A micromachined microcalorimeter with split-flow microchannel for biochemical sensing applications

This paper reports a micromachined microcalorimeter based on a split-flow microchannel structure for biochemical applications. It is characterized by measuring the reaction heat between biotin and streptavidin. For enhancing its sensitivity, the thermal components of the proposed microcalorimeter are fabricated on a high-thermal resistivity layer, SU-8 in this case, which leads to reduce the parasitic heat transfer to the silicon substrate. For removing additional heating elements, the split-flow microchannel is used. The split-flow microchannel scheme constantly keeps the output of the microcalorimeter near zero level when there is no biochemical reaction; in this state, a heater becomes unnecessary. The microchannel is based on the principle that target biomolecules applied to both the reaction and the reference chambers maintain the chambers at the same temperature, and then capture biochemicals are applied to the reaction chamber on hot junctions, only. Finally, the voltage generated by the biochemical reaction heat in the reaction chamber is measured. In order to verify characteristics of the fabricated sensor, reaction heat due to the biotin–streptavidin reaction was measured. For the experiment, 3.4 mg/ml biotin was used with various streptavidin concentrations of 1.0, 0.5, 0.25, 0.1, and 0.01 mg/ml. Three microliters of titrated biotin and streptavidin of various concentrations were injected into the sensor through a split-flow microchannel. The measurement results show that its sensitivity was 33.7 V/molarity (=0.21 V/cal) as the concentrations of streptavidin.