A "signal-on" photoelectrochemical aptasensor based on graphene quantum dots-sensitized TiO₂ nanotube arrays for sensitive detection of chloramphenicol

An ultrasensitive photoelectrochemical (PEC) aptasensor was designed for detection of chloramphenicol (CAP) based on graphene quantum dots-sensitized TiO₂ nanotube arrays (GQDs/TiO₂ NTs). The GQDs/TiO₂ NTs nanohybrids were prepared by a coupling technique of linker molecule binding and electrophoretic deposition. It exhibited significantly enhanced visible-light photoelectrochemical activity, which was firstly employed as the photoactive material for fabrication of PEC aptasensor. As the recognition unit, the aptamers of CAP were immobilized on GQDs/TiO₂ NTs photoelectrode via π-π stacking interaction between GQDs and the nucleobases of the aptamer. In this signal-on proposal, the aptasensor was used for the label-free analysis of CAP by monitoring the increase in photocurrent that resulted from the formation of aptamer-CAP bioaffinity complexes with ascorbic acid as an efficient electron donor for scavenging photogenerated holes. Under the optimized conditions, the aptasensor showed a wide linear range from 0.5 nM to 100 nM for CAP detection with a low detection limit of 57.9 pM (S/N = 3). With good selectivity and sensitivity, the PEC aptasensor was applied to the determination of CAP in spiked honey samples with satisfactory results, suggesting that the GQDs/TiO₂ NTs photoelectrode has a promising application in constructing PEC sensor platform.