In this research, we developed a multianalyte fluorescence sensing system through a carbon dots (CDs)-based fluorescent probe that can specifically recognize Fe(III) by fluorescence quenching. The CDs prepared using black tea by a hydrothermal method show outstanding properties like low cytotoxicity, high photostability, excellent biocompatibility, and high sensitivity. It was found that the fluorescence of CDs can be quenched by micromolar concentrations of Fe(III) in both aqueous solutions as well as living cells. It is well known that glucose can be oxidized by glucose oxidase (GOx) to release H2O2, which, in turn, can oxidize Fe(II) to Fe(III). Based on this consideration, a multianalyte sensing system was established. Therefore the quantitative analysis of Fe(III), H2O2, and glucose with detection limits of 0.25 μM, 0.82 μM, and 1.71 μM, respectively, was achieved by the simple and cost-effective multianalyte CDs sensing system constructed. The sensing system showed high photostability and negligible cytotoxicity toward HeLa cells, which enables it to be applied in the visualization of Fe(III) or H2O2 in living cells. The system was further applied in the detection of Fe(III) or glucose in human serum, and satisfactory results were obtained.

•Enantioselective immunogen and S-amlodipine specific antibody were prepared.•A magnetism based immunosensor was assembled.•S, R-amlodipine could be purely separated and collected from racemic amlodipine.•Captured S-amlodipine could be accurately quantitated with a LOD of 0.04 ng mL−1.•The magnetism based immunosensor is simple, reliable and multi-functional.Amlodipine is one of the most important anti-hypertension agents and S-amlodipine is 1000 folds more efficient than R-amlodipine. However, chiral separation of amlodipine remains a challenge. Here we present an effective strategy for chiral resolution of amlodipine using anti-S-amlodipine antibody for ultra-specific capture and magnetic beads for convenient collecting. The collected enantiomers are ultra-pure based on the chiral HPLC identification. Simultaneously, the captured S-amlodipine could be quantitatively detected with a linear range from 0.1 to 1000 ng mL−1 (R2 = 0.9937), along with a limit of detection of 0.04 ng mL−1. The advantages of the developed magnetic electrochemical biosensor for amlodipine include specific chiral separation, sensitive quantitation, easy-to-operate procedures and time-saving protocols. This method is demonstrated as a novel tool for highly confident separation and quantification of amlodipine enantiomers, in this study. The magnetic biosensor may open up new avenues for intensive study of amlodipine enantiomers and thus be potential in clinical pharmacy and pharmacokinetics studies.Download high-res image (86KB)Download full-size image

In this study, a specific antibody against sirolimus was produced by its well synthesized immunogen and a competitive chemiluminescence immunoassay (CLIA) was established. The sirolimus molecule was modified with succinic anhydride (hapten 1) and carboxymethoxylamine (hapten 2). Hapten 1 was conjugated with bovine serum albumin to serve as the immunogen whilst hapten 2 was conjugated with ovalbumin for the coating antigen. A polyclonal antibody was prepared by immunizing rabbits with the purified immunogen. A CLIA method was established using the antibody for the analysis of sirolimus in phosphate-buffered saline and plasma. The limits of detection of the method in the two samples could reach 0.20 and 0.25 ng mL−1, respectively. Furthermore, this immunoassay was successfully applied to the pharmacokinetic study of sirolimus and the calculation of its pharmacokinetic parameters. The results suggest that this immunoassay has significant potential to be developed as a kit which can provide a sensitive, specific and inexpensive approach to therapeutic drug monitoring of sirolimus.

•A 2p-HF-LPME based chiral SFC for 1,4-DHP was developed.•Several 1,4-DHP enantiomers could be well separated.•The method is rapid, practical, effective and environmentally friendly.Chiral separation of seven commonly used 1,4-dihydropyridines (1,4-DHP) was achieved by supercritical fluid chromatography (SFC) on a immobilised polysaccharide chiral selectors coated with cellulose-tris(3,5-dichlorophenylcarbamate) (Chiralpak IC). In this method, isopropanol was used as a modifier and a maximum resolution of 13.38 was resulted. Nimodipine content of actual samples was determined through two-phase hollow fibre-based liquid-phase microextraction (2p-HF-LPME). Under optimal conditions, the limits of detection of the two nimodipine enantiomers were 0.3 and 0.5 μg cm−3. Recoveries of 80.0–99.8% were achieved. The developed SFC technique coupled with 2p-HF-LPME is a rapid, effective and environment-friendly method for separating and quantifying 1,4-DHP enantiomers.

As one of the rarely allowable azo dyes, ponceau 4R can be added in some foods in some countries. However, it is necessary to develop a credible and rapid analytical method for its monitoring, because of its potentially harmful risk. The hapten of ponceau 4R was first designed and synthesized by introducing a primary amine group into the structure of ponceau 4R. Based on the well-prepared hapten, the immunogen of ponceau 4R was prepared using glutaraldehyde to link ponceau 4R to the carrier protein. The triggered polyclonal antibody was obtained and tested by ELISA to optimize the proper dilution. An icELISA was developed for ponceau 4R, and the IC50 of the method is 36.82 ng/mL. The limit of detection is 0.80 ng/mL, and the linear range is 1–10000 ng/mL. Five selected structural analogues have no cross-reactivity with the anti-ponceau 4R polyclonal antibody (<0.3). In three food samples (grape juice, carbonated beverage, and RIO cocktail), the assay exhibits good stability and reproducibility with a recovery range of 93.87–103.77%, and the intra- and interassay coefficients of variation were <11.73%. The results indicate that the proposed icELISA is sensitive, accurate, specific, and simple, which provides an alternative for the detection of ponceau 4R in foods.

•(E)-4,4'-(diazene-1,2-diyl)dibenzoic acid was selected as the hapten of benzoic acid.•The immunogen of benzoic acid was prepared by conjugating the hapten with protein.•A useful antibody against a small antigen – benzoic acid was obtained.•A homogeneous, simple and rapid FPIA was developed for sodium benzoate.A rapid and sensitive fluorescence polarization immunoassay (FPIA), based on a polyclonal antibody, has been developed for the detection of sodium benzoate in spiked samples. The immunogen and fluorescein-labeled analyte conjugate were successfully synthesized, and the tracer was purified by TLC. Under the optimal assay conditions, the FPIA shows a detection range of 0.3–20.0 μg mL−1 for sodium benzoate with a detection limit of 0.26 μg mL−1 in the borate buffer. In addition, the IC50 value was 2.48 μg mL−1, and the cross-reactivity of the antibodies with ten structurally and functionally related analogs were detected respectively. Four kinds of food samples (energy drink, candy, ice sucker, RIOTM cocktail) were selected to evaluate the application of FPIA in real systems. The recoveries were 96.68–106.55% in energy drink; 95.78–100.80% in candy, 86.97–102.70% in ice sucker, and 103.58–109.87% in benzoate contained sample RIOTM cocktail, and coefficients of variation of this method were all lower than 11.25%. Comparing with the detection results of HPLC, the developed FPIA has comparative performance in the real sample determination. The results suggest that the FPIA developed in this study is a rapid, convenient and simple method, which is suitable to be used as a screening tool for homogeneous detection of sodium benzoate in food products.

Amaranth (E 123) is a member of azo dyes, and it is allowed to use in various foods. The acceptable maximum addition of amaranth is strictly fixed because of its potential risk to physical health. The objective of this study was to prepare a specific anti-amaranth monoclonal antibody and develop an indirect competitive ELISA for amaranth quantification analysis. The immunogen and the coating antigen were designed by introducing a carboxyl group into amaranth for the conjugation with carrier proteins. Based on the immunogen, the monoclonal antibody exhibits satisfactory performances and the proposed ELISA shows an IC50 of 20.33 ng mL−1. The limit of detection is as low as 3.35 ng mL−1, and the linear standard curve of the method ranges from 3.0 to 243.0 ng mL−1. Additionally, the antibody reflects minimal cross-reactivity (<1 %) with six related food dyes (erythrosine, ponceau 4R, allura red, tartrazine, sunset yellow FCF, and brilliant blue). The recoveries of amaranth spiked beverage samples are in the range of 85.8–100.7 % with low coefficient of variation values (<11.5 %). The data shows that the developed ELISA provides a simple, sensitive, specific, and accurate alternative for amaranth determination and monitoring. Furthermore, it is the first time that icELISA of amaranth is developed based on monoclonal antibodies.

Sunset Yellow FCF is widely used as food additives to make foods more attractive. Due to its abuse and potential risk to human health, Sunset Yellow FCF is precisely limited to use in food. To monitor the illegal use of Sunset Yellow FCF, a polyclonal antibody-based indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) with satisfactory sensitivity and specificity was developed. A carboxyl group was introduced to Sunset Yellow FCF, then the modified hapten was coupled with carrier proteins to synthesize the immunogen and coating antigen. The IC50 value of 0.52 ng mL−1 and detection limit of 25 pg mL−1 (in buffer) were achieved by this method. The cross-reactivity values of the antibodies with six structurally related colorants were less than 1.5%, indicating the high selectivity. Three kinds of food samples (beverage, dried beancurd, braised pork) and serum were chosen to evaluate the application of the immunoassay in real systems. The limits of detection (LOD) in the above three food samples were 0.12, 0.04 and 1.11, respectively (mean+3SD). The recovery (94%–106%), intra-assay (<5%) and inter-assay (<12%) coefficients of variation in foods and serum samples were also acceptable. The results suggest that this ELISA method is a specific, sensitive and simple method for the determination of Sunset Yellow FCF additives.Highlights► A Sunset Yellow FCF hapten was synthesized. ► The immunogen and coating antigen was prepared. ► The polyclonal antibodies were produced. ► A specific, sensitive, and simple ic-ELISA method was developed for the detection of Sunset Yellow FCF.