Detection of microRNAs using electrocatalytic nanoparticle tags.

An ultrasensitive microRNA (miRNA) assay employing electrocatalytic nanoparticle tags to meet the need of miRNA expression analysis is described in this report. The assay utilizes an indium tin oxide electrode on which oligonucleotide capture probes are immobilized. After hybridization with periodate-treated miRNA, the nanoparticle tags, isoniazid-capped OsO2 nanoparticles, are brought to the electrode through a condensation reaction to chemically amplify the signal. The resulting electrode exhibits electrocatalytic activity toward the oxidation of hydrazine at -0.10 V, reducing the oxidation overpotential by as much as 900 mV. The effect of experimental variables on the amperometric response is investigated and optimized. A detection limit of 80 fmol/L in 2.5-microL droplets and a linear current-concentration relationship up to 200 pmol/L are obtained following a 60-min hybridization. Successful attempts are made in miRNA expression analysis of HeLa cells.