Abstract
Optical microcavities have become an attractive platform for precision measurement with merits of ultrahigh sensitivity, miniature footprint and fast response. Despite the achievements of ultrasensitive detection, optical microcavities still face significant challenges in the measurement of biochemical and physical processes with complex dynamics, especially when multiple effects are present. Here we demonstrate operando monitoring of the transition dynamics of a phase-change material via a self-referencing optofluidic microcavity. We use a pair of cavity modes to precisely decouple the refractive index and temperature information of the analyte during the phase-transition process. Through real-time measurements, we reveal the detailed hysteresis behaviors of refractive index during the irreversible phase transitions between hydrophilic and hydrophobic states. We further extract the phase-transition threshold by analyzing the steady-state refractive index change at various power levels. Our technology could be further extended to other materials and provide great opportunities for exploring on-demand dynamic biochemical processes.
Highlights
Micro-/nano-photonic devices have provided increasing opportunities for optical sensing and detection in the past decades, with intriguing features of miniature size, noninvasiveness and fast response, etc.[1,2,3,4,5,6,7,8,9]
The lower critical solution temperature (LCST), the hydrophilic amide group of PNIPA is connected with water via hydrogen bond and exists as a fully hydrated random coil
Since the cavity resonances are encoded with the structural transition information of PNIPA, the whispering-gallery modes (WGMs) spectra exhibit nonmonotonic red-shift in the heating process
Summary
Micro-/nano-photonic devices have provided increasing opportunities for optical sensing and detection in the past decades, with intriguing features of miniature size, noninvasiveness and fast response, etc.[1,2,3,4,5,6,7,8,9]. The detection limit of the microcavity sensors has reached levels of single molecules or single ions by employing mode-locking, optical spring, or plasmonic enhancement methods[18,19,20,21]. Despite their achievements of ultrahigh sensitivities, the conventional schemes of microcavity sensing, for example, by monitoring the shift of a single resonance mode[12,22], usually. By developing a self-referencing strategy with dual-modes of the microcavity, the changes of temperature and refractive index of PNIPA during the phase transition are individually extracted from the cavityresonance spectra. Under thermal-equilibrium conditions, it is found that the refractive index of PNIPA exhibits a
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