Spherical silicon optical resonators: Possible applications to biosensing

We observed whispering gallery modes in the 90 degrees elastic light scattering and 0 degrees transmission spectra of a 500 mu m silicon microsphere in the near-infrared telecommunication wavelengths. The whispering gallery modes have quality factors on the order of 10(5). An autocorrelation function analysis of the 90 degrees elastic light scattering and 0 degrees transmission spectra is performed. The differential autocorrelation of the 90 degrees elastic light scattering and 0 degrees transmission spectra reveal a spectral mode spacing 0.23nm of the whispering gallery modes, which can be used for spectral calibration as well as the calibration of the microsphere size. The spectral shift of the whispering gallery modes can be measured for biosensing applications. An estimation analysis is performed for the adsorption of 30 DNA base pairs on the microsphere results in a wavelength shift of 0.57 nm, which is approximately 40 times the linewidth of the whispering gallery modes. This high sensitivity heralds silicon microspheres as possible candidates for biosensing applications.