Post-assay growth of gold nanoparticles as a tool for highly sensitive lateral flow immunoassay. Application to the detection of potato virus X Microchim. Acta (IF 5.705) Pub Date : 2018-10-17 Vasily G. Panferov, Irina V. Safenkova, Anatoly V. Zherdev, Boris B. Dzantiev
This article demonstrates a new kind of a highly sensitive lateral flow immunoassay (LFIA). It is based on the enlargement of the size of gold nanoparticles (GNPs) directly on the test strip after a conventional LFIA. Particle size enlargement is accomplished through the catalytic reduction of HAuCl4 in the presence of H2O2 and through the accumulation of additional gold on the surface of the GNPs. To attain maximal enhancement of the coloration of the zone in the test strip and to achieve a minimal background, the concentration of precursors, the pH value, and the incubation time were optimized. GNPs on the test strip are enlarged from 20 to 350 nm after a 1-min treatment at room temperature. The economically important and widespread phytopathogen potato virus X (PVX) was used as the target analyte. The use of the GNP enlargement method results in a 240-fold reduction in the limit of the detection of PVX, which can be as low as 17 pg·mL−1. The total duration of the assay, including virus extraction from the potato leaves, lateral flow, and the enhancement process, is only 12 min. The diagnostic efficiency of the technique was confirmed by its application to the analysis of potato leave samples. No false positives or false negatives were found. The technique does not depend on specific features of the target analyte, and it is conceivably applicable to numerous GNP-based LFIAs for important analytes.
An amino-functionalized mesoporous silica (KIT-6) as a sorbent for dispersive and ultrasonication-assisted micro solid phase extraction of hippuric acid and methylhippuric acid, two biomarkers for toluene and xylene exposure Microchim. Acta (IF 5.705) Pub Date : 2018-10-11 Mohammad Behbahani, Saman Bagheri, Fariborz Omidi, Mostafa Mohammadpour Amini
The authors described a new application of amino-functionalized KIT-6 for dispersive ultrasonication-assisted micro solid phase extraction of hippuric acid (HA) and methyl hippuric acid (MHA) from human urine and water samples. In the first step, an amino-functionalized mesoporous silica of type KIT-6 was synthesized. It was characterized by field emission scanning electron microscopy, Fourier transform infrared spectrometry, nitrogen adsorption-desorption analysis, thermogravimetry and X-ray diffraction. Following sorption and desorption with 1.0 mL methanol/NH4OH (1%; v/v), HA and MHA were quantified by HPLC with UV detection. Various important parameters were optimized by Box-Behnken design. Under optimized conditions, The limit of detections (LOD) were calculated by a signal-to-noise ratio of 3, which were 0.5 μg L−1 and 0.2 μg L-1 for HA and MHA, respectively, and the calibration plot is linear in the 1–1000 μg L−1 concentration range. Only small matrix effects were found. The method was successfully implemented for the sensitive determination of HA and MHA in (spiked) human urine samples.
Nitrogen-rich core-shell structured particles consisting of carbonized zeolitic imidazolate frameworks and reduced graphene oxide for amperometric determination of hydrogen peroxide Microchim. Acta (IF 5.705) Pub Date : 2018-10-09 Zehui Li, Yuheng Jiang, Zhuoya Wang, Wenbo Wang, Yi Yuan, Xiaoxue Wu, Xingchen Liu, Mingjie Li, Sobia Dilpazir, Guangjin Zhang, Dongbin Wang, Chenming Liu, Jingkun Jiang
Core-shell structured particles were prepared from carbonized zeolitic imidazolate frameworks (ZIFs) and reduced graphene oxide (rGO). The particles possess a nitrogen content of up to 10.6%. The loss of nitrogen from the ZIF is avoided by utilizing the reduction and agglomeration of graphene oxide with suitable size (>2 μm) during pyrolysis. The resulting carbonized ZIF@rGO particles were deposited on a glassy carbon electrode to give an amperometric sensor for H2O2, typically operated at a voltage of −0.4 V (vs. Ag/AgCl). The sensor has a wide detection range (from 5 × 10−6 to 2 × 10−2 M), a 3.3 μM (S/N = 3) detection limit and a 0.272 μA·μM−1·cm−2 sensitivity, much higher than that of directly carbonized ZIFs. The sensor material was also deposited on a screen-printed electrode to explore the possibility of application.
A needle-like reusable surface-enhanced Raman scattering substrate, and its application to the determination of acetamiprid by combining SERS and thin-layer chromatography Microchim. Acta (IF 5.705) Pub Date : 2018-10-09 Yan Kang, Ting Wu, Xiaozhen Han, Haixin Gu, Xin Zhang
A micro surface-enhanced Raman scattering (SERS) substrate has been fabricated by electrochemical deposition of dendrite-like gold on carbon fiber needles (Au-CFNs). Scanning electron microscopy and energy dispersive spectroscopy were used to confirm the presence of the gold nanostructure on the CFNs. This substrate has a Raman scattering enhancement factor as high as 3.3 × 10^7 when using rhodamine 6G as the reporter molecule. The high SERS sensitivity is attributed to the massive hotspots on gold bulges that enhance the local surface plasmon resonance. The Au-CFN substrate was reproduced 10 times after electrochemically wiping off the analytes from the needle-like electrode. The substrate has attractive features such as convenient sampling, low sample dosage, and minimal invasion. It was applied, in combination with thin-layer chromatography, for the determination of acetamiprid on vegetables. The result was more accurate because the sample information of both the surface and the bulk can be obtained at the same time after inserting the tip of this needle substrate into the TLC plate. The limit of detection for acetamiprid is 0.05 μg⋅mL-1 and the linear range is 0.1–10 μg⋅mL-1.
A voltammetric assay for microRNA-25 based on the use of amino-functionalized graphene quantum dots and ss- and ds-DNAs as gene probes Microchim. Acta (IF 5.705) Pub Date : 2018-10-09 Azam Akbarnia, Hamid R. Zare
The authors describe a DNA based voltammetric assay for the cancer biomarker microRNA-25. A glassy carbon electrode (GCE) was modified with amino-functionalized graphene quantum dots and used as an amplifier of electrochemical signals. p-Biphenol is introduced as a new electroactive probe with a fairly low working potential of 0.3 V (vs. Ag/AgCl). The stages of fabricating the electrode were characterized by cyclic voltammetry and electrochemical impedance spectroscopy. ss-Probe DNA was immobilized on the modified GCE and then exposed to a sample containing microRNA-25. The results indicated that the electrode can distinguish complementary microRNA-25 from a single-base mismatch. The increase in the electrochemical response of PBP and the positive shift in the potential peak indicate that PBP is intercalated between two strands. Under optimized experimental conditions, the current of the electrode increases linearly with the logarithm of the microRNA-25 concentration in the range from 0.3 nM to 1.0 μM, and the detection limit is 95.0 pM. The assay was successfully employed to the determination of microRNA-25 in spiked human plasma.
Ultrasensitive determination of thrombin by using an electrode modified with WSe 2 and gold nanoparticles, aptamer-thrombin-aptamer sandwiching, redox cycling, and signal enhancement by alkaline phosphatase Microchim. Acta (IF 5.705) Pub Date : 2018-10-09 Yi-Han Wang, Huan Xia, Ke-Jing Huang, Xu Wu, Ying-Ying Ma, Rui Deng, Yun-Fei Lu, Zi-Wei Han
A sensitive aptamer/protein binding-triggered sandwich assay for thrombin is described. It is based on electrochemical-chemical-chemical redox cycling using a glassy carbon electrode (GCE) that was modified with WSe2 and gold nanoparticles (AuNPs). The AuNPs are linked to thrombin aptamer 1 via Au-S bonds. Thrombin is first captured by aptamer 1 and then sandwiched through the simultaneous interaction with AuNPs modified with thrombin-specific aptamer 2 and signalling probe. Subsequently, the DNA-linked AuNP hybrids result in the capture of streptavidin-conjugated alkaline phosphatase onto the modified GCE through the specific affinity reaction for further signal enhancement. As a result, a linear range of 0–1 ng mL−1 and a detection limit as low as 190 fg mL−1 are accomplished. The specificity for thrombin is excellent. Conceivably, this strategy can be easily expanded to other proteins by using the appropriate aptamer.
Fluorometric determination of doxycycline based on the use of carbon quantum dots incorporated into a molecularly imprinted polymer Microchim. Acta (IF 5.705) Pub Date : 2018-10-06 Xiaotong Feng, Jon Ashley, Tongchang Zhou, Yi Sun
A fluorometric assay is described for doxycycline detection. It is based on the use of nitrogen-doped carbon quantum dots (NCQDs) coated with molecularly imprinted polymers (MIPs). The NCQDs were prepared by a one-step hydrothermal reaction using citric acid and ethylenediamine (EDA) as the starting materials. Afterwards, the NCQDs were incorporated into the polymer that was molecularly imprinted with doxycycline. It is found that doxycycline quenches the fluorescence of the NCQDs, and that the functional groups on the surface of NCQDs play an important role in terms of quenching efficiency. A larger fraction of carboxyl groups presented on the surface of NCQDs leads to a higher quenching efficiency due to the enhanced electron transfer from NCQD to doxycycline. The NCQDs@MIP composite can specifically and rapidly recognize doxycycline. Fluorescence drops linearly in the 5 to 50 μM doxycycline concentration range, and the limit of detection is 87 nM. This method was successfully applied to the determination of doxycycline in spiked pig serum where it gave recovery rates of >94%.
Enzymatic determination of uric acid using water-soluble CuInS/ZnS quantum dots as a fluorescent probe Microchim. Acta (IF 5.705) Pub Date : 2018-10-05 Fangmei Zhang, Pinyi Ma, Xinyu Deng, Ying Sun, Xinghua Wang, Daqian Song
Glutathione-capped water-soluble CuInS/ZnS quantum dots (QDs) were prepared by a microwave-assisted method. Their fluorescence, with excitation/emission peaks at 380/570 nm, is found to be quenched by hydrogen peroxide (H2O2) that is produced by the uricase catalyzed oxidation of uric acid (UA) and oxygen. The findings are used in a quenchometric method for the determination of UA. The effects of different ligands on the QDs, of pH value, buffers, enzyme ratio and reaction time were optimized. The detection limit for UA is 50 nM which is lower than other QD-based method, and the detection ranges extends from 0.25–4.0 μM. The assay is simple and sensitive, and no further modification of the QDs is required.
Photoelectrochemical determination of the activity of M.SssI methyltransferase, and a method for inhibitor screening Microchim. Acta (IF 5.705) Pub Date : 2018-10-05 Xiao Liu, Chenghua Wei, Jing Luo, Yiping Wu, Xiaoyu Guo, Ye Ying, Ying Wen, Haifeng Yang
A photoelectrochemical (PEC) method is described for the determination of the activity of M.SssI methyltransferase (MTase). The assay relies on enzyme-linkage reactions and a DNA intercalator Ru(bpy)2(dppz)2+ (where bpy is 2,2′-bipyridine, and dppz is dipyrido[3,2-a:2′,3′-c]phenazine) which both serves as a PEC signal. The PEC electrode was obtained by immobilizing 5′-amino modified DNA strands (containing the methylation recognition site 5′-CCGG-3′) on a polyethylenimine (PEI) coated ITO/SnO2 electrode with glutaraldehyde as crosslinking agent. In the presence of MTase and S-adenosyl-L-methionine, the 5′-CCGG-3′ sequence in the DNA on the electrode is methylated. This protects the DNA strands from the shear of the methylation-sensitive restriction endonuclease HpaII. Consequently, more intact DNA strands remain on the surface of the electrode, providing more sites for Ru(bpy)2(dppz)2+ binding which in turn results in a high PEC response. The result demonstrates that the photocurrent increases linearly with the activity of MTase from 5 to 80 U·mL−1, and the limit of detection is 0.45 U·mL−1. The other MTases does not enhance the photocurrent, suggesting good selectivity of the assay. The method was also applied to rapid evaluate and screen the inhibitors of MTase. This strategy can be utilized to determinate the activity of other DNA MTases with specific DNA sequence.
A test strip for ochratoxin A based on the use of aptamer-modified fluorescence upconversion nanoparticles Microchim. Acta (IF 5.705) Pub Date : 2018-10-05 Shijia Wu, Lihong Liu, Nuo Duan, Wenyue Wang, Qianru Yu, Zhouping Wang
An aptamer-based test strip is described for visual and instrumental determination of the mycotoxin ochratoxin A (OTA). It is based on the use of NaYF4:Yb,Er upconversion nanoparticles (UCNPs) as a label for the aptamer and on the competition between OTA and its complementary sequence for an OTA-specific aptamer. To improve the analytical performance, the optical properties of the UCNPs, the fluidity of the UCNP-aptamer conjugate, and the migration rate on the nitrocellulose membranes were investigated. Under the optimal experimental conditions and by using a 980-nm laser, the relative fluorescence intensity (test line value/control line value) is proportional to the logarithm of the OTA concentration over a range from 5 to 100 ng·mL−1 (R2 = 0.9955). The limit of the detection is 1.86 ng·mL−1. This aptamer based flow assay can be performed within 15 min and has no serious cross-sensitivity to potentially interfering species. It was successfully applied to the determination of OTA in spiked wheat and beer samples.
HKUST-1 metal-organic framework for dispersive solid phase extraction of 2-methyl-4-chlorophenoxyacetic acid (MCPA) prior to its determination by ion mobility spectrometry Microchim. Acta (IF 5.705) Pub Date : 2018-10-04 Masoumeh Mohammadnejad, Zahra Gudarzi, Shokoofeh Geranmayeh, Vahideh Mahdavi
The authors describe a method for the extraction of the herbicide 2-methyl-4-chlorophenoxyacetic acid (MCPA) from agricultural products. The metal organic framework (MOF) HKUST-1 (a copper(II) benzene-1,3,5-tricarboxylate) was used as a sorbent for efficient clean-up and preconcentration of MCPA. The effects of pH value, stirring time, amount of sorbent on extraction were optimized by central composite design. Ultrasonic waves were used for desorption procedure and its advantage was demonstrated for an increase in extraction recovery. Corona discharge ion mobility spectrometry (IMS) was then applied for fast and sensitive determination of MCPA. The method was validated in terms of sensitivity, recovery and reproducibility. Under the optimum conditions the calibration plot is linear between 0.035–0.200 μg. L−1. The detection limit is 10 ng L−1, with relative standard deviations of <5%. Real samples (water, soil and agricultural product) were spiked and then analyzed by this method, and the results revealed efficient solid phase extraction and recovery.
Colorimetric determination of dopamine by exploiting the enhanced oxidase mimicking activity of hierarchical NiCo 2 S 4 -rGO composites Microchim. Acta (IF 5.705) Pub Date : 2018-10-04 Yanying Wang, Li Yang, Yaqin Liu, Qingbiao Zhao, Fang Ding, Ping Zou, Hanbing Rao, Xianxiang Wang
A composite consisting of NiCo2S4 and reduced graphene oxide (rGO) was prepared via a hydrothermal process. Compared to individual NiCo2S4 nanomaterials or reduced graphene oxide, the composite exhibits enhanced oxidase-like activity. It is found that dopamine (DA) inhibits the ability of NiCo2S4-rGO to oxidize the substrate 3,3′,5′,5′-tetramethylbenzidine (TMB) to form blue colored ox-TMB. Based on these findings, a colorimetric method for determination of DA was worked out. The absorption, best measured at 652 nm, increases linearly in the 0.5–100 μM DA concentration range, and the limit of detection is 0.42 μM. This method was successfully applied to the detection of DA in spiked human serum samples.
Correction to: A pregnancy test strip for detection of pathogenic bacteria by using concanavalin A-human chorionic gonadotropin-Cu 3 (PO 4 ) 2 hybrid nanoflowers, magnetic separation, and smartphone readout Microchim. Acta (IF 5.705) Pub Date : 2018-10-03 Shengjun Bu, Kuiyu Wang, Chuanjing Ju, Ye Han, Zhongyi Li, Peng Du, Zhuo Hao, Changtian Li, Wensen Liu, Jiayu Wan
The published version of this article, unfortunately, contained error. The authors are re-writing to express their sincere apology for a mistake that a mark “10-5, 10-4, 10-3, 10-2, 10-1 CFU•mL-1” in the legend of Fig. 2 was not corrected as “105, 104, 103, 102, 101 CFU•mL-1”.
SERS based aptasensor for ochratoxin A by combining Fe 3 O 4 @Au magnetic nanoparticles and Au-DTNB@Ag nanoprobes with multiple signal enhancement Microchim. Acta (IF 5.705) Pub Date : 2018-10-03 Dan Song, Rong Yang, Shunyan Fang, Yanping Liu, Feng Long, Anna Zhu
A SERS-based aptasensor for ochratoxin A (OTA) is described. It is making use of Fe3O4@Au magnetic nanoparticles (MGNPs) and of Au@Ag nanoprobes modified with the Raman reporter 5,5-dithiobis-(2-nitrobenzoic acid; DTNB). Au-DTNB@Ag NPs were modified with the OTA aptamer (aptamer-GSNPs) and used as Raman signal probes. The SERS peak of DTNB at 1331 cm−1 was used for quantitative analysis. MGNPs modified with cDNA (cDNA-MGNPs) were used as capture probes and reinforced substrates. When the Au-DTNB@Ag-Fe3O4@Au complexes are formed through oligonucleotide hybridization, the Raman signal intensity of the Raman probe is significantly enhanced. If the OTA concentration in samples increases, more Raman signal probes (aptamer-GSNPs) will dissociate from the cDNA-MGNPs because more OTA aptamer is bound by OTA. This leads to a lower Raman signal after magnetic separation. Under the optimal conditions, the detection limit for OTA is 0.48 pg·mL−1 based on 3σ criterion. This is attributed to the multiple Raman signal enhancement and the good performance of the OTA aptamer. The good recovery and accuracy of the assay was confirmed by evaluating spiked samples of wine and coffee.
Fluorometric determination of quercetin by using graphitic carbon nitride nanoparticles modified with a molecularly imprinted polymer Microchim. Acta (IF 5.705) Pub Date : 2018-10-03 Shengnan Xu, Ligang Chen, Ling Ma
The authors describe a fluorescent probe for sensitive and selective determination of quercetin, an indicator for the freshness of drinks. The probe consists of silica ball encapsulated graphitic carbon nitride (g-C3N4) modified with a molecularly imprinted polymer (MIP). It was synthesized via reverse microemulsion. The resulting MIP@g-C3N4 nanocomposite was characterized by fluorescence spectroscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray powder diffraction. Quercetin quenches the fluorescence of the MIP@g-C3N4 probe. The effect was used to quantify quercetin in grape juice, tea juice, black tea, and red wine by fluorometry (λexc = 350 nm, λem = 460 nm). Response is linear in the 10–1000 ng mL−1 quercetin concentration range. The detection limit is 2.5 ng mL−1, recoveries range between 90.7 and 94.1%, and relative standard deviations are between 2.1 and 5.5%.
Improving the fluorometric determination of the cancer biomarker 8-hydroxy-2′-deoxyguanosine by using a 3D DNA nanomachine Microchim. Acta (IF 5.705) Pub Date : 2018-10-03 Wei Wei, Min Wei, Lihong Yin, Yuepu Pu, Songqin Liu
The authors describe a fluorometric method for improving the determination of the cancer biomarker 8-hydroxy-2′-deoxyguanosine (8-OHdG). A nicking endonuclease (NEase)-powered 3-D DNA nanomachine was constructed by assembling hundreds of carboxyfluorescein-labeled single strand oligonucleotides (acting as signal reporter) and tens of swing arms (acting as single-foot DNA walkers) on a gold nanoparticle (AuNP). The activity of this DNA nanomachine was controlled by introducing the protecting oligonucleotides. In the presence of aptamer against 8-OHdG, the protecting oligonucleotides are removed from the swing arms by toehold-mediated strand displacement reaction. In the next step, detached DNA walker hybridizes to the labelled DNA so that the DNA nanomachine becomes activated. Special sequences of signal reporter in the formed duplex can be recognized and cleaved by NEase. As a result, the DNA walker autonomously and progressively moves along the surface of the AuNP, thereby releasing hundreds of signal reporters and causing a rapid increase in green fluorescence. This 3-D nanomachine is highly efficient because one aptamer can release hundreds of signal reporters. These unique properties allowed for the construction of a DNA nanomachine-based method for sensitively detecting 8-OHdG in concentrations as low as 4 pM. This is three orders of magnitude lower compared to previously reported methods.
An optoelectronic tongue based on an array of gold and silver nanoparticles for analysis of natural, synthetic and biological antioxidants Microchim. Acta (IF 5.705) Pub Date : 2018-10-03 Mohammad Mahdi Bordbar, Bahram Hemmateenejad, Javad Tashkhourian, S. F. Nami-Ana
A colorimetric array, which can discriminate 20 food antioxidants of natural, synthetic and biological groups, is described. It consists of gold and silver nanoparticles that were synthesized using six different reducing and/or capping agents. The function of the array relies on the interaction of the antioxidants with the nanoparticles which causes aggregation or morphological changes. This, in turn, causes a change in the sensors’ colors. The array produces a unique combination of colors for each antioxidant. The resulting colorations are determined by recording the absorbances of the arrays at wavelengths of 405, 450, 490 and 630 nm, or by capturing the images with a digital camera. The discriminatory ability of the array is investigated by principle component analysis and hierarchical cluster analysis. The method was applied to quantitative assay of gallic acid, caffeic acid, catechin, dopamine, citric acid, butylated hydroxytoluene and ascorbic acid. The respective limits of detection are 4.2, 13, 53, 6.9, 47, 3.5 and 43 nM, respectively. The simultaneous determination of 5 different antioxidants is achieved utilizing partial least square regression. The root mean square errors for prediction of the test set are 0.0650, 0.0782, 0.811, 0.0206 and 0.135 nM for gallic acid, catechin, butylated hydroxytoluene, dopamine, and ascorbic acid, respectively. This method demonstrates excellent potential for analysis of antioxidants in beverages such as tea and lemon juice.
Lanthanide doped carbon dots as a fluorescence chromaticity-based pH probe Microchim. Acta (IF 5.705) Pub Date : 2018-10-02 Lude Wang, Yang Chen
A colorimetric and fluorescent pH probe was designed by doping carbon dots (C-dots) with Eu(III), Tb(III) and 2,6-pyridinedicarboxylic acid (DPA). The resulting nanoparticles were applied as fluorescent indicators for pH values (best detected at excitation/emission wavelengths of 272/545, 614 nm). The pH induced optical effects are due to pH induced variations in energy transfer. The fluorescence of the probe shows a continuous color variation, and a linear change with pH values in the range from 3.0 to 10.0 can be established by using a Commission Internationale de L’Eclairage (CIE) chromaticity diagram. This new kind of pH nanoprobe is more accurate than previously reported pH indicator probes because the pH value can be calculated by using chromaticity coordinates that only depend on the chromaticity. The pH nanoprobe was applied to visualize pH values in human breast adenocarcinoma cells (MCF-7).
Colorimetric adenosine aptasensor based on DNA cycling amplification and salt-induced aggregation of gold nanoparticles Microchim. Acta (IF 5.705) Pub Date : 2018-10-02 Caiyun Kong, Linna Gao, Zhengbo Chen
An aptamer based assay is described for the colorimetric detection of adenosine. The presence of adenosine triggers the deformation of hairpin DNA oligonucleotide (HP1) containing adenosine aptamer and then hybridizes another unlabeled hairpin DNA oligonucleotide (HP2). This leads to the formation of a double strand with a blunt 3′ terminal. After exonuclease III (Exo III)-assisted degradation, the guanine-rich strand (GRS) is released from HP2. Hence, the adenosine-HP1 complex is released to the solution where it can hybridize another HP2 and initiate many cycles of the digestion reaction with the assistance of Exo III. This leads to the generation of a large number of GRS strands after multiple cycles. The GRS stabilize the red AuNPs against aggregation in the presence of potassium ions. If, however, GRS forms a G-quadruplex, it loses its ability to protect gold nanoparticles (AuNPs) from salt-induced AuNP aggregation. Therefore, the color of the solution changes from red to blue which can be visually observed. This colorimetric assay has a 0.13 nM detection limit and a wide linear range that extends from 5 nM to 1 μM.
A fluorometric aptasensor for patulin based on the use of magnetized graphene oxide and DNase I-assisted target recycling amplification Microchim. Acta (IF 5.705) Pub Date : 2018-10-01 Liang Ma, Ting Guo, Shuli Pan, Yuhao Zhang
A fluorometric patulin (PAT) assay is presented that is based on the use of magnetic reduced graphene oxide (rGO) and DNase I. The fluorescence of the PAT aptamer labelled with 6-carboxyfluorescein (FAM) is quenched by magnetized reduced graphene oxide (rGO-Fe3O4) due to fluorescence resonance energy transfer (FRET). However, in the presence of PAT, the labelled aptamer is stripped off from rGO-Fe3O4. The rGO-Fe3O4 is then magnetically separated so that the fluorescence of free labelled PAT aptamer is restored. DNase I cannot hydrolyze the aptamer on rGO-Fe3O4, but it can cleave the free aptamer-PAT complex. This will release FAM and PAT which can undergo a number of additional cycles to trigger the cleavage of abundant aptamer. Recycling of DNase I-assisted target therefore leads to a strong amplification of fluorescence and consequently to an assay with low limit of detection. The detection limit for PAT is as low as 0.28 μg L−1 which is about 13 times lower than that without using DNase I. The method offers a new approach towards rapid, sensitive and selective detection based on an aptamer. Conceivably, it has a wide scope in that it may be applied to numerous other analytes if appropriate aptamers are available.
Biodegradable nanoprobe based on MnO 2 nanoflowers and graphene quantum dots for near infrared fluorescence imaging of glutathione in living cells Microchim. Acta (IF 5.705) Pub Date : 2018-10-01 Zhi-Ling Song, Xin Dai, Mengru Li, He Teng, Zhen Song, Dexun Xie, Xiliang Luo
Near infrared (NIR) emitting semiconductor quantum dots can be excellent fluorescent nanoprobes, but the poor biodegradability and potential toxicity limits their application. The authors describe a fluorescent system composed of graphene quantum dots (GQDs) as NIR emitters, and novel MnO2 nanoflowers as the fluorescence quenchers. The system is shown to be an activatable and biodegradable fluorescent nanoprobe for the “turn-on” detection of intracellular glutathione (GSH). The MnO2-GQDs nanoprobe is obtained by adsorbing GQDs onto the surface of MnO2 nanoflowers through electrostatic interaction. This results in the quenching of the NIR fluorescence of the GQDs. In the presence of GSH, the MnO2-GQDs nanoprobe is degraded and releases Mn2+ and free GQDs, respectively. This gives rise to increased fluorescence. The nanoprobe displays high sensitivity to GSH and with a 2.8 μM detection limit. It integrates the advantages of NIR fluorescence and biodegradability, selectivity, biocompatibility and membrane permeability. All this makes it a promising fluorescent nanoprobe for GSH and for cellular imaging of GSH as shown here for the case of MCF-7 cancer cells.
Analyte-triggered cyclic autocatalytic oxidation amplification combined with an upconversion nanoparticle probe for fluorometric detection of copper(II) Microchim. Acta (IF 5.705) Pub Date : 2018-10-01 Hongyu Chen, Kaili He, Huan Li, Youyu Zhang, Shouzhuo Yao
The authors describe an upconversion nanoparticle-based (UCNP–based) fluorometric method for ultrasensitive and selective detection of Cu2+. The UCNPs show a strong emission band at 550 nm under near-infrared excitation at 980 nm. The principle of the strategy is that gold nanoparticles (AuNP) can quench the fluorescence of UCNP. In contrast, the addition of L-cysteine (Cys) can induce the aggregation of AuNP, resulting in a fluorescence recovery of the UCNPs. On addition of Cu2+, it oxidizes Cys to cystine and is reduced to Cu+. The Cu+ thusformed can be oxidized cyclically to Cu2+ by dissolved O2, which catalyzes and recycles the whole reaction. Thus, the aggregation of AuNP is inhibited and the fluorescence recovered by Cys is quenched. Under the optimal condition, the quenching efficiency shows a good linear response to the concentrations of Cu2+ in the 0.4–40 nM range. The limit of detection is 0.16 nM, which is 5 orders of magnitude lower than the U.S. Environmental Protection Agency limit for Cu2+ in drinking water (20 μM). The method has been further applied to monitor Cu2+ levels in real samples. The results of detection are well consistent with those obtained by atomic absorption spectroscopy.
Electrochemical determination of dopamine and uric acid using a glassy carbon electrode modified with a composite consisting of a Co(II)-based metalorganic framework (ZIF-67) and graphene oxide Microchim. Acta (IF 5.705) Pub Date : 2018-10-01 Jing Tang, Sixun Jiang, Yu Liu, Shengbiao Zheng, Lei Bai, Jiahao Guo, Jianfei Wang
A composite was prepared from a Co(II)-based zeolitic imidazolate framework (ZIF-67) and graphene oxide (GO) by an in situ growth method. The material was electrodeposited on a glassy carbon electrode (GCE). The modified GCE was used for the simultaneous voltammetric determination of dopamine (DA) and uric acid (UA), typically at working potentials of 0.11 and 0.25 V (vs. SCE). The morphology and structure of the nanocomposite were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction. The modified electrode exhibits excellent electroanalytical performance for DA and UA owing to the synergistic effect of the high electrical conductivity of GO and the porosity of ZIF-67. By applying differential pulse voltammetry, a linear response is found for DA in the 0.2 to 80 μM concentration range, and for UA between 0.8 and 200 μM, with detection limits of 50 and 100 nM (at S/N = 3), respectively. Further studies were performed on the effect of potential interferents, and on electrode stability and reproducibility. The modified GCE was applied to the simultaneous detection of DA and UA in spiked human urine and gave satisfying recoveries.
Protamine-stabilized gold nanoclusters as a fluorescent nanoprobe for lead(II) via Pb(II)–Au(I) interaction Microchim. Acta (IF 5.705) Pub Date : 2018-09-29 Yan-Qin Huang, Li-Na Yang, Yong-Sheng Wang, Jin-Hua Xue, Si-Han Chen
The authors report on a one-pot approach for synthesizing highly fluorescent protamine-stabilized gold nanoclusters. These are shown to be a viable nanoprobe for selective and sensitive fluorometric determination of lead(II) via quenching of fluorescence via Pb(II)-Au(I) interaction. Under optimized conditions, fluorescence measured at excitation/emission peaks of 300/599 nm drops in the 80 nM–15 μM lead(II) concentration range. The detection limit is 24 nM, and relative standard deviations (for n = 11) at concentrations of 0.10, 4.0 and 15 μM are 1.6, 2.5 and 1.9%, respectively. The relative recoveries of added lead(II) in the water samples ranged from 97.9 ± 2.29% to 101.2 ± 1.83%.
Synthesis of a three-dimensional interconnected carbon nanorod aerogel from wax gourd for amperometric sensing Microchim. Acta (IF 5.705) Pub Date : 2018-09-27 Cuxing Xu, Yashuang Hei, Jingju Liu, Mimi Sun, Tianze Sha, Nan Wang, Mehboob Hassan, Xiangjie Bo, Ming Zhou
The authors describe a method for synthesis of a three-dimensional (3D) interconnected carbon nanorod aerogel (3D-ICNA) starting from wax gourd (Benincasa hispida) which is a low-cost biomass. The 3D-ICNA possesses unique 3D interconnected and porous nanostructure, with abundant edge-plane-like defective sites, a large specific surface area (823 m2 g−1) and a large pore volume (0.12 cm3 g−1). This makes the material attractive in terms of electrochemical sensing. To validate the feasibility, the voltammetric response towards ferricyanide, hydrogen peroxide (H2O2), acetaminophen, ascorbic acid (AA), dopamine, uric acid and epinephrine was investigated by using a glassy carbon electrode (GCE) modified with 3D-ICNA. The modified GCE shows higher electron-transfer capacity than a conventional GCE. In addition, as an electrochemical sensor for AA or H2O2, the electrode exhibits better analytical performance with lower detection limit [3.5 μM for AA or 0.68 μM for H2O2 based on 3σ/m criterion (where σ is the standard deviation of the blank and m is the slope of the calibration plot)], wider linear range and higher sensitivity (0.14, 0.11 and 0.080 μA μM−1 cm−2 for AA or 0.24 and 0.20 μA μM−1 cm−2 for H2O2) compared to a plain GCE or a carbon nanotube-modified GCE. The modified GCE exhibits a large potential for the amperometric determination of AA or H2O2 in real samples.
Simultaneous voltammetric sensing of acetaminophen, epinephrine and melatonin using a carbon paste electrode modified with zinc ferrite nanoparticles Microchim. Acta (IF 5.705) Pub Date : 2018-09-26 Nahid Tavakkoli, Nasrin Soltani, Faezeh Shahdost-fard, Mahbobeh Ramezani, Hossein Salavati, Mohammad Reza Jalali
A highly selective electrochemical sensor was fabricated based on a modified carbon paste electrode with zinc ferrite nanoparticles (ZnFe2O4 NPs). The nanocomposite has attractive properties such as high surface-to-volume ratio and good electrocatalytic activity towards the drugs acetaminophen (AC), epinephrine (EP), and melatonin (MT), best at working voltages of 0.35, 0.09 and 0.55 V (vs. Ag/AgCl), respectively. The linear ranges (and detection limits) are 6.5–135 (0.4) μmol L−1 for AC, 5–100 (0.7) μmol L−1 for EP, and 6.5–145 (3) μmol L−1 for MT.
SERS detection of ceftriaxone and sulfadimethoxine using copper nanoparticles temporally protected by porous calcium carbonate Microchim. Acta (IF 5.705) Pub Date : 2018-09-26 Natalia E. Markina, Elena K. Volkova, Andrey M. Zakharevich, Irina Yu. Goryacheva, Alexey V. Markin
The authors describe a new composite based on SERS-active copper nanoparticles (CuNPs; 10 ± 2 nm) incorporated into calcium carbonate microspheres (CaCO3-CuNPs; 3.4 ± 0.3 μm). The CaCO3 coating acts as a temporal protector of CuNPs against oxidation. Incorporated CuNPs have significantly improved stability during storage and a month-long shelf lifetime. The composite was used for SERS detection of rhodamine 6G and two antibacterial drugs (ceftriaxone and sulfadimethoxine). Two analytical formats, one with and one without solid phase extraction, are introduced to demonstrate the flexibility of the method. Both formats imply the dissolution of CaCO3 matrix before SERS analysis to release CuNP used as SERS substrate. The study of the influence of pH value and acid nature on the SERS signal demonstrated that HCl is the most efficient candidate to release the CuNPs. Sensitivity (expressed as LOD) is shown to be improved by more than one order when solid phase extraction is used. The average SERS enhancement factor is 10^7 which makes the material efficiency comparable to the one of silver nanoparticles. The LOD (<5 μM), precision (RSDs between 20 and 24% at LOD levels), and trueness (apparent recoveries 84–113%) for the two antibiotics (ceftriaxone and sulfadimethoxine) make the method quite useful for quantitative analysis and therapeutic drug monitoring at physiologically relevant concentrations.
On-off-on luminescent pyrophosphate probe based on the use of Mn-doped ZnS quantum dots and using Eu(III) as a mediator Microchim. Acta (IF 5.705) Pub Date : 2018-09-26 Jiawei Pang, Yuexiang Lu, Xinyu Gao, Panshu Song, Fengyi Yang, Yueying Liu
A selective phosphorescent on-off-on probe with long decay lifetime has been designed for the detection of pyrophosphate ions (PPi). The detection scheme is based on the use of europium(III)-modulated Mn(II)-doped ZnS quantum dots capped with N-acetyl-L-cysteine. Both the aggregation of quantum dots and electron transfer induced by Eu(III) ions cause phosphorescence to be quenched (“off” state). Phosphorescence is, however, restored on addition of PPi to the system (“on” state). The effect is attributed to the removal of Eu(III) from the carboxy groups on the surface of the quantum dots owing to the stronger interaction between PPi and Eu(III). A linear relationship exists between phosphorescence intensity (best measured at excitation/emission wavelengths of 316/594 nm) and PPi concentration in the 400 nM to 6000 nM with a detection limit of 145 nM. An additional attractive feature is provided by the long-lived phosphorescence (1920 μs) of the quantum dots. It can be used to eliminate interference by short-lived fluorescence in biological samples by performing time resolved measurements. The probe was applied to the determination of PPi in spiked in urine samples and gave recoveries in the range from 98 to 105% with RSDs of <2.0%.
Two-dimensional nanomaterial based sensors for heavy metal ions Microchim. Acta (IF 5.705) Pub Date : 2018-09-25 Xiaorong Gan, Huimin Zhao, Romana Schirhagl, Xie Quan
Two-dimensional (2D) nanomaterials are promising building blocks for sensors due to their unique physical, chemical, electronic, and optical properties. This review (with 253 references) first summarizes the historical developments of 2D nanomaterials and discusses the advantages of 2D nanomaterials when applied for constructing sensors. Next, their properties are discussed, with subsections on electronic, optical, mechanical and chemical properties. This is followed by an overview on methods for syntheses and the effects of positive and/or negative charges on the properties and in sensing applications. Then, recent advances in 2D nanomaterial-based electrochemical, fluorometric, colorimetric, electrochemiluminescent, photoelectrochemical, and field-effect transistor sensors are discussed. The discussion also includes the preparation of sensing elements, the roles of such nanomaterials, and assay strategies. Finally, on the basis of the current achievements in the field of 2D nanomaterials, the perspectives on the challenges and opportunities for the exploration of 2D nanomaterial-based sensors are put forward.
SERS based monitoring of toluene vapors at ambient and elevated temperatures by using a ruffled silver nanolayer as a substrate Microchim. Acta (IF 5.705) Pub Date : 2018-09-22 Lina Ramanauskaite, Viktoras Mazeika, Valentinas Snitka
The authors describe a Surface enhanced Raman spectroscopy (SERS)-based method for the detection of gaseous toluene at different temperature regimes using 3D ruffled silver SERS substrates and a commercially available handheld Raman system equipped with a 785 nm laser. The 3D silver SERS substrates were synthesized via electroless deposition of silver on the ruffled sandpaper and HF-etched silicon wafers. The morphological characterization of the silver SERS substrates was carried out by atomic force microscopy and scanning electron microscopy. UV-Vis spectroscopy absorption spectra of the silver nanostructures showed plasmonic peaks at 522 nm and 731 nm. Toluene vapors were collected with a syringe at ambient temperature and at 100 °C, while SERS detection was always performed at room temperature. Toluene detection was based on the measurement of the Raman bands at 787 cm−1 and 1003 cm−1 (in the fingerprint region). The method allow gaseous toluene to be detected at its vapor concentrations of 522 ppm (mg/L), 261 ppm (mg/L) and 26 ppm (mg/L).
Double-decrease of the fluorescence of CdSe/ZnS quantum dots for the detection of zinc(II) dimethyldithiocarbamate (ziram) based on its interaction with gold nanoparticles Microchim. Acta (IF 5.705) Pub Date : 2018-09-21 Limin Yang, Xiaohui Zhang, Jinxin Wang, Haifeng Sun, Lei Jiang
A double-decrease strategy is described for ultrasensitive determination of the fungicide and vulcanization additive ziram. The assay principle is inspired by the interaction of ziram with gold nanoparticles (AuNPs). In this process, zinc ions are released, and ziram adsorption induces the aggregation of the AuNPs. The aggregated AuNPs decrease the intensity of the fluorescence of CdSe/ZnS quantum dots (QDs) capped with 3-mercaptopropionic acid via an inner filter effect. This is a result of the overlap between the absorption band of aggregated AuNPs (peaking at 680 nm) and the yellow emission of QDs (peaking at 608 nm). Zinc also exerts another decrease effect on the fluorescence of the CdSe/ZnS QDs, probably via a static quenching mechanism. Based on this double-decrease effect, ultrahigh sensitivity is achieved for ziram. The fluorescence response of the QDs (Ex / Em = 380/608 nm) is immediate. The relative fluorescence intensity is proportional to the ziram concentration within a wide range of 5 nM to 4 μM in two consecutive linear ranges. The limit of detection is as low as ~2 nM (signal-to-noise ratio of 3), which is much lower than the maximum residue limit defined by the EU pesticide database. It is also found that a similarly high sensitivity is obtained for another fungicide ferbam.
Colorimetric determination of mercury(II) via the inhibition by ssDNA of the oxidase-like activity of a mixed valence state cerium-based metal-organic framework Microchim. Acta (IF 5.705) Pub Date : 2018-09-21 Caihong Wang, Gonge Tang, Hongliang Tan
This work demonstrates the inhibition effects of single-stranded (ssDNA) on the oxidase-like activity of a mixed-valence state cerium-based metal-organic framework, denoted as MVC-MOF. The MVC-MOF was synthesized by partial oxidation of cerium(III) which leads to the presence of both Ce(III) and Ce(IV) ions. The latter endows the MVC-MOF with a typical oxidase-like activity. However, on addition of ssDNA, the catalytic activity of the MVC-MOF is inhibited because it binds the MVC-MOF and thereby shield its active sites. This prevents the access of substrates. The inhibition by ssDNA depends on its length but not its sequence. By contrast, negligible changes in the oxidase-mimicking activity are observed if double-stranded DNA (dsDNA) is added. By employing a thymine-rich ssDNA (T-ssDNA) as a model DNA, a colorimetric assay was developed for the determination of Hg(II). This ion binds to T-ssDNA and causes the formation of T-dsDNA. Hence, the oxidase-mimicking activity is compromised. By using the oxidase substrate 3,3′,5,5′-tetramethylbenzidine that gives a colored product in the presence of oxygen, the assay has a linear response that covers 0.05 to 6 μM Hg(II) with a detection limit of 10.5 nM, and exhibits high selectivity over other metal ions. The assay was successfully applied to the determination of Hg(II) in environmental water samples.
A molecularly imprinted chitosan doped with carbon quantum dots for fluorometric determination of perfluorooctane sulfonate Microchim. Acta (IF 5.705) Pub Date : 2018-09-21 Zhe Jiao, Jingwen Li, Liangji Mo, Jinming Liang, Hongbo Fan
A molecularly imprinted polymer (MIP) was fabricated for selective recognition of the highly persistent pollutant perfluorooctane sulfonate (PFOS). The MIP was prepared from chitosan and doped with fluorescent carbon quantum dots (CQDs). It was characterized by fluorescence spectrophotometry, scanning electron microscopy, and Fourier transform infrared spectroscopy. The fluorescence of the CQDs, best measured at excitation/emission wavelengths of 350/460 nm, is enhanced by PFOS, and the effect is much stronger for the MIP than for the nonimprinted polymer (NIP). The imprinting factor is 2.75. The method has good specificity over sodium dodecyl sulfate (SDS), perfluorooctanoic acid (PFOA), sodium dodecyl sulfonate (SDS’), sodium dodecyl benzene sulfonate (SDBS), perfluorooctanesulfonyl fluoride (POSF), perfluorobutane sulfonate (PFBS) and 1-octanesulfonic acid sodium (OSA). Fluorescence increases linearly in the 20–200 pg·L−1 POSF concentration range in aqueous solution. The method was applied to the determination of PFOS in spiked serum and urine samples. The limits of detection are 66 and 85 pg·L−1 for serum and urine samples respectively. The recoveries ranged from to 81–98%, with relative standard deviations in the range of 1.8–8.2%. Compared with LC-MS/MS, this assay is more convenient since the material can be prepared flexibly and the method can be applied on-site.
Amperometric sensing of ascorbic acid by using a glassy carbon electrode modified with mesoporous carbon nanorods Microchim. Acta (IF 5.705) Pub Date : 2018-09-21 Xiuxiu Li, Jingju Liu, Mimi Sun, Tianze Sha, Xiangjie Bo, Ming Zhou
Mesoporous carbon nanorods (MCNRs) were prepared from honey as the carbon source and by using crab (Brachyuran) shells as the hard template. The unique nanostructure of the MCNRs with their uniform mesoporous size, abundant defective sites and numerous oxygen-functional groups was characterized by nitrogen adsorption-desorption isotherms, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Cyclic voltammograms of a glassy carbon electrode (GCE) modified with MCNRs revel a higher peak current density and lower peak potential (−0.03 V vs. Ag/AgCl) for ascorbic acid (AA) electrooxidation compared to a conventional GCE and a carbon nanotube-modified GCE. Figures of merit for this sensor include (a) a wide linear range (10–2770 μM), (b) high electrochemical sensitivity (216.91 μA mM−1 cm−2) and (c) a low detection limit (2.3 μM). These compare favorably to the respective data for a CNT-modified GCE (50–2150 μM, 5.20 μA mM−1 cm−2 and 26.8 μM) and a plain GCE (100–2000 μM, 0.58 μA mM−1 cm−2 and 54.6 μM). The modified GCE was successfully applied to the determination of AA in (spiked) real samples including an injection, soft drinks and fresh lemon juice. Therefore, the new sensor can be considered as an affordable tool for electrochemical sensing of AA in real samples.
Carbon dots prepared from Litchi chinensis and modified with manganese dioxide nanosheets for use in a competitive fluorometric immunoassay for aflatoxin B 1 Microchim. Acta (IF 5.705) Pub Date : 2018-09-21 Dianping Tang, Youxiu Lin, Qian Zhou
An enzyme-linked immunoassay is described for the fluorometric determination of aflatoxin B1 (AFB1). It is based on the use of carbon dots (CDs) synthesized by using Litchi chinensis as the carbon source via a hydrothermal method. The CDs were modified with MnO2 nanosheets upon which their blue fluorescence (with excitation/emission peaks at 340/425 nm) is quenched. In the presence of AFB1, a competitive immunoreaction takes place between (1) AFB1 conjugated to bovine serum albumin and deposited in the wells of a microplate, and (2) antibody against AFB1 and labeled with alkaline phosphatase (ALP). On subsequent addition of ascorbic acid 2-phosphate, it will be hydrolyzed by ALP to form ascorbic acid and phosphate. The ascorbic acid produced reduces MnO2 nanosheets to Mn2+ ions which then are relased from the CDs. This causes the recovery of fluorescence. Under optimum conditions, fluorescence decreases linearly with increasing AFB1 concentration in the range from 1.0 ng·kg−1 to 10 μg·kg−1, and the limit of detection is 0.69 ng·kg−1. The precision of this method (expressed as RSD) is ±10.3%. The accuracy was tested by analyzing both naturally contaminated and spiked food samples, and the results were in good agreement with those obtained by the established ELISA.
Graphitic carbon nitride quantum dots as an “off-on” fluorescent switch for determination of mercury(II) and sulfide Microchim. Acta (IF 5.705) Pub Date : 2018-09-20 Xuan Wang, Xuefang Yang, Ning Wang, Junjie Lv, Haojiang Wang, Martin M. F. Choi, Wei Bian
A rapid method has been developed for the determination of Hg(II) and sulfide by using graphitic carbon nitride quantum dots (g-CNQDs) as a fluorescent probe. The interaction between Hg(II) and g-CNQDs leads to the quenching of the blue g-CNQD fluorescence (with excitation/emission peaks at 390/450 nm). However, the fluorescence can be recovered after addition of sulfide such that the “turn-off” state is switched back to the “turn-on” state. The g-CNQDs were fully characterized by transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, UV-vis absorption and fluorescence spectroscopy. Under the optimal experimental conditions, this probe is highly selective and sensitive to Hg(II). The linear response to Hg(II) extends from 0.20 to 21 μM with a detection limit of 3.3 nM. In addition, sulfide can be detected via the recovery of fluorescence. The linear response range for sulfide species is from 8.0 to 45 μM with a detection limit of 22 nM. The mechanism of the “turn-off-on” scheme is discussed. The methods have been applied to the analysis of spiked tap water, lake water and wastewater samples.
A nanocomposite probe consisting of carbon quantum dots and phosphotungstic acid for fluorometric determination of chromate(VI) with improved selectivity Microchim. Acta (IF 5.705) Pub Date : 2018-09-20 Yushan Liu, Zhijun Chen, Wei Li, Chunhui Ma, Peng Wu, Xueyun Wu, Shujun Li, Shouxin Liu
A fluorometric quenching assay is described for the determination of chromate(VI) by using a nanocomposite probe consisting of carbon quantum dots (CQDs) and phosphotungstic acid (HPW). The stable nanoprobe was synthesized via hydrothermal carbonization of glucose in the presence of HPW. HPW promotes the dehydration and carbonization and acts as an “electronic receptor”. It blocks the radiative electron/hole recombination in the CQDs and leads to a product whose fluorescence (with excitation/emission peaks at 360/463 nm) is quenched. The CQD/HPW was characterized by transmission electron microscopy, FT-IR spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, UV-vis absorption and fluorescence spectroscopy to characterize their surface morphology, functional groups and elemental composition, crystal structure and optical properties. The nanocomposite is nearly mono-disperse with an average particle diameter of 1.7 nm, and displays excitation wavelength-dependent and pH-dependent photoluminescence. Fluorescence drops on addition of chromate(VI) due to an inner filter effect. The ability of receiving electron for HPW can hinder the electron transfer from CQD/HPW to other metal ions, so the nanocomposite showed excellent selectivity towards chromate(VI). Fluorescence drops linearly with the concentration of chromate(VI) in the range from 2 to 80 μM, with a limit of detection of 0.16 μM.
A hybrid material composed of an amino-functionalized zirconium-based metal-organic framework and a urea-based porous organic polymer as an efficient sorbent for extraction of uranium(VI) Microchim. Acta (IF 5.705) Pub Date : 2018-09-19 Haniyeh Fotovat, Mostafa Khajeh, Ali Reza Oveisi, Mansour Ghaffari-Moghaddam, Saba Daliran
An amino-functionalized zirconium metal-organic framework was composed with a 3D urea-based porous organic polymer to give a hybrid material termed UiO-66-NH2/urea-POP. The material was characterized by Fourier transform infrared spectroscopy, powder X-ray diffraction, scanning electron microscopy, and Brunauer-Emmett-Teller surface area measurements. It is shown to be a viable sorbent for solid-phase extraction of uranium from water samples. Parameters such as the pH value of the sample, amount of adsorbent, type and volume of eluent, adsorption and desorption time, and sample volume were optimized. Uranyl ion was quantified by using UV-vis spectrophotometry by using 1-(2-pyridyl-azo)-2-naphthol as the indicator. Figures of merits include (a) a maximum sorption capacity of 278 mg g−1; (b) a detection limit of 0.6 μg L−1; and (c) intra-day and inter-day precisions (for n = 5 at a concentration of 100 μg L−1) of 4.8 and 1.9%, respectively. The sorbent can be recycled, and no significant change was observed in the capacity and repeatability of the sorbent after seven extractions. The high surface area, metal-binding sites, and stability of the sorbent makes it a most viable tool for efficient and fast extraction and removal of uranium.
A porous polyaniline nanotube sorbent for solid-phase extraction of the fluorescent reaction product of reactive oxygen species in cells, and its determination by HPLC Microchim. Acta (IF 5.705) Pub Date : 2018-09-19 Panhong Niu, Feifei Li, Xiaojing Liang, Xiudan Hou, Xiaofeng Lu, Xusheng Wang, Qiang Li, Yong Guo
A method is described for extracting and detecting the fluorescent reaction product (2′,7′-dichlorofluorescein, DCF) that is formed by reaction of reactive oxygen species (ROS) with dichlorodihydrofluorescein diacetate (DCFH-DA). DCF is extracted by using porous polyaniline nanotubes (PPN) which have a large specific surface and pore volume which favor the adsorption capacity. Additional attractive features include an appropriate pore size distribution, hydrophobic surface, and electron-attracting groups which contribute to DCF adsorption. A variety of methods was applied to characterize the morphology of PPN. Under optimal conditions and by performing DCF in 0.08–1.0 μM concentrations, the correlation coefficient of the calibration plot is 0.999. The limits of detection for standard DCF solutions is 20 nM. Compared with commercial sorbents for solid-phase extraction (SPE) such as commercially available carbon or Welchrom® C18, the use of the new sorbent results in better retraction recovery (92%) and longer reuse times (30 times). Doxorubicin and X-ray radiation were used to externally stimulate the ROS production in HepG2 and Hela cells. ROS was stabled by DCFH-DA and quantified by DCF. Following SPE, DCF was detected by HPLC and the concentration ROS was calculated.
Solvothermal synthesis of phosphorus and nitrogen doped carbon quantum dots as a fluorescent probe for iron(III) Microchim. Acta (IF 5.705) Pub Date : 2018-09-18 Khalid M. Omer, Diary I. Tofiq, Aso Q. Hassan
Carbon quantum dots (CQDs) doped with phosphorus and nitrogen were prepared via a hydrothermal method starting from citric acid, urea and phosphoric acid in dimethylformamide solution. The size, morphology, surface composition, energy levels, and optical properties of the CQDs were characterized. They show both green down-conversion and up-conversion fluorescence. Ferric ions (Fe3+) are found to quench the fluorescence. Cyclic voltammetry was used to identify the HOMO and LUMO levels of the doped CQDs. The quenching mechanism, as confirmed by energy level calculations and absorption spectra, can be attributed to the selective coordination of Fe3+ by the surface functional groups on the CQDs. This facilitates the photo-induced electron transfer from the CQDs to the d orbitals of Fe3+. The CQDs are shown to be viable fluorescent probes for determination of Fe3+ with high selectivity and sensitivity. The assay has a linear response in the 0.1 μM to 0.9 μM Fe3+ concentration range and a 50 nM as limit of detection (at a S/N ratio of 3).
A PCR microreactor machinery with passive micropump and battery-powered heater for thermo-cycled amplifications of clinical-level and multiplexed DNA targets Microchim. Acta (IF 5.705) Pub Date : 2018-09-18 Bing Shi, Gengxian He, Wenming Wu
A self-contained polymerase chain reaction (PCR) platform with miniaturized power-system is introduced. It is powered by portable lithium batteries and integrated continuous-flow PCR amplification platform. Generally speaking, traditional commercial thermal cyclers rely on external electric supply and thus they are too big in instrument size. This prevents real-timely and field testing during PCR diagnosis. The authors are introducing a continuous-flow 3D spiral microreactor for DNA amplifications and high-resolution multiplexed targets’ detection by utilizing the polyvinyl chloride (PVC) tubing-polymer to fabricate the microreactor for the first time. The whole setup (that can all be placed in one hand) includes (a) the thermo-cycled control (5.5 cm width, 10 cm length and 11 cm height), (b) the passive continuous-flow control, and (c) the trapezoidal PCR microreactor. The PCR platform can work for 4.5 h continuously. With minimal accessories and operations, the total cost of the self-contained PCR machinery is <20 $, much lower than the mainstream of commercial PCR machinery. By waiving external electric supply, this miniaturized PCR platform is applied to amplify the typical DNA fragments of plasma isolated hepatitis B virus (HBV), influenza virus (H7N9avian influenza) bacterium (Escherichia coli) plasmid and multiplexed targets. The efficiency of the method is 70% of that of commercial thermal cycler (CFX Connect, Bio Rad). The DNA of H7N9avian influenza can be detected in concentrations as low as 103 copies per μL.
Single cell immunodetection of Escherichia coli O157:H7 on an indium-tin-oxide electrode by using an electrochemical label with an organic-inorganic nanostructure Microchim. Acta (IF 5.705) Pub Date : 2018-09-17 Dung Quang Nguyen, Kengo Ishiki, Hiroshi Shiigi
A rapid and highly sensitive method is described for the detection of enterohemorrhagic Escherichia coli O157:H7. An organic-inorganic nanostructure in which numerous gold nanoparticles (AuNPs) are enclosed with polyaniline (PANI) was utilized as an electrochemical label. The nanostructure showed (a) strong light scattering intensity due to the coupling effect of the surface plasmon resonance based on the presence of AuNPs, and (b) high electrochemical response due to the redox activity of PANI. To achieve selectivity, antibody against E. coli O157:H7 was immobilized on the surface of the nanostructure. The method exploits the combination of strong adsorption of bacterial cells onto the indium-tin-oxide (ITO) glass electrode without any special processing and specific binding of the nanostructured label to E. coli O157:H7. This enables the electrochemical detection of a single cell on the ITO electrode. The electrochemical response to E. coli O157:H7 was 30-fold higher than that to other types of bacteria. This procedure can be applied to the determination of E. coli O157:H7 even in the presence of other bacteria.
A pregnancy test strip for detection of pathogenic bacteria by using concanavalin A-human chorionic gonadotropin-Cu 3 (PO 4 ) 2 hybrid nanoflowers, magnetic separation, and smartphone readout Microchim. Acta (IF 5.705) Pub Date : 2018-09-17 Shengjun Bu, Kuiyu Wang, Chuanjing Ju, Ye Han, Zhongyi Li, Peng Du, Zhuo Hao, Changtian Li, Wensen Liu, Jiayu Wan
Pregnancy test strips are widely used in daily life. A commercial pregnancy test strip was modified to obtain a point-of-care device for the detection of pathogenic bacteria. Hybrid nanoflowers were prepared from concanavalin A, human chorionic gonadotropin, and Cu3(PO4)2 via a one-pot method. They were used as signaling probes in an off-the-shelf pregnancy test strip. This modified lateral flow immunoassay can detect Escherichia coli O157:H7 with a detection limit of 4 CFU·mL−1, and Salmonella typhimurium with a detection limit of 3 CFU·mL−1. Conceivably, the method has high potential as a portable and cost-effective tool for rapid determination of a wide range of analytes, especially in resource-constrained settings.
Aptamer based electrochemiluminescent determination of bisphenol A by using carboxylated graphitic carbon nitride Microchim. Acta (IF 5.705) Pub Date : 2018-09-17 Hai-Xia Cao, Li Wang, Chang-Gang Pan, Yu-Sheng He, Guo-Xi Liang
An electrochemiluminescence (ECL) based assay is described for the determination of the endocrine disruptor bisphenol A (BPA). The method is based on the use of carboxylated graphitic carbon nitride (C-g-C3N4) carrying an immobilized aptamer against BPA. In the presence of BPA, the ECL signal decreases due to ECL energy transfer from excited-state C-g-C3N4 to the BPA oxidation product. Under the optimal conditions, ECL intensity increases linearly in the 0.1 pM to 1 nM BPA concentration range. The detection limit is as low as 30 fM. The assay has excellent sensitivity, outstanding stability and high selectivity. It was applied to the determination of BPA in spiked water samples.
Microwave-assisted synthesis of thymine-functionalized graphitic carbon nitride quantum dots as a fluorescent nanoprobe for mercury(II) Microchim. Acta (IF 5.705) Pub Date : 2018-09-15 Ojodomo J. Achadu, Neerish Revaprasadu
A microwave-assisted hydrothermal method was employed to prepare thymine-modified graphitic carbon nitride quantum dots (T-gCNQDs) which are shown to be a novel fluorescent nanoprobe for Hg(II). They exhibit excellent optical properties (blue emission with a fluorescence quantum yield of 46%) and water solubility. The incorporation of thymine into the gCNQDs results in an enhancement in photoluminescence properties. It is found that fluorescence, best measured at excitation/emission wavelengths of 350/445 nm, is much more strongly quenched by Hg(II) compared to the thymine-free nanoprobe. The quenching is highly selective even in the presence other metal ions. This is ascribed to the formation of T-Hg(II)-T base complexes. Fluorescence drops linearly in the 1.0 to 500 nM Hg(II) concentration range, and the limit of detection is 0.15 nM. The method was applied to the determination of Hg(II) in spiked samples of tap and pond water. Recoveries were found to be >95%, thus demonstrating the practical applicability of the assay.
A glassy carbon electrode modified with nitrogen-doped reduced graphene oxide and melamine for ultra-sensitive voltammetric determination of bisphenol A Microchim. Acta (IF 5.705) Pub Date : 2018-09-15 Jingyu Qin, Jing Shen, Xiangyang Xu, Yuan Yuan, Guangyu He, Haiqun Chen
A composite was prepared at room temperature from nitrogen-doped reduced graphene oxide (N-rGO) and melamine via π-interaction. An ultra-sensitive electrochemical sensor for the determination of trace levels of bisphenol A (BPA) was obtained by coating a glassy carbon electrode (GCE) with the composite. The structure and morphology of composite were characterized by FTIR, Raman, XRD, XPS, SEM and TEM. Because of the synergetic effects of N-rGO and melamine, the modified GCE displays considerably enhanced sensitivity to BPA. The voltammetric response, typically measured at a peak of 0.48 V (vs. SCE) is linear in the 0.05 to 20 μM BPA concentration range, and the detection limit is 0.8 nM (at S/N = 3). The sensor is reproducible, stable and selective. It was applied to analyze baby bottles, drinking cups, mineral water bottles and shopping receipts that were spiked with BPA, and the recoveries reached 99.1–101.4%.
Aptamer based voltammetric patulin assay based on the use of ZnO nanorods Microchim. Acta (IF 5.705) Pub Date : 2018-09-15 Baoshan He, Xiaoze Dong
The authors describe an aptamer based assay for the mycotoxin patulin (PAT). A gold electrode was modified with a composite made from ZnO nanorods (ZnO-NRs) and chitosan. The ZnO-NRs was prepared by reaction with ammonia and subsequent hydrothermal growth. Its properties were characterized by X-ray diffraction, Raman spectroscopy and scanning electron microscopy. Subsequently, thiol-modified aptamers were self-assembled on AuNPs that had been electrodeposited on the surface of the modified electrode. The presence of ZnO-NRs on the electrode increases the loading with AuNPs and aptamers. It also warrants a relatively stable microenvironment for the aptamers. In the presence of PAT, it will form a complex with the aptamer on the electrode surface. This hinders electron transfer from the electrode to the redox probe hexacyanoferrate and results in reduced current, which is typically measured at 0.176 V (vs. Ag/AgCl). The concentration of PAT can be calculated from the differences in the peak current before and after incubation with PAT. The assay has a linear response in the 50 ng·mL−1 to 0.5 pg·mL−1 PAT concentration range and a 0.27 pg·mL−1 lower detection limit. The sensor is specific, reproducible, repeatable, and long-term stable. It was successfully applied to the determination of PAT in spiked juice samples.
Impedimetric determination of Staphylococcal enterotoxin B using electrochemical switching with DNA triangular pyramid frustum nanostructure Microchim. Acta (IF 5.705) Pub Date : 2018-09-15 Xiaoye Chen, Xinping Shi, Yun Liu, Lixia Lu, Yichen Lu, Xiong Xiong, Yuanjian Liu, Xiaohui Xiong
An electrochemical switching strategy is presented for the sensitive determination of Staphylococcus enterotoxin B (SEB). It is based on the use of DNA triangular pyramid frustum nanostructure (TPFDNA) consisting of (a) three thiolated probes, (b) one auxiliary probe, and (c) an aptamer against SEB. The TPFDNA was assembled on the gold electrode, with the SEB aptamer designed on top of the TPFDNA. The electron transfer to hexacyanoferrate acting as an electrochemical probe is strongly inhibited in the TPFDNA-modified electrode. This is assumed to be due to the formation of a 3D TPFDNA structure that limits access of hexacyanoferrate to the electrode. Therefore, the Faradaic impedance is large. However, in the presence of SEB, it will bind to the aptamer and dehybridize the hybrid formed between aptamer and its complementary sequence. As a result, the TPFDNA nanostructure changes to an equilateral triangle DNA nanostructure. This results in a more efficient electron transfer and a smaller Faradaic impedance. The method has a detection limit of 0.17 ng mL−1 of SEB (at an S/N of 3) and a dynamic range that covers the 0.2–1000 ng mL−1 concentration range. The applicability and reliability of the method was demonstrated by anayzing (spiked) milk samples, and the results were compared to those obtained with an ELISA kit. The relative standard deviations between the two methods range between −6.59 and 9.33%.
A catalytic cleavage strategy for fluorometric determination of Hg(II) based on the use of a Mg(II)-dependent split DNAzyme and hairpins conjugated to gold nanoparticles Microchim. Acta (IF 5.705) Pub Date : 2018-09-14 Wen Yun, Fukun Li, Xingyan Liu, Ning Li, Lin Chen, Lizhu Yang
A catalytic cleavage strategy was developed for the fluorometric determination of Hg(II). The method is based on the use of a Mg(II)-dependent split DNAzyme. Fluorophore labeled hairpins were conjugated to gold nanoparticles (AuNPs) upon which fluorescence is quenched. Thymine-Hg(II)-thymine (T-Hg(II)-T) interaction causes the two DNA sequences to form an entire enzyme-strand DNA (E-DNA). The E-DNA bind to the hairpins on the AuNPs to form a Mg(II)-dependent DNAzyme structure. The circular cleavage of hairpins results in a signal amplification and in the recovery of fluorescence. The assay has a limit of detection (LOD) as low as 80 pM of Hg(II). This LOD is comparable to those obtained with other amplification strategies. The method was successfully applied to the determination of Hg(II) in Chinese herbs (Atractylodes macrocephala Koidz).
Graphene oxide wrapped with gold nanorods as a tag in a SERS based immunoassay for the hepatitis B surface antigen Microchim. Acta (IF 5.705) Pub Date : 2018-09-14 Minghuan Liu, Chaohui Zheng, Malin Cui, Xiaoyan Zhang, Da-Peng Yang, Xiansong Wang, Daxiang Cui
A composite consisting of graphene oxide and gold nanorods (GO-GNRs) was designed for the trace determination of hepatitis B surface antigen (HBsAg) using surface enhanced Raman spectroscopy (SERS). GO contains numerous carboxy and hydroxy groups on its surface and therefore can serve as the substrate for decoration with GNRs and for immobilizing antibody against HBsAg. The GNRs (carrying the SERS probe 2-mercaptopyridine) exhibit high SERS activity, and this improves the sensitivity of the biosensor. The antibody on the GO-GNRs binds HBsAg with high specificity, and it results in excellent selectivity. The SERS signal (measured at 1002 cm−1) increases in the 1–1000 pg·mL−1 HBsAg concentrations range, and the limit of detection is 0.05 pg·mL−1 (at an S/N ratio of 3). The immunoassay achieves the sensitive and selective determination of HBsAg in serum and expands the potential application of GO-GNR based SERS tag in clinical research.
Sonication-assisted preparation of a nanocomposite consisting of reduced graphene oxide and CdSe quantum dots, and its application to simultaneous voltammetric determination of ascorbic acid, dopamine and uric acid Microchim. Acta (IF 5.705) Pub Date : 2018-09-13 Ebrahim Tavakolian, Javad Tashkhourian
Cadmium selenide quantum dots were capped with reduced graphene oxide that was modified with thioglycolic acid. The nanocomposite was prepared by 5-min sonication of a solution of graphene oxide, thioglycolic acid, and cadmium(II) nitrate and selenium powder in the presence of NaBH4. X-ray diffraction and transmission electron microscopy were used to characterize the nanocomposite. A glassy carbon electrode (GCE) was modified with this nanocomposite and used for simultaneous determination of dopamine (DA), ascorbic acid (A) and uric acid (UA). The modified GCE was characterized by using cyclic voltammetry and differential pulse voltammetry. Simultaneous determination of AA, DA and UA was accomplished at working voltages of −50, +148 and + 280 mV (all vs. Ag/AgCl), respectively. The voltammetric response to DA is linear in the 4.9 to 74.0 μM concentration range, and the detection limit (defined as 3σ of the blank) is 0.11 μM. The respective data are 0.39–1.0 mM and 66 μM for AA, and 9.0 to 120.0 μM and 0.12 μM for UA. The electrode was successfully applied to the determination of the 3 species in spiked urine samples.
Electrochemical sandwich immunoassay for Escherichia coli O157:H7 based on the use of magnetic nanoparticles and graphene functionalized with electrocatalytically active Au@Pt core/shell nanoparticles Microchim. Acta (IF 5.705) Pub Date : 2018-09-13 Fanjun Zhu, Guangying Zhao, Wenchao Dou
A highly sensitive electrochemical sandwich immunoassay is described for determination of Escherichia coli O157:H7 (E. coli O157:H7). Silica coated magnetite nanoparticles (Fe3O4) were modified with primary antibody to capture E. coli O157:H7. Gold-platinum core/shell nanoparticles (Au@Pt NPs) with different Pt shell thicknesses were prepared via changing the molar ratio of H2PtCl6 to HAuCl4 in the precursor solution. The optimized Au@Pt NPs exhibit enhanced activity in the electrocatalytic reduction of hydrogen peroxide (H2O2). The Au@Pt NPs were modified with graphene that was functionalized with Neutral Red, and then used as an electrochemical label for secondary antibodies and horseradish peroxidase (HRP). The sandwich immunocomplexes were magnetically absorbed on a 4-channel screen printed carbon electrode. Due to the catalysis of the Au@Pt NPs and HRP, the signal is strongly amplified in the presence of H2O2 when using thionine as the electron mediator. Under optimal conditions, the immunoassay has a linear response in the 4.0 × 102 to 4.0 × 108 CFU·mL−1 concentration range, with a limit of detection of 91 CFU·mL−1 (at an S/N ratio of 3).
Colorimetric detection of L-histidine based on the target-triggered self-cleavage of swing-structured DNA duplex-induced aggregation of gold nanoparticles Microchim. Acta (IF 5.705) Pub Date : 2018-09-12 Yunfei Jiao, Qingyun Liu, Hong Qiang, Zhengbo Chen
A rapid, highly sensitive and selective colorimetric assay is presented for visually detecting L-histidine. It is based on L-histidine-triggered self-cleavage of DNA duplex-induced gold nanoparticle (AuNP) aggregation. The citrate-capped AuNPs easily aggregate in a high concentration of salt environment. However, in the presence of L-histidine aptamers (DNA1 and DNA2), the partial strands of DNA1 and DNA2 hybridize to form a DNA duplex with a swing structure. The swing-like DNA duplexes are adsorbed on the surface of AuNPs to improve the stability of AuNPs, and the AuNPs also are better dispersed in high-salt media. When L-histidine is added to the solutions, it catalyzes the self-cleavage of DNA1 to form many single-stranded DNA (ssDNA) fragments. These ssDNA segments are adsorbed on the AuNPs and weaken the stability of AuNPs. Hence, the AuNPs aggregate in high-salt environment, and this results in a red-to-blue color change. Under the optimized conditions, L-histidine can be determined with a limit of detection of 3.6 nM. In addition, the sensor was successfully applied to the determination of L-histidine in spiked serum samples.
Tungsten disulfide (WS 2 ) nanosheet-based photoelectrochemical aptasensing of chloramphenicol Microchim. Acta (IF 5.705) Pub Date : 2018-09-12 Yunlei Zhou, Chengji Sui, Huanshun Yin, Yue Wang, Minghui Wang, Shiyun Ai
A method is described for photoelectrochemical determination of chloramphenicol (CLOA). It is based on the use of (a) aptamers protected with photoactive WS2 nanosheets, and (b) DNase I-assisted target recycling. The DNA aptamer without label was employed for recognition of CLOA. In the absence of CLOA, the aptamer is adsorbed on the surface of WS2. This leads to a decrease of photocurrent due to the steric-hindrance effect of aptamer DNA. The adsorption of WS2 also protects the aptamer from digestion by DNase. In the presence of CLOA, the aptamer will be desorbed from the WS2 surface due to formation of an aptamer/CLOA conjugate. This results in an increased photocurrent due to a decreased amount of aptamer DNA on the electrode surface. The increase of photocurrent can be further improved by applying DNase triggered catalytic recycling of CLOA. Under optimal experimental conditions, the response is linear 10 pM – 10 nM CLOA concentration range, with a 3.6 pM lower detection limit (at 3σ). This method is acceptably selective, accurate and stable. It was applied to the determination of CLOA in spiked milk samples and gave satisfactory results.
A Zr(IV)-based porphyrinic metal-organic framework as a solid-phase sorbent for extraction of sulfonamides prior to their quantitation by LC-MS Microchim. Acta (IF 5.705) Pub Date : 2018-09-12 Ze-Hui Deng, Gui-Ju Xu, Xiao-Li Wang, Xia Wang, Ming-Lin Wang, Jin-Ming Lin, Ru-Song Zhao
A porphyrinic metal–organic framework (PCN-224) was fabricated and used as an adsorbent for solid-phase extraction of ultratrace levels of polar sulfonamide antibiotics from food and drinking waters. The PCN-224 was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and powder X-ray diffraction analyses. Parameters affecting the extraction efficiency were optimized. The sulfonamides were quantified by liquid chromatography-tandem mass spectrometry. Figures of merit include (a) low limits of detection (0.07–0.47 ng·L−1), (b) wide linear ranges (0.5–2000 ng·L−1), and (c) good repeatabilities (2.8%–6.7%) and reproducibilities (1.7%–5.1%). The method was successfully applied to the determination of sulfonamides in food and drinking water samples.
Determination of hypoxia-inducible factor-1 by using a ratiometric colorimetric test based on click-mediated growth of gold nanoparticles Microchim. Acta (IF 5.705) Pub Date : 2018-09-12 Hong Chen, Yan Sun, Yifei Li, Jing Zhao, Ya Cao
The authors describe a significantly improved colorimetric nanoprobe for the determination of transcription factors (TFs). It is making use of click-mediated growth of gold nanoparticles (AuNPs) to amplify the signal-to-noise ratio. Hypoxia-inducible factor-1 (HIF-1) is an important TF that acts as a mediator of cell response to hypoxia. So, the detection of HIF-1 was chosen as the model analyte. Specifically, target HIF-1 is designed to bind to the hypoxia response element within DNA duplex. The click chemistry between the DNA duplex and alkynyl-functionalized AuNPs (AF-AuNPs) is then inhibited because of significant steric hindrance. As a result, the AF-AuNPs grow into larger-sized highly-aggregated irregular nanostructures, which in turn enable colorimetric determination. The ratio of absorbances at 620 and 560 nm increases in the 0.5 to 10 nM HIF-1 concentration range, and the detection limit is 0.27 nM. This is better by a factor of 100 than that of aggregation-based colorimetric assays. The nanoprobe is selective and can be used in complex samples. Conceivably, it may also be extended to the determination of other TFs by simply changing the used DNA duplex.
Mesoporous silica coating NaYF 4 :Yb,Er@NaYF 4 upconversion nanoparticles loaded with ruthenium(II) complex nanoparticles: Fluorometric sensing and cellular imaging of temperature by upconversion and of oxygen by downconversion Microchim. Acta (IF 5.705) Pub Date : 2018-09-12 Sai Xu, Yang Yu, Yuefeng Gao, Yanqiu Zhang, Xiangping Li, Jinsu Zhang, Yunfeng Wang, Baojiu Chen
Accurate detection of temperature and oxygen concentration at the cellular level is important in tumor diagnosis. Multifunctional nanocomposites are described that consist of upconversion luminescent nanoparticles capped with mesoporous silica and loaded with an oxygen-sensitive luminescent ruthenium complex. The nanocomposites of type NaYF4:Yb,Er@NaYF4@mSiO2-Ru have two modes of operation: Its red downconversion luminescence (at excitation/emission peaks of 455/606 nm) is quenched by oxygen (O2), and this is used to sense and image O2. The green upconversion luminescence (typically acquired at excitation/emission wavelengths of 980/525 and 544 nm), in turn, is used to measure temperature. The nanocomposites were then applied to dual mode in-vitro imaging of temperature and O2 in hepatocellular carcinoma cells (HepG-2).
Electrochemical immunoassay for lactalbumin based on the use of ferrocene-modified gold nanoparticles and lysozyme-modified magnetic beads Microchim. Acta (IF 5.705) Pub Date : 2018-09-07 Abdelmoneim Mars, Sinda Ben jaafar, Amel Ben Ammar-El Gaied, Noureddine Raouafi
The authors describe a method for electrochemical determination of the breast cancer biomarker α-lactalbumin (α-LA) using disposable screen-printed carbon electrodes (SPCEs). Lysozyme-conjugated Fe3O4 nanoparticles (Lys-Fe3O4NPs) were used to capture α-LA on the surface of the SPCEs which then is trapped in an immunosandwich using secondary antibodies labeled with ferrocene-modified gold nanoparticles. The amperometric response of ferrocene (recorded at +0.1 V vs. silver pseudo-reference electrode) as well as the electrocatalytic activity of gold nanoparticles on the hydrogen evolution reaction (recorded at −1.0 V Vs Ag pseudo-reference electrode) was exploited to sense α-LA. A sensitive voltammetric response is observed, with (a) a sensitivity of 0.8789 μA·nM−1.cm−2, (b) a detection limit (LOD, at S/N = 3) as low as 0.07 ng·mL−1, and (c) linear response in the 0.75 to 630 ng mL−1 α-LA concentration range. The assay is selective and reproducible, and the SPCEs have good storage stability. The SPCEs were applied (a) to the analysis of (spiked) maternal milk, (b) of spiked serum from healthy and pregnant persons, and (c) of serum of patients suffering from breast cancer.
A colorimetric assay for acetylcholinesterase activity and inhibitor screening based on the thiocholine–induced inhibition of the oxidative power of MnO 2 nanosheets on 3,3′,5,5′–tetramethylbenzidine Microchim. Acta (IF 5.705) Pub Date : 2018-09-05 Yuan Sun, Haonan Tan, Yinhuan Li
The authors describe a colorimetric method for the determination of the activity of acetylcholinesterase (AChE). Manganese dioxide (MnO2) nanosheets directly reacts with 3,3′,5,5′–tetramethylbenzidine (TMB) in the absence of hydrogen peroxide (H2O2). This leads to the formation of a blue product (oxTMB) with an absorption peak at 652 nm. If AChE hydrolyzes its substrate acetylthiocholine chloride, thiocholine is formed which blocks the oxidative power of the MnO2 nanosheets. Hence, oxTMB will not be formed. The decreased absorbance is directly related to the AChE activity in the 0.01–1.0 mU·mL−1 range. The detection limit is 0.01 mU·mL−1 and the relative standard deviation is 1.2% (for n = 11 at 0.5 mU·mL−1). The method was also applied to screen for inhibitors of AChE.
Fluorometric determination of zinc(II) by using DNAzyme-modified magnetic microbeads Microchim. Acta (IF 5.705) Pub Date : 2018-09-05 Wei Shen, Yana Li, Tong Qi, Suncheng Wang, Jun Sun, Huimin Deng, Hongfei Lu, Chuanxiang Chen, Lizhuang Chen, Sheng Tang
A fluorometric assay for zinc ion is described that relies (a) on the use of an isothermal cycle to amplify the fluorescence signal, and (b) of magnetic beads (MBs) to completely remove unreacted DNA detection probes. Biotin and fluorophore-labeled substrate (Zn-Sub) strands acting as detection probes were first assembled on MBs. Next, Zn(II)-specific DNAzyme (Zn-Enz) strands were hybridized with the Zn-Sub strands. In the presence of Zn(II), the Zn-Sub strands are cleaved. This results in the release of the shorter DNA fragments (containing fluorescent label) and in the dissociation of Zn-Enz strands. The dissociated Zn-Enz strands then hybridize with the residual Zn-Sub strands and cleave them in a similar fashion. This leads to a target recycling amplification mechanism and in a cumulative signal amplification process. A strongly amplified signal is thus obtained in the presence of Zn(II). The use of MBs warrants that unreacted Zn-Sub strands can be magnetically separated from the solution. The method has a detection limit as low as 33 fM at a signal-to-noise ratio of 3 and a linear response in the 100 fM to 11 nM Zn(II) concentration range. It was applied to the determination of Zn(II) in spiked tap water and seawater samples, and the results compared well with data obtained by ICP-MS analysis. The method was also applied to the determination of Zn(II) in infant milk powder and breast milk.
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