Nano-matrixes propped self-enhanced electrochemiluminescence biosensor for microRNA detection

MicroRNAs (miRNA) are the potential biomarker for breast cancer, a biosensor for detecting miRNA-21 was successfully prepared by covalently linking carbohydrazide (CON₄H₆) and tris (4,4 '- dicarboxylic acid-2,2' - bipyridyl) ruthenium dichloride (Ru (dcbpy)₃²⁺) as a self-enhanced emitter (Ru-CON₄H₆). The biosensor was prepared by coating the electrode with mesoporous silica encapsulated Ru-CON₄H₆ as luminophores (RMSNs) to covalently link a couple of DNA strands (Q1-H2). The RMSNs coated electrode exhibited strong ECL emission due to the intramolecular electron transfer between the electrochemically oxidized Ru (dcbpy)₃²⁺ and co-reactant CON₄H₆. In the presence of target miRNA-21 and an assistant hairpin H1, H2 could be released from the surface through a strand displacement reaction (SDR), and the reserved Q1 could form G-quadruplex upon the addition of K⁺. The formed G-quadruplex then interacted with Q2-Fc in the presence of Mg²⁺ to form a DNA complex on the biosensor surface, which quenched the nano-matrixes propped self-enhanced ECL emission through the electron exchange between Fc and electrode or oxidized ECL intermediates. Under optimal conditions, the ECL decrease showed a correlation with target concentration, leading to a biosensing method for sensitive detection of miRNA-21. The proposed ECL method demonstrated a detectable concentration range from 0.1 fM to 1 nM along with a detection limit of 0.03 fM, good accuracy, and acceptable reproducibility, showing that the self-enhanced ECL biosensing strategy supported by nano-matrix provided a new way for the ultrasensitive detection of miRNA, and promoted the development of breast cancer diagnosis.