Photoelectrochemical aptasensor based on nanocomposite of CdSe@SnS for ultrasensitive and selective detection of sulfamethazine.

A photoelectrochemical (PEC) aptasensor based on CdSe@SnS nanocomposite has been developed to detect sulfamethazine (SMZ). The introduction of CdSe into SnS displayed an amplified PEC signal, which was higher than that of pure CdSe and SnS, attributable to its enhanced light harvesting capacity and promoted PEC energy conversion efficiency. Due to the formation of specific non-covalent bonds, the SMZ-binding aptamer (SBA) has significant specificity and sensitivity. When SMZ was incubated on a CdSe@SnS modified electrode fixed with aminated SBA, the formation of the SMZ/SBA complex increased the space resistance of electron transfer and hindered the electronic migration between the electrodes, resulting in a decrease in photocurrent. The greater the adsorbed amount on the SBA, the lower the photocurrent produced.  Under optimized conditions the photocurrent response of MCH/SBA/CdSe@SnS/FTO was inversely proportional to the SMZ concentration in the range 0.1 to 100 pM, with a detection limit (3 S/N) of 0.025 pM (at 0 V vs. Hg/HgCl). The recoveries ranged from 95.8 to 104% with relative standard deviations (RSDs) < 6.3% (n = 3) in actual water sample. This PEC aptasensor which shows considerable potential in SMZ detection applications has high selectivity, reproducibility, and good stability.