We present a MEMS differential thermal biosensor integrated with microfluidics for metabolite concentration measurements either in flow-injection or flow-through modes. The biosensor consists of two identical freestanding polymer thin membranes, resistive on-chip heaters, and a metal thermoelectric differential temperature sensor between the two membranes. Integrated with polymer microfluidic channels and chambers, the biosensor allows efficient handling and measurements of small volumes (~1 μl) of liquid samples. Calibrated with on-chip resistive heaters, the biosensor shows a sensitivity of 1.2 V/W and time constant of 0.58 s. Enzyme-functionalized beads are packed in the chambers and interacted with metabolite solutions. The heat released from the enzymatic reactions is detected by the temperature sensor and used to measure the metabolite concentration. The biosensor demonstrated a glucose concentration resolution of 0.12 mM for flow-injection mode, and 0.48 mM for flow-through mode with a flow rate of 0.5 ml/h. It is found that there exists an optimal flow rate that corresponds to the maximum thermopile output voltage when the biosensor works in the flow-through mode.

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