Lasing‐Encoded Microsensor Driven by Interfacial Cavity Resonance Energy Transfer

Abstract

for use in biomedical and biological applications. [1][2][3][4][5] Various types of optical microcavities have been developed, such as Fabry-Perot cavities, [6][7][8] photonic crystals, [9] and whispering-gallery-modes (WGMs), as implemented in ring resonators, [10][11][12] micro-/nanodisks, [13,14] and microspheres. [3][4][5][15][16][17][18][19][20] In particular, microsphere-based WGM lasers are appealing candidates for sensing probes owing to their convenience, extremely high Q factor, and potential for application in intracellular and extracellular probes. [13,15,16,21,22] Moreover, analytes can be positioned outside of the optical cavity, where an evanescent field exists at the external interface between the resonant cavity and surrounding medium. [23][24][25] At present, most microsphere or droplet-based WGM lasers are considered to be passive-detection devices, as they require physical changes (e.g., refractive indexes) to induce a resonance spectral shift, and thus cannot provide detailed biochemical information. [26][27][28] In contrast, active-detection devices, which employ analytes as the gain medium, can provide more selective and sensitive information about the biospecies. [8,29] Therefore, the ability to utilize a biological gain medium on the external surface of a microsphere cavity will allow us to amplify subtle changes in the gain medium and the resultant spectra, threshold, and lasing modes. However, the overlap factor for the optical mode and gain medium is much lower than the value of the gain within the cavity, and the background fluorescence also interferes with the external cavity sensing, making this amplification a difficult task. Thus, to enable amplification of these subtle changes, we have applied the concept of Förster resonance energy transfer (FRET) at the interface of a droplet-based laser to separate the donor and acceptor at the droplet-surface interface (Figure 1a). FRET is an electrodynamic phenomenon that is highly sensitive to distance, spectral overlap, and the orientation between donor and acceptor molecules. In the past decade, FRET has been used as a powerful tool for providing nanoscale information in many biosensing applications. The performance of FRET is mainly dependent on the design of the donor and acceptor pairs. Several groups recently utilized FRET by using donor molecules as exciton funnels, [30,31] or light-harvesting antennas, [31] to realize a wavelength tunable laser, [30] single molecule nanoprobes, [32] or light redirectioning devices [33] that strongly amplify the emission of acceptor molecules when Microlasers are emerging tools for biomedical applications. In particular, whispering-gallery-mode (WGM) microlasers are promising candidates for sensing at the biointerface owing to their high quality-factor and potential in molecular assays, and intracellular and extracellular detection. However, lasing particles with sensing functionality remain challenging since the overlap between the WGM optical mode and external gain medium is much lower compared to ...

A new ultrafast energy funneling material harvests three times more diffusive solar energy for GaInP photovoltaics

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Tunable Microlasers Modulated by Intracavity Spherical Confinement with Chiral Liquid Crystal

“…Conventional FP cavity relies on two highly reflected planar mirrors to form a resonator, in which whole‐body interactions between the electromagnetic field and the gain medium can be utilized for intracavity detection and manipulation. [ 14–18 ] The structure of within the FP cavity can also alter the lasing output characteristics sensitively (e.g., laser mode, threshold, and lasing spectrum). Herein, we developed a tunable laser by configuring the optical confinement, chirality, and polarization at the nanoscale with liquid crystals (LCs) in FP microcavity.…”

Review of biosensing with whispering-gallery mode lasers

“…Another interesting sensing mechanism for WGM microsphere lasers makes use of the concepts of Förster resonance energy transfer (FRET) and coherent radiative energy transfer (CRET) 47 . Following these mechanisms, the WGM microlaser doped with donor molecules can exhibit changes in its emission intensity and wavelength upon surface binding of acceptor molecules.…”

“…WGM cavities composed of liquid crystal (LC) droplets and doped with donor/acceptor molecules were used to detect the FRET signals in the emission spectrum of the droplets. WGM microlaser LC droplets were used to detect FRET signals of fluorophores such as rhodamine B isothiocyanate and rhodamine-phycoerythrin as they attached to the LC droplet surface 47 .…”