Using optical resonance of whispering gallery modes in microspheres for real-time detection and identification of biological compounds

We have experimentally developed a technique for obtaining optical resonance of whispering gallery modes in quartz microspheres in solutions of biological molecules. We have estimated the sensitivity of the method with respect to the change in the refractive index of the medium surrounding the microsphere, and have also estimated the change in the concentration of the dissolved molecules using ethanol, glucose, ascorbic acid, and biotin as examples. According to this estimate, we found that a 1% change in the ethanol concentration in water is comparable with a change in refractive index by 0.00058 RIU (refractive index units), while with a 3% increase in glucose and ascorbic acid concentration in deionized water, a resonance shift of 170 nm and 200 nm was achieved. © 2010 Springer Science+Business Media, Inc.