A bioelectrostatic responsive microlaser based on liquid crystal droplets was developed and explored for ultrasensitive detection of negatively charged biomolecules.

Advances in switchable microlasers have emerged as a building block with immense potential in controlling light–matter interactions and integrated photonics. Compared to artificially designed interfaces, a stimuli-responsive biointerface enables a higher level of functionalities and versatile ways of tailoring optical responses at the nanoscale. However, switching laser emission with biological recognition has yet to be addressed, particularly with reversibility and wavelength tunability over a broad spectral range. Here we demonstrate a self-switchable laser exploiting the biointerface between label-free DNA molecules and dye-doped liquid crystal matrix in a Fabry–Perot microcavity. Laser emission switching among different wavelengths was achieved by utilizing DNA conformation changes as the switching power, which alters the orientation of the liquid crystals. Our findings demonstrate that different concentrations of single-stranded DNA lead to different temporal switching of lasing wavelengths and intensities. The lasing wavelength could be reverted upon binding with the complementary sequence through DNA hybridization process. Both experimental and theoretical studies revealed that absorption strength is the key mechanism accounting for the laser shifting behavior. This study represents a milestone in achieving a biologically controlled laser, shedding light on the development of programmable photonic devices at the sub-nanoscale by exploiting the complexity and self-recognition of biomolecules.

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. Timeresolved 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.

Dust deposition is an important nutrient source to the South China Sea (SCS), but few in situ experiments were conducted on phytoplankton response to the deposition. We conducted onboard incubation experiments at three stations near Luzon Strait in the SCS, with addition of multiple dissolved inorganic nutrients, Asian dust, and rainwater. From our results, nitrogen and phosphorus were both urgently needed for phytoplankton growth in the SCS, indicated by the evident Chl a response to the addition of nitrogen and phosphorus together. Almost no evident response was observed by adding phosphorus or iron alone to incubation waters, although a delayed response of Chl a in mass concentration was observed by adding nitrogen alone. The latter implied a possible utilization of dissolved organic phosphorus because of insufficient dissolved inorganic phosphorus in incubation waters. Under such nutrient condition, Asian dust showed an apparent promotion effect on phytoplankton growth by providing sufficient amounts of nitrogen but low phosphorus. Meanwhile, it was found that large sized (> 5 μm) phytoplankton community showed different responses to dust addition at different stations. At stations A3 and A6, Chaetoceros spp. became the dominant species during the bloom period, while at station WG2, Nitzschia spp. became dominant. In combination with different initial nutrients and Chl a levels at the three stations, the different phytoplankton community evolution implied the response difference to external inputs between oligotrophic (stations A3 and A6) and ultraoligotrophic (station WG2) conditions in the SCS.

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