An ultrasensitive label-free immunosensor based on CdS sensitized Fe-TiO2 with high visible-light photoelectrochemical activity.

An ultrasensitive label-free immunosensor was developed for the detection of squamous cell carcinoma antigen (SCCA) based on CdS sensitized Fe-TiO2 nanocomposites with high visible-light photoelectrochemical (PEC) activity. In this protocol, ascorbic acid was used as an efficient electron donor for scavenging photogenerated holes. The Fe-doped TiO2 improved the absorption of TiO2 in the visible light region and promoted the photocurrent production distinctly. Especially, 0.1% Fe-TiO2 showed the highest photocurrent, which was 7.4 times that of pure TiO2. Carboxyl functionalized CdS nanoparticles (CdS NPs) were bonded onto Fe-TiO2 composite through interactions between carboxyl groups and TiO2, which further enhanced the PEC signal strength by approximately 2.9 fold compared with 0.1% Fe-TiO2. The specific binding between SCCA and antibody resulted in a decrease in photocurrent intensity and the intensity decreased linearly with the logarithm of SCCA concentration in the range of 0.001-75 ng mL(-1) with a detection limit of 0.22 pg mL(-1). The developed CdS enhanced Fe-TiO2 PEC immunosensor exhibited high sensitivity, good reproducibility, and low cost, which may have potential applications in clinical diagnosis of cancers, aptasensors, photocatalysis, and other related fields.