Consequences of Extreme Photon Confinement in Micro- Cavities: I. Ultra-Sensitive Dedection of Perturbations by Bio-Molecules

It is becoming possible to confine optical photons within a dielectric microparticle (radius∼100µm) for microseconds. This lifetime would allow a free-ranging photon to travel ∼300 m in vacuum. In the frequency domain such a mode resonates with a ratio of frequency to line-width Q }109. With such a narrow line-width, the sensitivity to size and refractive index perturbations is extreme. An average size change of less than 1 picometer shifts the resonance line through its complete width. These resonances may be stimulated evanescently by coupling to the guided wave in an optical fiber core. Researchers recently used this fiber-microsphere system to detect hybridization of DNA on a microsphere surface, and found that a single nucleotide polymorphism (SNP, one base mismatch) in a long DNA target could be detected with a signal to noise ratio of 54.