Aaron Wood

Influence of silver grain size, roughness, and profile on the extraordinary fluorescence enhancement capabilities of grating coupled surface plasmon resonance

Since the development of fluoroimmunoassays, researchers have sought a method of substantially enhancing fluorescence intensity to extend the limits of detection to new levels of sensitivity. Surface plasmon resonance (SPR) and metal enhanced fluorescence has long been a topic of research and has led to the development of prism- and grating-based SPR systems. However, with the wide coupling range and ease of exciting SPR on plasmonic gratings with a simple microscope objective, they have tremendous potential for revolutionizing the fields of plasmonics, fluorescence, and sensors. In an effort to better understand the influence of grating profile and metal film properties on the extraordinary fluorescence enhancement capabilities of plasmonic gratings, a novel microcontact printing process and different metal deposition techniques were used to fabricate silver gratings with varying grain diameters, roughnesses, heights, and duty cycles using thermal evaporation and RF sputtering. The resulting plasmonic gratings exhibited fluorescence enhancements up to 116× that of dye-coated glass slides using an epifluorescence microscope, much higher than more expensive prism-based SPR systems. This silver grating represents an extraordinary opportunity to quickly and easily enhance fluorescence and widen the detection limits of common fluorescence based assays with little to no equipment modification.

Enhanced DNA Detection Through the Incorporation of Nanocones and Cavities Into a Plasmonic Grating Sensor Platform

In this paper, a novel plasmonic grating sensor platform was developed and tested for feasibility using a lights-ON fluorescence-based DNA assay. The sensor platform combined the fluorescence enhancement of a grating-based plasmonic platform with the electric field intensifying effects of nanoscale cones and cavities. The gratings were made through a microcontact printing process that replicated HD-DVD disks in polymethylsilsesquioxane and coated with a thin gold film. Nanocavities were incorporated into the sensor platform during the printing process and nanocones were incorporated during the 100-nm gold deposition process. Fluorescently tagged single-strand (ss) DNA molecules were immobilized onto the surface and were designed such that the molecules would fluoresce when bound to a complementary sequence. Sensor substrates were imaged after exposure to a mismatched and matched ssDNA to quantify the fluorescence enhancement of the sensor. Exposure to matched ssDNA resulted in fluorescent emission from the grating that was 13.6× brighter than flat gold, while the nanocones and nanocavities were 37.5× and 47.4× brighter than flat gold, respectively.

Enhanced fluorescence through the incorporation of nanocones/gaps into a plasmonic gratings sensor platform

In this article, a novel plasmonic grating sensor platform was developed and tested for feasibility in sensor applications using a “lights-on” fluorescence based DNA sensor. The sensor platform combined the fluorescence enhancement of a grating-based plasmonic platform with the electric field intensifying effects of nano-scale cones and cavities. The gratings were made through a microcontact printing process that replicated HD-DVD discs in polymethylsilsesquioxane (PMSSQ) and coated in a thin gold film. Nanocavities were incorporated into the sensor platform during the printing process and nanocones were incorporated during the 100 nm gold deposition process. Fluorescently-tagged single-strand (SS) DNA molecules were immobilized onto the surface and were designed such that the molecules would fluoresce when bound to a complementary sequence. Sensor substrates were imaged after exposure to a mismatched and matched oligomer to quantify the fluorescence enhancement of the sensor. Much higher fluorescence intensity was observed on all of the plasmonic structures as compared to flat gold.

Hecke algebra correspondences for the metaplectic group

Over a p-adic field of odd residual characteristic, Gan and Savin proved a correspondence between the Bernstein components of the even and odd Weil representations of the metaplectic group and the components of the trivial representation of the equal rank odd orthogonal groups. In this paper, we extend their result to the case of even residual characteristic.

Single-Molecule Surface Plasmon-Coupled Emission with Plasmonic Gratings

The ability to image single molecules (SM) has been the dream of scientists for centuries, and because of the substantial recent advances in microscopy, individual fluorescent molecules can now be observed on a regular basis. However, the development of such imaging systems was not without dilemmas, such as the detection and separation of individual fluorescence emissions. One method to solve this problem utilized surface plasmon resonance (SPR) to enhance the emission intensity of SMs. Although enhancing the SM emission intensity has yielded promising results, this method does not fully utilize the unique plasmonic properties that could vastly improve the SM imaging capabilities. Here, we use SPR excitation as well as surface plasmon-coupled emission from a high-definition digital versatile disc grating structure to image and identify different fluorophores using the angular emission of individual molecules. Our results have important implications for research in multiplexed SM spectroscopy and SM fluorescence imaging.

Highly sensitive plasmonic grating platform for the detection of a wide range of infectious diseases

We report the cost-effective fabrication of a plasmonic grating for improved light coupling in a fluorescence-based sensor platform by a simple micro-contact printing technique. The fluorescence of Rhodamine 6G (R6G) film on gratings was enhanced by up to 239-fold with respect to glass using a fluorescence microplate reader. The silver gratings are made suitable for use in biological buffers by a protective alumina layer. The platform has been optimized to detect Interferon-gamma (IFNδ), a commonly used biomarker for M. tuberculosis infection and other autoimmune diseases, with an immunofluorescence assay. The platform demonstrates 500 fg/ml limit of detection (LOD) while commercial enzyme-linked immunosorbent assays (ELISA) report 2 pg/mL LOD. The extraordinary fluorescence enhancement was compared with simulation result to predict and support the experimental analysis. These results can be used to expand the platform for numerous fast, robust, sensitive biosensors.

Anti-corrosive films on silver plasmonic gratings for fluorescence imaging of single molecules and cancer cells

Silver plasmonic gratings with a thin corrosion protection film enable enhanced fluorescence-based detection, including single molecule, over a much wider fluorescent dye concentration range, 100 μM-1fM, and deeper field penetration than traditional sensor substrates.