A highly sensitive microRNA biosensor based on hybridized microRNA-guided deposition of polyaniline

• The proposed biosensor allows EIS detection of microRNAs (miRNAs) with excellent sensitivity.
• The label-free approach greatly simplifies the procedure.
• The utilization of peptide nucleic acid probes greatly improves the selectivity of the biosensor.
• The proposed biosensor is an attractive candidate for the development of a simple and robust miRNA expression profiling platform for uses at point-of-care.

On the basis of hybridized microRNA (miRNA)-guided deposition of polyaniline (PAn), a highly sensitive impedimetric miRNA biosensor is developed in this report. Briefly, a gold electrode coated with charge neutral peptide nucleic acid (PNA) capture probes (CPs) is first hybridized to a target miRNA. After a very brief rinsing the hybridized electrode is incubated in pH 3.0 of 0.10 M potassium phosphate buffer-based cocktail containing aniline, H2O2, and a G-qudraplex-hemin DNAzyme. The DNAzyme catalyzes the polymerization of aniline and the hybridized miRNA strands guide the deposition of PAn, thus resulting in the formation of a thin PAn film on the biosensor surface. Electron-transfer impeding power of the PAn film in alkaline medium is utilized to determine the concentration of the target miRNA. Under optimized experimental conditions, 0.50 fM target miRNA is successfully detected. Excellent mismatch discrimination capability of the biosensor was observed largely due to the excellent hybridization selectivity of the PNA CPs. Attempts were made in profiling miRNAs in total RNA samples extracted from cancer cells and blood.