Chris D. Geddes

Editorial Metal-Enhanced Fluorescence

As fluorescence spectroscopists we are mostly all yields, decreased lifetimes, increased photostability, and familiar with doing spectroscopy in bulk samples, where an increase in Forster transfer distances and directional the solutions are typically transparent to the emitted radia- emission. Such opportunities are truly refreshing, because tion, and the fluorophores emit isotropically into free although fluorescence methodology and subsequent space and are observed in the far field. There may be applications are routinely practiced in many laboratories changes in the refractive index, such as for a fluorophore around the world, little research on such basic principles in a membrane, but these changes typically have only has probably hindered fluorescence growth from further minor effects on the fluorophores free-space spectral revolutionalizing the analytical and clinical sciences. For properties.

Metal-enhanced fluorescence

Preface. Contributors. Mental-Enhanced Fluorescence: Progress Towards a Unified Plasmon-Fluorophore Description (Kadir Aslan and Chris D. Geddes). Spectral Profile Modifications In Metal-Enhanced Fluorescence (E. C. Le Ru, J. Grand, N. Felidj, J. Aubard, G. Levi, A. Hohenau, J. R. Krenn, E. Blackie and P. G. Etchegoin). The Role Of Plasmonic Engineering In Metal-Enhanced Fluorescence (Daniel J. Ross, Nicholas P.W. Pieczonka and R. F. Aroca). Importance of Spectral Overlap: Fluorescence Enhancement by Single Metal Nanoparticles (Keiko Munechika, Yeechi Chen, Jessica M. Smith and.David S. Ginger). Near-IR Metal Enhanced Fluorescence And Controlled Colloidal Aggregation (Jon P. Anderson, Mark Griffiths, John G. Williams, Daniel L. Grone, Dave L. Steffens, and Lyle M. Middendorf). Optimisation Of Plasmonic Enhancement Of Fluorescence For Optical Biosensor Applications (Colette McDonagh, Ondrej Stranik, Robert Nooney and Brian D. MacCraith). Microwave-Accelerated Metal-Enhanced Fluorescence (Kadir Aslan and Chris D. Geddes). Localized Surface Plasmon Coupled Fluorescence Fiber Optic Based Biosensing (Chien Chou, Ja-An Annie Ho, Chii-Chang Chen, Ming-Yaw, Wei-Chih Liu, Ying-Feng Chang, Chen Fu, Si-Han Chen and Ting-Yang Kuo). Surface Plasmon Enhanced Photochemistry (Stephen K. Gray). Metal-Enhanced Generation of Oxygen Rich Species (Yongxia Zhang, Kadir Aslan and Chris D. Geddes). Synthesis Of Anisotropic Noble Metal Nanoparticles (Damian Aherne, Deirdre M. Ledwith and John M. Kelly). Enhanced Fluorescence Detection Enabled By Zinc Oxide Nanomaterials (Jong-in Hahm). ZnO Platforms For Enhanced Directional Fluorescence Applications (H.C. Ong, D.Y. Lei, J. Li and J.B. Xu). E-Beam Lithography And Spontaneous Galvanic Displacement Reactions For Spatially Controlled MEF Applications (Luigi Martiradonna, S. Shiv Shankar and Pier Paolo Pompa). Metal-Enhanced Chemiluminescence (Yongxia Zhang, Kadir Aslan and Chris D. Geddes). Enhanced Fluorescence From Gratings (Chii-Wann Lin, Nan-Fu Chiu, Jiun-Haw Lee and Chih-Kung Lee). Enhancing Fluorescence with Sub-Wavelength Metallic Apertures (Steve Blair and Jerome Wenger). Enhanced Multi-Photon Excitation of Tryptophan-Silver Colloid (Renato E. de Araujo, Diego Rativa and Anderson S. L. Gomes). Plasmon-enhanced radiative rates and applications to organic electronics (Lewis Rothberg and Shanlin Pan). Fluorescent Quenching Gold Nanoparticles: Potential Biomedical Applications (Xiaohua Huang, Ivan H. El-Sayed, and Mostafa A. El-Sayed). Index.

Advances in Surface-Enhanced Fluorescence

We report recent achievements in metal-enhanced fluorescence from our laboratory. Several fluorophore systems have been studied on metal particle-coated surfaces and in colloid suspensions. In particular, we describe a distance dependent enhancement on silver island films (SIFs), release of self-quenching of fluorescence near silver particles, and the applications of fluorescence enhancement near metalized surfaces to bioassays. We discuss a number of methods for various shaped silver particle deposition on surfaces.

Annealed Silver-Island Films for Applications in Metal-Enhanced Fluorescence: Interpretation in Terms of Radiating Plasmons

The effects of thermally annealed silver island films have been studied with regard to their potential applicability in applications of metal-enhanced fluorescence, an emerging tool in nano-biotechnology. Silver island films were thermally annealed between 75 and 250°C for several hours. As a function of both time and annealing temperature, the surface plasmon band at ≈420 nm both diminished and was blue shifted. These changes in plasmon resonance have been characterized using both absorption measurements, as well as topographically using Atomic Force Microscopy. Subsequently, the net changes in plasmon absorption are interpreted as the silver island films becoming spherical and growing in height, as well as an increased spacing between the particles. Interestingly, when the annealed surfaces are coated with a fluorescein-labeled protein, significant enhancements in fluorescence are osbserved, scaling with annealing temperature and time. These observations strongly support our recent hypothesis that the extent of metal-enhanced fluorescence is due to the ability of surface plasmons to radiate coupled fluorophore fluorescence. Given that the extinction spectrum of the silvered films is comprised of both an absorption and scattering component, and that these components are proportional to the diameter cubed and to the sixth power, respectively, then larger structures are expected to have a greater scattering contribution to their extinction spectrum and, therefore, more efficiently radiate coupled fluorophore emission. Subsequently, we have been able to correlate our increases in fluorescence emission with an increased particle size, providing strong experiment evidence for our recently reported metal-enhanced fluorescence, facilitated by radiating plasmons hypothesis.

Optical halide sensing using fluorescence quenching: theory, simulations and applications - a review

In the last century the production and application of halides assumed an ever greater importance. In the fields of medicine, dentistry, plastics, pesticides, food, photography etc many new halogen containing compounds have come into everyday use. In an analogous manner many techniques for the detection and determination of halogen compounds and ions have been developed with scientific journals reporting ever more sensitive methods. The 19th century saw the discovery of what is now thought of as a classical method for halide determination, namely the quenching of fluorescence. However, little analytically was done until over 100 years after its discovery, when the first halide sensors based on the quenching of fluorescence started to emerge. Due to the typical complexity of fluorescence quenching kinetics of optical halide sensors and their lack of selectivity, they have found little if any place commercially, despite their sensitivity, where other techniques such as ion-selective electrodes, x-ray fluorescence spectroscopy and colorimetry have dominated the analytical market. In this review article the author summarizes the relevant theory and work to date for halide sensing using fluorescence quenching methods and outlines the future potential that fluorescence quenching based optical sensors have to offer in halide determination.

A Glucose Sensing Contact Lens: A Non-Invasive Technique for Continuous Physiological Glucose Monitoring

We have developed a range of glucose sensing contact lenses, using a daily, disposable contact lens embedded with newly developed boronic acid containing fluorophores. Our findings show that our approach may be suitable for the continuous monitoring of tear glucose levels in the range 50–1000 μM, which typically track blood glucose levels, which are ≈5–10 fold higher. Our non-invasive approach may well offer an alternative solution to current invasive glucose monitoring techniques for diabetes, such as “finger pricking.”

Saccharide Sensing Using Gold and Silver Nanoparticles-A Review

We review new methodologies for glucose sensing from our laboratories based on the specific biological interactions between Con A, dextran-coated gold nanoparticles and glucose, and the interactions between dextran, glucose, and boronic-acid capped silver nanoparticles in solution. Our new approaches promise new tunable glucose sensing platforms. Dextran-coated gold nanoparticles were aggregated with the addition of Con A resulting in increase an in absorbance of nanoparticles at 650 nm, where the post-addition of glucose caused the dissociation of the aggregates and thus a decrease in the absorbance at 650 nm. The interaction of glucose and dextran with boronic acid-capped silver nanoparticles in solution resulted in enhanced luminescence intensity cumulatively due to surface-enhanced fluorescence and the decrease in absorbance at 400 nm, with an increase in absorbance at 640 nm. Lifetime measurements were used to distinguish the contribution from the surface-enhanced fluorescence. TEM was employed to assess the aggregation of nanoparticles.

Metal-enhanced emission from indocyanine green: a new approach to in vivo imaging

Indocyanine green (ICG) is widely used in medical imaging and testing. Its complex spectral behavior and low quantum yield limits some applications. We show that proximity of ICG to a metallic silver particle increases its intensity approximately 20-fold and decreases the decay time. Since the rate of photobleaching is not increased, our results suggest that ICG-silver particle complexes can yield at least 20-fold more photons per ICG molecule for improved medical imaging.

Plasmonic engineering of singlet oxygen generation

In this article, we report metal-enhanced singlet oxygen generation (ME1O2). We demonstrate a direct relationship between the singlet oxygen yield of a common photosensitizer (Rose Bengal) and the theoretical electric field enhancement or enhanced absorption of the photosensitizer in proximity to metallic nanoparticles. Using a series of photosensitizers, sandwiched between silver island films (SiFs), we report that the extent of singlet oxygen enhancement is inversely proportional to the free space singlet oxygen quantum yield. By modifying plasmon coupling parameters, such as nanoparticle size and shape, fluorophore/particle distance, and the excitation wavelength of the coupling photosensitizer, we can readily tune singlet oxygen yields for applications in singlet oxygen-based clinical therapy.

Metal-Enhanced Fluorescence Solution-Based Sensing Platform

In recent years our laboratories have reported the favorable effects for fluorophores placed in close proximity to surface immobilized silver nanostructures. These include; greater quantum yields, reduced lifetimes (increased photostability) and directional emission. However, while these findings are likely to find multifarious applications for surface assays based on enhanced fluorescence detection, a solution based enhanced sensing platform has yet to be realized. In this short, note, we show how SiO2-coated silver colloids, indeed provide for a solution based enhanced fluorescence sensing platform with a 3–5 fold enhancement typically observed.