A new colorimetric aptasensor equipped with a novel composite of graphitic carbon nitride (g-C3N4) nanosheets and copper oxide(I) (Cu2O) nanocrystals is presented for Salmonella typhimurium (S .typhimurium). The dual-purpose structure of this composite simultaneously contributes to superb peroxidase-like activity and interaction with a label-free aptamer. Although g-C3N4@Cu2O effectively creates a visible blue color following the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in presence of hydrogen peroxide (H2O2), this catalytic activity of the composite severely decreases after the interaction with aptamers. In the presence of S. typhimurium in sample, aptamers bound to their specific target. Subsequently, g-C3N4@Cu2O catalytic activity was enhanced in proportion to S. typhimurium concentration. Under optimized conditions, this aptasensor exhibited an excellent detection performance in a range from 1.5 × 101 to 1.5 × 105 CFU/ml, with a detection limit of 15 CFU/ml. Besides, portable detection of S. typhimurium by paper-based model of this method operated successfully in just 6 min. Analysis of spiked milk samples revealed high potential of this method as a sensitive, rapid, and label-free promising tool for S. typhimurium detection. A novel composite of g-C3N4 nanosheets and Cu2O nanocrystals was constructed through this study, which represented a collection of significant properties for designing an aptasensor. The simultaneous capability of this composite for peroxidase-like activity and interaction with aptamer led to design a fast accurate biosensor for detecting as low as 15 CFU/ml Salmonella typhimurium as one of the most important foodborne pathogens which is a persistent burden for societies.
Keywords: Colorimetric aptasensor; Foodborne pathogen; G-C3N4@Cu2O composite; Peroxidase-like activity; Salmonella typhimurium.