This paper reports the design and investigation of a digital micro magnetofluidic platform for lab-on-a-chip applications. The platform allows a ferrofluid droplet to be driven along a preprogrammed path. The platform consists of a programmable x-y-positioning stage, a permanent magnet and a glass plate coated with a thin layer of Teflon. First, the actuation of a stand-alone water-based ferrofluid droplet was investigated. Circular, rectangular, triangular and number-eight-shape trajectories were tested and alyzed. The speed of the droplet is evaluated from the position data of the black ferrofluid using a customized MATLAB program. The results show that better positioning accuracy and steady movement can be achieved with smooth trajectories. Next, the ferrofluid droplet as the driving engine for a cargo of other diamagnetic liquid droplets is demonstrated. The characteristics of different cargo volumes are investigated. Due to the liquid/liquid cohesion, a large cargo of five times the volume of a 3-uL ferrofluid droplet can be transported. If the cargo is larger than the driving ferrofluid droplet, the liquid system forms a long trail that faithfully follows the preprogrammed path. Various mixing experiments were carried out. The effectiveness of mixing in this system is demonstrated with a titration test as well as a chemiluminescence assay. The platform shows a robust, simple and flexible concept for implementing a complex alysis protocol with multiple reaction steps.
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