Finger-powered microfluidic systems using multilayer soft lithography and injection molding processes

Transformative laboratory medicine enabled by microfluidic automation and artificial intelligence

Laboratory medicine provides pivotal medical information through analyses of body fluids and tissues, and thus, it is essential for diagnosis of diseases as well as monitoring of disease progression. Despite its universal importance, the field is currently suffering from the limited workforce and analytical capabilities due to the increasing pressure from expanding global population and unexpected rise of noncommunicable diseases. The emerging technologies of microfluidic automation and artificial intelligence (AI) has led to the development of advanced diagnostic platforms, positioning themselves as adaptable solutions to enable highly efficient and accessible laboratory medicine. In this review, we will provide a comprehensive review of microfluidic automation, focusing on the microstructure design and automation principles, along with its intended functionalities for diagnostic purposes. Subsequently, we exemplify the integration of AI with microfluidics and illustrating how their combination benefits for the applications and what the challenges are in this rapidly evolving field. Finally, the review offers a balanced perspective on the microfluidics and AI, discussing their promising role in advancing laboratory medicine.

A gravity-driven microfluidic metering system for automation of multiplexed bioassays

Automatic and precise fluid manipulation is essential in microfluidic applications. Microfluidic metering, in particular, plays a critical role in achieving the multiplexity of assays, reaction consistency, quantitative analysis, and the scalability of microfluidic operations. However, existing fluid metering techniques often face limitations, such as high complexity, high cost, reliance on external accessories, and lack of precision, which have restricted their use in multiplexed and quantitative analysis, especially in portable applications. In this study, we present a novel portable gravity-driven metering system designed for automated multiplexed fluid metering, multistep fluid control, and multi-chamber signal readout. Our metering chip utilizes gravitational force to dispense sample liquids, allowing for versatile and precise metering. Guided by a series of numerical simulations, we optimized the design of our metering chip to achieve rapid and accurate liquid metering. Furthermore, thermal control valves were employed to facilitate automated and programmable fluid transfer, eliminating the need for external equipment. To enhance user experience, we developed a smartphone-assisted readout pod for seamless integration with the metering chip. We validated the efficacy of our platform through a proof-of-concept multiplexed analysis of urinary biomarkers, demonstrating high sensitivity, specificity, and absolute quantification capabilities. Our gravity-driven metering system shows significant potential for applications in multiplexed diagnostics, drug screening, and material synthesis, effectively addressing critical needs in fluid manipulation and analysis.

Pipette-operable microfluidic devices with hydrophobic valves in sequential dispensing with various liquid samples: multiplex disease assay by RT-LAMP

Microfluidic dispensing technologies often require additional equipment, posing challenges for their integration into point-of-care testing (POCT) applications. In response to this challenge, we have developed a pipette-operable microfluidic device fabricated using 3D printing technology for precise liquid dispensing. This device features three reaction chambers and three distinct hydrophobic valves to control the flow direction of liquids. Through these valves, the pipette-operable microfluidic device can sequentially dispense and isolate the liquid into the three reaction chambers, allowing for the individual conduction of three distinct reactions. These hydrophobic valves, with optimized flow resistance and burst pressure, can sustain a volumetric flow rate of up to 25 μL s-1, making them compatible with a standard pipette, a syringe, or a dropper operation. Furthermore, the device is successfully used to operate with various liquids, including BSA, DMEM, FBS, plasma, and blood, representing that the device has the potential to be used for various applications. Additionally, distinct RT-LAMP primer sets have been incorporated for diagnosing SARS-CoV-2, influenza A, and influenza B within each chamber through lyophilization. This pipette-operable microfluidic device serves as a versatile tool for diagnosing these three diseases using a single loading process, with results readable by the naked eye or image assay within 30 minutes of incubation. Finally, the design concepts are extended to engineer a microfluidic device with 20 reaction chambers, offering significant potential for multi-disease diagnostics.

Evaluation of Fluid Behaviors in a Pushbutton-Activated Microfluidic Device for User-Independent Flow Control

Although numerous studies have been conducted to realize ideal point-of-care testing (POCT), the development of a user-friendly and user-independent power-free microfluidic platform is still a challenge. Among various methods, the finger-actuation method shows a promising technique that provides a user-friendly and equipment-free way of delivering fluid in a designated manner. However, the design criteria and elaborate evaluation of the fluid behavior of a pushbutton-activated microfluidic device (PAMD) remain a critical bottleneck to be widely adopted in various applications. In this study, we have evaluated the fluid behavior of the PAMD based on various parameters, such as pressing velocity and depth assisted by a press machine. We have further developed a user-friendly and portable pressing block that reduces user variation in fluid behavior based on the evaluation.

Advancements in the research of finger-actuated POCT chips

Microfluidic point-of-care testing (POCT) chips are used to enable the mixing and reaction of small sample volumes, facilitating target molecule detection. Traditional methods for actuating POCT chips rely on external pumps or power supplies, which are complex and non-portable. The development of finger-actuated chips has reduced operational difficulty and improved portability, promoting the development of POCT chips. This paper reviews the significance, developments, and potential applications of finger-actuated POCT chips. Three methods for controlling the flow accuracy of finger-actuated chips are summarized: direct push, indirect control, and sample injection control method, along with their respective advantages and disadvantages. Meanwhile, a comprehensive analysis of multi-fluid driving modes is provided, categorizing them into single-push multi-driving and multi-push multi-driving modes. Furthermore, recent research breakthroughs in finger-actuated chips are thoroughly summarized, and their structures, driving, and detection methods are discussed. Finally, this paper discusses the driving performance of finger-actuated chips, the suitability of detection scenarios, and the compatibility with existing detection technologies. It also provides prospects for the future development and application of finger-actuated POCT chips.

Additively manufactured multiplexed electrochemical device (AMMED) for portable sample-to-answer detection

Portable sample-to-answer devices with applications in point-of-care settings have emerged to obviate the necessity of centralized laboratories for biomarker analysis. In this work, a smartphone-operated and additively manufactured multiplexed electrochemical device (AMMED) is presented for the portable detection of biomarkers in blood and saliva. AMMED is comprised of a customized portable potentiostat with a multiplexing feature, a 3D-printed sample collection cartridge to handle three samples of saliva and blood at the same time, a smartphone application to remotely control the potentiostat, and a 3D-printed-based multiplexed microfluidic electrochemical biosensor (test chip). Here, by employing additive manufacturing techniques, a simple, cleanroom-free, and scalable approach was proposed for the fabrication of the test chip. Moreover, these techniques can bring about easy integration of AMMED components. Additionally, the test chip can be compatible with different affinity-based bioassays which can be implemented in a multiplexed manner for detection. The AMMED components were successfully characterized in terms of electrochemical and fluidic performance. Particularly, to demonstrate the biosensing capabilities of the device, the spike protein of the SARS-CoV-2 omicron variant and a well-established aptameric assay were selected as the representative biomarker and the bioassay, respectively. The proposed device accurately and selectively detected the target of interest in a rapid (5 min) and multiplex manner with a dynamic detection range of 1-10 000 pg ml-1 in different media, and the clinical feasibility was assessed by several saliva patient samples. AMMED offers a versatile sample-to-answer platform that can be used for the detection of various biomarkers present in biofluids.

Additive manufacturing leveraged microfluidic setup for sample to answer colorimetric detection of pathogens

Colorimetric readout for the detection of infectious diseases is gaining traction at the point of care/need owing to its ease of analysis and interpretation, and integration potential with highly specific loop-mediated amplification (LAMP) assays. However, coupling colorimetric readout with LAMP is rife with challenges including, rapidity, inter-user variability, colorimetric signal quantification, and user involvement in sequential steps of the LAMP assay, hindering its application. To address these challenges, for the first time, we propose a remotely smartphone-operated automated setup consisting of (i) an additively manufactured microfluidic cartridge, (ii) a portable reflected-light imaging setup with controlled epi-illumination (PRICE) module, and (iii) a control and data analysis module. The microfluidic cartridge facilitates sample collection, lysis, mixing of amplification reagents stored on-chip, and subsequent isothermal heating for initiation of amplification in a novel way by employing tunable elastomeric chambers and auxiliary components (heaters and linear actuators). PRICE offers a new imaging setup that captures the colorimetric change of the amplification media over a plasmonic nanostructured substrate in a controlled and noise-free environment for rapid minute-scale nucleic acid detection. The control and data analysis module employs microprocessors to automate cartridge operation in tandem with the imaging module. The different device components were characterized individually and finally, as a proof of concept, SARS-CoV-2 wild-type RNA was detected with a turnaround time of 13 minutes, showing the device's clinical feasibility. The suggested automated device can be adopted in future iterations for other detection and molecular assays that require sequential fluid handling steps.

Rapid microfluidics prototyping through variotherm desktop injection molding for multiplex diagnostics

In this work, we demonstrate an inexpensive method of prototyping microfluidics using a desktop injection molding machine. A centrifugal microfluidic device with a novel central filling mechanism was developed to demonstrate the technique. We overcame the limitations of desktop machines in replicating microfluidic features by variotherm heating and cooling the mold between 50 °C and 110 °C within two minutes. Variotherm heating enabled good replication of microfeatures, with a coefficient of variation averaging only 3.6% attained for the measured widths of 100 μm wide molded channels. Using this methodology, we produced functional polystyrene centrifugal microfluidic chips, capable of aliquoting fluids into 5.0 μL reaction chambers with 97.5% accuracy. We performed allele-specific loop-mediated isothermal amplification (AS-LAMP) reactions for genotyping CYP2C19 alleles on these chips. Readouts were generated using optical pH sensors integrated onto chips, by drop-casting sensor precursor solutions into reaction chambers before final chip assembly. Positive reactions could be discerned by decreases in pH sensor fluorescence, thresholded against negative control reactions lacking the primers for nucleic acid amplification and with time-to-results averaging 38 minutes. Variotherm desktop injection molding can enable researchers to prototype microfluidic devices more cost-effectively, in an iterative fashion, due to reduced costs of smaller, in-house molds. Designs prototyped this way can be directly translated to mass production, enhancing their commercialization potential and positive impacts.

Microfluidics engineering towards personalized oncology-a review

Identifying and monitoring the presence of cancer metastasis and highlighting inter-and intratumoral heterogeneity is a central tenet of targeted precision oncology medicine (POM). This process of relocation of cancer cells is often referred to as the missing link between a tumor and metastasis. In recent years, microfluidic technologies have been developed to isolate a plethora of different biomarkers, such as circulating tumor cells (CTCs), tumor-derived vesicles (exosomes), or cell/free nucleic acids and proteins directly from patients' blood samples. With the advent of microfluidic developments, minimally invasive and quantitative assessment of different tumors is becoming a reality. This short review article will touch briefly on how microfluidics at early-stage achievements can be combined or developed with the active vs passive microfluidic technologies, depending on whether they utilize external fields and forces (active) or just microchannel geometry and inherent fluid forces (passive) from the market to precision oncology research and our future prospectives in terms of the emergence of ultralow cost and rapid prototyping of microfluidics in precision oncology.

Aptamer-Based Electrochemical Microfluidic Biosensor for the Detection of Cryptosporidium parvum

Cryptosporidium parvum is a high-risk and opportunistic waterborne parasitic pathogen with highly infectious oocysts that can survive harsh environmental conditions for long periods. Current state-of-the-art methods are limited to lengthy imaging and antibody-based detection techniques that are slow, labor-intensive, and demand trained personnel. Therefore, the development of new sensing platforms for rapid and accurate identification at the point-of-care (POC) is essential to improve public health. Herein, we propose a novel electrochemical microfluidic aptasensor based on hierarchical 3D gold nano-/microislands (NMIs), functionalized with aptamers specific to C. parvum. We used aptamers as robust synthetic biorecognition elements with a remarkable ability to bind and discriminate among molecules to develop a highly selective biosensor. Also, the 3D gold NMIs feature a large active surface area that provides high sensitivity and a low limit of detection (LOD), especially when they are combined with aptamers,. The performance of the NMI aptasensor was assessed by testing the biosensor's ability to detect different concentrations of C. parvum oocysts spiked in different sample matrices, i.e., buffer, tap water, and stool, within 40 min detection time. The electrochemical measurements showed an acceptable LOD of 5 oocysts mL-1 in buffer medium, as well as 10 oocysts mL-1 in stool and tap water media, over a wide linear range of 10-100,000 oocysts mL-1. Moreover, the NMI aptasensor recognized C. parvum oocysts with high selectivity while exhibiting no significant cross-reactivity to other related coccidian parasites. The specific feasibility of the aptasensor was further demonstrated by the detection of the target C. parvum in patient stool samples. Our assay showed coherent results with microscopy and real-time quantitative polymerase chain reaction, achieving high sensitivity and specificity with a significant signal difference (p < 0.001). Therefore, the proposed microfluidic electrochemical biosensor platform could be a stepping stone for the development of rapid and accurate detection of parasites at the POC.

Finger-Actuated Micropump of Constant Flow Rate without Backflow

This paper presents a finger-actuated micropump with a consistent flow rate and no backflow. The fluid dynamics in interstitial fluid (ISF) extraction microfluidics are studied through analytical, simulation, and experimental methods. Head losses, pressure drop, diodocity, hydrogel swelling, criteria for hydrogel absorption, and consistency flow rate are examined in order to access microfluidic performance. In terms of consistency, the experimental result revealed that after 20 s of duty cycles with full deformation on the flexible diaphragm, the output pressure became uniform and the flow rate remained at nearly constant levels of 2.2 μL/min. The flow rate discrepancy between the experimental and predicted flow rates is around 22%. In terms of diodicity, when the serpentine microchannel and hydrogel-assisted reservoir are added to the microfluidic system integration, the diodicity increases by 2% (Di = 1.48) and 34% (Di = 1.96), respectively, compared to when the Tesla integration (Di = 1.45) is used alone. A visual and experimentally weighted analysis finds no signs of backflow. These significant flow characteristics demonstrate their potential usage in many low-cost and portable microfluidic applications.

Toward Personalized Nanomedicine: The Critical Evaluation of Micro and Nanodevices for Cancer Biomarker Analysis in Liquid Biopsy

Liquid biopsy for the analysis of circulating cancer biomarkers (CBs) is a major advancement toward the early detection of cancer. In comparison to tissue biopsy techniques, liquid biopsy is relatively painless, offering multiple sampling opportunities across easily accessible bodily fluids such as blood, urine, and saliva. Liquid biopsy is also relatively inexpensive and simple, avoiding the requirement for specialized laboratory equipment or trained medical staff. Major advances in the field of liquid biopsy are attributed largely to developments in nanotechnology and microfabrication that enables the creation of highly precise chip-based platforms. These devices can overcome detection limitations of an individual biomarker by detecting multiple markers simultaneously on the same chip, or by featuring integrated and combined target separation techniques. In this review, the major advances in the field of portable and semi-portable micro, nano, and multiplexed platforms for CB detection for the early diagnosis of cancer are highlighted. A comparative discussion is also provided, noting merits and drawbacks of the platforms, especially in terms of portability. Finally, key challenges toward device portability and possible solutions, as well as discussing the future direction of the field are highlighted.

Smartphone-based platforms implementing microfluidic detection with image-based artificial intelligence

The frequent outbreak of global infectious diseases has prompted the development of rapid and effective diagnostic tools for the early screening of potential patients in point-of-care testing scenarios. With advances in mobile computing power and microfluidic technology, the smartphone-based mobile health platform has drawn significant attention from researchers developing point-of-care testing devices that integrate microfluidic optical detection with artificial intelligence analysis. In this article, we summarize recent progress in these mobile health platforms, including the aspects of microfluidic chips, imaging modalities, supporting components, and the development of software algorithms. We document the application of mobile health platforms in terms of the detection objects, including molecules, viruses, cells, and parasites. Finally, we discuss the prospects for future development of mobile health platforms.

Microfluidic solutions for biofluids handling in on-skin wearable systems

On-skin wearable systems for biofluid sampling and biomarker sensing can revolutionize the current practices in healthcare monitoring and personalized medicine. However, there is still a long path toward complete market adoption and acceptance of this fascinating technology. Accordingly, microfluidic science and technology can provide excellent solutions for bridging the gap between basic research and clinical research. The research gap has led to the emerging field of epidermal microfluidics. Moreover, recent advances in the fabrication of highly flexible and stretchable microfluidic systems have revived the concept of micro elastofluidics, which can provide viable solutions for on-skin wearable biofluid handling. In this context, this review highlights the current state-of-the-art platforms in this field and discusses the potential technologies that can be used for on-skin wearable devices. Toward this aim, we first compare various microfluidic platforms that could be used for on-skin wearable devices. These platforms include semiconductor-based, polymer-based, liquid metal-based, paper-based, and textile-based microfluidics. Next, we discuss how these platforms can enhance the stretchability of on-skin wearable biosensors at the device level. Next, potential microfluidic solutions for collecting, transporting, and controlling the biofluids are discussed. The application of finger-powered micropumps as a viable solution for precise and on-demand biofluid pumping is highlighted. Finally, we present the future directions of this field by emphasizing the applications of droplet-based microfluidics, stretchable continuous-flow micro elastofluidics, stretchable superhydrophobic surfaces, liquid beads as a form of digital micro elastofluidics, and topological liquid diodes that received less attention but have enormous potential to be integrated into on-skin wearable devices.

Direct 3D printed biocompatible microfluidics: assessment of human mesenchymal stem cell differentiation and cytotoxic drug screening in a dynamic culture system

BACKGROUND

In vivo-mimicking conditions are critical in in vitro cell analysis to obtain clinically relevant results. The required conditions, comparable to those prevalent in nature, can be provided by microfluidic dynamic cell cultures. Microfluidics can be used to fabricate and test the functionality and biocompatibility of newly developed nanosystems or to apply micro- and nanoelectromechanical systems embedded in a microfluidic system. However, the use of microfluidic systems is often hampered by their accessibility, acquisition cost, or customization, especially for scientists whose primary research focus is not microfluidics.

RESULTS

Here we present a method for 3D printing that can be applied without special prior knowledge and sophisticated equipment to produce various ready-to-use microfluidic components with a size of 100 µm. Compared to other available methods, 3D printing using fused deposition modeling (FDM) offers several advantages, such as time-reduction and avoidance of sophisticated equipment (e.g., photolithography), as well as excellent biocompatibility and avoidance of toxic, leaching chemicals or post-processing (e.g., stereolithography). We further demonstrate the ease of use of the method for two relevant applications: a cytotoxicity screening system and an osteoblastic differentiation assay. To our knowledge, this is the first time an application including treatment, long-term cell culture and analysis on one chip has been demonstrated in a directly 3D-printed microfluidic chip.

CONCLUSION

The direct 3D printing method is tested and validated for various microfluidic components that can be combined on a chip depending on the specific requirements of the experiment. The ease of use and production opens up the potential of microfluidics to a wide range of users, especially in biomedical research. Our demonstration of its use as a cytotoxicity screening system and as an assay for osteoblastic differentiation shows the methods potential in the development of novel biomedical applications. With the presented method, we aim to disseminate microfluidics as a standard method in biomedical research, thus improving the reproducibility and transferability of results to clinical applications.

A Soft Wearable Microfluidic Patch with Finger-Actuated Pumps and Valves for On-Demand, Longitudinal, and Multianalyte Sweat Sensing

Easy sample collection, physiological relevance, and ability to noninvasively and longitudinally monitor the human body are some of the key attributes of wearable sweat sensors. Examples typically include reversible sensors or an array of single-use sensors embedded in specialized microfluidics for temporal analysis of sweat. However, evolving this field to a level that truly represents "lab-on-skin" technology will require the incorporation of advanced functionalities that give the user the freedom to (1) choose the precise time for performing sample analysis and (2) select sensors from an array embedded within the device for performing condition-specific sample analysis. Here, we introduce new concepts in wearable microfluidic platforms that offer such capabilities. The described technology involves a series of finger-actuated pumps, valves, and sensors incorporated within soft, wearable microfluidics. The incoming sweat collects in the inlet chamber and can be analyzed by the user at the time of their choosing. On-demand sweat analyte assessment is achieved by pulling a thin tab to activate a pump which opens a valve and allows the pooled sweat to enter a chamber embedded with sensors for the desired analytes. The article describes a thorough characterization of the platform that demonstrates the robustness of the pumping, valving, and sensing aspects of the device under conditions mimicking real-life scenarios. A two-day-long human pilot study validates the system and illustrates the device's ability to offer on-demand, longitudinal, and multianalyte sensing. Our work represents the first example of a wearable system with such on-demand sensing capabilities and opens exciting avenues in sweat sensing for acquiring new insights into human physiology.

A Battery-Powered Fluid Manipulation System Actuated by Mechanical Vibrations

Miniaturized fluid manipulation systems are an important component of lab-on-a-chip platforms implemented in resourced-limited environments and point-of-care applications. This work aims to design, fabricate, and test a low-cost and battery-operated microfluidic diffuser/nozzle type pump to enable an alternative fluid manipulation solution for field applications. For this, CNC laser cutting and 3D printing are used to fabricate the fluidic unit and casing of the driving module of the system, respectively. This system only required 3.5-V input power and can generate flow rates up to 58 µL/min for water. In addition, this portable pump can manipulate higher viscosity fluids with kinematic viscosities up to 24 mPa·s resembling biological fluids such as sputum and saliva. The demonstrated system is a low-cost, battery-powered, and highly versatile fluid pump that can be adopted in various lab-on-a-chip applications for field deployment and remote applications.

Design, fabrication and assembly of lab-on-a-chip and its uses

Lab-on-a-chip diagnostic devices can be used as quick tools to identify the onset of diseases at an early stage. An integrated LoC platform usually consists of a set of microfluidic elements, each of which has dedicated functions like fluid mixing, fluid manipulation, and flow control, sample preparation, detection, and a read-out that can perform the conventional laboratory procedures on a miniaturized chip. The lab-on-a-chip device can be developed on a paper or polymeric platform and is usually fabricated using pattern transfer techniques or additive and subtractive manufacturing processes. Thorough knowledge of the physics involved in microfluidic technology is essential for developing miniaturized components required for a stand-alone Point-of-Care LoC device. This chapter discusses different types of lab-on-a-chip devices, the essential principles governing the design of these systems, and different fabrication techniques. The chapter concludes with some of the prominent applications of lab-on-a-chip devices.

A finger-driven disposable micro-platform based on isothermal amplification for the application of multiplexed and point-of-care diagnosis of tuberculosis

Tuberculosis (TB) remains the high-risk infectious pathogen that caused global pandemic and high mortality, particularly in the areas lack in health resources. Clinical TB screening and diagnosis are so far mainly conducted on limited types of commercial platforms, which are expensive and require skilled personnel. In this work, we introduced a low-cost and portable finger-driven microfluidic chip (named Fd-MC) based on recombinase polymerase amplification (RPA) for rapid on-site detection of TB. After injection of the pre-treated sample solution, the pre-packaged buffer was driven by the pressure generated by the finger-actuated operation to accomplish sequential processes of diagnosis in a fully isolated microchannel. An in-situ fluorescence strategy based on FAM-probe was implemented for on-chip results read-out though a hand-held UV lamp. Hence, the Fd-MC proved unique advantageous for avoiding the risk of infection or environmental contamination. In addition, the Fd-MC was designed for multiplexed detection, which is able to not only identify TB/non-TB infection, but also differentiate between human Mycobacterium tuberculosis and Mycobacterium bovis. The platform was verified in 37 clinical samples, statistically with 100% specificity and 95.2% sensitivity as compared to commercial real-time RPA. Overall, the proposed platform eliminates the need on external pumps and skilled personnel, holding promise to POC testing in the resource-limited area.

Coil spring-powered pump with inertial microfluidic chip for size-based isolation and enrichment of biological cells

Coil spring-powered device for circulating biomarker isolation.

Hand-Powered Inertial Microfluidic Syringe-Tip Centrifuge

Conventional sample preparation techniques require bulky and expensive instruments and are not compatible with next-generation point-of-care diagnostic testing. Here, we report a manually operated syringe-tip inertial microfluidic centrifuge (named i-centrifuge) for high-flow-rate (up to 16 mL/min) cell concentration and experimentally demonstrate its working mechanism and performance. Low-cost polymer films and double-sided tape were used through a rapid nonclean-room process of laser cutting and lamination bonding to construct the key components of the i-centrifuge, which consists of a syringe-tip flow stabilizer and a four-channel paralleled inertial microfluidic concentrator. The unstable liquid flow generated by the manual syringe was regulated and stabilized with the flow stabilizer to power inertial focusing in a four-channel paralleled concentrator. Finally, we successfully used our i-centrifuge for manually operated cell concentration. This i-centrifuge offers the advantages of low device cost, simple hand-powered operation, high-flow-rate processing, and portable device volume. Therefore, it holds potential as a low-cost, portable sample preparation tool for point-of-care diagnostic testing.

Droplet microfluidic devices for organized stem cell differentiation into germ cells: capabilities and challenges

Demystifying the mechanisms that underlie germline development and gamete production is critical for expanding advanced therapies for infertile couples who cannot benefit from current infertility treatments. However, the low number of germ cells, particularly in the early stages of development, represents a serious challenge in obtaining sufficient materials required for research purposes. In this regard, pluripotent stem cells (PSCs) have provided an opportunity for producing an unlimited source of germ cells in vitro. Achieving this ambition is highly dependent on accurate stem cell niche reconstitution which is achievable through applying advanced cell engineering approaches. Recently, hydrogel microparticles (HMPs), as either microcarriers or microcapsules, have shown promising potential in providing an excellent 3-dimensional (3D) biomimetic microenvironment alongside the systematic bioactive agent delivery. In this review, recent studies of utilizing various HMP-based cell engineering strategies for appropriate niche reconstitution and efficient in vitro differentiation are highlighted with a special focus on the capabilities of droplet-based microfluidic (DBM) technology. We believe that a deep understanding of the current limitations and potentials of the DBM systems in integration with stem cell biology provides a bright future for germ cell research.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12551-021-00907-5.

High-throughput injection molded microfluidic device for single-cell analysis of spatiotemporal dynamics

Single-cell level analysis of various cellular behaviors has been aided by recent developments in microfluidic technology. Polydimethylsiloxane (PDMS)-based microfluidic devices have been widely used to elucidate cell differentiation and migration under spatiotemporal stimulation. However, microfluidic devices fabricated with PDMS have inherent limitations due to material issues and non-scalable fabrication process. In this study, we designed and fabricated an injection molded microfluidic device that enables real-time chemical profile control. This device is made of polystyrene (PS), engineered with channel dimensions optimized for injection molding to achieve functionality and compatibility with single cell observation. We demonstrated the spatiotemporal dynamics in the device with computational simulation and experiments. In temporal dynamics, we observed extracellular signal-regulated kinase (ERK) activation of PC12 cells by stimulating the cells with growth factors (GFs). Also, we confirmed yes-associated protein (YAP) phase separation of HEK293 cells under stimulation using sorbitol. In spatial dynamics, we observed the migration of NIH 3T3 cells (transfected with Lifeact-GFP) under different spatiotemporal stimulations of PDGF. Using the injection molded plastic devices, we obtained comprehensive data more easily than before while using less time compared to previous PDMS models. This easy-to-use plastic microfluidic device promises to open a new approach for investigating the mechanisms of cell behavior at the single-cell level.

An ultra-portable, self-contained point-of-care nucleic acid amplification test for diagnosis of active COVID-19 infection

There is currently a high level of demand for rapid COVID-19 tests, that can detect the onset of the disease at point of care settings. We have developed an ultra-portable, self-contained, point-of-care nucleic acid amplification test for diagnosis of active COVID-19 infection, based on the principle of loop mediated isothermal amplification (LAMP). The LAMP assay is 100% sensitive and specific to detect a minimum of 300 RNA copies/reaction of SARS-CoV-2. All of the required sample transportation, lysing and amplification steps are performed in a standalone disposable cartridge, which is controlled by a battery operated, pocket size (6x9x4cm³) unit. The test is easy to operate and does not require skilled personnel. The total time from sample to answer is approximately 35 min; a colorimetric readout indicates positive or negative results. This portable diagnostic platform has significant potential for rapid and effective testing in community settings. This will accelerate clinical decision making, in terms of effective triage and timely therapeutic and infection control interventions.

Pushbutton-activated microfluidic cartridge as a user-friendly sample preparation tool for diagnostics

Microfluidic technologies have several advantages in sample preparation for diagnostics but suffer from the need for an external operation system that hampers user-friendliness. To overcome this limitation in microfluidic technologies, a number of user-friendly methods utilizing capillary force, degassed poly(dimethylsiloxane), pushbutton-driven pressure, a syringe, or a pipette have been reported. Among these methods, the pushbutton-driven, pressure-based method has a great potential to be widely used as a user-friendly sample preparation tool for point-of-care testing or portable diagnostics. In this Perspective, we focus on the pushbutton-activated microfluidic technologies toward a user-friendly sample preparation tool. The working principle and recent advances in pushbutton-activated microfluidic technologies are briefly reviewed, and future perspectives for wide application are discussed in terms of integration with the signal analysis system, user-dependent variation, and universal and facile use.

Finger-Actuated Microneedle Array for Sampling Body Fluids

The application of microneedles (MNs) for minimally invasive biological fluid sampling is rapidly emerging, offering a user-friendly approach with decreased insertion pain and less harm to the tissues compared to conventional needles. Here, a finger-powered microneedle array (MNA) integrated with a microfluidic chip was conceptualized to extract body fluid samples. Actuated by finger pressure, the microfluidic device enables an efficient approach for the user to collect their own body fluids in a simple and fast manner without the requirement for a healthcare worker. The processes for extracting human blood and interstitial fluid (ISF) from the body and the flow across the device, estimating the amount of the extracted fluid, were simulated. The design in this work can be utilized for the minimally invasive personalized medical equipment offering a simple usage procedure.

STUDY ON A RAPID MANUFACTURING OF DIAMOND MICROMIXER BY CO2 LASER

In this paper, the influence of the parameters of CO2 laser cutting system on the rhombus microchannel is studied. In the experiment, we changed the laser processing speed, laser processing power, and laser processing number of CO2 laser cutting system, and the depth and width of microchannel are studied by changing these three parameters. It is found that the depth and width of microchannel increase with the increase of laser processing number and laser processing power. For example, when the speed is 6[Formula: see text]mm/s and the number of laser processing is three times, the width of microchannel increases from 0.51[Formula: see text]mm to 0.64[Formula: see text]mm and the depth increases from 0.75[Formula: see text]mm to 1.60[Formula: see text]mm with the increase of power. However, the depth and width of the microchannel decrease with the increase of laser processing speed. For example, when the power is 8[Formula: see text]W and the number of laser processing is three times, the width of the microchannel decreases from 0.51[Formula: see text]mm to 0.39[Formula: see text]mm, and the depth of the microchannel decreases from 0.75[Formula: see text]mm to 0.34[Formula: see text]mm.

Pushbutton-activated microfluidic dropenser for droplet digital PCR

Here, we report a portable microfluidic device to generate and dispense droplets simply operated by pushbutton for droplet digital polymerase chain reaction (ddPCR), which is named pushbutton-activated microfluidic dropenser (droplet dispenser) (PAMD). After loading the PCR mixtures and the droplet generation oil to PAMD, digitized PCR mixtures are prepared in PCR tubes after the actuation of a pushbutton. Multiple droplet generation units are simultaneously operated by a single pushbutton, and the size of droplets is controllable by adjusting the geometry of the droplet generation channel. To examine the performance of PAMD, digitized PCR mixtures containing genomic DNA of Escherichia coli (E. coli) O157:H7 prepared by PAMD were assessed by a fluorescence signal analyzer after PCR with a thermal cycler. As a result, PAMD can produce analytical droplets for ddPCR as much as a conventional droplet generator even though any external equipment is not required.

A practical microfluidic pump enabled by acoustofluidics and 3D printing

Simple and low-cost solutions are becoming extremely important for the evolving necessities of biomedical applications. Even though, on-chip sample processing and analysis has been rapidly developing for a wide range of screening and diagnostic protocols, efficient and reliable fluid manipulation in microfluidic platforms still require further developments to be considered portable and accessible for low-resource settings. In this work, we present an extremely simple microfluidic pumping device based on three-dimensional (3D) printing and acoustofluidics. The fabrication of the device only requires 3D-printed adaptors, rectangular glass capillaries, epoxy and a piezoelectric transducer. The pumping mechanism relies on the flexibility and complexity of the acoustic streaming patterns generated inside the capillary. Characterization of the device yields controllable and continuous flow rates suitable for on-chip sample processing and analysis. Overall, a maximum flow rate of ~ 12 μL/min and the control of pumping direction by frequency tuning is achieved. With its versatility and simplicity, this microfluidic pumping device offers a promising solution for portable, affordable and reliable fluid manipulation for on-chip applications.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10404-020-02411-w.

Characterizing microfluidic approaches for a fast and efficient reagent exchange in single-molecule studies

Single-molecule experiments usually take place in flow cells. This experimental approach is essential for experiments requiring a liquid environment, but is also useful to allow the exchange of reagents before or during measurements. This is crucial in experiments that need to be triggered by ligands or require a sequential addition of proteins. Home-fabricated flow cells using two glass coverslips and a gasket made of paraffin wax are a widespread approach. The volume of the flow cell can be controlled by modifying the dimensions of the channel while the reagents are introduced using a syringe pump. In this system, high flow rates disturb the biological system, whereas lower flow rates lead to the generation of a reagent gradient in the flow cell. For very precise measurements it is thus desirable to have a very fast exchange of reagents with minimal diffusion. We propose the implementation of multistream laminar microfluidic cells with two inlets and one outlet, which achieve a minimum fluid switching time of 0.25 s. We additionally define a phenomenological expression to predict the boundary switching time for a particular flow cell cross section. Finally, we study the potential applicability of the platform to study kinetics at the single molecule level.

Finger-powered fluidic actuation and mixing via MultiJet 3D printing

Additive manufacturing, or three-dimensional (3D) printing, has garnered significant interest in recent years towards the fabrication of sub-millimeter scale devices for an ever-widening array of chemical, biological and biomedical applications. Conventional 3D printed fluidic systems, however, still necessitate the use of non-portable, high-powered external off-chip sources of fluidic actuation, such as electro-mechanical pumps and complex pressure-driven controllers, thus limiting their scope towards point-of-need applications. This work proposes entirely 3D printed sources of human-powered fluidic actuation which can be directly incorporated into the design of any 3D printable sub-millifluidic or microfluidic system where electrical power-free operation is desired. Multiple modular, single-fluid finger-powered actuator (FPA) designs were fabricated and experimentally characterized. Furthermore, a new 3D fluidic one-way valve concept employing a dynamic bracing mechanism was developed, demonstrating a high diodicity of ∼1117.4 and significant reduction in back-flow from the state-of-the-art. As a result, fabricated FPA prototypes achieved tailorable experimental fluid flow rates from ∼100 to ∼3000 μL min^-1 without the use of electricity. Moreover, a portable human-powered two-fluid pulsatile fluidic mixer, capable of generating fully-mixed fluids in 10 seconds, is presented, demonstrating the application of FPAs towards on-chip integration into more complex 3D printed fluidic networks.

Reciprocating flow-assisted nucleic acid purification using a finger-actuated microfluidic device

Molecular diagnostics can provide a powerful diagnostic tool since it can detect pathogens with high sensitivity, but complicated sample preparation procedures limit its widespread use as an on-site detection tool that relies on the skilled person and external equipment. To resolve these limitations, we report a solid-phase nucleic acid purification using a finger-actuated microfluidic device, which can control a set amount of flow regardless of differences in end-users. To increase the recovery rate, a finger-actuated reciprocator was newly developed and integrated into the microfluidic device that can efficiently react with silica microbeads and reagents. After verifying the finger-actuated microfluidic reciprocator, the effect of the reciprocating flow on the recovery rate was assessed to purify the standard DNA of the hepatitis B virus (HBV). The recovery rate was increased up to ∼50% and 955 to 955 000 IU mL^-1 of HBV standard DNA was successfully purified and detected by a real-time polymerase chain reaction. Furthermore, the proposed microfluidic device was exploited to purify the HBV DNA from the patient's blood plasma samples.

Roll-to-Roll Manufacturing of Integrated Immunodetection Sensors

Lack of functional integration and high manufacturing costs have been identified as major challenges in commercialization of point-of-care devices. In this study, roll-to-roll (R2R) fabrication process was developed for large-scale manufacturing of disposable microfluidic devices. The integrated, user-friendly device included a plasma separation membrane for simple blood filtration, immobilized antibodies for specific immunodetection, microfluidics for plasma transport and reagent mixing, and a blister for actuation and waste storage. These functionalities were designed to be compatible with R2R processing, which was demonstrated using pilot-scale printing lines producing 60 devices in an hour. The produced sensors enabled rapid (10 min) and sensitive (2 μg/mL) fluorescence-based immunodetection of C-reactive protein from 20 μL of whole blood.

Optical Etching to Pattern Microstructures on Plastics by Vacuum Ultraviolet Light

We proposed and demonstrated an optical dry etching method for transferring a pattern on a photomask to a surface of plastics by decomposing the irradiated area using the high energy of vacuum ultraviolet light (VUV) at room temperature and pressure. Two kinds of wavelengths of 160 nm and 172 nm were used as the vacuum ultraviolet light, and the patterning performances for polymethyl methacrylate (PMMA) and polycarbonate (PC) were compared. As a result, it was revealed that proportional relationships were obtained between the etching rate and the irradiation dose for both wavelengths, and the cross-sectional profiles were anisotropic. In addition, both PMMA and PC were etched at a wavelength of 160 nm, whereas PC could not be etched at a wavelength of 172 nm, suggesting that it correlates with the bond dissociation energies of the molecular bonds of the materials and the energies of the photons. Furthermore, by combining this method with the optical bonding method that we had previously developed to bond surfaces irradiated with VUV, we have demonstrated a method for fabricating microfluidic devices by irradiating only with VUV. This paper shows that this technique is a new microfabrication method suitable for simple and mass production of plastic materials.

CO2 LASER ABLATION MICROCHANNEL BASED ON KOCH FRACTAL PRINCIPLE

In this paper, we focussed on the processing power of CO2 laser systems and the impact of scanning speed, scanning power and number of scans on the quality of microchannels. We created microchannels which are based on the Koch fractal principle through a flexible and low-cost CO2 laser system. The processing and manufacturing method of Koch fractal micromixer on polymethyl methacrylate (PMMA) substrate was also studied. The microchannel structure based on the Koch fractal principle can increase the contact area and mixing time of the fluid and improve the mixing efficiency of the micromixer. In the experiment, our speed is 2, 4 and 6[Formula: see text]mm/s, the number of scans is 2/3/4 times and the power is 4, 8 and 12[Formula: see text]W. As the power and number of scans increase and the speed decreases, the width and depth of the microchannel are changed more clearly, which contributes to the successful thermal bonding of the Koch fractal micromixer and avoids thermal bonding due to overvoltage. By comparing the experimental data, we found that the width and depth of the channel are ideal when the speed is 2[Formula: see text]mm/s, the number of scans is 4 and the power is 12[Formula: see text]W. Because of the lower cost of PMMA, the use of CO2 laser systems to fabricate microchannels on PMMA substrates will have broad application value, reduce cost and be easier to manufacture.

Colorimetric Detection of Escherichia coli O157:H7 with Signal Enhancement Using Size-Based Filtration on a Finger-Powered Microfluidic Device

Although immunomagnetic separation is a useful sample pretreatment method that can be used to separate target pathogens from a raw sample, it is challenging to remove unbound free magnetic nanoparticles (MNPs) for colorimetric detection of target pathogens. Here, size-based filtration was exploited for the rapid on-site detection of pathogens separated by immunomagnetic separation in order to remove unbound free MNPs using a finger-powered microfluidic device. A membrane filter and an absorbent pad were integrated into the device and a mixture of unbound free MNPs and MNP-bound Escherichia coli (E. coli) O157:H7 was dispensed over the membrane filter by pressing and releasing the pressure chamber. A colorimetric signal was generated by MNP-bound E. coli O157:H7 while unbound free MNPs were washed out by the absorbent. Furthermore, the colorimetric signals can be amplified using a gold enhancer solution when gold-coated MNPs were used instead of MNPs. As a result, 10² CFU/mL E. coli O157:H7 could be detected by the enhanced colorimetric signal on a proposed device.

Towards practical sample preparation in point-of-care testing: user-friendly microfluidic devices

Microfluidic technologies offer a number of advantages for sample preparation in point-of-care testing (POCT), but the requirement for complicated external pumping systems limits their wide use. To facilitate sample preparation in POCT, various methods have been developed to operate microfluidic devices without complicated external pumping systems. In this review, we introduce an overview of user-friendly microfluidic devices for practical sample preparation in POCT, including self- and hand-operated microfluidic devices. Self-operated microfluidic devices exploit capillary force, vacuum-driven pressure, or gas-generating chemical reactions to apply pressure into microchannels, and hand-operated microfluidic devices utilize human power sources using simple equipment, including a syringe, pipette, or simply by using finger actuation. Furthermore, this review provides future perspectives to realize user-friendly integrated microfluidic circuits for wider applications with the integration of simple microfluidic valves.

O. Microfluidic Point-of-Care Devices: New Trends and Future Prospects for eHealth Diagnostics

Point-of-care (PoC) diagnostics is promising for early detection of a number of diseases, including cancer, diabetes, and cardiovascular diseases, in addition to serving for monitoring health conditions. To be efficient and cost-effective, portable PoC devices are made with microfluidic technologies, with which laboratory analysis can be made with small-volume samples. Recent years have witnessed considerable progress in this area with "epidermal electronics", including miniaturized wearable diagnosis devices. These wearable devices allow for continuous real-time transmission of biological data to the Internet for further processing and transformation into clinical knowledge. Other approaches include bluetooth and WiFi technology for data transmission from portable (non-wearable) diagnosis devices to cellphones or computers, and then to the Internet for communication with centralized healthcare structures. There are, however, considerable challenges to be faced before PoC devices become routine in the clinical practice. For instance, the implementation of this technology requires integration of detection components with other fluid regulatory elements at the microscale, where fluid-flow properties become increasingly controlled by viscous forces rather than inertial forces. Another challenge is to develop new materials for environmentally friendly, cheap, and portable microfluidic devices. In this review paper, we first revisit the progress made in the last few years and discuss trends and strategies for the fabrication of microfluidic devices. Then, we discuss the challenges in lab-on-a-chip biosensing devices, including colorimetric sensors coupled to smartphones, plasmonic sensors, and electronic tongues. The latter ones use statistical and big data analysis for proper classification. The increasing use of big data and artificial intelligence methods is then commented upon in the context of wearable and handled biosensing platforms for the Internet of things and futuristic healthcare systems.

Advances in passively driven microfluidics and lab-on-chip devices: a comprehensive literature review and patent analysis

The development of passively driven microfluidic labs on chips has been increasing over the years. In the passive approach, the microfluids are usually driven and operated without any external actuators, fields, or power sources. Passive microfluidic techniques adopt osmosis, capillary action, surface tension, pressure, gravity-driven flow, hydrostatic flow, and vacuums to achieve fluid flow. There is a great need to explore labs on chips that are rapid, compact, portable, and easy to use. The evolution of these techniques is essential to meet current needs. Researchers have highlighted the vast potential in the field that needs to be explored to develop rapid passive labs on chips to suit market/researcher demands. A comprehensive review, along with patent analysis, is presented here, listing the latest advances in passive microfluidic techniques, along with the related mechanisms and applications.

Finger-powered agglutination lab chip with CMOS image sensing for rapid point-of-care diagnosis applications

Agglutination is an antigen-antibody reaction with visible expression of aggregation of the antigens and their corresponding antibodies. Applications extend to the identification of acute bacterial infection, hemagglutination, such as blood grouping, and diagnostic immunology. Our finger-powered agglutination lab chip with external CMOS image sensing was developed to support a platform for inexpensive, rapid point-of-care (POC) testing applications related to agglutination effects. In this paper, blood grouping (ABO and Rh grouping) was utilized to demonstrate the function of our finger-powered agglutination lab chip with CMOS image sensing. Blood antibodies were preloaded into the antibody reaction chamber in the lab chip. The blood sample was pushed through the antibody reaction chamber using finger-powered pressure actuation to initiate a hemagglutination reaction to identify the blood type at the on-chip detection area using our homemade CMOS image sensing mini-system. Finger-powered actuation without the need for external electrical pumping is excellent for low-cost POC applications, but the pumping liquid volume per finger push is hard to control. In our finger-powered agglutination lab chip with CMOS image sensing, we minimized the effects of different finger push depths and achieved robust performance for the test results with different push depths. The driving sample volume per finger push is about 0.79 mm³. For different chips and different pushes, the driven sample volume per finger push was observed to vary in the range of 0.64 to 1.18 mm³. The red blood cells were separated from the plasma on-chip after the whole blood sample was finger pumped and before the red blood cells reached the antibody chamber via an embedded plasma-separation membrane. Our homemade CMOS image mini-system robustly read and identified the agglutination results on our agglutination lab chip.

Sliding walls: a new paradigm for fluidic actuation and protocol implementation in microfluidics

Currently, fluidic control in microdevices is mainly achieved either by external pumps and valves, which are expensive and bulky, or by valves integrated in the chip. Numerous types of internal valves or actuation methods have been proposed, but they generally impose difficult compromises between performance and fabrication complexity. We propose here a new paradigm for actuation in microfluidic devices based on rigid or semi-rigid walls with transversal dimensions of hundreds of micrometres that are able to slide within a microfluidic chip and to intersect microchannels with hand-driven or translation stage-based actuation. With this new concept for reconfigurable microfluidics, the implementation of a wide range of functionalities was facilitated and allowed for no or limited dead volume, low cost and low footprint. We demonstrate here several fluidic operations, including on/off or switch valving, where channels are blocked or reconfigured depending on the sliding wall geometry. The valves sustain pressures up to 30 kPa. Pumping and reversible compartmentalisation of large microfluidic chambers were also demonstrated. This last possibility was applied to a "4D" migration assay of dendritic cells in a collagen gel. Finally, sliding walls containing a hydrogel-based membrane were developed and used to concentrate, purify and transport biomolecules from one channel to another, such functionality involving complex fluidic transport patterns not possible in earlier microfluidic devices. Overall, this toolbox is compatible with "soft lithography" technology, allowing easy implementation within usual fabrication workflows for polydimethylsiloxane chips. This new technology opens the route to a variety of microfluidic applications, with a focus on simple, hand-driven devices for point-of-care or biological laboratories with low or limited equipment and resources.

Resettable skin interfaced microfluidic sweat collection devices with chemesthetic hydration feedback

Recently introduced classes of thin, soft, skin-mounted microfluidic systems offer powerful capabilities for continuous, real-time monitoring of total sweat loss, sweat rate and sweat biomarkers. Although these technologies operate without the cost, complexity, size, and weight associated with active components or power sources, rehydration events can render previous measurements irrelevant and detection of anomalous physiological events, such as high sweat loss, requires user engagement to observe colorimetric responses. Here we address these limitations through monolithic systems of pinch valves and suction pumps for purging of sweat as a reset mechanism to coincide with hydration events, microstructural optics for reversible readout of sweat loss, and effervescent pumps and chemesthetic agents for automated delivery of sensory warnings of excessive sweat loss. Human subject trials demonstrate the ability of these systems to alert users to the potential for dehydration via skin sensations initiated by sweat-triggered ejection of menthol and capsaicin.

Self-sufficient, low-cost microfluidic pumps utilising reinforced balloons

Here, we introduce a simple method for increasing the inflation pressure of self-sufficient pressure pumps made of latex balloons. Our method involves reinforcing the latex balloon with elastane fibres to restrict the expansion of the balloon and increase its inflation pressure. This allowed us to increase the operational inflation pressure of a latex balloon from 2.5 to 25 kPa. Proof-of-concept experiments show the suitability of the reinforced balloon for inducing lateral forces and recirculating flows, which are employed for hydrodynamic capturing of large human monocytes. We also demonstrate the ability for the rapid exchange of solutions in repeated cycles upon manual squeezing of the reinforced balloons. We also show the suitability of the reinforced balloon for studying the mechanobiology of human aortic endothelial cells under various shear stress levels. The simplicity, portability, affordability, hyper-elasticity and scalability of the reinforced balloon pumps make them suitable for a wide range of microfluidic applications.

Vacuum pouch microfluidic system and its application for thin-film micromixers

In this paper, a new type of lab-on-a-chip system, called vacuum pouch microfluidic (VPM) system, is reported. The core of this technology is a thin-film vacuum pouch that provides negative pumping pressure once it is activated. It is a degassed plastic bag that encloses a microfluidic chip. To demonstrate its performance, a passive thin-film micromixer is developed to integrate with the vacuum pouch. Since both the vacuum pouch and the thin-film micromixer are made of plastic film, they can be laminated together to construct a multi-layered microfluidic system. Excluding the storage reservoir, the overall thickness is 0.4 mm and the total weight is 0.3 g. This system provides a simple and straightforward strategy to construct a standalone, portable, flexible and low cost microfluidic system. The thin-film micromixer uses a serpentine channel to perform the mixing process, and it is found to have distinct mixing mechanisms under different Reynolds (Re) numbers, where lateral diffusion dominates for Re < 1 and chaotic mixing starts to contribute for Re > 10. Integrating this thin-film micromixer with the vacuum pouch, it is demonstrated that the negative pumping pressure can be adjusted by different storage reservoirs being placed at the channel exit. Reynolds numbers ranging from 0.0064 to 45.2 can be achieved. It also is verified that the VPM micromixer can be stored for 4 weeks to provide a sufficient flow rate for mixing applications. Finally, to demonstrate the feasibility of applying this VPM-based thin-film micromixer for on-site detection, this system is integrated with the colorimetric method. It is verified that a 10 μl ferrous ion solution and a 10 μl potassium ferricyanide solution can be mixed in 12 seconds, and concentrations of 10 ppm to 1000 ppm can be quantified by analyzing the colorimetric signal in hue values.

Finger-Actuated Microfluidic Concentration Gradient Generator Compatible with a Microplate

The generation of concentration gradients is an essential part of a wide range of laboratory settings. However, the task usually requires tedious and repetitive steps and it is difficult to generate concentration gradients at once. Here, we present a microfluidic device that easily generates a concentration gradient by means of push-button actuated pumping units. The device is designed to generate six concentrations with a linear gradient between two different sample solutions. The microfluidic concentration gradient generator we report here does not require external pumps because changes in the pressure of the fluidic channel induced by finger actuation generate a constant volume of fluid, and the design of the generator is compatible with the commonly used 96-well microplate. Generation of a concentration gradient by the finger-actuated microfluidic device was consistent with that of the manual pipetting method. In addition, the amount of fluid dispensed from each outlet was constant when the button was pressed, and the volume of fluid increased linearly with respect to the number of pushing times. Coefficient of variation (CV) was between 0.796% and 13.539%, and the error was between 0.111% and 19.147%. The design of the microfluidic network, as well as the amount of fluid dispensed from each outlet at a single finger actuation, can be adjusted to the user’s demand. To prove the applicability of the concentration gradient generator, an enzyme assay was performed using alkaline phosphatase (ALP) and para-nitrophenyl phosphate (pNPP). We generated a linear concentration gradient of the pNPP substrate, and the enzyme kinetics of ALP was studied by examining the initial reaction rate between ALP and pNPP. Then, a Hanes–Woolf plot of the various concentration of ALP was drawn and the V_max and K_m value were calculated.