Non-intrusive measurement of microscale temperature distribution by spontaneous Raman imaging

A non-intrusive and spatially resolved temperature measurement technique based on spontaneous Raman imaging was developed to measure two-dimensional temperature distributions in microfluidic systems. Raman scattering arising from OH stretching vibrations of H₂O molecules was used to measure the local channel flow temperature because of its high sensitivity to temperature. The OH stretching band has two parts with contrasting temperature dependences: hydrogen-bonded (HB) and non-hydrogen-bonded (NHB) modes. Raman images of HB and NHB modes were separately captured by an electron-multiplying charge-coupled device camera using two bandpass filters with center wavelengths of 642 and 660 nm, respectively. The two-dimensional temperature distributions were obtained from the intensity ratio of the two images by applying a calibration curve, which showed that there was a linear relationship between the temperature and the intensity ratio of HB to NHB modes for temperatures in the range 293-333 K. Temperature distribution measurements were demonstrated in the mixing flow field in the junction area of a T-shaped channel composed of a poly(dimethylsiloxane) chip and borosilicate glass slides. Non-uniform temperature distributions were quantitatively visualized at a spatial resolution of 12.8 × 12.8 μm² for three different heating conditions.