Enhanced photoelectrochemical aptasensing platform amplified through the sensitization effect of CdTe@CdS core–shell quantum dots coupled with exonuclease-I assisted target recycling

Abstract

A novel, enhanced photoelectrochemical aptasensing platform was developed through integrating the sensitization effect of CdTe@CdS core–shell quantum dots (QDs) coupled with exonuclease-I (Exo-I) assisted target recycling for significant signal amplification. Carcinoembryonic antigen (CEA) was selected as the target analyte to exhibit the analytical performance of this platform. Specifically, nitrogen-doped mesoporous TiO₂ (mTiO₂:N) was firstly synthesized through an evaporation-induced self-assembly (EISA) method. Then, an mTiO₂:N/Au hybrid structure was prepared through depositing Au nanoparticles on the surface of the mTiO₂:N film and this acted as the photoelectrochemical matrix to immobilize the complementary DNA (cDNA) of the CEA aptamer probe (pDNA). CdTe@CdS core–shell QDs as sensitization agents were covalently bound at the front-end of pDNA. After pDNA was hybridized with cDNA, the labels of the CdTe@CdS core–shell QDs were very close to the mTiO₂:N/Au electrode surface, resulting in an evidently enhanced photocurrent intensity due to the generation of the sensitization effect. When the aptasensor was incubated with CEA and Exo-I simultaneously, CdTe@CdS QD labeled pDNA (denoted QD–pDNA) became specifically bound with CEA and meanwhile was separated from the electrode surface, leading to an obviously weakened sensitization effect and a decreased photocurrent intensity. Moreover, as Exo-I could digest the single strand form of pDNA, the previously bound CEA was released and continuously interacted with the rest of the pDNA on the electrode surface, causing further decreased photocurrent intensity. The well-designed photoelectrochemical aptasensor exhibited a low detection limit of 0.12 pg mL⁻¹ and a wide linear range from 0.5 pg mL⁻¹ to 10 ng mL⁻¹ for CEA detection, and it also showed good selectivity, reproducibility and stability. The proposed signal amplification strategy provides a promising universal photoelectrochemical platform for sensitively detecting various biomolecules at low levels.