Nanostructured graphitic carbon nitride based ultrasensing electrochemical biosensor for food toxin detection

We report results of the studies related to the fabrication of thionine functionalized graphitic carbon nitride nanosheets based ultrasensing platform for food toxin (Aflatoxin B1, AfB₁) detection. The synthesis of graphitic carbon nitride nanosheets (g-C₃N₄) was carried out by polycondensation of melamine followed by chemical exfoliation. Further, thionine was used for the functionalization of g-C₃N₄ (Thn/g-C₃N₄) and deposited electrophoretically onto the indium tin oxide (ITO) coated glass electrode. The fabricated Thn/g-C₃N₄/ITO electrode was covalently immobilized by EDC-NHS chemistry with anti-aflatoxin B1 (anti-AfB₁) followed by blocking of non-specific sites using BSA molecules. For structural, morphological, functional and electrochemical properties analysis of synthesized nanomaterials and fabricated electrodes X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, atomic force microscopy and cyclic voltammetry techniques were used. The electrochemical response studies of the fabricated biosensing platform (BSA/anti-AfB₁/Thn/g-C₃N₄/ITO) were carried out towards detection of AfB₁ antigen using cyclic voltammetry technique. The obtained electrochemical results indicate that the fabricated biosensing electrode having ability to detect AfB₁ with lower limit of detection of 0.328 fg mL^-1, linear detection range in between 1 fg mL^-1 to 1 ng mL^-1, sensitivity of 4.85 μA log [ng^-1 mL] cm^-2 with stability upto 7 weeks.