Rapid electrochemical detection of MiRNA-21 facilitated by the excellent catalytic ability of Pt@CeO₂ nanospheres

Pt@CeO2 nanospheres (NSs) were first synthesized by simply mixing Ce(NO3)3 and K2PtCl4 under the protection of pure argon at 70 °C for 1 h, which exhibited excellent catalytic ability toward hydrogen peroxide (H2O2). An electrochemical biosensor was successfully developed using Pt@CeO2 NSs as a capture probe for the ultra-sensitive and fast detection of miRNA-21, a new type of biomarker for disease diagnostics, especially for cancer. During the step-by-step construction process of the RNA sensor, Pt@CeO2 NSs were functionalized with streptavidin (SA) to obtain SA-Pt@CeO2 NSs through amide bonds. Gold nanoparticles (Au NPs) were electrodeposited on the surface of the glassy carbon electrode to improve the transmission capacity of electrons and provided Au atoms for fixing the thiolated capture probe (SH-CP) with a hairpin structure on the electrode via forming Au-S bonds. The target miRNA-21 specifically hybridized with SH-CP and opened the hairpin structure to form a rigid duplex so as to activate the biotin at the end of the capture probe. SA-Pt@CeO2 NSs were thus specially attached to the electrode surface through the biotin-streptavidin affinity interaction, finally leading to the significant signal amplification. The ultra-sensitive and rapid detection of miRNA-21 was finally realized as expected benefiting from the excellent catalytic ability of Pt@CeO2 NSs toward H2O2 in a wide linear concentration range from 10 fM to 1 nM with the detection limit as low as 1.41 fM. The results achieved with this new RNA sensor were quite satisfactory during the blood sample analysis.