A new and independent method to investigate biological reactions and their products based upon the accurate and real-time measurement of the thermal conductivity of the reacting samples is presented. A micromachined thermopile based thermal sensor integrated with a planar heater and microfluidic channel has been fabricated for these measurements. The device was calibrated by measuring the thermal conductivity of standard fluids such as DI water and isopropyl alcohol. The calibrated device was then used to measure the thermal properties of biological molecules such as glucose, urea, Bovine Serum Albumin (BSA), Human Fibrinogen (HF), their antibodies, and the bound product. To the best of our knowledge, this is the first report of the observation of the real-time monitoring of antibody-antigen binding based on the change in the thermal properties of the reacting fluids.