A micro-pipette thermal sensing technique for measuring the thermal conductivity of non-volatile fluids

This research work demonstrates an innovative technique to measure the thermal conductivity of a small volume of non-volatile liquids. The method utilizes a micro-pipette thermal sensor (MPTS) (tip diameter < 2 μm) and is based on laser point heating thermometry and transient heat transfer. A laser beam is irradiated at the sensor tip immersed in a few microliters of the test fluid and the transient temperature change is recorded with the sensor. This temperature change is dependent on the surrounding fluid's thermal properties, such as thermal conductivity and diffusivity. The numerical solution for transient temperature profile for a point source is obtained using the finite element method in the COMSOL software. To determine the optimizing parameters such as thermal conductivity and power absorbed at the sensor tip, the multi-parameter fitting technique is used in MATLAB, which will fit the COMSOL simulation result with the experimental data. Three liquids with known thermal conductivity were tested to verify that the technique can be used to determine the thermal conductivity with high accuracy, and in addition, the thermal conductivity of growth media and serum used for culturing cancer cells is estimated. With the sensor size of 1-2 μm, we demonstrate the possibility of using this described method as the MPTS technique for measuring the thermal properties of microfluidic samples and biological fluids.