Relative Standard Derivations Research Articles

Imprinted membrane-covalent organic framework platform for efficient label-free visual detection of Listeria monocytogenes and Salmonella typhimurium in food samples

BackgroundRapid and sensitive detection of foodborne pathogens in food plays a crucial role in controlling outbreaks of foodborne diseases, of which Listeria monocytogenes and Salmonella typhimurium are representative and notable pathogens. Thus, it’s of great importance to achieve the effective detection of these pathogens. However, the most common detection methods (culture-based technique, Polymerase Chain Reaction and immunological methods) have disadvantages that cannot be ignored, such as time-consuming, laborious, complex sample preparation process, and the possibility of cross-reaction. Hence, it is essential to develop a facile detection method for the pathogens with high sensitivity and specificity to avoid the above-mentioned disadvantages. ResultsWe report a label-free visual platform for the simultaneous capture and detection of Listeria monocytogenes and Salmonella typhimurium. For the first time, we have prepared polydimethylsiloxane-Chromotrope 2R membrane which serves as the substrate for bacterial capture and enrichment through the formation of specific recognition sites. The positively charged Pt-covalent organic framework combines with the pathogens through surface charge interaction, thereby the label-free sandwich platform is formed. Remarkable peroxidase activity of Pt-covalent organic framework converts the conversion of bacterial quantity into amplified color signal by catalyzing 3,3',5,5'-Tetramethylbenzidine to oxidized 3,3',5,5'-Tetramethylbenzidine. The platform demonstrates the capability to identify two representative food-borne pathogens within a time frame of 100 min, exhibiting high sensitivity and excellent specificity without the interference from non-target bacteria. The limit of detection of the visual platform toward Listeria monocytogenes and Salmonella typhimurium was 1.61 CFU·mL-1 and 1.31 CFU·mL-1, respectively. And the limit of quantification toward Listeria monocytogenes and Salmonella typhimurium was 4.94 CFU·mL-1 and 2.47 CFU·mL-1, respectively. The relative standard derivations of the visual platform for both bacteria were lower than 4.9%. Furthermore, our proposed platform has obtained reliable and satisfactory results on analyzing diverse food samples. SignificanceThis research expands the application of a label-free platform combined with unlabeled nanocomponents in the rapid isolation and detection of diverse of food-borne pathogens. The platform possesses the advantages of simple operation and real-time monitoring, without complicated sample pretreatment process. The whole detection process can realize the simultaneous monitoring of Listeria monocytogenes and Salmonella typhimurium within 100 minutes. Furthermore, it is also of reference significance for the detection of other common pathogens.

Immunoelectrochemical Detection of Prostate-Specific Antigen on PEDOT/Cerium Phosphate Nanotubes Modified ITO Electrode

Herein, a label-free electrochemical immunosensor was developed to detect prostate-specific antigen (PSA), a biomarker for prostate cancer. The immunosensor was fabricated by modifying one-dimensional nanomaterial CePO4 nanotubes, electrodepositing poly-3,4-ethylenedioxythiophene layer, anchoring monoclonal antibodies to PSA, and blocking with bovine serum albumin on the surface of the indium tin oxide sheet. The morphologies and electrochemical performance of the electrochemical sensor were characterized by Fourier transform infrared spectrophotometry, field-emission scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. For PSA, it exhibits a wide dynamic range from 0.1 ng ml−1 to 100 ng ml−1 and a detection limit of 0.012 ng ml−1 (at a signal-to-noise ratio of 3) with differential pulse voltammetry. Average recoveries from rat serum (a simulated human serum) are between 97.00%–103.17% with relative standard derivations less than 4.25% (n = 3) at three spiked levels. Moreover, it shows high reproducibility, well selectivity, and good stability. The immunosensor provides an effective tool in the clinical diagnosis of prostate cancer.

Analysis and contamination levels of ten phthalic acid esters (PAEs) in Chinese commercial bubble tea: a comparison with commercial milk.

Phthalic acid ester (PAE) contamination in popular drink bubble tea has been hardly studied in the world. In this work, a liquid-liquid extraction following solid phase extraction (LLE-SPE)-UPLC-MS/MS method was first established for trace determination of ten PAEs in bubble tea. The developed method was validated with respect to linearity (R2 > 0.992), low limit of detections (LODs, 0.49-3.16µg/L), and satisfactory recoveries (61.8-127.6%) with a low relative standard derivations (RSDs, 1.1-16.4%), which was also validated for commercial milk. Six out of ten PAEs, i.e., diethylhexyl phthalate (DEHP), dibutyl phthalate (DBP), diisobutyl phthalate (DIBP), diethyl phthalate (DEP), dihexyl phthalate (DHP), and diphenyl phthalate (DPP) were detected in Chinese bubble tea with concentrations ranging from not detection (ND) to 53.43µg/L, while DEHP, DBP, DIBP, DEP, and dimethyl phthalate (DMP) were detected in commercial milk with concentrations ranging from ND to 110.58µg/L. The respective average concentrations of DEHP in Chinese bubble tea and commercial milk were 19.40 and 23.46µg/L, which were over two times that in drinking water quality standards of several countries including Israel, Korea, Oman, and Singapore (i.e., 8µg/L). Calculated with human estimated daily intake (EDI), the average EDIs of five out of seven PAEs in bubble tea were higher than those in commercial milk. For example, the calculated EDI of DIBP in bubble tea was 5 times that in commercial milk, while their respective corresponding EDIs of DBP and DEHP were over 2.4 and 1.6 times. Based on estrogen equivalence (EEQ) with the unit of ng E2/L, the average EEQs of the ten PAEs in Chinese bubble tea and commercial milk were 14.26 and 17.06ng E2/L, which were 52.8 and 62.3 times the observed effect concentration that could cause egg mortality of zebrafish. It is evident that the potential estrogenic effect of PAEs in bubble tea and commercial milk cannot be negligible. Given the fact that PAE contamination in bubble tea has been hardly investigated, such study is urgently to be performed in a global view.

Molecularly Imprinted Polymer Modified Electrode Prepared by In Situ Polymerization for Specific Determination of Norfloxacin

Herein, a molecularly imprinted sensor was proposed via in situ polymerization technique for specifically sensing norfloxacin (NFX). The sensor indicates high stability due to the imprinting layer covalently conjugated on the surface of aminated glass carbon electrode. Emphasized, it shows excellent selectivity and specificity towards NFX ascribed to the unique characteristics of molecularly imprinted polymers (MIPs). Even in the presence of 10-fold concentration of its structural analog ciprofloxacin, there is no evident interference in the determination of NFX. Under optimized conditions, the oxidation current of square wave voltammetry (typically at +1.03 V vs Ag/AgCl) increases linearly with the concentration of NFX increasing in the ranges of 0.1–10 μM and 10−160 μM. And the limit of detection is 0.004 μM (based on a signal-to-noise ratio of 3). Average recoveries from (spiked) real water samples are between 99.63% and 103.20% with relative standard derivations less than 4.67% (n = 3) at three spiked levels, validated by independent assays of HPLC. This work provides a successful model for fast preparing MIP-based electrochemical sensors for detecting trace drug residues in environmental samples.

Determination of polychlorinated naphthalenes in soil using accelerated solvent extraction-molecular sieves solid-phase extraction coupled with gas chromatography-tandem mass spectrometry

新污染物引发的环境和健康风险正逐步受到社会各界的广泛关注,我国第十四个五年规划和2035年远景目标纲要明确“重视新污染物治理”。作为新型的持久性有机污染物,多氯萘(PCNs)在土壤中通常处于痕量水平,一般需要经过多层硅胶柱/氧化铝柱等复杂的净化方法,再结合有效的分析手段才能实现准确测定。关注土壤中多氯萘分离分析方法可以为掌握和监管其在土壤中的污染状况提供技术和方法支持。研究以13X分子筛作为固相萃取吸附剂,评价了其对多氯萘的净化效果。研究发现:使用正己烷作为上样溶剂和淋洗剂,10 mL二氯甲烷/正己烷(2∶15, v/v)为洗脱溶剂,可以实现PCNs与脂类大分子等干扰物的选择性分离,且多氯萘内标的平均回收率为56.1%~88.0%。与凝胶渗透色谱法、弗罗里硅土固相萃取柱以及多层硅胶柱/氧化铝柱相比,13X分子筛对土壤提取液的净化效果优于前两种净化方法,可以获得与多层硅胶/氧化铝柱相近的净化效果(53.0%~117.0%),而且操作更加简单,环境更加友好,分析成本大幅度下降。在此基础之上,建立了加速溶剂萃取-分子筛固相萃取,结合气相色谱-三重四极杆质谱法测定土壤中PCNs的分析方法。PCNs同族体的方法检出限为0.009~0.6 ng/g。采用基质加标法评价了本方法的精密度和准确度,CN-3、13、42、46、52、53、73、75在低、中、高加标水平下的平均加标回收率分别为70%~128%、71%~115%和61%~114%,测定结果的相对标准偏差分别为4.2%~23%、6.5%~31%和4.7%~22%,满足痕量分析的要求且平行性较好。从整个分析流程来看,13X分子筛有望成为新污染物净化的新型固相萃取吸附剂,并在土壤新污染物普查中发挥重要作用。

Electrochemical fabrication of Co(OH)2 nanoparticles decorated carbon cloth for non-enzymatic glucose and uric acid detection.

Cobalt hydroxide nanoparticles (Co(OH)2 NPs) were uniformly deposited on flexible carbon cloth substrate (Co(OH)2@CC) rapidly by a facile one-step electrodeposition, which can act as an enzyme-free glucose and uric acid sensor in an alkaline electrolyte. Compositional and morphological characterization were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS), which confirmed the deposited nanospheres were Co(OH)2 nanoparticles (NPs). The electrochemical oxidation of glucose and uric acid at Co(OH)2@CC electrode was investigated by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), differential pulse voltammetry (DPV), and chronoamperometry methods. The results revealed a remarkable electrocatalytic activity toward the single and simultaneous determination of glucose and uric acid at about 0.6 V and 0.3V (vs. Ag/AgCl), respectively, which isattributed to a noticeable synergy effect between Co(OH)2 NPs and CC with good repeatability, satisfactory reproducibility, considerable long-term stability, superior selectivity, outstanding sensitivity, and wide linear detection range from 1 uM to 2mM and 25nM to 1.5 uM for glucose and UA, respectively. The detection limits were 0.36nM for UA and 0.24μM for glucose (S/N = 3). Finally, theCo(OH)2@CC electrode was utilized for glucose and uric acid determination in human blood samples and satisfying results were obtained. The relative standard derivations (RSDs) for glucose and UA were in the range 6 to 14% and 0 to 3%, respectively. The recovery ranges for glucose an UA were 97 to 103% and 95 and 101%, respectively. These features make the novel Co(OH)2@CC sensor developed by a low-cost, efficient, and eco-friendly preparation method apotentially practical candidate for application to biosensors.

Target-induced photocurrent-polarity-switching photoelectrochemical aptasensor with gold nanoparticle-ZnIn2S4 nanohybrids for the quantification of 8-hydroxy-2′-deoxyguanosine

This work reports on an ultrasensitive photoelectrochemical (PEC) aptasensor for the detection of 8-hydroxy-2′-deoxyguanosine (8-OHdG) by using target-triggered hemin/G-quadruplex photocurrent polarity switching on ultrathin ZnIn2S4 nanosheets (ZISNS). Hemin/G-quadruplexes were assembled on indium tin oxide (ITO) electrodes coated with gold nanoparticle-modified ZISNS (AuNPs-ZISNS) as signaling labels for the polarity inversion mechanism in PEC aptasensors. Benefiting from the excellent photoelectronic properties of AuNPs-ZISNS and the photocurrent polarity switching reliability of hemin, the proposed aptasensor for 8-OHdG detection was in a broad range from 1.0 pM to 10,000 pM with a detection limit of 0.3 pM. Moreover, this assay has shown sufficient sensitivity, favorable stability, and high selectivity in the detection of complex biological matrices. The recoveries were in the range of 92–108%, and the relative standard derivations (RSD) were ranged from 2.1% to 5.1%, indicating the good accuracy and high precision of this approach. Impressively, the concept of photocurrent-polarity-switching mode provides an alternative for constructing accurate and plausible PEC bioanalysis and inspires more interest in the design of advanced PEC bioanalysis through readout signal regulation.

Enzyme-modulated photothermal immunoassay of chloramphenicol residues in milk and egg using a self-calibrated thermal imager

Highly sensitive and accurate detection of chloramphenicol is of paramount importance for food safety. Herein, an enzyme-modulated photothermal immunosensor that uses a self-calibrated thermal imaging system (SCTIS) as signal read-out was developed for detecting chloramphenicol. In this immunosensor, alkaline phosphatase was used as a modulator of the photothermal conversion. It could hydrolyze the substrate into ascorbic acid, thereby reducing oxidized 3,3′,5,5′-tetramethylbenzidine, which exhibited a near-infrared laser-driven photothermal effect. For precise temperature measurement, the SCTIS was designed by using the temperature compensation of a ceramic chip to enable real-time self-calibration of the temperature. This SCTIS-based immunosensor could detect chloramphenicol with a LOD of 9 pg/mL in 2 h, and relative standard derivations from 3.95% to 13.58%. The average recoveries in milk and egg samples ranged from 76% to 114%. This versatile sensing strategy can detect various targets by altering recognition elements, thus has wide applicability in food safety testing and monitoring.

A Vancomycin HPLC Assay for Use in Gut Microbiome Research.

ABSTRACTThe human microbiome project has revolutionized our understanding of the interaction between commensal microbes and human health. By far, the biggest perturbation of the microbiome involves use of broad-spectrum antibiotics excreted in the gut. Thus, pharmacodynamics of microbiome changes in relation to drug exposure pharmacokinetics is an emerging field. However, reproducibility studies are necessary to develop the field. A simple and fast high-performance liquid chromatography-photodiode array detector (HPLC) method was validated for quantitative fecal vancomycin analysis. Reproducibility of results were tested based on sample storage time, homogeneity of antibiotic within stool, and concentration consistency after lyophilization. The HPLC method enabled the complete elution of vancomycin within ~4.2 min on the reversed-phase C18 column under the isocratic elution mode, with excellent recovery (85% to 110%) over a 4-log, quantitative range (0.4–100 μg/mL). Relative standard derivations (RSD) of intra-day and inter-day results ranged from 0.4% to 5.4%. Using sample stool aliquots of various weights consistently demonstrated similar vancomycin concentrations (mean RSD: 6%; range: 2–16%). After correcting for water concentrations, vancomycin concentrations obtained after lyophilization were similar to the concentrations obtained from the original samples (RSD less than 10%). These methodologies establish sample condition standards for a quantitative HPLC to enable vancomycin pharmacokinetic studies with the human microbiome.IMPORTANCE Research on antibiotic effect on the gut microbiome is an emerging field with standardization of research methods needed. In this study, a simple and fast high-performance liquid chromatography method was validated for quantitative fecal vancomycin analysis. Reproducibility of results were tested to standardize storage time, homogeneity of antibiotic within stool, and concentration consistency after lyophilization. These methodologies establish sample condition standards for a quantitative HPLC to enable vancomycin pharmacokinetic studies with the human microbiome.

Development of a novel analytical method for inflammation and immunity-related metabolites in serum based on liquid chromatography tandem mass spectrometry

Some metabolites have been found to play key roles in inflammation and immunity events that are associated with diseases such as cancer, diabetes and cytokine release syndrome. Characterization upon the inflammation and immunity-related metabolites (IIMs) will be helpful to the assessment of related pathological states. Although these metabolites have been partially reported in previous studies, the methods for specific measurement of them remain lacking. In the present study, a liquid chromatography - mass spectrometry based method was developed for the targeted analyses of 45 IIMs including amino acids, organic acids, phosphatidylcholines (PCs), polyunsaturated fatty acids and hormones selected based on the literature knowledge. Direct extraction with dansyl-chloride in acetonitrile was proved to be the most efficient and time-saving strategy, in which precipitation, extraction and derivatization were integrated. IIMs derivatized for 4 min and quenched for 2 min revealed the most comprehensive abundance. Based on the defined conditions, all the IIMs had a low limit of detection smaller than 1 ng/mL with the linear range greater than three orders of magnitude. The relative standard derivations of intra-day and inter-day precisions were ranged from 2.2% to 13.4% and 1.7% to 19.5%, respectively. The recovery rates and accuracy in low concentration were 98.9% ± 5.6% and 106.7% ± 11.6%, in medium concentration were 97.1% ± 6.8% and 106.9% ± 9.5%, and in high concentration were 98.4% ± 8.9% and 98.1% ± 8.1%, respectively. Matrix effect and stability were ranged from −37.8% to 35.6% and 2.9% to 14.2%, respectively. To show the usefulness of the method, serum IIMs in hepatitis B virus (HBV) infected patients and healthy subjects were determined and compared. Bile acids, lipoxygenase-mediated lipid mediators and non-enzymatic products showed global increases, whereas most of LysoPCs and cyclooxygenase-mediated prostaglandin D2 decreased in HBV serum samples. This study provided a robust approach for the characterization of IIMs.

Freestanding Fully Porous Polyimide Membrane for Thin Film Microextraction

In this study, freestanding fully porous polyimide (FFPP) membranes were prepared in batches by the scraping technique and vapor-induced phase separation (VIPS) and used for thin film microextraction (FFPP-TFME). When water vapor was applied simultaneously during scraping, the resulting membrane surface was highly porous, in contrast to the dense and smooth surface obtained without vapor. The micro/nanocomposite pore structure was revealed by scanning electron microscopy and nitrogen adsorption–desorption. The diameters of the micropores, nanopores and fibrous polyimide (PI) nanofibers were 0.5–1.5 μm, ca. 30 nm and ca. 250 nm, respectively. The extraction performance of the FFPP-TFME method was evaluated with organochlorine pesticides (OCPs) as model analytes in water. The extracted OCPs were desorbed in acetone and then quantified by gas chromatography–mass spectrometry. The effects of extraction time, ionic strength, desorption solvent, desorption volume and desorption time were investigated. Under the optimized conditions, the limits of detection (LODs) for eight OCPs (4.4–83 ng L−1), linear ranges (0.05–50 μg L−1), correlation coefficients (0.997–0.999), intrabatch relative standard derivations (RSDs, 0.88–9.20%) and interbatch RSDs (6.35–13.5%) were obtained. The method was also successfully applied to the analysis of environmental water samples, and the relative recoveries of all real water samples were 73.6–116.4%. These results show that the FFPP-TFME method is a simple, efficient and environmentally friendly method for the pretreatment of trace organic pollutants in water samples.

Label-Free Detection of Staphylococcus aureus Based on Bacteria-Imprinted Polymer and Turn-on Fluorescence Probes.

The effective identification and quantitative determination of Staphylococcus aureus is a major public health concern. Here, an innovative strategy that combines a bacteria-imprinted polydimethylsiloxane film for bacterial recognition and fluorescence resonance energy transfer platform for turn-on fluorescence sensing is demonstrated. The bacteria-imprinted polydimethylsiloxane film was facilely fabricated to generate corresponding specific sites on the polydimethylsiloxane surface via stamp imprinting using Staphylococcus aureus as template followed by modification with 1H,1H,2H,2H-perfluorooctyltriethoxysilane. The fluorescence resonance energy transfer platform was developed through electrostatic interaction between citrate-functional copper clusters and dopamine-stabilized gold nanoparticles. When the Staphylococcus aureus are present, the 1H,1H,2H,2H-perfluorooctyltriethoxysilane-modified bacteria-imprinted polydimethylsiloxane film can precisely capture the target; subsequently, the negatively charged bacteria compete with citrate-functional copper clusters and bind to dopamine-stabilized gold nanoparticles, leading to the fluorescence recovery of citrate-functional copper clusters. The entire detection process was achieved within 135 min, showing a wide linear calibration response from 10 to 1 × 107 cfu mL-1 with a low detection limit of 11.12 cfu mL-1. Furthermore, the recoveries from spiked samples were from 97.7 to 101.90% with relative standard derivations lower than 10%. The established label-free assay of measuring Staphylococcus aureus is rapid, sensitive, specific, and efficient.

Simultaneous determination of five pesticides residues in Anoectochilus roxburghii by HPLC-MS/MS method

Objective： To establish a HPLC-MS/MS method for simultaneous determination of five pesticides residues including tebuconazole，metalaxyl-M，thiophanate-methyl，oxytetracycline and abamectin in Anoectochilus roxburghii.Methods： The samples were extracted by acetonitrile solution and purified by QuEChERS method.Separation was performed on Agilent Eclipse Plus C18 column（50 mm×2.1 mm，1.8 μm） with the mobile phase consisting of 0.1% formic acid（A） and acetonitrile（B） by gradient elution（0-1.0 min，90% A；1.0-3.0 min，90%-70% A;3.0-5.0 min，70%-30% A;5.0-8.0 min，30%-10% A;8.0-14.0 min，10% A;14.0-15.0 min，10%-90% A;15.0-17.0 min，90% A）.Detection was performed on a triple quadrupole tandem mass spectrometry with electrospray ionization source operating in positive ion mode under multiple reaction monitoring（MRM） mode.Results： The calibration curves of five pesticides showed good linearity coefficients（r>0.99）.The average recoveries ranged from 72.7% to 94.9%（n=6），and the relative standard derivations（RSDs） were within 1.8%-10.3%（n=6）.The detection limits of tebuconazole，metalaxyl-M，thiophanate-methyl，oxytetracycline and abamectin were 0.6，0.2，0.3，0.2，5.0 μg/kg，and the quantitation limits of 5 pesticides were 2.0，0.5，1.0，0.6 and 10.0 μg/kg respectively.Conclusion： The established method was proved to be sensitive，simple and reliable，and could be applied for the determination of these five pesticides in Anoectochilus roxburghii and quality control in the planting process.

Development of an Atmospheric Pressure Chemical Ionization Interface for GC-MS.

A closed atmospheric pressure chemical ionization (APCI) ion source as interface between a gas chromatograph (GC) and a triple quadrupole mass spectrometer (QqQ-MS) was developed. The influence of different ion source conditions, such as humidity, make-up gas flow, and the position of the GC column, were investigated and determined as main factors to increase sensitivity and repeatability of the system. For a performance test under real conditions, the new APCI ion source was used for the determination of plant protection products in commercially available coffee beans from Vietnam. The ionization behavior was investigated and the majority of the analytes were detected as [MH]+, [M]+∙, or as characteristic fragment ions, which have been assigned to ion source fragmentation. The developed GC-MS methods are based on tandem MS (MS/MS) and revealed for the plant protection products limits of detection (LOD) between 1 and 250 pg on column and relative standard derivations for all compounds < 16%. The used ultrasonic solid–liquid extraction yielded recovery rates of approximately 60 to 100%. Residues of herbicide methyl esters, organophosphorus compounds, and organonitrogen compounds have been detected in the analyzed coffee beans.

Aptamer-quantum dots and teicoplanin-gold nanoparticles constructed FRET sensor for sensitive detection of Staphylococcus aureus

The detection of bacterial pathogen such as Staphylococcus aureus (S. aureus) is essential for the regulation of food hygiene and disease diagnosis. Herein, we developed a simple one-step fluorescence resonance energy transfer (FRET)-based sensor for specific and sensitive detection of S. aureus in food and serum samples, in which aptamer-modified quantum dots (aptamer-QDs) was employed as the energy donor and antibiotic of teicoplanin functionalized-gold nanoparticles (Teico-AuNPs) was chosen as the energy acceptor. Within 1h, the FRET-based sensor showed a linear range of from 10 cfu/mL to 5×108 cfu/mL, with the low limit of detection (LOD, 2 cfu/mL) for S. aureus in buffer. When further applied to assay S. aureus in real samples, the FRET-based sensor showed good recoveries ranging from 84.5% to 110.0%, with relative standard derivations (RSDs) of 0.01%–0.44% and a LOD of 100 cfu/mL in milk, orange juice and human serum.

Signal-off tuned signal-on (SF-T-SN) colorimetric immunoassay for amantadine using activity-metalmodulated peroxidase-mimicking nanozyme

Immunoassays facilitate a wide range of rapid, simple and sensitive biochemical detection analyses. We developed a signal-off tuned signal-on (SF-T-SN) colorimetric immunoassay for the detection of the antiviral drug, amantadine (AMD). Using this strategy, the conventional competitive signal-off immunoassay acts as a foundation to induce different immune recognition events in the absence and presence of AMD. The introduction of activity-metal modulated peroxidase-mimicking nanozymes converts the conventional signal-off model to a signal-on model, thereby facilitating drug detection, and overcoming disadvantages with natural enzymes. Importantly, due to switching of the reporting mechanism, and the high catalytic activity of the nanozyme, this “off-to-on” pathway makes the nanozyme-based colorimetric signal proportional to AMD concentrations, thereby circumventing the inherent drawbacks of limited signaling abilities and sensitivities with conventional signal-off immunoassay-based small molecule detection systems. AMD concentrations can be read by the eye or by the optical signals. Based on this protocol, system sensitivity (0.195 ng mL−1 AMD for the naked eye, and 0.134 ng mL−1 AMD for optical detection) not only outperformed reported methods, but it dramatically improved the naked eye observations and UV–vis measurements, when compared with conventional signal-off immunoassays. AMD concentrations spiked into chicken samples were also detected with acceptable recoveries, and relative standard derivations (RSD), indicating this method is highly applicable for biochemical analyses and food safety monitoring.

Determination of acrylamide in coffee by ultra performance liquid chromatography-atmospheric pressure chemical ionization tandem mass spectrometry

A method using ultra high performance liquid chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry (UHPLC-APCI-MS/MS) was developed for the determination of acrylamide in coffee. The coffee samples spiked with 13C3-acrylamide as the internal standard were extracted with methanol, and cleaned using HLB solid phase extraction (SPE) cartridges. The liquid chromatography separation was performed on a Brownlee validated AQ C18 column with isocratic elution. Methanol and 0.1% (volume percentage) formic acid aqueous solution were used as the mobile phase. Identification of acrylamide was achieved by APCI-MS/MS with multiple reaction monitoring (MRM) in the positive mode. The quantification analysis was performed by the internal standard method. The calibration curve showed good linearity with a correlation coefficient of 0.999 in the range of 0.5-100.0 μg/L. The limit of detection (LOD) was 5.0 μg/kg. The limit of quantification (LOQ) was 10.0 μg/kg. Recovery of acrylamide from coffee sample was evaluated at concentrations of 100.0, 200.0 and 1000.0 μg/kg. The average recoveries of acrylamide were between 94.6%-115.0% with relative standard derivations (RSDs) in the range of 2.8%-3.6% (n=6). This simple, accurate and sensitive method was proven to be suitable for the determination of acrylamide in coffee.

Polyethyleneimine/Graphene Multilayer Film Supported Ferric Cobalt Modified Electrode for High-Performance Sensing of L-cysteine

One novel chemically modified electrode (CME) was prepared through fabricating polyethyleneimine/oxidized graphene multilayers on indium tin oxide (ITO) slide via layer-by-layer assembly followed by electrochemically depositing cobalt hexacyanoferrate. A large range of methods were used to characterize the morphology and electrochemical properties of the electrode including field-emission scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, cyclic voltammetry, differential pulse voltammetry (DPV), electrochemical impedance spectroscopy and chronoamperometry. Under optimized conditions, the oxidation current of DPV (typically at 0.2 V vs. saturated calomel electrode) increased linearly in the range of 5 × 10−5 to 2 × 10−3 mol L−1. And the limit of detection and the limit of quantity were 4.6 × 10−7 mol L−1 and 1.5 × 10−6 mol L−1 (based on signal-to-noise ratio of 3 and 10), respectively. Average recoveries from (spiked) commercial mask were between 98.1% and 104.5% with relative standard derivations less than 3.14% (n = 3) at three spiked levels. The method was validated by HPLC. Furthermore, the possible mechanism of L-Cys detection was studied based on chronoamperometric experiments.

Facile Preparation of a Bacteria Imprinted Artificial Receptor for Highly Selective Bacterial Recognition and Label-Free Impedimetric Detection.

The effective identification and quantification of pathogenic bacteria is essential for addressing serious public health issues. Here, we demonstrate a simple and universal impedimetric sensor for highly selective and sensitive detection of pathogenic bacteria based on the recognition by a bacteria-imprinted polypyrrole (BIP) film. The BIP film was facilely prepared via one-step electro-polymerization followed by in situ removal of the bacterial template. The film structure is novel with noncavity-like imprinted sites situated at the surface of the polypyrrole (PPy) matrix, which are more accessible for the target bacteria and should enhance the mass transfer and the binding kinetics. A limit of quantitation low to 103 CFU/mL was achieved within 1 h for the detection of E. coli O157:H7, which is comparable to the antibody-based assays. Moreover, the sensor displayed remarkable selectivity, especially regarding the specific identification of bacterial serotypes. When employed to analyze E. coli O157:H7 in real drinking water, apple juice, and milk samples, the sensor showed recoveries from 96.0% to 107.9% with relative standard derivations (RSDs) less than 4%. The BIP-based sensing strategy provides a universal approach for specific, selective, and rapid detection of pathogenic bacteria. As compared to conventional biosensors based on biomolecular recognition, this sensor shows clear advantages including easy-of-preparation, robustness, and low cost, which may hold great potential in fields of food/public safety monitoring.

Determination of Doxycycline, 4-epidoxycycline, and 6-epidoxycycline in Aquatic Animal Muscle Tissue by an Optimized Extraction Protocol and Ultra-performance Performance Liquid Chromatography with Ultraviolet Detection

A fast ultra-performance liquid chromatography method was developed for the separation and quantification of doxycycline, 4-epidoxycycline, and 6-epidoxycycline in the muscles of channel catfish, shrimp, eel and turtle. The analytes were separated by comprehensive optimization of the chromatographic conditions. The extraction method was performed using a modified QuEChERS methodology. 2 g of muscle sample were mixed with 5 mL Mcllvaine buffer (pH 4), and 4 g of sodium sulfate and 2 g of sodium chloride were added for liquid–liquid partitioning. The mixture was agitated for 30 s and extracted with 10 mL of acidified acetonitrile. The resulting extract was purified using 200 mg of a C18-silica adsorbent. The samples were analyzed using ultra-performance liquid chromatography with ultraviolet detection using a BEH C18 column (2.1 mm ×100 mm, 1.7 μm). The limits of detection were less than 25 μg/kg and the limits of quantitation were less than 50 μg/kg for all analytes. The recoveries of the analytes were from 62.3% to 89.0% with relative standard derivations below 10.0%. The method provided efficient extraction and purification that enabled rugged and low-cost determination of the analytes.