▎ 摘　　要

We report the electrocatalytic activity of a new class of superparamagnetic nanoparticles, graphene-oxide-loaded iron oxide (GO/IO hybrid material), towards the reduction of ruthenium hexaammine(III) chloride (Ru(NH3)(6)](3+), RuHex). Leveraging the electrocatalytic activity of the GO/IO hybrid material and the signal enhancement capacity of [Ru(NH3)(6)](3+) /[Fe(CN)(6)](3-) in an electrocatalytic cycle, an ultrasensitive and specific electrochemical sensor was developed for the detection of cancerrelated microRNA (miRNA). Using the direct affinity interaction purified target miRNA were directly adsorbed onto a screen-printed electrode modified with the GO/IO hybrid material. The detection was enabled by chronocoulometric (CC) readout of charge-compensating [Ru(NH3)(6)](3+) followed by an enhancement in CC charge display through the Ru(NH3)(6)](3+)/[Fe(CN)(6)](3- )system. We demonstrate an excellent limit of detection of 1.0 fM by accurately detecting miR-21 in synthetic samples and showcase its clinical utility in ovarian cancer cell lines with high sensitivity (ten cells) and good reproducibility between RNA and graphene oxide, magnetically isolated and (%RSD= <5%, for n=3).