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Chris D Geddes

Publications and source records attributed to Chris D Geddes.

At least 37 records · Page 2Linked to original sources
PubMed2005

Boronic acid fluorescent sensors for monosaccharide signaling based on the 6-methoxyquinolinium heterocyclic nucleus: progress toward noninvasive and continuous glucose monitoring.

The synthesis, characterization, and spectral properties of strategically designed boronic acid containing fluorescent sensors, o-, m-, p-BMOQBA, for the potential detection of tear glucose concentrations when immobilized in plastic disposable contact lenses is described. The new probes, BMOQBAs, consist of the 6-methoxyquinolinium nucleus as a fluorescent indicator, and the boronic acid moiety as a glucose chelating group. A control compound BMOQ, which has no boronic acid group and therefore does not bind monosaccharides has also been prepared. In this paper, we show that structural design considerations of the new probes have afforded for their compatibility within the lenses, with reduced probe sugar-bound pK(a) favorable with the mildly acidic lens environment. In addition, the new probes are readily water soluble, have high quantum yields, and can be prepared by a simple one-step synthetic procedure.

Boronic Acids↗
PubMed2005

Enhanced ratiometric pH sensing using SNAFL-2 on silver island films: metal-enhanced fluorescence sensing.

We have explored the opportunities for enhanced ratiometric pH sensing using the well-known carboxy seminaphthofluorescein (SNAFL-2) and silver island films (SiFs). Our results show that the metallic surfaces can provide up to a 40-fold increase in probe fluorescence intensity as compared to nonmetallic surfaces with the same probe coverage. However, while the S/N is significantly better for pH sensing, the emission wavelength ratiometric values are similar to that obtained in solution, due to the fact that the emission of both the acidic and basic forms of the probe are enhanced to similar extents. To the best of our knowledge this is the first report of enhanced ratiometric fluorescence sensing on metallic surfaces.

Fluoresceins↗
PubMed2005

Enhanced lanthanide luminescence using silver nanostructures: opportunities for a new class of probes with exceptional spectral characteristics.

The photophysical effects of europium tetracycline immobilized in thin polyvinyl alcohol films coated onto silver nanostructures have been investigated. Complimentary to recent reports from our laboratories that the close proximity of luorophores to silver nanostructures can enhance their intrinsic radiative decay rate, we show that up to a 16-fold enhancement in lanthanide luminescence is possible, accompanied by a notable reduction in luminescence lifetime. These results suggest the potential future development of a new class of significantly brighter lanthanide based probes with exceptional spectral properties, which can probably undergo significantly more excitation-emission event cycles due to the reduced lifetime, substantially increasing detectability.

Europium↗
PubMed2005

Metal-enhanced fluorescence from plastic substrates.

We report the first findings of Metal-Enhanced Fluorescence (MEF) from modified plastic substrates. In the past several years our laboratories have reported the favorable effects of fluorophores in close proximity to silver nanoparticles. These effects include, enhanced fluorescence intensities, (increased detectability), and reduced lifetimes, (enhanced fluorophore photostability). All of these reports have featured silver nanostructures and fluorophores which have been immobilized onto clean glass or quartz surfaces. In this report we show how plastic surfaces can be modified to obtain surface functionality, which in turn allows for silver deposition and therefore metal-enhanced fluorescence of fluorophores positioned above the silver using a protein spacer. Our findings show that plastic substrates are ideal surfaces for metal-enhanced phenomena, producing similar enhancements as compared to clean glass surfaces. Subsequently, we speculate that plastic substrates for MEF will find common place, as compared to the more expensive and less versatile traditional silica based supports.

Fluorescence↗
PubMed2005

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 degrees C for several hours. As a function of both time and annealing temperature, the surface plasmon band at approximately 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 observed, 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.

Journal Article↗
PubMed2005

Plasmon light scattering in biology and medicine: new sensing approaches, visions and perspectives.

Surface plasmons are collective oscillations of free electrons at metallic surfaces. These oscillations can give rise to the intense colors of solutions of plasmon resonance nanoparticles and/or very intense scattering. While the use of plasmonic particle absorption based bioaffinity sensing is now widespread throughout biological research, the use of their scattering properties is relatively ill explored. We refer to the use, utility and control of surface plasmons as plasmonics. In this review and forward-looking article, we discuss the current opinions and uses of plasmonics, as well as speculate on areas of future research. These include the use of plasmon scatter for long-range immunosensing and macromolecular conformation studies, as well as the ability to Stokes shift plasmon scatter, a plasmonics phenomenon recently referred to as metal-enhanced fluorescence.

Fluorescence↗
PubMed2005

A glucose-sensing contact lens: from bench top to patient.

In the past few years we have seen the development of several new technologies for the continuous and non-invasive monitoring of physiological glucose, such as the GlucoWatch, glucose-sensing skin patches and approaches based on a glucose-sensing tattoo. One approach that differs from current thinking is based on the determination and monitoring of tear glucose, which is well known to track blood glucose with an approximate 30 min lag time, using disposable and colorless contact lenses. These contact lenses can be worn by diabetics who can colorimetrically see changes in their contact lens color or other fluorescence-based properties, giving an indication of tear and blood glucose levels.

Biosensing Techniques↗
PubMed2005

Metal-enhanced fluorescence: an emerging tool in biotechnology.

Over the past 15 years, fluorescence has become the dominant detection/sensing technology in medical diagnostics and biotechnology. Although fluorescence is a highly sensitive technique, where single molecules can readily be detected, there is still a drive for reduced detection limits. The detection of a fluorophore is usually limited by its quantum yield, autofluorescence of the samples and/or 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 these fluorophore photophysical constraints. The use of fluorophore-metal interactions has been termed radiative decay engineering, metal-enhanced fluorescence or surface-enhanced fluorescence.

Biotechnology↗
PubMed2004

Complexation of polysaccharide and monosaccharide with thiolate boronic acid capped on silver nanoparticle.

Synthesized thiolate boronic acid was found to complex with both a polysaccharide (dextran) and a monosaccharide (glucose) with similar affinities but displayed more affinity with dextran than with glucose when capped as a ligand on silver nanoparticle. Coupling on multiple sites of dextran, the silver particles were aggregated. The aggregated particles displayed a decrease of absorbance at 397 nm and an increase at 640 nm. Luminescence intensity displayed an upward deviation increase with the concentration of dextran. The luminescence spectral change was ascribed to surface-enhanced fluorescence by the enhanced field from the aggregated metallic particles.

Boronic Acids↗
PubMed2004

Nanogold-plasmon-resonance-based glucose sensing.

Noble metal nanoparticles are well known for their strong interactions with light through the resonant excitations of the collective oscillations of the conduction electrons on the particles, the so-called surface plasmon resonances. The close proximity of two nanoparticles is known to result in a red-shifted resonance wavelength peak, due to near-field coupling. We have subsequently employed this phenomenon and developed a new approach to glucose sensing, which is based on the aggregation and disassociation of 20-nm gold particles and the changes in plasmon absorption induced by the presence of glucose. High-molecular-weight dextran-coated nanoparticles are aggregated with concanavalin A (Con A), which results in a significant shift and broadening of the gold plasmon absorption. The addition of glucose competitively binds to Con A, reducing gold nanoparticle aggregation and therefore the plasmon absorption when monitored at a near-red arbitrary wavelength. We have optimized our plasmonic-type glucose nanosensors with regard to particle stability, pH effects, the dynamic range for glucose sensing, and the observation wavelength to be compatible with clinical glucose requirements and measurements. In addition, by modifying the amount of dextran or Con A used in nanoparticle fabrication, we can to some extent tune the glucose response range, which means that a single sensing platform could potentially be used to monitor microM --> mM glucose levels in many physiological fluids, such as tears, blood, and urine, where the glucose concentrations are significantly different.

Biosensing Techniques↗
PubMed2004

Ophthalmic glucose sensing: a novel monosaccharide sensing disposable and colorless contact lens.

We have developed a technology for continuous tear glucose monitoring, and therefore potentially blood glucose monitoring, using a daily use, disposable contact lens embedded with sugar-sensing boronic acid containing fluorophores. The novelty of our approach is two fold. Firstly, the notion of sensing extremely low glucose concentrations in tears by our approach, and secondly, the unique compatibility of our new probes with the internal environment of the disposable, off-the-shelf, contact lenses, chosen because the physiological compatibility of disposable plastic contact lenses has already been assessed and optimized with regard to vision correction, size and oxygen/analyte permeability. Our findings show that our approach is indeed suitable for the continuous monitoring of tear glucose levels in the concentration range (50-500 microM), which track blood glucose levels which are approximately 5-10 fold higher. We believe our approach offers unique opportunities for non-invasive continuous glucose monitoring for diabetics, especially since many have eye disorders and require vision correction by either contact lenses or glasses, which is thought to be due to glycation of protein in blood vessels.

Boronic Acids↗
PubMed2004

Excitation and emission wavelength ratiometric cyanide-sensitive probes for physiological sensing.

We characterize three new fluorescent probes that show both spectral shifts and intensity changes in the presence of aqueous cyanide, allowing for both excitation and fluorescence emission wavelength ratiometric and colorimetric sensing. The relatively high binding constants of the probes for cyanide enables a distinct colorimetric change to be visually observed with as little as 10 microM cyanide. The response of the new probes is based on the ability of the boronic acid group to interact with the CN(-) anion, changing from the neutral form of the boronic acid group R-B(OH)(2) to the anionic R-B(-)(OH)3 form, which is an electron-donating group. The presence of an electron-deficient quaternary heterocyclic nitrogen center and a strong electron-donating amino group in the 6 position on the quinolinium backbone provides for the spectral changes observed upon CN(-) complexation. We have determined the binding constants for the ortho-, meta-, and para-boronic acid probes to be 0.12, 0.17, and 0.14 microM(-3). In addition we have synthesized a control compound that does not contain the boronic acid moiety, allowing for structural comparisons and a rationale for the sensing mechanism to be made. Finally we show that the affinity for monosaccharides, such as glucose or fructose, is relatively low as compared to that for cyanide, enabling the potential detection of cyanide in physiologies up to lethal levels.

Biosensing Techniques↗
PubMed2004

Noninvasive continuous monitoring of physiological glucose using a monosaccharide-sensing contact lens.

We have tested the feasibility of tear glucose sensing using a daily, disposable contact lens embedded with boronic acid-containing fluorophores as a potential alternative to current invasive glucose-monitoring techniques. Our findings show that our approach may, indeed, be suitable for the continuous monitoring of tear glucose levels in the range 50-500 microM, which track blood glucose levels that are approximately 5-10-fold higher. We compare the response of the boronic acid probes in the contact lens to solution-based measurements and can conclude that both the pH and polarity within the contact lens need to be considered with respect to choosing/designing and optimizing glucose-sensing probes for contact lenses.

Biosensing Techniques↗
PubMed2004

Roughened silver electrodes for use in metal-enhanced fluorescence.

Roughened silver electrodes are widely used for surface-enhanced Raman scattering (SERS). We tested roughened silver electrodes for metal-enhanced fluorescence. Constant current between two silver electrodes in pure water resulted in the growth of fractal-like structures on the cathode. This electrode was coated with a monolayer of human serum albumin (HSA) protein that had been labeled with a fluorescent dye, indocyanine green (ICG). The fluorescence intensity of ICG-HSA on the roughened electrode increased by approximately 50-fold relative to the unroughened electrode, which was essentially non-fluorescent and increased typically two-fold as compared to the silver anode. No fractal-like structures were observed on the anode. Lifetime measurements showed that at least part of the increased intensity was due to an increased radiative decay rate of ICG. In our opinion, the use of in situ generated roughened silver electrodes will find multifarious applications in analytical chemistry, such as in fluorescence based assays, in an analogous manner to the now widespread use of SERS. To the best of our knowledge this is the first report of roughened silver electrodes for metal-enhanced fluorescence.

Electrodes↗
PubMed2004

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.

Algorithms↗
PubMed2004

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.

Algorithms↗
PubMed2004

Plasmonics.

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Biosensing Techniques↗