A micro fuel cell sensor having laminated gas permeable membrane. Specifically, butanol, preferably isobutanol is produced by the fermentative growth of a recombinant bacterium expressing an isobutanol biosynthetic pathway. An electric drive motor is disposed within the second tube and is longitudinally movable therein between upper and lower positions. The elongated sections may be symmetrically arranged about an axis. These operations can be repeated to deposit multiple layers of dielectric material until a desired dielectric thickness is achieved. The reference voltage supplied to the comparator is indicative of a threshold voltage at which an output of the circuit changes states.