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.