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Sketch (not in scale) of the monolithic optical sensor with indicated materials and refractive indices. PM: Polystyrene microsphere. The inset shows a transmission image of the sample inside the flow chamber. Some scattering of the WGM light from the resonator is visible.
Transmission microscopy images with focus at the Cytop surface of a PM sample immersed in (a) oil or (b) water, (c) sketch of PM attachment region, (d) Cytop height profile in the attachment region, measured by DIC with the PM removed, (e) reflectance spectrum of the sample outside the attachment region in air.
WGM resonance of the PM in water attached to the glass coupler, measured with the intensity (open circles) and the interference (closed circles) detections, and fitted lineshapes (solid lines). The detected subensemble of azimuthal modes is shown on the top axis in intensity detection.
Refractive index sensogram: WGM energy shift upon change in the refractive index of the surrounding medium by a water/glycerol mixture at the indicated glycerol concentration. The inset shows the fitted responsivity. The right axis indicates the corresponding refractive index change in the medium.
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