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Current bulk or thick film solid electrolyte CO₂ sensors are expensive, difficult to batch fabricate, and large in size. In contrast, this new amperometric, solid-state, oxide-based electrolyte CO₂ microsensor is affordable, easy to fabricate, and is so small that it could easily be integrated onto a substrate the size of a postage stamp. The basic composition of the sensor is identical to a previously designed NASA Glenn technology in which a solid electrolyte of Na₃Zr₂Si₂PO₁₂ is deposited between interdigitated electrodes on an alumina substrate and is covered by Na₂CO₃/BaCO₃. Unlike its predecessor, however, this innovation includes an additional layer of nanocrystalline SnO₂ sol gel, an electron donor type (N-type) semiconductor, on top of the Na₂CO₃/BaCO₃ . This new layer provides a greater number of electrons for reduction reaction at the working electrode to detect CO₂. As a result, overall performance is enhanced, and this new state-of-the-art sensor has the ability to operate at temperatures as low as 375°C. This low temperature capability significantly decreases the amount of power required to operate the sensor, opening the door to a multitude of new applications that were previously unattainable.