Biothiols such as cysteine (Cys), homocysteine (Hcy) and glutathione (GSH) participate in numerous cellular functions and physiological processes. Because changes in the levels of these biological important substances are associated with various clinical disorders and diseases, methods for their selective sensitive and quantitative detection are in high demand. In the current study, we developed a new, selective and sensitive colorimetric and fluorometric biothiol chemosensor that is comprised of a mercury-complexed, pyridine-containing polydiacetylene (PDA). Owing to its high affinity toward sulfur, biothiols promote decomposition of the pyridine-mercury complex in the PDA in conjunction with colorimetric and fluorescence changes. Specifically, upon addition of biothiols the new chemosensor undergoes a blue-to-red color transition and generates red fluorescence. Moreover, incorporation of the chemosensor in electrospun PEO nanofibers leads to an enhanced sensitivity for biothiol detection. The strategy developed in this study should be applicable to the design of other thiol-specific sensors that utilize pyridine-containing conjugated molecules.

In this work, we proposed the concept of fluorescent speed sensing (FSS) of glycoprotein in chip supramolecular electrophoresis (CSE). To achieve a stable FSS run, we firstly synthesized a novel boronic acid-based diben-zoxanthene receptor (Rp3) by a simple one-pot reaction and the complex probe of [email protected] containing Rp3 and fluorescein (F1), and performed a series of experiments to assess the complex probe's ability for recognition of saccharides and glycoproteins. Secondly, we revealed the mechanism of 'balance electromigration of supramolecular complex probe' in FSS and developed the relevant theory of FSS via a series of theoretical derivation. The FSS theory showed that the moving speed of F1 was a function of glycoprotein content, indicating a novel model of glycoprotein sensing. To demonstrate the validity and utility of developed model and theory, IgG and ovalbumin were selected as model glycoproteins for the relevant experiments. The results verified the validity of FSS concept to glycoprotein assay with good accuracy (less than 6.33% difference from standard HPLC method), stability (less than 6.04% RSD) and linearity (higher than R2 = 0.99) as well as fair sensitivity (8.48 ng). Finally, the FSS was successfully used for the analysis of HbA1c (a key biomarker in diabetes blood). The developed FSS concept and complex probe have great potential for glycoprotein sensing, particularly for the diagnosis of diabetes.

We report a very simple biosensor based on the direct observation of leaky waveguide (LW) modes as exponentially decaying interference fringes in the reflectivity curve. This phenomenon was only observed when the refractive index contrast between the waveguide and sample was low (0.002-0.005) and the LW was illuminated with a range of angles of incidence simultaneously. The LW acts as a phase object in angle space, resulting in Fresnel diffraction and formation of interference fringes for each waveguide mode. We present theory, a qualitative explanation and a mathematical model governing the formation of these fringes. The binding of an analyte to recognition elements immobilised in the LW changes its refractive index and thus the angular position of the fringes, which provides the biosensing mechanism. The reported LWs comprised a film of polyacrylamide and copolymers on glass slides, and provided high sensitivity, mass manufacturability and simple instrumentation.

As one of the BTEX (benzene, toluene, ethylbenzene, xylene) from living environment, benzene has the greatest carcinogenic, anesthetic and neurotoxic effects. At the same time, due to its chemical inertness and nonpolar characteristics, benzene is also the most difficult to detect in BTEX. Herein, based on QCM (quartz crystal microbalance) platform, MOF-14, a metal-organic framework, is first employed to detect benzene vapor by the host − guest interaction of MOF with benzene molecule, as well as Lewis acid-base interaction. By comparing with other three types of MOF materials, it was found that the effect of the ligand on the adsorption is greater than that of the metal point of junction. On the other hand, the different steric hindrance effects in BTEX restrict their adsorption capacity. Thus, the MOF-14 modified QCM sensor exhibits high sensing performance to benzene vapor with a detection limit at the level of 150 ppb. Our studies also indicate that the sensor shows good selectivity to oppose various kinds of interfering gases. Even toluene has a structure similar to that of benzene, it also can be distinguished. And the measurements on repeatability and long-term stability are both approved for the excellent reliability of the MOF-14 modified QCM sensor. By using computational simulation, we explored that why benzene and toluene can be distinguished by MOF-14 modified QCM sensor. This work extended the usages of MOF based QCM for high performance benzene sensing.

Moisture plays a critical role in reinforced concrete corrosion, underpinning structural degradation which costs the global economy a staggering $350 bn per year (0.5% GDP). Both moisture sensors and repair materials that limit water ingress are required, but monitoring and maintenance are often viewed as separate challenges. This paper outlines a first-time demonstration of moisture sensors based on low calcium fly ash geopolymers — a class of cementitious, electrolytically conductive repair materials. Electrochemical impedance spectroscopy and equivalent circuit models are used to understand and optimize the electrical response of geopolymer sensors to water content and temperature. Moisture and temperature precisions of 0.1 wt% and 0.1 ° C are demonstrated respectively, and sensor drifts over 20 minute periods were found to be within 1–3%. Sensor responses were also shown to be repeatable to within 3% between wetting and thermal cycles. Results from spectrometry and chromatography analyses link this repeatability to the minimal ion leaching from the sensors. The study demonstrates the feasibility of moisture sensing using geopolymers, and furthers our current understanding of the role of moisture in the ionic conductivity of alkali-activated materials. This work is anticipated to be the first stage in developing 2D, distributed sensor-repairs for concrete structures, and other chemical sensors that support concrete structural health monitoring and prognostics.

To overcome the widespread misuse of antibiotics and reduce the growing problem of multidrug resistance, rapid, sensitive and specific novel methods to determine bacterial antibiotic susceptibility are needed. This study presents a combined dielectrophoresis (DEP) - Raman Spectroscopy (RS) method to obtain direct, real-time measurements of the susceptibility of a suspension of planktonic bacteria without labelling or other time-consuming and intrusive sample preparation processes. Using an in-house constructed DEP-Raman device, we demonstrated the susceptibility of Escherichia coli MG1655 towards the second-generation fluoroquinolone antibiotic ciprofloxacin (CP) after only 1 h of treatment, by monitoring spectral changes in the chemical fingerprint of bacteria related to the mode of action of the drug. Spectral variance was modelled by multivariate techniques and a classification model was calculated to determine bacterial viability in the exponential growth phase at the minimum bactericidal concentration (MBC) over a 3 h time span. Further tests at a sub-minimum inhibitory concentration (MIC) and with a CP-resistant E. coli were carried out to validate the model. The method was then successfully applied for class prediction in a biocide cross-induced tolerance assay that involved pre-treating E. coli with triclosan (TCS), an antimicrobial used in many consumer products. High specificity and adequate sensitivity of the proposed method was thereby demonstrated. Simultaneously, standard microbiological assays based on cell viability, turbidity and fluorescence microscopy, were carried out as reference methods to confirm the observed Raman response.

Electrochemical sensing signal is easily interfered by substance with similar redox, which is difficult to be eliminated. The adjusting effect of interfacial barrier on electrochemical response was proposed to suppress this interference. Porous reduced graphene oxide encapsulated ZnO microspheres were prepared and used for detecting dopamine. The response to dopamine is enhanced and the responses to ascorbic acid and uric acid are decreased by changing the barrier height. An ultrahigh sensitivity (1240.74 μA mM-1 cm-2) with a wide linear range is 1-600 μM and excellent selectivity to dopamine is achieved. Employing the interfacial barrier to adjust electrochemical response is a promising approach to improve the specificity and sensitivity of electrochemical sensors.

Ultra-low humidity detection is significant in some important industrial fields, such as integrated circuit manufacturing, chip packaging. However, the traditional ionic-type humidity sensor is not competent for the detection of ultra-low humidity, but can only realize the detection of medium humidity to high humidity. Here, moisture-induced discoloration material Nickel(II) iodide (NiI2) is found to be highly sensitive to moisture, and both its electrical properties and color will change with environmental humidity variation. Especially, NiI2 exhibits the largest impedance change to date in the ultra-low humidity range compared with state of the art. The impedance variation is up to 2 orders of magnitude in the range of 0.4% - 11% RH, which means that NiI2 can realize the detection of ultra-low humidity. The excellent performance of NiI2 in ultra-low humidity is attributed to the material transition characteristics susceptible to humidity rather than the traditional surface mechanism of water adsorption. Moreover, combining the reversible black-to-transparency moisture-induced discoloration behavior with humidity sensing properties, a flexible wristband based on NiI2 is developed to realize the dual-mode detection of wide range environmental humidity. These results demonstrate that NiI2 has great application prospects in professional ultra-low humidity detection and wearable humidity detection equipment.

Inspired by the intrinsic catalytic properties of alkaline phosphatase (ALP) and tyrosinase (TYR) as well as the fluorogenic reaction between levodopa and resorcinol, a ratiometric fluorescent probe based on the CdTe/CdS/ZnS/SiO2 QDs for visual monitoring the activity of ALP was developed. Phosphotyrosine was catalyzed into tyrosine by ALP, and then tyrosine was catalyzed into levodopa by TYR. Carboxyazamonardine, the reactive product of levodopa and resorcinol, gave rise to a strong blue fluorescence at 470 nm and quenched the red fluorescence of CdTe/CdS/ZnS/SiO2 QDs at 620 nm due to their inner filter effect. Thus, the resulting ratiometric fluorescence acted as the signal output for quantitative ALP detection, accompanying with the fluorescence color changing from red to purple and finally blue for semiquantitative ALP detection. A good linear relationship was obtained ranging from 0.08-500 U L-1 with the detection limit of 0.02 U L-1. Moreover, the probe was successfully applied to monitoring ALP activity in human serum samples without any pretreatment, and also used to screen ALP inhibitors. These results suggested that the developed method offered a highly sensitive and promising analytical platform for ALP in clinical diagnostics and paved a new way for monitoring enzymes activity visually for point-of-care diagnosis.

Solid state electrolyte type formaldehyde (HCHO) gas sensors based on a novel pyrochlore structure Gd2Zr2O7 solid electrolyte coupled with rod-shaped ZnO sensing electrode (SE) were initially designed and fabricated in this paper. The incorporation of alkaline-earth metal Ca can significantly improve sensing performance of the Gd2Zr2O7 based sensors to HCHO. The response value (ΔV) of the sensors based on Gd2-xCaxZr2O7 (x = 0, 0.02, 0.05 and 0.1) varied approximately linear with the logarithm of HCHO concentration in the range of 1-100 ppm at 600 °C, with sensitivities of -25, -30, -15 and -5 mV/decade, respectively. The optimal sensor based on Gd1.98Ca0.02Zr2O7 (GCZ(0.02)) exhibited the excellent sensing characteristics with maximum response value (-61.3 mV) and extremely short response time (3 s) to 100 ppm HCHO. In addition, the GCZ(0.02) sensor also showed good selectivity and stability within 20-day period of continuous high-temperature aging under high-humidity condition. Conclusively, the sensing behavior and mechanism based on mixed potential were investigated and demonstrated by the mearsurement of the polarization curves.

Detecting biomarkers with high sensitivity is key for the early diagnosis of hepatocellular carcinoma (HCC). Nanostructure units with knobby surface are bridged to obtain significant surface-enhanced Raman scattering (SERS) signals. This changes the plasma coupling mode and the hotspots distribution between neighboring units as confirmed by finite-difference time-domain simulations. These arrays of bridged knobby units are used to quantitatively analyze the concentrations of α-Fetoprotein (AFP) and AFP-L3 by immunoanalysis using a combination of frequency shifts and intensity changes of SERS. By using these arrays of bridged knobby units as SERS immunochips, the detection limits of AFP and AFP-L3 decrease to 3 pg/mL. This immunoanalytic method has potential value for the diagnosis of early liver cancer in patients, offering advantages of convenience, time saving, low detection limit, and high precision.

In this paper, we report the real-time, ultrasensitive, reproducible detection of volatile odorant molecules emitted by human based on free-standing silicon nanowire (SiNW) array functionalized with Anopheles gambiae odorant binding protein (AgOBP). Highly responsive SiNW array was fabricated with a novel low-cost top-down fabrication approach. The free-standing and triangular cross sectional structure allowed efficient sensing of AgOBP conformational change induced by odorant binding. The resulting bioelectronic nose (B-nose) possessed high sensitivity down to several ppb, and outstanding size and functional group selectivity. The device showed reproducible and long-lasting performances. We also demonstrated the multiplex detection of various odorants with a sensor array functionalized with three different AgOBPs. The AgOBP-SiNW B-nose reported herein provides a powerful and effective platform for future development of multiplexed human body odor sensor arrays.

Cancer cells’ MMP9 activity plays vital roles in tumor development. Tumor cells are in an adhesion profile during cell-cell and cell-matrix interaction. However, it is challenging for current platforms (e.g., typical droplet systems) to measure MMP9 secreted by single cells in an adhesion profile and retrieve the cells of interest for downstream analysis. Herein, we report a single-cell protease sensor (SCPS) based on ‘virtual droplet’ that can fulfill the above two requirements. SCPS can form 648 virtual droplets within one minute as a one-cell-per-droplet profile, which offers an isolated space with a substrate to support cells’ adhesion and enables MMP9 measurement for hundreds of single adhered cells within two hours. In addition to high cellular heterogeneity of cancer cells in MMP9 production, we also found that adhered MDA-MB-231 cells produced relatively more MMP9 than that done by suspended cells. Furthermore, the cells producing high MMP9 and low MMP9 were retrieved and mRNA-sequence was performed on them. The results demonstrated that some KEGG pathways associated with cell migration and invasion were enriched and a few related genes (e.g., FYN, MAPK3, RAF) were upregulated in high-MMP9 cells. This SCPS system provides a promising strategy for measuring single-cell’s protease activity.

Point-of-care quantitative detection of biochemical markers has broad applications in resource-limited settings. However, current challenges including difficulty in sample preparation and limitation in result quantitation make point-of-care detection platforms failed to achieve fully sample-to-answer detection or meet the clinical quantitative demands. Here, we developed a novel point-of-care platform to realize fully sample-to-answer biochemical marker quantitation in whole blood. Our platform integrated a plasma separation module and a detection module. The plasma separation module contained a plasma separation strip could rapidly separate the plasma from whole blood samples by lateral flow. The detection module generated a colorimetric signal which could be quantified by the smartphone ambient light sensor (ALS) in an equipment-free manner. As a proof-of-concept, two hepatobiliary disease-associated markers, total bilirubin (TBil) and direct bilirubin (DBil), were detected from whole blood to quantitative result. The quantitative performance for clinical samples was highly consistent with the well-established clinical chemistry analyzer. Our platform exhibited remarkable advantages of significant portability (< 40 g), low cost (< $5), rapidity (< 5 min), instrument-free, high sensitivity (< 1 μM), and accuracy (89.5 % for TBil, 94.7 % for DBil), which showed up a great potential for biochemical markers detection in resource-limited settings.

Mode noise suppression in off-axis integrated cavity output spectroscopy (OA-ICOS) is a key for improving the signal-to-noise ratio (SNR) of a sensor system, which basically depends on the ability to smooth out the cavity mode structure and to reduce the cavity mode linewidth. We demonstrated a novel dual-input dual-output (DIDO) coupling scheme of OA-ICOS for mode noise suppression. The influences of beam splitting ratio and light reflection number to the output intensity and cavity mode linewidth were theoretically studied. Experimental investigation on the suppression of cavity mode noise was carried out in terms of detection sensitivity and SNR through methane (CH4) measurements. A SNR of 221 and a detection sensitivity of 1.73 × 10-8 cm-1 Hz-1/2 was obtained for the DIDO-based OA-ICOS sensor system. The SNR was improved by a factor of ∼ 2.5 and the sensitivity was improved by a factor of ∼ 2.2 compared to the regular single-input single-output (R-SISO) approach. Multi-input multi-output (MIMO) configuration was further numerically studied to verify the noise suppression ability of this detection concept. This work reveals a new laser-to-cavity coupling method and provides a novel way to exploit OA-ICOS sensors with improved SNR and sensitivity.

W-doped NiO nanotubes (NTs) were successfully synthesized for efficient sensing of ethanol vapor using a low cost and economical electrospinning method. The response (resistance ratio) of sensor based on 4% W-NiO NTs to100 ppm ethanol is as high as 40.56 at 200 °C, which is 10 times higher than that of pure NiO sensor. This significant enhancement in sensor response can be attributed to the change in morphology, increase in oxygen vacancies, and the decrease in hole concentration in NiO by W doping. Based on the adsorption and desorption theory of oxygen, we also demonstrated that the atmospheric oxygen content can improve the sensor response and shorten the response time by increasing the amount of adsorbed oxygen.

Pure and Ti-doped NiO multiroom spheres were prepared via ultrasonic spray pyrolysis, and their gas sensing characteristics were investigated. The sensor using 10 at% Ti-doped NiO multiroom spheres exhibited an unprecedented high response (resistance ratio = 337.8) to 1 ppm p-xylene at 350 ℃, whereas the sensor using pure NiO multiroom spheres exhibited a negligibly low response (1.3). Moreover, the control of the Ti doping and film thickness provided intriguing strategies for tuning the xylene and methylbenzene sensing characteristics, such as the selectivity, response, sensitivity (slope between response and gas concentration), and detection limit. The versatile tunability on gas sensing characteristics was explained by the Ti-doping-induced variation of the oxygen adsorption, mesoporosity, specific surface area, and charge-carrier concentration, as well as the control over the reforming and oxidation of the analyte gases using the multiroom-structured micro-reactors with high catalytic activity.

In this study, we developed a simple and sensitive surface-enhanced Raman scattering (SERS) technique for the detection of choline in infant formulas based on a filter-based flexible substrate. The flexible substrate with excellent SERS activity and reproducibility was fabricated using a syringe filter and Ag triangular nanoplates. The Raman marker, 3-mercaptophenylboronic acid, was oxidised to 3-hydroxythiophenol in the presence of H2O2, which caused a decrease in the SERS peak intensity ratio (I1021 cm-1: I996 cm-1). Utilising the enhanced flexible substrate, a quantitative detection method for H2O2 was developed. Additionally, choline could be hydrolysed by choline oxidase to generate betaine and H2O2. Thus, the SERS method was successfully applied to detect choline in the concentration range of 10-3–10-7 M with a beneficial limit of detection as low as 8.36 nM. Importantly, the recovery of choline from infant formula milk powder was approximately 99%. The excellent performance of the flexible substrate-based SERS method demonstrated its potential for application in H2O2-generated oxidase-based biosensing.

In this study we report for the first time on a surface acoustic wave (SAW) sensor modified with a molecularly imprinted polymer (MIP) selectively recognizing the cerebral dopamine neurotrophic factor (CDNF) protein. CDNF-MIP as a synthetic recognition element was prepared by a simple electrochemical surface imprinting approach allowing its reliable interfacing with SAW sensor. The optimal thickness of the MIP layer as well as a suitable pretreatment method were adjusted in order to improve the recognition capacity and selectivity of the resulting CDNF-MIP sensor. The selectivity of the sensor was studied by the carefully designed competitive binding experiments, which revealed that the sensor can sense CNDF confidently in label-free manner starting from 0.1 pg/ml. We anticipate that the findings can be a premise for fabrication of cost-effective research or diagnostics tools in the field of neurodegenerative diseases.

Traditional colorimetric sensors often suffer from the low color resolution and the not well-defined boundary between the yes and no answers, especially for distinguishing the similar color readouts with the naked eye. Herein, a simple strategy is communicated for greenly converting colorimetric sensor into a photothermal sensor, which is based on the simple color-to-thermal (temperature) signal readout conversion. The colorimetric system based on simply mixing commercially available chemicals of 3,3,5,5-tetramethylbenzidine (TMB) and silver ions (Ag+), provides a straightforward blue color readout owing to the generation of oxidized TMB (TMBox). In the presence of the target alkaline phosphatase (ALP), ascorbic acid phosphate (AAP) in the system could be hydrolyzed into ascorbic acid (AA), subsequently reducing the blue colored TMBox into colorless TMB. The blue-to-colorless change-based colorimetric system also exhibits the highly sensitive near-infrared (NIR) laser-driven photothermal response, allowing the successful thermometer-detectable signal-based assay for point-of-care testing (POCT) of ALP levels just using a common thermometer. This study not only demonstrated a regulatory strategy to convert color-based signal readout into thermal (temperature)-based signal readout, but also established a facile method to design affordable thermometric sensors for POCT and instrument-free bioanalysis, especially in low-resource settings.

Structure and surface properties of the sensing materials have been recognized as the primary consideration for fabricating metal oxide semiconductor gas sensors. In this study, one-dimensional ZnO nanowires with large length-to-diameter ratio were firstly synthesized by a facile hydrothermal method. Then, different contents of ultra-fine In2O3 nanoparticles were directly grown on their surface. The structural characterization confirmed that the In2O3 nanoparticles were only 3∼5 nm in diameter and well dispersed on the surface of ZnO nanowires. The gas sensing results showed that the ultra-fine In2O3 nanoparticles gave rise to a significant improvement in NO2 response at their optimal operating temperature of 150 °C. The highest response of 54.6 to 1 ppm NO2 was obtained for the sensor based on In2O3/ZnO composites with the In/Zn molar ratio of 5%, which was about 8 times higher than that of pure ZnO nanowires. Importantly, a high response of 18.4 to a relatively low NO2 concentration of 250 ppb was also observed for In2O3-functionalized ZnO nanowires. The enhanced NO2 sensing mechanisms of ZnO nanowires functionalized with ultra-fine In2O3 nanoparticles were discussed.

In this paper, a micro thermal conductivity detector (TCD) with suspended thermistors based on a Silicon-On-Insulator (SOI) substrate was successfully fabricated by using a MEMS technique. The top layer of silicon of the SOI substrate was utilized as the supporting layer of the thermistor, which possessed excellent mechanical strength. The buried SiO2 was utilized as the etch stop layer of deep reactive ion etching in the thermistor release process, which precisely defined the channels with a high depth-to-width ratio and acquired an ultra-small dead volume (∼200 nL). The micro TCD showed sensitive detection at levels as low as 5 ppm of n-alkanes C14-C16 mixtures. Besides, the micro TCD demonstrated excellent universal detection to gas mixtures, which detected all thirteen analytes in the standard sample of n-alkanes C8-C20 mixtures and all eight analytes in the standard sample of VOCs (volatile organic compounds).

Circulating microRNAs (miRNAs) are effective cancer biomarkers that are highly stable in body fluids enabling noninvasive detection. Portable, low-cost and efficient biosensing systems is crucial for early on-site diagnosis, especially in resource-limited settings. Present work deals with the development of a smartphone-based biosensing system for electrochemical detection of circulating microRNA-21 (miR-21) biomarker in saliva as a proof-of-concept. The smartphone-based biosensing system composed of a disposable screen-printed biosensor modified with reduced graphene oxide/gold (rGO/Au) composite, a circuit board for detection and a Bluetooth-enabled smartphone equipped with specially designed Android application. The hybridization between miR-21 target and ssDNA probe on the rGO/Au-modified electrode resulted in the decrease in peak current with increase in miR-21 target concentration. The smartphone-based biosensing system showed comparable performance with commercial electrochemical workstation, for miR-21 detection in the concentration range of 1 × 10-4 M to 1 × 10-12 M with correlation coefficient (r2) of 0.99. In addition to good selectivity in discriminating mismatched and non-target sequences, the biosensing system also showed acceptable recovery rate ranging from 96.2% to 107.2% in spiked artificial saliva. The smartphone-based biosensing system is envisioned to be able to realize rapid and highly sensitive detection of circulating miRNA biomarker in body fluid for point-of-care testing in remote areas.

Hierarchical urchin-like Co3O4/CoWO4 core/shell microspheres are fabricated using a hydrothermal ion exchange approach. Co3O4/CoWO4 microspheres are made using Co3O4 nanowires, which are then covered using thin CoWO4 nanosheets. Capture of cobalt ions from Co3O4 nanowires by the tungsten acid radical is responsible for the CoWO4 nanosheet covering. The gas sensing characteristics show that urchin-like Co3O4/CoWO4 core/shell microspheres-based sensors shows high response towards acetone vapor, which is larger than that of either Co3O4 or CoWO4. A possible gas sensing mechanism for the improved performance of Co3O4/CoWO4 core/shell microspheres-sensor is the formation of heterostructure, which modulates the hole accumulation layer of Co3O4.

A novel visual detection method was developed for H2O2 and glucose detection via the L-Cysteine (L-Cys) mediated synthesis of quantum dots (QDs). The mechanism of the ligand effect during QDs synthesis was also studied by theoretical calculation. This strategy is based on that L-Cys can be used as both H2O2 substrate and ligand to mediate biomimetic synthesis of luminescent CdTe QDs. Iodide (I-) can catalytic oxidized L-Cys to L-cystine in the presence of H2O2, which inhibits the synthesis of QDs. Hence, the degree of inhibition for the QDs synthesis is proportional to the H2O2 concentration. Additionally, the ligand effect of L-Cys and L-cystine for CdTe QDs synthesis was studied. The density functional theory (DFT) calculations showed that the combination of CdTe QDs with L-Cys had higher energy and more stable configuration than that with L-cystine, indicating that L-Cys is the more stable ligand of QDs. Under the optimized conditions, a low limit of detection (LOD) was obtained for H2O2 (0.3 nM). Then, we used H2O2 as a bridge for glucose detection, with a LOD of 5 nM. The feasibility of this sensor was demonstrated by rapid detection of H2O2 and glucose by naked-eye at a level of 10 nM.

Amyloid-β (Aβ) is a peptide that is produced in the brain and carried across the blood brain barrier to the blood. It is an important biomarker for the blood-based diagnosis of early stage Alzheimer's disease (AD). However, the challenges of using blood Aβ are that there are several isoforms of the peptide and that the difference in concentration of the peptide in the blood between AD patient and normal individual is extremely low. Here, we developed interdigitated microelectrodes (IMEs) as an impedance biosensor for the blood-based Aβ detection using gold nanoparticles (AuNPs) sandwich assay. It provided logarithmically linear sensitivity and enhancements in the detection limits of approximately 2.87-fold and 74.84%, respectively. We prepared mouse plasma sample from the blood of double-mutated APP/PS1 transgenic (TG) and wild-type (WT) mouse group, and AD diagnostic ability was tested by Aβ detection in the plasma samples. Our results showed that AuNPs sandwich assay assisted Aβ detection successfully discriminated TG and WT mouse groups. Thus, with this sensing system, we detected Aβ with high sensitivity and selectivity. This Aβ sensing system with AuNPs sandwich assay could lead to a significant advance in human blood sample based clinical diagnosis.

In this paper, a novel fuel cell-type methanol gas sensor based on platinized mesoporous titanium nitride is fabricated. Mesoporous TiN, synthesized from ammonolysis of Zn-containing oxide precursor, is utilized as a support for platinum for both anode and cathode. Its performance is compared to that of Vulcan XC-72R carbon blacks. Hot press method is used for the fabrication of the sensor device. The results for methanol gas detection at room temperature reveal that Pt/TiN sensor has enhanced sensitivity. The response current towards 50 ppm methanol reaches 9.68 μA, which is ∼20 times higher than that of Pt/C sensor (0.41 μA). The Pt/TiN sensor also exhibits excellent repeatability, selectivity and long-term stability. This work reveals the potential of titanium nitride as support materials for gas sensing technologies.

Protein S-nitrosylation is an important post-translational modification, which has important effect on protein functions and is relevant to various diseases. For quantification of the S-nitrosated proteins, it is still challenging to establish a detection method in combination of fast and one-step determination, highly sensitivity and accuracy. Here, we develop a label-free, direct detection method for S-nitrosated proteins based on resonance Raman scattering of ferrous cytochrome c. The laser source of the Raman spectrometer is utilized both for inducing NO leakage and for Raman scattering excitation. The heme ligation alteration and oxidation enable fast quantification of the released NO by the resonance Raman spectroscopy of the cytochrome c. All the results shown in this study demonstrate the great potential of the proposed method for fast, sensitive and reliable assessment of total S-nitrosated proteins in the clinical applications.

In this work, a novel high electro-catalytic material was synthesized using PtNi nanospheres to functionalize two-dimensional (2D) ultrathin Cu-TCPP(Fe) nanosheets ([email protected](Fe)), and was further applied to develop an enzyme-free electrochemical immunosensor for the ultrasensitive determination of calprotectin (CALP). The bimetallic Cu-TCPP(Fe) nanosheets with large surface area and massive accessible active sites permitted multiple PtNi to attach their surface, which not only enhanced the catalytic ability and conductivity for non-enzymatic amplification but also provided the modified active sites for antibody immobilization as signal labels. Upon the dual electro-catalytic activity of Cu-TCPP(Fe) and PtNi towards H2O2 reduction for signal amplification, this proposed sandwich CALP immunosensor exhibited a wide linear range of 200 fg mL-1 ∼ 50 ng mL-1 and a low detection limit of 137.7 fg mL-1. The functionalized MOF nanosheets-based biosensing method offered an enzyme-free signal amplification strategy, which provided great promise for further bioanalysis and clinical study.

Hollow waveguide (HWG) based gas sensors boast fast response time, high-sensitivity, compactness, but less-precision for their intrinsic very small bore-diameter and sampling volume. We investigated the effects of gas flow regimes on the complicated spectral line broadening in HWGs, and analyzed quantitatively by taking atmospheric water vapor spectrum as an example. We derived an equivalent pressure to simplify the calculation of spectral line broadening in nonuniform pressure of HWGs, and proposed to enhance the performance of such kinds of sensors with wavelength modulation spectroscopy by laminar flow regime, pump down mode, and the optimized flow rate. Experimental results showed dramatic improvements with the scheme: sensitivity increase by 18.6%, lower uncertainty, and immune to flow fluctuation. The method is efficient, convenient and with no extra cost. It can promote both HWG and substrate-integrated HWG (iHWG) based gas sensors.

With the benefits of device simplicity and functionality, optoelectrowetting (OEW) has been studied as a liquid-handling approach for lab-on-a-chip applications. Recent studies have further demonstrated three-dimensional (3D) OEW technology by using a polymer-based photoconductive material, titanium oxide phthalocyanine (TiOPc), which allows device fabrication on flexible substrates via a low-temperature spin-coating method. However, one critical drawback of this TiOPc material is its low-quality photoconductive property and thus corresponds to very poor OEW modulation. Our study herein presents light absorption of the TiOPc largely enhanced by using plasmonic nanoparticles to significantly improve OEW performance for effective light-driven droplet manipulation. Metallic nanoparticles dispersed on the TiOPc layer enable to induce plasmonic light scattering with an increased optical path length. Consequently, more light rays can be absorbed onto the TiOPc and dramatically increase its photoconductivity to enhance OEW performance. Our measurement studies have verified a 2-order improvement in the TiOPc’s light absorption performance by using aluminum (Al) nanoparticles. We have experimentally demonstrated that a 4 µm thick layer of Al nanoparticles fabricated with a 2.0 wt% solution enables 60.4° more contact angle modulation than the one used with no nanoparticles. The droplet dynamics study has also presented the light-actuation speed of a droplet as 12.5 mm/s enhanced by plasmonic light scattering, which is a 39-fold faster speed than that without nanoparticles. Our plasmonic nanoparticle-enhanced OEW technology can offer device simplicity, flexibility and functionality, while providing much enhanced OEW performance useful for various digital microfluidic (DMF) applications by allowing effective light-driven droplet manipulations.

A piezoelectric peptide-hpDNA based gas sensor array has been used for the detection of terpenes coming from Cannabis sativa samples. The array consisted in 11 sensors, 6 having pentapeptides and 5 having hairpin DNA as binding elements. The volatile composition of 28 Cannabis sativa samples, assessed by GC-MS analysis, allowed their classification into 2 groups having as monoterpenes and sesquiterpenes in different amounts. The response of the gas sensor array to the same samples demonstrated that both type of sensors are sensitive to the terpenes and contribute to classification. A satisfactory classification (79% of correctly identified samples) was found using a PLS-DA approach. Using the same dataset and a simple ANN approach the headspace analytical profile of the two different groups was predicted with an average prediction error ≤1%.

We propose a highly sensitive immunosensor based on the Localized Surface Plasmon Resonance (LSPR) for 17β-estradiol (E2) quantification in water. E2 molecules are recognized by polyclonal antibodies immobilized onto gold nanoparticles (AuNPs) and act as linkers that cause nanoparticles aggregation. This leads to the change in the optical properties of the solution visible even by naked eyes. The aggregates were characterized by Dynamic Light Scattering (DLS) and Scanning Transmission Electron Microscopy (STEM) and provided an accurate assessment of the inter-particle distance. The finite-difference time-domain (FDTD) method applied to a Mie problem like workspace allowed us to describe the optical behaviour of the AuNP aggregates with excellent agreement between the experimental and numerical results. The limit of detection (LOD), without any preconcentration step, is 3 pg/mL (11 pM), whereas the detection range extends over five decades up to 105 pg/mL. The proposed E2 immunosensor was tested in tap water, where no significant cross-reaction signal was detected by similar molecules (testosterone, progesterone, estrone and estriol). The device described here represents a significant improvement of low E2 levels determination in terms of affordability, time and measuring simplicity, making it suitable for environmental applications.