Abstract
Distinctive from other forms of microfluidic system, capillary microfluidics is of great interest in autonomous micro-systems due to its well-engineered fluidic control based on capillary force. As an essential component of fluidic control in capillaric circuits, micro-valves enable sequential fluidic operations by performing actions such as stopping and triggering. In this paper, we present a stair-step liquid-triggered valve; the functionality of the valve and its dependencies on geometry and surface modification are studied. The surface contact angle of the microfabricated valves that are coated by polyethylene glycol (PEG) or (3-Aminopropyl) triethoxysilane (APTES) is evaluated experimentally, and the corresponding reliability of the valve structure is discussed. Moreover, the variation in the surface contact angle over time is investigated, indicating the shelf time of the device. We further discuss the overall fluidic behavior in such capillary valves, which benefits the capillaric circuit designs at the initial stage.
Highlights
Microfluidic devices offer the promise of rapid, miniaturized, and automated biochemical assays, as they have potential to realize large-scale applications at a much smaller scale in order to reduce instrument size and sample consumption
Microfluidic devices have been suggested as powerful tools for a variety of applications, including point-of-care diagnosis and bio analysis [1,2,3]
Capillary microfluidics offer a solution for self-powered fluidic control to get rid of external peripheral instruments
Summary
Microfluidic devices offer the promise of rapid, miniaturized, and automated biochemical assays, as they have potential to realize large-scale applications at a much smaller scale in order to reduce instrument size and sample consumption. When the liquid trigger valve is fabricated on silicon substrate, the superhydrophilic nature of the bare Si surface provides an overwhelming capillary pressure against the energy barrier of the expansion geometry in the stop flow channel [40]. This could lead to a complete flow-through action without the need of a secondary trigger flow, meaning the failure of the valve structure. A one-step surface modification method is presented to prepare the silicon microfluidic devices with either PEG or APTES in an aqueous solution We discuss their influences on valve functionality, and the stability of different surface functional groups is evaluated as well
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