Autonomous Microfluidic Devices Research Articles

Automated sample preparation for electrospray ionization mass spectrometry based on CLOCK-controlled autonomous centrifugal microfluidics.

We report a centrifugal microfluidic device that automatically performs sample preparation under steady-state rotation for clinical applications using mass spectrometry. The autonomous microfluidic device was designed for the control of liquid operation on centrifugal hydrokinetics (CLOCK) paradigm. The reported device was highly stable, with less than 7% variation with respect to the time of each unit operation (sample extraction, mixing, and supernatant extraction) in the preparation process. An agitation mechanism with bubbling was used to mix the sample and organic solvent in this device. We confirmed that the device effectively removed the protein aggregates from the sample, and the performance was comparable to those of conventional manual sample preparation procedures that use high-speed centrifugation. In addition, probe electrospray ionization mass spectrometry (PESI-MS) was performed to compare the device-treated and manually treated samples. The obtained PESI-MS spectra were analyzed by partial least squares discriminant analysis, and the preparation capability of the device was found to be equivalent to that of the conventional method.

Fast Electrochemical Actuator with Ti Electrodes in the Current Stabilization Regime.

The actuators needed for autonomous microfluidic devices have to be compact, low-power-consuming, and compatible with microtechnology. The electrochemical actuators could be good candidates, but they suffer from a long response time due to slow gas termination. An actuator in which the gas is terminated orders of magnitude faster has been demonstrated recently. It uses water electrolysis performed by short voltage pulses of alternating polarity (AP). However, oxidation of Ti electrodes leads to a rapid decrease in the performance. In this paper, we demonstrate a special driving regime of the actuator, which is able to support a constant stroke for at least 10 cycles. The result is achieved using a new driving regime when a series of AP pulses are interspersed with a series of single-polarity (SP) pulses. The new regime is realized by a special pulse generator that automatically adjusts the amplitude of the SP pulses to keep the current flowing through the electrodes at a fixed level. The SP pulses increase the power consumption by 15–60% compared to the normal AP operation and make the membrane oscillate in a slightly lifted position.

Electrochemical Circuits for Autonomous Microfluidic Solution Processing

Introduction In realizing smart micro analytical devices, controlled solution transport in microfluidic channels is indispensable. The procedures have predominantly been conducted using external pumps (or a pressure source) and valves. However, because of this, the entire setups become very bulky, although the chips themselves may be small. If solutions can be processed using integrated microfluidic components, it will accelerate automation and realization of user-friendly devices. Apart from chemical analysis, realization of soft robots 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. The components were connected electrically to form a network of electrochemical components that may be called electrochemical circuits. Method Figure 1 shows the structure and function of the valve [1]. Doped polypyrrole (PPy) was used to create the valve. First, patterns of platinum electrodes were formed on a glass substrate. To form the PPy layer, 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 (10 μA). In as-deposited PPy, the alkyl chains of NaDBS stand upward and the surface is hydrophobic. When PPy is reduced, polar groups of NaDBS come to the surface to make it hydrophilic. The valve was placed in a flow channel structure formed with hydrophilic glass and hydrophobic polydimethylsiloxane (PDMS). A solution injected into the flow channel moves by capillary action but stops at the valve which is initially hydrophobic. The valve can be opened by applying an appropriate potential to the valve electrode. When the valve is opened, the solution passes through the valve area and moves forward again. Although sequential switching of the valves is possible by using an external potentiostat, autonomous switching was realized by using a zinc electrode formed in a control flow channel and connected to the valve [2]. Figure 2 shows how the autonomous switching is conducted. The device consists of a main flow channel (MFC) with the valve and a control flow channel (CF). A zinc electrode is formed in the CF and is connected to the valve electrically using a lead pattern. Also, solutions in the reservoirs of the two flow channels are connected with an iridium wire with oxides on both ends as an alternative for a liquid junction. When a solution is injected into the MFC, it stops at the valve. When another solution is injected into the CF and wets the zinc electrode, PPy on the valve is reduced. As a result, the valve opens and the solution moves again in the flow channel. Results and Conclusions Based on the technique shown in Figure 2, autonomous bidirectional transport of a solution was achieved by using a circuit shown in Figure 3. The PPy valve was formed in flow channel 3 (FC 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 (FC 2). Solution reservoirs were connected with metal patterns and were closed with a polyimide tape. When a KCl solution was introduced into flow channel 1 (FC 1) and wets a zinc electrode in the flow channel, hydrogen bubbles were produced on one of the interdigitated electrodes in FC 2 by the reduction of protons. When the solution in FC2 reached the zinc electrode at the end, the PPy valve in FC3 connected to the zinc electrode opened and a AgNO3 solution was injected. Following this, Ag+ ions were reduced to silver there and the hydrogen bubbles in FC2 were oxidized on one of the interdigitated electrodes. As a result, the bubbles shrank and the solution in FC2 moved backward. Figure 4A-C show the movement of solutions.Multiple devices shown in Figure 3 can be integrated and operated sequentially and autonomously by additionally forming a zinc electrode at the end of FC3 of each device and connect it to a PPy valve additionally formed at the solution reservoir of FC1 of the device that is operated next (Figure 4D). To operate the integrated device, all we need to do is to inject a KCl solution to FC1 of the first unit as a trigger. All the following procedures are conducted autonomously to inject and remove solutions into and out of the reaction chamber sequentially. In addition to these, we are developing other autonomous devices for other purposes by designing other electrochemical circuits. This technique will enable autonomous multiplexed and/or sequential processing of solutions within microfabricated analytical devices and autonomous actuation of soft robots.

Modular design of paper based switches for autonomous lab-on paper micro devices.

This paper presents a new approach towards the design of paper based autonomous microfluidic devices. Autonomy in the device operation is achieved through the incorporation of mechanically actuated microfluidic switches that are versatile in their design and may be configured to be simple time triggered ON or OFF switches or more complex switches that can be timed to be in multiple states (timed ON, followed by timed OFF). These switches are self-contained and require no external power for their operation, deriving their functionality solely through stored elastic energy. This paper presents the design and fabrication of these switches as fluidic analogs of electronic transistors, and their integration into microfluidic paper based circuit demonstrating their operation as a programmable paper-based microfluidic device.

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

Microfluidic Adapter Converting a 96-Well Cartridge into an Autonomous Microfluidic Device.

In this study, an immunosensing platform by integrating a single array of conventional 96-well cartridges with low-cost polydimethylsiloxane (PDMS) pillars and thermoplastic chip was designed and developed to execute enzyme-linked immunosorbent assay (ELISA). The platform provides multiple (eight) reaction chambers for sequentially detecting multiple analytes under similar assay environments. For multiple immunoassays, the reaction chambers are consequently activated using a microvalve integrated with the sensing zones via the thermoplastic chip. Because the reaction zones are able to be selected and isolated from each other by the microvalve, multiple immunoassays can be implemented, avoiding cross-contamination. The performance of the sensing platform demonstrated its effectiveness in assaying with an optimal sample volume of 10 μL with an assay time of 10-15 min for different assay steps, which is much lower than the conventional immunoassay using 96-well plates. Thus, a low detection limit of 9.75 pg/mL is achieved using the developed platform to successfully detect the cardiac troponin I (cTnI). As a result, the cost-effectively made PDMS pillars and 96-well cartridge based hybrid immunosensing platform are widely applicable for high-throughput multiple lab-on-a-chip immunoassays.

Information transmission and signal permutation in active flow networks

Recent experiments show that both natural and artificial microswimmers in narrow channel-like geometries will self-organise to form steady, directed flows. This suggests that networks of flowing active matter could function as novel autonomous microfluidic devices. However, little is known about how information propagates through these far-from-equilibrium systems. Through a mathematical analogy with spin-ice vertex models, we investigate here the input–output characteristics of generic incompressible active flow networks (AFNs). Our analysis shows that information transport through an AFN is inherently different from conventional pressure or voltage driven networks. Active flows on hexagonal arrays preserve input information over longer distances than their passive counterparts and are highly sensitive to bulk topological defects, whose presence can be inferred from marginal input–output distributions alone. This sensitivity further allows controlled permutations on parallel inputs, revealing an unexpected link between active matter and group theory that can guide new microfluidic mixing strategies facilitated by active matter and aid the design of generic autonomous information transport networks.

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.

Direct digital manufacturing of autonomous centrifugal microfluidic device

This paper presents strategies that attempt to solve two key problems facing the commercialization of microfluidics: cost reduction in microfluidic chip manufacturing and microfluidic device driver development. To reduce the cost of microfluidic chip manufacturing, we propose to use of three-dimensional (3D) printers for direct digital manufacturing (DDM). An evaluation of 3D micro-scale structure printing using several 3D printers is reported, and some of the technical issues to be addressed in the future are suggested. To evaluate micro-scale printing, three types of 3D printers, with the ability to print structures on the scale of several hundred meters, were selected by first screening six 3D printers. Line and space patterns with line widths of 100–500 µm and an aspect ratio of one were printed and evaluated. The estimated critical dimension was around 200 µm. The manufacturing of a monolithic microfluidic chip with embedded channels was also demonstrated. Monolithic microfluidic chips with embedded microchannels having 500 × 500 and 250 × 250 µm2 cross sections and 2–20 mm lengths were printed, and the fidelity of the channel shape, residual supporting material, and flow of liquid water were evaluated. The liquid flow evaluation showed that liquid water could flow through all of the microchannels with the 500 × 500 µm2 cross section, whereas this was not possible through some of the channels with the 250 × 250 µm2 cross section because of the residual resin or supporting material. To reduce the device-driver cost, we propose to use of the centrifugal microfluidic concept. An autonomous microfluidic device that could implement sequential flow control under a steadily rotating condition was printed. Four-step flow injection under a steadily rotating condition at 1500 rpm was successfully demonstrated without any external triggering such as changing the rotational speed.

Superhydrophobic, passive microvalves with controllable opening threshold: exploiting plasma nanotextured microfluidics for a programmable flow switchboard

Plasma processing is used to create passive superhydrophobic on–off valves with tailored opening pressure inside microfluidic devices. First, anisotropic O2 plasma etching on polymeric microchannels is utilized to controllably roughen (nanotexture) the bottom of the microchannel. Second, the nanotextured surfaces are hydrophobized by means of a C4F8 plasma deposition step through a stencil mask creating superhydrophobic stripes or patches. The superhydrophobic patches play the role of on/off valves with predesigned opening pressure threshold (in the range 40–110 mbar), determined by the microchannel dimensions and the size of the nanotexture on the patch. These valves are integrated inside microchannel networks paving the way to autonomous microfluidic devices. To this aim, we present a novel preprogrammable flow switchboard that can split and control the liquid flow for multiple analysis purposes. The proposed valves present an example of how effectively plasma nanoscience and nanotechnology can be applied to microfluidics/nanofluidics and analytical chemistry.

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.

Rapid identification of ESKAPE bacterial strains using an autonomous microfluidic device.

This article describes Bacteria ID Chips (‘BacChips’): an inexpensive, portable, and autonomous microfluidic platform for identifying pathogenic strains of bacteria. BacChips consist of a set of microchambers and channels molded in the elastomeric polymer, poly(dimethylsiloxane) (PDMS). Each microchamber is preloaded with mono-, di-, or trisaccharides and dried. Pressing the layer of PDMS into contact with a glass coverslip forms the device; the footprint of the device in this article is ∼6 cm2. After assembly, BacChips are degased under large negative pressure and are stored in vacuum-sealed plastic bags. To use the device, the bag is opened, a sample containing bacteria is introduced at the inlet of the device, and the degased PDMS draws the sample into the central channel and chambers. After the liquid at the inlet is consumed, air is drawn into the BacChip via the inlet and provides a physical barrier that separates the liquid samples in adjacent microchambers. A pH indicator is admixed with the samples prior to their loading, enabling the metabolism of the dissolved saccharides in the microchambers to be visualized. Importantly, BacChips operate without external equipment or instruments. By visually detecting the growth of bacteria using ambient light after ∼4 h, we demonstrate that BacChips with ten microchambers containing different saccharides can reproducibly detect the ESKAPE panel of pathogens, including strains of: Enterococcus faecalis, Enteroccocus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter aerogenes, and Enterobacter cloacae. This article describes a BacChip for point-of-care detection of ESKAPE pathogens and a starting point for designing multiplexed assays that identify bacterial strains from clinical samples and simultaneously determine their susceptibility to antibiotics.

Fuel cell-powered microfluidic platform for lab-on-a-chip applications

The achievement of a higher degree of integration of components--especially micropumps and power sources--is a challenge currently being pursued to obtain portable and totally autonomous microfluidic devices. This paper presents the integration of a micro direct methanol fuel cell (μDMFC) in a microfluidic platform as a smart solution to provide both electrical and pumping power to a Lab-on-a-Chip system. In this system the electric power produced by the fuel cell is available to enable most of the functionalites required by the microfluidic chip, while the generated CO(2) from the electrochemical reaction produces a pressure capable of pumping a liquid volume through a microchannel. The control of the fuel cell operating conditions allows regulation of the flow rate of a liquid sample through a microfluidic network. The relation between sample flow rate and the current generated by the fuel cell is practically linear, achieving values in the range of 4-18 μL min(-1) while having an available power between 1-4 mW. This permits adjusting the desired flow rate for a given application by controlling the fuel cell output conditions and foresees a fully autonomous analytical Lab-on-a-Chip in which the same device would provide the electrical power to a detection module and at the same time use the CO(2) pumping action to flow the required analytes through a particular microfluidic design.

Integrated IR laser system for micro-fluidic detection and analysis

This paper presents a novel integrated infra-red laser system (λ = 1550 nm) for micro and nano-fluidic investigation and analysis. Its principle of detection is based on attenuated total internal reflection from a diffraction grating, which is for a first time adapted and applied to operate with near infra-red laser source. The sensor is integrated in an autonomous micro-fluidic device and realized by unique fabrication technology. An analysis of aqueous solutions of sucrose is performed by the micro-fluidic chip. The response of the diffraction efficiency of the integrated detector is investigated for the strongest diffraction orders and for different light polarizations. A resolution of the sucrose concentration below 1 wt.% is achieved.

Autonomous microfluidics with stimuli-responsive hydrogels

There has been increasing interest in integrated microfluidic systems because performing biological and chemical laboratory tasks on a single chip is appealing. One straightforward approach to constructing these 'lab on chips' is to fabricate individual components and to assemble them for desired functionalities. As the functionalities of the microfluidic systems become increasingly complicated, more functional components and relevant controls need to be integrated on a miniaturized chip, especially when a closed loop is needed for autonomous functionality. Instead, an emerging approach is to incorporate stimuli-responsive hydrogels directly into microfluidics to reduce the system complexity. Due to the hydrogels' ability of transducing stimuli into mechanical actions in response to their surrounding aqueous environment, hydrogel-based microfluidic elements can act as both sensors and actuators simultaneously, alleviating the requirement of most controls and even power sources. This provides microfluidic systems with autonomous functionalities. In this article, we will focus on a few autonomous microfluidic devices including valves, flow sorters, pH regulators, pumps, mixers, drug-delivery devices, fluidic cooling devices, and liquid microlenses.

Diffraction under total internal reflection for micro-fluidic analysis

This work presents the principles of a novel micro-optical system for micro- and nano-fluidic analysis. It is based on diffraction, occurring in total internal reflection conditions. The developed detector is integrated in an autonomous micro-fluidic device, produced by a unique combination of different techniques for micro- and nano-structuring and micro-machining. The micro-fluidic sensor is examined both experimentally and theoretically with respect to the parameters of the light and the diffraction grating. The most beneficial configurations with respect to maximum sensitivity towards the fluidic optical constants are discussed. Optical experiments show sensitivity of 5×10-4 to the fluidic refractive index and of 3.5×106 m-1 to the absorption coefficient. Envisioned applications of the integrated micro-sensor are concentration and composition analysis, environmental protection control, medical, biological and chemical diagnostics, and so on.

Micro-fluidic analysis based on total internal light reflection

The work presents a novel micro-optical sensor for micro and nano-fluidic analysis. It is based on diffraction, occurred in total internal reflection conditions. The detector is integrated on an autonomous micro-fluidic device and produced by a unique combination of different techniques for micro- and nano-structuring and micromachining. The preliminary optical investigation shows sensitivity to the fluidic refractive index of 2 × 10 −3 and to the absorption coefficient of 6 × 10 6 m −1. Envisioned applications of the integrated micro-sensor are medical, biological and chemical diagnostic of liquid substances and dispersions of drugs, serums, proteins, peptides, DNA, RNA, etc.