Signal-on electrochemical aptasensor for sensitive detection of sulfamethazine based on carbon quantum dots/tungsten disulfide nanocomposites

In this paper, a novel electroactive material named as carbon quantum dots-tungsten disulfide nanocomposite (CQDs-WS2) was prepared via a facile self-assembly method. Based on CQDs-WS2 modified glassy carbon electrode (CQDs-WS2/GCE), a label-free electrochemical aptasensing strategy was proposed to sensitively determine sulfamethazine (SMZ). Cationic polyethyleneimine (PEI) were employed to form complexes with negatively charged SMZ-binding aptamers immobilized on CQDs-WS2/GCE by amidation reaction, which decreased the adsorption capacity of [Ru(NH3)6]3+ to aptamers. When SMZ existed, the change of aptamer conformation due to the formation of SMZ/aptamer complex would lead to decrease in adsorption amount of PEI. More adsorbed [Ru(NH3)6]3+ on aptamer can produce enhanced reduction current. On the basis of CQDs-WS2 as electroactive materials, aptamer as a recognition receptor, PEI as electrostatic adsorbent of aptamer, and [Ru(NH3)6]3+ as an electroactive indicator, a signal-on electrochemical aptasensor was constructed for detection of SMZ with high sensitivity. The SMZ aptasensor displayed wide linear response in the 10 pM to 1.0 µM concentration range and a low detection limit of 4.0 pM. The method can be applied to quantitation analysis of antibiotic residue in food and environmental samples.