Reversible thermo-pneumatic valves on centrifugal microfluidic platforms (original) (raw)
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We report a novel principle to actuate liquids based on centrifugo-thermopneumatic effects. This approach enables us to reliably realize temperature-controlled valves and aliquoting structures on the centrifugal microfluidic platform. We present special geometries that force liquids to generate gas entrapments when exposed to a centrifugal field. The gas entrapments expand (or contract) when heated (or cooled) thus displacing the liquid volumes. Successful implementation of this principle is demonstrated by a microfluidic chip for automated real-time PCR based genotyping of nucleic acids. INTRODUCTION Development of lab-on-a-chip systems is driven by the great demand for automated and integrated solutions in the market of life science and molecular diagnostics. A particular challenge is the establishment of such microfluidic systems in conventional lab environments. One solution to this task is to automate standard laboratory devices by integration of microfluidic chips. Here we rep...
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2008
We present a new microvalve that can be monolithically integrated in centrifugally driven lab-on-achip systems. In contrast to existing operation principles that use hydrophobic patches [1], geometrically defined capillary stops [2] or siphons [3], here we present a pneumatic principle. It needs neither additional local coatings [1] nor expensive micro sized geometries . The valve is controlled by the spinning frequency and can be switched to be open when the centrifugal pressure overcomes the pneumatic pressure inside an unvented reaction cavity. We designed and characterized valves ranging in centrifugal burst pressure from 6700 Pa to 2100 Pa. Based on this valving principle we present a new structure for aliquoting of liquids. We experimentally demonstrated this by splitting 105 µL volumes into 16 aliquots with a volume CV of 3 %.
Thermo-pneumatic pumping in centrifugal microfluidic platforms
Microfluidics and Nanofluidics, 2011
The pumping of fluids in microfluidic discs by centrifugal forces has several advantages, however, centrifugal pumping only permits unidirectional fluid flow, restricting the number of processing steps that can be integrated before fluids reach the edge of the disc. As a solution to this critical limitation, we present a novel pumping technique for the centrifugal microfluidic disc platform, termed the thermo-pneumatic pump (TPP), that enables fluids to be transferred the center of a rotating disc by the thermal expansion of air. The TPP is easy to fabricate as it is a structural feature with no moving components and thermal energy is delivered to the pump via peripheral infrared (IR) equipment, enabling pumping while the disc is in rotation. In this report, an analytical model for the operation of the TPP is presented and experimentally validated. We demonstrate that the experimental behavior of the pump agrees well with theory and that flow rates can be controlled by changing how well the pump absorbs IR energy. Overall, the TPP enables for fluids to be stored near the edge of the disc and transferred to the center on demand, offering significant advantages to the microfluidic disc platform in terms of the handling and storage of liquids.
Aliquoting on the centrifugal microfluidic platform based on centrifugo-pneumatic valves
Microfluidics and Nanofluidics, 2011
We present a new method for aliquoting liquids on the centrifugal microfluidic platform. Aliquoting is an essential unit operation to perform multiple parallel assays (“geometric multiplexing”) from one individual sample, such as genotyping by real-time polymerase chain reactions (PCR), or homogeneous immunoassay panels. Our method is a two-stage process with an initial metering phase and a subsequent transport phase initiated by switching a centrifugo-pneumatic valve. The method enables aliquoting liquids into completely separated reaction cavities. It includes precise metering that is independent on the volume of pre-stored reagents in the receiving cavities. It further excludes any cross-contamination between the receiving cavities. We characterized the performance for prototypes fabricated by three different technologies: micro-milling, thermoforming of foils, and injection molding. An initial volume of ~90 μl was split into 8 aliquots of 10 μl volume each plus a waste reservoir on a thermoformed foil disk resulting in a coefficient of variation (CV) of the metered volumes of 3.6%. A similar volume of ~105 μl was split into 16 aliquots of 6 μl volume each on micro-milled and injection-molded disks and the corresponding CVs were 2.8 and 2.2%, respectively. Thus, the compatibility of the novel aliquoting structure to the aforementioned prototyping and production technologies is demonstrated. Additionally, the important question of achievable volume precision of the aliquoting structure with respect to the production tolerances inherent to each of these production technologies is addressed experimentally and theoretically. The new method is amenable to low cost mass production, since it does not require any post-replication surface modifications like hydrophobic patches.
Pneumatic pumping in centrifugal microfluidic platforms
Microfluidics and Nanofluidics, 2010
Centrifugal microfluidics has emerged as a unique approach to the development of integrated total analysis systems for medical diagnostics. However, despite its many advantages, the platform has a size limitation due to the centripetal pumping mechanism in which fluids can only be moved from the center of the disc to the rim. This limits the footprint of the microfluidic network to one radius of the disc, and this in turn limits the amount of space available to embed complex assays. In order to overcome this space limitation problem, we are developing new techniques to pump fluids back toward the center of the disc as to allow greater path lengths for the fluidic network. This study presents a novel pumping mechanism for centrifugal microfluidics utilizing a combination of centrifugation and pneumatic compression. Pneumatic energy is stored during high-speed centrifugation with sample fluids trapping then compressing air in specially designed chambers. The accumulated pneumatic energy is released by spinning down, which expands the trapped air and thus pumps liquids back toward the center of the CD. This newly developed method overcomes current limitations of centripetal pumping avoiding external manipulation or surface treatments. In this article, we explore the design of appropriate chambers to induce pneumatic pumping and analytically describe the mechanics behind the pumping action. For proof of principle, we have applied pneumatic pumping to siphon priming.
Biosensors & bioelectronics, 2018
In this paper we present a wirelessly powered array of 128 centrifugo-pneumatic valves that can be thermally actuated on demand during spinning. The valves can either be triggered by a predefined protocol, wireless signal transmission via Bluetooth, or in response to a sensor monitoring a parameter like the temperature, or homogeneity of the dispersion. Upon activation of a resistive heater, a low-melting membrane (Parafilm™) is removed to vent an entrapped gas pocket, thus letting the incoming liquid wet an intermediate dissolvable film and thereby open the valve. The proposed system allows up to 12 heaters to be activated in parallel, with a response time below 3 s, potentially resulting in 128 actuated valves in under 30 s. We demonstrate, with three examples of common and standard procedures, how the proposed technology could become a powerful tool for implementing diagnostic assays on Lab-on-a-Disc. First, we implement wireless actuation of 64 valves during rotation in a freely...
Tape underlayment rotary-node (TURN) valves for simple on-chip microfluidic flow control
Biomedical Microdevices, 2010
We describe a simple and reliable fabrication method for producing multiple, manually activated microfluidic control valves in polydimethylsiloxane (PDMS) devices. These screwdriver-actuated valves reside directly on the microfluidic chip and can provide both simple on/off operation as well as graded control of fluid flow. The fabrication procedure can be easily implemented in any soft lithography lab and requires only two specialized tools-a hot-glue gun and a machined brass mold. To facilitate use in multi-valve fluidic systems, the mold is designed to produce a linear tape that contains a series of plastic rotary nodes with small stainless steel machine screws that form individual valves which can be easily separated for applications when only single valves are required. The tape and its valves are placed on the surface of a partially cured thin PDMS microchannel device while the PDMS is still on the softlithographic master, with the master providing alignment marks for the tape. The tape is permanently affixed to the microchannel device by pouring an over-layer of PDMS, to form a full-thickness device with the tape as an enclosed underlayment. multiple valves, low risk of damaging a microfluidic device during valve installation, high torque, elimination of stripped threads, the capabilities of TURN hydraulic actuators, and facile customization of TURN molds. We have utilized these valves to control microfluidic flow, to control the onset of molecular diffusion, and to manipulate channel connectivity. Practical applications of TURN valves include control of loading and chemokine release in chemotaxis assay devices, flow in microfluidic bioreactors, and channel connectivity in microfluidic devices intended to study competition and predator/prey relationships among microbes.
Development of a Passive Liquid Valve (PLV) Utilizing a Pressure Equilibrium Phenomenon on the Centrifugal Microfluidic Platform, 2015
In this paper, we propose an easy-to-implement passive liquid valve (PLV) for the microfluidic compact-disc (CD). This valve can be implemented by introducing venting chambers to control the air flow of the source and destination chambers. The PLV mechanism is based on equalizing the main forces acting on the microfluidic CD (i.e., the centrifugal and capillary forces) to control the burst frequency of the source chamber liquid. For a better understanding of the physics behind the proposed PLV, an analytical model is described. Moreover, three parameters that control the effectiveness of the proposed valve, i.e., the liquid height, liquid density, and venting chamber position with respect to the CD center, are tested experimentally. To demonstrate the ability of the proposed PLV valve, microfluidic liquid switching and liquid metering are performed. In addition, a Bradford assay is performed to measure the protein concentration and evaluated in comparison to the benchtop procedure. The result shows that the proposed valve can be implemented in any microfluidic process that requires simplicity and accuracy. Moreover, the developed valve increases the flexibility of the centrifugal CD platform for passive control of the liquid flow without the need for an external force or trigger. Link to full text journal articles : http://www.mdpi.com/1424-8220/15/3/4658/pdf http://www.ncbi.nlm.nih.gov/pubmed/25723143