Environment-Friendly MnO2 Quantum Dots with Highly Efficient Electrochemiluminescence for Ultrasensitive Assay of Liver Cancer Markers

In this work, environment-friendly MnO2 quantum dots (MnO2 QDs) with high efficiency were first proposed as electrochemiluminescence (ECL) emitters to construct a biosensor for ultrasensitive detection of microRNA-222 (miRNA-222) related to liver cancer markers. Compared with reported QDs containing heavy metal elements, MnO2 QDs not only exhibited remarkable ECL efficiency but also displayed the advantage of good biocompatibility, showing promising application prospects in the biosensor field. Impressively, silver nanoparticles (Ag NPs) as coreaction accelerators could promote the conversion of the coreactant S2O82– into abundant SO4•– to produce more MnO2 QDs* to significantly enhance the ECL efficiency of MnO2 QDs. Furthermore, an efficient DNAzyme-Induced Self-Feedback DNA Amplification (DISFA) strategy was developed by employing DNAzyme to specifically cleave double-loop hairpins and release target analogues, achieving the conversion of trace miRNA-222 into abundant output DNA and improving the amplification efficiency and detection sensitivity. The ECL biosensor composed of a MnO2 QDs/S2O82–/Ag NP ternary system and DISFA strategy displayed an excellent linear response of miRNA-222 from 100 aM to 100 pM with a low detection limit of 12.90 aM (S/N = 3) and was successfully implemented for the analysis of miRNA-222 in cancer cell (MHCC-97L and HeLa) lysates. This study proposed transition metal oxide QDs (TMO QDs) with good biocompatibility as efficient and stable ECL emitters for the sensitive detection of biomarkers, demonstrating immense potential for disease diagnosis.