Ratiometric fluorescence immunoassay based on silver nanoclusters and calcein-Ce3+ for detecting ochratoxin A.

Ochratoxin A (OTA), a dangerous mycotoxin, is found in many crops. It is essential to create sensitive OTA detection techniques to ensure food safety. Based on the principle of p-nitrophenol (PNP) quenched the fluorescence of bovine serum albumin silver nanocluster (BSA-AgNCs) through an internal filtering effect, and phosphate activated fluorescence of calcein-Ce3+ system, a ratiometric fluorescence immunoassay for OTA detection was developed. In this strategy, the value of F518/F640 was used as a signal for response of OTA concentration. The detection range of this strategy was 0.625-25 ng/mL, the limit of detection (LOD) was 0.04 ng/mL. This new immunoassay offered a brand-new platform for detecting OTA.

Fluorescence and colorimetric dual-mode immunoassay based on G-quadruplex/N-methylmesoporphyrin IX and p-nitrophenol for detection of zearalenone.

In this work, a fluorescence and colorimetric dual-mode immunoassay for detecting zearalenone (ZEN) was established. This platform relied on the dephosphorylation of p-nitrophenyl phosphate (PNPP) by alkaline phosphatase (ALP) to produce yellow p-nitrophenol (PNP). And the internal filtration effect between G-quadruplex/N-methylmesoporphyrin IX (G4/NMM) and PNP led to fluorescence quenching of G4/NMM. Therefore, the color change of PNP and the fluorescence change of G4/NMM can be used as double signals to report the results of ALP mediated immunoassay. In this dual-mode immunoassay, the detection limit of fluorescence mode was 0.0072 ng/mL with a linear range 7.5-17.5 ng/mL. And the detection limit of colorimetric mode was 0.036 ng/mL with a linear range 7.5-20 ng/mL. In addition, the dual-mode immunoassay showed good selectivity for ZEN and satisfactory recovery in corn samples (fluorescence mode: 94.40-106.80%, colorimetric mode: 96.51-108.27%).

Fluorescence and absorbance dual-mode immunoassay for detecting Ochratoxin A.

In this work, a simple dual-mode immunoassay for detecting Ochratoxin A (OTA) was developed by mixing G-quadruplex/N-methylmesoporphyrin IX (G4/NMM) and 3,3',5,5'-tetramethylbenzidine (TMB). The fluorescence of G4/NMM can be quenched by oxidized TMB (oxTMB) because the absorbance of oxTMB overlapped with the fluorescence emission of G4/NMM. In the absence of OTA, large amounts of oxTMB were formed with blue color and the fluorescence of G4/NMM was quenched. In the presence of OTA, the concentration of oxTMB was decreased, therefore the fluorescence of G4/NMM increased. The linear range of fluorescence immunoassay was 0.195-25 ng/mL, and the linear range of the absorbance immunoassay was 0.049-1.563 ng/mL. Thus, the linear range of this dual-mode immunoassay can be expanded to 0.049-25 ng/mL. Meanwhile, the new method showed good selectivity for OTA. Besides, the satisfactory recovery rates implied the new method had a potential value for practical sample detection.

Fluorescence determination of glyphosate based on a DNA-templated copper nanoparticle biosensor.

A rapid and convenient fluorescence glyphosate (GLYP) biosensor was developed based on DNA-templated copper nanoparticles (DNA-CuNPs). In the absence of GLYP, the DNA-CuNPs were formed through the reduction of Cu2+ by vitamin C (Vc). The DNA-CuNPs emitted intense fluorescence at 615 nm when being excited at 340 nm. In the presence of GLYP, GLYP can strongly chelate with Cu2+ by the phosphate and carboxyl groups to decrease the amount of free Cu2+. Due to the lack of free Cu2+, DNA-CuNPs cannot be formed, which caused the fluorescence to decrease. The whole detection process of this proposed GLYP biosensor can be completed within 14 min. Titration experiments showed that this biosensor had a linear relationship for GLYP in the range 1 to 18 µM with a limit of detection (LOD) of 0.47 µM. This biosensor showed obvious selectivity among other pesticides, even between GLYP and organophosphorus pesticides. This biosensor performed well for GLYP detection in real samples with recoveries of 88.0-104.0%.

Highly Sensitive Alkaline Phosphatase Biosensor Based on Internal Filtration Effect between G-Quadruplex/N-methylmesoporphyrin IX and p-Nitrophenol.

In this work, an alkaline phosphatase (ALP) biosensor was established based on G-quadruplex/N-methylmesoporphyrin IX (G4/NMM) and p-nitrophenol (PNP). Because the absorption of PNP was close to the excitation wavelength of G4/NMM, PNP could reduce the fluorescence of G4/NMM. Meanwhile, PNP was the hydrolysis product of p-nitrophenylphosphate (PNPP) by ALP. Therefore, ALP could be detected. This ALP biosensor had a linear analytical range from 2.5 to 25 U/L a the detection limit of 0.81 U/L. Moreover, it showed a satisfactory selectivity and recovery rates.