Signal-on low background electrochemiluminescence biosensor based on the target-triggered dual signal amplifications and difference of electrostatic attraction

The electrostatic attraction difference between negatively charged report probes and positively charged electrode had been applied to develop a signal-on low background electrochemiluminescence (ECL) biosensor for microRNA-141 (miRNA141, chosen as a model target) detection. Indium tin oxide (ITO) electrode was modified with poly-(allylamine hydrochloride) (PAH) to generate a positively charged surface. The electrostatic repulsion between dichlorotris (1,10-phenanthroline) ruthenium (Ⅱ) hydrate (Ru(phen)32+) and ITO electrode results in the low background signal. The target can trigger an enzyme-free isothermal catalytic hairpin self-assembly (CHA) and hybrid chain reaction (HCR) cascade reaction to generate a large amount of negatively charged long dsDNAs, which can be used to load Ru(phen)32+ (Ru-dsDNA) with high efficiency. Ru-dsDNA complexes are negatively charged and can easily accumulate on ITO electrode surface because of electrostatic attraction, which results in a strong ECL signal detected. The ECL intensity of the system was linearly correlated with the logarithm of microRNA-141 concentration in the range of 1 fM ∼ 5 pM with a detection limit of 0.17 fM (S/N = 3). The reliability of the proposed biosensor had been verified through the detection of targets in cell lysates.