Advances in label-free optical biosensing: direct comparison of whispering gallery mode sensors with surface plasmon resonance

ABSTRACT Whispering gallery modes (WGM) in fluorescent dielectric micr ocavities have recently become an attractive alternative to state-of-the-art label-free optical biosensors due to their high sensitivity to molecular adsorption and their ease of operation under a variety of environmental conditions. In partic ular the true microscopic dimension of the sensor as well as its purely radiative control without any need for external coupling opens ne w opportunities for label-free biosensing on microscopic scale. While these are obvious advantages, a direct comparison of the performance of WGM biosensors with well-established techniques of known high sensitivity, such as surface plasmon resonanc e sensors, has not been undertaken to date, thus obscuring the opportunities of the newly rising approach. We have therefore studied the performance of both WGM biosensors and a commercial SPR sensor using a selection of specifically and non-specifically binding biomolecules in-situ and under same conditions. The WGM biosensors consist of 10 P m dye-doped polystyrene beads immobilized in a flow cell. The performance of the two techniques is compared in view of the efficiency and sensitivity towards detection of both model interaction pairs (e.g. biotin/Streptavidin) and specific interaction pairs such as antigen-antibody with a lower degree of interaction affinities. Keywords: Whispering Gallery Mode, Surface Plasmon Resona nce, specific interaction, affinity, biosensor