Liquid temperature measurement method in microchannels by using fluorescence polarization

A novel optical method that can measure fluid temperature at the microscopic scale by measuring fluorescence polarization is described in this paper. The measurement is much less influenced by fluorescence quenching effects, which is a significant issue in conventional laser-induced fluorescence methods. Therefore, the effects of the other properties of the fluid can be reduced considerably in the proposed method, thus has the potential of leading to greater reliability in measuring the temperature. An experiment was performed in a microchannel flow by using fluorescent molecule probes. The relationship between the fluid temperature and the measured fluorescence polarization degree is evaluated to derive the correlation curve. In addition, the effects of the fluid viscosity and fluid pH on the fluorescence polarization degree are discussed to evaluate the influence of the quenching effects. The results showed that the fluorescence polarization is considerably less sensitive to the quenching factors as compared with the fluorescence intensity measurements. Furthermore, a strong linear correlation between the polarization degree and the fluid temperature was obtained. This relationship agreed well with the theoretical one qualitatively and confirmed the validity of the measurements and feasibility of the proposed method.