Abstract
A Faraday cage-type electrochemiluminescence (ECL) biosensor for ultrasensitive detection of cancer-associated microRNA-21 was constructed based on Fe3O4@Au magnetic nanoparticles (Fe3O4@Au MNPs) and multi-functionalized graphene oxide. The capture unit (Fe3O4@Au MNPs-cDNA) was prepared by immobilizing capture DNA (cDNA) on Fe3O4@Au MNPs, while the multi-functionalized graphene oxide acted as the signal unit ((sDNA&luminol)@GO). In this biosensor, the capture unit, which was used to catch the microRNA-21, could be easily attracted onto the magnetic glassy carbon electrode surface. After the hybridization of microRNA-21 with the capture unit, the signal unit was further hybridized to form a Faraday cage-type structure, in which the signal unit was directly fixed onto the electrode surface, resembling a huge net and even becoming a part of the electrode surface. All luminol molecules labeled on the signal unit could take part in the electrode reaction, thus greatly enhancing the ECL signal. The ECL intensity was found to increase with the logarithm of microRNA-21 concentrations from 1 fM to 10 pM with a detection limit of 0.3 fM. In addition, this proposed Faraday cage-type ECL biosensor can be used for practical analysis of microRNA-21 in human serum, providing an ultrasensitive detection platform for microRNAs in clinical diagnosis.
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