Fluorometric aptasensor for determination of escherichia coli O157:H7 by FRET effect between aminated carbon quantum dots and graphene oxide

A fluorometric aptasensor based on Escherichia coli O157:H7 (E. coli O157:H7) aptamer labeled aminated carbon quantum dots (NH₂-CQDs) and graphene oxide (GO) for the determination of E. coli O157:H7 was developed. In this research, carboxyl group (-COOH) terminated E. coli O157:H7 aptamer was steadily labeled to NH₂-CQDs by amidation reaction, and played the role of energy donor and was responsible for chemical recognition. Correspondingly, GO served as an energy acceptor. The introduction of NH₂-CQDs not only made the aptamer bond stably through covalent bond, but also significantly enhanced the fluorescence intensity compared with general CQDs. The NH₂-CQDs-aptamer is adsorbed on the surface of GO through π-π stacking and hydrophobic interaction. The fluorescence of NH₂-CQDs-aptamer was quenched via fluorescence resonance energy transfer (FRET) between NH₂-CQDs and GO. After adding E. coli O157:H7, the specific binding affinity between NH₂-CQDs-aptamer and E. coli O157:H7 lead to desorption of NH₂-CQDs-aptamer from GO, and recovery of the fluorescence intensity of NH₂-CQDs-aptamer. Under the optimal conditions, the increased fluorescence intensity showed a good linear relationship to concentrations of E. coli O157:H7 in the range 10² - 10⁷ cells/mL, with a detection limit of 89 cells/mL. Furthermore, the developed method was successfully applied to the determination of E. coli O157:H7 in commercial milk samples. (author)