negatively charged part of the peptide can be hydrolyzed by trypsin, resulting in the releasing of shorter and positively charged peptides. These shorter peptides then induces AuNPs aggregation due to the strong electrostatic interaction between positively charged peptides and the negatively charged AuNPs, thus leading to the restoration of the FRET-quenched fluorescence emission of C-dots. Measuring the changes in the fluorescence of C-dots, the concentrations of trypsin can be determined. Under the optimized conditions, we achieved quantitative evaluation of trypsin in a range of 2.5-80 ng mL-1 with the detection limit of 0.84 ng mL-1. Meanwhile, this sensing system also exhibited excellent selectivity and sensitivity for trypsin, and we successfully applied it for the detection of trypsin in human serum samples. Based on the above findings, we conclude that this new FRET based sensor might be significant in disease diagnosis in the future.
3D inverse opal nanostructured multilayer films of two-component heterostructure composites: a new-generation synthetic route and potential application as high-performance acetone detector Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-05 Tianshuang Wang, Sufang Zhang, Qi Yu, Xueying Kou, Peng Sun, Fangmeng Liu, Huiying Lu, Yan Xu, Geyu Lu
The preparation of highly ordered porous semiconducting metal oxides (SMOs) films is a hot issue in the field of chemical sensor. Herein, we successfully fabricated 3D inverse opal (IO) ZnO-In2O3 composites multilayer films (MFs) via a novel strategy that combing ultrasonic nebulization deposition technique with polystyrene (PS) spheres template. Such one-step synthetic method is advantageous to achieve the construction of large-scale interconnected macro-porous (pore size: ~170 nm) structure in composites materials, which is beneficial for facilitating gas molecule transport into the sensing layers and accelerating the surface reactions process. More significantly, by using this method, the large-scale 3D IO MFs made in this work can be easily transferred onto any target substrates without being destroyed. Due to the IO multilayer films structure and abundant heterointerfaces, the 3D IO ZnO-In2O3 MFs-based gas sensor exhibited higher response toward acetone at lower operating temperature, better selectivity and long-term stability, faster recovery speed and lower detection limit. Consequently, the approach described herein is more suitable for the synthesis of porous composites materials films, in order to fabricate high performance chemical sensor.
Advanced antifouling zwitterionic layer based impedimetric HER2 biosensing in human serum: Glycoprofiling as a novel approach for breast cancer diagnostics Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-06 Erika Chocholova, Tomas Bertok, Lenka Lorencova, Alena Holazova, Pavol Farkas, Alica Vikartovska, Vladimir Bella, Darina Velicova, Peter Kasak, Anita Andicsova Eckstein, Jaroslav Mosnacek, Daniel Hasko, Jan Tkac
There are two key novel components presented here behind identification of potential novel breast cancer (BCa) diagnostic approach: 1. application of photoimmobilizable zwitterionic hydrogels resisting non-specific protein adsorption for preparation of the biosensor interfaces and 2. integration of lectins (carbohydrate recognizing proteins) within biosensors to evaluate changes in the glycan profile of HER2 protein on the molecular level. A disposable, electrochemical biosensor based on screen printed carbon electrodes (SPCE) with a deposited hydrogel layer was applied for covalent attachment of antibodies for a specific interaction with HER2. In the subsequent step, HER2 molecules were in situ glycoprofiled using lectins. The impedimetric immunosensor was able to detect HER2 down to 5 pg mL-1 (≈ 77 fM) with a minimal non-specific protein adsorption. The biosensor was then combined with lectins to glycoprofile HER2 in two serum samples (one from a healthy, high BCa risk woman and the other from a woman with a 2nd stage BCa). The results obtained by the glycoprofiling via the impedimetric biosensor were successfully verified by independent lectin-based enzyme-linked immunosorbent assays (ELISA). To our best knowledge it is a very first biosensor applying zwitterionic polymeric hydrogel-modified interface for glycoprofiling of a cancer biomarker.
Highly Sensitive Pressure Sensors Based on Conducting Polymer-Coated Paper Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-06 Xiaoling Zang, Yuqian Jiang, Xusheng Wang, Xiaowei Wang, Junhui Ji, Mianqi Xue
Pressure sensor, as one of the most common components in the sensing systems, has attracted plenty of attention in recent years with urgent needs. Herein, a highly sensitive flexible pressure sensor based on conducting polymer (CP)-coated paper is developed via an ultra-simple approach of synthesis and fabrication. This paper-based sensor displays an ultra-low detection limit as low as 0.3 Pascal level, and outstanding sensitivity (~2 kPa−1, P ≤ 75 Pa), which can rank the top among that of the reported pressure sensors. The advantages based on paper framework such as low cost, portability, and easy disposability further enhance its feasibility. Meanwhile, combining its rapid and precise response at room temperature and the recognized stability of PPy in the ambient environment, the sensor would ensure direct and continuous environment monitoring with low energy consumption.
All-fiber-optic VOC Gas Sensor Based on Side-polished Fiber Wavelength Selectively Coupled with Cholesteric Liquid Crystal Film Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-06 Jieyuan Tang, Junbing Fang, Yinling Liang, Biao Zhang, Zhe Chen, Xingyu Liu, Zhibin Li, Xiaojie Cai, Jiaqi Xian, Hai Lin, Wenguo Zhu, Heyuan Guan, Huihui Lu, Jun Zhang, Jianhui Yu
In the work, a cholesteric liquid crystal film coated side polished fiber (CLCFC-SPF) is demonstrated to sense the volatile organic compound (VOC) gas. In the CLCFC-SPF, the wavelength selectively coupling from the SPF to the cholesteric liquid crystal film (CLCF) results in the resonant dips in the transmitted spectrum. It is found that the pitch of the CLCF increases with VOC gas concentration, which reduces the refractive index (RI) of CLCF and results in a blue shift of the resonant dips. By tracing the blue shift of the resonant dips, the VOC gas sensing characteristic of the CLCFC-SPF were investigated experimentally. For tetrahydrofuran, acetone and methanol gas, the sensitivities of the CLCFC-SPF are respectively measured as 7.08 nm⋅L/mmol, 3.46 nm⋅L/mmol, 0.52 nm⋅L/mmol. Using the wavelength selectively coupling theory, gaseous-optic coefficient of the CLC can also be obtained and were measured in the experiment as 6.6 × 10-4 RIU⋅L/mmol, 2.9 × 10-4 RIU⋅L/mmol, 0.6 × 10-4 RIU⋅L/mmol, respectively, for tetrahydrofuran, acetone, and methanol gas. Additionally, the experimental results also show that both the sensitivity of CLCFC-SPF and the gaseous-optic coefficient of the CLCF increase with the molar mass of the VOC gas. The work provides a way to incorporate the sensitive liquid crystal onto the fiber for implementation of liquid-crystal-based fiber sensors.
Detection of dyestuffs with an impedimetric sensor based on Cu2+-methyl-naphthyl cyclen complex functionalized gold electrodes Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-06 Hassen Touzi, Yves Chevalier, François Bessueille, Hafedh Ben Ouada, Nicole Jaffrezic-Renault
This work explored the elaboration of dyestuffs chemical sensors based on methyl-naphthyl cyclen (1,4,7,10-tetraazacyclododecane) (MNCyclen) thin films, deposited on gold electrodes and characterized by electrochemical impedance spectroscopy (EIS). The methyl-naphthyl cyclen was synthesized in three steps: first, the cyclen was protected by the formation of its glyoxal bisaminal derivative, then the glyoxal aminal of cyclen was mono-alkylated, and finally the amine groups were deprotected by removal of the aminal bridges, and the product was characterized by liquid 1H and 13C NMR spectroscopy. Thin films of MNCyclen were deposited on gold wafers using the spin-coating technique and characterized by means of infrared spectroscopy in ATR mode, contact angle measurements and atomic force microscopy. The chemical sensor was studied in the presence of Acid Yellow 25 (AY25), Acid Violet 7 (AV7), Indigo Blue (IB) and Acid red 1 (AR1) dyestuffs. Nyquist plots were fitted with an equivalent electrical circuit including two RC circuits in series corresponding to the MNCyclen film and its interface with the electrolyte. The main parameter that varies with dyestuff concentration is the resistance of the film/electrolyte interface (RP). The highest sensitivity was obtained for AY25 dyestuff with a detection limit of 10-12M, based on an equivalent electrical model.
A novel quinoline-derived fluorescent “turn-on” probe for Cu2+ with highly selectivity and sensitivity and its application in cell imaging Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-06 Peng Wang, Jiaxin Fu, Kun Yao, Yongxin Chang, Kuoxi Xu, Yuanqing Xu
We have developed a novel quinoline-derived Schiff base fluorescent Cu2+ ion probe fluorescent probe 2-(2-hydroxybenzylidene)hydrazono)methyl)- quinolin-8-ol (QH). The probe QH showed a highly selective and sensitive detection of Cu2+ with significant fluorescence “turn-on” response and the solution color changed from colorless to yellowish green. The results of fluorescence titration, Job's plot and HRMS analysis suggested that the stoichiometry of probe QH and Cu2+ was found to be 1:1. The detection limit was found to be 8.08×10−9 M, which far lower than the maximum allowable level of the U.S. Environmental Protection Agency limit (20 μM) for drinking water. The bonding mechanism has been discussed according to FT-IR and DFT calculations. Furthermore, probe QH has been successfully applied to living cell imaging.
A highly sensitive plasmonic sensor for detection of selenium based on the shape transformation of silver nanoprisms Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-06 Mohammad Amjadi, Tooba Hallaj, Rana Salari
We report on a plasmonic probe for detection of ultra-trace amounts of Se(IV) based on morphological transformation of silver nanoprisms (AgNPRs). AgNPRs were synthesized in a mild condition and characterized by UV-Vis absorption spectroscopy and transmission electron microscopy (TEM). It was found that in the presence of Se(IV), SPR peak of AgNPRs at 720 nm shifts to lower wavelengths and the color of solution changes from light blue to violet. This is due to the shape transformation of AgNPRs to nanodisks which is proved by TEM images, and probably results from the etching of corners of NPRs by selenite ions. Based on this phenomenon, a sensitive colorimetric probe was developed for determination of Se(IV) in the concentration range of 2.5-100 μg L-1 with a detection limit of 1.2 μg L-1. The developed method was applied for the analysis of water and food samples.
A highly sensitive multifunctional sensor based on phenylene-acetylene for colorimetric detection of Fe2+ and ratiometric fluorescent detection of Cd2+ and Zn2+ Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-06 Yuan-Yuan Zhang, Xiang-Zhu Chen, Xing-Yue Liu, Mian Wang, Jing-Jing Liu, Gui Gao, Xue-Yan Zhang, Run-Ze Sun, Shi-Cong Hou, Hong-Mei Wang
A new multifunctional sensor (L1) based on phenylene-acetylene was designed and synthesized. L1 showed an excellently colorimetric response toward Fe2+ with a detection limit of 2.0☓10-8 M. This result indicated that L1 can sensitive detect Fe2+ by “naked eye” and discriminate iron types in different oxidative states. Simultaneously, L1 can ratiometric fluorescent detection of Cd2+ and Zn2+ with detection limits of 2.62☓10-8 M and 2.03☓10-9 M, respectively. L1 can distinguish Cd2+ and Zn2+ according to differently emissive colours, after addition of Cd2+ and Zn2+ to the blue emissive solution of L1, cyan and yellow-green fluorescence emission were observed, respectively. The binding modes of L1 with Fe2+, Cd2+ and Zn2+ were evidenced by 1H NMR, Job’s plot and ESI-MS. Water samples and On-site test paper experiments for detecting Fe2+, Cd2+ and Zn2+ were successfully implemented for practical application in environment.
Radio frequency- and impedance-based sensing of ionic liquids supported on porous carriers and their limitations Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-07 Marie-Luise Anke, Martin Hämmerle, Andreas Jess, Ralf Moos
The analysis of the pore filling degree of supported ionic liquids (ILs) is essential for industrial applications. In this study, two methods to detect the loading of IL supported on solid carriers are presented, a radio frequency-based one and one using impedance spectroscopy. With the radio frequency-based method, the pore filling degree can be determined contactless and in operando. Some unexpected deviations at non-relevant high pore filling degrees occur. They can be explained by the combination of the results from the radio frequency-based method (at 1.2 GHz) and the impedance spectroscopy (at 1 Hz to 2 MHz). A transition from low polarization losses to high conduction losses occurs with increasing ionic liquid loading of the porous carrier.
Synthesis of catalytically active carbon quantum dots and its application for colorimetric detection of glutathione Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-07 Qingmei Zhong, Yuye Chen, Anmei Su, Yilin Wang
Carbon quantum dots (CQDs) were prepared from wood soot, and the CQDs could catalyze the oxidation of 3, 3′, 5, 5′-tetramethylbenzidine (TMB) in the presence of H2O2 to form oxidized TMB (ox-TMB) with an absorption peak at 652 nm. It was found that the introduction of glutathione (GSH) could cause the reduction of ox-TMB, resulting in a decrease of the absorbance at 652 nm. Based on this, a highly sensitive colorimetric sensor for detection of GSH was fabricated. The influences of various experimental variables, including pH, temperature, and the concentrations of H2O2, CQDs and TMB, on the analytical performance of the method were systematically investigated. Under the conditions of pH 3.5, temperature 35 °C, H2O2 1.0 mM, CQDs 2.5 μg/mL and TMB 0.5 mM, the response was linearly proportional to the concentration of GSH within the range of 0.05 to 20 μM with a low detect limit (3 σ/k) of 0.016 μM. The method was successfully applied to determination of GSH in human serum samples with the recovery of 95.7% –103.6%.
Integrated microfluidic paper-based system for determination of whole blood albumin Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-07 Ruey-Jen Yang, Chin-Chung Tseng, Wei-Jhong Ju, Lung-Ming Fu, Meng-Ping Syu
A method is proposed for determining the concentration of albumin (ALB) in human whole blood samples using a 3-dimensional (3D) microfluidic paper-based chip and a smart detection module. In fabricating the paper-based chip, the reaction area is implanted with bromocresol green (BCG) reagent and the device is stored in a nitrogen (N2) environment at a temperature of —15 °C until needed for use. In the detection process, 10 µl of whole blood is dropped onto the entrance area of the chip and the plasma within the sample diffuses through a separation channel into the reaction zone. A reaction is induced between the ALB in the plasma and the BCG reagent in the reaction area by heating the chip at 37 °C for 6 min. The ALB concentration is then detected using a colorimetry technique implemented on a cell phone in the form of a self-written app. It is shown that the detection results obtained for 40 pure ALB samples and 30 whole blood samples are consistent with those obtained using a traditional spectrophotometry method (R2 = 0.9837 and R2 = 0.9968). The proposed detection system thus provides a reliable tool for practical ALB determination purposes.
Thermal desorption–ion mobility spectrometry: A rapid sensor for the detection of cannabinoids and discrimination of Cannabis sativa L. chemotypes Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-07 María del Mar Contreras, Natividad Jurado-Campos, Carolina Sánchez-Carnerero Callado, Natalia Arroyo-Manzanares, Luis Fernández, Salvatore Casano, Santiago Marco, Lourdes Arce, Carlos Ferreiro-Vera
Existing analytical techniques used for the determination of cannabinoids in Cannabis sativa L. (Cannabis) plants mostly rely on chromatography-based methods. As a rapid alternative for the direct analysis of them, thermal desorption (TD)-ion mobility spectrometry (IMS) was used for obtaining spectral fingerprints of single cannabinoids from Cannabis plant extracts and from plant residues on hands after their manipulation. The ionization source was 63Ni, with automatic switchable polarity. Although in both ionization modes there were signals in the TD-IMS spectra of the plant extracts and residues that could be assigned to concrete cannabinoids and chemotypes, most of them could not be clearly distinguished. Alternatively, the global spectral data of the plant extracts and residues were pre-processed and then, using principal component analysis (PCA)-linear discriminant analysis (LDA), grouped in function of their chemotype in a more feasible way. Using this approach, the possibility of false positive responses was also studied analyzing other non-Cannabis plants and tobacco, which were clustered in a different group to those of Cannabis. Therefore, TD-IMS, as analytical tool, and PCA-LDA, as a strategy for data reduction and pattern recognition, can be applied for on-site chemotaxonomic discrimination of Cannabis varieties and detection of illegal marijuana since the IMS equipment is portable and the analysis time is highly short.
An ultrasensitive fluorescence sensing strategy for detection and in situ imaging of chronic myeloid leukemia-related BCR-ABL1 mRNA Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-07 Xiao-yan Zhou, Jian-hua Pan, Yong-neng Ma, Xiu-juan Peng, Hai-ping Wu, Qin Zhou, Shi-jia Ding, Huang-xian Ju
In this study, a fluorescent sensing strategy has been developed for rapid and ultrasensitive detection of BCR-ABL1 mRNA in chronic myeloid leukemia (CML) based on DNAzyme Cleavage-induced Rolling circle amplification (DCR for short). In the presence of BCR-ABL1 mRNA, DNAzyme was activated to split the target sequence into two fragments, producing the 3’ terminus on the forward cleavage fragments. After T4 polynucleotide kinase (PNK) modification reaction, the forward cleavage fragments were extended by rolling circle amplification (RCA). Plenty of long single DNA strands were produced and partially hybridized with the fluorescence-quenching decorator probes, thus inducing the separation of fluorophore and quencher decorator probes and recovery of fluorescence. Highly sensitive detection of BCR-ABL1 was achieved with a limit of detection at 9.4 fM. In addition, the DCR strategy was adopted to successfully in situ image the BCR-ABL1 mRNA in the cytoplasm of human leukemia bone marrow cells. Moreover, results of the BCR-ABL1 mRNA expression in clinical samples achieved by DCR sensing were well consistent with that of reverse transcription PCR (RT-PCR) and fluorescence in situ hybridization (FISH) analysis. Therefore, this developed DCR sensing strategy might provide a potential alternative tool for precise diagnosis of CML.
An efficient probe for sensing different concentration ranges of glutathione based on AIE-active Schiff base nanoaggregates with distinct reaction mechanism Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-07 Lingyun Wang, Simei Wu, Hao Tang, Herbert Meier, Derong Cao
A novel tetraphenylethene- diketopyrrolopyrrole Schiff base (TPE-DPP) was synthesized by one-pot protocol. Based on thiol group and acid-base property of glutathione, nanoaggregates of TPE-DPP for sensitive and selective detection of diﬀerent concentration ranges of glutathione by two distinct reaction mechanisms was reported. It showed a turn-on mode of ﬂuorescence signals towards low concentration of GSH by hydrolysis of TPE-DPP, but a ratiometric mode of ﬂuorescence signal was elicited towards high concentration of GSH by addition reaction of thiol with TPE-DPP. What’s more, the probe was successfully utilized for monitoring GSH in living cells.
One-step selective wettability modification of PMMA microfluidic devices by using controllable gradient UV irradiation (CGUI) Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-07 Chao Liang, Yuanchang Liu, Chong Liu, Xia Li, Li Chen, Chunzheng Duan, Jingmin Li
Poly (methyl methacrylate) (PMMA) has become increasingly popular to fabricate microfluidic devices. In a microfluidic device, different functional areas usually require different wettability to achieve a better performance. However, most of the existing wettability modification methods have been applied to the whole PMMA surface making the device have minimum wettability difference. In this paper, a controllable gradient UV irradiation (CGUI) method was presented. In this method, a series of quartz plates sputtered with different thickness of Cu were arranged on top of the PMMA surface. By controlling the thickness of Cu film, the UV irradiation, which transmitted though the quartz plates onto the PMMA surface, can be adjusted making the modification performance able to be varied accordingly. The validation of the proposed CGUI was conducted through contact angle measurements. Our results showed that through 5 mins CGUI process, the contact angle for different parts of the PMMA surface can be varied from 45.48° to 77.41° continuously with a long-term stability of 60 days. To demonstrate this method, a fully integrated Point-of-Care Test (POCT) device was designed and fabricated for the detection of cardiac Troponin I achieving the lower detection limit of 85 pg/ml within 10 min.
Optically transparent silica film with pH-sensing properties: influence of chemical immobilization and presence of β-cyclodextrin on protolytic properties of alizarin yellow Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-07 Nadiia V. Roik, Lyudmila A. Belyakova, Marina O. Dziazko
A sol-gel synthetic rote was proposed for preparation of optically transparent silica films with covalently bonded azobenzene dye, alizarin yellow. Effect of chemical immobilization on protolytic properties of pH sensor moieties was studied using UV-Vis spectroscopy. It was found that indicator dye attached to the silica framework through amide linkage retains the ability to respond on pH change by color transition. The response time of surface azobenzene groups evaluated from the kinetic studies in acidic and neutral medium consists of 10 and 5 min, correspondingly. Acid ionization constants of individual and grafted alizarin yellow were evaluated by spectrophotometric titration in phosphate buffer solutions. It was found that involving of indicator dye carboxylic group in covalent bonding with silica surface leads to the shift of pKa2 value, reflecting the dissociation of phenolic hydroxyl group, from 10.9 to 5.5. Influence of β-cyclodextrin on pH-sensing properties of individual and grafted alizarin yellow was evaluated by spectrophotometric titration in phosphate buffer solutions. Sensor material showed good reversibility, repeatability and long-term stability at immersion in aqueous solutions with pH in the range from 1 to 8.
Electrical Properties and Electromechanical Modeling of Plasticized PVC Gel Actuators Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-08 Kinji Asaka, Minoru Hashimoto
We studied the detailed electrochemical and electromechanical properties of a polyvinyl chloride (PVC) gel with dibutyladipate (DBA) as a plasticizer and developed an electromechanical model based on the electrochemical data. We evaluated the electric deformation of the PVC gel by the bending displacement response of the PVC gel strip when a square-wave voltage is applied. For every electrode, the bending responses were to the anode side and increased with the applied voltage. The bending response of the PVC gel is considered to be due to the electric creep movement on the anode surface. We checked this result by optical microscopy. We studied the electrochemical impedance measurements of the PVC gel under bias voltages and the voltage–current and voltage–displacement measurements in response to a triangle-wave voltage. Based on the above electromechanical and electrochemical experimental results, we developed a deformation model of the PVC gel where the electric bending response is basically due to the electrochemical formation of the solvent-rich layer and its deformation from the Maxwell stress. We estimated the displacements with applied voltages of 200 and 1000 V, and the model results were in good agreement with the experimental results despite the rough estimation.
Origami-Enabled Signal Amplification for Paper-Based Colorimetric Biosensors Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-04 Alejandra Alba-Patiño, Steven Russell, Roberto de la Rica
Signal amplification in colorimetric biosensors usually requires labile reagents and/or additional steps, which are not ideal for in-field measurements. Here we show that the limit of detection of a gold nanoparticle-labeled colorimetric immunosensor can be decreased 10-fold by performing the assay on a folded piece of paper. In this approach, the intrinsic porosity of the substrate enables generating multiple signals with a single drop of reagent. This yields combined signals with higher optical density thanks to the semitransparent nature of the wet material. It will be shown that this method can decrease the limit of detection 10 times in a model immunosensor for the detection of immunoglobulins. The procedure is so straightforward that it could be easily implemented to decrease the limit of detection of microfluidic paper-based analytical devices with colorimetric readouts.
An Aza-Cope mediated fluorescent probe based on aggregation-induced emission for highly selective and sensitive detection of formaldehyde in living cells and tissues Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-04 Tang Gao, Xiaozheng Cao, Anyao Bi, Jie Dong, Shuai Huang, Xueyan Huang, Shijun Wen, Wenbin Zeng
Formaldehyde (FA) is a product of an endogenous production that is formed through demethylase and oxidase enzymes, which regulate epigenetics and metabolism. However, the presence of abnormally high levels of FA are often associated with a variety of disease pathologies, including chronic liver, heart and neurodegenerative diseases, in addition to diabetes and various cancers. Hence, a more efficient tool for monitoring FA in living systems is required to better investigate the biological roles of FA in physiology and pathology. Herein, describe a new aggregation-induced emission based fluorescent probe (MPIPA) to detect formaldehyde (FA) with high selectivity and an ultra-low detection limit (123 nM). Importantly, the new probe permits the successfully detection of exogenous and endogenous FA in living cells and clinical cancer tissues for the first time, which has important implications.
A Red Fluorescent Probe for Ribonucleic Acid (RNA) Detection, Cancer Cell Tracing and Tumor Growth Monitoring Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-04 Lei Wang, Qi Xia, Ruiyuan Liu, Jinqing Qu
A red fluorescent probe, PFB, is designed and synthesized, which presents several remarkable features including a large Stokes shift (85 nm), long emission wavelength, high photostability and good biocompatibility. PFB also displays the solvent-dependent effect, which is verified by the density functional theory (DFT) calculations. Additionally, PFB can act as a fluorescent probe for cellular imaging with high uptake efficiency and highly sensitive detection toward RNA under low optimum concentration (1 μM), which enables it to achieve cancer cell tracing in vitro and tumor growth monitoring in vivo. The results of real-time tracking experiment reveal that PFB can be traced in stained HepG-2 cells for 11 generations and monitor tumor growth for 18 days. This work highlights the potential application of PFB as a promising alternative to the commercial RNA fluorescent probes.
Pt Nanoparticles Functionalized Tungsten Oxynitride Hybrid Chemiresistor: Low-Temperature NO2 Sensing Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-04 Dong-Ha Kim, Ji-Won Jung, Seon-Jin Choi, Ji-Soo Jang, Won-Tae Koo, Il-Doo Kim
Semiconducting metal oxides (SMOs) based gas sensors are inherently hampered by requirement of high working temperature because of their wide bandgaps. Consequently, there are remain challenges to utilize SMOs based gas sensors with regard to continuous gas monitoring platform with low power consumption. To address the inherent limitation, nitridation (i.e., N doping) of WO3 NFs to WOxNy NFs was herein introduced for realization of low-temperature NO2 sensing. Importantly, nitridation was conducted at intervals of 50 °C from 400 to 600 °C to adjust the degree of phase transition from semiconducting WO3 to conductive WON phases. To further optimize the conductivity and improve the sensing characteristics, i.e., reduction of optimal operating temperature and enhancement of sensitivity, WOxNy NFs were functionalized with platinum (Pt) catalytic nanoparticles (NPs) by physical mixing. Pt NPs functionalized WOxNy NFs nitrided at 550 °C exhibited improved normalized resistance change and superior selectivity against C2H5OH, C7H8, CH4, CO, NH3, and NO at 50 °C. The noble metal catalyst–metal oxynitride hybrid system is suggested as an effective NO2 sensing platform for low-temperature chemical sensor.
A Sensitive Fluorescence “Turn-Off-On” Biosensor for Poly(ADP-ribose) Polymerase-1 Detection Based on Cationic Conjugated Polymer-MnO2 Nanosheets Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-04 Shuangshuang Wu, Changhui Chen, Haitang Yang, Wei Wei, Min Wei, Yuanjian Zhang, Songqin Liu
Poly(ADP-ribose) polymerase-1 (PARP-1) monitoring has attracted extensive attention because it serves a vital role in human pathologies. However, only a few researches about its detection methods have been reported because PARP-1 and its catalyzed product poly(ADP-ribose) polymer (PAR) are lack of optical or electrochemical activity. Herein, a convenient fluorescence “turn-off-on” nanosensor based on cationic conjugated polymer (PFP) and MnO2 nanosheets has been designed for selective detection of PARP-1 in vitro. To the best of our knowledge, it is the first time to use manganese dioxide (MnO2) nanosheets for PARP-1 detection. The fluorescence intensity of PFP can be quenched by MnO2 nanosheets via a fluorescence resonance energy transfer (FRET). While the subsequently joined electronegative poly(ADP-ribose) polymer (PAR), catalysate of PARP-1, take positively charged MnO2 nanosheets away from PFP via electrostatic interaction, causing sufficient recovery of fluorescent signal. The sensing platform displayed a sensitive response to PARP-1 in a linear range of 0.03 − 1.5 U (0.024 − 1.2 nM), with a detection limit of 0.004 U (0.003 nM), which is 10-100 lower than reported methods. As expected, this method was successfully applied to the detection of PARP-1 in human serum samples with recoveries ranging from 97.6 − 102.7 %. Especially, it has also been applied to the determination of PARP-1 in human breast cancer cells SK-BR-3 in the 40 to 1000 cells per mL range, with a detection limit as low as 25 cells per mL.
Improved spatial resolution of the chemical imaging sensor with a hybrid illumination that suppresses lateral diffusion of photocarriers Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-04 Ko-ichiro Miyamoto, Kosuke Seki, Takeyuki Suto, Carl Frederik Werner, Torsten Wagner, Michael J. Schöning, Tatsuo Yoshinobu
The chemical imaging sensor is a semiconductor-based chemical sensor capable of visualizing pH and ion distributions. The spatial resolution depends on the lateral diffusion of photocarriers generated by illumination of the semiconductor substrate. In this study, two types of optical setups, one based on a bundle of optical fibers and the other based on a binocular tube head, were developed to project a hybrid illumination of a modulated light beam and a ring-shaped constant illumination onto the sensor plate. An improved spatial resolution was realized by the ring-shaped constant illumination, which suppressed lateral diffusion of photocarriers by enhanced recombination due to the increased carrier concentration.
Recent advances of conjugated polymer (CP) nanocomposite-based chemical sensors and their applications in food spoilage detection: A comprehensive review Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-03 Tushar Ramesh Pavase, Hong Lin, Qurat-ul-ain Shaikh, Hussain Sameer, Zhenxing Li, Ishfaq Ahmed, Liangtao Lv, Lirui Sun, Syed Babar Hussain Shah, Muhammad Talib Kalhoro
Food quality and safety has been a great public concern all over the globe and reliable sensors or monitoring systems has become a prerequisite to affirm quality of various food commodities, especially highly perishable foods, such as seafood, pork, beef, lamb and chicken. Food freshness chemosensors is an emerging sensing technology in the field of food industrial research and development. Although the application of chemosensors is evidently on the move and concurrently lacking commercial viability, it has tremendous potential to empower onsite monitoring of food quality and safety in the food processing industry. This review aims to (a) elaborate different classes of CPs and CPs nanocomposite based chemosensors; (b) sensor systems with special focus on innovative conjugated polymer (CPs) chemical sensors for food freshness detection; and (c) applications of highly sensitive and selective (CPs) nanocomposite based chemosensors with Active/Intelligent technologies for meat and seafood spoilage detection Via colorimetric (naked eye detection) and fluorometric "turn - on/off" response, providing new pathways of CPs based nanocomposite chemosensor-application in the food industry. Thus, this review illustrates the potential scope of such intelligent sensor systems in food spoilage detection for commercial viability, resulting as a very simple, cost-efficient, consumer approved and other multipurpose tool.
Combined detection of C-reactive protein and PBMC quantification from whole blood in an integrated lab-on-a-disc microfluidic platform Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-03 Rokon Uddin, Marco Donolato, En-Te Hwu, Mikkel Fougt Hansen, Anja Boisen
There is an increasing need for portable and low-cost diagnostic devices for detecting inflammatory/infectious diseases in a rapid and user-friendly fashion. Here, we present a lab-on-a-disc solution, which performs automated sample pre-treatment and combinedly detects small molecules and counts cells in a whole blood sample with a volume of 8.75 µL with a sample to answer time of 14 min. It is used to detect two common inflammation/infection biomarkers, C-reactive protein (CRP) and peripheral blood mononuclear cell (PBMC) count. The whole blood sample was separated into plasma and PBMC fractions using density gradient centrifugation and centrifugo-pneumatic valving. On-disc CRP detection was performed in the extracted plasma using a CRP-antibody-functionalized magnetic nanobead (MNB)-based agglutination assay and a Blu-ray-based optomagnetic detection unit. On-disc PBMC scanning and quantification was performed using an optical imaging unit. Both detection units were integrated on the centrifugal platform and the entire study was automated in order to ensure reliability of the assay and user-friendliness of the method. We measured the CRP level of subjects with different CRP levels and obtained approximately 73% PBMC extraction efficiency compared to hospital results. The concurrent/combined detection of these two common biomarkers in an automated microfluidic platform with integrated detection units and with a low sample-to-answer time is a significant step forward towards a low-cost, out-of-lab, and portable tool to detect multiple biomarkers of significantly different nature (molecules and cells).
Self-Assembled Micellar Nanosensor toward pH with high photo-stability and its application in living cells Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-03 Huanhuan Song, Weiwei Du, Chunxia Liu, Zhanxian Li, Hongyan Zhang, Liuhe Wei, Mingming Yu
Based on photo-induced electron transfer, 1,8-naphthalic anhydride-based organic molecular fluorescent pH-sensor (1) was designed and synthesized. Hydrophobic, fluorescent hybrid nanosensor (1-PS35-b-PAA30) encapsulated with the hydrophobic pH responsive fluorophore for sensing intracellular pH has been fabricated based on the self-assembly of amphiphilic diblock copolymer PS35-b-PAA30 and 1. The as-synthesized 1-PS35-b-PAA30 sensor exhibits excellent photo-stability, good anti-disturbance ability, and enhanced fluorescence intensity under acidic environment with respect to the corresponding free dye in highly polar aqueous system because of the encapsulation of 1 inside nanoparticle cores with weak polarity environment. The fluorescence intensity of 1-PS35-b-PAA30 is enhanced by 7.3-fold upon changing from base (pH = 9.0) to acid (pH = 4) in aqueous system, which can exactly meet the physiological pH range in cells. Moreover, its linear fluorescent response from pH 5.2 to 7.4 makes this sensor suitable for the practical tracking of pH fluctuation in live cells. The fluorescence imaging and TEM experiments indicated that the sensor permeated into cells and could not be observed because of aggregation in acidic condition.
Self-Sacrificing Templated Formation of Co3O4/ZnCo2O4 composite hollow Nanostructures for Highly Sensitive Detecting Acetone Vapor Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-03 Fengdong Qu, Tiju Thomas, Bingxue Zhang, Xinxin Zhou, Shendan Zhang, Shengping Ruan, Minghui Yang
Hollow nanostructures derived from metal-organic frameworks have attracted considerable interest for prospective applications in gas separation/storage, drug delivery, catalysis device and gas sensors. Herein, porous hollow nanostructures, namely Co3O4/ZnCo2O4 composite hollow nanostructures, are prepared through a self-sacrificing template method. The method includes the synthesis of zeolite imidazolate frameworks-67 self-sacrificing template and then transformation into Co/Zn-ZIF@Co-Zn layered double hydroxides precursor. Finally, the Co3O4/ZnCo2O4 composite hollow nanostructures are obtained through thermal annealing of Co/Zn-ZIF@Co-Zn LDH precursor in air. The gas sensing investigations revealed that the Co3O4/ZnCo2O4 composite hollow nanostructures-based gas sensor exhibited high response (16.3-100 ppm) and selectivity towards acetone. Besides, enhanced gas sensing properties of Co3O4/ZnCo2O4 composite hollow nanostructures are observed when compared with Co3O4 and ZnCo2O4 hollow nanostructures. The excellent gas sensing characteristics of Co3O4/ZnCo2O4 composite hollow nanostructures might be attributed to their high porosity, large specific surface area, and heterostructure between Co3O4 and ZnCo2O4.
Real-time detection of prostate-specific antigens using a highly reliable fiber-optic localized surface plasmon resonance sensor combined with micro fluidic channel Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-03 Hyeong-Min Kim, Jae-Hyoung Park, Dae Hong Jeong, Ho-Young Lee, Seung-Ki Lee
Conventional assays using fiber-optic localized surface plasmon resonance (FO LSPR) sensors involve soaking the sensor in solution, which exposes the sensor to air during measurement. Although the exposure time is short, for a small sensor surface area, this can result in drying of biomolecules and rearrangement of nanoparticles caused by the surface tension. To minimize the resulting errors, FO LSPR sensor was combined with a micro fluidic channel. To verify the improved performance of the sensor chip combined with a micro fluidic channel, we conducted real-time detection of various concentrations of prostate-specific antigen (PSA). A calibration method was used to correct nonuniformity among the detected PSA results, arising from differences in sensors because of nonuniform metal nanoparticles on the sensor surface. A micro fluidic channel and calibration increased linearity and improved the sensitivity and dynamic range of PSA measurements. Additionally, the fabricated sensors were applied to detect the test samples and the measured sample concentrations were compared to actual values. Confirming the selectivity towards the target, the proposed system detected the control antigen. Finally, we used our sensor system to detect PSA in patient serum and acquired comparable results to those obtained using a commercialized method.
A Fluorescent and Colorimetric Probe for Imaging the Mitochondrial Sulfur Dioxide in Living Cells Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-03 Haidong Li, Jiangli Fan, Saran Long, Jianjun Du, Jingyun Wang, Xiaojun Peng
Sulfur dioxide (SO2), one of active sulfur species (RSS), plays important roles in various physiologies and pathological processes. Hence, it is urgent to monitor the fluctuation of mitochondrial SO2in vivo. In this work, a novel mitochondria-targeting probe CZ was designed and synthesized based on carbazole derivative, which showed that probe was employed to the detection of SO2 with high selectivity, rapid response as well as naked eyes. Besides, an excellent linear relationship (R2 = 0.9977) was observed and the detection limit was calculated as low as 0.504 μM (3σ/k). Surprisingly, with addition of SO2 derivative, fluorescence intensity ratios (F475 nm/F607 nm) of probe CZ increased by 1104-fold ranging from 0.007 to 7.73. Owing to its biocompatibility, probe CZ was also successfully employed for monitoring of mitochondrial SO2 by fluorescence confocal microscopy.
Recent Progress in Biological and Chemical Sensing by Luminescent Metal-Organic Frameworks Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-03 Deepak Kukkar, Kowsalya Vellingiri, Akash Deep, Ki-Hyun Kim
Luminescent metal organic frameworks (LMOFs), formed by coordinated bridging between metal ions and multidentate organic ligands with relevant fluorescent structures, have been the subject of intense research due to their tunable photoluminescent properties. The numerous permutations and combinations of available metal ions and organic linkers can yield novel LMOFs for countless applications. The luminescent characteristics of LMOFs depend upon many factors, including their structural components, coordination milieu of the metal ions, chemical structure/volume of the pore surfaces, and host-guest interactions between the LMOFs and reacting species (e.g., non-covalent interactions, coordination bonds, and π-π interactions). The combined effects of these parameters justify the expansion of their application in various fields. In addition, they are recognized as ideal candidates for biological applications due to their high loading capacity of functional molecules, facile surface modification and conjugation with biocompatible ligands (such as antibodies and proteins), tunable structural geometry, and intrinsic biocompatibility. By elaborating on these points, this article provides up-to-date information on the developments in the scientific/technological application of LMOFs, with special emphasis on the types, properties, and potential in sensing and biological applications. The discussion is further expanded to describe the major challenges and constraints of this research field.
Comparative investigation of interdigitated and Parallel-plate capacitive gas sensors based on Cu-BTC nanoparticles for selective detection of polar and apolar VOCs indoors Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-04 S Zeinali, S. Homayoonnia, G. Homayoonnia
Capacitive chemosensors are commonly found in two configurations: parallel-plate (PP) and interdigitated electrode (IDE) based on different sensing layers. Metal organic frameworks (MOFs) can play an important role as a dielectric layer of the capacitors because of their insulating properties. However, to date there are few reports on MOFs which were used as a key component of a capacitive sensors. In the limited reports on using MOFs in capacitive sensors, PP configuration was mostly considered. Within the class of MOFs, Cu-BTC (copper:1, 3, 5-benzenetricarboxylate) is a well-studied structure. Although the structure of Cu-BTC has high porosity and large surface area which can improve the sensitivity of IDE capacitive sensors, there are no reports on using this kind of MOF for this purpose. This article is developed in the following order: first, the Cu-BTC nanoparticle is synthesised to make a Cu-BTC sensing layer. The dried Cu-BTC layer is characterized by infrared (IR) spectroscopy, X-ray diﬀraction (XRD) analysis, scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) analysis. These characterization methods confirm the identity of the synthesized material, the nanoscale size of the particles, its VOCs stability and the rigidity of its structure. Secondly, for the first time, Cu-BTC nanoparticles are introduced as a sensing layer in IDE capacitive gas sensors. In order to reduce fabrication costs and time of the conducting elements in IDE configuration, a simple, fast and cost-effective method is introduced which does not need any equipment and pre-treatment for better adhesion. Third, to have a comparative investigation between the sensing performance of IDE and PP capacitive sensors, their performance in detection of some VOCs vapours is examined. Subsequently, the selectivity, recovery time, reproducibility, repeatability and reversibility, sensitivity and limit of detection (LOD) of the IDE and PP capacitive sensors are studied for detection of some VOCs such as acetone, toluene and dichloromethane with different dielectric constants. All experiments were carried out at different concentrations (250–1500 ppm) of VOCs in ambient conditions (atmospheric pressure, 25 ℃ and 10% relative humidity).
Electrochemical multisensor system for monitoring hydrogen peroxide, hydrogen and oxygen in direct synthesis microreactors Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-04 Sebastian Urban, Andreas Weltin, Hubert Flamm, Jochen Kieninger, Benedikt J. Deschner, Manfred Kraut, Roland Dittmeyer, Gerald A. Urban
We present an electrochemical microsensor system for the monitoring of hydrogen peroxide, dissolved hydrogen and dissolved oxygen inside a direct synthesis microreactor. The setup allows the online, in situ measurement of high reactant concentrations by amperometric detection of all three reactants in aqueous solution using chronoamperometric protocols. Hydrogen peroxide is a key chemical for industrial oxidation applications, and its catalyzed direct synthesis is an attractive process route. For the first time, we integrated an electrochemical cell into a high pressure stainless steel microreactor environment (pressures up to 100 bar, pH of 3-4 and presence of bromide) by fabricating sensor plugs with 300 µm platinum microelectrodes encapsulated into a robust epoxy housing. The first microfabricated silver/silver bromide pseudo-reference electrode, integrated by electrodeposition, allowed to obtain a stable measurement potential directly from the electrolyte containing bromide. The investigation of platinum electrochemistry in the presence of bromide by cyclic voltammetry led to the development of chronoamperometric protocols for the stable, precise and reproducible measurement in this environment. Hydrogen peroxide was detected under reaction conditions showing linear behaviour up to 20 mM with high sensitivity of 55 μA cm−2 mM−1 and excellent stability by application of a diffusion limiting hydrogel layer to the electrode surface. This linear range surpasses most micro- and nanostructured platinum approaches. Oxygen and hydrogen were both measured at elevated pressures up to 70 bar and high dissolved concentrations up to 52 mM and 40 mM with measured sensitivities of 26 μA cm−2 mM−1 and 356 μA cm−2 mM−1, respectively. We have successfully shown the application of electrochemical sensors for online, in situ monitoring of analyte concentrations under conditions found in direct synthesis microreactors.
Barium titanate nanoparticle based nonlinear optical humidity sensor Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-02 Aaron Reynolds, John Conboy
A second harmonic generation humidity sensor was constructed with a sensing layer composed of cubic phase barium titanate nanoparticles. The sensor shows a linear response up to a relative humidity of 80%, with response times of 40 ± 10 seconds for decreasing, and 39 ± 7 seconds for increasing humidity. The mechanism of humidity sensitivity is attributed to the modulation of interfacial electric fields due to water vapor adsorption. This research represents the first attempt to bring the surface sensitivity of second harmonic generation to bear on the issue of humidity sensing.
Wearable Potentiometric Tattoo Biosensor for On-body Detection of G-type Nerve Agents Simulants Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-02 Rupesh K. Mishra, Abbas Barfidokht, Aleksandar Karajic, Juliane R. Sempionatto, Joshua Wang, Joseph Wang
Magnetically Three-Dimensional Au Nanoparticles/Reduced Graphene/ Nickel Foams for Raman Trace Detection Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-07-02 Yaoyao Liu, Ying Liu, Yue Xing, Xiaoyu Guo, Ye Ying, Yiping Wu, Ying Wen, Haifeng Yang
Despite much effort has been done to improve the design of magnetic surface-enhanced Raman spectroscopy (SERS) substrates, it still remains a great challenge to develop a clean and efficient substrate for quick and sensitive target detection incorporating with separation and enrichment. Herein, we proposed the synthesis of a three-dimensional structure of Au nanoparticles/reduced graphene oxide/nickel foams (AuNPs/rGO/NFs) for improving SERS detection. The reduced graphene is firstly prepared on the surface of the nickel foams through surface reduction reaction, and then the Au NPs was formed in-situ on the rGO/NFs. Taking advantage of the magnetic properties of nickel foams, the adsorption of graphene and porous nickel foams, and hot spots of Au nanoparticles, the AuNPs/rGO/NFs-based SERS assay can probe 4-pyridinethiol and 6-mercaptopurine as low as 5 × 10−10 M.
Direct Heating of Aqueous Droplets using High Frequency Voltage Signals on an EWOD Platform Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-06-30 Krishnadas Narayanan Nampoothiri, Mahadevan Subramanya Seshasayee, Vinod Srinivasan, M.S. Bobji, Prosenjit Sen
We demonstrate a new technique of heating aqueous droplets on conventional EWOD electrodes by using high-frequency high-voltage AC signals. At high actuation frequencies (10-50 kHz), the droplet temperature rises due to Joule heating from the ohmic currents inside the drop. Using this direct heating technique, we were able to achieve temperatures of 93-94 °C, which is significant for several biochemical applications. The technique is studied extensively using experiments and modelling. Several performance parameters of this heating technique were compared with a standard microheater through experiments and simulation. For the presented technique, the substrate near the droplet was cooler in comparison to the microheater. This will reduce parasitic heating of nearby droplets. A comprehensive study regarding the optimization of the geometrical parameters and the capability to heat solutions to higher temperatures using lower voltage and higher frequency were also performed using simulations. As conventional EWOD electrodes are used for heating the liquid, separate microheaters are not required. This significantly simplifies design and allows us to heat any droplet at any location on the chip. This on demand reconfigurability of droplet heating is the primary benefit of this technique. To establish the abilities of our suggested method, two biochemical experiments were demonstrated.
Discrimination between abiotic and biotic drought stress in tomatoes using hyperspectral imaging Sens Actuators B Chem. (IF 5.667) Pub Date : 2018-06-30 Nik Susič, Uroš Žibrat, Saša Širca, Polona Strajnar, Jaka Razinger, Matej Knapič, Andrej Vončina, Gregor Urek, Barbara Gerič Stare
Crop plants are subjected to various biotic and abiotic stresses. Both root-knot nematodes (biotic stress) and water deficiency (abiotic stress) lead to similar drought symptoms in the plant canopy. In this work, hyperspectral imaging was used for early detection of nematode infestation and water deficiency (drought) stress in tomato plants. Hyperspectral data in the range from 400 to 2500 nm of plants subjected to different watering regimes and nematode infestation levels were analysed by partial least squares - discriminant analysis (PLS-DA) and partial least squares - support vector machine (PLS-SVM) classification. PLS-SVM classification achieved up to 100 % accuracy differentiating between well-watered and water-deficient plants, and between 90 and 100 % when identifying nematode-infested plants. Grouping the data according to the time of imaging increased the accuracy of classification. Shortwave infrared spectral regions associated with the O-H and C-H stretches were most relevant for the identification of nematode infested plants and severity of infestation. This study demonstrates the capability of hyperspectral imaging to identify and discriminate between biotic and abiotic plant stresses.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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