“Signal-On” Photoelectrochemical Biosensor Based on CdS Quantum Dot/ZnO and Ag Nanoparticles for Sensitive Determination of Interleukin-6

A photoelectrochemical (PEC) biosensor was developed through the resonance energy transfer (RET) process between CdS quantum dots/ZnO nanoparticles (CdS/ZnO) and silver nanoparticles (AgNPs), and the detection of interleukin-6 (IL-6) was realized based on the competitive reaction with aptamer. The complementary sequence of aptamer (cDNA) modified CdS/ZnO (cDNA-CdS/ZnO) was constructed by stepwise assembly on a fluorine-doped tin oxide (FTO) electrode. In the absence of IL-6, AgNP-labeled aptamer reduced out the photocurrent of quantum dots through the RET process at the FTO electrode. After the addition of IL-6, the binding site of the aptamer was affected by competitive occupation and spatial effects, which greatly hindered the hybridization with cDNA and resulted in a large increase in the PEC signal. Under optimized experimental parameters, a wide linear range from 5 to 10000 pM based on a photocurrent change versus logarithm of IL-6 concentration calibration plot and a detection of 0.43 pM were achieved. Additionally, the PEC biosensor had good stability, selectivity, and strong anti-interference ability. More importantly, the proposed PEC biosensor could successfully detect IL-6 in human serum samples, which was of great significance for clinical treatment.