Mr. Joshy Francis John Profile

Joshy Francis John

Ph.D. Candidate at Univ of Tennessee

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Publications (1)

Proceedings Article | 4 October 2007 Paper

Chemical and biochemical analysis using microfluidic-localized field platforms

Michael Sepaniak, Nahla Abu-Hatab, Amber Wellman, Joshy John, Maggie Connatser

Proceedings Volume 6759, 675902 (2007) https://doi.org/10.1117/12.747606

KEYWORDS: Surface enhanced Raman spectroscopy, Silver, Microfluidics, Biological research, Statistical analysis, Chemical analysis, Calibration, Magnetism, Waveguides, Microscopes

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Microfluidics offer the advantages of multiplexed analysis on small, inexpensive platforms. We describe herein two distinct optical detection techniques that have the common point of sequestering and measuring analyte signals in highly localized EM fields. The first technique mates a microfluidic polydimethylsiloxane (PDMS) platform with colloidal-based surface enhanced Raman scattering (SERS) in order to perform parallel, high throughput vibrational spectroscopy. Spectra are acquired for analytes localized in surface plasmon fields associated with conventional and uniquely synthesized cubic silver colloids. SERS studies such as pH of the colloidal solution, and the type of colloid are used to demonstrate the efficiency and applicability of the method. In addition, a facile passive pumping method is used to deliver Ag colloids and analytes into the channels where all SERS measurements were completed under nondestructive flowing conditions. With this approach, SERS signal reproducibility was found to be better than 7%. A calibration curve for the drug mitoxantrone (resonance enhanced) was generated. The second technique seeks to integrate a passively-pumped, microfluidic, PDMS platform and planar waveguide technology, utilizing magnetic beads as solid supports for fluoro-assays with direct detection of bound analyte within the sample mixture accomplished by selectively driving functionalized beads to a localized evanescent field. Because analyte binding occurs in free solution, the reaction is not diffusion limited and, once magnetically delivered to the evanescent wave, the analyte can be detected with fewer complications arising from non-optically homogeneous, biological matrices. Additionally, the evanescent sensing surface can be easily regenerated by simply removing the bead-retaining magnetic field. Initial testing, optimization and calibration were performed using a model sandwich immunoassay system for the detection of rabbit IgG, with which we demonstrate a linear dynamic range of 3 orders of magnitude and physiologically relevant detection limits of nanograms per milliliter.

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