Autonomous Microfluidic Systems Research Articles

Novel Pumping Methods for Microfluidic Devices: A Comprehensive Review.

This review is an account of methods that use various strategies to control microfluidic flow control with high accuracy. The reviewed systems are divided into two large groups based on the way they create flow: passive systems (non-mechanical systems) and active (mechanical) systems. Each group is presented by a number of device fabrications. We try to explain the main principles of operation, and we list advantages and disadvantages of the presented systems. Mechanical systems are considered in more detail, as they are currently an area of increased interest due to their unique precision flow control and "multitasking". These systems are often applied as mini-laboratories, working autonomously without any additional operations, provided by humans, which is very important under complicated conditions. We also reviewed the integration of autonomous microfluidic systems with a smartphone or single-board computer when all data are retrieved and processed without using a personal computer. In addition, we discuss future trends and possible solutions for further development of this area of technology.

Electrochemical Circuits for Autonomous Microfluidic Solution Processing

Electrochemical Circuits for Autonomous Microfluidic Solution Processing

Microfluidic Devices Using Electrochemical Micropumps and Microvalves for Autonomous Solution Processing

In realizing sophisticated micro analytical devices, controlled solution transport in microfluidic channels is indispensable. The procedures have predominantly been conducted using external pumps (or pressure source) and valves. However, because of this, the entire setups become very bulky, although the chips may be small. If the control of solution transport is realized using integrated microfluidic components, it will accelerate automation and realization of user-friendly devices. Apart from chemical analysis, realization of artificial lives that move by direct conversion of chemical energy to mechanical energy is becoming a hot topic. Independent autonomous microfluidic systems that can control chemical reactions in a coordinated manner can also be critical components in these devices. In this study, we attempted to realize such autonomous microfluidic devices by integrating simple switchable hydrophobic microvalves that employ a conducting polymer and pressure changes by electrochemical production and shrinkage of hydrogen bubbles.Doped polypyrrole (PPy) was used for the valve. A platinum electrode was formed on a glass substrate, and PPy was grown on the electrode. For this purpose, the electrode was immersed in a solution containing 0.2 M pyrrole and 0.2 M sodium dodecylbenzenesulfonate (NaDBS), and electropolymerization was carried out at a constant current of 10 μA. In as-deposited PPy, the alkyl chains of NaDBS stand upward and the surface is hydrophobic. When PPy is reduced, polar groups come to the surface and becomes hydrophilic.First, a two-channel test device with a control flow channel and a main flow channel was fabricated (Figure 1). The valve was formed in the main flow channel and a zinc electrode was formed in the control flow channel. The electrodes were connected each other. Also, solutions in the solution reservoirs of the two flow channels were connected with an iridium wire with oxides on both ends as an alternative for a liquid junction. When a solution was injected into the main flow channel, it stopped at the valve. When another solution was injected into the control channel and wetted the zinc electrode, PPy on the valve was reduced. As a result, and the valve opened.As the next step, a three-channel device was fabricated (Figure 2). Interdigitated platinum electrodes were formed in flow channel 2 in the figure. One of them was connected to a zinc electrode in flow channel 1 and the other was connected to a platinum electrode in flow channel 3. Solutions in the reservoirs of the flow channels were connected with Ag/AgCl wires. As a preliminary experiment, a pH indicator (thymol blue) was first injected into flow channel 2. When a KCl solution was injected into flow channel 1, the color of the area around the interdigitated electrodes of flow channel 2 changed to blue by the electrolysis of water. When a 0.1 M AgNO3 solution was injected into flow channel 3, the color changed to yellow again because of the oxidization of hydrogen bubbles.Another device with the same basic structure was used to demonstrate autonomous bidirectional transport of a solution (Figure 3). In addition to the structures shown in Figure 2, the PPy valve used in the device shown in Figure 1 was formed in flow channel 3 to control the injection of the solution in the reservoir. The valve was connected to a zinc electrode formed at the end of flow channel 2. Furthermore, solution reservoirs were closed with a polyimide tape. Following the same procedure for the previous device, hydrogen bubbles were produced on one of the interdigitate electrodes in flow channel 2 by the reduction of protons. When the solution in flow channel 2 reached the zinc electrode at the end, the valve in flow channel 3 opened and a AgNO3 solution flowed through the platinum electrode. Following this, Ag+ ions were reduced to silver there and the hydrogen bubbles in flow channel 2 were oxidized on one of the interdigitate electrodes. As a result, the bubbles shrank and the solution in the flow channel moved backward.For the device shown in Figure 3, the injection of the solution in flow channel 1 can be carried out by forming an additional valve at the solution reservoir and open it using another zinc electrode in another control flow channel. Many units like the one shown in Figure 3 can be connected to the same control flow channel and operated sequentially. The technique will enable autonomous multiplexed and/or sequential processing of solutions within microfabricated analytical devices and autonomous actuation of soft robots. Figure 1

Detection of red blood cell surface antigens by probe-triggered cell collision and flow retardation in an autonomous microfluidic system

Microfluidic devices exploit combined physical, chemical and biological phenomena that could be unique in the sub-millimeter dimensions. The current goal of development of Point-of-Care (POC) medical devices is to extract the biomedical information from the blood. We examined the characteristics of blood flow in autonomous microfluidic devices with the aim to realize sensitive detection of interactions between particulate elements of the blood and the appropriately modified surfaces of the system. As a model experiment we demonstrated the fast analysis of the AB0 blood group system. We observed that the accumulation of red blood cells immobilized on the capillary wall leads to increased lateral movement of the flowing cells, resulting in the overall selective deceleration of the red blood cell flow column compared to the plasma fraction. We showed that by monitoring the flow rate characteristics in capillaries coated with blood type reagents it is possible to identify red blood cell types. Analysis of hydrodynamic effects governing blood flow by Finite Element Method based modelling supported our observations. Our proof-of-concept results point to a novel direction in blood analysis in autonomous microfluidic systems and also provide the basis for the construction of a simple quantitative device for blood group determination.

Effects of embedded surfactants on the surface properties of PDMS; applicability for autonomous microfluidic systems

Controlled surface modification of the PDMS (polydimethylsiloxane) was developed and studied in this work to develop autonomous capillary-driven microfluidic system to be applied in bioanalytical devices. The characteristics of the PDMS surfaces were modified by embedding adequate surfactant molecules in the polymer matrix to be moved onto the free surface by diffusion. The change of the surface characteristics was studied considering the expected performance in autonomous biomicrofluidic applications and the influence on non-specific human blood protein binding also. The method was evaluated from technological aspects also, as the integrability of the microfluidic system, considering the previously published results critically. Compositions were defined to be adequate for fabrication autonomous capillary system with enhanced transport efficiency and moderated non-specific protein adsorption.

Switchable Hydrophobic Valve for Controlled Microfluidic Processing.

A simple microfluidic valve, without any moving parts, is presented that can control solution flow on demand in microchannels of many different materials using a low-power electric signal. Many independently operating valves can easily be integrated into complex microfluidic systems. The valve consists of a self-assembled monolayer (SAM) formed on a platinum electrode that is incorporated directly in the microchannel. The normally-on valve stops the solution flow due to a hydrophobic SAM on the electrode surface. The solution is allowed to pass the valve by applying a potential to the electrode, which removes the SAM due to reductive desorption. The valve operation is highly stable and has switching times of the order of 1 s. The valve is ideal for controlled solution manipulation in integrated micro-analytical systems and autonomous microfluidic systems.

Label-free Microfluidic Sensing by Detection of Interaction-triggered Change in Blood Flow Characteristics

Microfluidic devices exploit combined physical, chemical and biological phenomena that could be unique in the sub-millimeter dimensions. The blood is a non-Newtonian fluid, containing particulate and soluble elements, which penetrates the whole body carrying a wealth of biomedical information. The design of microfluidic devices capable of extracting immediately this information is the current goal of development Point-of-Care (POC) medical devices. We examined the characteristics of blood flow in specially designed microfluidic devices having different geometric structure and material composition with the aim of defining suitable conditions for sensitive detection of changes in the interactions between particulate elements of the blood and the adequately modified surfaces of the microfluidic system. As a model experiment we demonstrated the fast analysis of the AB0 blood group system, applying respective antibody reagents and capillary blood samples with different blood groups. We showed that by tuning the hydrophilicity of the surface and capillary dimensions of the microfluidic system it is possible to detect precisely the red blood cell binding to the capillary walls by monitoring the flow rate characteristics in an autonomous microfluidic system. Our proof-of-concept results point to a novel direction in blood analysis in autonomous microfluidic systems and also provide the basis for the construction of a simple quantitative device for blood group determination.

Synthesis and cell-free cloning of DNA libraries using programmable microfluidics.

Microfluidics may revolutionize our ability to write synthetic DNA by addressing several fundamental limitations associated with generating novel genetic constructs. Here we report the first de novo synthesis and cell-free cloning of custom DNA libraries in sub-microliter reaction droplets using programmable digital microfluidics. Specifically, we developed Programmable Order Polymerization (POP), Microfluidic Combinatorial Assembly of DNA (M-CAD) and Microfluidic In-vitro Cloning (MIC) and applied them to de novo synthesis, combinatorial assembly and cell-free cloning of genes, respectively. Proof-of-concept for these methods was demonstrated by programming an autonomous microfluidic system to construct and clone libraries of yeast ribosome binding sites and bacterial Azurine, which were then retrieved in individual droplets and validated. The ability to rapidly and robustly generate designer DNA molecules in an autonomous manner should have wide application in biological research and development.

Characterization and Theoretical Analysis of Rapidly Prototyped Capillary Action Autonomous Microfluidic Systems

Capillary action arising from surface tension-based forces has been demonstrated to be an effective means of passively actuating various fluids through simple and sophisticated microfluidic channel networks. Systems based on this technique are advantageous compared with standard pumping strategies, as they have zero power requirements, are readily integrated into the overall fluidic chip design, and can be fabricated rapidly in a single manufacturing step. This paper comprehensively investigates time lapsed average velocity profiles of various capillary action microfluidic systems, including channels and pumping structures, and compares experimental data against prominent, competing, and flow-based theoretical models. We demonstrate that the average meniscus flow velocity of CO 2 laser ablated capillary systems can be adequately predicted and characterize smooth fluidic velocity profiles in simple microchannels and complex interlinking channel pump/filling structures. Such systems offer a useful, rapid, and low cost alternative to traditional fluidic actuation and flow control systems such as those found in on-chip based biological and chemical analysis.

Piezoelectric Micro-pump with PZT Thin Film for Low Consumption Microfluidic Devices

Abstract We report on the first peristaltic micropump with active microvalves actuated by piezoelectric thin-films. We developed an original process to combine state of the art sol-gel Pb(Zr,Ti)O3 (PZT) thin-films with a highly performing silicon micropump. The device thus takes advantage of both technologies, especially with respect to low voltage actuation and high precision. It can produce μl/min flows for 24 V actuation voltage, opening a new range of applications for low consuming pumps and autonomous microfluidic systems, especially implanted devices for drug delivery.

Applications of autonomous microfluidic systems in environmental monitoring

Concern about the environment is increasing and so is the search for analytical methods that make continuous monitoring possible. Microfluidic devices such as lab-on-a-chip emerge as an alternative to the laboratory-based conventional techniques, making possible the development of unmanned monitoring tools. This review covers the last five years on the application of autonomous microfluidic devices for continuous environmental monitoring and addresses the existing demands in this field.

Self-priming of liquids in capillary autonomous microfluidic systems

We present a numerical approach to the capillary rise dynamics in microfluidic channels of complex 3D geometries. In order to optimize the delivery of specific biological fluids to target regions in microfluidic capillary autonomous systems (CAS), we analyze self-priming of liquid water into a microfluidic device consisting of a microfluidic channel that feeds a rectangular microfluidic cavity trough an appropriately designed micro-chamber. The target performance criteria in our optimization are (1) fast and complete wetting of the cavity bottom while (2) minimizing the probability of trapping air bubble in the device. The numerical model is based on the lattice Boltzmann method (LBM) and a three-dimensional single-component multiple-phase (SCMP) scheme. By using a parallel implementation of this algorithm, we investigate the physical processes related to the invasion of the liquid–gas interfaces in rectangular cavities at different liquid–solid contact angle and shapes of the transition micro-chamber. The numerical results has successfully captured important qualitative and some key quantitative effects of the liquid–solid contact angle, the roughness of the cavity edges, the depth of the holes and shape of the micro-chambers. Moreover, we present and validate experimentally simple geometrical optimizations of the microfluidic device that ensure the complete filling the microfluidic cavity with liquid. Critical parameters related to the overall priming time of the device are presented as well.

Autonomous microfluidic system for phosphate detection

Miniaturization of analytical devices through the advent of microfluidics and micro total analysis systems is an important step forward for applications such as medical diagnostics and environmental monitoring. The development of field-deployable instruments requires that the entire system, including all necessary peripheral components, be miniaturized and packaged in a portable device. A sensor for long-term monitoring of phosphate levels has been developed that incorporates sampling, reagent and waste storage, detection, and wireless communication into a complete, miniaturized system. The device employs a low-power detection and communication system, so the entire instrument can operate autonomously for 7 days on a single rechargeable, 12 V battery. In addition, integration of a wireless communication device allows the instrument to be controlled and results to be downloaded remotely. This autonomous system has a limit of detection of 0.3 mg/L and a linear dynamic range between 0 and 20 mg/L.

Microfluidic tectonics: a comprehensive construction platform for microfluidic systems.

A microfluidic platform for the construction of microscale components and autonomous systems is presented. The platform combines liquid-phase photopolymerization, lithography, and laminar flow to allow the creation of complex and autonomous microfluidic systems. The fabrication of channels, actuators, valves, sensors, and systems is demonstrated. Construction times can be as short as 10 min, providing ultrarapid prototyping of microfluidic systems.