Rapid and sensitive detection of chlordimeform in cucumber and tomato samples using an immunochromatographic assay.

Chlordimeform (CDM) is a broad-spectrum and highly effective insecticide and acaricide used to control pests in agriculture. We produced two monoclonal antibodies (mAbs) against CDM and developed an immunochromatographic assay to screen CDM in cucumbers and tomatoes. MAb 4A3 had high sensitivity with a 50% inhibitory concentration of 0.287 ng mL-1. The assay had a cut-off value of 25 µg kg-1 and a visual limit of detection (vLOD) of 1 µg kg-1 in cucumbers and a cut off value of 50 µg kg-1 and a vLOD of 2.5 µg kg-1 in tomatoes. The calculated limit of detection (cLOD) in cucumbers and tomatoes was 0.115 µg kg-1 and 0.215 µg kg-1, respectively. The recovery rates were 97.9% to 106.9% for cucumbers and 97.8% to 107.4% for tomatoes, consistent with the results obtained from indirect competitive ELISA. Our findings showed that the immunochromatographic assay is an efficient and accurate method for CDM detection in cucumbers and tomatoes.

Taking glucose as intermediate bridge-signal-molecule for on-site and convenient detection of ochratoxin A in rice with portable glucose meter.

On-site screening of biotoxins is of great importance for food safety. A new electrochemical-biosensing strategy was constructed for ochratoxin A (OTA) detection by direct using ready-made commercial portable-glucose-meter (PGM). Aptamer against OTA was adopted as the recognition probe and pre-immobilized onto the sensing interface. The complementary biotin-modified probe was further decorated by hybridization. Biotinylated invertase was further introduced onto the sensing system with streptavidin, which also acted as the signal amplification unit. The invertase, which was depended on the amount of OTA, produced the glucose from sucrose in the sensing solution. The glucose could be directly and conveniently measured with PGM. Quantitative analysis of OTA was achieved with a linear range from 0.5 ng/mL to 10 ng/mL and detection limit of 0.45 ng/mL. Of significance, it has been successfully applied for OTA analysis in rice with satisfied recoveries. This unique PGM-based electrochemical platform reveals prospective potential in food safety monitoring.

Ultrasensitive paper sensor for simultaneous detection of alpha-amanitin and beta-amanitin by the production of monoclonal antibodies.

Amanitin (AMA) is responsible for human fatalities after ingestion of poisonous mushrooms, thus, a rapid and accurate detection method is urgently needed. Here, gold nanoparticle-based immunosensor with monoclonal antibody against AMA was constructed for rapid detection of alpha- and beta-amanitin (α- and ß-AMA) in mushroom, serum and urine samples. Under optimized conditions, the visual limits of detection (vLOD) and calculated LOD for α-AMA and ß-AMA in mushroom were 10 ng/g, 20 ng/g, and 0.1 ng/g, 0.2 ng/g, respectively. Analysis of wild mushroom samples was also performed using a strip scan reader in the 10 min range. Furthermore, in mushrooms containing amatoxins results were confirmed and compared with those determined by liquid chromatography tandem mass spectrometry. Thus, this immunosensor provided a useful monitoring tool for rapid detection and screening of mushroom samples and in serum and urine from subjects who accidentally consumed AMA-containing mushrooms.

Immunological quantitative detection of dicofol in medicinal materials.

In this study, a highly specific and sensitive monoclonal antibody against dicofol (DIC) was prepared and used to create a colloidal gold immunochromatographic strip (ICS) for the quantitative analysis of DIC in liquorice and Angelica sinensis samples. We found that for both the liquorice and Angelica sinensis samples, the cut-off value for the ICS was 500 ng g-1, respectively, and using a colloidal gold test strip reader, the half-maximal inhibitory concentrations (IC50) were found to be 35 ng g-1 and 88 ng g-1, the limits of detection were 2 ng g-1 and 3 ng g-1, and the linear detection scopes (IC20-IC80) were from 6 to 201 ng g-1 and from 10 to 819 ng g-1, respectively. In the recovery test, we found that recoveries were within the range of 90.6% to 97.2% and the coefficients of variation were less than 8.6% in the intra-assay and inter-assay for the liquorice samples and the recoveries ranged from 90.8% to 97.3% and the coefficients of variation were less than 9.1% in the intra-assay and inter-assay for the Angelica sinensis samples. The established ICS assay could be used for the rapid quantitative screening of chemicals in Chinese traditional medicinal materials.

Experimental Measurement of Out-of-Time-Ordered Correlators at Finite Temperature.

Out-of-time-ordered correlators (OTOCs) are a key observable in a wide range of interconnected fields including many-body physics, quantum information science, and quantum gravity. Measuring OTOCs using near-term quantum simulators will extend our ability to explore fundamental aspects of these fields and the subtle connections between them. Here, we demonstrate an experimental method to measure OTOCs at finite temperatures and use the method to study their temperature dependence. These measurements are performed on a digital quantum computer running a simulation of the transverse field Ising model. Our flexible method, based on the creation of a thermofield double state, can be extended to other models and enables us to probe the OTOC's temperature-dependent decay rate. Measuring this decay rate opens up the possibility of testing the fundamental temperature-dependent bounds on quantum information scrambling.

Optimization of microemulsion cleaning sludge conditions using response surface method.

Microemulsion cleaning method has been proved to be an effective way to clean oily sludge with low interfacial tension and high solubilizing ability for non-miscible liquids. In this paper, the percentage range of the microemulsion in the formulation was obtained by studying phase behavior of the microemulsion. The response surface method was used to model and optimize the microemulsion to obtain the best formulation: n-BuOH content at 9.89%, NaCl content at 2.24% and AES/APG ratio at 3.75, and the oil removal rate reached 97.28%. Meanwhile, the cleaning conditions of oil sludge were also optimized by the response surface method and the optimal cleaning parameters were determined as liquid-solid ratio at 4.2, stirring rate at 157 r·min-1, and stirring time at 38 min. In addition, some experiments were carried out to confirm the simulation results, affording the oil removal rate of 98.79%. SEM and FTIR confirmed that the oil on the sludge can be removed by microemulsion.

Endogenic oxidative stress response contributes to glutathione over-accumulation in mutant Saccharomyces cerevisiae Y518.

Mechanisms of glutathione (GSH) over-accumulation in mutant Saccharomyces cerevisiae Y518 screened by ultraviolet and nitrosoguanidine-induced random mutagenesis were studied. Y518 accumulated higher levels of GSH and L-cysteine than its wild-type strain. RNA-Seq and pathway enrichment analysis indicated a difference in the expression of key genes involved in cysteine production, the GSH biosynthesis pathway, and antioxidation processes. GSH1, MET17, CYS4, GPX2, CTT1, TRX2, and SOD1 and the transcriptional activators SKN7 and YAP1 were up-regulated in the mutant. Moreover, Y518 showed a dysfunctional respiratory chain resulting from dramatically weakened activity of complex III and significant elevation of intracellular reactive oxygen species (ROS) levels. The supplementation of antimycin A in the culture of the parent strain showed equivalent changes of ROS and GSH level. This study indicates that defective complex III prompts abundant endogenic ROS generation, which triggers an oxidative stress response and upregulation of gene expression associated with GSH biosynthesis. This finding may be helpful for developing new strategies for GSH fermentation process optimization or metabolic engineering.

Building an aptamer/graphene oxide FRET biosensor for one-step detection of bisphenol A.

Bisphenol A (BPA) is an important industrial chemical for polycarbonate (PC) and epoxy resins in paper and plastic industries. In our work, a kind of new method for detection of BPA was designed based on graphene oxide and anti-BPA aptamer. The graphene oxide can specifically adsorb and quench the fluorescence of fluorescently modified ssDNA probes. Meanwhile, the BPA can combine with anti-BPA optamer and switch its configuration to prevent the aptamer from adsorbing on the surface of graphene oxide (GO). Under different concentrations of BPA, based on the target-induced conformational change of anti-BPA aptamer and the interactions between the fluorescently modified anti-BPA aptamer (FAM-ssDNA) and GO, the experimental results show that the intensity of the fluorescence signal was changed. A low limit of detection of 0.05 ng/mL was obtained in the range 0.1-10 ng/mL. In addition, the specificity was outstanding among analogues of BPA. The recovery rate in actual water samples spiked with BPA can be 96.0% to 104.5%. The developed method was successfully used to determine BPA in actual water samples.

Highly sensitive colorimetric sensor for Hg(2+) detection based on cationic polymer/DNA interaction.

The detection of ultralow concentrations of mercury is a currently significant challenge. Here, a novel strategy is proposed: the colorimetric detection of Hg(2+) based on the aggregation of gold nanoparticles (AuNPs) driven by a cationic polymer. In this three-component system, DNA combines electrostatically with phthalic diglycol diacrylate (PDDA) in a solution of AuNPs. In the presence of Hg(2+), thymine (T)-Hg(2+)-T induced hairpin turns are formed in the DNA strands, which then do not interact with PDDA, enabling the freed PDDA to subsequently facilitate aggregation of the AuNPs. Thus, according to the change in color from wine-red to blue-purple upon AuNPs aggregation, a colorimetric sensor is established to detect Hg(2+). Under optimal conditions, the color change is clearly seen with the naked eye. A linear range of 0.25-500nM was obtained by absorption spectroscopy with a detection limit of approximately 0.15nM. Additionally, the proposed method shows high selectivity toward Hg(2+) in the presence of other heavy metal ions. Real sample analysis was evaluated with the use of lake water and the results suggest good potential for practical application.

Enhancement of phenyllactic acid biosynthesis by recognition site replacement of D-lactate dehydrogenase from Lactobacillus pentosus.

OBJECTIVES: The Tyr52 residue of D-lactate dehydrogenase (D-LDH) from Lactobacillus pentosus was replaced with small hydrophobic residues and overexpressed in E. coli BL21 (DE3) to enhance 3-phenyllactic acid (PLA) synthesis by whole-cell catalyst. RESULTS: Escherichia coli pET-28a-d-ldh produced 12.2 g PLA l(-1) in 3 h, with a molar conversion rate of 61 %, while E. coli pET-28a-d-ldh (Y52V) produced 15.6 g PLA l(-1), with a molar conversion rate of 77 %. This study demonstrates the feasibility of using engineered E. coli for PLA production from phenylpyruvate (PPA) and showed that site-directed mutagenesis of d-ldh markedly improved PLA yield and substrate conversion rate. CONCLUSION: This biocatalytic system is a promising platform for PLA production from PPA.

Recent trends in SELEX technique and its application to food safety monitoring.

The method referred to as "systemic evolution of ligands by exponential enrichment" (SELEX) was introduced in 1990 and ever since has become an important tool for the identification and screening of aptamers. Such nucleic acids can recognize and bind to their corresponding targets (analytes) with high selectivity and affinity, and aptamers therefore have become attractive alternatives to traditional antibodies not the least because they are much more stable. Meanwhile, they have found numerous applications in different fields including food quality and safety monitoring. This review first gives an introduction into the selection process and to the evolution of SELEX, then covers applications of aptamers in the surveillance of food safety (with subsections on absorptiometric, electrochemical, fluorescent and other methods), and then gives conclusions and perspectives. The SELEX method excels by its features of in vitro, high throughput and ease of operation. This review contains 86 references.

A one-step homogeneous plasmonic circular dichroism detection of aqueous mercury ions using nucleic acid functionalized gold nanorods.

In this work, we report the application of gold nanorods ladder assemblies as chiroptical sensors for detecting mercury ions (Hg(2+)). By taking advantage of the Hg(2+)-mediated T-T base pair of DNA and the high sensitivity of CD measurements, the method offers a simple and sensitive detection of target Hg(2+) residues in water. Therefore, the developed method will be a promising tool for monitoring heavy metal ions, other small molecules and biomacromolecules.

Metabonomics approaches and the potential application in foodsafety evaluation.

It is essential that the novel biomarkers discovered by means of advanced detection tools based on metabonomics could be used for long-term monitoring in food safety. By summarizing the common biomarkers discovery flowsheet based on metabonomics, this review evaluates the possible application of metabonomics in new biomarker discovery, especially in relation to food safety issues. Metabonomics have the advantages of decreasing detection limits and constant monitoring. Although metabonomics is still in the developmental stage, we believe that, based on its properties, such as noninvasiveness, sensitivity, and persistence, together with rigorous experimental designs, new and novel technologies, as well as increasingly accurate chemometrics and a relational database, metabonomics can demonstrate extensive application in food safety in the postgenome period.

Chirality based sensor for bisphenol A detection.

A universal chirality detection platform based on immuno-recognition-driven nanoparticle assembly has been fabricated for the first time. A strong shifted chiral signal was produced by asymmetric plasmonic nanoparticle dimers. Using bisphenol A (BPA) as a model target substrate, the LOD was 0.02 ng mL(-1).

A simple, sensitive, rapid and specific detection method for Bisphenol A based on Fluorescence Polarization Immunoassay.

A rapid, sensitive, specific and simple method based on Fluorescence Polarization Immunoassay (FPIA) was developed for the quantitative detection of Bisphenol A in water. 4, 4-Bis (4-hydroxyphenyl) valeric acid (BHPVA) was selected as the hapten to produce the immunogen. Fluorescein-labeled Bisphenol A derivatives (tracers) with different structures were synthesized and purified by thin layer chromatography. Based on the polyclonal antibody and tracers, an optimized FPIA method was developed with a detection limit (10% inhibition) of 2 µg L(-1) and a linear working range of 20 to 800 µg L(-1). FPIA was suitable for screening a large number of samples. The recoveries of fortified Tai lake water samples ranged from 91.85 to 102.78%, and tap water samples ranged from 90.36 to 96.01%. The coefficients of variation were all less than 20%. This FPIA method, which did not require a complicated cleanup process, proved to be very useful for the screening of Bisphenol A in environmental water samples.

G-quadruplex DNAzyme-based microcystin-LR (toxin) determination by a novel immunosensor.

In this paper, we demonstrate the application of versatile G-quadruplex-hemin DNAzymes in an immunoassay for detecting Microcystin-LR (MC-LR). Taking advantage of the high peroxidase activity of G-quadruplex-hemin complexes and the enhancement effect of gold nanoparticles (AuNPs), the method showed simple, high sensitive and selectivity detection of target toxin residues in water samples. The coated antigen, MC-LR-ovalbumin (OVA) coated on a plate, competed for MC-LR antibody with added target analyte to form antibody-antigen immune complexes. Subsequently, the immune complex reacted with G-quadruplex-labeled secondary antibodies for colorimetric detection of MC-LR. This assay specifically determined MC-LR in the linear range of 0.1-10 ng/ml, with a limit of detection (LOD) of 0.05 ng/mL for MC-LR. The results indicated that the novel immunoassay was an alternative to traditional plate-based immunoassay for MC-LR residue screening due to this method met the standard of World Health Organization (WHO) requirements for MC-LR content in drinking water (1 ng/mL).

Simple, rapid and sensitive detection of antibiotics based on the side-by-side assembly of gold nanorod probes.

In this work, we report on the application of versatile gold nanorods (GNRs) in optical sensors for the detection of antibiotics. The target analyte, Gentamicin (GM) and ovalbumin (OVA)-antigen-modified GNRs together competed with antibody-modified GNRs, then influenced the formation of side-by-side aggregates of the GNRs by antibody-antigen interactions. Accordingly, the UV-vis absorption intensity of the side-by-side aggregates was changed in the presence of the target analyte. This assay allowed the selective determination of GM in the range of 0.1-20 ng/mL, and the limit of detection (LOD) of GM was 0.05 ng/mL. Furthermore, compared with the traditional plate-based immunoassay, the developed method was easy to perform without washing cycles and the results could be read as soon as the nanoprobe-analyte incubation was complete. Therefore, the developed method could be a promising tool for the detection of antibiotic residues.

The cell adhesion molecule DdCAD-1 regulates morphogenesis through differential spatiotemporal expression in Dictyostelium discoideum.

During development of Dictyostelium, multiple cell types are formed and undergo a coordinated series of morphogenetic movements guided by their adhesive properties and other cellular factors. DdCAD-1 is a unique homophilic cell adhesion molecule encoded by the cadA gene. It is synthesized in the cytoplasm and transported to the plasma membrane by contractile vacuoles. In chimeras developed on soil plates, DdCAD-1-expressing cells showed greater propensity to develop into spores than did cadA-null cells. When development was performed on non-nutrient agar, wild-type cells sorted from the cadA-null cells and moved to the anterior zone. They differentiated mostly into stalk cells and eventually died, whereas the cadA-null cells survived as spores. To assess the role of DdCAD-1 in this novel behavior of wild-type and mutant cells, cadA-null cells were rescued by the ectopic expression of DdCAD-1-GFP. Morphological studies have revealed major spatiotemporal changes in the subcellular distribution of DdCAD-1 during development. Whereas DdCAD-1 became internalized in most cells in the post-aggregation stages, it was prominent in the contact regions of anterior cells. Cell sorting was also restored in cadA(-) slugs by exogenous recombinant DdCAD-1. Remarkably, DdCAD-1 remained on the surface of anterior cells, whereas it was internalized in the posterior cells. Additionally, DdCAD-1-expressing cells migrated slower than cadA(-) cells and sorted to the anterior region of chimeric slugs. These results show that DdCAD-1 influences the sorting behavior of cells in slugs by its differential distribution on the prestalk and prespore cells.

Crown ether assembly of gold nanoparticles: melamine sensor.

Melamine toxicity causing the renal failure and death of animals and humans has recently attracted worldwide attention. Developing an easy, fast, and sensitive method for the routine melamine detection is of great importance. Herein, we report the colorimetric sensing of melamine, based on the 18-crown-6 ether functionalized gold nanoparticles (GNPs) through the formation of cavity complexes with amines. Based on high extinction coefficients and spectral sensitivity of the surface plasmon resonance band of the GNPs, the rapid and sensitive melamine detection was achieved both visually and spectroscopically. Under the optimal conditions, melamine could be selectively detected in a concentration range from 10 to 500 ppb with a limit of detection as 6 ppb (3σ), which is much lower than the strictest melamine safety requirement of 1 ppm. To demonstrate the selectivity and practicality of the method, melamine detection was realized in the real complex samples (dairy) with excellent analyte concentration recovery, indicating its applicability for real-time monitoring of toxins in common products. Crown ether assembly of GNP also opens a new route for the formation of three-dimensional pseudorotaxane-like assemblies of nanoparticles that can be applicable to a variety of amine-bearing ligands.

An aptamer-based chromatographic strip assay for sensitive toxin semi-quantitative detection.

An aptamer-based chromatographic strip assay method for rapid toxin detection was developed. The aptamer-based strip assay was based on the competition for the aptamer between ochratoxin A and DNA probes. The sensing results indicated that the sensitivity of the aptamer-based strip was better than that of conventional antibody-based strips. The visual limit of detection of the strip for qualitative detection was 1 ng/mL while the LOD for semi-quantitative detection could down to 0.18 ng/mL by using scanning reader. The recoveries of test samples were from 96% to 110%. All detections could be achieved in less than 10 min, indicating that the aptamer-based strip could be a potential useful tool for rapid on-site detections.