We present an innovative, simple, and versatile hydrophobic valve enabling all-important complex liquid manipulations on self-powered, channel-based microfluidic devices and as such being extremely valuable for the design of highly demanding point-of-care (POC) platforms. The presented hydrophobic valve is made of filter paper treated with a fluorinated compound (i.e., Aquapel) and shows both superhydrophobic properties (contact angle up to 155°) and high resistance to liquid pressure (up to 9 kPa), while retaining gas permeability and utter fabrication simplicity. Whereas this valve can be integrated in any channel-based system and can be used both as a vent, to delay liquid displacement on chip, or as a barrier, to stop the liquid flow in a certain direction, in this work we demonstrate some of its capacities by combining it with our in house developed self-powered SIMPLE and iSIMPLE platforms. First, we integrated it with the infusion iSIMPLE pump, thus generating completely fail-proof activation regardless of how the operator is actuating the system. Second, we used hydrophobic valves as both barrier and vent in the same microfluidic chip, which allowed the combination of two SIMPLE pumps for splitting one sample in two parallel channels. This attribute is fundamental for achieving multiplex analysis on completely autonomous microfluidic platforms. Finally, we achieved an unprecedented liquid manipulation for a self-powered microfluidic platform, namely, shuttling of liquid, after a single user activation by combining for the first time SIMPLE and iSIMPLE with the developed hydrophobic vent and barrier, all in a single chip. These results convincingly demonstrated that the developed hydrophobic valve combined with SIMPLE/iSIMPLE presents an essential building block for an ideal POC system, which is self-powered, inexpensive, and robust and can perform complex bioassays upon a single user activation.
Keywords: hydrophobic valve; microfluidic valve; point-of-care diagnostics; programmable liquid manipulation; self-powered microfluidics.