An “on-off” ratiometric electrochemiluminescence biosensor based on LSPR-enhanced by Ag@Au nanostructures combined with Pd NCs catalysing a single luminophore for MiRNA let-7a detection

In this study, we reported a ratiometric electrochemiluminescence (ECL) biosensor based on localized surface plasmon resonance (LSPR)-enhanced Ag@Au nanostructures combined with palladium nanoclusters (Pd NCs) catalyzing the luminol-gold nanoparticles (L-Au NPs). Firstly, L-Au NPs were synthesized, hydrogen peroxide (H₂O₂) was used as a co-reactant, and Ag@Au nanostructures acted as an LSPR source to enhance the initial signal at the anode. Next, with the help of strand displacement amplification (SDA), the trace target miRNA let-7a was able to be converted to a number of output DNA. And then the Visual DNA Strand Displacement (DSD) was used to evaluate the conversion efficiency of miRNA let-7a into output DNA, thereby verifying that the SDA achieved signal amplification in the construction of biosensor. It was thereafter experimentally verified that the first decrease in anodic signal was achieved by strand amplification based on magnetic beads and polymerase excitation. In contrast, Pd NCs were synthesized using double-stranded DNA (dsDNA) as a template and excited with a cathodic signal, while a second decrease of the anodic signal was also achieved. The developed ratiometric ECL biosensor demonstrated a sensitive detection of miRNA let-7a with a linear range from 0.1 pM to 10 aM and a detection limit of 5.45 aM (S/N = 3). In conclusion, the study presented a new idea for the construction of ratiometric ECL sensors based on a single luminophore, providing technical support for the early diagnosis of cancer.