"Microfluidic devices offer unique opportunities for diagnosing rapidly many types of diseases using pre-integrated reagents and small volumes of samples next to patients. One major limitation of microfluidics for POC diagnostics is the need to always adapt microfluidic chip architectures and assay protocols for each specific application. Given the huge number of POC tests that can be used to monitor human health, having a flexible, programmable microfluidic device would be ideal. However, this flexibility is largely hindered by the long-standing challenge to control and manipulate the autonomous flow of liquids along microfluidic channels in a simple and reliable manner without using active micro-components, which are typically complex to manufacture, bulky, power-hungry and expensive.
This project aimed to introduce a novel concept for controlling the flow of liquids filling microchannels in microfluidic chips. The concept is based on the stop-and-go actuation of gates, located at key locations along a flow path. When a liquid or sample is pipetted onto a loading pad (See. Fig. 1a), it spontaneously fills the flow path serviced by the loading pad due to capillary action and stops precisely at any gates that the liquid encounters. Stopping the flow is achieved by having a geometrical discontinuity along the flow path that pins the liquid due to a Laplace pressure barrier. However, the flow can be resumed by applying a voltage to the meniscus of liquid pinned at the gate, (Fig. 1b). The voltage increases the wetting properties of the geometrical discontinuity, which makes the liquid able to pass the gate. We termed such gates ""electrogates"" and bias them using a peripheral and specific protocols (selection of gate, voltage, voltage duration). The peripheral can be controlled using a smartphone application and standard wireless communication (e.g. Bluetooth), (Fig. 1c, d).
Electrogates can be integrated to microfluidic chips in silicon to select a flow path post-fabrication of the chips. This brings significant flexibility to such chips with flow paths and timing being programmed in a convenient manner using a simple user interface on a smartphone. One can envision deploying such a method to microfluidic chips used for diagnostics where duration of key biochemical steps can be optimized to match a desired sensitivity or where a liquid or sample can be passed inside specific microchannels for mixing, filtration, processing, etc. depending on what step would be optimal for a test. This offers remarkable opportunities considering that such a simple but efficient control over liquids can still be obtained using capillary forces and a simple peripheral for activating the desired electrogates. In addition, electrogates remain easy to fabricate and use low voltage and little power. They can also be multiplied on a microfluidic chip to allow multiplexed control of various liquids filling microfluidic chips in parallel.
"
