A continuous flow with reagent injection method on a novel inlaid microfluidic platform for nitrite determination has been successfully developed. The significance of the high-frequency monitoring of nutrient fluctuations in marine environments is crucial for understanding our impacts on the ecosystem. Many in-situ systems face limitations in high-frequency data collection and have restricted deployment times due to high reagent consumption. The proposed microfluidic device employs automatic colorimetric absorbance spectrophotometry, using the Griess assay for nitrite determination, with minimal reagent usage. The sensor incorporates 10 solenoid valves, four syringes, two LEDs, four photodiodes, and an inlaid microfluidic technique to facilitate optical measurements of fluid volumes. In this flow system, Taylor–Aris dispersion was simulated for different injection volumes at a constant flow rate, and the results have been experimentally confirmed using red food dye injection into a carrier stream. A series of tests were conducted to determine a suitable injection frequency for the reagent. Following the initial system characterization, seven different standard concentrations ranging from 0.125 to 10 µM nitrite were run through the microfluidic device to acquire a calibration curve. Three different calibrations were performed to optimize plug length, with reagent injection volumes of 4, 20, and 50 µL. A straightforward signal processing method was implemented to mitigate the Schlieren effect caused by differences in refractive indexes between the reagent and standards. The results demonstrate that a sampling frequency of at least 10 samples per hour is achievable using this system. The obtained attenuation coefficients exhibited good agreement with the literature, while the reagent consumption was significantly reduced. The limit of detection for a 20 µL injection volume was determined to be 94 nM from the sample intake, and the limit of quantification was 312 nM. Going forward, the demonstrated system will be packaged in a submersible enclosure to facilitate in-situ colorimetric measurements in marine environments. Full article

Acoustofluidics is an emerging research field wherein either mixing or (bio)-particle separation is conducted. High-power acoustic streaming can produce more intense and rapid flow patterns, leading to faster and more efficient liquid mixing. However, without cooling, the temperature of the piezoelectric element that is used to supply acoustic power to the fluid could rise above 50% of the Curie point of the piezomaterial, thereby accelerating its aging degradation. In addition, the supply of excessive heat to a liquid may lead to irreproducible streaming effects and gas bubble formation. To control these phenomena, in this paper, we present a feedback temperature control system integrated into an acoustofluidic setup using bulk acoustic waves (BAWs) to elevate mass transfer and manipulation of particles. The system performance was tested by measuring mixing efficiency and determining the average velocity magnitude of acoustic streaming. The results show that the integrated temperature control system keeps the temperature at the set point even at high acoustic powers and improves the reproducibility of the acoustofluidic setup performance when the applied voltage is as high as 200 V. Full article

Optofluidic dye lasers integrated into microfluidic chips are promising miniature coherent light sources for biosensing. However, achieving the accurate and efficient tuning of lasers remains challenging. This study introduces a novel pneumatically tunable optofluidic distributed feedback (DFB) dye laser in a multilayer microfluidic chip. The dye laser device integrates microfluidic channels, grating structures, and vacuum chambers. A second-order DFB grating configuration is utilized to ensure single-mode lasing. The application of vacuum pressure to the chambers stretches the soft grating layer, enabling the sensitive tuning of the lasing wavelength at a high resolution of 0.25 nm within a 7.84 nm range. The precise control of pressure and laser tuning is achieved through an electronic regulator. Additionally, the integrated microfluidic channels and optimized waveguide structure facilitate efficient dye excitation, resulting in a low pump threshold of 164 nJ/pulse. This pneumatically tunable optofluidic DFB laser, with its high-resolution wavelength tuning range, offers new possibilities for the development of integrated portable devices for biosensing and spectroscopy. Full article

Microfluidics is a highly interdisciplinary field where the integration of deep-learning models has the potential to streamline processes and increase precision and reliability. This study investigates the use of deep-learning methods for the accurate detection and measurement of droplet diameters and the image restoration of low-resolution images. This study demonstrates that the Segment Anything Model (SAM) provides superior detection and reduced droplet diameter error measurement compared to the Circular Hough Transform, which is widely implemented and used in microfluidic imaging. SAM droplet detections prove to be more robust to image quality and microfluidic images with low contrast between the fluid phases. In addition, this work proves that a deep-learning super-resolution network MSRN-BAM can be trained on a dataset comprising of droplets in a flow-focusing microchannel to super-resolve images for scales ×2, ×4, ×6, ×8. Super-resolved images obtain comparable detection and segmentation results to those obtained using high-resolution images. Finally, the potential of deep learning in other computer vision tasks, such as denoising for microfluidic imaging, is shown. The results show that a DnCNN model can denoise effectively microfluidic images with additive Gaussian noise up to $\sigma$ = 4. This study highlights the potential of employing deep-learning methods for the analysis of microfluidic images. Full article

Microfluidic devices have revolutionized the field of lab-on-a-chip by enabling precise manipulation of small fluid volumes for various biomedical applications. However, most existing microfluidic pumps struggle to handle high-viscosity fluids, limiting their applicability in certain areas that involve bioanalysis and on-chip sample processing. In this paper, the design and fabrication of a miniaturized Archimedean screw pump for pumping high-viscosity fluids within microfluidic channels are presented. The pump was 3D-printed and operated vertically, allowing for continuous and directional fluid pumping. The pump’s capabilities were demonstrated by successfully pumping polyethylene glycol (PEG) solutions that are over 100 times more viscous than water using a basic mini-DC motor. Efficient fluid manipulation at low voltages was achieved by the pump, making it suitable for point-of-care and field applications. The flow rates of water were characterized, and the effect of different screw pitch lengths on the flow rate was investigated. Additionally, the pump’s capacity for pumping high-viscosity fluids was demonstrated by testing it with PEG solutions of increasing viscosity. The microfluidic pump’s simple fabrication and easy operation position it as a promising candidate for lab-on-a-chip applications involving high-viscosity fluids. Full article

A control chip with a multistage flow-rate regulation function based on the correlation between the flow resistance and flow rate has been developed in this article. Compared with the traditional proportional solenoid valve, this kind of flow valve based on microfluidic technology has the characteristics of being light-weight and having no electric drive. It solves such technical problems as how the current digital microfluidic chip can only adjust the flow switch, and the adjustment of the flow rate is difficult. To linearize the output signal, we propose a design method of weighted resistance. The output flow is controlled by a 4-bit binary pressure signal. According to the binary value of the 4-bit pressure signal at the input, the output can achieve 16-stage flow adjustment. Furthermore, we integrate the three-dimensional flow resistance network, multilayer structure microvalve, and parallel fluid network into a single chip by using 3D printing to obtain a modular flow control unit. This structure enables the microflow control signal to be converted from a digital signal to an analogue signal (DA conversion), and is suitable for microflow driving components, such as in microfluidic chip sampling systems and proportional mixing systems. In the future, we expect this device to even be used in the automatic control system of a miniature pneumatic soft actuator. Full article

The shortcomings of standard plasma-separation methods limit the point-of-care application of microfluidics in clinical facilities and at the patient’s bedside. To overcome the limitations of this inconvenient, laborious, and costly technique, a new plasma-separation technique and device were developed. This new separation method relies on immunological capture and filtration to exclude cells from plasma, and is convenient, easy to use, and cost-effective. Most of the RBCs can be captured and immobilized by antibody which coated in separation matrix, and residue cells can be totally removed from the sample by a commercially plasma purification membranes. A 400 µL anti-coagulated whole blood sample with 65% hematocrit (Hct) can be separated by the device in 5 min with only one pipette. Up to 97% of the plasma can be recovered from the raw blood sample with a separation efficiency at 100%. The recovery rate of small molecule compounds, proteins, and nucleic acid biomarkers is evaluated; there are no obvious differences from the centrifuge method. The results demonstrate that this method is an excellent replacement for traditional plasma preparation protocols. Full article

Minimum inhibition concentration (MIC) of antibiotic is an effective value to ascertain the agent and minimum dosage of inhibiting bacterial growth. However, current techniques to determine MIC are labor intensive and time-consuming, and require skilled operator and high initial concentration of bacteria. To simplify the operation and reduce the time of inhibition test, we developed a microfluidic system, containing a concentration generator and sub-micro-liter chambers, for rapid bacterial growth and inhibition test. To improve the mixing effect, a micropillar array in honeycomb-structure channels is designed, so the steady concentration gradient of amoxicillin can be generated. The flanged chambers are used to culture bacteria under the condition of continuous flow and the medium of chambers is refreshed constantly, which could supply the sufficient nutrient for bacteria growth and take away the metabolite. Based on the microfluidic platform, the bacterial growth with antibiotic inhibition on chip can be quantitatively measured and MIC can be obtained within six hours using low initial concentration of bacteria. Overall, this microfluidic platform has the potential to provide rapidness and effectiveness to screen bacteria and determine MIC of corresponding antibiotics in clinical therapies. Full article

The sensitive quantification of low-abundance nucleic acids holds importance for a range of clinical applications and biological studies. In this study, we describe a facile microfluidic chip for absolute DNA quantifications based on the digital loop-mediated isothermal amplification (digital LAMP) method. This microfluidic chip integrates a cross-flow channel for droplet generation with a micro-cavity for droplet tiling. DNA templates in the LAMP reagent were divided into ~20,000 water-in-oil droplets at the cross-flow channel. The droplets were then tiled in the micro-cavity for isothermal amplification and fluorescent detection. Different from the existing polydimethylsiloxane (PDMS) microfluidic chips, this study incorporates gold nanoparticles (AuNPs) into PDMS substrate through silica coating and dodecanol modification. The digital LAMP chip prepared by AuNPs-PDMS combines the benefits of the microstructure manufacturing performance of PDMS with the light-to-heat conversion advantages of AuNPs. Upon illumination with a near infrared (NIR) LED, the droplets were stably and efficiently heated by the AuNPs in PDMS. We further introduce an integrated device with a NIR heating unit and a fluorescent detection unit. The system could detect HBV (hepatitis B virus)-DNA at a concentration of 1 × 10¹ to 1 × 10⁴ copies/μL. The LED-driven digital LAMP chip and the integrated device; therefore, demonstrate high accuracy and excellent performance for the absolute quantification of low-abundance nucleic acids, showing the advantages of integration, miniaturization, cost, and power consumption. Full article

The modular-based multi-organ-on-a-chip enables more stable and flexible configuration to better mimic the complex biological phenomena for versatile biomedical applications. However, the existing magnetic-based interconnection modes are mainly realized by directly embedding and/or fixing magnets into the modular microfluidic devices for single use only, which will inevitably increase the complexity and cost during the manufacturing process. Here, we present a novel design of a reusable standardized universal interface module (RSUIM), which is highly suitable for generic organ-on-chip applications and their integration into multi-organ systems. Both pasting-based and clamping-based interconnection modes are developed in a plug-and-play manner without fluidic leakage. Furthermore, due to the flexibility of the modular design, it is simple to integrate multiple assembled modular devices through parallel configuration into a high throughput platform. To test its effectiveness, experiments on the construction of both the microvascular network and vascularized tumor model are performed by using the integration of the generic vascularized organ-on-a-chip module and pasting-based RSUIM, and their quantitative analysis results on the reproducibility and anti-cancer drug screening validation are further performed. We believe that this RSUIM design will become a standard and critical accessory for a broad range of organ-on-a-chip applications and is easy for commercialization with low cost. Full article

The microvalve for accurate flow control under low fluidic pressure is vital in cost-effective and miniaturized microfluidic devices. This paper proposes a novel microfluidic passive valve comprising of a liquid chamber, an elastic membrane, and an ellipsoidal control chamber, which actualizes a high flow rate control under an ultra-low threshold pressure. A prototype of the microvalve was fabricated by 3D printing and UV laser-cutting technologies and was tested under static and time-dependent pressure conditions. The prototype microvalve showed a nearly constant flow rate of 4.03 mL/min, with a variation of ~4.22% under the inlet liquid pressures varied from 6 kPa to 12 kPa. In addition, the microvalve could stabilize the flow rate of liquid under the time-varying sinusoidal pressures or the square wave pressures. To validate the functionality of the microvalve, the prototype microvalve was applied in a gas-driven flow system which employed an air blower or human mouth blowing as the low-cost gas source. The microvalve was demonstrated to successfully regulate the steady flow delivery in the system under the low driving pressures produced by the above gas sources. We believe that this new microfluidic passive valve will be suitable for controlling fluid flow in portable microfluidic devices or systems of wider applications. Full article

A passive microvalve has appealing advantages in cost-effective and miniaturized microfluidic applications. In this work, we present a passive flow regulatory device for enhanced flow control in a microfluidic environment. The device was integrated with two functional elements, including a flow regulating valve and a flow check valve. Importantly, the flow regulating valve could maintain a stable flow rate over a threshold liquid pressure, and the flow check valve enabled effective liquid on/off control, thus accurate forward flow without any backward leakage was achieved. The flow performance of the flow regulating valve was analyzed through 3D FSI (Fluid-Structure Interaction) simulation, and several key parameters (i.e., fluidic channel height and width, control channel length, and Young’s modulus) were found to influence valve flow rate directly. To examine the flow characteristics of the device, we fabricated a prototype using 3D printing and UV laser cutting technologies, and the flow rates of the prototype under varied test pressures were measured in forward and reverse modes, respectively. Experimental results showed that nearly a constant flow rate of 0.42 ± 0.02 mL s⁻¹ was achieved in the forward mode at an inlet pressure range of 70 kPa to 130 kPa, and liquid flow was totally stopped in the reverse mode at a maximum pressure of 200 kPa. The proposed microfluidic flow regulatory device could be employed for accurate flow control in low-cost and portable Lab-on-a-Chip (LoC) applications. Full article

Biofilms exist in the natural world and applied to many industries. However, due to the variety of characteristics caused by their complex components, biofilms can also lead to membrane fouling and recurrent infections which pose threats to human health. So, to make the best use of their advantages and avoid their disadvantages, knowing the best time and methods for improving or preventing biofilm formation is important. In situ observation without fluorescence labeling in microscale and according to a time scale is useful to research biofilm and confine its formation. In this study, we developed a microfluidic system for real-time observation of bacteria culture and biofilms development at microscale. We cultured E. coli ATCC 25922 on a chip at continuous flow of the velocity, which could promote bacterial formation. Biofilms formation under the condition of adding amoxicillin at different times is also discussed. In addition, the mixed strains from sludge were also cultured on chip, and possible factors in biofilm formation are discussed. Our results show that a microfluidic device could culture microorganisms in continuous flow and accelerate them to adhere to the surface, thereby promoting biofilm formation. Overall, this platform is a useful tool in research on initial biofilm formation, which can contribute to preventing biofouling and infections. Full article

A multifunction detection sensor for hydraulic oil contaminants based on a microfluidic chip is proposed, which consists of double solenoid coils and a straight microchannel. The inductance detection model of metal particles and capacitance detection model of nonmetal particles are constructed theoretically. In order to further improve detection sensitivity, experiments of effects of silicon steel sheets on the sensitivity of detection are carried out. Experimental results show that the silicon steel sheets can significantly improve the detection sensitivity of metal particles. The inductance amplitude and signal-to-noise (SNR) of iron particles ranging from 60–130 μm and copper particles ranging from 120–180 μm can be increased by at least 7.0–2.4 and 4.5–2.0 times, respectively. We demonstrate the successful detection of 30 μm iron particles and 90 μm copper particles using double solenoid coils with silicon steel sheets. In capacitance detection experiments, the silicon steel sheets can improve the sensitivity of capacitance detection, but the improvement effect is not obvious. We demonstrate the successful detection of 140 μm water droplets and 240 μm bubbles using double solenoid coils with and without silicon steel sheets. The capacitance amplitude and SNR of detecting water droplets ranging from 140–150 μm and bubbles ranging from 240–250 μm can be increased by 37.4–21.9% and 18.5–8.0% using double solenoid coils with silicon steel sheets, respectively. Full article

A handy liquid metal based non-invasive particle microtrap was proposed and demonstrated in this work. This kind of microtrap can be easily designed and fabricated at any location of a microfluidic chip to perform precise particle trapping and releasing without disturbing the microchannel itself. The microsystem demonstrated in this work utilized silicon oil as the continuous phase and fluorescent particles (PE-Cy5, SPHERO^TM Fluorescent Particles, BioLegend, San Diego, CA, USA, 10.5 μm) as the target particles. To perform the particle trapping, the micro system utilized liquid-metal-filled microchannels as noncontact electrodes to generate different patterns of electric field inside the fluid channel. According to the experimental results, the target particle can be selectively trapped and released by switching the electric field patterns. For a better understanding the control mechanism, a numerical simulation of the electric field was performed to explain the trapping mechanism. In order to verify the model, additional experiments were performed and are discussed. Full article

Dielectrophoresis in microfluidics provides a useful tool to test biomechanics of living cells, regardless of surface charges on cell membranes. We have designed an experimental method to characterize the nonlinear viscoelastic behaviors of single cells using dielectrophoresis in a microfluidic channel. This method uses radio frequency, low voltage excitations through interdigitated microelectrodes, allowing probing multiple cells simultaneously with controllable load levels. Dielectrophoretic force was calibrated using a triaxial ellipsoid model. Using a Kelvin–Voigt model, the nonlinear shear moduli of cell membranes were determined from the steady-state deformations of red blood cells in response to a series of electric field strengths. The nonlinear elastic moduli of cell membranes ranged from 6.05 µN/m to up to 20.85 µN/m, which were identified as a function of extension ratio, rather than the lumped-parameter models as reported in the literature. Value of the characteristic time of the extensional recovery of cell membranes initially deformed to varied extent was found to be about 0.14 s. Shear viscosity of cell membrane was estimated to be 0.8–2.9 (µN/m)·s. This method is particularly valuable for rapid, non-invasive probing of mechanical properties of living cells. Full article

Droplet-based microfluidics are capable of transporting very small amounts of fluid over long distances. This characteristic may be applied to conventional fluid delivery using needles if droplets can be reliably expelled from a microfluidic channel. In this paper, we demonstrate a system for the extraction of water droplets from an oil-phase in a polymer microfluidic device. A hydrophilic membrane with a strong preference for water over oil is integrated into a droplet microfluidic system and observed to allow the passage of the transported aqueous phase droplets while blocking the continuous phase. The oil breakthrough pressure of the membrane was observed to be 250 ± 20 kPa, a much greater pressure than anywhere within the microfluidic channel, thereby eliminating the possibility that oil will leak from the microchannel, a critical parameter if droplet transport is to be used in needle-based drug delivery. Full article

A simple and robust co-flowing microfluidic device for double emulsion preparation is designed and assembled to visually study the double emulsion formation by the use of a microscope and high-speed camera. Using a visualization system, the transient processes of double emulsion formation in co-flowing stream are observed and recorded for a variety of flow rates. The effects of flow rates of each fluid on flow modes, drop sizes, and polydispersities are examined and analyzed. The results indicate that the detaching of the inner drops accelerates the detaching of the outer drops and speeds up the drop formation process of double emulsions. The manipulation of flow rates is capable to actively control the sizes of the inner and outer drops as well as the number of inner drops encapsulated. Without surface modification, the microfluidic device produces a variety of emulsions, including the single-core and multi-core O/W/O double emulsions as well as binary emulsions of single and double emulsions. The proposed co-flowing microfluidic device is highly desirable in producing double emulsions in an easy and cheap way. Full article

A multi-purpose microfluidic device that can be used for both micromixing and micropropulsion operations has always been in demand, as it would simplify the various process flows associated with the current micro-total analysis systems. In this aspect, we propose a biomimetic artificial cilia-based microfluidic device that can efficiently facilitate both mixing and propulsion sequentially at the micro-scale. A rectangular microfluidic device consists of four straight microchannels that were fabricated using the microfabrication technique. An array of artificial cilia was embedded within one of the channel’s confinement through the aforementioned technique. A series of image processing and micro-particle image velocimetry technologies were employed to elucidate the micromixing and micropropulsion phenomena. Experiment results demonstrate that, with this proposed microfluidic device, a maximum micromixing efficiency and flow rate of 0.84 and 0.089 µL/min, respectively, can be achieved. In addition to its primary application as a targeted drug delivery system, where a drug needs to be homogeneously mixed with its carrier prior to its administration into the target body, this microfluidic device can be used as a micro-total analysis system for the handling of other biological specimens. Full article

Effective and rapid mixing is essential for various chemical and biological assays. The present work describes a simple and low-cost micromixer based on magnetofluidic actuation. The device takes advantage of magnetoconvective secondary flow, a bulk flow induced by an external magnetic field, for mixing. A superparamagnetic stream of diluted ferrofluid and a non-magnetic stream are introduced to a straight microchannel. A permanent magnet placed next to the microchannel induced a non-uniform magnetic field. The magnetic field gradient and the mismatch in magnetic susceptibility between the two streams create a body force, which leads to rapid and efficient mixing. The micromixer reported here could achieve a high throughput and a high mixing efficiency of 88% in a relatively short microchannel. Full article

In this paper we present a method to fabricate a fused silica microfluidic device by employing low viscosity KMPR photoresists. The resulting device is a continuous-flow microfluidic mixer based on hydrodynamic focusing. The advantages of this new fabrication method compared to the traditional approach using a poly-silicon mask are simplification, and time and cost reduction, while still preserving the quality and the performance of the mixers. This process results in devices in which the focusing channel has an aspect ratio of 10:1. The newly-fabricated mixer is successfully used to observe the folding of the Pin1 WW domain at the microsecond time scale. Full article

In this paper, we focus on the mechanical characterization of co-cultured spheroids of human umbilical vein endothelial cells (HUVECs) and mesenchymal stem cells (MSC) (HUVEC/MSC spheroids). HUVEC/MSC spheroids aggregate during culture, thereby decreasing in size. Since this size decrease can be caused by the contractility generated by the actomyosin of MSCs, which are intracellular frames, we can expect that there is a temporal transition for the mechanical characteristics, such as stiffness, during culture. To measure the mechanical characteristics, we use a microfluidic chip that is integrated with force sensor probes. We show the details of the measurement configuration and the results of mechanical characterization of the HUVEC/MSC spheroids. To evaluate the stiffness of the spheroids, we introduce the stiffness index, which essentially shows a spring constant per unit size of the spheroid at a certain time during measurement. From the measurement results, we confirmed that the stiffness index firstly increased during the days of culture, although after four days of culture, the stiffness index decreased. We confirmed that the proposed system can measure the stiffness of HUVEC/MSC spheroids. Full article

The flow of liquids in centrifugal microfluidics is unidirectional and dominated by centrifugal and Coriolis forces (i.e., effective only at T-junctions). Developing mechanisms and discovering efficient techniques to propel liquids in any direction other than the direction of the centrifugal force has been the subject of a large number of studies. The capillary force attained by specific surface treatments, pneumatic energy, active and passive flow reciprocation and Euler force have been previously introduced in order to manipulate the liquid flow and push it against the centrifugal force. Here, as a new method, the moment of inertia of the liquid inside a chamber in a centrifugal microfluidic platform is employed to manipulate the flow and propel the liquid passively towards the disc center. Furthermore, the effect of the moment of inertia on the liquid in a rectangular chamber is evaluated, both in theory and experiments, and the optimum geometry is defined. As an application of the introduced method, the moment of inertia of the liquid is used in order to mix two different dyed deionized (DI) waters; the mixing efficiency is evaluated and compared to similar mixing techniques. The results show the potential of the presented method for pumping liquids radially inward with relatively high flow rates (up to 23 mm³/s) and also efficient mixing in centrifugal microfluidic platforms. Full article

While there have been huge advances in the field of biosensors during the last decade, their integration into a microfluidic environment avoiding external tubing and pumping is still neglected. Herein, we show a new microfluidic design that integrates multiple reservoirs for reagent storage and single-use electrochemical pumps for time-controlled delivery of the liquids. The cartridge has been tested and validated with a silicon nitride-based photonic biosensor incorporating multiple optical ring resonators as sensing elements and an immunoassay as a potential target application. Based on experimental results obtained with a demonstration model, subcomponents were designed and existing protocols were adapted. The newly-designed microfluidic cartridges and photonic sensors were separately characterized on a technical basis and performed well. Afterwards, the sensor was functionalized for a protein detection. The microfluidic cartridge was loaded with the necessary assay reagents. The integrated pumps were programmed to drive the single process steps of an immunoassay. The prototype worked selectively, but only with a low sensitivity. Further work must be carried out to optimize biofunctionalization of the optical ring resonators and to have a more suitable flow velocity progression to enhance the system’s reproducibility. Full article

A microfluidic device capable of precise chemical control is helpful to mimic tumor microenvironments in vitro, which are closely associated with malignant progression, including metastasis. Cancer cells under a concentration gradient of oxygen and other sustenance materials inside a tumor in vivo have recently been reported to increase the probability of metastasis. The influence of glucose concentration on cancer cells has not been measured well, whereas that of oxygen concentration has been thoroughly examined using microfluidic devices. This is because glucose concentrations can be controlled using microfluidic concentration gradient generators, which trade off temporal stability of the glucose concentration and shear stress on the cells; by contrast, oxygen concentration can be easily controlled without microfluidic device-induced shear stresses. To study cell division and migration responses as a function of glucose concentration, we developed a microfluidic device to observe cell behaviors under various chemical conditions. The device has small-cross-section microchannels for generating a concentration gradient and a large-cross-section chamber for cell culture. With this design, the device can achieve both a cell culture with sufficiently low shear stress on cell activity and a stable glucose concentration gradient. Experiments revealed that a low glucose concentration increased the total migration length of HeLa cells and that HeLa cells under a glucose concentration gradient exhibit random motion rather than chemotaxis. Full article

Microfluidic system is widely employed in the detection of environmental contaminants and biological specimens. One of the critical issues which limits the applications of microfluidic chips is the limit of detection of trace specimens. Liquid–liquid extraction is of great importance in the preprocessing in microfluidic devices. In this paper, we developed a real-time fluorescence detection microfluidic chip combined with a microstructure-enhanced liquid–liquid laminar extraction technique, which concentrated the trace compound and realized real-time monitoring. Auxiliary microstructures integrated in the microfluidic chip were applied to increase the extraction efficiency, which was proved by the FEM (finite element method) simulation as well. A common fluorescence probe, Rhodamine 6G (Rh6g), was used in the experiment to demonstrate the performance of the microfluidic system. It revealed that the liquid–liquid laminar extraction combined with auxiliary microstructures of a cross shape was an effective method for enrichment. The efficiency of microstructure-enhanced liquid–liquid extraction was increased by 350% compared to the traditional laminar flow extraction. Full article

We proposed a thermal engraving technology based on heat transfer theory and polymer rheology in microfluidic field. Then, we established a 3D model of the thermal engraving process based on polymethyl methacrylate (PMMA) material. We could employ the model to analyze the influence of temperature and speed on microchannel processing through the finite element simulation. Thus, we gained the optimal processing parameters. The orthogonal experiments were carried out within the parameter ranges obtained by the simulation results. Finally, we fabricated the smooth microchannel, the average roughness of which was 0.3 μm, by using the optimal parameters. Furthermore, we examined the surface morphology and wettability. Our work provides a convenient technological support for a fast, low-cost, and large-scale manufacturing method of microfluidic chips. Full article

Herein, we assess the functionality of magnetic helical microswimmers as basic tools for the manipulation of soft materials, including microdroplets and single cells. Their ability to perform a range of unit operations is evaluated and the operational challenges associated with their use are established. In addition, we also report on interactions observed between the head of such helical swimmers and the boundaries of droplets and cells and discuss the possibilities of assembling an artificial swimming microorganism or a motorized cell. Full article

This paper reviews the past and recent studies on thermocapillarity in relation to microfluidics. The role of thermocapillarity as the change of surface tension due to temperature gradient in developing Marangoni flow in liquid films and conclusively bubble and drop actuation is discussed. The thermocapillary-driven mass transfer (the so-called Benard-Marangoni effect) can be observed in liquid films, reservoirs, bubbles and droplets that are subject to the temperature gradient. Since the contribution of a surface tension-driven flow becomes more prominent when the scale becomes smaller as compared to a pressure-driven flow, microfluidic applications based on thermocapillary effect are gaining attentions recently. The effect of thermocapillarity on the flow pattern inside liquid films is the initial focus of this review. Analysis of the relation between evaporation and thermocapillary instability approves the effect of Marangoni flow on flow field inside the drop and its evaporation rate. The effect of thermocapillary on producing Marangoni flow inside drops and liquid films, leads to actuation of drops and bubbles due to the drag at the interface, mass conservation, and also gravity and buoyancy in vertical motion. This motion can happen inside microchannels with a closed multiphase medium, on the solid substrate as in solid/liquid interaction, or on top of a carrier liquid film in open microfluidic systems. Various thermocapillary-based microfluidic devices have been proposed and developed for different purposes such as actuation, sensing, trapping, sorting, mixing, chemical reaction, and biological assays throughout the years. A list of the thermocapillary based microfluidic devices along with their characteristics, configurations, limitations, and improvements are presented in this review. Full article

A discrete microfluidic element with integrated thermal sensor was fabricated and demonstrated as an effective probe for process monitoring and prototyping. Elements were constructed using stereolithography and market-available glass-bodied thermistors within the modular, standardized framework of previous discrete microfluidic elements demonstrated in the literature. Flow rate-dependent response due to sensor self-heating and microchannel heating and cooling was characterized and shown to be linear in typical laboratory conditions. An acid-base neutralization reaction was performed in a continuous flow setting to demonstrate applicability in process management: the ratio of solution flow rates was varied to locate the equivalence point in a titration, closely matching expected results. This element potentially enables complex, three-dimensional microfluidic architectures with real-time temperature feedback and flow rate sensing, without application specificity or restriction to planar channel routing formats. Full article

This study presents experiments and computational simulations of single-layer passive micromixer designs. The proposed designs consist of chains of interlocking semicircles and omega-shaped mixing modules. The performance of the new designs is compared with the concentric spiral channel configuration. The micromixers are intended to be integrated into a lab on chip (LOC) micro-system that operates under continuous flow conditions. The purpose behind the multi-curvature in these designs is the introduction of Dean vortices in addition to molecular diffusion in order to enhance the mixing performance. The micromixers were fabricated in PDMS (Polydimethylsiloxane) and bonded to a glass substrate. A three-dimensional computational model of micromixers was carried out using Fluent ANSYS. In experiments, the mixing of a 1 g/L fluorescein isothiocyanate diluted in distilled water was observed and photographed using a charge-coupled device (CCD) microscopic camera. The obtained images were processed to determine the mixing intensity at different Reynolds numbers. The standard deviation (σ) of the fluorescence indicates the mixing completeness, which was calculated along the width of the channel at various locations downstream from the channel inlet. The value of σ = 0.5 indicates unmixed streams and 0 is for complete mixing. It is found that the two new designs have a standard deviation of nearly 0.05. Additionally, complete mixing was observed at the channel outlet as demonstrated by the fluorescence images and the numerical results. However, the location of complete mixing at different positions depends on the Reynolds number, which varies between 0.01 and 50. Good agreement was found between the experiment and the numerical results. A correlation to predict the length scale where complete mixing can be achieved is given in terms of the radius of curvature, the mixing module, and the Reynolds number. Full article

When Raman microscopy is adopted to detect the chemical and biological processes in the silicon microfluidic channel, the laser-induced heating effect will cause a temperature rise in the sample liquid. This undesired temperature rise will mislead the Raman measurement during the temperature-influencing processes. In this paper, computational fluid dynamics simulations were conducted to evaluate the maximum local temperature-rise (MLT). Through the orthogonal analysis, the sensitivity of potential influencing parameters to the MLT was determined. In addition, it was found from transient simulations that it is reasonable to assume the actual measurement to be steady-state. Simulation results were qualitatively validated by experimental data from the Raman measurement of diffusion, a temperature-dependent process. A correlation was proposed for the first time to estimate the MLT. Simple in form and convenient for calculation, this correlation can be efficiently applied to Raman measurement in a silicon microfluidic channel. Full article

We propose a method to characterize the mechanical properties of cells using a robot-integrated microfluidic chip (robochip) and microscopy. The microfluidic chip is designed to apply the specified deformations to a single detached cell using an on-chip actuator probe. The reaction force is simultaneously measured using an on-chip force sensor composed of a hollow folded beam and probe structure. In order to measure the cellular characteristics in further detail, a sub-pixel level of resolution of probe position is required. Therefore, we utilize the phase detection of moiré fringe. Using this method, the experimental resolution of the probe position reaches 42 nm. This is approximately ten times smaller than the optical wavelength, which is the limit of sharp imaging with a microscope. Calibration of the force sensor is also important in accurately measuring cellular reaction forces. We calibrated the spring constant from the frequency response, by the proposed sensing method of the probe position. As a representative of mechanical characteristics, we measured the elastic modulus of Madin-Darby Cannie Kidney (MDCK) cells. In spite of the rigid spring constant, the resolution and sensitivity were twice that achieved in our previous study. Unique cellular characteristics can be elucidated by the improvements in sensing resolution and accuracy. Full article

We propose a system that transports oocytes and measures their mechanical characteristics in an open environment using a robot integrated microfluidic chip (chip). The cells are transported through a micropillar array in the chip, and their characteristics are measured by a mechanical probe and a force sensor. Because the chip has an open microchannel, important cells such as oocytes are easily introduced and collected without the risk for losing them. In addition, any bubbles trapped in the chip, which degrade the measurement precision, are easily removed. To transport the oocytes through the open microchannel, we adopt a transportation technique based on a vibration-induced flow. Under this flow, oocytes arrive at the measurement point, where their mechanical characteristics are determined. We demonstrate the introduction, transportation, measurement of mechanical characteristics, and collection of oocytes using this system. Full article

The choice of substrate material in a chip that combines ultrasound with microfluidics for handling biological and synthetic microparticles can have a profound effect on the performance of the device. This is due to the high surface-to-volume ratio that exists within such small structures and acquires particular relevance in polymer-based resonators with 3D standing waves. This paper presents three chips developed to perform particle flow-through separation by ultrasound based on a polymeric SU-8 layer containing channelization over three different substrates: Polymethyl methacrylate (PMMA); Pyrex; and a cracked PMMA composite-like structure. Through direct observations of polystyrene microbeads inside the channel, the three checked chips exhibit their potential as disposable continuous concentration devices with different spatial pressure patterns at frequencies of resonance close to 1 Mhz. Chips with Pyrex and cracked PMMA substrates show restrictions on the number of pressure nodes established in the channel associated with the inhibition of 3D modes in the solid structure. The glass-substrate chip presents some advantages associated with lower energy requirements to collect particles. According to the results, the use of polymer-based chips with rigid substrates can be advantageous for applications that require short treatment times (clinical tests handling human samples) and low-cost fabrication. Full article

This work describes an improvement in the layout of coplanar electrodes for electrical impedance spectroscopy. We have developed, fabricated, and tested an improved electrode layout, which improves the sensitivity of an impedance flow cytometry chip. The improved chip was experimentally tested and compared to a chip with a conventional electrode layout. The improved chip was able to discriminate 0.5 μm beads from 1 μm as opposed to the conventional chip. Furthermore, finite element modeling was used to simulate the improvements in electrical field density and uniformity between the electrodes of the new electrode layout. Good agreement was observed between the model and the obtained experimental results. Full article

The ability to elicit distinct duty cycles from the same self-regulating microfluidic oscillator device would greatly enhance the versatility of this micro-machine as a tool, capable of recapitulating in vitro the diverse oscillatory processes that occur within natural systems. We report a novel approach to realize this using the coordinated modulation of input volumetric flow rate ratio and fluidic capacitance ratio. The demonstration uses a straightforward experimental system where fluid inflow to the oscillator is provided by two syringes (of symmetric or asymmetric cross-sectional area) mounted upon a single syringe pump applying pressure across both syringes at a constant linear velocity. This produces distinct volumetric outflow rates from each syringe that are proportional to the ratio between their cross-sectional areas. The difference in syringe cross-sectional area also leads to differences in fluidic capacitance; this underappreciated capacitive difference allows us to present a simplified expression to determine the microfluidic oscillators duty cycle as a function of cross-sectional area. Examination of multiple total volumetric inflows under asymmetric inflow rates yielded predictable and robust duty cycles ranging from 50% to 90%. A method for estimating the outflow duration for each inflow under applied flow rate ratios is provided to better facilitate the utilization of this system in experimental protocols requiring specific stimulation and rest intervals. Full article

The dispersion of cell deformability mapping is affected not only by the resolution of the sensing system, but also by cell deformability itself. In order to extract the pure deformability characteristics of cells, it is necessary to improve the resolution of cell actuation in the sensing system, particularly in the case of active sensing, where an actuator is essential. This paper proposes a novel concept, a “flow reduction mechanism”, where a flow is generated by a macroactuator placed outside of a microfluidic chip. The flow can be drastically reduced at the cell manipulation point in a microchannel due to the elasticity embedded into the fluid circuit of the microfluidic system. The great advantage of this approach is that we can easily construct a high resolution cell manipulation system by combining a macro-scale actuator and a macro-scale position sensor, even though the resolution of the actuator is larger than the desired resolution for cell manipulation. Focusing on this characteristic, we successfully achieved the cell positioning based on a visual feedback control with a resolution of 240 nm, corresponding to one pixel of the vision system. We show that the utilization of this positioning system contributes to reducing the dispersion coming from the positioning resolution in the cell deformability mapping. Full article

Circulating tumor cells (CTCs) from blood of cancer patients are valuable prognostic markers and enable monitoring responses to therapy. The extremely low number of CTCs makes their isolation and characterization a major technological challenge. For label-free cell identification a novel combination of Raman spectroscopy with a microhole array platform is described that is expected to support high-throughput and multiplex analyses. Raman spectra were registered from regularly arranged cells on the chip with low background noise from the silicon nitride chip membrane. A classification model was trained to distinguish leukocytes from myeloblasts (OCI-AML3) and breast cancer cells (MCF-7 and BT-20). The model was validated by Raman spectra of a mixed cell population. The high spectral quality, low destructivity and high classification accuracy suggests that this approach is promising for Raman activated cell sorting. Full article

Mini and micro robots, which can swim in an underwater environment, have drawn widespread research interests because of their potential applicability to the medical or biological fields, including delivery and transportation of bio-materials and drugs, bio-sensing, and bio-surgery. This paper reviews the recent ideas and developments of these types of self-propelling devices, ranging from the millimeter scale down to the micro and even the nano scale. Specifically, this review article makes an emphasis on various propulsion principles, including methods of utilizing smart actuators, external magnetic/electric/acoustic fields, bacteria, chemical reactions, etc. In addition, we compare the propelling speed range, directional control schemes, and advantages of the above principles. Full article

We report a novel approach to study cell migration under physical stresses by utilizing established growth factor chemotaxis. This was achieved by studying cell migration in response to epidermal growth factor (EGF) chemoattraction in a gradually tapered space, imposing mechanical stresses. The device consisted of two 5-mm-diameter chambers connected by ten 600 µm-long and 10 µm-high tapered microchannels. The taper region gradually changes the width of the channel. The channels tapered from 20 µm to 5 µm over a transition length of 50 µm at a distance of 250 µm from one of the chambers. The chemoattractant drove cell migration into the narrow confines of the tapered channels, while the mechanical gradient clearly altered the migration of cells. Cells traversing the channels from the wider to narrow-end and vice versa were observed using time-lapsed imaging. Our results indicated that the impact of physical stress on cell migration patterns may be cell type specific. Full article

Here we report the application of monodisperse double emulsion droplets, produced in a single step within partially hydrophilic/partially hydrophobic microfluidic devices, as defined containers for quantitative flow cytometric analysis. Samples with varying fluorophore concentrations were generated, and a clear correlation between dye concentration and fluorescence signals was observed. Full article

A mono-dispersed emulsion is of great significance in many chemical, biomedical and industrial applications. The current study reports a new microfluidic chip capable of forming tunable micro-droplets in liquids for emulsification applications. It can precisely generate size-tunable, uniform droplets using flow-focusing channels and a normally-closed valve, which is opened by a pneumatic suction force. Experimental data showed that micro-droplets with a diameter ranging from several to tens of micrometers could be precisely generated with a high uniformity. The droplet size is experimentally found to be dependent on the velocity of the dispersed-phase liquid, which is controlled by the deflection of the suction membrane. Emulsions with droplet sizes ranging from 5.5 to 55 μm are successfully observed. The variation in droplet sizes is from 3.8% to 2.5%. The micro-droplets have a uniform size and droplets smaller than those reported in previous studies are possible with this approach. This new microfluidic device can be promising for emulsification and other related applications. Full article

We present a novel integrated device for preparing metaphase chromosomes spread slides (FISHprep). The quality of cytogenetic analysis from patient samples greatly relies on the efficiency of sample pre-treatment and/or slide preparation. In cytogenetic slide preparation, cell cultures are routinely used to process samples (for culture, arrest and fixation of cells) and/or to expand limited amount of samples (in case of prenatal diagnostics). Arguably, this expansion and other sample pretreatments form the longest part of the entire diagnostic protocols spanning over 3–4 days. We present here a novel device with an integrated expansion chamber to culture, arrest and fix metaphase cells followed by a subsequent splashing protocol leading to ample metaphase chromosome spreads on a glass slide for metaphase FISH analysis. The device provides an easy, disposable, low cost, integrated solution with minimal handling for metaphase FISH slide preparation. Full article