A Sensitive Photoelectrochemical Aptasensor for miRNA-21 Based on the Sensitization Effect of CdSe Quantum Dots

A novel photoelectrochemical aptasensor for the sensitive detection of miRNA-21 was designed based on the sensitization effect of CdSe quantum dots as a signal amplification strategy. The TiO2NTs/RGO/AuNPs electrode was prepared by the electrodeposition of graphene oxide and Au nanoparticles on TiO2 nanotubes with electrochemical reduction. The electrode was prepared as the matrix of the electrochemical aptasensor. The hairpin DNA strands decorated with CdSe quantum dots were immobilized on the surface of the electrode by Au−S bonds. Because of the card-type structure of the hairpin DNA (HP-DNA), the CdSe quantum dots were close to the base electrode, which would lead to the sensitization effect and cause the increase of the photocurrent intensity. When a certain concentration of the miRNA-21 was added, miRNA-21 hybridized with the complementary part of the HP-DNA. At the same time, the hairpin structure of HP-DNA was broken into a straight chain structure, so the CdSe quantum dots on the end of the DNA would move away from the electrode surface, the sensitization effect would be weakened, and the photocurrent intensity would be decreased. The designed photoelectrochemical aptasensor exhibited a low detection limit of 5.6 fM and a wide linear range from 20 fM to 0.2 nM, and it also showed good specificity, reproducibility and stability. The signal amplification strategy was also expected to provide a significant photoelectrochemical biosensor platform for the sensitive detection of biomolecules.