Abstract

Low-Q-Whispering Gallery Modes-A New Platform For Label-Free Investigation of Surface Processes

Lars Dähne, Founder & Managing Director, Surflay Nanotec GmbH

Low Q whispering gallery modes (WGM) are light waves that circulate up to 15 000 times inside spherical microparticles by total reflection on the inner surface, thereby sensitively scanning the surface. When molecules are adsorbed on the surface of the particles, there is a change in refractive index, leading to shifts of resonance frequency of the WGM. The shift is readout by a high-resolution spectrometer and can be used to quantify surface interactions and their kinetics. In contrast to other WGM setups in toroids or High Q WGM in larger silica particles where the light is coupled in by tangentially arranged light guides, we are using fluorescent molecules inside of 10 µm polymer particles for the generation of the WGM. Consequently the sensor can be activated and readout contactless in smallest cavities like in three dimensional cell arrays or even inside of living cells.

For the specific detection of biomolecules, the WGM sensors are functionalized with antigens or oligonucleotides. An arbitrary number of particles are immobilized inside a chip for which several possibilities are available. After incubation with the analyte, for example a serum sample, the adsorption of complementary molecules is readout as a shift of the WGM signals without the need of special washing or subsequent incubation with “secondary” antibodies. One measurements point require less than 0.1 second per particle. Using large numbers of sensor particles enables high statistical relevance, as well as parallel analysis of almost unlimited number of complementary biomolecules. The talk presents the Low Q WGM technology and indicates its advantages by some application examples.