A novel high-precision digital droplet pipetting method that is used for nanoliter liquid handling with a reversibly pluggable microfluidic pipetting chip.

The controlled rotation of individual cells plays a crucial role in enabling three-dimensional multi-angle observation of cellular structure, function, and dynamic processes. Reported cell rotation techniques often struggle to strike a balance between high precision and simple control, and they exhibit limited control flexibility, typically achieving only uniaxial cell rotation. In this study, we propose a cell rotation technique in three dimensions based on optofluidics, which utilizes optical tweezers to immobilize the cell and exploits the asymmetry of the surrounding flow to drive cell rotation. By adjusting the focal position of the optical tweezers, cells can be positioned within various flow profiles, enabling control of the rotation speed, rotation direction, and rotation axis of cells. This approach simplifies the manipulation procedure, achieving desirable control precision and greater rotation flexibility. Using our approach, multi-angle surface imaging projections of target cells can be rapidly obtained, followed by capturing the cell contour data from the images. By combining the cell contour data with corresponding angular position information, we have reconstructed the 3D surface of the target cell. We have employed this technique in experiments for the analysis of red blood cell morphology. Based on the constructed 3D surface images of diverse-shaped red blood cells, we quantified structural parameters including cell surface area, volume, sphericity, and surface roughness, which demonstrates the potential application of this cell rotation technique for cellular morphological analysis.

The precise and efficient sorting of microscopic particles is critical in diverse fields, including biomedical diagnostics, drug development, and environmental monitoring. Fluorescence imaging-activated sorting refers to a strategy where fluorescence images are used to dynamically identify target particles and trigger selective manipulation for sorting purposes. In this study, we introduce a novel microfluidic particle sorting platform that combines optical tweezers with real-time fluorescence imaging for detection. High-speed image analysis enables accurate particle identification and classification, while the optical trap is selectively activated to redirect target particles. To validate the system’s performance, we used 10 µm green and orange fluorescent polystyrene particles. The platform achieved a sorting purity of 94.4% for orange particles under continuous flow conditions. The proposed platform provides an image-based sorting solution, advancing the development of microfluidic systems for high-resolution particle sorting in complex biological and environmental applications.

Microfluidic impact printing (MIP), which was recently proposed as a drop-on-demand microdroplet generation technology, shows a promising future in precision liquid handling. However, the working principle of the droplet formation and the performances of the generated droplets from the microfluidic chip are still unclear. In this article, we build an MIP system for multiplexed microdroplet dispensing, and develop a theoretical model to analyze the process of the droplet generation. As a result of the theoretical model which was validated against finite element simulations and experiments, the volume and the ejection velocity of the printed droplets can be predicted, demonstrating that the structure of the microfluidic cartridge plays the core role in the system. Based on the model, we have introduced a converging channel in the design of the cartridge to improve the performance of the printing system. Owning to the asymmetric transfer characteristic of the converging channel, the aspirated volume of the air could be reduced by 40% during the membrane restoring, and the liquid in the cartridge reaches stability to the initial pre-printing state faster, this enables the MIP system to have a wider adjustable range of droplet volume and a higher printing frequency.