Measurement of Temperature Differences between Micro-regions in Water Using Near-Infrared Spectroscopy

Abstract

We have developed a method for measuring the temperature of micro-regions in aqueous solutions using near-infrared spectroscopy that enables us to measure the temperature of biological cells, tissues, and biochemical solutions in vitro. The measurement principle is based on the fact that the peak wavelength of the water absorption band with its center near 1450 nm shifts with changes in temperature. The measurement system, which consists of a biological microscope and two spectrophotometers, can measure respective absorbance spectra for two areas that are each 80 microm in diameter. We formed the temperature distribution in a 500-microm thick water film by heating an immersed Nichrome wire and measured the temperature difference between the two areas. The results of the measurement were compared to a calculated temperature distribution.

Temperature imaging of sub-millimeter-thick water using a near-infrared camera

“…3756 cm À1 ), would be useful for a thinner sample because its absorbance and temperature coefficient are larger than those of the m 1 + m 3 band [24,26]. Indeed, by analyzing spectra of the m 2 + m 3 band, we predicted the temperatures of water less than 0.1 mm thick [22]. Note, however, that InGaAs detectors cannot cover the m 2 + m 3 band.…”

“…The authors have been studying a convenient non-contact way of using near-infrared spectroscopy (NIRS) for measuring the temperature of aqueous solutions [21][22][23]. This method is based on the temperature dependence of the near-infrared (NIR) absorption of water.…”

“…First, we acquired temperature images of temperature-controlled 0.5-mm thick water in order to calibrate the signals against temperature. Next, we locally heated the water by immersing a thin hot wire in it [18,21] and obtained temperature images. The most effective way of verifying the obtained images is numerical simulation.…”