A visible and label-free colorimetric sensor for miRNA-21 detection based on peroxidase-like activity of graphene/gold-nanoparticle hybrids

A visible and label-free colorimetric sensor for microRNA-21 (miRNA-21) detection was developed based on the peroxidase-like activity of graphene/gold-nanoparticle (Au-NP) hybrids which could be flexibly controlled by using single-stranded PNA-21 (ssPNA-21). The spontaneous absorption of ssPNA-21 on graphene/Au-NP hybrid surfaces causes the peroxidase-like catalytic activity of hybrids to be almost completely deactivated via pi-pi stacking interactions between ssPNA and graphene, so that TMB could not be oxidized to oxTMB in the presence of H2O2, leading to no color change. The addition of miRNA-21 triggered a hybridization reaction between the PNA probe (ssPNA-21) and miRNA-21. The decrease of the exposed base groups could lead to the release of PNA/DNA duplexes from the hybrid surface, which would restore the catalytic activity of hybrids with a concomitant colorless-to-blue color change. As a result, this sensor emitted a low background signal and responded linearly to miRNA-21 from 10 nM to 0.98 mu M with a detection limit of 3.2 nM (S/N = 3) under the optimal conditions. In addition, the biosensor could be also extended to miRNA-21 detection in human serum. Therefore, this colorimetric sensor platform is a potential alternative assay for miRNA detection in biomedical research.