Abstract
Zero-mode waveguides (ZMWs) are capable of modifying fluorescence emission through interactions with surface plasmon modes leading to either plasmon-enhanced fluorescence or quenching. Enhancement requires spectral overlap of the plasmon modes with the absorption or emission of the fluorophore. Thus, enhancement is limited to fluorophores in resonance with metals (e.g. Al, Au, Ag) used for ZMWs. The ability to tune interactions to match a wider range of fluorophores across the visible spectra would significantly extend the utility of ZMWs. We fabricated ZMWs composed of aluminum and gold individually and also in mixtures of three different ratios, (Al : Au; 75 : 25, 50 : 50, 25 : 75). We characterized the effect of mixed-metal ZMWs on single-molecule emission for a range fluorophores across the visible spectrum. Mixed metal ZMWs exhibited a shift in the spectral range where they exhibited the maximum fluorescence enhancement allowing us to match the emission of fluorophores that were nonresonant with single metal ZMWs. We also compared the effect of mixed-metal ZMWs on the photophysical properties of fluorescent molecules due to metal–molecule interactions. We quantified changes in fluorescence lifetimes and photostability that were dependent on the ratio of Au and Al. Tuning the enhancement properties of ZMWs by changing the ratio of Au and Al allowed us to match the fluorescence of fluorophores that emit in different regions of the visible spectrum.
Highlights
Single molecule spectroscopy is widely used for biological applications including single particle tracking, protein folding, and protein–protein interactions.[1]
Mixed metal Zero-mode waveguides (ZMWs) exhibited a shift in the spectral range where they exhibited the maximum fluorescence enhancement allowing us to match the emission of fluorophores that were nonresonant with single metal ZMWs
Spectral overlap between the surface plasmon resonance (SPR) of metal nanostructures and the uorophore spectrum is the key component for metal enhanced uorescence, shi s in SPR lead to overlap with different spectral regions
Summary
Single molecule spectroscopy is widely used for biological applications including single particle tracking, protein folding, and protein–protein interactions.[1]. The uorescence intensity time trace of $100 single ATTO 550 uorophores on glass and in all ZMW types were recorded at 532 nm laser excitation (1.03 mW). Enhancement in uorescence intensity coupled with improved photostability for molecules in 100Al, 75Al and 25Al could be an indication of both excitation and decay rate enhancement.
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