This paper presents a lithium battery powered small size wireless sensor node with a sensor bridge biased by an energy- efficient DC-DC converter. To reduce the switching noise of the DC-DC converter, the conventional Wheatstone bridge is added capacitor. Circuit parameters, such as bridge resistances and amplifier offset are automatically set to the optimal values in the startup sequence. Prototype sensor interface achieved power reduction by 57.3% and intermittent operation further reduces the power consumption by 78.6%. Developed a tiny wireless sensor node with a nanoscale gas sensor device successfully demonstrated 100ppm hydrogen gas detection.