Opto-electrical gradient wetting for reliable and reconfigurable transport of droplets on crystal silicon

Droplet directional transportation plays a crucial role in many fields such as microfluidics, device thermal management, and water harvesting. Gradient wetting is an important approach to drive droplets by establishing a patterned surface energy distribution. However, existing chemical or physical gradient methods suffer from limitations such as contamination, irreversibility, and insufficient reconfigurability, making it difficult to achieve stable and dynamic manipulation. In this work, we propose an opto-electrical gradient wetting system on a crystal silicon (OE-GWOS) device for programmable droplet manipulation. By applying patterns with a grayscale gradient, the resistivity of crystal silicon is spatially and continuously modulated, inducing continuous variation in voltage distribution across the dielectric layer, thereby constructing a reconfigurable wetting gradient on the surface for stable and continuous droplet driving. Moreover, the gradient can be dynamically reconstructed along arbitrary directions and at arbitrary locations on the chip, enabling flexible and programmable droplet operations. Compared to discrete light spot driving, this strategy significantly improves motion continuity and stability, reduces system control complexity, and supports complex manipulations, including multidirectional motion and path planning with no need for real-time addressing. It provides a new route toward highly reliable, reconfigurable, and programmable digital microfluidics with potential for integration with microelectronics.