title: Magnetic timing valves for fluid control in paper-based microfluidics.
abstract: Multi-step analytical tests, such as an enzyme-linked immunosorbent assay (ELISA), require delivery of multiple fluids into a reaction zone and counting the incubation time at different steps. This paper presents a new type of paper-based magnetic valves that can count the time and turn on or off a fluidic flow accordingly, enabling timed fluid control in paper-based microfluidics. The timing capability of these valves is realized using a paper timing channel with an ionic resistor, which can detect the event of a solution flowing through the resistor and trigger an electromagnet (through a simple circuit) to open or close a paper cantilever valve. Based on this principle, we developed normally-open and normally-closed valves with a timing period up to 30.3 ± 2.1 min (sufficient for an ELISA on paper-based platforms). Using the normally-open valve, we performed an enzyme-based colorimetric reaction commonly used for signal readout of ELISAs, which requires a timed delivery of an enzyme substrate to a reaction zone. This design adds a new fluid-control component to the tool set for developing paper-based microfluidic devices, and has the potential to improve the user-friendliness of these devices.
authors.affiliation: Department of Mechanical Engineering, McGill University, 817 Sherbrooke Street West, MD270, Montreal, Quebec, Canada H3A 0C3.
authors.forename: Xiao
authors.initials: X
authors.lastname: Li
authors.forename: Philip
authors.initials: P
authors.lastname: Zwanenburg
authors.forename: Xinyu
authors.initials: X
authors.lastname: Liu
mesh_terms: D003124:Colorimetry; D004560:Electricity; D004797:Enzyme-Linked Immunosorbent Assay; D004867:Equipment Design; D008280:Magnetics; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation*; D010209:Paper; D013997:Time Factors