Abstract
Compact disc (CD)-based centrifugal microfluidics is an increasingly popular choice for academic and commercial applications as it enables a portable platform for biological and chemical assays. By rationally designing microfluidic conduits and programming the disc’s rotational speeds and accelerations, one can reliably control propulsion, metering, and valving operations. Valves that either stop fluid flow or allow it to proceed are critical components of a CD platform. Among the valves on a CD, wax valves that liquify at elevated temperatures to open channels and that solidify at room temperature to close them have been previously implemented on CD platforms. However, typical wax valves on the CD fluidic platforms can be actuated only once (to open or to close) and require complex fabrication steps. Here, we present two new multiple-use wax valve designs, driven by capillary or magnetic forces. One wax valve design utilizes a combination of capillary-driven flow of molten wax and centrifugal force to toggle between open and closed configurations. The phase change of the wax is enabled by heat application (e.g., a 500-mW laser). The second wax valve design employs a magnet to move a molten ferroparticle-laden wax in and out of a channel to enable reversible operation. A multi-phase numerical simulation study of the capillary-driven wax valve was carried out and compared with experimental results. The capillary wax valve parameters including response time, angle made by the sidewall of the wax reservoir with the direction of a valve channel, wax solidification time, minimum spin rate of the CD for opening a valve, and the time for melting a wax plug are measured and analyzed theoretically. Additionally, the motion of the molten wax in a valve channel is compared to its theoretical capillary advance with respect to time and are found to be within 18.75% of the error margin.
Highlights
Introduction iationsCentrifugal microfluidics platforms are becoming widely implemented for various applications due to the possibility of integrating sample preparation steps with assays
We have demonstrated two new types of wax valves for application in centrifugal microfluidics
Once the wax is molten, it flows into the valve channel and upon solidification it cuts off the flow between the inner and outer reservoirs that are connected by the valve channel
Summary
The ferrowax used our experiments is prepared by mixing paraffin wax A camera (MA1000, Amscope, Irvine, CA, USA) captures a side view image of the molten ferrowax droplet on the polyacrylic and adhesive surfaces. These images are analyzed with the Im‐. (MA1000, Amscope, Irvine, CA, USA) captures a side view image of the molten ferrowax droplet on the polyacrylic and adhesive surfaces. These images are analyzed with the ImageJ program (National Institute of Health, Bethesda, MA, USA) using the software’s in-built contact angle plugin [22].
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