Dissolution-guided wetting for microarray and microfluidic devices

A technology of a different sort: microraft arrays

A common procedure performed throughout biomedical research is the selection and isolation of biological entities such as organelles, cells and organoids from a mixed population. In this review, we describe the development and application of microraft arrays, an analysis and isolation platform which enables a vast range of criteria and strategies to be used when separating biological entities. The microraft arrays are comprised of elastomeric microwells with detachable polymer bases (microrafts) that act as capture and culture sites as well as supporting carriers during cell isolation. The technology is elegant in its simplicity and can be implemented for samples possessing tens to millions of objects yielding a flexible platform for applications such as single-cell RNA sequencing, subcellular organelle capture and assay, high-throughput screening and development of CRISPR gene-edited cell lines, and organoid manipulation and selection. The transparent arrays are compatible with a multitude of imaging modalities enabling selection based on 2D or 3D spatial phenotypes or temporal properties. Each microraft can be individually isolated on demand with retention of high viability due to the near zero hydrodynamic stress imposed upon the cells during microraft release, capture and deposition. The platform has been utilized as a simple manual add-on to a standard microscope or incorporated into fully automated instruments that implement state-of-the-art imaging algorithms and machine learning. The vast array of selection criteria enables separations not possible with conventional sorting methods, thus garnering widespread interest in the biological and pharmaceutical sciences.

A High-Throughput, Multi-Index Isothermal Amplification Platform for Rapid Detection of 19 Types of Common Respiratory Viruses Including SARS-CoV-2

Fast and accurate diagnosis and the immediate isolation of patients infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are regarded as the most effective measures to restrain the coronavirus disease 2019 (COVID-19) pandemic. Here, we present a high-throughput, multi-index nucleic acid isothermal amplification analyzer (RTisochip™-W) employing a centrifugal microfluidic chip to detect 19 common respiratory viruses, including SARS-CoV-2, from 16 samples in a single run within 90 min. The limits of detection of all the viruses analyzed by the RTisochip™-W system were equal to or less than 50 copies·μL^-1, which is comparable to those of conventional reverse transcription polymerase chain reaction. We also demonstrate that the RTisochip™-W system possesses the advantages of good repeatability, strong robustness, and high specificity. Finally, we analyzed 201 cases of preclinical samples, 14 cases of COVID-19-positive samples, 25 cases of clinically diagnosed samples, and 614 cases of clinical samples from patients or suspected patients with respiratory tract infections using the RTisochip™-W system. The test results matched the referenced results well and reflected the epidemic characteristics of the respiratory infectious diseases. The coincidence rate of the RTisochip™-W with the referenced kits was 98.15% for the detection of SARS-CoV-2. Based on these extensive trials, we believe that the RTisochip™-W system provides a powerful platform for fighting the COVID-19 pandemic.

A scalable microfluidic chamber array for sample-loss-free and bubble-proof sample compartmentalization by simple pipetting

Sample compartmentalization is a pivotal technique in many bioanalytical applications, such as multiplex polymerase chain reaction (PCR) and digital PCR (dPCR). In this study, we successfully developed a novel self-compartmentalization device containing an array of microchambers, each of which is connected to a main microchannel with three capillary burst valves (CBVs) for fluid switching and partitioning. As these CBVs can be automatically opened in a predefined sequence, an incoming solution can be spontaneously directed into the chamber and held in place without further mixing. After that, either air or oil can be loaded into the main channel to isolate each chamber completely. By optimizing the relative burst pressures of the CBVs, a 100% sample utilization rate can be achieved even using a manual pipette and air bubbles in the sample cannot interfere with the loading. In addition, the number of the microchambers in an array can be easily scaled from a few to tens of thousands. To verify the feasibility of this self-compartmentalization method, we successfully conducted mock multiplex loop-mediated isothermal amplifications (LAMP) in an array that contains 144 microchambers, proving that our design method will provide a robust and versatile platform for various sample discretization purposes in the future.

Nip the bubble in the bud: a guide to avoid gas nucleation in microfluidics

Gas bubbles are almost a routine occurrence encountered by researchers working in the field of microfluidics. The spontaneous and unexpected nature of gas bubbles represents a major challenge for experimentalists and a stumbling block for the translation of microfluidic concepts to commercial products. This is a startling example of successful scientific results in the field overshadowing the practical hurdles of day-to-day usage. We however believe such hurdles can be overcome with a sound understanding of the underlying conditions that lead to bubble formation. In this tutorial, we focus on the two main conditions that result in bubble nucleation: surface nuclei and gas supersaturation in liquids. Key theoretical concepts such as Henry's law, Laplace pressure, the role of surface properties, nanobubbles and surfactants are presented along with a view of practical implementations that serve as preventive and curative measures. These considerations include not only microfluidic chip design and bubble traps but also often-overlooked conditions that regulate bubble formation, such as gas saturation under pressure or temperature gradients. Scenarios involving electrolysis, laser and acoustic cavitation or T-junction/co-flow geometries are also explored to provide the reader with a broader understanding on the topic. Interestingly, despite their often-disruptive nature, gas bubbles have also been cleverly utilized for certain practical applications, which we briefly review. We hope this tutorial will provide a reference guide in helping to deal with a familiar foe, the "bubble".

Bubble removal with the use of a vacuum pressure generated by a converging-diverging nozzle

Bubbles are an intrinsic problem in microfluidic devices and they can appear during the initial filling of the device or during operation. This report presents a generalizable technique to extract bubbles from microfluidic networks using an adjacent microfluidic negative pressure network over the entire microfluidic channel network design. We implement this technique by superimposing a network of parallel microchannels with a vacuum microfluidic channel and characterize the bubble extraction rates as a function of negative pressure applied. In addition, we generate negative pressure via a converging-diverging (CD) nozzle, which only requires inlet gas pressure to operate. Air bubbles generated during the initial liquid filling of the microfluidic network are removed within seconds and their volume extraction rate is calculated. This miniaturized vacuum source can achieve a vacuum pressure of 7.23 psi which corresponds to a bubble extraction rate of 9.84 pL/s, in the microfluidic channels we characterized. Finally, as proof of concept it is shown that the bubble removal system enables bubble removal on difficult to fill microfluidic channels such as circular or triangular shaped channels. This method can be easily integrated into many microfluidic experimental protocols.

Staggered trap arrays for robust microfluidic sample digitization

A sample digitization method that exploits the controlled pinning of fluid at geometric discontinuities within an array of staggered microfluidic traps is presented. The staggered trap design enables reliable sample filling within high aspect ratio microwells, even when employing substrate materials such as thermoplastics that are not gas permeable. A simple geometric model is developed to predict the impact of device geometry on sample filling and discretization, and validated experimentally using fabricated cyclic olefin polymer devices. Using the developed design guidelines, a 768-element staggered trap array is demonstrated, with reliable passive loading and discretization achieved within 5 min. The resulting discretization platform offers a simplified workflow with flexible trap design, reliable discretization, and repeatable operation using low-cost thermoplastic substrates.

Digital PCR using micropatterned superporous absorbent array chips

Digital PCR (dPCR) is an emerging technology for genetic analysis and clinical diagnostics. To facilitate the widespread application of dPCR, here we developed a new micropatterned superporous absorbent array chip (μSAAC) which consists of an array of microwells packed with highly porous agarose microbeads. The packed beads construct a hierarchically porous microgel which confers superior water adsorption capacity to enable spontaneous filling of PDMS microwells for fluid compartmentalization without the need of sophisticated microfluidic equipment and operation expertise. Using large λ-DNA as the model template, we validated the μSAAC for stochastic partitioning and quantitative digital detection of DNA molecules. Furthermore, as a proof-of-concept, we conducted dPCR detection and single-molecule sequencing of a mutation prevalent in blood cancer, the chromosomal translocation t(14;18), demonstrating the feasibility of the μSAAC for analysis of disease-associated mutations. These experiments were carried out using the standard molecular biology techniques and instruments. Because of its low cost, ease of fabrication, and equipment-free liquid partitioning, the μSAAC is readily adaptable to general lab settings, which could significantly facilitate the widespread application of dPCR technology in basic research and clinical practice.