Boosting the Sensitivity of a Photoelectrochemical Immunoassay by Using SiO₂@polydopamine Core–Shell Nanoparticles as a Highly Efficient Quencher

By use of SiO2@polydopamine (PDA) core–shell nanoparticles (NPs) as a quencher for a CdTe quantum dots (QDs) probe, a “signal-off” photoelectrochemical (PEC) immunosensor with boosted sensitivity was reported. In the proposed SiO2@PDA NPs, PDA that was prepared by self-polymerization of dopamine had many features, such as broad absorption in the ultraviolet–visible (UV–vis) region, high fluorescence quenching efficiency, and surface functional groups that can further conjugate with biomolecules. More importantly, the coupling of SiO2 NPs improved the dispersibility and loading of PDA and increased the charge transfer impedance. All these factors jointly led to enhanced PEC quenching efficiency of the CdTe probe, which was up to 10 times that of PDA alone. Taking the detection of CA125 as an example, the PEC immunosensor showed a detectable range of 1 mU mL–1 to 100 U mL–1 and an ultralow detection limit of 0.3 mU mL–1 (S/N = 3), the most sensitive sensor for CA125 reported so far. The constructed PEC immunosensor also had high selectivity and good accuracy for detecting tumor markers. This work shows the great potential of SiO2@PDA for boosting sensitivity in “signal-off” PEC clinical diagnosis.