Photonic crystal microcavity engineering and high-density bio-patterning for chip-integrated microarray applications

While Q similar to 1million has been demonstrated in freely suspended photonic crystal (PC) membranes, the reduced refractive index contrast when PC microcavities are immersed in phosphate buffered saline (PBS), a typical ambient for biomolecules, reduces Q by more than 2 orders of magnitude. We experimentally demonstrate photonic crystal microcavity based resonant sensors coupled to photonic crystal waveguides in silicon on insulator for chemical and bio-sensing. Linear L-type microcavities are considered. In contrast to cavities with small modes volumes but low quality factors for bio-sensing, we show that increasing the length of the microcavity enhances the quality factor of the resonance by an order of magnitude and also increases the resonance wavelength shift while still retaining compact device characteristics. Q similar to 26,760 and sensitivity down to 7.5ng/ml and similar to 9pg/mm(2) in bio-sensing was experimentally demonstrated in SOI devices for goat anti-rabbit IgG antibodies with K-d similar to 10(-6)M. The increase in cavity length follows from fundamental engineering limitations in ink-jet printing or microfluidic channels when unique receptor biomolecules are coated on separate adjacent sensors in a microarray.