Graphene quantum dots-based nano-biointerface platform for food toxin detection

Due to the similar electrochemical properties to graphene oxide (GO), graphene quantum dots (GQDs) are considered as a highly potential candidate for designing an electrochemical biosensor. In this report, GQDs were synthesized having an average diameter of 7 nm and utilized for the fabrication of an electrochemical immunosensor for the detection of food toxin, aflatoxin B1 (AFB1). An electrophoretic deposition technique was utilized to deposit the chemically synthesized GQDs onto indium tin oxide (ITO)-coated glass substrate. Further, the monoclonal antibodies of AFB1 were covalently immobilized onto deposited electrode GQDs/ITO using EDC-NHS as a crosslinker. The structural and morphological studies of GQDs and conjugated anti-AFB1 with GQDs have been investigated using UV-visible spectroscopy, photoluminescence spectroscopy, Raman spectroscopy, transmission electron microscopy, scanning electron microscopy techniques, etc. The electrochemical impedance spectroscopy and cyclic voltammetry measurements were carried out for electrical characterization and biosensing studies. This simple monodisperse GQDs-based platform yields heterogeneous electron transfer (97.63 × 10−5 cm s−1), the time constant (0.005 s) resulting in improved biosensing performance. The electrochemical immunosensor shows high sensitivity 213.88 Ω (ng mL−1)−1 cm−2. The limit of detection for standard samples and contaminated maize samples was found to be 0.03 ng mL−1 and 0.05 ng g−1, respectively, which is lower than the maximum acceptable limit according to the European Union. This result indicates its potential application for aflatoxin B1 detection in food contents.