A fluorescent aptasensor for the detection of Aflatoxin B1 by graphene oxide mediated quenching and release of fluorescence

Aflatoxin B1 contamination in food and agro commodities has been major concern of global food safety and trade industry. There is an urgent need to develop sensitive and on-site detection methods for aflatoxins mainly, AFB1 monitoring. In the present study, a fluorophore (Alexa Fluor 488) based aptamer biosensor was devised in combination with graphene oxide (GO) for the detection of Aflatoxin B1 (AFB1). The optimized diagnostic procedure consisted of a fluorescent modified aptamer (Ax-AFLA5) as detection probe and GO mediated quenching of the same; to the quenched system AFB1 was added resulting in subsequent release of fluorescence. The principle of GO based adsorption of ssDNA and successive desorption in the presence of target mycotoxin was utilised in development of the bioassay. In presence of target mycotoxin, the GO adsorbed ssDNA attained a structural conformation resulting in desorption and subsequent release of fluorescence. Assay parameters such as concentration of fluorescent probe, GO and incubation time were evaluated and optimized. The optical signal thus generated could determine presence of AFB1 in the given sample. Selectivity of the method with other mycotoxins was evaluated. The linear range of AFB1 from 0.2-200 ppb was assessed. Visible green fluorescence release was observed at 20 ppb under UV transilluminator and the detection limit of the developed assay was interpreted as 20 ppb of AFB1. The suitability of the assay for AFB1 quantification in groundnut and natural samples was also evaluated. Thus, the developed assay can be a field deployable, reliable and rapid alternative tool for onsite screening method of aflatoxins and other mycotoxins at field level.