Silicone oil–based ferrofluid microrobots for versatile magnetic digital microfluidics

Abstract

Magnetic digital microfluidics offers a promising alternative to the dominant electrowetting-based digital microfluidics but faces significant challenges regarding system portability, sample contamination, and limited functionality. Here, we report a magneto-silicobotic system utilizing silicone oil–based ferrofluid droplets as inert microrobots for versatile manipulation of droplets and solid particles. The system combines a cost-effective and portable microcoil array with a millimeter-scale permanent magnet to generate localized magnetic fields for precise actuation. It achieves precise droplet manipulation with an average tracking error of 0.15 mm, stable operation over 360 cycles, and speeds up to 52 mm/s. It can transport droplets 50 times its volume, achieve maximum transport speeds of 35 mm/s, maintain long-term residual-free transport, and handle diverse liquids, including organic solvents and biological samples. We further design a ferrofluid-based pipette to perform droplet splitting and dispensing, thus completing all basic operations of digital microfluidics. Additionally, we extend the robot's capability to include the transport and automated assembly of solid particles using integrated visual feedback. We envision that this portable, additive-free platform will have a significant impact on point-of-care testing, miniaturized biochemical assays, and automated lab-on-a-chip systems.