DBR-structured smart particles for sensing applications

The micro-particles containing a periodic nanostructure have been generated from the distributed Bragg reflector (DBR) porous silicon (PSi) by ultrasono-method and exhibit a sharp photonic band in the optical reflectivity spectrum. These particles are optically encoded with Bragg-structured photonic band and their sizes are about 500 nm to few micron. Reflection spectrum of smart particles indicates that the full-width at half-maximum (FWHM) is of 18 nm and much narrower than that of fluorescent organic molecules or quantum dot. The detection of volatile organic compounds (VOCs) using these particles has been achieved. The surface of these particles has been chemically modified to have different physical surface properties. When the vapor of VOCs condenses in the nanopores, the refractive indices of entire particle increase. This results in a red shift in the photonic peak depending on the surface property. Particles modified with dodecyl functionality exhibit the most red-shifted photonic feature for nonpolar VOCs (ca. hexane, 25 nm; methanol, 12 nm), however particles modified with hydroxyl group display vice versa (ca. hexane, 15 nm; methanol, 24 nm).