Silver island film substrates for ultrasensitive fluorescence detection of (bio)molecules

Abstract

A silver island film (SIF) substrate was used to demonstrate that Metal-Enhanced Fluorescence (MEF) is a powerful tool to enable detection of emission from (bio)molecules at very low concentrations. The experiments were carried out with the Fenna-Matthews-Olson (FMO) pigment-protein complex from the photosynthetic green sulfur bacterium Chlorobaculum tepidum. FMO was diluted to a level, at which no emission was detectable on a glass substrate. In contrast, the fluorescence of FMO was readily observed on the SIF substrate, even though the emission wavelength of FMO is displaced by over 300 nm from the maximum of the plasmon resonance of the SIF layer. Estimated enhancements of the fluorescence intensity of FMO on SIF are about 40-fold. The enhancement factor correlates with the improvement of the signal-to-noise ratio for FMO emission on SIF substrates.

Origin of bimodal fluorescence enhancement factors of Chlorobaculum tepidum reaction centers on silver island films

“…One of the maxima appears at around the intensity of 200 kpcs, while the other is at slightly over 300 kcps. In comparison with the results obtained for the reference (RCs deposited on glass), the lower maximum results in an enhancement factor of about 40, which is very similar to values previously observed for pure FMO complexes deposited on SIF .…”

“…Notably, in both cases, the contribution from plasmonic enhancement of the radiative rate of the RC will be the same. It is known from previous work that plasmons induced in SIF can have strong effects on FMO fluorescence, resulting in considerable enhancement of its fluorescence intensity . Another explanation may be the attachment of different numbers of FMO trimers to the RC cores.…”

Silver Island Film for Enhancing Light Harvesting in Natural Photosynthetic Proteins

“…This RC can be associated with one or several Fenna-Matthews-Olson (FMO) protein complexes [39,41], whose absorption spectrum is shown in Figure 2c. The structure of the FMO complex is known, FMO forms trimers, each monomer contains seven (or eight) BChl a molecules, very strongly coupled to each other [23,[42][43][44][45][46]. Fingerprints of FMO absorption can be recognized in the RC absorption spectrum (cf.…”

“…Scanning electron microscopy (SEM) pictures of the obtained SIF substrates are presented in Figure 3a. Although plasmonic SIF substrates fabricated using this approach have been widely applied in metal-enhanced fluorescence studies [22,23,41,53], some of the glucose used in the synthesis tends to adhere to the SIF surface forming a layer. This may be sufficiently thin to allow for efficient plasmonic interactions; however, it may still form a barrier for chemical functionalization of the surface and controlled immobilization of emitters.…”

“…One of the key issues related to developing solar energy conversion devices concerns the improvement of the absorption rate [9,17], conversion efficiency [18], stability of the working modules [19] and selectivity of the catalytic reactions in the case of solar-to-chemical devices. With respect to increasing and/or tuning the absorption of natural and artificial photosynthetic molecular systems, encouraging results have been achieved using metallic nanostructures [9,[20][21][22][23]. These nanostructures exhibit a unique property associated with collective oscillations of electrons induced by electromagnetic waves: so-called plasmons [9,17].…”