Cell separation by the combination of microfluidics and optical trapping force on a microchip

Recent Advances in Microfluidics-Based Monitoring of Waterborne Pathogens: From Isolation to Detection

Waterborne pathogens seriously threaten human life and can cause diarrhea, gastrointestinal disorders, and more serious systemic infections. These pathogens are usually caused by contaminated water sources that contain disease-causing microorganisms, such as bacteria, viruses, and parasites, which cause infection and disease when they enter the human body through drinking water or other means. Due to the wide range of transmission routes and the high potential risk of waterborne pathogens, there is an urgent need for an ultrasensitive, rapid, and specific pathogenic microorganism monitoring platform to meet the critical monitoring needs of some water bodies' collection points daily monitoring needs. Microfluidics-based pathogen surveillance methods are an important stage towards automated detection through real-time and multi-targeted monitoring, thus enabling a comprehensive assessment of the risk of exposure to waterborne pathogens and even emerging microbial contaminants, and thus better protection of public health. Therefore, this paper reviews the latest research results on the isolation and detection of waterborne pathogens based on microfluidic methods. First, we introduce the traditional methods for isolation and detection of pathogens. Then, we compare some existing microfluidic pathogen isolation and detection methods and finally look forward to some future research directions and applications of microfluidic technology in waterborne pathogens monitoring.

Phononic-Crystal-Based Particle Sieving in Continuous Flow: Numerical Simulations

Sieving specific particles from mixed samples is of great value in fields such as biochemistry and additive manufacturing. In this study, a particle sieving method for microfluidics was proposed based on a phononic crystal plate (PCP), the mechanism of which originates from the competition between the trapping effect of the resonant PCP-induced acoustic radiation force (ARF), disturbance effect of acoustic streaming (AS), and flushing effect of the continuous inlet flow on particles suspended in microfluidic channels. Specifically, particles with different sizes could be separated under inlet flow conditions owing to ARF and AS drag forces as functions of the particle diameter, incident acoustic pressure, and driving frequency. Furthermore, a comprehensive numerical analysis was performed to investigate the impacts of ARF, AS, and inlet flow conditions on the particle motion and sieving efficiency, and to explore proper operating parameters, including the acoustic pressure and inlet flow velocity. It was found that, for each inlet flow velocity, there was an optimal acoustic pressure allowing us to achieve the maximum sieving efficiency, but the sieving efficiency at a low flow velocity was not as good as that at a high flow velocity. Although a PCP with a high resonant frequency could weaken the AS, thereby suiting the sieving of small particles (<5 μm), a low channel height corresponding to a high frequency limits the throughput. Therefore, it is necessary to design a PCP with a suitable resonant frequency based on the size of the particles to be sieved. This investigation can provide guidance for the design of massive acoustic sorting mi-crofluidic devices based on phononic crystals or acoustic metamaterials under continuous flow.

Pipette-Tip-Enabled Digital Nucleic Acid Analyzer for COVID-19 Testing with Isothermal Amplification

Herein, a pipette-tip-enabled digital nucleic acid analyzer for high-performance COVID-19 testing is demonstrated. This is achieved by digital loop-mediated isothermal amplification (digital LAMP or dLAMP) using common laboratory equipment and materials. It is shown that simply fixing a glass capillary inside conventional pipette tips enables the generation of monodisperse, water-in-oil microdroplets with benchtop centrifugation. It is shown that using LAMP, the ORF1a/b gene, a standard test region for COVID-19 screening, can be amplified without a thermal cycler. The amplification allows counting of fluorescent microdroplets so that Poisson analysis can be performed to allow quantification with a limit of detection that is 1 order of magnitude better than those of nondigital techniques and comparable to those of commercial dLAMP platforms. It is envisioned that this work will inspire studies on ultrasensitive digital nucleic acid analyzers demanding both sensitivity and accessibility, which is pivotal to their large-scale applications.

Progress of Microfluidic Continuous Separation Techniques for Micro-/Nanoscale Bioparticles

Separation of micro- and nano-sized biological particles, such as cells, proteins, and nucleotides, is at the heart of most biochemical sensing/analysis, including in vitro biosensing, diagnostics, drug development, proteomics, and genomics. However, most of the conventional particle separation techniques are based on membrane filtration techniques, whose efficiency is limited by membrane characteristics, such as pore size, porosity, surface charge density, or biocompatibility, which results in a reduction in the separation efficiency of bioparticles of various sizes and types. In addition, since other conventional separation methods, such as centrifugation, chromatography, and precipitation, are difficult to perform in a continuous manner, requiring multiple preparation steps with a relatively large minimum sample volume is necessary for stable bioprocessing. Recently, microfluidic engineering enables more efficient separation in a continuous flow with rapid processing of small volumes of rare biological samples, such as DNA, proteins, viruses, exosomes, and even cells. In this paper, we present a comprehensive review of the recent advances in microfluidic separation of micro-/nano-sized bioparticles by summarizing the physical principles behind the separation system and practical examples of biomedical applications.

Progress of Inertial Microfluidics in Principle and Application

Inertial microfluidics has become a popular topic in microfluidics research for its good performance in particle manipulation and its advantages of simple structure, high throughput, and freedom from an external field. Compared with traditional microfluidic devices, the flow field in inertial microfluidics is between Stokes state and turbulence, whereas the flow is still regarded as laminar. However, many mechanical effects induced by the inertial effect are difficult to observe in traditional microfluidics, making particle motion analysis in inertial microfluidics more complicated. In recent years, the inertial migration effect in straight and curved channels has been explored theoretically and experimentally to realize on-chip manipulation with extensive applications from the ordinary manipulation of particles to biochemical analysis. In this review, the latest theoretical achievements and force analyses of inertial microfluidics and its development process are introduced, and its applications in circulating tumor cells, exosomes, DNA, and other biological particles are summarized. Finally, the future development of inertial microfluidics is discussed. Owing to its special advantages in particle manipulation, inertial microfluidics will play a more important role in integrated biochips and biomolecule analysis.

Magnetophoretic manipulation in microsystem using carbonyl iron-polydimethylsiloxane microstructures

This paper reports the use of a recent composite material, noted hereafter i-PDMS, made of carbonyl iron microparticles mixed in a PolyDiMethylSiloxane (PDMS) matrix, for magnetophoretic functions such as capture and separation of magnetic species. We demonstrated that this composite which combine the advantages of both components, can locally generate high gradients of magnetic field when placed between two permanent magnets. After evaluating the magnetic susceptibility of the material as a function of the doping ratio, we investigated the molding resolution offered by i-PDMS to obtain microstructures of various sizes and shapes. Then, we implemented 500 μm i-PDMS microstructures in a microfluidic channel and studied the influence of flow rate on the deviation and trapping of superparamagnetic beads flowing at the neighborhood of the composite material. We characterized the attraction of the magnetic composite by measuring the distance from the i-PDMS microstructure, at which the beads are either deviated or captured. Finally, we demonstrated the interest of i-PDMS to perform magnetophoretic functions in microsystems for biological applications by performing capture of magnetically labeled cells.

Cell manipulation in microfluidics

Recent advances in the lab-on-a-chip field in association with nano/microfluidics have been made for new applications and functionalities to the fields of molecular biology, genetic analysis and proteomics, enabling the expansion of the cell biology field. Specifically, microfluidics has provided promising tools for enhancing cell biological research, since it has the ability to precisely control the cellular environment, to easily mimic heterogeneous cellular environment by multiplexing, and to analyze sub-cellular information by high-contents screening assays at the single-cell level. Various cell manipulation techniques in microfluidics have been developed in accordance with specific objectives and applications. In this review, we examine the latest achievements of cell manipulation techniques in microfluidics by categorizing externally applied forces for manipulation: (i) optical, (ii) magnetic, (iii) electrical, (iv) mechanical and (v) other manipulations. We furthermore focus on history where the manipulation techniques originate and also discuss future perspectives with key examples where available.

Ensemble method to measure the potential energy of nanoparticles in an optical trap

A method is described for measuring the potential energy of nanoparticles in an optical trap by trapping an ensemble of particles with a focused laser beam. The force balance between repulsive osmotic and confining gradient-force pressures determines the single-particle trapping potential independent of interactions between the particles. The ensemble nature of the measurement permits evaluation of single-particle trapping energies much smaller than k_BT. Energies obtained by this method are compared to those of single-particle methods as well as to theoretical calculations based on classical electromagnetic optics.

Microfluidic devices for bioapplications

Harnessing the ability to precisely and reproducibly actuate fluids and manipulate bioparticles such as DNA, cells, and molecules at the microscale, microfluidics is a powerful tool that is currently revolutionizing chemical and biological analysis by replicating laboratory bench-top technology on a miniature chip-scale device, thus allowing assays to be carried out at a fraction of the time and cost while affording portability and field-use capability. Emerging from a decade of research and development in microfluidic technology are a wide range of promising laboratory and consumer biotechnological applications from microscale genetic and proteomic analysis kits, cell culture and manipulation platforms, biosensors, and pathogen detection systems to point-of-care diagnostic devices, high-throughput combinatorial drug screening platforms, schemes for targeted drug delivery and advanced therapeutics, and novel biomaterials synthesis for tissue engineering. The developments associated with these technological advances along with their respective applications to date are reviewed from a broad perspective and possible future directions that could arise from the current state of the art are discussed.

A design for a photonic syringe with multimode coupled slot waveguides

A design is proposed that allows non-stationary field distribution with Bragg gratings in multiple slot waveguides. Selective coupling between modes is achieved or suppressed, according to controllable selection rules, based on mode symmetry. By applying such rules, backward pulling radiation pressure - i.e. toward the light source - can be obtained inside the slots. A mode-switching filter is also proposed, which allows the switching between forward and backward direction of radiation pressure. This "light-actuated" syringe could have potential applications for bidirectional particle trapping and manipulation, optofluidics, optomechanics and biotechnology.

Fast benchtop fabrication of laminar flow chambers for advanced microscopy techniques

BACKGROUND

Fluid handling technology is acquiring an ever more prominent place in laboratory science whether it is in simple buffer exchange systems, perfusion chambers, or advanced microfluidic devices. Many of these applications remain the providence of laboratories at large institutions with a great deal of expertise and specialized equipment. Even with the expansion of these techniques, limitations remain that frequently prevent the coupling of controlled fluid flow with other technologies, such as coupling microfluidics and high-resolution position and force measurements by optical trapping microscopy.

METHOD

Here we present a method for fabrication of multiple-input laminar flow devices that are optically clear [glass] on each face, chemically inert, reusable, inexpensive, and can be fabricated on the benchtop in approximately one hour. Further these devices are designed to allow flow regulation by a simple gravity method thus requiring no specialized equipment to drive flow. Here we use these devices to perform total internal reflection fluorescence microscopy measurements as well as position sensitive optical trapping experiments.

SIGNIFICANCE

Flow chamber technology needs to be more accessible to the general scientific community. The method presented here is versatile and robust. These devices use standard slides and coverslips making them compatible with nearly all types and models of light microscopes. These devices meet the needs of groups doing advanced optical trapping experiments, but could also be adapted by nearly any lab that has a function for solution flow coupled with microscopy.