A bioelectrostatic responsive microlaser based on liquid crystal droplets was developed and explored for ultrasensitive detection of negatively charged biomolecules.
Recent investigations on the design and application of liquid crystal-based biosensors have been reviewed, according to the phenomenon that orientations of liquid crystals can be directly influenced by interactions between biomolecules and liquid crystal molecules. With the ability to detect external stimuli with high sensitivity, liquid crystal biosensors can help realize a new biosensing era.
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 ...
Protein assays show great importance in medical research and disease diagnoses. Liquid crystals (LCs), as a branch of sensitive materials, offer promising applicability in the field of biosensing. Herein, we developed an ultrasensitive biosensor for the detection of low-concentration protein molecules, employing LC-amplified optofluidic resonators. In this design, the orientation of LCs was disturbed by immobilized protein molecules through the reduction of the vertical anchoring force from the alignment layer. A biosensing platform based on the whispering-gallery mode (WGM) from the LC-amplified optofluidic resonator was developed and explored, in which the spectral wavelength shift was monitored as the sensing parameter. The microbubble structure provided a stable and reliable WGM resonator with a high Q factor for LCs. It is demonstrated that the wall thickness of the microbubble played a key role in enhancing the sensitivity of the LC-amplified WGM microcavity. It is also found that protein molecules coated on the internal surface of microbubble led to their interactions with laser beams and the orientation transition of LCs. Both effects amplified the target information and triggered a sensitive wavelength shift in WGM spectra. A detection limit of 1 fM for bovine serum albumin (BSA) was achieved to demonstrate the high-sensitivity of our sensing platform in protein assays. Compared to the detection using a conventional polarized optical microscope (POM), the sensitivity was improved by seven orders of magnitude. Furthermore, multiple types of proteins and specific biosensing were also investigated to verify the potential of LC-amplified optofluidic resonators in the biomolecular detection. Our studies indicate that LC-amplified optofluidic resonators offer a new solution for the ultrasensitive real-time biosensing and the characterization of biomolecular interactions.
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