Quartz Glass Fiber Sheet–Based Method for Enhancing Raman Scattering in Serum and Urine

Background/objectives: Diagnostic methods for minimally invasive disease are needed worldwide; Raman spectroscopy is a promising technology. In this study aiming to improve diagnostic technology using Raman spectroscopy, we evaluated a Raman spectroscopic substrate made of a quartz glass fiber sheet to obtain high sensitivity Raman spectra with a high signal-to-noise ratio. Methods: We investigated methods to amplify the intensity of Raman scattered light from humoral biological samples such as serum and urine. We evaluated two methodologies: 1) the needle method (NM) [for capturing Raman spectra by irradiating a droplet of liquid sample at the tip of a fine stainless-steel needle with a laser]; and 2) the quartz sheet method (QSM) [a quartz glass fiber sheet is saturated with a liquid sample, and the sheet surface is irradiated with a laser to obtain Raman spectra]. The Raman spectra of sodium benzoate, sodium sulfate, human serum, and human urine were recorded. Results: The samples crystallized and became concentrated in the quartz glass fiber sheet, allowing Raman spectra with highly intense scattered light to be recorded even from low-concentration samples. The QSM produced scattered light intensity ~7.3 and ~7.8 times higher for serum and urine, respectively, than the NM, which obtains spectra while the sample is still in liquid form. Conclusions: Our QSM enables quick and convenient acquisition of Raman spectra from samples using a very low-cost quartz glass fiber sheet and a standard Raman microscope. The QSM may be useful for obtaining Raman spectra from liquid biological samples with low analyte concentrations.