Biological microlasers, which utilize lasing emission as a sensing signal, has recently emerged as a promising approach in biotechnology. As such, biolasers with functionality are of great significance for the detection of tiny molecular interactions in biological systems. Despite considerable progress achieved in biomaterial-based microlasers, the ability to manipulate nanoscaled biostructures and functionalize molecules in microcavity represents a grand challenge. Herein we report the development of hydrogel microlasers by exploiting the versatility and controllability of hydrogels, where whispering-gallery-mode lasing was achieved by printing hydrogel droplets on a mirror. Lasing behaviors and fundamental characteristics of hydrogel lasers were explored under various water-monomer ratios and crosslinking degrees. Furthermore, hydrogel lasing microarray was developed, providing a novel approach to study molecular interactions within the 3D hydrogel network structure. To demonstrate the potential application and functionality, FRET peptide lasing was exploited for molecular analysis. Single-mode FRET laser emission was achieved by tuning the Forster distance in hydrogel droplets. Finally, different types of biomolecules were encapsulated to form biolasing. These findings not only highlight the ability of hydrogel biolasers for high-throughput biomolecular analysis but also provides deep insights into the relationship between biostructure and laser physics.
Liquid droplets offer a great number of opportunities in biochemical and physical research studies in which droplet-based microlasers have come into play over the past decade. While the recent emergence of droplet lasers has demonstrated their powerful capabilities in amplifying subtle molecular changes inside the cavity, the optical interactions between droplet resonators and an interface remain unclear. We revealed the underlying mechanism of droplet lasers when interacting with a droplet–solid interface and explored its correlation with intermolecular forces. A vertically oriented oscillation mode—arc-like mode—was discovered, where the number of lasing modes and their Q-factors increase with the strength of interfacial hydrophobicity. Both experimental and theoretical results demonstrated that hydrophobicity characterized by contact angle and interfacial tension plays a significant role in the geometry of droplet cavity and laser mode characteristics. Finally, we demonstrated how tiny forces induced by proteins and peptides could strongly modulate the lasing output in droplet resonators. Our findings illustrate the potential of exploiting optical resonators to amplify intermolecular force changes, providing comprehensive insights into lasing actions modulated by interfaces and applications in biophysics.
Optical barcodes have demonstrated a great potential in multiplexed bioassays and cell tracking for their distinctive spectral fingerprints. The vast majority of optical barcodes were designed to identify a specific target by fluorescence emission spectra, without being able to characterize dynamic changes in response to analytes through time. To overcome these limitations, the concept of the bioresponsive dynamic photonic barcode was proposed by exploiting interfacial energy transfer between a microdroplet cavity and binding molecules. Whispering-gallery modes resulting from cavity-enhanced energy transfer were therefore converted into photonic barcodes to identify binding activities, in which more than trillions of distinctive barcodes could be generated by a single droplet. Dynamic spectral barcoding was achieved by a significant improvement in terms of signal-to-noise ratio upon binding to target molecules. Theoretical studies and experiments were conducted to elucidate the effect of different cavity sizes and analyte concentrations. Time-resolved fluorescence lifetime was implemented to investigate the role of radiative and non-radiative energy transfer. Finally, microdroplet photonic barcodes were employed in biodetection to exhibit great potential in fulfilling biomedical applications.
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