Photoelectrochemical aptasensor for sulfadimethoxine using g-C3N4 quantum dots modified with reduced graphene oxide

A novel photoelectrochemical (PEC) aptasensor with graphitic-phase carbon nitride quantum dots (g-C 3 N 4 ; QDs) and reduced graphene oxide (rGO) was fabricated. The g-C 3 N 4 QDs possess enhanced emission quantum yield (with an emission peak at 450 nm), improved charge separation ability and effective optical absorption, while rGO has excellent electron transfer capability. Altogether, this results in improved PEC performance. The method is making use of an aptamer against sulfadimethoxine (SDM) that was immobilized on electrode through π stacking interaction. Changes of the photocurrent occur because SDM as a photogenerated hole acceptor can further accelerate the separation of photoexcited carriers. Under optimized conditions and at an applied potential of +0.2 V, the aptasensor has a linear response in the 0.5 nM to 80 nM SDM concentration range, with a 0.1 nM detection limit (at S/ N  = 3). The method was successfully applied to the analysis of SDM in tap, lake and waste water samples. Graphitic-phase carbon nitride (g-C 3 N 4 ) quantum dots (QDs) and reduced graphene oxide (rGO) were used to modify fluorine-doped SnO 2 (FTO) electrodes for use in a photoelectrochemical (PEC) aptasensor. SDM oxidized by the hole on valance band (VB) of g-C 3 N 4 QDs promote the separation of electron in the conductive band (CB), which made the changes of photocurrent signal.