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Centrifugal microfluidic system (Lab-on-CD) is attractive for realizing the conventional laboratory processes on a single microfluidic platform. Efficient valving technology for centrifugal microfluidics is highly desired for fluidic sample regulation. This paper reports a new valving technology based on the intrinsic centrifugal force. The valving system is mechanically programed to achieve sequential control of fluidic samples. The performance of the valving system was tested using a microfluidic chip fabricated using 3D printing technology. The valve can be controlled by manipulating the rotational speed and showed good performance. The effect of the system’s physical parameters on the burst frequencies of the valve and the interaction between different valves were investigated both experimentally and theoretically. The burst frequencies of the valves can be tuned easily by changing the physical parameters of the mechanical system. An active flow switch was designed and tested based on sequential control of multiple valves. It is capable of operation at low rotation frequency with no requirement for reversed rotation direction as in other reported work. The valving system is highly reliable, compact, and easy to be fabricated. It works independent of the microfluidic chip, thus could be reversibly used and easily reconfigured for different application on the centrifugal platform. [ABSTRACT FROM AUTHOR]

This paper describes, for the first time, the use of alginate hydrogels as miniaturised microvalves within microfluidic devices. These biocompatible and biodegradable microvalves are generated in situ and on demand, allowing for microfluidic flow control. The microfluidic devices were fabricated using an origami inspired technique of folding several layers of cyclic olefin polymer followed by thermocompression bonding. The hydrogels can be dehydrated at mild temperatures, 37 °C, to slightly open the microvalve and chemically erased using an ethylenediaminetetraacetic acid disodium salt (EDTA) solution, to completely open the channel, ensuring the reusability of the whole device and removal of damaged or defective valves for subsequent regeneration. [ABSTRACT FROM AUTHOR]

Centrifugal microfluidic platforms aim to integrate and perform complex biological and chemical processes within disc-like substrates and valving through centrifugal forces and the Coriolis effect. Although the integration of active valves within such system can be used to enhance fluid control, the ability to fabricate and integrate addressable valves within centrifugal platforms remains a significant challenge. To address this issue, herein, we present and test an addressable electrowetting centrifugal (EWC) valve. The EWC valve comprises a hydrophobic burst valve, integrated side electrodes and a dielectric layer between the microfluidic channel and electrode structures. The burst valve is made from a hydrophobic material able hold a specified pressure. Specifically, application of an external electric field is used to alter the valve wettability, making the valve more hydrophilic, decreasing the threshold pressure and triggering the opening of the valve. To assess valve performance, we investigate the influence of electric properties and channel geometry on valve response and then demonstrate multiple operations on different fluid samples. Finally, and to highlight the utility of EWC valves, we demonstrate the detection and analysis of CD4 human immune cells. • This electrowetting centrifugal valve is the first electrowetting based fluid switching method on centrifugal microfluidic platform. • These electrowetting valves can be triggered independently, thus increasing the control flexibility. • The valves are controlled wirelessly via a WiFi-integrated PCB and can be used to perform complex fluid manipulation. [ABSTRACT FROM AUTHOR]

Abstract: In this work, autonomously functioning artificial ion channels were fabricated and assessed. An electrowetting-based valve was formed in a constricted region surrounded by poly(dimethylsiloxane) walls with a gold electrode at the base. The gold electrode was connected to an integrated hydrogen electrode to detect the pH of a solution to be transported. A mixed potential was generated when the gold valve electrode and a platinum black electrode in the hydrogen electrode were connected by the solution, which polarized the gold electrode. As a result, the gold electrode became sufficiently hydrophilic at pH values above a certain threshold, and the solution was able to pass through the valve region. The threshold potential could be adjusted by changing the width of the valve. To expand the range of application to biomolecules, a urea-responsive valve was also fabricated by immobilizing the enzyme urease on the platinum black electrode. Moreover, passage of the solution through the valve was coupled with the transportation of a second solution through a separate flow channel, using a composite electrode consisting of a gold electrode used to form the electrowetting-based valve and a zinc electrode to detect the arrival of a solution. [Copyright &y& Elsevier]

Abstract: A microanalysis system with functions including automatic valve operation for mixing solutions, pH regulation, and detection based on electrochemiluminescence (ECL) was fabricated. Automatic valve operation was achieved by means of direct electrowetting using one of two solutions as a part of an electronic circuit. A valve formed with a gold electrode was opened when the second solution was filled in a compartment, causing the mixing of the two solutions. The pH regulation was achieved by using a nonstandard three-electrode system. The pH of the solution could be changed as desired by changing the working electrode potential, and the negative feedback function maintained the pH at a constant level. The ECL was generated on a platinum working electrode. Amino acids were detected as model analytes. A reagent solution containing tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)3 2+) and a sample solution containing an amino acid were mixed, and the pH was adjusted using the pH regulator. When +1.1V (vs. Ag/AgCl) was applied to the electrode, red luminescence was observed. An increase in the ECL intensity was observed with an increase in the concentration. Amino acids of concentrations ranging from sub nM to 1mM could be determined on the integrated device. [Copyright &y& Elsevier]

Abstract: On-chip microfluidic transport was achieved using only integrated microfluidic components, including two pumps and four valves; furthermore, optical biosensing was conducted on the chip following the mixing of solutions by diffusion in a mixing channel. The basic components for the pumps and valves were three-electrode systems and a polydimethylsiloxane (PDMS) diaphragm to separate the electrolyte solution from the sample solution in the microflow channel. For the pump, hydrogen bubbles were grown or shrunk around platinum black working electrodes on the walls of anisotropically etched through-holes in a silicon substrate. The volume change of the bubbles caused deformation of the PDMS diaphragm over the working electrode, and the solution in the flow channel was mobilized. The same principle was used to open or close the valves in the flow channels. Two different solutions were introduced from two injection ports and transported through the flow channels by sequential operation of the pumps and the valves. When the flows were stopped, we were able to mix the solutions in a mixing channel. To demonstrate the applicability of the microfluidic system to microanalysis systems, a solution containing an enzyme and another solution containing enzyme substrates were injected from two injection ports, mixed, and allowed to react in the mixing channel. Fluorometric detection of the progress of enzymatic reactions and quantitative analysis of hydrogen peroxide and l-glutamate were conducted. [Copyright &y& Elsevier]

Fluid control is a key element in the performance of microfluidic “lab-on-a-chip” devices. The development of integrated multi-function micro-chemical reactors and analysis platforms depends upon on-chip valving and pumping. In this work, microfluidic valves and pumps were fabricated from etched glass substrates each bonded to a second glass substrate lid that had ultrasonically drilled access holes. The devices contained ferrofluid plugs of approximately 10 mm in length that were actuated by external magnets. The ferrofluid used in the devices was a colloidal suspension of ferromagnetic particles in a hydrophobic fluorocarbon carrier and was immiscible in water. With air in the channels, ferrofluid devices could withstand pressures of 12 kPa and could be opened and closed against pressures of 8.5 and 5.0 kPa, respectively, under a magnetic field of 2.8 kG. A ferrofluid pump comprising a ferrofluid piston and two ferrofluid valves was able to generate air pressures in excess of 5 kPa. In untreated glass channels, leakage of water around ferrofluid seals was significant. However, when the portions of the channel network that contained the ferrofluid were coated with a hydrophobic organo-silane, leakage was not detectable. [Copyright &y& Elsevier]

Smart hydrogels show phase transition behavior. This property can be used to operate sensors and actuators in a reversible and reproducible mode. Ignoring phenomena occurring at volume phase transition can result in a malfunction or even failure of the system. In this paper, the influence of volume phase transition phenomena on the behavior of hydrogel-based valves are discussed. Furthermore, the operation mode of such valves in dependence of various design parameters and hydrogel properties are described. [Copyright &y& Elsevier]

A microfluidic system was constructed by integrating on-chip micropumps and check valves that function by means of a hydrogen bubble that is generated or extinguished electrochemically. Essential elements consisted of thin-film three-electrode systems, including a platinum black working electrode. Micro flow channels and containers for electrolyte solutions were formed on a polydimethylsilixane (PDMS) substrate. The growth and shrinkage of the bubble were controlled reproducibly by setting the working electrode potential at a constant value. The elastic nature of the bubble clogged in a valve compartment in the middle of the flow channel hindered the effective passage of the solution. The bubble was also effective in separating two different solutions. By making the valves open and close cooperatively, a solution could be introduced into the system and transported in the flow channel. When two dye solutions were transported and merged in a flow channel, sheath flows were observed, reflecting a low Reynolds number. As a model system, two solutions containing luciferin and luciferase were introduced separately, transported, and mixed. Chemiluminescence originating from the enzymatic reaction was observed. [Copyright &y& Elsevier]