Label-free visualization of microfluidic mixture concentration fields using a surface plasmon resonance (spr) reflectance imaging

A label-free visualization technique based on surface plasmon resonance (SPR) illumination sensing is applied for the nonintrusive and real-time mapping of microscale mixture concentration fields. The key idea is that the SPR reflectance sensitively varies with the refractive index of the near-wall region of the test mixture fluid contacting the metal (Au) layer, of tuned 47.5 nm thickness. The Fresnel equation, based on Kretschmann’s theory, correlates the SPR reflectance with the refractive index, or dielectric constant, of the test medium, and then, the measured refractive index correlates with the mixture concentration. An example application is presented for the case of ethanol penetrating into water contained in a micro-channel with a rectangular cross-section of 91 μm wide and 50 μm high. The measurement sensitivity, uncertainties and detection limitations of the implemented SPR imaging sensor are carefully examined for its potential as a nonintrusive means of microscale concentration field mapping.

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Kenneth D. KihmEmail: Phone: +1-865-974-5292URL: http://www.minsfet.utk.edu