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.
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