Resonant-enhanced evanescent-wave fluorescence biosensing with cylindricaloptical cavities

We show that the artificial resonances of dielectric optical cavities can b e used to enhance the detection sensitivity of evanescent-wave optical fluo rescence biosensors to the binding of a labeled analyte with a biospecific monolayer. Resonant coupling of power into the optical cavity allows for ef ficient use of the long photon lifetimes (or equivalently, the high interna l power) of the high-Q whispering gallery modes to increase the probability of photon absorption into the fluorophore, thereby enhancing fluorescence emission. A method to compare the intrinsic sensitivity between resonant ca vity and waveguide formats is also developed. Using realistic estimates for dielectric cylindrical cavities in both bulk and integrated configurations , we can expect sensitivity enhancement by at least an order of magnitude o ver standard waveguide evanescent sensors of equivalent sensing geometries. In addition, the required sample volume can be reduced significantly. The cylindrical cavity format is compatible with a large variety of sensing mod alities such as immunoassay and molecular diagnostic assay. (C) 2001 Optica l Society of America.