Abstract
Ultrasensitive capsaicin sensor based on endogenous single‐molecule fluorophore enhancement and quenching interface on gold nanoislands (GNIs) was developed by correlative fluorescence fluctuation optical spectroscopy. Endogenous fluorescence of capsaicinoids was enhanced by plasmon resonance energy transfer in the proximity of GNIs. The enhanced fluorescence signals exhibited large fluctuation from the average intensity reflecting the characteristic to‐and‐fro Brownian motion of fluorophores to the proximity of GNIs. The fluctuation of fluorophores showed enhancement, quenching, and equilibrium lifetimes depending on fluorophore‐GNI distance. The correlation diffusion of fluorophore signal decreased with increasing concentration of capsaicinoids. In the cross‐correlative quantification of capsaicinoids using the GNI array chip, the method showed excellent detection limits of 290 zM for capsaicin and 467 zM for dihydrocapsaicin. This method consisting of fluorophore fluctuation analysis and correlation diffusion‐based quantification has potential application to the study of label‐free single‐molecule interactions.
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