Highly sensitive homogeneous electrochemiluminescence biosensor for microRNA-155 based on enzyme-free cascade signal amplification and magnetic assisted enrichment

MicroRNA-155 (miR-155) can act as a suitable biomarker for dry eye diseases caused by Sjogren's syndrome. Since the concentration of miR-155 in the clinic samples is low, it is necessary to develop some simple but sen-sitive detection methods. In this study, a homogeneous electrochemiluminescence (ECL) biosensor for miR-155 detection based on catalyze hairpin assembly (CHA) and hybridization chain reaction (HCR) and magnetic assisted enrichment had been constructed. Firstly, biotin-modified hairpin H1 (bio-H1) had been connected with the streptavidin-modified magnetic beads (SAMBs) to capture target, which can be used to trigger CHA reaction to complete the first signal amplification with the assistance of hairpin H2. Then the stick end of H2 of the CHA production can trigger the HCR reaction of H3 and H4 and generate long double-stranded DNAs (dsDNAs) on the surface of SAMBs to realize the second signal amplification. Ru(phen)32+ can insert into the dsDNAs to produce SAMBs/dsDNA/Ru and act as signal tags, which can be purified by magnetic separation easily, making the background signal significantly reduced. The ECL intensity of the system had a linear rela-tionship with logarithm of miR-155 concentration in the range of 1 fM similar to 10 nM, with a detection limit as low as 0.63 fM. The proposed biosensor had been applied to monitor miR-155 in clinical samples with satisfied results.