“Smart dust”—small particles of optically encoded microporous Si—can detect organic vapors by measurement of the intensity of reflected light using a laser probe and a detector stationed 20 m away (see Figure and inside front cover). The porous particles absorb condensable vapors, producing a change in refractive index and consequently a quantitative change in optical reflectivity at the wavelength of the laser.
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Schmedake et al. (2002) studied this question.