Nanobodies-based colloidal gold immunochromatographic assay for specific detection of parathion.

Parathion is one of organophosphorus pesticide, which has been prohibited in agricultural products due to its high toxicity to human beings. However, there are still abuse cases for profit in agricultural production. Hence, we established nanobodies-based colloidal gold immunochromatographic assay (GICA) in which nanobodies (Nbs) as an excellent recognition element, greatly improving the stability and sensitivity of ICA. Under the optimal conditions, the developed Nbs-based GICA showed a cut-off value of 50 ng/mL for visual judgment and a half-inhibitory concentration (IC50) of 2.39 ng/mL for quantitative detection. The limit of detection (LOD) was as low as 0.15 ng/mL which was significantly 50-fold higher sensitivity than the commercial mAb-ICA. Additionally, this method exhibited good recoveries for the detection of cabbage, cucumber, and orange samples and excellent correlation with the UPLC-MS/MS method. The results showed that this method developed in this work based on nanobody can be used in practical detection of parathion in foods and nanobody is novel prospective antibody resource for immunoassays of chemical contaminants.

A signal on-off fluorescence sensor based on the self-assembly DNA tetrahedron for simultaneous detection of ochratoxin A and aflatoxin B1.

Highly rigid and versatile functionality of DNA tetrahedron nanostructures is often used in biosensing systems as a potential detection technique. In this work, a signal on-off fluorescence sensor based on the self-assembly DNA tetrahedron was developed for the rapid simultaneous detection of ochratoxin A (OTA) and aflatoxin B1 (AFB1). The fluorophore labeled DNA tetrahedron as probe was successfully synthesized via a simple denaturing annealing, the distance between fluorophore and quencher was regulated according to the change of hairpin structure on the tetrahedron. The fluorescence intensity of Cy3 decreased significantly in the presence of OTA, while the fluorescence intensity of Cy5 kept almost unchanged. And the fluorescence intensity of Cy5 decreased significantly in the presence of AFB1, while the fluorescence intensity of Cy3 kept almost unchanged. In the present of OTA and AFB1, the fluorescence intensity of Cy3 and Cy5 showed decreased significantly simultaneously, indicating the fluorescence sensor can be applied to simultaneous detect OTA and AFB1. Hence, the quantitative analysis of OTA and AFB1 was performed indirectly by the fluorescence intensity changes. The limits of detection (LOD) are as low as 0.005 ng/mL for OTA and 0.01 ng/mL for AFB1. In addition, the novel DNA tetrahedron-based fluorescence sensor possessed a universal applicability, which could be well applied in corn and wine.