A flow focusing microfluidic device with an integrated Coulter particle counter for production, counting and size characterization of monodisperse microbubbles

Spectrometric characterization of suspension liquid and light extinction model update

On the basis of the classical light scattering models, the light extinction model is the first to establish as [Formula: see text] (ϕ, N and γ - average diameter in μm, number and relative refractive index of the suspending particles, λ, A and δ - incident light wavelength in μm, absorbance and optical path in cm of the suspension liquid) by spectrometric characterization of ten standard suspension liquids. It has been used to determine the suspending particles in the calcium oxalate, Formazine, soil, milk and sewage suspension water samples. As the result, the light extinction model method brought out less than 12% error of ϕ and 18% error of the suspending particles' quality by comparing with the conventional methods. It provides a simple and reliable spectroptometric determination of a suspension liquid. Also, it is very potential to in-situ monitor the growth and working state of the suspending particles using in synthesis of materials, culture of cells, treatment of wastewater and safety of drinking water and foods.

Electronic Immunoassay Using Enzymatic Metallization on Microparticles

We present here an inexpensive method for generating a sensitive direct electronic readout in bead-based immunoassays without the use of any intermediate optical instrumentation (e.g., lasers, photomultipliers, etc.). Analyte binding to capture antigen-coated beads or microparticles is converted to probe-directed enzymatically amplified silver metallization on microparticle surfaces. Individual microparticles are then rapidly characterized in a high-throughput manner via single-bead multifrequency electrical impedance spectra captured using a simple and inexpensive microfluidic impedance spectrometry system we develop here, where they flow through a three-dimensional (3D)-printed plastic microaperture sandwiched between plated through-hole electrodes on a printed circuit board. Metallized microparticles are found to have unique impedance signatures distinguishing them from unmetallized ones. Coupled with a machine learning algorithm, this enables a simple electronic readout of the silver metallization density on microparticle surfaces and hence the underlying analyte binding. Here, we also demonstrate the use of this scheme to measure the antibody response to the viral nucleocapsid protein in convalescent COVID-19 patient serum.

Acoustofluidic cell micro-dispenser for single cell trajectory control

The precise manipulation of individual cells is a key capability for the study of single cell physiological characteristics or responses to stimuli. Currently, only large cell populations can be transferred with certainty using expensive and laborious flow cytometry platforms. However, when approaching small populations of cells, this task becomes increasingly challenging. Here, we report an effective acoustofluidic micro-dispenser, utilising surface acoustic waves (SAWs), with the ability to trap and release cells on demand, which when combined with an external valve can guide the trajectory of individual cells. We demonstrate single cell trap and release with a single cell trapping effectiveness of 74%, enabling the capability of dispensing a highly controlled amount of cells without any harmful effects. This device has the potential to be easily integrated into a wide range of analytical platforms for applications such as single cell fluorescent imaging and single cell proteomic studies.

One-step homogeneous micro-orifice resistance immunoassay for detection of chlorpyrifos in orange samples

In this work, a one-step homogeneous micro-orifice resistance immunoassay has been proposed for chlorpyrifos detection by integrating functionalized polystyrene (PS) microsphere probes with particle counting technology. The particle counter is highly sensitive and accurate for detecting the state of PS microspheres, where the particles of different states exhibit significant differences in resistance. The state of the functionalized PS microspheres is altered from dispersed to aggregated during the antigen-antibody recognition. Based on the degree of aggregation of the functionalized PS microsphere probes, chlorpyrifos can be quantitatively detected through the competitive immune response between PS antibodies and PS complete antigens. This one-step homogeneous micro-orifice resistance immunoassay simplified the procedures and greatly increased the sensitivity of detection, which has been successfully applied to detect chlorpyrifos in orange samples within 0.5 h, with the detection limit of 0.058 ng/mL.

Scaleable production of microbubbles using an ultrasound-modulated microfluidic device

Surfactant-coated gas microbubbles are widely used as contrast agents in ultrasound imaging and increasingly in therapeutic applications. The response of microbubbles to ultrasound can be strongly influenced by their size and coating properties, and hence the production method. Ultrasonic emulsification (sonication) is the most commonly employed method and can generate high concentrations of microbubbles rapidly, but with a broad size distribution, and there is a risk of contamination and/or degradation of sensitive components. Microfluidic devices provide excellent control over microbubble size, but are often challenging or costly to manufacture, offer low production rates (<10⁶s^-1), and are prone to clogging. In this study, a hybrid sonication-microfluidic or "sonofluidic" device was developed. Bubbles of ∼180 μm diameter were produced rapidly in a T-junction and subsequently exposed to ultrasound (71-73 kHz) within a microchannel, generating microbubbles (mean diameter: 1-2 μm) at a rate of >10⁸s^-1 using a single device. Microbubbles were prepared using either the sonofluidic device or conventional sonication, and their size, concentration, and stability were comparable. The mean diameter, concentration, and stability were found to be comparable between techniques, but the microbubbles produced by the sonofluidic device were all <5 μm in diameter and thus did not require any post-production fractionation.

Versatile Biosensing Toolkit Using an Electronic Particle Counter

Development of a versatile biosensing toolkit is in urgent need for rapid and multiplexed detection applications. In this work, an electronic particle counter-implemented versatile biosensing toolkit has been developed for detecting a range of targets with high sensitivity, broad detection range, multiplexibility, simple operation, and low cost. The electrical resistance-based particle counter conventionally measuring the number of microspheres (1-100 μm) can quantify analytes. The versatility of this approach is verified by assaying small molecules, protein biomarkers, pathogen bacteria, and tumor cells using three strategies: (1) antigen-antibody interaction, (2) DNA hybridization, and (3) polypeptide recognition. More importantly, this biosensing toolkit allows the simultaneous detection of multiple targets with a broad detection range from pg mL^-1 to μg mL^-1, showing great potential as a powerful technique for food safety testing and biomedical diagnosis.

Feedback-controlled microbubble generator producing one million monodisperse bubbles per second

Monodisperse lipid-coated microbubbles are a promising route to unlock the full potential of ultrasound contrast agents for medical diagnosis and therapy. Here, we present a stand-alone lab-on-a-chip instrument that allows microbubbles to be formed with high monodispersity at high production rates. Key to maintaining a long-term stable, controlled, and safe operation of the microfluidic device with full control over the output size distribution is an optical transmission-based measurement technique that provides real-time information on the production rate and bubble size. We feed the data into a feedback loop and demonstrate that this system can control the on-chip bubble radius (2.5 μm-20 μm) and the production rate up to 10⁶ bubbles/s. The freshly formed phospholipid-coated bubbles stabilize after their formation to a size approximately two times smaller than their initial on-chip bubble size without loss of monodispersity. The feedback control technique allows for full control over the size distribution of the agent and can aid the development of microfluidic platforms operated by non-specialist end users.

The emerging role of microfluidics in multi-material 3D bioprinting

To assist the transition of 3D bioprinting technology from simple lab-based tissue fabrication, to fully functional and implantable organs, the technology must not only provide shape control, but also functional control. This can be accomplished by replicating the cellular composition of the native tissue at the microscale, such that cell types interact to provide the desired function. There is therefore a need for precise, controllable, multi-material printing that could allow for high, possibly even single cell, resolution. This paper aims to draw attention to technological advancements made in 3D bioprinting that target the lack of multi-material, and/or multi cell-type, printing capabilities of most current devices. Unlike other reviews in the field, which largely focus on variations in single-material 3D bioprinting involving the standard methods of extrusion-based, droplet-based, laser-based, or stereolithographic methods; this review concentrates on sophisticated multi-material 3D bioprinting using multi-cartridge printheads, co-axial nozzles and microfluidic-enhanced printing nozzles.

Closed-loop feedback control of microbubble diameter from a flow-focusing microfluidic device

Real-time observation and control of particle size and production rate in microfluidic devices are important capabilities for a number of applications, including the production, sorting, and manipulation of microbubbles and droplets. The production of microbubbles from flow-focusing microfluidic devices had been investigated in multiple studies, but each lacked an approach for on-chip measurement and control of microbubble diameter in real time. In this work, we implement a closed-loop feedback control system in a flow-focusing microfluidic device with integrated on-chip electrodes. Using our system, we measure and count microbubbles between 13 and 28  μ m in diameter and control their diameter using a proportional-integral controller. We validate our measurements against an optical benchmark with R 2 = 0.98 and achieve a maximum production rate of 1.4 × 10 5 /s. Using the feedback control system, the device enabled control in microbubble diameter over the range of 14-24  μ m.

An integrated microfluidic device for studying controllable gas embolism induced cellular responses

Gas embolism is the abnormal emergence of bubble in the vascular system, which can induce local ischemic symptoms. For studying the mechanism underlying gas embolism and revealing local ischemic diseases information, novel technique for analyzing cells response to bubble contact with high controllability is highly desired. In this paper, we present an integrated microfluidic device for the precise generation and control of microbubble based on the gas permeability of polydimethysiloxane (PDMS) to study the effect of bubble's mechanical contact on cells. Cell viability analysis demonstrated that short-term (<15 min) bubble contact was generally non-lethal to cultured endothelial cells. The significant increase in intracellular calcium of the microbubble-contacted cells and cell-to-cell propagation of calcium signal in the adjacent cells were observed during the process of bubble expansion. In addition, the analysis of intercellular calcium signal in the cells treated with suramin and octanol revealed that cell-released small nucleotides and gap junction played an important role in regulating the propagation of calcium wave triggered by bubble contact. Thus, our microfluidic method provides an effective platform for studying the effect of gas embolism on cultured adherent cells and can be further needed for anti-embolism drugs test.

Oil-in-Water fL Droplets by Interfacial Spontaneous Fragmentation and Their Electrical Characterization

Inkjet printing is here employed for the first time as a method to produce femtoliter-scale oil droplets dispersed in water. In particular, picoliter-scale fluorinated oil (FC40) droplets are printed in the presence of perfluoro-1-octanol surfactant at a velocity higher than 5 m/s. Femtoliter-scale oil droplets in water are spontaneously formed through a fragmentation process at the water/air interface using minute amounts of nonionic surfactant (down to 0.003% v/v of Tween 80). This fragmentation occurs by a Plateau-Rayleigh mechanism at a moderately high Weber number (10¹). A microfluidic chip with integrated microelectrodes allows droplets characterization in terms of number and diameter distribution (peaked at about 3 μm) by means of electrical impedance measurements. These results show an unprecedented possibility to scale oil droplets down to the femtoliter scale, which opens up several perspectives for a tailored oil-in-water emulsion fabrication for drug encapsulation, pharmaceutic preparations, and cellular biology.

Efficacy of Sonothrombolysis Using Microbubbles Produced by a Catheter-Based Microfluidic Device in a Rat Model of Ischemic Stroke

Limitations of existing thrombolytic therapies for acute ischemic stroke have motivated the development of catheter-based approaches that utilize no or low doses of thrombolytic drugs combined with a mechanical action to either dissolve or extract the thrombus. Sonothrombolysis accelerates thrombus dissolution via the application of ultrasound combined with microbubble contrast agents and low doses of thrombolytics to mechanically disrupt the fibrin mesh. In this work, we studied the efficacy of catheter-directed sonothrombolysis in a rat model of ischemic stroke. Microbubbles of 10-20 µm diameter with a nitrogen gas core and a non-crosslinked albumin shell were produced by a flow-focusing microfluidic device in real time. The microbubbles were dispensed from a catheter located in the internal carotid artery for direct delivery to the thrombus-occluded middle cerebral artery, while ultrasound was administered through the skull and recombinant tissue plasminogen activator (rtPA) was infused via a tail vein catheter. The results of this study demonstrate that flow focusing microfluidic devices can be miniaturized to dimensions compatible with human catheterization and that large-diameter microbubbles comprised of high solubility gases can be safely administered intraarterially to deliver a sonothrombolytic therapy. Further, sonothrombolysis using intraarterial delivery of large microbubbles reduced cerebral infarct volumes by approximately 50% vs. no therapy, significantly improved functional neurological outcomes at 24 h, and permitted rtPA dose reduction of 3.3 (95% CI 1.8-3.8) fold when compared to therapy with intravenous rtPA alone.