Gold-loaded nanoporous ferric oxide nanocubes for electrocatalytic detection of microRNA at attomolar level

A crucial issue in microRNA (miRNA) detection is the lack of sensitive method capable of detecting the low levels of miRNA in RNA samples. Herein, we present a sensitive and specific method for the electrocatalytic detection of miR-107 using gold-loaded nanoporous superparamagnetic iron oxide nanocubes (Au-NPFe 2 O 3 NC). The target miRNA was directly adsorbed onto the gold surfaces of Au-NPFe 2 O 3 NC via gold-RNA affinity interaction. The electrocatalytic activity of Au-NPFe 2 O 3 NC was then used for the reduction of ruthenium hexaammine(III) chloride (RuHex, [Ru(NH 3 ) 6 ] 3+ ) bound with target miRNA. The catalytic signal was further amplified by using the ferri/ferrocyanide [Fe(CN) 6 ] 3-/4- system. These multiple signal enhancement steps enable our assay to achieve the detection limit of 100 aM which is several orders of magnitudes better than most of the conventional miRNA sensors. The method was also successfully applied to detect miR-107 from cancer cell lines and a panel of tissue samples derived from patients with oesophageal squamous cell carcinoma with excellent reproducibility (% RSD = < 5%, for n = 3) and high specificity. The analytical accuracy of the method was validated with a standard RT-qPCR method. We believe that our method has the high translational potential for screening miRNAs in clinical samples.