(627g) Multi Spatiotemporal Spectroscopy From a Novel Nano-Structured Plasmonic Grating Hotspots Platform

Physiologically relevant processes to pharmacogenomics need to be simultaneously scrutinized, visualized and simulated to study local effects and molecular conformations for multiple applications from disease prognosis drug delivery to protein folding. However, a single biophysical instrument with sufficient spatial and temporal resolution to detect complex biological kinetics over broad spatiotemporal scales at the single molecule (SM) level is non-existent. In my talk today, I will show you a cost effective soft lithography technique to fabricate plasmonic structures that can lead to the development of multi spatial/temporal techniques from a single platform. The substrate are made using a simple PDMS stamping of grating structures from commercially produced HD-DVDs with a thermally deposited metallic cap. By modifying the metallic capping process using oblique (non-normal) angular thermal deposition, extra-ordinary (173.12 times) fluorescence enhancements is observed from the substrate than quartz for the same dye. A nano-patterned substrate with three major surface morphological features is obtained at definite deposition angles for a fixed deposition thickness. The surface consists of a shallow nano-gap region, a conical grating peak with a plateau region between the two aforementioned regions that leads to a concentration of the electric field due to antenna (nano-gap) and lightning rod (grating peak) effects. On closer inspection with SEM, AFM images show distinct secondary peaks on the grating peak that gives rise to an extreme concentration of the electric field, leading to localized surface plasmon resonance, called “hot-spots”. This causes any fluorophore localized on a “hot-spot” to fluoresce with intensities that show higher enhancement in comparison to the bulk of the grating structure from the same substrate. We found that these substrates (specifically the nano-peaks) are ideally suited to study SM phenomenon like SM Förster resonance energy transfer (smFRET), due to an increased signal to noise ratio and high enhancement factors using a simple epi-fluorescence microscope. In addition, dyes close to the hotspot region show an increase in the Förster distance as a result of the localized SPR. The same plasmonic substrates are used also for Surface Enhanced Raman Spectroscopy (SERS). The Raman spectrum from a 1mM 2-naphthalenethiol self-assembled monolayer on the nano-grating structure at multiple spatial positions shows consistent signals with significantly enhanced Raman peaks. The spatial homogeneity (less than 10 % standard deviation) in signal enhancement of Raman Peaks clearly demonstrates the uniformity of the patterned nano-structure. In comparison with commercial substrates, we clearly observe higher enhancements of our substrate with regular spatial distribution of hot-spots with minimal signal variation in contrast to commercial substrate Klarite™ (high signal variation, no spatial uniformity, lower Raman signal strength). The enhancement was found to critically depend on the structural moiety and on the incident laser angle with correct optimization leading to SM-SERS. To conclude, we show here an inexpensive, easy method to obtain both uniform Raman hotspots that show large enhancement and extraordinary fluorescence enhancement with single molecule resolution. Combined with microfluidic architecture, an opto-fluidic device can be easily implemented to increase detection sensitivity and selectivity as a novel bio-diagnostic platform or to simultaneously observe pertinent and biological motions and kinetics from a single platform.