Research & Technology Development

Translating Fundamental Research from the Benchtop to Bedside

Dr Geddes’s research is focused at the development of new Fluorescence and Plasmonics concepts and theory, with a view to their downstream biomedical application in health care, safeguard and diagnostics. Under his leadership, the IoF (Institute of Fluorescence) has earned a well-deserved international reputation for its advances in Fluorescence Spectroscopy and Plasmonics. Approaches and concepts both developed and discovered by his research group, such as Metal-Enhanced Fluorescence (MEF), Metal-Enhanced Chemiluminescence (MEC), Surface-Plasmon Coupled Phenomenon, Microwave-based Lysing, "Lyse-it™" (see Figure 1), Plasmonic Electricity, Microwave-Accelerated Metal-Enhanced Fluorescence (MAMEF), and the glucose-sensing contact lens, are both well-recognized, highly cited and currently used in laboratories and government research facilities around the world today. Dr Geddes’s research has been cited over 5000 times in the peer reviewed literature.

In addition, Dr Geddes receives significant press attention and research coverage. In past years, Dr Geddes has given numerous TV interviews, appeared on the Discovery Channel, has appeared in newspapers as well as being reviewed in popular magazines, such as Photonics Spectra, Pharmagenomics, Biophotonics International, to name but just a few. More significantly, Dr Geddes’s research has been highlighted in editorials at the front of several notable journals, including, Nature, JACS and Analytical Chemistry.

Figure 1. Thermal imaging of a cell suspension on a a Lyse-it™ platform under microwave irradiation. The distance between the apexes of the Au triangles is ~2 mm.

Research by Chris Geddes

Metal-Enhanced Fluorescence (MEF): Near-Field Fluorescence

The majority of Dr Geddes’s research is focused on metal-enhanced fluorescence (MEF), a term he introduced into the literature in 2002 [1].

Although fluorescence is a very highly sensitive technique, where single molecules can routinely be detected, there is still a significant drive for reduced detection limits. The detection limit is usually limited by the quantum yield of the fluorophore, the autofluorescence of the samples and the photostability of the fluorophores. However, there has been a recent explosion in the use of metallic nanostructures to favorably modify the spectral properties of fluorophores and to alleviate some of their photophysical constraints. The uses of MEF have included the increased detectability and photostability of fluorophores, improved protein, DNA / RNA detection, the release of self-quenched fluorescence of over labeled proteins, enhanced wavelength-ratiometric sensing and the application of metallic surfaces to amplified assay detection, to name but just a very few. In recent years, Dr Geddes has been clinically validating his MAMEF technology (microwave-accelerated Metal-enhanced luorescence), a technology which has been shown to be able to detect less than 10 copies of a genome of interest in under 1 minute, a profound technology) that has multiple applications in clinical healthcare, food safeguard and bioagent detection [2-5].

Dr Geddes’s laboratories have also developed many nanostructured surfaces for metal-enhanced fluorescence such as those comprised of silver islands, silver colloids, silver nano triangles, silver nanorods, and even fractal-like silvered surfaces to name but just a very few. The Quatawell™ range of products, commercialized by Dr Geddes’s first spin out company Plasmonix Inc. applies the Metal-Enhanced Fluorescence technology to 96-well plates, producing enhanced fluorescence signatures > 25x for its users. Several modes of silver deposition have also been developed, such as silver deposition by light and electrochemically, on glass, plastics and even using electrodes. Figure 2 visually demonstrates the benefits of Metal-enhanced Fluorescence. As the laser excitation source is moved over an equally coated fluorophore-protein labeled silvered surface, enhanced fluorescence can be observed. The enhanced fluorescence is not due to reflected photons from the mirrored surface as the photographs were taken through an emission filter, but is in fact due to plasmon-coupling and amplification. The ability to increase fluorescence signatures, is finding profound applications in the biosciences and in microscopy, where photon flux and detectability is a primary concern.

Research by Chris Geddes

Figure 2. The top panel shows a plastic strip where half of the area has been coated with silver nanoparticles. The coated and uncoated regions are evident by the gray-green tint originating from the Ag particles. Subsequently the strip is coated with a thin layer of a fluorophore-protein macromolecule and is illuminated with a laser centered at 474 nm. Due to fluorophore Ag-plasmon coupling the emission from the coated area [bottom panel] is much more intense as compared to emission from the uncoated area [middle panel].

Metal-Enhanced Fluorescence (MEF): Changing the way we think and use Fluorescence today

Fluorescence was originally discovered by Sir George Stokes in the 1840s. Since that time we have made notable achievements as a community in understanding all the far-field concepts related to fluorescence. It is for this reason that we have only observed incremental advances in fluorescence and its practices in the last 20 or so years. For example, we can develop new fluorophores with more finely tuned properties, we can develop better instruments and software for fluorescence analysis, but these developments are only incremental, the free space properties and oscillator strength of the fluorophores fundamentally unchanged, with the spatial distribution of the far-field emission remaining for the most part constant. However, Metal-Enhanced Fluorescence (MEF) and indeed plasmonics as a whole, threatens to change the way we both use and think about fluorescence and its applications. In the near-field, fluorophores (dipoles) and metals can couple and favorably modify both near & far-field fluorescence properties. In contrast to typical fluorescence spectroscopy we know very little about near-field fluorescence properties as a community. Subsequently, Dr Geddes’s research is focused at fundamentally understanding these near-field photophysical properties with outcomes focused at translating plasmonic applications into the biosciences. It is Dr Geddes’s opinion that we are on the verge of a paradigm shift in the uses and utility of Fluorescence spectroscopy, with the next 10 years focusing heavily on new near-field fluorescence concepts.

Metal-Enhanced Fluorescence (MEF): Theory

Over the last 5 or so years, Dr Geddes and the IoF have extensively studied many metal-enhanced photophysical phenomenon. Accordingly, a mechanism for MEF has been postulated. In the current mechanistic interpretation of MEF, non-radiative energy transfer occurs from excited distal fluorophores to the surface plasmon electrons on non-continuous films, in essence an induced mirror dipole, Figure 3. The surface plasmons in-turn, radiate the photophysical characteristics of the coupled quanta. Subsequently, armed with a developed understanding of MEF, research has been intensely focused at both predicting and then experimentally verifying a whole host of metal (plasmon) enhanced photophysical phenomenon, such as Metal-enhanced S2 emission, Metal-enhanced singlet oxygen generation and superoxide generation, the generation of electricity via the presence of fluorophores (plasmonic electricity, and the ability to change the color of excited state fluorophore emission via plasmon coupling, to name but just a few.

These collective observations have also led us to postulate generalized plasmon-fluorophore descriptions, which account for many past and present plasmon-dipole observations. At present, this description is still being developed by Professor Geddes and his colleagues, and intense research is likely to continue for several years to come.

The Plasmon Radiating Model proposed for metal enhanced fluorescence mechanism by Chris D. Geddes.

Figure 3. Radiating Plasmon Model proposed by Professor Geddes as the mechanism underpinning the Metal-Enhanced Fluorescence (MEF) phenomenon.

Cited References:

[1] Geddes, C.D., Lakowicz, J.R. (2002). Metal-enhanced fluorescence, Journal of Fluorescence, 12(2), 121-129.

[2] Melendez, J.H., Huppert, J.S., Jett-Goheen, M., Hesse, E.A., Quinn, N., Gaydos, C.A. and Geddes, CD. (2013). Blind Evaluation of the Microwave-Accelerated Metal-Enhanced Fluorescence Ultrarapid and Sensitive Chlamydia Trachomatis test by use of Clinical Samples, Journal of Clinical Microbiology, 51(9), 2913-2920.

[3] Joshi, T., Mali., B., Geddes, C.D., Baillie, L., (2014). Extraction and Sensitive Detection of Toxins A and B from the human pathogen Clostridium difficile in 40 seconds using Microwave-Accelerated Metal-Enhanced Fluorescence, Plos One, 9,8,e104334.

[4] Zhang, Y., Agreda, P., Kelly, S., Gaydos, C., and Geddes, C. D., (2011). Development of a Microwave-Accelerated Metal-Enhanced Fluorescence 40 seconds, < 100 cfu/ml point of care assay for the detection of Chlamydia Trachomatis. IEEE Transactions on Biomedical Engineering, 58(3), 781-784.

[5] Tennant, S. M., Zhang, Y., Galen, J. E., Geddes, C. D., and Levine, M.M. (2011). Ultra-fast and Sensitive detection of Non-typhoidal Salmonella using Microwave-Accelerated Metal-Enhanced Fluorescence (MAMEF), PloS One, 6, 4, e18700.