Enhanced Photoelectrochemical Immunosensing Platform Based on CdSeTe@CdS:Mn Core–Shell Quantum Dots-Sensitized TiO₂ Amplified by CuS Nanocrystals Conjugated Signal Antibodies

A new, ultrasensitive photoelectrochemical immunosensing platform was established on the basis of CdSeTe@CdS:Mn core–shell quantum dots-sensitized TiO₂ coupled with signal amplification of CuS nanocrystals conjugated signal antibodies. In this proposal, carcinoembryonic antigen (CEA, Ag) was selected as an example of target analyte to show the analytical performances of the platform. Specifically, TiO₂-modified electrode was first assembled with CdSeTe alloyed quantum dots (AQDs) via electrostatic adsorption assisted by oppositely charged polyelectrolyte, and then further deposited with CdS:Mn shells on the surface of CdSeTe AQDs via successive ionic layer adsorption and reaction strategy, forming TiO₂/CdSeTe@CdS:Mn sensitization structure, which was used as photoelectrochemical matrix to immobilize capture CEA antibodies (Ab₁); signal CEA antibodies (Ab₂) were labeled with CuS nanocrystals (NCs) to form Ab₂–CuS conjugates, which were employed as signal amplification elements when specific immunoreaction occurred. The ultrahigh sensitivity of this immunoassay resulted from the following two aspects. Before detection of target Ag, the TiO₂/CdSeTe@CdS:Mn sensitization structure could adequately harvest the exciting light with different bands, evidently expedite the electron transfer, and effectively depress the charge recombination, resulting in noticeably increased photocurrent. When target Ag existed, the Ab₂–CuS conjugates could dramatically decrease the photocurrent due to competitive absorption of exciting light and consumption of electron donor for CuS NCs coupled with steric hindrance of Ab₂ molecules. The fabricated photoelectrochemical immunosensor showed a low limit of detection of 0.16 pg/mL and a wide linear range from 0.5 pg/mL to 100 ng/mL for CEA detection, and it also exhibited good specificity, reproducibility, and stability