Chemical and Biological Sensing through Optical Resonances in Microcavities

A microdroplet or a latex microsphere often acts as an optical cavity that supports Morphology Dependent Resonances (MDRs) at wavelengths where the droplet circumference is an integer multiple of the emission wavelength. Enhanced radiative energy transfer through these optical resonances can also be utilized as a transduction mechanism for chemical and biological sensing. Enhancement in radiative energy transfer is observed when a donor/acceptor pair is present in the resonant medium of a microcavity. Here, we demonstrate avidin-biotin binding and its detection through a FRET pair as a potential application for ultra-sensitive detection for fluoroimmunoassays. The binding interaction between the biotinylated fluorescent beads (donor) and streptavidin-Alexa Fluor 555 (acceptor) conjugate was used to observe the energy transfer between the dye pairs. Strong coupling of acceptor emission into optical resonances shows that the energy transfer is efficiently mediated through these resonances.