Chris D. Geddes

University of Maryland, Baltimore County, Baltimore, Maryland, United States

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Publications (294)838.94 Total impact

  • Jan Karolin · Chris D. Geddes
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    ABSTRACT: Spectroscopic properties of the particle sizing fluorophore Dipole Blue are reported. The probe is cationic in nature, highly water-soluble, and strongly adheres to anionic silica surfaces by electrostatic interactions, as is demonstrated here by Ludox SM 30. The probe has a distinct absorbance band centered at 320 nm, and the fluorescence emission band is Stokes-shifted 100 nm with a peak centered at 426 nm. From time-correlated single-photon counting experiments, the fluorescence lifetime was found to be adequately described by a three-exponential decay model with an intensity-averaged lifetime of 15.6 ns. Perrin graph analysis of steady-state anisotropy shows the presence of silica particles with a radius of (5.44 ± 0.16) nm, which, considering the distribution of particle sizes, is in reasonable agreement with 3.5 nm found from dynamic light scattering experiments.Keywords: particle sizing fluorophore; fluorescence anisotropy; Perrin analysis; Ludox; colloidal silica; Dipole Blue
    Journal of Physical Chemistry Letters 03/2015; 6(6):918-922. DOI:10.1021/acs.jpclett.5b00185 · 7.46 Impact Factor
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    ABSTRACT: Marine sponges are major habitat-forming organisms in coastal benthic communities and have an ancient origin in evolution history. Here, we report significant accumulation of polyphosphate (polyP) granules in three common sponge species of the Caribbean coral reef. The identity of the polyP granules was confirmed by energy-dispersive spectroscopy (EDS) and by the fluorescence properties of the granules. Microscopy images revealed that a large proportion of microbial cells associated with sponge hosts contained intracellular polyP granules. Cyanobacterial symbionts cultured from sponges were shown to accumulate polyP. We also amplified polyphosphate kinase (ppk) genes from sponge DNA and confirmed that the gene was expressed. Based on these findings, we propose here a potentially important phosphorus (P) sequestration pathway through symbiotic microorganisms of marine sponges. Considering the widespread sponge population and abundant microbial cells associated with them, this pathway is likely to have a significant impact on the P cycle in benthic ecosystems.
    Proceedings of the National Academy of Sciences 02/2015; 112(14). DOI:10.1073/pnas.1423768112 · 9.81 Impact Factor
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    ABSTRACT: Metal-enhanced fluorescence enhancement factors up to 7-fold have been observed for Basic Fuchsin (BF) in close proximity to Zinc nano particulate substrates. In addition, the emission spectra of BF close-to Zinc as compared to a control sample are heavily distorted, particularly on the red-edge, giving systematic trends in enhancement, anywhere from 3- to 7-fold. We discuss these remarkable wavelength dependent effects with regard to the mechanism of metal-enhanced fluorescence. (C) 2015 AIP Publishing LLC.
    Applied Physics Letters 02/2015; 106(8):081605. DOI:10.1063/1.4913671 · 3.52 Impact Factor
  • Rachel D. Schmitz · Jan O. Karolin · Chris D. Geddes
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    ABSTRACT: In this Letter we characterize both the photophysical and plasmonic enhanced photophysical properties of carbon nanodots produced by a combustion method. In addition, we have found that max entropy analysis of luminescence decay reveals inhomogeneous distribution of radiative lifetimes. Further, while quantum yields of intrinsic carbon nanodots emission are low [<2%], when in close proximity to plasmonic supporting materials, carbon nanodots emission can be enhanced 30 times (30×).
    Chemical Physics Letters 02/2015; 622. DOI:10.1016/j.cplett.2015.01.035 · 1.99 Impact Factor
  • Jan Karolin · Chris D. Geddes
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    ABSTRACT: We report spectroscopic properties of a new nanoparticle sizing fluorophore and demonstrate its applicability to characterize silica particles in colloidal solutions using steady-state anisotropy measurements and Perrin graph analysis. The strong electrostatic interaction between the cationic particle sizing fluorophore and the SiO2 surface is demonstrated by comparing data to that recorded for the anionic fluorophore fluorescein. The Perrin analysis reports a mean particle radius of 6.35 nm, which is larger than the manufacture specified radius of 3.5 nm, possibly indicating a degree of aggregation of the particles. The anionic fluorophore fluorescein shows no interaction with the SiO2 surface, and reports a hydrodynamic radius of 0.40 nm. We thus speculate that fluorescein can be used as an internal microviscosity probe for colloidal silica systems. The intensity averaged fluorescence lifetime of the particle sizing fluorophore and fluorescein are approximately 16 ns and 4 ns, respectively.
    Dyes and Pigments 01/2015; 112:50–53. DOI:10.1016/j.dyepig.2014.06.020 · 3.97 Impact Factor
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    ABSTRACT: AimsIsolation of Salmonella Typhi from blood culture is the standard diagnostic for confirming typhoid fever but it is unavailable in many developing countries. We previously described a Microwave Accelerated Metal Enhanced Fluorescence (MAMEF)-based assay to detect Salmonella in medium. Attempts to detect Salmonella in blood were unsuccessful, presumably due to the interference of erythrocytes. The objective of this study was to evaluate various blood treatment methods that could be used prior to PCR, real-time PCR or MAMEF to increase sensitivity of detection of Salmonella.Methods and ResultsWe tested ammonium chloride and erythrocyte lysis buffer, water, Lymphocyte Separation Medium, BD Vacutainer® CPT™ Tubes and dextran. Erythrocyte lysis buffer was the best isolation method as it is fast, inexpensive and works with either fresh or stored blood. The sensitivity of PCR- and real-time PCR-detection of Salmonella in spiked blood was improved when whole blood was first lysed using erythrocyte lysis buffer prior to DNA extraction. Removal of erythrocytes and clotting factors also enabled reproducible lysis of Salmonella and fragmentation of DNA, which are necessary for MAMEF sensing.Conclusions Use of the erythrocyte lysis procedure prior to DNA extraction has enabled improved sensitivity of Salmonella detection by PCR and real-time PCR and has allowed lysis and fragmentation of Salmonella using microwave radiation (for future detection by MAMEF).Significance and Impact of the studyAdaptation of the blood lysis method represents a fundamental breakthrough that improves the sensitivity of DNA-based detection of Salmonella in blood.This article is protected by copyright. All rights reserved.
    Journal of Applied Microbiology 01/2015; 118(5). DOI:10.1111/jam.12769 · 2.39 Impact Factor
  • Jan O. Karolin · Hilla Ben Hamo · Chris D. Geddes
    Biophysical Journal 01/2015; 108(2):623a-624a. DOI:10.1016/j.bpj.2014.11.3390 · 3.97 Impact Factor
  • Rachel Taylor · Jan Karolin · Chris Geddes
    Biophysical Journal 01/2015; 108(2):623a. DOI:10.1016/j.bpj.2014.11.3387 · 3.97 Impact Factor
  • Hirdyesh Mishra · Chris D. Geddes
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    ABSTRACT: Metal-enhanced fluorescence (MEF) and delayed fluorescence (alpha α-S1) studies of acriflavin have been undertaken using steady-state and time-resolved fluorescence measurements on silver island films (SiFs) supporting a thin poly(vinyl alcohol) (PVA) polymer film. Nearly a 3.5-fold enhancement in the far-field fluorescence intensity of acriflavin is observed coupled with a decrease in decay times and an improved fluorophore photostability. Our findings are consistent with our proposed model of the coupling and transferring of the excited state energies of fluorophores to silver surface plasmons. Further, an excitation power dependence of MEF is observed in these films, consistent with our postulate of MEF EVE (MEF excitation volumetric effect) and, ultimately, resulting in a ∼7-fold enhancement in fluorescence intensity. Our findings suggest a significant opportunity for the development of shorter-lived, brighter, high photon flux luminescent materials for multifarious applications in the life-sciences.
    The Journal of Physical Chemistry C 12/2014; 118(49):28791-28796. DOI:10.1021/jp5092587 · 4.77 Impact Factor
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    ABSTRACT: We report the use of bioluminescence signal enhancement via proximity to deposited silver nanoparticles for bioactive compound discovery. This approach employs a whole-cell bioreporter harboring a plasmid-borne fusion of a specific promoter incorporated with a bioluminescence reporter gene. The silver deposition process was first optimized to provide optimal nanoparticle size in the reaction time dependence with fluorescein. The use of silver deposition of 350 nm particles enabled the doubling of the bioluminescent signal amplitude by the bacterial bioreporter when compared to an untouched non-silver-deposited microtiter plate surface. This recording is carried out in the less optimal but necessary far-field distance. SEM micrographs provided a visualization of the proximity of the bioreporter to the silver nanoparticles. The electromagnetic field distributions around the nanoparticles were simulated using Finite Difference Time Domain, further suggesting a re-excitation of non-chemically excited bioluminescence in addition to metal-enhanced bioluminescence. The possibility of an antiseptic silver effect caused by such a close proximity was eliminated disregarded by the dynamic growth curves of the bioreporter strains as seen using viability staining. As a highly attractive biotechnology tool, this silver deposition technique, coupled with whole-cell sensing, enables increased bioluminescence sensitivity, making it especially useful for cases in which reporter luminescence signals are very weak.
    Journal of Nanoparticle Research 12/2014; 16(12). DOI:10.1007/s11051-014-2770-y · 2.28 Impact Factor
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    Anatoliy Dragan · Chris D Geddes
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    ABSTRACT: We present a potentially highly sensitive and selective bio-assay for the potential detection of any five different DNA sequences from one sample in one well. The assay is based on a DNA "rapid catch and signal" (DNA-RCS) technology developed for the detection of different DNA sequences from a sample well area. Our signal amplification utilizes the metal-enhanced fluorescence (MEF) of dyes attached to the probe-DNAs, which hybridizes with the pre-formed mixture of anchor-DNA scaffolds on silver island films (SiFs). Low-power microwave irradiation accelerates both the formation of the anchor-DNA scaffold on the SiF-surface and anchor/probe DNA hybridization, i.e. "rapid catch" of target DNAs from a bulk solution, decreasing the assay run time from hours to only a few seconds. Localization of signaling dye-labels close to the SiFs make them extremely photostable, which allows for collecting/integrating the signal over a long time period. To demonstrate a 5 color DNA assay (5-plex) we have used a range of readily available Alexa™ dyes. Advantages and perspectives of the RCS-technologies ability to detect 5 different DNA sequences from within one plate-well are discussed.
    Journal of Fluorescence 09/2014; 24(6). DOI:10.1007/s10895-014-1458-0 · 1.67 Impact Factor
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    Lovleen Tina Joshi · Buddha L. Mali · Chris D. Geddes · Les Baillie
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    ABSTRACT: Clostridium difficile is the primary cause of antibiotic associated diarrhea in humans and is a significant cause of morbidity and mortality. Thus the rapid and accurate identification of this pathogen in clinical samples, such as feces, is a key step in reducing the devastating impact of this disease. The bacterium produces two toxins, A and B, which are thought to be responsible for the majority of the pathology associated with the disease, although the relative contribution of each is currently a subject of debate. For this reason we have developed a rapid detection assay based on microwave-accelerated metal-enhanced fluorescence which is capable of detecting the presence of 10 bacteria in unprocessed human feces within 40 seconds. These promising results suggest that this prototype biosensor has the potential to be developed into a rapid, point of care, real time diagnostic assay for C. difficile
    PLoS ONE 08/2014; 9(8):e104334. DOI:10.1371/journal.pone.0104334 · 3.23 Impact Factor
  • Jan Karolin · Chris D. Geddes
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    ABSTRACT: We report a 2 nm red shift in the fluorescence spectra observed for Rhodamine 800 dissolved in glycerol on copper substrates as compared to glass reference samples, suggesting a wavelength dependence of metal enhanced fluorescence. The full width half maximum of the blue-red spectra is about 1 nm narrower as compared to the reference sample. We speculate that the observation correlates with a specific interaction mechanism between the Rhodamine 800 transition dipole, the enhanced electric field, and subsequent plasmon coupling, an observation not yet reported.
    Applied Physics Letters 08/2014; 105(6):063102-063102-3. DOI:10.1063/1.4892925 · 3.52 Impact Factor
  • Chris D. Geddes
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    ABSTRACT: The year 2013 marked the 30th anniversary of the publication of a paper that changed the world of chemical and biomedical diagnostics: The manuscript of Bo Liedberg, Claes Nylander, and Ingemar Lundström entitled “Surface plasmon resonance for gas detection and biosensing” (Sensors and Actuators 4: 299) introduced the application of a physical concept, i.e., the optical excitation of plasmon surface polaritons (or surface plasmons for short) at a metal/dielectric interface for the quantitative analysis of affinity reactions happening at this interface between a surface-immobilized binding group and an analyte approaching from the adjacent solution. Based on a rather old optical phenomenon, first described as Wood’s anomaly in the spectral reflectivity of a metal grating, this report on how to use this surface light for biosensing triggered a paradigm change in the way we can quantify interfacial binding reactions in situ and in real time. By monitoring the time dependence of the associ ...
    Plasmonics 08/2014; 9(4):727-727. DOI:10.1007/s11468-014-9763-7 · 2.74 Impact Factor
  • Jan Karolin · Rachel Taylor · Chris Geddes
    Biophysical Journal 01/2014; 106(2):620a. DOI:10.1016/j.bpj.2013.11.3429 · 3.97 Impact Factor
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    Rachel Taylor · Chris Geddes
    Biophysical Journal 01/2014; 106(2):625a. DOI:10.1016/j.bpj.2013.11.3455 · 3.97 Impact Factor
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    Anatoliy Dragan · August E Graham · Chris D Geddes
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    ABSTRACT: We introduce two new fluorescent viscosity probes, SYBR Green (SG) and PicoGreen (PG), that we have studied over a broad range of viscosity and in collagen solutions. In water, both dyes have low quantum yields and excited state lifetimes, while in viscous solvents or in complex with DNA both parameters dramatically (300-1000-fold) increase. We show that in log-log scale the dependence of the dyes' quantum yield vs. viscosity is linear, the slope of which is sensitive to temperature. Application of SG and PG, as a fluorescence-based broad dynamic range viscosity probes, to the life sciences is discussed.
    Journal of Fluorescence 11/2013; 24(2). DOI:10.1007/s10895-013-1304-9 · 1.67 Impact Factor
  • Chris D. Geddes
    Physical Chemistry Chemical Physics 10/2013; 15(45). DOI:10.1039/C3CP90129G · 4.20 Impact Factor
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    ABSTRACT: Distance dependent singlet and triplet metal-enhanced emission of eosin from silica coated silver island films (SiFs) has been studied by steady-state and time resolved fluorescence techniques, along with theoretical finite difference time domain (FDTD) numerical simulations, to understand how the thickness of the dielectric coating surrounding silver nanoparticles fundamentally affects luminescence enhancement. Our findings suggest that the distance dependence of metal-enhanced phenomena such as fluorescence, phosphorescence and delayed fluorescence is underpinned by the decay of the electric near-field, and depending on the actual silver silica sample embodiment, one can see either decreased or enhanced luminescence. These results not only expand our current MEF thinking but also suggest that one may well be able to approximate plasmon-enhanced luminescence values.
    Physical Chemistry Chemical Physics 10/2013; 15(45). DOI:10.1039/c3cp50633a · 4.20 Impact Factor
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    ABSTRACT: Accurate point-of-care (POC) diagnostic tests for Chlamydia trachomatis infection are urgently needed for the rapid treatment of patients. In a blind comparative study, we evaluated microwave-accelerated metal-enhanced fluorescence (MAMEF) assays for ultrafast and sensitive detection of C. trachomatis DNA from vaginal swabs. The results of two distinct MAMEF assays were compared to those of nucleic acid amplification tests (NAATs). The first assay targeted the C. trachomatis 16S rRNA gene, and the second assay targeted the C. trachomatis cryptic plasmid. Using pure C. trachomatis, the MAMEF assays detected as few as 10 inclusion-forming units/ml of C. trachomatis in less than 9 min, including DNA extraction and detection. A total of 257 dry vaginal swabs from 245 female adolescents aged 14 to 22 years were analyzed. Swabs were eluted with water, the solutions were lysed to release and to fragment genomic DNA, and MAMEF-based DNA detection was performed. The prevalence of C. trachomatis by NAATs was 17.5%. Of the 45 samples that were C. trachomatis positive and the 212 samples that were C. trachomatis negative by NAATs, 33/45 and 197/212 were correctly identified by the MAMEF assays if both assays were required to be positive (sensitivity, 73.3%; specificity, 92.9%). Using the plasmid-based assay alone, 37/45 C. trachomatis-positive and 197/212 C. trachomatis-negative samples were detected (sensitivity, 82.2%; specificity, 92.9%). Using the 16S rRNA assay alone, 34/45 C. trachomatis-positive and 197/212 C. trachomatis-negative samples were detected (sensitivity, 75.5%; specificity, 92.9%). The overall rates of agreement with NAAT results for the individual 16S rRNA and cryptic plasmid assays were 89.5% and 91.0%, respectively. Given the sensitivity, specificity, and rapid detection of the plasmid-based assay, the plasmid-based MAMEF assay appears to be suited for clinical POC testing.
    Journal of Clinical Microbiology 09/2013; 51(9):2913-2920. · 4.23 Impact Factor

Publication Stats

7k Citations
838.94 Total Impact Points

Institutions

  • 2010–2015
    • University of Maryland, Baltimore County
      • Department of Chemistry and Biochemistry
      Baltimore, Maryland, United States
  • 2001–2010
    • University of Maryland, Baltimore
      • Department of Biochemistry and Molecular Biology
      Baltimore, Maryland, United States
  • 1998–2010
    • University of Strathclyde
      • Department of Physics
      Glasgow, Scotland, United Kingdom
  • 2009
    • Umeå University
      • Department of Chemistry
      Umeå, Västerbotten, Sweden
    • Georgia Institute of Technology
      Atlanta, Georgia, United States
    • Indian Association for the Cultivation of Science
      • Department of Physical Chemistry
      Calcutta, Bengal, India
    • University of Southern Denmark
      • Department of Biochemistry and Molecular Biology
      Copenhagen, Capital Region, Denmark
    • University of California, Davis
      • Department of Physiology and Membrane Biology
      Davis, CA, United States
    • VU University Amsterdam
      • Department of Analytical Chemistry and Spectroscopy
      Amsterdam, North Holland, Netherlands
    • Montana State University
      • Department of Chemistry & Biochemistry
      Bozeman, MT, United States
    • Saha Institute of Nuclear Physics
      Kolkata, Bengal, India
    • University of Minho
      • Centro de Física
      Braga, Distrito de Braga, Portugal
    • South China University of Technology
      • Department of Chemical Engineering
      Shengcheng, Guangdong, China
  • 2007
    • University of Maryland Medical Center
      Baltimore, Maryland, United States
  • 2004–2007
    • Loyola University Maryland
      Baltimore, Maryland, United States
    • Microcosm, Inc.
      Hawthorne, California, United States
  • 2003
    • University of Baltimore
      Baltimore, Maryland, United States
  • 1999–2001
    • Swansea University
      Swansea, Wales, United Kingdom
  • 1998–1999
    • University of Wales
      • Department of Chemistry
      Cardiff, WLS, United Kingdom