Biomedical subjects

Chris D Geddes

Publications and source records attributed to Chris D Geddes.

At least 19 recordsLinked to original sources

PubMed2006

Metal-enhanced phosphorescence: interpretation in terms of triplet-coupled radiating plasmons.

We report our detailed metal-enhanced phosphorescence (MEP) findings using Rose Bengal at low temperature. Silver Island Films (SiFs) in close proximity to Rose Bengal significantly enhance the phosphorescence emission intensity. In this regard, a 5-fold brighter phosphorescence intensity of Rose Bengal was observed from SiFs as compared to a glass control sample at 77 K. In addition, several factors affecting MEP, such as distance dependence and silver film morphology, were also investigated. Our findings suggest that both singlet and triplet states can couple to surface plasmons and enhance both fluorescence and phosphorescence yields. This finding suggests that MEP can be used to promote triplet-based assays, such as those used in photodynamic therapy.

Fluorescent Dyes↗

PubMed2006

Metal-enhanced fluorescence from gold surfaces: angular dependent emission.

The first observation of Metal-Enhanced Fluorescence (MEF) from large gold colloids is presented. Gold colloids, 40 and 200 nm diameter, were deposited onto glass substrates in a homogeneous fashion. The angular-dependent fluorescence emission of FITC-HSA, adsorbed onto gold colloids, was measured on a rotating stage which was used to evaluate MEF at all spatial angles. The emission intensity of FITC-HSA was found to be up to 2.5-fold brighter than the emission on bare glass substrates at an angle of 270 degrees. This is explained by the Radiating Plasmon Model, whereby the combined system, composed of the fluorophore and the metal colloids, emits with the photophysical characteristics of the fluorophore, after the excitation and the partial radiationless energy transfer between the excited states of the fluorophore and the surface plasmons of the gold colloids. The fluorescence enhancement was found to be higher with 200 nm gold colloids as compared to 40 nm colloids due to the increased contribution of the scattering portion of the 200 nm gold colloid extinction spectrum. These observations suggest that gold colloids could be used in MEF applications, offering more stable surfaces than the commonly used silvered surfaces, for applications requiring longer term storage and use.

Colloids↗

PubMed2006

Microwave triggered metal enhanced chemiluminescence: Quantitative protein determination.

We present a new technology that offers a faster alternative to the chemiluminescence-based detection that is used in protein assay platforms today. By combining the use of silver nanostructures with chemiluminescent species, a technique that our laboratories have recently shown can enhance the system photon flux over 50-fold, with the use of low-power microwave heating to additionally accelerate, in essence "trigger", chemiluminescence-based reactions, then both ultrafast and ultrabright chemiluminescence assays can be realized. In addition, the preferential heating of the nanostructures by microwaves affords for microwave triggered metal enhanced chemiluminescence (MT-MEC) to be localized in proximity to the silvered surfaces, alleviating unwanted emission from the distal solution. To demonstrate MT-MEC, we have constructed a model assay sensing platform on both silvered and glass surfaces, where comparison with the identical glass substrate-based assay serves to confirm the significant benefits of using silver nanostructures for metal-enhanced chemiluminescence. Our new model assay technology can detect femtomoles of biotinylated BSA in less than 2 min and can indeed be modified to both detect and quantify a great many other biomolecules as well. As compared to traditional western blot approaches, MT-MEC offers protein quantification, high-sensitivity detection combined with ultrafast assay times, i.e., <2 min.

Animals↗

PubMed2006

Multicolor directional surface plasmon-coupled chemiluminescence.

In reports over the past several years, we have demonstrated the efficient collection of optically excited fluorophore emission by its coupling to surface plasmons on thin metallic films, where the coupled luminescence was highly directional and polarized. This phenomenon is referred to as surface plasmon-coupled emission (SPCE). In this current study, we have extended this technique to include chemiluminescing species and subsequentially now report the observation of surface plasmon-coupled chemiluminescence (SPCC), where the luminescence from chemically induced electronic excited states couples to surface plasmons in thin continuous metal films. The SPCC is highly directional and predominantly p-polarized, strongly suggesting that the emission is from surface plasmons instead of the luminophores themselves. This indicates that surface plasmons can be directly excited from chemically induced electronic excited states and excludes the possibility that the plasmons are created by incident excitation light. This phenomenon has been observed for a variety of chemiluminescent species in the visible spectrum, ranging from blue to red, and also on a variety of metals, namely, aluminum, silver, and gold. Our findings suggest new chemiluminescence sensing strategies on the basis of localized, directional, and polarized chemiluminescence detection, especially given the wealth of assays that currently employ chemiluminescence-based detection.

Aluminum↗

PubMed2006

Multicolor microwave-triggered metal-enhanced chemiluminescence.

We describe a novel platform technology for both significantly enhancing and obtaining chemiluminescence signatures "on-demand", subsequently named Microwave-Triggered Metal-Enhanced Chemiluminescence. By combining the use of silver nanoparticles to plasmon enhance chemiluminescence with the use of low power microwaves to localize heating around the nanostructures, we can both optically amplify and trigger chemiluminescence reactions. This approach is a significant advantage over traditional chemiluminescence techniques and methodologies, such as those used for Western Blots, which typically require long periods of time to collect chemiluminescence and offer few possibilities of optically amplifying the signatures.

Algorithms↗

PubMed2006

Microwave-triggered metal-enhanced chemiluminescence (MT-MEC): application to ultra-fast and ultra-sensitive clinical assays.

In this rapid communication we describe a new approach to protein detection with chemiluminescence. By combining common practices in protein detection with chemiluminescence, microwave technology, and metal-enhanced chemiluminescence, we show that we can use low power microwaves to substantially increase enzymatic chemiluminescent reaction rates on metal substrates. As a result, we have found that we can in essence trigger chemiluminescence with low power microwave (Mw) pulses and ultimately, perform on-demand protein detection assays. Using microwave triggered metal-enhanced chemiluminescence (MT-MEC), we not only improve the sensitivity of immunoassays with enhanced signal-to-noise ratios, but we also show that we can accurately quantify protein concentrations by integrating the photon flux for discrete time intervals.

Avidin↗

PubMed2006

Fast and sensitive DNA hybridization assays using microwave-accelerated metal-enhanced fluorescence.

A new, fast, and sensitive DNA hybridization assay platform based on microwave-accelerated metal-enhanced fluorescence (MAMEF) is presented. Thiolated oligonucleotide anchors were immobilized onto silver nanoparticles on a glass substrate. The hybridization of the complementary fluorescein-labeled DNA target with the surface-bound oligonucleotides was completed within 20 s upon heating with low-power microwaves. In addition, the signal is optically amplified, a consequence of close proximity of the fluorophore to the silvered substrate. In this proof-of-principle methodology, as low as 50 nM of a target DNA was detected, although we envisage far-lower detection limits. Control experiments, where the surface-bound oligonucleotide was omitted, were also performed to determine the extent of non-specific binding. In these studies a significantly reduced non-specific adsorption was found when using microwave heating near to silvered structures as compared to room temperature incubation. These findings suggest that MAMEF could be a most useful alternative to the DNA hybridization assays used today, especially with regard to substantially increasing both the assay rapidity and sensitivity.

Aminoacridines↗

PubMed2006

Metal-enhanced chemiluminescence.

In this short paper we report the interactions of silver island films with chemiluminescing species. Our findings show that silver island films can increase the detectability of chemiluminescent reactions/species, with an approximately 5-fold increase in signal intensity. This finding not only suggests the use of silver nanostructures to amplify chemiluminscent signatures in assay platforms, and therefore increase the detectability of analytes or biospecies, but more importantly, suggests that surface plasmons can be directly excited by chemically induced electronically excited molecules. This finding is of significance towards our understanding of fluorophore-metal interactions, a relatively new near-field fluorescence concept, recently named metal-enhanced fluorescence and also radiative decay engineering.

Energy Transfer↗

PubMed2006

Microwave-Accelerated Metal-Enhanced Fluorescence (MAMEF) with silver colloids in 96-well plates: Application to ultra fast and sensitive immunoassays, High Throughput Screening and drug discovery.

Fluorescence detection is the basis of most assays used in drug discovery and High Throughput Screening (HTS) today. In all of these assays, assay rapidity and sensitivity is a primary concern, the sensitivity determined by both the quantum yield of the fluorophores and efficiency of the detection system, while rapidity is determined by the physical and biophysical parameters of temperature, concentration, assay bioaffinity, etc. In this paper we describe a platform technology that promises to fundamentally address these two physical constraints of sensitivity and rapidity. By combining the use of Metal-Enhanced Fluorescence (MEF), a near-field effect that can significantly enhance fluorescence signatures, with low power microwave heating, we can significantly increase the sensitivity of surface assays as well as >95% kinetically complete the assay within a few seconds. In addition, the metallic nanostructures used to facilitate MEF appear to be preferentially heated as compared to the surface assay fluid, advantageously localizing the MEF and heating around the nanostructures. To demonstrate proof of principle, a 96-well plate has been functionalized with silver nanostructures, and a model protein avidin-biotin assay studied. In our findings, a greater than 5-fold fluorescence enhancement coupled with a approximately 90-fold increase in assay kinetics was observed, but with no assay washing steps needed due to the silver-enhanced evanescent field mode of excitation. These findings promise to strongly facilitate high throughput fluorescence-based processes, such as in biology, drug discovery and general compound screening.

Colloids↗

PubMed2006

Metal-enhanced fluorescence-based RNA sensing.

In this communication, we present the proof-of-principle of a new RNA sensing technique, based on metal-enhanced fluorescence, which may improve the potential of solid substrate-based RNA capture assays. In this regard, the detection of RNA is accomplished by annealing a target RNA tagged with a fluorophore to a DNA anchor probe in a single step on a solid surface, where the fluorescence signal is enhanced by silver nanoparticles. Furthermore, the proposed method is highly amenable to high-throughput screening applications and is capable of detecting less than 25 fmol of RNA at a signal-to-noise ratio greater than 20, in several hours compared to that of reverse transcription-PCR at >24 h.

Biosensing Techniques↗

PubMed2005

Microwave-accelerated metal-enhanced fluorescence (MAMEF): application to ultra fast and sensitive clinical assays.

In this rapid communication we describe an exciting platform technology that promises to fundamentally address two underlying constraints of modern assays and immunoassays, namely sensitivity and rapidity. By combining the use of Metal-enhanced Fluorescence (MEF) with low power microwave heating (Mw), we can significantly increase the sensitivity of surface assays as well as >95% kinetically complete the assay within a few seconds. This technology is subsequently likely to find significant importance in certain clinical assays, such as in the clinical assessment of myoglobin, where both the assay rapidity and sensitivity are paramount for the assessment and treatment of acute myocardial infarction.

Fluorescence↗

PubMed2005

Microwave-accelerated metal-enhanced fluorescence: platform technology for ultrafast and ultrabright assays.

We describe an exciting assay platform technology that promises to fundamentally address two underlying physical constraints of modern assays and immunoassays, namely, assay sensitivity and rapidity. By combining the use of metal-enhanced fluorescence with low-power microwave heating, we can indeed significantly increase the sensitivity of surface assays as well as >95 % kinetically complete the assay within a few seconds. Subsequently, this new technology promises to fundamentally change the way we currently employ immunoassays in clinical medicine. This new model platform system can be potentially applied to many other important assays, such as to the clinical assessment of myoglobin, where both assay speed and sensitivity is paramount for the assessment and treatment of acute myocardial infarction. To demonstrate the utility of microwave-accelerated metal-enhanced fluorescence (MAMEF), we show that a simple protein-based assay system can be optically amplified approximately 10-fold by using silver nanostructures, while being kinetically complete in less than 20 s. This new platform approach is subsequently over 10-fold more sensitive and approximately 90 times faster than a control assay that operates both at room temperature and without the use of metal-enhanced fluorescence. Finally, we show that low-power heating by microwaves in our model system does not denature proteins, as evidenced by no protein structural changes, probed by fluorescence resonance energy transfer.

Avidin↗

PubMed2005

Angular-ratiometric plasmon-resonance based light scattering for bioaffinity sensing.

We describe an exciting opportunity for affinity biosensing using a ratiometric approach to the angular-dependent light scattering from bioactivated and subsequently aggregated noble metal colloids. This new model sensing platform utilizes the changes in particle scattering from very small colloids, which scatter light according to traditional Rayleigh theory, as compared to the changes in scattering observed by much larger colloidal aggregates, formed due to a bioaffinity reaction. These larger aggregates no longer scatter incident light in a Cos(2) theta dependence, as is the case for Rayleigh scattering, but instead scatter light in an increased forward direction as compared to the incident geometry. By subsequently taking the ratio of the scattered intensity at two angles, namely 90 degrees and 140 degrees , relative to the incident light, we can follow the association of biotinylated bovine serum albumin-coated 20 nm gold colloids, cross-linked by additions of streptavidin. This new model system can be potentially applied to many other nanoparticle assays and has many advantages over traditional fluorescence sensing and indeed light-scattering approaches. For example, a single nanoparticle can have the equivalent scattered intensity as 10(5) fluorescing fluorescein molecules substantially increasing detection; the angular distribution of scattered light from noble metal colloids is substantially easier to predict as compared to fluorescence; the scattered light is not quenched by biospecies; the ratiometric measurements described here are not dependent on colloid concentration as are other scattering techniques; and finally, the noble metal colloids are not prone to photodestruction, as is the case with organic fluorophores.

Affinity Labels↗

PubMed2005

Metal-enhanced fluorescence using anisotropic silver nanostructures: critical progress to date.

In this critical and timely review, the effects of anisotropic silver nanostructures on the emission intensity and photostability of a key fluorophore that is frequently used in many biological assays is examined. The silver nanostructures consist of triangular, rod-like, and fractal-like nanoparticles of silver deposited on conventional glass substrates. The close proximity to silver nanostructures results in greater intensity and photostability of the fluorophore than for fluorophores solely deposited on glass substrates. These new anisotropic silver nanostructure-coated surfaces show much more favorable effects than silver island films or silver colloid-coated substrates. Subsequently, the use of metal-enhanced fluorescence (MEF) for biosensing applications is discussed.

Anisotropy↗

PubMed2005

Rapid deposition of triangular silver nanoplates on planar surfaces: application to metal-enhanced fluorescence.

A simple and rapid wet-chemical technique for the deposition of silver triangles on conventional glass substrates, which alleviates the need for lithography, has been developed. The technique is based on the seed-mediated cetyltrimethylammonium-bromide-directed growth of silver triangles on glass surfaces, where smaller spherical silver seeds that were attached to the surface were subsequently converted and grown into silver triangles in the presence of a cationic surfactant and silver ions. The size of the silver triangles was controlled by sequential immersion of silver seed-coated glass substrates into a growth solution and by the duration time of immersion. Atomic force microscopy studies revealed that the size of the silver triangles ranged between 100 and 500 nm. Interestingly, these new surfaces are a significant improvement over traditional silver island films for applications in metal-enhanced fluorescence. A routine 16-fold enhancement in emission intensity was typically observed, for protein-immobilized indocyanine green, with a relatively very low loading density of silver triangles on the glass surface.

Adsorption↗

PubMed2005

Nanogold plasmon resonance-based glucose sensing. 2. Wavelength-ratiometric resonance light scattering.

Gold colloids are well known to display strong plasmon absorption bands due to electron oscillations induced by the incident light. When the colloids are in proximity, the plasmon absorption bands are often perturbed. This has enabled us recently to successfully develop a glucose sensing platform based on the disassociation of dextran-coated gold colloids, cross-linked with Con A, by glucose. However, a much more useful and simpler property of gold colloids, which has been ill explored with regard to sensing, is their ability to efficiently scatter excitation light. We have found that our nanogold sensing aggregates are indeed efficient light scatters around the nanogold plasmon absorption band. By measuring the ratio of scattered light intensities at two different arbitrary wavelengths, 560 and 680 nm, glucose concentrations can be readily determined from a few millimolar up to approximately 60 mM, using a simple white light LED and detection system. Further, by measuring the ratio of the scattered intensities, this sensing approach is independent of the total sensing aggregate concentration and the excitation and detection instrumentation fluctuations or drifts. This simplistic and low-cost approach to glucose sensing, coupled with the sensing aggreagates' ability to scatter red light, suggests the potential use of these aggregates for use in physiological transdermal glucose monitoring, either for implantable skin sensors or glucose sensing tattoos (discussed later).

Biosensing Techniques↗

PubMed2005

Enhanced fluorescence cyanide detection at physiologically lethal levels: reduced ICT-based signal transduction.

Three water-soluble fluorescent probes have been specifically designed to determine free cyanide concentrations up to physiologically lethal levels, >20 microM. The probes have been designed in such a way as to afford many notable sensing features, which render them unique with regard to signal transduction, photophysical characteristics, and their application to physiological cyanide determination and safeguard. The probes are readily able to reversibly bind free aqueous cyanide with dissociation constants around 4 microM3. Subsequent cyanide binding modulates the intramolecular charge transfer within the probes, a change in the electronic properties within the probes, resulting in enhanced fluorescence optical signals as a function of increased solution cyanide concentration. The ground-state chelation with cyanide produces wavelength shifts, which also enable the probes to sense cyanide in both an excitation and emission ratiometric manner, in addition to enhanced fluorescence signaling. This has enabled a generic cyanide sensing platform to be realized that is not dependent on fluorescent probe concentration, probe photodegradation, or fluctuations in the intensity of any employed excitation sources, ideal for remote cyanide sensing applications. Further, the >600 nm fluorescence emission of the probes potentially allows for enhanced fluorescence ratiometric cyanide sensing in the optical window of tissues and blood, facilitating their use for the transdermal monitoring of cyanide for mammalian safeguard or postmortem in fire victims, both areas of active research.

Cyanides↗

PubMed2005

Fast and slow deposition of silver nanorods on planar surfaces: application to metal-enhanced fluorescence.

Two methods have been considered for the deposition of silver nanorods onto conventional glass substrates. In the first method, silver nanorods were deposited onto 3-(aminopropyl)triethoxysilane-coated glass substrates simply by immersing the substrates into the silver nanorod solution. In the second method, spherical silver seeds that were chemically attached to the surface were subsequently converted and grown into silver nanorods in the presence of a cationic surfactant and silver ions. The size of the silver nanorods was controlled by sequential immersion of silver seed-coated glass substrates into a growth solution and by the duration of immersion, ranging from tens of nanometers to a few micrometers. Atomic force microscopy and optical density measurements were used to characterize the silver nanorods deposited onto the surface of the glass substrates. The application of these new surfaces is for metal-enhanced fluorescence (MEF), whereby the close proximity of silver nanostructures can alter the radiative decay rate of fluorophores, producing enhanced signal intensities and an increased fluorophore photostability. In this paper, it is indeed shown that irregularly shaped silver nanorod-coated surfaces are much better MEF surfaces as compared to traditional silver island or colloid films. Subsequently, these new silver nanorod preparation procedures are likely to find a common place in MEF, as they are a quicker and much cheaper alternative as compared to surfaces fabricated by traditional nanolithographic techniques.

Chemical Phenomena↗