SlipChip

Microfluidic Platform for Generating and Releasing Patient-Derived Cancer Organoids with Diverse Shapes: Insight into Shape-Dependent Tumor Growth

Multicellular spheroids and patient-derived organoids find many applications in fundamental research, drug discovery, and regenerative medicine. Advances in the understanding and recapitulation of organ functionality and disease development require the generation of complex organoid models, including organoids with diverse morphologies. Microfluidics-based cell culture platforms enable time-efficient confined organoid generation. However, the ability to form organoids with different shapes with a subsequent transfer from microfluidic devices to unconstrained environments for studies of morphology-dependent organoid growth is yet to be demonstrated. Here, a microfluidic platform is introduced that enables high-fidelity formation and addressable release of breast cancer organoids with diverse shapes. Using this platform, the impact of organoid morphology on their growth in unconstrained biomimetic hydrogel is explored. It is shown that proliferative cancer cells tend to localize in high positive curvature organoid regions, causing their faster growth, while the overall growth pattern of organoids with diverse shapes tends to reduce interfacial tension at the organoid-hydrogel interface. In addition to the formation of organoids with diverse morphologies, this platform can be integrated into multi-tissue micro-physiological systems.

SlipO2Chip - single-cell respiration under tuneable environments

In disciplines like toxicology and pharmacology, oxygen (O2) respiration is a universal metric for evaluating the effects of chemicals across various model systems, including mammalian and microalgal cells. However, for these cells the common practice is to segregate populations into control and exposure groups, which assumes direct equivalence in their responses and does not take into account heterogeneity among individual cells. This lack of resolution impedes our ability to precisely investigate differences among experimental groups with small or limited sample sizes. To overcome this barrier, we introduce SlipO2Chip, an innovative glass microfluidic platform for precisely quantifying single-cell O2 respiration in the coordinated absence and presence of chemical solutes. SlipO2Chip comprises a wet-etched fused silica channel plate on the top and a dry-etched borosilicate microwell plate at the bottom. The microwells are coated with Pt(II) meso-tetra(pentafluorophenyl)porphine (PtTFPP), an O2 sensing optode material and an O2-independent reference dye. A custom 3D-printed holder facilitates the controlled horizontal movement ('slipping') of the channel plate over the microwell plate, thereby establishing or disrupting the fluid path over microwells. Collectively, these design elements enable the immobilization of single-cells in microwells, their exposure to controlled fluid flows, the coordinated opening and closing of microwells and repeated measurements of single-cell O2 respiration. Uniquely, by sequentially executing opening and closing it becomes possible to measure single-cell respiration prior to and after exposure to chemical solutes. In a proof-of-concept application, we utilized SlipO2Chip to measure the impact of increasing exposures of the marine bacterial signal 2-heptyl-4-quinolone (HHQ) on the dark respiration of the diatom Ditylum brightwellii at single-cell resolution. Results revealed a concentration-dependent decrease in per-cell O2 dark respiration, with a maximum reduction of 40.2% observed at HHQ concentrations exceeding 35.5 μM, and a half-maximal effective concentration (EC50) of 5.8 μM, consistent with that obtained via conventional bulk respiration methods. The ability of SlipO2Chip to sequentially assess the effects of chemical substances on single-cell O2 metabolism is advantageous for research where sample volumes are limited, such as clinical biopsies, studies involving rare microbial isolates, and toxicological studies aiming to address exposure effects while accounting for cell-to-cell variability.

Microfluidic programmable strategies for channels and flow

This review summarizes programmable microfluidics, an advanced method for precise fluid control in microfluidic technology through microchannel design or liquid properties, referring to microvalves, micropumps, digital microfluidics, multiplexers, micromixers, slip-, and block-based configurations. Different microvalve types, including electrokinetic, hydraulic/pneumatic, pinch, phase-change and check valves, cater to diverse experimental needs. Programmable micropumps, such as passive and active micropumps, play a crucial role in achieving precise fluid control and automation. Due to their small size and high integration, microvalves and micropumps are widely used in medical devices and biological analysis. In addition, this review provides an in-depth exploration of the applications of digital microfluidics, multiplexed microfluidics, and mixer-based microfluidics in the manipulation of liquid movement, mixing, and splitting. These methodologies leverage the physical properties of liquids, such as capillary forces and dielectric forces, to achieve precise control over fluid dynamics. SlipChip technology, which branches into rotational SlipChip and translational SlipChip, controls fluid through sliding motion of the microchannel. On the other hand, innovative designs in microfluidic systems pursue better modularity, reconfigurability and ease of assembly. Different assembly strategies, from one-dimensional assembly blocks and two-dimensional Lego®-style blocks to three-dimensional reconfigurable modules, aim to enhance flexibility and accessibility. These technologies enhance user-friendliness and accessibility by offering integrated control systems, making them potentially usable outside of specialized technical labs. Microfluidic programmable strategies for channels and flow hold promising applications in biomedical research, chemical analysis and drug screening, providing theoretical and practical guidance for broader utilization in scientific research and practical applications.

A programmable and automated optical electrowetting-on-dielectric (oEWOD) driven platform for massively parallel and sequential processing of single cell assay operations

Recently, there has been an increasing emphasis on single cell profiling for high-throughput screening workflows in drug discovery and life sciences research. However, the biology underpinning these screens is often complex and is insufficiently addressed by singleplex assay screens. Traditional single cell screening technologies have created powerful sets of 'omic data that allow users to bioinformatically infer biological function, but have as of yet not empowered direct functional analysis at the level of each individual cell. Consequently, screening campaigns often require multiple secondary screens leading to laborious, time-consuming and expensive workflows in which attrition points may not be queried until late in the process. We describe a platform that harnesses droplet microfluidics and optical electrowetting-on-dielectric (oEWOD) to perform highly-controlled sequential and multiplexed single cell assays in massively parallelised workflows to enable complex cell profiling during screening. Soluble reagents or objects, such as cells or assay beads, are encapsulated into droplets of media in fluorous oil and are actively filtered based on size and optical features ensuring only desirable droplets (e.g. single cell droplets) are retained for analysis, thereby overcoming the Poisson probability distribution. Droplets are stored in an array on a temperature-controlled chip and the history of individual droplets is logged from the point of filter until completion of the workflow. On chip, droplets are subject to an automated and flexible suite of operations including the merging of sample droplets and the fluorescent acquisition of assay readouts to enable complex sequential assay workflows. To demonstrate the broad utility of the platform, we present examples of single-cell functional workflows for various applications such as antibody discovery, infectious disease, and cell and gene therapy.

Nucleic Acid Target Sensing Using a Vibrating Sharp-Tip Capillary and Digital Droplet Loop-Mediated Isothermal Amplification (ddLAMP)

Nucleic acid tests are key tools for the detection and diagnosis of many diseases. In many cases, the amplification of the nucleic acids is required to reach a detectable level. To make nucleic acid amplification tests more accessible to a point-of-care (POC) setting, isothermal amplification can be performed with a simple heating source. Although these tests are being performed in bulk reactions, the quantification is not as accurate as it would be with digital amplification. Here, we introduce the use of the vibrating sharp-tip capillary for a simple and portable system for tunable on-demand droplet generation. Because of the large range of droplet sizes possible and the tunability of the vibrating sharp-tip capillary, a high dynamic range (~2 to 6000 copies/µL) digital droplet loop-mediated isothermal amplification (ddLAMP) system has been developed. It was also noted that by changing the type of capillary on the vibrating sharp-tip capillary, the same mechanism can be used for simple and portable DNA fragmentation. With the incorporation of these elements, the present work paves the way for achieving digital nucleic acid tests in a POC setting with limited resources.

Advances in the isolation, cultivation, and identification of gut microbes

The gut microbiome is closely associated with human health and the development of diseases. Isolating, characterizing, and identifying gut microbes are crucial for research on the gut microbiome and essential for advancing our understanding and utilization of it. Although culture-independent approaches have been developed, a pure culture is required for in-depth analysis of disease mechanisms and the development of biotherapy strategies. Currently, microbiome research faces the challenge of expanding the existing database of culturable gut microbiota and rapidly isolating target microorganisms. This review examines the advancements in gut microbe isolation and cultivation techniques, such as culturomics, droplet microfluidics, phenotypic and genomics selection, and membrane diffusion. Furthermore, we evaluate the progress made in technology for identifying gut microbes considering both non-targeted and targeted strategies. The focus of future research in gut microbial culturomics is expected to be on high-throughput, automation, and integration. Advancements in this field may facilitate strain-level investigation into the mechanisms underlying diseases related to gut microbiota.

Research progress in isolation and identification of rumen probiotics

With the increasing research on the exploitation of rumen microbial resources, rumen probiotics have attracted much attention for their positive contributions in promoting nutrient digestion, inhibiting pathogenic bacteria, and improving production performance. In the past two decades, macrogenomics has provided a rich source of new-generation probiotic candidates, but most of these "dark substances" have not been successfully cultured due to the restrictive growth conditions. However, fueled by high-throughput culture and sorting technologies, it is expected that the potential probiotics in the rumen can be exploited on a large scale, and their potential applications in medicine and agriculture can be explored. In this paper, we review and summarize the classical techniques for isolation and identification of rumen probiotics, introduce the development of droplet-based high-throughput cell culture and single-cell sequencing for microbial culture and identification, and finally introduce promising cultureomics techniques. The aim is to provide technical references for the development of related technologies and microbiological research to promote the further development of the field of rumen microbiology research.

Digital microfluidics methods for nucleic acid detection: A mini review

Many serious infectious diseases have occurred throughout human history. Rapid and accurate detection as well as the isolation of infected individuals, through nucleic acid testing, are effective means of containing the spread of these viruses. However, traditional nucleic acid testing methods rely on complex machines and specialized personnel, making it difficult to achieve large-scale, high-throughput, and rapid detection. In recent years, digital microfluidics has emerged as a promising technology that integrates various fields, including electrokinetics, acoustics, optics, magnetism, and mechanics. By leveraging the advantages of these different technologies, digital microfluidic chips offer several benefits, such as high detection throughput, integration of multiple functions, low reagent consumption, and portability. This rapid and efficient testing is crucial in the timely detection and isolation of infected individuals to prevent the virus spread. Another advantage is the low reagent consumption of digital microfluidic chips. Compared to traditional methods, these chips require smaller volumes of reagents, resulting in cost savings and reduced waste. Furthermore, digital microfluidic chips are portable and can be easily integrated into point-of-care testing devices. This enables testing to be conducted in remote or resource-limited areas, where access to complex laboratory equipment may be limited. Onsite testing reduces the time and cost associated with sample transportation. In conclusion, bioassay technologies based on digital microfluidic principles have the potential to significantly improve infectious disease detection and control. By enabling rapid, high-throughput, and portable testing, these technologies enhance our ability to contain the spread of infectious diseases and effectively manage public health outbreaks.

Combination-Lock SlipChip Integrating Nucleic Acid Sample Preparation and Isothermal LAMP Amplification for the Detection of SARS-CoV-2

Nucleic acid analysis with an easy-to-use workflow, high specificity and sensitivity, independence of sophisticated instruments, and accessibility outside of the laboratory is highly desirable for the detection and monitoring of infectious diseases. Integration of laboratory-quality sample preparation on a hand-held system is critical for performance. A SlipChip device inspired by the combination lock can perform magnetic bead-based nucleic acid extraction with several clockwise and counterclockwise rotations. A palm-sized base station was developed to assist sample preparation and provide thermal control of isothermal nucleic acid amplification without plug-in power. The loop-mediated isothermal amplification reaction can be performed with a colorimetric method and directly analyzed by the naked eye or with a mobile phone app. This system achieves good bead recovery during the sample preparation workflow and has minimal residue carryover from the lysis and elution buffers. Its performance is comparable to that of the standard laboratory protocol with real-time qPCR amplification methods. The entire workflow is completed in less than 35 min and the device can achieve 500 copies/mL sensitivity. Thirty clinical nasal swab samples were collected and tested with a sensitivity of 95% and a specificity of 100% for SARS-CoV-2. This combination-lock SlipChip provides a promising fast, easy-to-use nucleic acid test with bead-based sample preparation that produces laboratory-quality results for point-of-care settings, especially in home use applications.

Development of the viscosity biosensor for the detection of DNase I based on the flow distance on the paper with DNA mucus

Deoxyribonuclease I (DNase I) is a biomarker which has important applications in various biological processes. Thus, it is highly important to develop a user-friendly method for the detection of DNase I. Here, we present a paper-based distance sensor for the rapid detection of DNase I based on changes in the viscosity of DNA mucus. The viscosity of DNA mucus varies with different concentrations of DNase I, showing different water flow lengths on the pH test papers, this makes the quantification of DNase I possible. This method has a wide linear range (0.01-10 U/mL), excellent sensitivity, remarkable specificity and excellent reproducibility. The detection limit reaches 0.003 U/mL. Additionally, it can be well applied to detection of DNase I inhibitors, assay of DNase I in human serum and quality evaluation of nucleic acid scavengers. In general, this study offers a brief, convenient, label-free, and economical method to construct paper-based distance sensors using DNA mucus, which is very promising in the detection of DNase I in various applications.

Digital Cascade Assays for ADP- or ATP-Producing Enzymes Using a Femtoliter Reactor Array Device

Digital enzyme assays are emerging biosensing methods for highly sensitive quantitative analysis of biomolecules with single-molecule detection sensitivity. However, current digital enzyme assays require a fluorogenic substrate for detection, which limits the applicability of this method to certain enzymes. ATPases and kinases are representative enzymes for which fluorogenic substrates are not available; however, these enzymes form large domains and play a central role in biology. In this study, we implemented a fluorogenic cascade reaction in a femtoliter reactor array device to develop a digital bioassay platform for ATPases and kinases. The digital cascade assay enabled quantitative measurement of the single-molecule activity of F1-ATPase, the catalytic portion of ATP synthase. We also demonstrated a digital assay for human choline kinase α. Furthermore, we developed a digital cascade assay for ATP-synthesizing enzymes and demonstrated a digital assay for pyruvate kinase. These results show the high versatility of this assay platform. Thus, the digital cascade assay has great potential for the highly sensitive detection and accurate characterization of various ADP- and ATP-producing enzymes, such as kinases, which may serve as disease biomarkers.

Quantitative Investigation of Methylation Heterogeneity by Digital Melting Curve Analysis on a SlipChip for Atrial Fibrillation

Methylation is an essential epigenetic modification involved in regulating gene expression and maintaining genome stability. Methylation patterns can be heterogeneous, exhibiting variations in both level and density. However, current methods of methylation analysis, including sequencing, methylation-specific PCR, and high-resolution melting curve analysis (HRM), face limitations of high cost, time-consuming workflows, and the difficulty of both accurate heterogeneity analysis and precise quantification. Here, a droplet array SlipChip-based (da-SlipChip-based) digital melting curve analysis (MCA) method was developed for the accurate quantification of both methylation level (ratio of methylated molecules to total molecules) and methylation density (ratio of methylated CpG sites to total CpG sites). The SlipChip-based digital MCA system supplements an in situ thermal cycler with a fluorescence imaging module for real-time MCA. The da-SlipChip can generate 10,656 droplets of 1 nL each, which can be separated into four lanes, enabling the simultaneous analysis of four samples. This method's clinical application was demonstrated by analyzing samples from ten healthy individuals and twenty patients with atrial fibrillation (AF), the most common arrhythmia. This method can distinguish healthy individuals from those with AF of both the paroxysmal and persistent types. It also holds potential for broader application in various research and clinical settings requiring methylation analysis.

Automated and semi-automated packed sorbent solid phase (micro) extraction methods for extraction of organic and inorganic pollutants

In this study, the packed sorbent solid phase (micro) extraction methods from manual to automated modes are reviewed. The automatic methods have several remarkable advantages such as high sample throughput, reproducibility, sensitivity, and extraction efficiency. These methods include solid-phase extraction, pipette tip micro-solid phase extraction, microextraction by packed sorbent, in-tip solid phase microextraction, in-tube solid phase microextraction, lab-on-a-chip, and lab-on-a-valve. The recent application of these methods for the extraction of organic and inorganic compounds are discussed. Also, the combination of novel technologies (3D printing and robotic platforms) with the (semi)automated methods are investigated as the future trend.

A gravity-driven droplet fluidic point-of-care test

We report a simple droplet fluidic point-of-care test (POCT) that uses gravity to manipulate the sequence, timing, and motion of droplets on a surface. To fabricate this POCT, we first developed a surface coating toolbox of nine different coatings with three levels of wettability and three levels of slipperiness that can be independently tailored. We then fabricated a device that has interconnected fluidic elements-pumps, flow resistors and flow guides-on a highly slippery solid surface to precisely control the timing and sequence of motion of multiple droplets and their interactions on the surface. We then used this device to carry out a multi-step enzymatic assay of a clinically relevant analyte-lactate dehydrogenase (LDH)-to demonstrate the application of this technology for point-of-care diagnosis.

Single-molecule immunoassay technology: Recent advances

Detecting diseases at the molecular level aids in early diagnosis and treatment. However, traditional immunological detection techniques, such as enzyme-linked immunosorbent assay (ELISA) and chemiluminescence, have detection sensitivities between 10^-16 and 10^-12 mol/L, which are inadequate for early diagnosis. Single-molecule immunoassays can reach detection sensitivities of 10^-18 mol/L and can detect biomarkers that are difficult to measure using conventional detection techniques. It can confine molecules to be detected in a small spatial area and provide absolute counting of the detected signal, offering the advantage of high efficiency and accuracy. Herein, we demonstrate the principles and equipment of two single-molecule immunoassay techniques and discuss their applications. It is shown that the detection sensitivity can be improved by 2-3 orders of magnitude compared to common chemiluminescence or ELISA assays. The microarray-based single-molecule immunoassay technique can test 66 samples in 1 h, which is more efficient than conventional immunological detection techniques. In contrast, microdroplet-based single-molecule immunoassay techniques can generate 107 droplets in 10 min, which is more than 100 times faster than a single droplet generator. By comparing the two single-molecule immunoassay techniques, we highlight our personal perspectives on the current limitations of point-of-care applications and future development trends.

Recent Advances on Cell Culture Platforms for In Vitro Drug Screening and Cell Therapies: From Conventional to Microfluidic Strategies

The clinical translations of drugs and nanomedicines depend on coherent pharmaceutical research based on biologically accurate screening approaches. Since establishing the 2D in vitro cell culture method, the scientific community has improved cell-based drug screening assays and models. Those advances result in more informative biochemical assays and the development of 3D multicellular models to describe the biological complexity better and enhance the simulation of the in vivo microenvironment. Despite the overall dominance of conventional 2D and 3D cell macroscopic culture methods, they present physicochemical and operational challenges that impair the scale-up of drug screening by not allowing a high parallelization, multidrug combination, and high-throughput screening. Their combination and complementarity with microfluidic platforms enable the development of microfluidics-based cell culture platforms with unequivocal advantages in drug screening and cell therapies. Thus, this review presents an updated and consolidated view of cell culture miniaturization's physical, chemical, and operational considerations in the pharmaceutical research scenario. It clarifies advances in the field using gradient-based microfluidics, droplet-based microfluidics, printed-based microfluidics, digital-based microfluidics, SlipChip, and paper-based microfluidics. Finally, it presents a comparative analysis of the performance of cell-based methods in life research and development to achieve increased precision in the drug screening process.

On the Application of Microfluidic-Based Technologies in Forensics: A Review

Microfluidic technology is a powerful tool to enable the rapid, accurate, and on-site analysis of forensically relevant evidence on a crime scene. This review paper provides a summary on the application of this technology in various forensic investigation fields spanning from forensic serology and human identification to discriminating and analyzing diverse classes of drugs and explosives. Each aspect is further explained by providing a short summary on general forensic workflow and investigations for body fluid identification as well as through the analysis of drugs and explosives. Microfluidic technology, including fabrication methodologies, materials, and working modules, are touched upon. Finally, the current shortcomings on the implementation of the microfluidic technology in the forensic field are discussed along with the future perspectives.

A targeted liquid cultivation method for previously uncultured non-colony forming microbes

A large number of microbes are not able to form colonies using agar-plating methods, which is one of the reasons that cultivation based on solid media leaves the majority of microbial diversity in the environment inaccessible. We developed a new Non-Colony-Forming Liquid Cultivation method (NCFLC) that can selectively isolate non-colony-forming microbes that exclusively grow in liquid culture. The NCFLC method involves physically separating cells using dilution-to-extinction (DTE) cultivation and then selecting those that could not grow on a solid medium. The NCFLC was applied to marine samples from a coastal intertidal zone and soil samples from a forest area, and the results were compared with those from the standard direct plating method (SDP). The NCFLC yielded fastidious bacteria from marine samples such as Acidobacteriota, Epsilonproteobacteria, Oligoflexia, and Verrucomicrobiota. Furthermore, 62% of the isolated strains were potential new species, whereas only 10% were novel species from SDP. From soil samples, isolates belonging to Acidobacteriota and Armatimonadota (which are known as rare species among identified isolates) were exclusively isolated by NCFLC. Colony formation capabilities of isolates cultivated by NCFLC were tested using solid agar plates, among which approximately one-third of the isolates were non-colony-forming, approximately half-formed micro-colonies, and only a minority could form ordinary size colonies. This indicates that the majority of the strains cultivated by NCFLC were previously uncultured microbial species unavailable using the SDP method. The NCFCL method described here can serve as a new approach to accessing the hidden microbial dark matter.

Double emulsions as a high-throughput enrichment and isolation platform for slower-growing microbes

Our understanding of in situ microbial physiology is primarily based on physiological characterization of fast-growing and readily-isolatable microbes. Microbial enrichments to obtain novel isolates with slower growth rates or physiologies adapted to low nutrient environments are plagued by intrinsic biases for fastest-growing species when using standard laboratory isolation protocols. New cultivation tools to minimize these biases and enrich for less well-studied taxa are needed. In this study, we developed a high-throughput bacterial enrichment platform based on single cell encapsulation and growth within double emulsions (GrowMiDE). We showed that GrowMiDE can cultivate many different microorganisms and enrich for underrepresented taxa that are never observed in traditional batch enrichments. For example, preventing dominance of the enrichment by fast-growing microbes due to nutrient privatization within the double emulsion droplets allowed cultivation of slower-growing Negativicutes and Methanobacteria from stool samples in rich media enrichment cultures. In competition experiments between growth rate and growth yield specialist strains, GrowMiDE enrichments prevented competition for shared nutrient pools and enriched for slower-growing but more efficient strains. Finally, we demonstrated the compatibility of GrowMiDE with commercial fluorescence-activated cell sorting (FACS) to obtain isolates from GrowMiDE enrichments. Together, GrowMiDE + DE-FACS is a promising new high-throughput enrichment platform that can be easily applied to diverse microbial enrichments or screens.

The emerging landscape of microfluidic applications in DNA data storage

DNA has been considered a promising alternative to the current solid-state devices for digital information storage. The past decade has witnessed tremendous progress in the field of DNA data storage contributed by researchers from various disciplines. However, the current development status of DNA storage is still far from practical use, mainly due to its high material cost and time consumption for data reading/writing, as well as the lack of a comprehensive, automated, and integrated system. Microfluidics, being capable of handling and processing micro-scale fluid samples in a massively paralleled and highly integrated manner, has gradually been recognized as a promising candidate for addressing the aforementioned issues. In this review, we provide a discussion on recent efforts of applying microfluidics to advance the development of DNA data storage. Moreover, to showcase the tremendous potential that microfluidics can contribute to this field, we will further highlight the recent advancements of applying microfluidics to the key functional modules within the DNA data storage workflow. Finally, we share our perspectives on future directions for how to continue the infusion of microfluidics with DNA data storage and how to advance toward a truly integrated system and reach real-life applications.

Acoustic Trapping: An Emerging Tool for Microfabrication Technology

The high throughput deposition of microscale objects with precise spatial arrangement represents a key step in microfabrication technology. This can be done by creating physical boundaries to guide the deposition process or using printing technologies; in both approaches, these microscale objects cannot be further modified after they are formed. The utilization of dynamic acoustic fields offers a novel approach to facilitate real-time reconfigurable miniaturized systems in a contactless manner, which can potentially be used in physics, chemistry, biology, as well as materials science. Here, the physical interactions of microscale objects in an acoustic pressure field are discussed and how to fabricate different acoustic trapping devices and how to tune the spatial arrangement of the microscale objects are explained. Moreover, different approaches that can dynamically modulate microscale objects in acoustic fields are presented, and the potential applications of the microarrays in biomedical engineering, chemical/biochemical sensing, and materials science are highlighted alongside a discussion of future research challenges.

Construction and Manipulation of Serial Gradient Dilution Array on a Microfluidic Slipchip for Screening and Characterizing Inhibitors against Human Pancreatic Lipase

Obesity is one of the foremost public health concerns. Human pancreatic lipase (hPL), a crucial digestive enzyme responsible for the digestion of dietary lipids in humans, has been validated as an important therapeutic target for preventing and treating obesity. The serial dilution technique is commonly used to generate solutions with different concentrations and can be easily modified for drug screening. Conventional serial gradient dilution is often performed with tedious multiple manual pipetting steps, where it is difficult to precisely control fluidic volumes at low microliter levels. Herein, we presented a microfluidic SlipChip that enabled formation and manipulation of serial dilution array in an instrument-free manner. With simple slipping steps, the compound solution could be diluted to seven gradients with the dilution ratio of 1:1 and co-incubated with the enzyme (hPL)-substrate system for screening the anti-hPL potentials. To ensure complete mixing of solution and diluent during continuous dilution, we established a numerical simulation model and conducted an ink mixing experiment to determine the mixing time. Furthermore, we also demonstrated the serial dilution ability of the proposed SlipChip using standard fluorescent dye. As a proof of concept, we tested this microfluidic SlipChip using one marketed anti-obesity drug (Orlistat) and two natural products (1,2,3,4,6-penta-O-galloyl-β-D-glucopyranose (PGG) and sciadopitysin) with anti-hPL potentials. The IC₅₀ values of these agents were calculated as 11.69 nM, 8.22 nM and 0.80 μM, for Orlistat, PGG and sciadopitysin, respectively, which were consistent with the results obtained by conventional biochemical assay.

Digital CRISPR Systems for the Next Generation of Nucleic Acid Quantification

Digital CRISPR (dCRISPR) assays are an emerging platform of molecular diagnostics. Digital platforms introduce absolute quantification and increased sensitivity to bulk CRISPR assays. With ultra-specific targeting, isothermal operation, and rapid detection, dCRISPR systems are well-prepared to lead the field of molecular diagnostics. Here we summarized the common Cas proteins used in CRISPR detection assays. The methods of digital detection and critical performance factors are examined. We formed three strategies to frame the landscape of dCRISPR systems: (1) amplification free, (2) in-partition amplification, and (3) two-stage amplification. We also compared the performance of all systems through the limit of detection (LOD), testing time, and figure of merit (FOM). This work summarizes the details of digital CRISPR platforms to guide future development. We envision that improvements to LOD and dynamic range will position dCRISPR as the leading platform for the next generation of molecular biosensing.

Multiplex Digital Polymerase Chain Reaction on a Droplet Array SlipChip for Analysis of KRAS Mutations in Pancreatic Cancer

Pancreatic cancer is a terminal disease with high mortality and very poor prognosis. A sensitive and quantitative analysis of KRAS mutations in pancreatic cancer provides a tool not only to understand the biological mechanisms of pancreatic cancer but also for diagnosis and treatment monitoring. Digital polymerase chain reaction (PCR) is a promising tool for KRAS mutation analysis, but current methods generally require a complex microfluidic handling system, which can be challenging to implement in routine research and point-of-care clinical diagnostics. Here, we present a droplet-array SlipChip (da-SlipChip) for the multiplex quantification of KRAS G12D, V, R, and C mutant genes with the wild-type (WT) gene background by dual color (FAM/ROX) fluorescence detection. This da-SlipChip is a high-density microwell array of 21,696 wells of 200 pL in 4 by 5424 microwell format with simple loading and slipping operation. It does not require the same precise alignment of microfeatures on the different plates that are acquired by the traditional digital PCR SlipChip. This device can provide accurate quantification of both mutant genes and the WT KRAS gene. We collected tumor tissue, paired normal pancreatic tissue, and other normal tissues from 18 pancreatic cancer patients and analyzed the mutation profiles of KRAS G12D, V, R, and C in these samples; the results from the multiplex digital PCR on da-SlipChip agree well with those of next-generation sequencing (NGS). This da-SlipChip moves digital PCR closer to the practical point-of-care applications not only for detecting KRAS mutations in pancreatic cancer but also for other applications that require precise nucleic acid quantification with high sensitivity.

LAMP-Based Point-of-Care Biosensors for Rapid Pathogen Detection

Seeking optimized infectious pathogen detection tools is of primary importance to lessen the spread of infections, allowing prompt medical attention for the infected. Among nucleic-acid-based sensing techniques, loop-mediated isothermal amplification is a promising method, as it provides rapid, sensitive, and specific detection of microbial and viral pathogens and has enormous potential to transform current point-of-care molecular diagnostics. In this review, the advances in LAMP-based point-of-care diagnostics assays developed during the past few years for rapid and sensitive detection of infectious pathogens are outlined. The numerous detection methods of LAMP-based biosensors are discussed in an end-point and real-time manner with ideal examples. We also summarize the trends in LAMP-on-a-chip modalities, such as classical microfluidic, paper-based, and digital LAMP, with their merits and limitations. Finally, we provide our opinion on the future improvement of on-chip LAMP methods. This review serves as an overview of recent breakthroughs in the LAMP approach and their potential for use in the diagnosis of existing and emerging diseases.

Combinatorial screening SlipChip for rapid phenotypic antimicrobial susceptibility testing

Antimicrobial resistance (AMR) by bacteria is a serious global threat, and a rapid, high-throughput, and easy-to-use phenotypic antimicrobial susceptibility testing (AST) method is essential for making timely treatment decisions and controlling the spread of antibiotic resistant micro-organisms. Traditional culture-based methods are time-consuming, and their capability to screen against a large number of different conditions is limited; meanwhile genotypic based methods, including sequencing and PCR based methods, are constrained by rarely identified resistance genes and complicated resistance mechanisms. Here, a combinatorial-screening SlipChip (cs-SlipChip) containing 192 nanoliter-sized compartments is developed which can perform high-throughput phenotypic AST within three hours by monitoring the bacterial growth within nanoliter-sized droplets with bright-field imaging and analyzing the changes in bacterial number and morphology. The minimum inhibitory concentration (MIC) of Escherichia coli ATCC 25922 against four antibiotics (ampicillin, ciprofloxacin, ceftazidime, and nitrofurantoin) can be measured in one chip within 3 hours. Furthermore, five antibiotic-resistant E. coli strains were isolated from patients diagnosed with urinary tract infections (UTIs), and an individual isolate was tested using four antibiotics and eleven antibiotic combinations simultaneously with three different concentrations of each. The results from the cs-SlipChip agree with those of a VITEK 2 automated system. This cs-SlipChip provides a practical high-throughput and rapid phenotypic method for AST and can also be used to screen different chemicals and antibiotic combinations for the treatment of multiple antibiotic-resistant bacteria.

Absolute Counting Method with Multiplexing Capability for Estimating the Number Concentration of Nanoparticles Using Anisotropically Collapsed Gels

Number concentration─the number of nanoparticles in a given volume─is an important characteristic of any nanoparticle dispersion. However, its estimation for small nanoparticles (∼30 nm) is generally challenging. We introduce an absolute and widely applicable method for analyzing aqueous dispersions of nanoparticles. An innovative immobilization of nanomaterials in the anisotropically collapsed agarose gel is pioneered, followed by optical microscopy and nanoparticle counting. The number of counted nanoparticles is inherently coupled with sampled volume (517 pL) and translates to the number concentration. Photon-upconversion, fluorescence, bright-field, and dark-field microscopy techniques have been proven applicable and used for imaging lanthanide-doped photon-upconversion nanoparticles, their bioconjugates with antibodies, silica dye-doped fluorescent nanoparticles, quantum dots, and pure silica submicron particles. The precision and linearity were characterized by constructing a dilution series of photon-upconversion nanoparticles. The limit of detection was 2.0 × 10⁶ mL^-1, and the working range was from 4.4 × 10⁷ to 2.2 × 10¹⁰ mL^-1. The quantification of nanoparticle clusters was achieved by a thorough analysis of the micrographs. The accuracy was confirmed using gravimetric analysis and transmission electron microscopy as a reference. Multiplexed detection of two nanoparticle types in a mixed dispersion was feasibly demonstrated. The low thickness of the collapsed gel (<1 μm) supported extremely sensitive imaging. This was proven by imaging Tm³⁺-doped photon-upconversion nanoparticles (17 nm hydrodynamic diameter) with a nanoparticle emission rate of only ∼900 photons/s at a wavelength of 800 nm (excitation wavelength 976 nm).

Microfluidics for antibiotic susceptibility testing

The rise of antibiotic resistance is a threat to global health. Rapid and comprehensive analysis of infectious strains is critical to reducing the global use of antibiotics, as informed antibiotic use could slow down the emergence of resistant strains worldwide. Multiple platforms for antibiotic susceptibility testing (AST) have been developed with the use of microfluidic solutions. Here we describe microfluidic systems that have been proposed to aid AST. We identify the key contributions in overcoming outstanding challenges associated with the required degree of multiplexing, reduction of detection time, scalability, ease of use, and capacity for commercialization. We introduce the reader to microfluidics in general, and we analyze the challenges and opportunities related to the field of microfluidic AST.

Microfluidics-Based Urine Biopsy for Cancer Diagnosis: Recent Advances and Future Trends

Urine biopsy, allowing for the detection, analysis and monitoring of numerous cancer-associated urinary biomarkers to provide insights into cancer occurrence, progression and metastasis, has emerged as an attractive liquid biopsy strategy with enormous advantages over traditional tissue biopsy, such as noninvasiveness, large sample volume, and simple sampling operation. Microfluidics enables precise manipulation of fluids in a tiny chip and exhibits outstanding performance in urine biopsy owing to its minimization, low cost, high integration, high throughput and low sample consumption. Herein, we review recent advances in microfluidic techniques employed in urine biopsy for cancer detection. After briefly summarizing the major urinary biomarkers used for cancer diagnosis, we provide an overview of the typical microfluidic techniques utilized to develop urine biopsy devices. Some prospects along with the major challenges to be addressed for the future of microfluidic-based urine biopsy are also discussed.

Emerging microfluidic technologies for microbiome research

The importance of the microbiome is increasingly prominent. For example, the human microbiome has been proven to be strongly associated with health conditions, while the environmental microbiome is recognized to have a profound influence on agriculture and even the global climate. Furthermore, the microbiome can serve as a fascinating reservoir of genes that encode tremendously valuable compounds for industrial and medical applications. In the past decades, various technologies have been developed to better understand and exploit the microbiome. In particular, microfluidics has demonstrated its strength and prominence in the microbiome research. By taking advantage of microfluidic technologies, inherited shortcomings of traditional methods such as low throughput, labor-consuming, and high-cost are being compensated or bypassed. In this review, we will summarize a broad spectrum of microfluidic technologies that have addressed various needs in the field of microbiome research, as well as the achievements that were enabled by the microfluidics (or technological advances). Finally, how microfluidics overcomes the limitations of conventional methods by technology integration will also be discussed.

Parallel multistep digital analysis SlipChip demonstrated with the quantification of nucleic acid by digital LAMP-CRISPR

Digital biological analysis compartmentalizes targets of interest, such as nucleic acids, proteins, and cells, to a single event level and performs detection and further investigation. Microfluidic-based digital biological analysis methods, including digital PCR, digital protein analysis, and digital cell analysis, have demonstrated superior advantages in research applications and clinical diagnostics. However, most of the methods are still based on a one-step "divide and detect" strategy, and it is challenging for these methods to perform further parallel manipulation of reaction partitions to achieve "divide, manipulate, and analyze" capabilities. Here, we present a parallel multistep digital analysis (PAMDA) SlipChip for the parallel multistep manipulation of a large number of droplets for digital biological analysis, demonstrated by the quantification of SARS-CoV-2 nucleic acids by a two-step digital isothermal amplification combined with clustered regularly interspaced short palindromic repeats (CRISPR). This PAMDA SlipChip utilizes a "chain-of-pearl" channel with a self-partitioning droplet formation mechanism that does not require the precise alignment of microfeatures for fluidic loading as the traditional SlipChip design. This device can first generate 2400 3.2 nanoliter droplets to perform digital loop-mediated isothermal amplification (LAMP) and then deliver reagents containing Cas12a protein and crRNA to each individual partition in parallel to simultaneously initiate digital CRISPR detection by a simple multistep slipping operation. This PAMDA SlipChip not only provides a promising tool to perform digital CRISPR with a flexible assay and workflow design but can also be applied for a broad range of applications in digital biological analysis that require multistep manipulation of partitions in parallel.

Formation and Parallel Manipulation of Gradient Droplets on a Self-Partitioning SlipChip for Phenotypic Antimicrobial Susceptibility Testing

Flexible, robust, and user-friendly screening systems with a large dynamic range are highly desired in scientific research, industrial development, and clinical diagnostics. Droplet-based microfluidic systems with gradient concentrations of chemicals have been demonstrated as promising tools to provide confined microenvironments for screening tests with small reaction volumes. However, the generation and manipulation of gradient droplets, such as droplet merging, generally require sophisticated fluidic manipulation systems, potentially limiting their application in decentralized settings. We present a gradient-droplet SlipChip (gd-SlipChip) microfluidic device that enables instrument-free gradient droplet formation and parallel manipulation. The device can establish a gradient profile by free interfacial diffusion in a continuous fluidic channel. With a simple slipping step, gradient droplets can be generated by a surface tension-driven self-partitioning process. Additional reagents can be introduced in parallel to these gradient droplets with further slipping operations to initiate screening tests of the droplets over a large concentration range. To profile the concentration in the gradient droplets, we establish a numerical simulation model and verify it with hydrogen chloride (HCl) diffusion, as tested with a dual-color pH indicator (methyl orange and aniline blue). As a proof of concept, we tested this system with a gradient concentration of nitrofurantoin for the phenotypic antimicrobial susceptibility testing (AST) of Escherichia coli. The results of our gd-SlipChip-based AST on both reference and clinical strains of E. coli can be indicated by the bacterial growth profile within 3 h and are consistent with the clinical culture-based AST.

A microreactor sealing method using adhesive tape for digital bioassays

Digital assays using microreactors fabricated on solid substrates are useful for carrying out sensitive assays of infectious diseases and other biological tests. However, sealing of the microchambers using fluid oil is difficult for non-experts, and thus hinders the widespread use of digital microreactor assays. Here, we propose the physical isolation of tiny reactors with adhesive tape (PITAT) using simple, commercially available pressure-sensitive adhesive (PSA) tape as a separator of the microreactors. We confirmed that PSA tape can effectively seal the microreactors and prevent molecules from diffusing out. By testing several types of adhesive tape, we found that rubber-based adhesives are the most suitable for this purpose. In addition, we demonstrated that single-molecule enzyme assays can be successfully performed inside microreactors sealed with PSA tape. The results obtained using PITAT are quantitatively comparable to conventional oil sealing, although it is quick and cost-effective. Finally, we demonstrated that single-particle virus counting of the influenza virus can be achieved using PITAT. Collectively, our results suggest that PITAT may be suitable for use in the design of sensitive tests for infectious diseases at the point of care, where no sophisticated equipment or machines are available.

Nanomaterial-assisted microfluidics for multiplex assays

Simultaneous detection of different biomarkers from a single specimen in a single test, allowing more rapid, efficient, and low-cost analysis, is of great significance for accurate diagnosis of disease and efficient monitoring of therapy. Recently, developments in microfabrication and nanotechnology have advanced the integration of nanomaterials in microfluidic devices toward multiplex assays of biomarkers, combining both the advantages of microfluidics and the unique properties of nanomaterials. In this review, we focus on the state of the art in multiplexed detection of biomarkers based on nanomaterial-assisted microfluidics. Following an overview of the typical microfluidic analytical techniques and the most commonly used nanomaterials for biochemistry analysis, we highlight in detail the nanomaterial-assisted microfluidic strategies for different biomarkers. These highly integrated platforms with minimum sample consumption, high sensitivity and specificity, low detection limit, enhanced signals, and reduced detection time have been extensively applied in various domains and show great potential in future point-of-care testing and clinical diagnostics.

Micro-Technologies for Assessing Microbial Dynamics in Controlled Environments

With recent advances in microfabrication technologies, the miniaturization of traditional culturing techniques has provided ideal methods for interrogating microbial communities in a confined and finely controlled environment. Micro-technologies offer high-throughput screening and analysis, reduced experimental time and resources, and have low footprint. More importantly, they provide access to culturing microbes in situ in their natural environments and similarly, offer optical access to real-time dynamics under a microscope. Utilizing micro-technologies for the discovery, isolation and cultivation of "unculturable" species will propel many fields forward; drug discovery, point-of-care diagnostics, and fundamental studies in microbial community behaviors rely on the exploration of novel metabolic pathways. However, micro-technologies are still largely proof-of-concept, and scalability and commercialization of micro-technologies will require increased accessibility to expensive equipment and resources, as well as simpler designs for usability. Here, we discuss three different miniaturized culturing practices; including microarrays, micromachined devices, and microfluidics; advancements to the field, and perceived challenges.

Spot tests: past and present

Microchemistry, i.e., the chemistry performed at the scale of a microgram or less, has its roots in the late eighteenth and early nineteenth centuries. In the first half of the twentieth century a wide range of spot tests have been developed. For didactic reasons, they are still part of the curriculum of chemistry students. However, they are even highly important for applied analyses in conservation of cultural heritage, food science, forensic science, clinical and pharmacological sciences, geochemistry, and environmental sciences. Modern pregnancy tests, virus tests, etc. are the most recent examples of sophisticated spot tests. The present ChemTexts contribution aims to provide an overview of the past and present of this analytical methodology.

A Rapid Digital PCR System with a Pressurized Thermal Cycler

We designed a silicon-based fast-generated static droplets array (SDA) chip and developed a rapid digital polymerase chain reaction (dPCR) detection platform that is easy to load samples for fluorescence monitoring. By using the direct scraping method for sample loading, a droplet array of 2704 microwells with each volume of about 0.785 nL can be easily realized. It was determined that the sample loading time was less than 10 s with very simple and efficient characteristics. In this platform, a pressurized thermal cycling device was first used to solve the evaporation problem usually encountered for dPCR experiments, which is critical to ensuring the successful amplification of templates at the nanoliter scale. We used a gradient dilution of the hepatitis B virus (HBV) plasmid as the target DNA for a dPCR reaction to test the feasibility of the dPCR chip. Our experimental results demonstrated that the dPCR chip could be used to quantitatively detect DNA molecules. Furthermore, the platform can measure the fluorescence intensity in real-time. To test the accuracy of the digital PCR system, we chose three-channel silicon-based chips to operate real-time fluorescent PCR experiments on this platform.

Electrochemical DNA synthesis and sequencing on a single electrode with scalability for integrated data storage

DNA has been considered as a compelling candidate for digital data storage due to advantages such as high coding density, long retention time, and low energy consumption. Despite many works reported, the development of a DNA-based database of full integration, high efficiency, and practical applicability is still challenging. In this work, we report the synthesis and sequencing of DNA on a single electrode with scalability for an integrated DNA-based data storage system. The synthesis of DNA is based on phosphoramidite chemistry and electrochemical deprotection. The sequencing relies on charge redistribution originated from polymerase-catalyzed primer extension, leading to a measurable current spike. By regeneration of the electrode after sequencing, repeated sequencing can be achieved to improve the accuracy. A SlipChip device is developed to simplify the liquid introduction involved in DNA synthesis and sequencing. As the proof-of-concept experiment, text information is stored in the system and then accurately retrieved.

Rapid Fabrication by Digital Light Processing 3D Printing of a SlipChip with Movable Ports for Local Delivery to Ex Vivo Organ Cultures

SlipChips are two-part microfluidic devices that can be reconfigured to change fluidic pathways for a wide range of functions, including tissue stimulation. Currently, fabrication of these devices at the prototype stage requires a skilled microfluidic technician, e.g., for wet etching or alignment steps. In most cases, SlipChip functionality requires an optically clear, smooth, and flat surface that is fluorophilic and hydrophobic. Here, we tested digital light processing (DLP) 3D printing, which is rapid, reproducible, and easily shared, as a solution for fabrication of SlipChips at the prototype stage. As a case study, we sought to fabricate a SlipChip intended for local delivery to live tissue slices through a movable microfluidic port. The device was comprised of two multi-layer components: an enclosed channel with a delivery port and a culture chamber for tissue slices with a permeable support. Once the design was optimized, we demonstrated its function by locally delivering a chemical probe to slices of hydrogel and to living tissue with up to 120 µm spatial resolution. By establishing the design principles for 3D printing of SlipChip devices, this work will enhance the ability to rapidly prototype such devices at mid-scale levels of production.

Protein Crystallization in a Microfluidic Contactor with Nafion®117 Membranes

Protein crystallization still remains mostly an empirical science, as the production of crystals with the required quality for X-ray analysis is dependent on the intensive screening of the best protein crystallization and crystal’s derivatization conditions. Herein, this demanding step was addressed by the development of a high-throughput and low-budget microfluidic platform consisting of an ion exchange membrane (117 Nafion^® membrane) sandwiched between a channel layer (stripping phase compartment) and a wells layer (feed phase compartment) forming 75 independent micro-contactors. This microfluidic device allows for a simultaneous and independent screening of multiple protein crystallization and crystal derivatization conditions, using Hen Egg White Lysozyme (HEWL) as the model protein and Hg²⁺ as the derivatizing agent. This microdevice offers well-regulated crystallization and subsequent crystal derivatization processes based on the controlled transport of water and ions provided by the 117 Nafion^® membrane. Diffusion coefficients of water and the derivatizing agent (Hg²⁺) were evaluated, showing the positive influence of the protein drop volume on the number of crystals and crystal size. This microfluidic system allowed for crystals with good structural stability and high X-ray diffraction quality and, thus, it is regarded as an efficient tool that may contribute to the enhancement of the proteins’ crystals structural resolution.

Label-free E. coli detection based on enzyme assay and a microfluidic slipchip

An enzyme assay based method in a microfluidic slipchip was proposed for the rapid and label-free detection of E. coli. The specific target analyte of E. coli was β-d-glucuronidase (GUS) which could catalyze the substrate 6-chloro-4-methyl-umbelliferyl-β-d-glucuronide (6-CMUG) to release the fluorescent molecule 6-chloro-4-methyl-umbelliferyl (6-CMU). E. coli culture, lysis and enzymatic reaction steps could be conducted in a microfluidic slipchip without any pumps and valves, which was tailored for fluorescence detection using a commercial plate reader, to achieve a rapid E. coli test. A mixture of the culture broth, enzyme inducer and E. coli was injected into the chambers on the top layer. A mixture of the substrate and lysis solution was injected into the chambers on the bottom layer. Then, the slipchip was slid to make each chamber independent. E. coli was cultured in the chamber in the LB broth for 2.5 h. After that, the slipchip was slid again to introduce the lysis solution into the culture solution for GUS release and enzyme reaction, and then incubated in the plate reader at 42 °C for another 2.5 h. During incubation, the fluorescence intensity of each chamber was recorded. This proposed label-free method can directly detect E. coli with a low concentration of 8 CFU per chamber within 5 h, thus showing great potential in on-site E. coli detection.

Selective Fluorination of the Surface of Polymeric Materials after Stereolithography 3D Printing

With the microfluidics community embracing 3D resin printing as a rapid fabrication method, controlling surface chemistry has emerged as a new challenge. Fluorination of 3D-printed surfaces is highly desirable in many applications due to chemical inertness, low friction coefficients, antifouling properties, and the potential for selective hydrophobic patterning. Despite sporadic reports, silanization methods have not been optimized for covalent bonding with polymeric resins. As a case study, we tested the silanization of a commercially available (meth)acrylate-based resin (BV-007A) with a fluoroalkyl trichlorosilane. Interestingly, plasma oxidation was unnecessary for silanization of this resin and indeed was ineffective. Solvent-based deposition in a fluorinated oil (FC-40) generated significantly higher contact angles than deposition in ethanol or gas-phase deposition, yielding hydrophobic surfaces with contact angle >110° under optimized conditions. Attenuated total reflectance-Fourier transform infrared spectroscopy indicated that the increase in the contact angle correlated with consumption of a carbonyl moiety, suggesting covalent bonding of silane without plasma oxidation. Consistent with a covalent bond, silanization was resistant to mechanical damage and hydrolysis in methanol and was stable over long-term storage. When tested on a suite of photocrosslinkable resins, this silanization protocol generated highly hydrophobic surfaces (contact angle > 110°) on three resins and moderate hydrophobicity (90-100°) on the remainder. Selective patterning of hydrophobic regions in an open 3D-printed microchannel was possible in combination with simple masking techniques. Thus, this facile fluorination strategy is expected to be applicable for resin-printed materials in a variety of contexts including micropatterning and multiphase microfluidics.

Innovations to culturing the uncultured microbial majority

Despite the surge of microbial genome data, experimental testing is important to confirm inferences about the cell biology, ecological roles and evolution of microorganisms. As the majority of archaeal and bacterial diversity remains uncultured and poorly characterized, culturing is a priority. The growing interest in and need for efficient cultivation strategies has led to many rapid methodological and technological advances. In this Review, we discuss common barriers that can hamper the isolation and culturing of novel microorganisms and review emerging, innovative methods for targeted or high-throughput cultivation. We also highlight recent examples of successful cultivation of novel archaea and bacteria, and suggest key microorganisms for future cultivation attempts.

Gas-propelled biosensors for quantitative analysis

Gas-propelled biosensors display a simple gas-based signal amplification with quantitative detection features based on the target recognition event in combination with gas propulsion. Due to the liquid-gas conversion, the gas not only pushes the ink bar forward in the microchannel, but also serves as the power to propel the micromotors in the liquid. Thus, this continuous motion leads to a shift in distances which is associated with the target amount. Therefore, gas-propelled biosensors provide a visual quantification based on distance or speed signals without the need for expensive instruments. In this review, we focus on current developments in gas-propelled biosensors for quantitative analysis. First, we list the types of gas utilized as actuators in biosensors. Second, we review the representative gas-propelled biosensors, including the propulsion mechanisms and fabrication methods. Moreover, gas-propelled quantification based on distance and speed is summarized. Finally, we cover applications and provide a future perspective of gas-propelled biosensors.

Microdroplet Operations in Polymeric Microtubes

Microsystem technologies allow a plethora of operations to be achieved for microemulsion- and microdroplet-based assays, providing miniaturized, yet large-throughput capabilities to assist experimentation in analytical chemistry, biology, and synthetic biology. Many of such approaches have been implemented on-chip, using microfluidic and lab-on-a-chip technologies. However, the microfabrication of such devices relies on expensive equipment and time-consuming methods, thus hindering their uptake and use by many research laboratories where microfabrication expertise is not available. Here, we demonstrate how fundamental water-in-oil microdroplet operations, such as droplet trapping, merging, diluting, and splitting, can be obtained using straightforward, inexpensive, and manually fabricated polymeric microtube modules. The modules are based on creating an angled tubing interface at the interconnection between two polymeric microtubes. We have characterized how the geometry and fluid dynamic conditions at this interface enabled different droplet operations to be achieved in a versatile and functional manner. We envisage this approach to be an alternative solution to expensive and laborious microfabrication protocols for droplet microfluidic applications.

Composable Microfluidic Plates (cPlate): A Simple and Scalable Fluid Manipulation System for Multiplexed Enzyme-Linked Immunosorbent Assay (ELISA)

Enzyme-linked immunosorbent assay (ELISA) is the gold standard method for protein biomarkers. However, scaling up ELISA for multiplexed biomarker analysis is not a trivial task due to the lengthy procedures for fluid manipulation and high reagent/sample consumption. Herein, we present a highly scalable multiplexed ELISA that achieves a similar level of performance to commercial single-target ELISA kits as well as shorter assay time, less consumption, and simpler procedures. This ELISA is enabled by a novel microscale fluid manipulation method, composable microfluidic plates (cPlate), which are comprised of miniaturized 96-well plates and their corresponding channel plates. By assembling and disassembling the plates, all of the fluid manipulations for 96 independent ELISA reactions can be achieved simultaneously without any external fluid manipulation equipment. Simultaneous quantification of four protein biomarkers in serum samples is demonstrated with the cPlate system, achieving high sensitivity and specificity (∼ pg/mL), short assay time (∼1 h), low consumption (∼5 μL/well), high scalability, and ease of use. This platform is further applied to probe the levels of three protein biomarkers related to vascular dysfunction under pulmonary nanoparticle exposure in rat's plasma. Because of the low cost, portability, and instrument-free nature of the cPlate system, it will have great potential for multiplexed point-of-care testing in resource-limited regions.

Modernizing the Toolkit for Arthropod Bloodmeal Identification

Simple Summary

The ability to identify the source of vertebrate blood in mosquitoes, ticks, and other blood-feeding arthropod vectors greatly enhances our knowledge of how vector-borne pathogens are spread. The source of the bloodmeal is identified by analyzing the remnants of blood remaining in the arthropod at the time of capture, though this is often fraught with challenges. This review provides a roadmap and guide for those considering modern techniques for arthropod bloodmeal identification with a focus on progress made in the field over the past decade. We highlight genome regions that can be used to identify the vertebrate source of arthropod bloodmeals as well as technological advances made in other fields that have introduced innovative new ways to identify vertebrate meal source based on unique properties of the DNA sequence, protein signatures, or residual molecules present in the blood. Additionally, engineering progress in miniaturization has led to a number of field-deployable technologies that bring the laboratory directly to the arthropods at the site of collection. Although many of these advancements have helped to address the technical challenges of the past, the challenge of successfully analyzing degraded DNA in bloodmeals remains to be solved.

Abstract

Understanding vertebrate–vector interactions is vitally important for understanding the transmission dynamics of arthropod-vectored pathogens and depends on the ability to accurately identify the vertebrate source of blood-engorged arthropods in field collections using molecular methods. A decade ago, molecular techniques being applied to arthropod blood meal identification were thoroughly reviewed, but there have been significant advancements in the techniques and technologies available since that time. This review highlights the available diagnostic markers in mitochondrial and nuclear DNA and discusses their benefits and shortcomings for use in molecular identification assays. Advances in real-time PCR, high resolution melting analysis, digital PCR, next generation sequencing, microsphere assays, mass spectrometry, and stable isotope analysis each offer novel approaches and advantages to bloodmeal analysis that have gained traction in the field. New, field-forward technologies and platforms have also come into use that offer promising solutions for point-of-care and remote field deployment for rapid bloodmeal source identification. Some of the lessons learned over the last decade, particularly in the fields of DNA barcoding and sequence analysis, are discussed. Though many advancements have been made, technical challenges remain concerning the prevention of sample degradation both by the arthropod before the sample has been obtained and during storage. This review provides a roadmap and guide for those considering modern techniques for arthropod bloodmeal identification and reviews how advances in molecular technology over the past decade have been applied in this unique biomedical context.

Reagent integration and controlled release for multiplexed nucleic acid testing in disposable thermoplastic 2D microwell arrays

The seamless integration of reagents into microfluidic devices can serve to significantly reduce assay complexity and cost for disposable diagnostics. In this work, the integration of multiplexed reagents into thermoplastic 2D microwell arrays is demonstrated using a scalable pin spotting technique. Using a simple and low-cost narrow-bore capillary spotting pin, high resolution deposition of concentrated reagents within the arrays of enclosed nanoliter-scale wells is achieved. The pin spotting method is further employed to encapsulate the deposited reagents with a chemically modified wax layer that serves to prevent disruption of the dried assay components during sample introduction through a shared microchannel, while also enabling temperature-controlled release after sample filling is complete. This approach supports the arbitrary patterning and release of different reagents within individual wells without crosstalk for multiplexed analyses. The performance of the in-well spotting technique is characterized using on-chip rolling circle amplification to evaluate its potential for nucleic acid-based diagnostics.