Vanadium oxide thermal microsensor integrated in a microfluidic chip for detecting cholesterol and glucose concentrations

A highly sensitive thermal measurement device based on a vanadium oxide (VO_x) microthermistor is developed for detecting biological molecules based on enzymatic reactions. The measurement principle of the VO_x thermistor relies on the temperature dependence of its electrical resistance owing to the heat generation of enzymatic reactions. The device comprises a microfluidic channel and chambers, and VO_x thermistors on a suspended Si₃N₄ membrane for thermal insulation. The enzyme is immobilized in silica gel on the sensor. The temperature coefficient of the resistance of the fabricated VO_x thermistor is −1.3 %/K. The fabricated device has a temperature resolution of 0.30 mK/√Hz and a temperature response of 4.9 mV/K. Thermal measurements of cholesterol and glucose are demonstrated using the heat production caused by enzymatic reactions. The detectable concentrations of glucose and cholesterol were 30 and 15 µM/√Hz, respectively.