Sandwich-type microRNA biosensor based on magnesium oxide nanoflower and graphene oxide-gold nanoparticles hybrids coupling with enzyme signal amplification

An ultrasensitive sandwich-type electrochemical biosensor for microRNA (miRNA) detection is developed based on magnesium oxide (MgO) nanoflower and graphene oxide-gold nanoparticles (GO-AuNPs) hybrids coupling with electrochemical-chemical-chemical (ECC) detection system. In this bioassay system, MgO nanoflowers and AuNPs are modified on electrode to act as sensing platform. The thiolated capture probe is then self-assembled onto AuNPs/MgO substrate via formation of Au-S bonds. Subsequently, a biotinylated DNA signal probe is conjugated to GO-AuNPs hybrids. When miRNA-21 is added, a sandwich complex is formed and a lot of signal indicators streptavidin-conjugated alkaline phosphatases (SA-ALP) are immobilized upon electrode by the specific reaction between avidin and biotin. Finally, ECC reaction is performed in the system to improve detection signal. The proposed sandwich-type assay benefits from advantages of sandwich-type structure for enhanced sensitivity and specificity, MgO nanoflowers/AuNPs as sensing platform and GO-AuNPs hybrids as signal carriers for signal amplification, and ECC as a sensitive detection system for low detection limit. This biosensor exhibits a good dynamic ranging from 0.1 to 100 fM and a low detection limit of 50 aM (S/N = 3) toward target miRNA-21.