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 x 12.8 mu m(2) for three different heating conditions.