A highly sensitive photoelectrochemical immunosensor for cancer antigen (CA 125) based on a nanoplatform of carbon dots and cadmium sulphide

The prognosis for ovarian cancer is often poor due to late diagnosis. This is because the disease rarely presents with any specific symptoms in the early stage. There is therefore a need to develop a sensitive device for the routine screening of CA 125, the most widely used biomarker for detecting and monitoring ovarian malignancy. Herein, we report the development of a photoelectrochemical (PEC) immunosensor based on a screen-printed carbon electrode (SPCE) modified with a carbon nanodot/cadmium sulphide (CND/CdS) heterostructure for the sensitive detection of CA 125. Using a drop-casting technique and a self-assembly process, the immunosensor was constructed by the successive immobilization of CND, CdS, an <i>N</i>-hydroxysuccinimide/1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (NHS-EDC) complex, anti-CA 125, and the blocking agent bovine serum albumin (BSA) on the SPCE. CND and CdS nanoparticles provided adequate surface area for electrochemical processes and served as photoactive materials, working synergistically to amplify signals and enhance the sensitivity of the sensor. The NHS-EDC complex activated the carboxyl groups on the modified electrode and served as a linker for antibody attachment. Under optimized conditions, the developed PEC immunosensor exhibited good sensitivity, selectivity, repeatability and reproducibility for CA 125 over a linear range of 100-0.0001 μg mL^-1, with a detection limit of 2.7 pg mL^-1. It also showed excellent short- and long-term stability and successfully detected CA 125 in serum samples. The excellent performance of the biosensor makes it a potential diagnostic tool for the real-time detection of CA 125 and other physiologically important analytes.