Jennifer O Foley

University of Washington Seattle, Seattle, WA, United States

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Publications (7)30.37 Total impact

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    ABSTRACT: We present a fractional sensitivity analysis of a competitive microfluidic heterogeneous immunoassay for a small molecule analyte. A simple two-dimensional finite element model is used to determine the fractional sensitivity of the assay signal with respect to analyte concentration, flow rate, initial surface density of binding sites, and antibody concentration. The fractional sensitivity analysis can be used to identify (1) the system parameters for which it is most crucial to control or quantify the variability between assays and (2) operating ranges for these parameters that improve assay sensitivity (within the constraints of the experimental system). Experimental assay results for the drug phenytoin, obtained using surface plasmon resonance imaging, are shown to be consistent with the predictions of the model.
    Analytical Chemistry 05/2009; 81(9):3407-13. · 5.70 Impact Factor
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    ABSTRACT: A microfluidic device known to mix bulk solutions, the herringbone microchannel, was incorporated into a surface-binding assay to determine if the recirculation of solution altered the binding of a model protein (streptavidin) to the surface. Streptavidin solutions were pumped over surfaces functionalized with its ligand, biotin, and the binding of streptavidin to those surfaces was monitored using surface plasmon resonance imaging. Surface binding was compared between a straight microchannel and herringbone microchannels in which the chevrons were oriented with and against the flow direction. A 3-dimensional finite-element model of the surface binding reaction was developed for each of the geometries and showed strong qualitative agreement with the experimental results. Experimental and model results indicated that the forward and reverse herringbone microchannels substantially altered the distribution of protein binding (2-dimensional binding profile) as a function of time when compared to a straight microchannel. Over short distances (less than 1.5 mm) down the length of the microchannel, the model predicted no additional protein binding in the herringbone microchannel compared to the straight microchannel, consistent with previous findings in the literature.
    Lab on a Chip 05/2008; 8(4):557-64. · 5.70 Impact Factor
  • Jennifer O Foley, Elain Fu, Lara J Gamble, Paul Yager
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    ABSTRACT: The function of microcontact printed protein was investigated using surface plasmon resonance (SPR) imaging, X-ray photoelectron spectroscopy spectroscopy (XPS), and XPS imaging. We chose to analyze a model protein system, the binding of an antibody from solution to a microcontact printed protein antigen immobilized to a gold surface. SPR imaging experiments indicated that the microcontact printed protein antigen was less homogeneous, had increased nonspecific binding, and bound less antibody than substrates to which the protein antigen had been physically adsorbed. SPR images of substrates contacted with a poly(dimethylsiloxane) stamp inked with buffer alone (i.e., no protein) revealed that significant amounts of silicone oligomer were transferred to the surface. The transfer of the silicone oligomer was not homogeneous, and the oligomer nonspecifically bound protein (BSA and IgG) from solution. XPS spectroscopy and imaging were used to quantify the amount of silicon (due to the presence of silicone oligomer), as well as the amounts of other elements, transferred to the surface. The results suggest that the silicone oligomer introduced by the printing process reduces the overall binding capacity of the microcontact-printed protein compared to physically adsorbed protein.
    Langmuir 05/2008; 24(7):3628-35. · 4.38 Impact Factor
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    ABSTRACT: A novel microfluidic surface-based competition immunoassay, termed the concentration gradient immunoassay (described in detail in a companion paper (Nelson, K.; Foley, J.; Yager, P. Anal. Chem. 2007, 79, 3542-3548.) uses surface plasmon resonance (SPR) imaging to rapidly measure the concentration of small molecules. To conduct this assay, antibody and analyte are introduced into the two inlets of a T-sensor (Weigl, B. H.; Yager, P. Science 1999, 283, 346-347. Kamholz, A. E.; Weigl, B. H.; Finlayson, B. A.; Yager, P. Anal. Chem. 1999, 71, 5340-5347). Several millimeters downstream, antibody molecules with open binding sites can bind to a surface functionalized with immobilized antigen. This space- and time-dependent binding can be sensitively observed using SPR imaging. In this paper, we describe a complex three-dimensional finite element model developed to better understand the dynamic processes occurring with this assay. The model shows strong qualitative agreement with experimental results for small-molecule detection. The model confirms the experimental finding that the position within the microchannel at which the antibody binds to the immobilized analyte may be used to quantify the concentration of analyte in the sample. In addition, the model was used to explore the sensitivity of assay performance to parameters such as antibody and analyte concentrations, thereby giving insight into ways to optimize analysis speed and accuracy. Given the experimental verification of the computational results, this model serves as an efficient method to explore the influence of the flow rate, microchannel dimensions, and antibody concentration on the sensitivity of the assay.
    Analytical Chemistry 06/2007; 79(10):3549-53. · 5.70 Impact Factor
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    Kjell E Nelson, Jennifer O Foley, Paul Yager
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    ABSTRACT: We describe a novel microfluidic immunoassay method based on the diffusion of a small-molecule analyte into a parallel-flowing stream containing a cognate antibody. This interdiffusion results in a steady-state gradient of antibody binding site occupancy transverse to convective flow. In contrast to the diffusion immunoassay (Hatch, A.; Kamholz, A. E.; Hawkins, K. R.; Munson, M. S.; Schilling, E. A.; Weigl, B. H.; Yager, P. Nat. Biotechnol. 2001, 19, 461-465.), this antibody occupancy gradient is interrogated by a sensor surface coated with a functional analogue of the analyte. Antibodies with at least one unoccupied binding site may specifically bind to this functionalized surface, leading to a quantifiable change in surface coverage by the antibody. SPR imaging is used to probe the spatial distribution of antibody binding to the surface and, therefore, the outcome of the assay. We show that the pattern of antibody binding to the SPR sensing surface correlates with the concentration of a model analyte (phenytoin) in the sample stream. Using an inexpensive disposable microfluidic device, we demonstrate assays for phenytoin ranging in concentration from 75 to 1000 nM in phosphate buffer. At a total volumetric flow rate of 90 nL/s, the assays are complete within 10 min. Inclusion of an additional flow stream on the side of the antibody stream opposite to that of the sample enables simultaneous calibration of the assay. This assay method is suitable for rapid quantitative detection of low molecular weight analytes for point-of-care diagnostic instrumentation.
    Analytical Chemistry 06/2007; 79(10):3542-8. · 5.70 Impact Factor
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    ABSTRACT: We have built and characterized the operation and performance of a surface plasmon resonance microscope that uses the rotation of an interference filter to vary the imaging wavelength of the system. The operation of the microscope with respect to signal processing, the dynamic range, and the limit of detection of the system, are described. © 2004 American Institute of Physics.
    Review of Scientific Instruments 06/2004; 75(7):2300-2304. · 1.60 Impact Factor
  • Elain Fu, Jennifer Foley, Paul Yager
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    ABSTRACT: We report the development of a simple surface plasmon resonance microscope that uses a method of varying the operating wavelength of the system. The instrument is based on the Kretschmann configuration and uses a single compact rotation element and an interference filter to vary the imaging wavelength of the system. The operation of the instrument is demonstrated.
    Review of Scientific Instruments 01/2003; 74:3182-3184. · 1.60 Impact Factor