Silver doping-induced electrochemiluminescence enhancement of CdTe quantum dots combined with hairpin-fueled entropy-driven reactions strategy for ultrasensitive bioanalysis.

Herein, silver-doped cadmium telluride quantum dots (Ag-CdTe QDs) as electrochemiluminescence (ECL) emitter with intense ECL signal and hairpin-fueled entropy-driven reactions (H-EDR) as signal amplifier with high conversion efficiency and low signal leakage were exploited to construct an ECL biosensor for ultrasensitive determination of microRNA 222 (miRNA-222) related to liver cancer. Interestingly, the ECL intensity of Ag-CdTe QDs has been improved by 2.5 times compared to that of undoped CdTe QDs for improving the detection sensitivity, which attributed to the crystal shape transformation of Ag-CdTe QDs through silver doping for the reduction of band gap to change the electron-hole recombination path. Moreover, H-EDR could reduce the background signal by introducing a hairpin DNA module rather than a linear DNA single strand as a fuel strand to conquer the undesired signal leakage deriving from the dynamic breathing of the DNA components, which achieved the target conversion from trace miRNA-222 to abundant output DNA for further enhancing the detection sensitivity. Thus, the developed ECL biosensor realizes the sensitive detection of miRNA-222 with a detection limit of 44 aM (aM), which was further applied in miRNA-222 analysis of cancer cell (MHCC-97L, a human hepatocellular carcinoma cell line and HeLa, a cervical cancer cell line) lysate. This work proposed a sensitive strategy by improving the ECL signal of the developed CdTe QDs and reducing the background signal during the target amplification process, which was expected to detect trace biomarkers for early clinical testing and disease monitoring.