Composite Elastomer-Enabled Rapid Photofabrication of Microfluidic Devices

Rapid and multi-target genotyping of Helicobacter pylori with digital microfluidics

Helicobacter pylori (H. pylori) infection correlates closely with gastric diseases such as gastritis, ulcers, and cancer, influencing more than half of the world's population. Establishing a rapid, precise, and automated platform for H. pylori diagnosis is an urgent clinical need and would significantly benefit therapeutic intervention. Recombinase polymerase amplification (RPA)-CRISPR recently emerged as a promising molecular diagnostic assay due to its rapid detection capability, high specificity, and mild reaction conditions. In this work, we adapted the RPA-CRISPR assay on a digital microfluidics (DMF) system for automated H. pylori detection and genotyping. The system can achieve multi-target parallel detection of H. pylori nucleotide conservative genes (ureB) and virulence genes (cagA and vacA) across different samples within 30 min, exhibiting a detection limit of 10 copies/rxn and no false positives. We further conducted tests on 80 clinical saliva samples and compared the results with those derived from real-time quantitative polymerase chain reaction, demonstrating 100% diagnostic sensitivity and specificity for the RPA-CRISPR/DMF method. By automating the assay process on a single chip, the DMF system can significantly reduce the usage of reagents and samples, minimize the cross-contamination effect, and shorten the reaction time, with the additional benefit of losing the chance of experiment failure/inconsistency due to manual operations. The DMF system together with the RPA-CRISPR assay can be used for early detection and genotyping of H. pylori with high sensitivity and specificity, and has the potential to become a universal molecular diagnostic platform.

Integrated microfluidic platforms for heavy metal sensing: a comprehensive review

Heavy metals are found naturally; however, anthropogenic activities such as mining, inappropriate disposal of industrial waste, and the use of pesticides and fertilizers containing heavy metals can cause their unwanted release into the environment. Conventionally, detection of heavy metals is performed using atomic absorption spectrometry, electrochemical methods and inductively coupled plasma-mass spectrometry; however, they involve expensive and sophisticated instruments and multistep sample preparation that require expertise for accurate results. In contrast, microfluidic devices involve rapid, cost-efficient, simple, and reliable approaches for in-laboratory and real-time monitoring of heavy metals. The use of inexpensive and environment friendly materials for fabrication of microfluidic devices has increased the manufacturing efficiency of the devices. Different types of techniques used in heavy metal detection include colorimetry, absorbance-based, and electrochemical detection. This review provides insight into the detection of toxic heavy metals such as mercury (Hg), cadmium (Cd), lead (Pb), and arsenic (As). Importance is given to colorimetry, optical, and electrochemical techniques applied for the detection of heavy metals using microfluidics and their modifications to improve the limit of detection (LOD).

Microfluidic Devices: A Tool for Nanoparticle Synthesis and Performance Evaluation

The use of nanoparticles (NPs) in nanomedicine holds great promise for the treatment of diseases for which conventional therapies present serious limitations. Additionally, NPs can drastically improve early diagnosis and follow-up of many disorders. However, to harness their full capabilities, they must be precisely designed, produced, and tested in relevant models. Microfluidic systems can simulate dynamic fluid flows, gradients, specific microenvironments, and multiorgan complexes, providing an efficient and cost-effective approach for both NPs synthesis and screening. Microfluidic technologies allow for the synthesis of NPs under controlled conditions, enhancing batch-to-batch reproducibility. Moreover, due to the versatility of microfluidic devices, it is possible to generate and customize endless platforms for rapid and efficient in vitro and in vivo screening of NPs' performance. Indeed, microfluidic devices show great potential as advanced systems for small organism manipulation and immobilization. In this review, first we summarize the major microfluidic platforms that allow for controlled NPs synthesis. Next, we will discuss the most innovative microfluidic platforms that enable mimicking in vitro environments as well as give insights into organism-on-a-chip and their promising application for NPs screening. We conclude this review with a critical assessment of the current challenges and possible future directions of microfluidic systems in NPs synthesis and screening to impact the field of nanomedicine.

Patterning Wettability on Solvent-Resistant Elastomers with High Spatial Resolution for Replica Mold Fabrication of Droplet Microfluidics

Controlling the surface wetting properties of channels is crucial to the robust and reliable performance of microfluidic devices. Spatially patterned hydrophobic/hydrophilic microchannels have found utility across various applications, notably in the generation of higher-order emulsions. Unfortunately, the patterning of surface wettability currently requires multistep processes with limited spatial resolution, making it impractical for many applications. In this work, we take inspiration from soft lithography and have developed a new replica mold fabrication technique wherein both the channel geometry and surface wettability are transferred from the mold to the replica. In this approach, the mold is a silicon wafer with lithographically defined features etched into its surface to define the channel geometry and lithographically defined patterns of hydrophobic silanes to define surface wetting properties. The replica is a co-polymer network of PFPE-PEG, for which PFPE can be locally enriched by the mold's patterned silanes to define the spatially patterned wetting properties. We demonstrated the utility of this approach by fabricating a PFPE-PEG-based microfluidic chip, with hydrophobic/hydrophilic patterned microchannels, to generate double emulsions.

Electropolishing and Shaping of Micro-Scale Metallic Features

Electropolishing (EP) is most widely used as a metal finishing process. It is a non-contact electrochemical process that can clean, passivate, deburr, brighten, and improve the biocompatibility of surfaces. However, there is clear potential for it to be used to shape and form the topology of micro-scale surface features, such as those found on the micro-applications of additively manufactured (AM) parts, transmission electron microscopy (TEM) samples, micro-electromechanical systems (MEMs), biomedical stents, and artificial implants. This review focuses on the fundamental principles of electrochemical polishing, the associated process parameters (voltage, current density, electrolytes, electrode gap, and time), and the increasing demand for using environmentally sustainable electrolytes and micro-scale applications. A summary of other micro-fabrication processes, including micro-milling, micro-electric discharge machining (EDM), laser polishing/ablation, lithography (LIGA), electrochemical etching (MacEtch), and reactive ion etching (RIE), are discussed and compared with EP. However, those processes have tool size, stress, wear, and structural integrity limitations for micro-structures. Hence, electropolishing offers two-fold benefits of material removal from the metal, resulting in a smooth and bright surface, along with the ability to shape/form micro-scale features, which makes the process particularly attractive for precision engineering applications.zx3.

A photofabricated honeycomb micropillar array for loss-free trapping of microfluidic droplets and application to digital PCR

Droplet microfluidics is a promising platform for various biological and biomedical applications. Among which, droplet-based digital PCR (ddPCR) is one of the most challenging examples, with practical issues involving possible fusion/fission of droplets during PCR thermocycling and difficulties of indexing them for real-time monitoring. While spatially trapped droplet arrays may be helpful, they currently are either of low trapping density or suffer from high droplet loss. In this paper, we, for the first time, report a photofabricated honeycomb micropillar array (PHMA) for high-density and loss-free droplet trapping. By rationally designing high-aspect-ratio micropillars into a honeycomb configuration, droplets can be captured at a density of 160-250 droplets per mm² and, more interestingly, without any loss. The PHMA device can be fabricated from several photocurable materials, with one gasproof photopolymer being optimally selected herein to enable the simple design to avoid sample evaporation and tedious surface modification, thereby making the fabrication very convenient. Moreover, by using a photocurable oil as a continuous phase, the trapped droplets can be further immobilized, and thus, become more stable even in PCR thermocycling. With these features, the proposed PHMA has shown promising potential in ddPCR, and is expected to find a wide range of applications in various biological and biomedical research.