  We have discovered and studied the effect of the asymmetric deformation of a
photonic crystal in the form of a change in the slope of the crystal planes as
it is filled with a gaseous analyte. We have demonstrated that the use of a new
effect leading to the displacement of the stop band against the unchanged
spectrum of diffracted white light at the (glass-thin opal film) interface can
be used as fast, compact, high sensitive and reproducible optical chemical
sensor for ammonia. Low cost and simplicity of sensor fabrication, the response
of which can be easily observed without resorting to spectral instruments are
therefore likely to be attractive. The basis for high sensitivity (1 ppm), fast
response (120 ms) is capillary vapor condensation. On the basis of this effect
a cheap high-speed and highly sensitive gas sensors has been built.
