Quantitative concentration measurements of creatinine dissolved in water and urine using Raman spectroscopy and a liquid core optical fiber.

We describe the use of a Teflon-AF liquid core optical fiber (LCOF) geometry to enhance the collection of Raman scattering from the biochemical creatinine, dissolved in water and in urine. At short integration times, where shot noise is most troublesome, the enhanced signal leads to greater accuracy in estimating the creatinine concentration from the spectrum. At longer integration times, instabilities in the LCOF geometry manifest themselves, and the predictions are the same as or worse than those from standard cuvette-based spectral measurements. Photobleaching of fluorescence from urine is more extensive and more stable in the LCOF as well. Starting from the measured enhancement of a major creatinine Raman band, we calculate the expected ratio of prediction errors obtained using the two geometries, and it agrees closely with the observed ratio. These results indicate that Raman spectroscopy with these Teflon-AF LCOFs is stable enough for quantitative concentration predictions, accurate to a few percent of the concentration range spanned.