The detection sensitivity of optoacoustic spectroscopy at the short-wavelength infrared (SWIR) region is reduced by water absorption in aqueous solutions. Our work reports marked improvements in the sensitivity of optoacoustic spectroscopic measurements of proteins, lipids, and glucose when performed at 4 °C, compared to conventional optoacoustic or IR spectroscopy. Studying the effect of water temperature on optoacoustic signals revealed a polarity change at temperatures below 4 °C (muting temperature). The dependence of the optoacoustic signal and the muting temperature on sample concentration were further investigated, demonstrating that changes in these dependencies enable accurate quantification of the solute concentration.
In this work we developed a novel near-infrared two-path optoacoustic spectrometer (NiR-TAOS) that could sense OA intensity changes due to metabolite concentration changes in-vivo. The main aim of dividing the optical path in two is 1) perform real time correction of the laser emission profile of the laser source at different wavelengths and, 2) perform pulse to pulse correction to remove laser beam fluctuation and instability to increase signal to noise ratio. Signal to noise ratio improvement was significant not only at spectral peaks, but also at all other wavelengths. The system can be used for broad applications in biomedical measurements such as various metabolites in the SWIR.