Label-free Photoelectrochemical Aptasensor for the Determination of Carcinoembryonic Antigen Using a Cadmum Sulfide Quantum Dot Sensitized Titanium (IV) Oxide Nanotube Electrode

A label-free photoelectrochemical aptasensor for the sensitive and selective determination of carcinoembryonic antigen was constructed based on a CdS quantum dot sensitized TiO₂ nanotube electrode. TiO₂ nanotubes with highly ordered structure and more active sites than bulk TiO₂ were prepared with an electrochemical anodic oxidation process. The CdS quantum dots were immobilized on the TiO₂ nanotubes using poly(diallyldimethylammonium chloride) as a bridge. Due to the energy level match between TiO₂ and CdS, the CdS quantum dots/TiO₂ nanotubes electrode exhibits excellent photoelectrochemical performance. The large surface area of the electrode also allows for capturing large numbers of aptamers. The fine photoelectrochemical performance and the large surface area of the electrode greatly enhanced the detection sensitivity. Under the optimal conditions, the prepared photoelectrochemical aptasensor presents desirable analytical properties for the determination of carcinoembryonic antigen in the range of 0.05 to 10?ng?mL^?1 with a detection limit of 0.014?ng?mL^?1. The application of the designed protocol was investigated by analyzing carcinoembryonic antigen in human serum samples with recoveries from 80.0 to 115.0%. This simple and sensitive method provides an alternative tool to standard biochemical assays.