Optofluidic lasers are an emerging technology for the development of miniaturized light sources and biological and chemical sensors. However, most optofluidic lasers demonstrated to date are operated at the single optical cavity level, which limits their applications in high-throughput biochemical sensing, high-speed wavelength switching, and on-chip spectroscopic analysis. Here, we demonstrated an optofluidic droplet laser array on a silicon chip with integrated microfluidics, in which four individual droplet optical cavities are generated and controlled by a 2 × 2 nozzle array. Arrays of droplets with a diameter ranging from 115 to 475 μm can be generated, removed, and regenerated on demand. The lasing threshold of the droplet laser array is in the range of 0.63–2.02 μJ/mm2. An image-based lasing threshold analysis method is developed, which enables simultaneous lasing threshold measurement for all laser units within the laser array using a low-cost camera. Compared to the conventional spectrum-based threshold analysis method, the lasing threshold obtained from the image-based method showed consistent results. Our droplet laser array is a promising technology in the development of cost-effective and integrated coherent light source on a chip for point-of-care applications.

Ultrasensitive, versatile sensors for molecular biomarkers are a critical component of disease diagnostics and personalized medicine as the COVID-19 pandemic has revealed in dramatic fashion. Integrated electrical nanopore sensors can fill this need via label-free, direct detection of individual biomolecules, but a fully functional device for clinical sample analysis has yet to be developed. Here, we report amplification-free detection of SARS-CoV-2 RNAs with single molecule sensitivity from clinical nasopharyngeal swab samples on an electro-optofluidic chip. The device relies on optically assisted delivery of target carrying microbeads to the nanopore for single RNA detection after release. A sensing rate enhancement of over 2,000x with favorable scaling towards lower concentrations is demonstrated. The combination of target specificity, chip-scale integration and rapid detection ensures the practicality of this approach for COVID-19 diagnosis over the entire clinically relevant concentration range from 10 4 -10 9 copies/mL.

We report optofluidic lasers with a monolayer gain material that self-assembles at the two-phase liquid−liquid interface. The selfassembly process deterministically introduces the gain at the surface of a microdroplet optical cavity, where the lasing mode has maximal interaction with the gain medium. A complete monolayer gain can be achieved in this surface-gain geometry, giving a surface density on the order of 10 14 cm −2 , which proves to be difficult, if not impossible, to achieve in the monolayer gain created at the solid−liquid interface via the surface immobilization method. We demonstrated that the lasing characteristics are drastically different between the gain material that is confined to the liquid−liquid interface and that homogeneously distributed in the bulk liquid solution. Our study reveals the unique capabilities of the surface-gain geometry optofluidic laser, which can be developed into a novel sensing platform to study biophysical and biochemical processes at the molecular level and has vast applications in biomedical diagnostics.

We present an optofluidic droplet dye laser that is generated by an array of microfluidic nozzles fabricated on a polycarbonate chip. A droplet resonator forms upon pressurizing the nozzle backside microfluidic channel. Multimode low-threshold lasing is observed from individual microdroplets doped with dye. Additionally, droplets can be conveniently released from the nozzle by water rinsing from the top microfluidic channel and subsequently regenerated, and thus achieve optofluidic lasers on-demand. Our work demonstrates a new approach to generating on-chip laser source and laser arrays in a simple, reproducible, reconfigurable, and low-cost fashion.

Polydimethylsiloxane-based optofluidics provides a powerful platform for a complete analytical lab-on-chip. Here, we report on a novel on-chip laser source that can be integrated with sample preparation and analysis functions. A corrugated sidewall structure is integrated into a microfluidic channel to form a distributed feedback (DFB) laser using rhodamine 6G dissolved in an ethylene glycol and water solution. Lasing is demonstrated with a threshold pump power of 87.9 µW, corresponding to a pump intensity of 52.7 m W / c m 2 . Laser threshold and output power are optimized with respect to rhodamine 6G concentration and core index and found to be in good agreement with a rate equation model. Additionally, the laser can be switched on and off mechanically using a pneumatic cell inducing positive pressure on the grating.