Multifunctional Yolk–Shell Nanostructure as a Superquencher for Fluorescent Analysis of Potassium Ion Using Guanine-Rich Oligonucleotides

The excellent performance of a biosensor generally depends on the high signal-to-noise ratio, and the superquencher plays a dominant role in fluorescent sensors. Novel nanoquenchers exhibited high quenching efficiency in various fluorescent assays of biological/chemical molecules. Here, we developed a novel nano-biosensor using Fe 3 O 4 @C yolk–shell nanoparticles (YSNPs) and studied their quenching effect. We found Fe 3 O 4 @C YSNP was a superquencher and exhibited an ultrastrong quenching ability, up to almost 100% quenching efficiency, toward fluorophores. Also, Fe 3 O 4 @C YSNPs possessed the most superior fluorescence restoration efficiency, due to biomolecular recognition event, compared to the other nanoquenchers, including bare Fe 3 O 4 NPs, graphene oxide (GO), and single-wall carbon nanotubes (SWCNTs). On the basis of that, a fluorescent sensing platform for potassium-ion (K + ) analysis with guanine (G)-rich oligonucleotides was designed. As a result, Fe 3 O 4 @C YSNP-based fluorescent sensors demonstrated excellent performance, with an ultrahigh sensitivity of a detection limit as low as 1.3 μM, as well as a wide dynamic range from 50 μM to 10 mM. The proposed method is fast, simple, and cost-effective, suggesting the great potential for practical applications in biomedical detection and clinical diagnosis.