A compartmentalization-free microfluidic digital assay for detecting picogram levels of protein analytes

Digitalizing the signals generated from single protein molecules has significantly improved the sensitivity of immunoassays compared to traditional analog "bulk" measurements. The single molecule array (Simoa) technology, for instance, leverages counting of single molecules on magnetic beads to detect low-abundance proteins in biofluids. While existing digital detection platforms are ultra-sensitive, they typically require compartmentalization and complex and bulky analysis equipment, limiting their applicability in resource-limited settings. Here, we introduce a compartmentalization-free digital detection technique, that allows for much more straightforward detection analysis. We applied this method to a model assay for detecting the SARS-CoV-2 spike protein and compared its performance to alternative techniques. We optimized the new method for digital microfluidics and present preliminary results using an automated system to analyze undiluted human saliva samples, with imaging performed on a portable optical system. We propose that future iterations of the scheme introduced here have the potential to enable a wide range of applications beyond the laboratory.

A combined digital microfluidic test for assessing infection and immunity status for viral disease in saliva

Population assessments of infection and immunity status are critical for public health response to infectious disease. Most microfluidic tools are developed to assess one or the other - few assess both. This study introduces a multiplexed, fully automated digital microfluidic (DMF) platform designed to detect viral protein as a proxy for infection status and host IgG and IgA antibodies as a marker for immunity status. SARS-CoV-2 and patient saliva were used as a model system to evaluate the concept. Specifically, the infection assay relied on nanobody-based capture and detection agents specific to SARS-CoV-2 trimeric spike protein, with a limit of detection (LOD) of 3.8 ng mL-1 in saliva. And the immunity relied on monoclonal antibodies for host IgG and IgA specific to SARS-CoV-2 spike S1 domain, with LODs of 4.8 ng mL-1 and 13.3 ng mL-1 in saliva, respectively. Clinical validation in saliva samples from human subjects experiencing symptoms (n = 14) showed strong correlation with PCR and commercial ELISA, achieving 100% sensitivity and 100% specificity for infection detection and 100% sensitivity with 91.7% and 90.9% specificity for host IgG and IgA, respectively. These results highlight potential applications for the new system as a portable diagnostic tool for outbreak surveillance and public health management, as a step toward preparing for the next global pandemic.

A review of electrochemical sensing in droplet systems: Droplet and digital microfluidics

BACKGROUND

Microfluidic technologies based on droplets provide discrete volumes within which chemical and/or biological processes can take place. Two major platforms in this space include droplet microfluidics (emulsions within channels) and digital microfluidics (discrete droplet manipulation by electric fields). The integration of electrochemical sensing with both microfluidic platforms offers advantages in miniaturization and portability, as sensors can be integrated directly within the microfluidic devices and instrumentation is relatively compact.

RESULTS

This review provides background on droplet and digital microfluidic technologies and electrochemical sensing before moving to methods and applications. A discussion of the various strategies to integrate sensing electrodes with both droplet and digital microfluidics and the merits of each method are included. A review of the many different applications of these integrated systems is provided.

SIGNIFICANCE AND NOVELTY

To date, there are no reviews that solely focus on the integration of electrochemical sensing with droplet and digital microfluidics. There are many advantages to combining electrochemical sensing with these platforms, especially for applications where portability or small form factors are paramount. While early reports on integrating electrochemical sensing with droplet and digital microfluidics are more than a decade old, the field is still relatively nascent, offering opportunity for many applications.

Automated Electroosmotic Digital Optofluidics for Rapid and Label-Free Protein Detection

Rapid protein detection is crucial for medical diagnosis, clinical trials, and drug development but often faces challenges in balancing sensitivity with multiplex detection, low reagent consumption, and a short detection time. In this work, we developed an automated and sensitive electroosmotic digital optofluidics (e-DOF) platform for rapid and label-free protein biomarker quantification in microliter blood samples. The hyperspectral computation reveals nanoscale morphology changes caused by target protein capture, eliminating multifarious enzyme-linked labeling. Electroosmosis-driven molecular circulation accelerates the immuno-hybridization, enhancing sensitivity (with a detection limit of 0.21 nM) and reducing the detection time to 15 min, compared to 2-3 h for a traditional enzyme-linked immunosorbent assay. In multiplex detection of hepatitis A and E IgM in 17 clinical samples, the results were completely consistent with clinical trial outcomes. This e-DOF system presents an automated, rapid, and label-free platform for multiplex detection in microliter samples, highlighting potential applications in clinical diagnosis and immunoassay research.

A digital microfluidic approach to increasing sample volume and reducing bead numbers in single molecule array assays

We report methods that improve the manipulation of magnetic beads using digital microfluidics (DMF) that can enhance the performance of single molecule array (Simoa) digital protein assays in miniaturized analytical systems. Despite significant clinical and biomedical applications for digital protein detection, the development of miniaturized Simoa systems has been limited by the requirements for use of large sample volumes (∼100 μL) and low numbers of beads (∼5000) for high sensitivity tests. To address these challenges, we improved the integration of DMF with Simoa-based assays by developing strategies for loading mixtures of sample and beads into DMF networks using methods relying on either virtual channels or small liquid segments that were applied either in parallel or in a stepwise manner. We have also demonstrated a dedicated densifying electrode technique that captures low numbers of beads within a droplet, allowing high bead retention with minimal residual volumes of liquid. Based on these improvements, we optimized the front-end assay processing of beads using DMF and demonstrated a method to detect tumor necrosis factor α (TNF-α) by Simoa that showed equivalent performance to a microtitre plate assay. The new strategies described here form a step toward integrating DMF and Simoa for a wide range of applications.

All-in-one multiple extracellular vesicle miRNA detection on a miniaturized digital microfluidic workstation

Extracellular vesicles (EVs) and EV-derived microRNAs (EV-miRNAs) are emerging as promising circulating biomarkers for early detection of malignant tumors such as non-small cell lung cancer (NSCLC). However, utilization of the gold standard method of RNA detection, the reverse transcription - quantitative polymerase chain reaction (RT-qPCR), on EV-miRNAs is hindered by laborious sample purification requirements and time-consuming multi-step procedures. Herein, we propose and demonstrate a miniaturized digital microfluidic (DMF) workstation for all-in-one EV-miRNA detection based on RT-qPCR. In comparison with the previously reported DMF platform for EV isolation, the system further integrates parallel on-chip real-time PCR capability with a comparable detection sensitivity with in-vitro RT-qPCR (limit of detection = 2 copies/μL), realizing automated, miniaturized, and facile EV-miRNA detection. Meanwhile, major methodological improvements were made, including one-step stem-looped RT-qPCR for miRNAs with both high sensitivity and specificity, and a simplified DMF substrate rework strategy for cost-effectiveness. As a demonstration, the detection of NSCLC-related EV-miRNAs within 20 μL of plasma samples was implemented, indicating the potential applicability of the DMF workstation and its automated protocol on point-of-care diagnosis of a wide range of diseases.

Bead-Based DNA Synthesis and Sequencing for Integrated Data Storage Using Digital Microfluidics

DNA is considered as a prospective candidate for the next-generation data storage medium, due to its high coding density, long cold-storage lifespan, and low energy consumption. Despite these advantages, challenges remain in achieving high-fidelity, fully integrated, and cost-efficient DNA storage system. In this study, a homemade digital microfluidic (DMF)-based compact DNA data storing pipeline is orchestrated to complete the entire process from the synthesis to the sequencing. The synthetic half employs phosphoramidite chemistry on 200 nm magnetic beads (MBs), where the dimethyltrityl protecting group is removed by droplet manipulation of trichloroacetic acid. The sequencing counterpart relies on pyrophosphate releasing originated from polymerase-catalyzed primer extension, which leads to photon-countable chemiluminescence (CL) signal in 2.5-μL drops of trienzyme cascading reactions. Further by DNA denaturation, repeated pyrosequencing plus plurality voting can improve the nucleobase accuracy beyond 95 %. As a proof-of-concept trial, semantic information is saved in DNA via the Huffman coding algorithm plus the Reed-Solomon error-correction, and then robustly retrieved from this streamlined platform. As a result, it took a net total of approximately 6.5 h to writing and reading 8 bytes of data, that equal to a storaging speed of 49 min/byte, much quicker than the previously reported 2.8-4.2 h/byte. This bead-based miniaturized device promises an unattended protocol for achieving high-throughput, full-packaged, and above all, neatly precision DNA storage.

Digital Microfluidics for Sample Preparation in Low-Input Proteomics

Low-input proteomics, also referred to as micro- or nanoproteomics, has become increasingly popular as it allows one to elucidate molecular processes in rare biological materials. A major prerequisite for the analytics of minute protein amounts, e.g., derived from low cell numbers, down to single cells, is the availability of efficient sample preparation methods. Digital microfluidics (DMF), a technology allowing the handling and manipulation of low liquid volumes, has recently been shown to be a powerful and versatile tool to address the challenges in low-input proteomics. Here, an overview is provided on recent advances in proteomics sample preparation using DMF. In particular, the capability of DMF to isolate proteomes from cells and small model organisms, and to perform all necessary chemical sample preparation steps, such as protein denaturation and proteolytic digestion on-chip, are highlighted. Additionally, major prerequisites to making these steps compatible with follow-up analytical methods such as liquid chromatography-mass spectrometry will be discussed.

Integration of paper-based analytical devices with digital microfluidics for colorimetric detection of creatinine

Digital microfluidics (DMF) is a platform that enables the automated manipulation of individual droplets of sizes ranging from nanoliter to microliter and can be coupled with numerous techniques, including colorimetry. However, although the DMF electrode architecture is highly versatile, its integration with different analytical methods often requires either changes in sample access, top plate design, or the integration of supplementary equipment into the system. As an alternative to overcome these challenges, this study proposes a simple integration between paper-based analytical devices (PADs) and DMF for automated and eco-friendly sample processing aiming at the colorimetric detection of creatinine (CR, an important biomarker for kidney disease) in artificial urine. An optimized and selective Jaffé reaction was performed on the device, and the reaction products were delivered to the PAD, which was subsequently analyzed with a bench scanner. The optimal operational parameters on the DMF platform were a reaction time of 45 s with circular mixing and image capture after 5 min. Under optimized conditions, a linear behavior was obtained for creatinine concentrations ranging from 2 to 32 mg dL-1, with limits of detection and quantitation equal to 1.4 mg dL-1 and 2.0 mg dL-1, respectively. For the concentration range tested, the relative standard deviation varied from 2.5 to 11.0%, considering four measurements per concentration. CR-spiked synthetic urine samples were subjected to analysis via DMF-PAD and the spectrophotometric reference method. The concentrations of CR determined using both analytical techniques were close to the theoretical values, with the resultant standard deviations of 2-9% and 1-4% for DMF-PADs and spectrophotometry, respectively. Furthermore, the recovery values were within the acceptable range, with DMF-PADs yielding 96-108% and spectrophotometry producing 95-102%. Finally, the greenness of the DMF-PAD and spectrophotometry methods was evaluated using the Analytical Greenness (AGREE) metric software, in which 0.71 and 0.51 scores were obtained, respectively. This indicates that the proposed method presents a higher greenness level, mainly due to its miniaturized characteristics using a smaller volume of reagent and sample and the possibility of automation, thus reducing user exposure to potentially toxic substances. Therefore, the DMF-PADs demonstrated great potential for application in the clinical analysis of creatinine, aiding in routine tests by introducing an automated, simple, and environmentally friendly process.

A multimodal digital microfluidic testing platform for antibody-producing cell lines

In recent years, monoclonal antibodies (mAbs) have become a powerful tool in the treatment of human diseases. Currently, over 100 mAbs have received approval for therapeutic use in the US, with wide-ranging applications from cancer to infectious diseases. The predominant method of producing antibodies for therapeutics involves expression in mammalian cell lines. In the mAb production process, significant optimization is typically done to maximize antibody titres from cells grown in bioreactors. Therefore, systems that can miniaturize and automate cell line testing (e.g., viability and antibody production assays) are valuable in reducing therapeutic mAb development costs. Here we present a novel platform for cell line optimization for mAb production using digital microfluidics. The platform enables testing of cell culture samples in 6-8 μL droplets with semi-automated viability, media pH, and antibody production assays. This system provides a unique bridge between cell growth and productivity metrics, while minimizing culture volume requirements for daily testing. We propose that this technology and its future iterations has the potential to help reduce the time-to-market and development costs of antibody-producing cell lines.

Emerging Trends in Integrated Digital Microfluidic Platforms for Next-Generation Immunoassays

Technologies based on digital microfluidics (DMF) have made significant advancements in the automated manipulation of microscale liquids and complex multistep processes. Due to their numerous benefits, such as automation, speed, cost-effectiveness, and minimal sample volume requirements, these systems are particularly well suited for immunoassays. In this review, an overview is provided of diverse DMF manipulation platforms and their applications in immunological analysis. Initially, droplet-driven DMF platforms based on electrowetting on dielectric (EWOD), magnetic manipulation, surface acoustic wave (SAW), and other related technologies are briefly introduced. The preparation of DMF is then described, including material selection, fabrication techniques and droplet generation. Subsequently, a comprehensive account of advancements in the integration of DMF with various immunoassay techniques is offered, encompassing colorimetric, direct chemiluminescence, enzymatic chemiluminescence, electrosensory, and other immunoassays. Ultimately, the potential challenges and future perspectives in this burgeoning field are delved into.

Toward Analysis at the Point of Need: A Digital Microfluidic Approach to Processing Multi-Source Sexual Assault Samples

Forensic case samples collected in sexual assaults typically contain DNA from multiple sources, which complicates short-tandem repeat (STR) profiling. These samples are typically sent to a laboratory to separate the DNA from sperm and non-sperm sources prior to analysis. Here, the automation and miniaturization of these steps using digital microfluidics (DMF) is reported, which may eventually enable processing sexual assault samples outside of the laboratory, at the point of need. When applied to vaginal swab samples collected up to 12 h post-coitus (PC), the new method identifies single-source (male) STR profiles. When applied to samples collected 24-72 h PC, the method identifies mixed STR profiles, suggesting room for improvement and/or potential for data deconvolution. In sum, an automated, miniaturized sample pre-processing method for separating the DNA contained in sexual assault samples is demonstrated. This type of automated processing using DMF, especially when combined with Rapid DNA Analysis, has the potential to be used for processing of sexual assault samples in hospitals, police offices, and other locations outside of the laboratory.

A versatile dilution-treatment-detection microfluidic chip platform for rapid In vitro lung cancer drug combination sensitivity evaluation

Combination drug therapy represents an effective strategy for treating certain drug-resistant and intractable cancer cases. However, determining the optimal combination of drugs and dosages is challenging due to clonal diversity in patients' tumors and the lack of rapid drug sensitivity evaluation methods. Microfluidic technology offers promising solutions to this issue. In this study, we propose a versatile microfluidic chip platform capable of integrating all processes, including dilution, treatment, and detection, for in vitro drug sensitivity assays. This platform innovatively incorporates several modules, including automated discrete drug logarithmic concentration generation, on-chip cell perfusion culture, and parallel drug treatments of cancer cell models. Moreover, it is compatible with microplate readers or high-content imaging systems for swift detection and automated monitoring, simplifying on-chip drug evaluation. Proof of concept is demonstrated by assessing the in vitro potency of two drugs, cisplatin, and etoposide, against the lung adenocarcinoma A549 cell line, under both single-drug and combination treatment conditions. The findings reveal that, compared to conventional microplate approaches with static cultivation, this on-chip automated perfusion bioassays yield comparable IC50 values with lower variation and a 50 % reduction in drug preparation time. This versatile dilution-treatment-detection microfluidic platform offers a promising tool for rapid and precise drug assessments, facilitating in vitro drug sensitivity evaluation in personalized cancer chemotherapy.

Open and closed microfluidics for biosensing

Biosensing is vital for many areas like disease diagnosis, infectious disease prevention, and point-of-care monitoring. Microfluidics has been evidenced to be a powerful tool for biosensing via integrating biological detection processes into a palm-size chip. Based on the chip structure, microfluidics has two subdivision types: open microfluidics and closed microfluidics, whose operation methods would be diverse. In this review, we summarize fundamentals, liquid control methods, and applications of open and closed microfluidics separately, point out the bottlenecks, and propose potential directions of microfluidics-based biosensing.

Programmable Gravity Self-Driven Microfluidic Chip for Point-of-Care Multiplied Immunoassays

Point-of-care testing (POCT) is experiencing a groundbreaking transformation with microfluidic chips, which offer precise fluid control and manipulation at the microscale. Nevertheless, chip design or operation for existing platforms is rather cumbersome, with some even heavily depending on external drivers or devices, impeding their broader utilization. This study develops a unique programmable gravity self-driven microfluidic chip (PGSMC) capable of simultaneous multi-reagent sequential release, multi-target analysis, and multi-chip operation. All necessary reagents are introduced in a single step, and the process is initiated simply by flipping the PGSMC vertically, eliminating the need for additional steps or devices. Additionally, it demonstrates successful immunoassays in less than 60 min for antinuclear antibodies testing, compared to more than 120 min by traditional methods. Assessment using 25 clinically diagnosed cases showcases remarkable sensitivity (96%), specificity (100%), and accuracy (99%). These outcomes underscored its potential as a promising platform for POCT with high accuracy, speed, and reliability, highlighting its capability for automated fluid control.

Polar coordinate active-matrix digital microfluidics for high-resolution concentration gradient generation

Automated concentration gradient generation is one of the most important applications of lab-on-a-chip devices. Digital microfluidics is a unique platform that can effectively achieve digitalized gradient concentration preparation. However, the dynamic range and concentration resolution of the prepared samples heavily rely on the size and the number of effective electrodes. In this work, we report an active-matrix digital microfluidic device with polar coordinate electrode arrangement. The device contains 33 different electrode sizes, generating digital droplets of different volumes. To compare with the conventional rectangular coordinate arrangement with a similar electrode number, this work shows an approximately 19 times resolution enhancement for the achievable concentration gradient. We characterized the stability and uniformity of droplets generated by electrodes of different sizes, and the coefficient of variation of stable droplets was less than 3%. The fluorescent nanomaterial's concentration quantification and glucose concentration characterization experiments were also conducted, and the correlation coefficients for the linearities were all above 0.99.

Rapid automated extracellular vesicle isolation and miRNA preparation on a cost-effective digital microfluidic platform

As a prerequisite for extracellular vesicle (EV) -based studies and diagnosis, effective isolation, enrichment and retrieval of EV biomarkers are crucial to subsequent analyses, such as miRNA-based liquid biopsy for non-small-cell lung cancer (NSCLC). However, most conventional approaches for EV isolation suffer from lengthy procedure, high cost, and intense labor. Herein, we introduce the digital microfluidic (DMF) technology to EV pretreatment protocols and demonstrate a rapid and fully automated sample preparation platform for clinical tumor liquid biopsy. Combining a reusable DMF chip technique with a low-cost EV isolation and miRNA preparation protocol, the platform completes automated sample processing in 20-30 min, supporting immediate RT-qPCR analyses on EV-derived miRNAs (EV-miRNAs). The utility and reliability of the platform was validated via clinical sample processing for EV-miRNA detection. With 23 tumor and 20 non-tumor clinical plasma samples, we concluded that EV-miR-486-5p and miR-21-5p are effective biomarkers for NSCLC with a small sample volumn (20-40 μL). The result was consistent to that of a commercial exosome miRNA extraction kit. These results demonstrate the effectiveness of DMF in EV pretreatment for miRNA detection, providing a facile solution to EV isolation for liquid biopsy.

PhageBox: An Open Source Digital Microfluidic Extension With Applications for Phage Discovery

OBJECTIVE

Recent advancements demonstrate the significant role of digital microfluidics in automating laboratory work with DNA and on-site viral testing. However, since commercially available instruments are limited to droplet manipulation, our work addresses the need for accelerated integration of other components, such as temperature control, that can expand the application domain.

METHODS

We developed PhageBox-an accessible device that can be used as a biochip extension. At hardware level, PhageBox integrates temperature and electromagnetic control modules. At software level, PhageBox is controlled by embedded software containing a unique model for bio-protocol programming, and a graphical user interface for visual device feedback and operation.

RESULTS

To evaluate PhageBox's efficacy for biomedical applications, we performed functional testing. Similarly, we validated the temperature control using thermography, obtaining a range of ±0.2[Formula: see text]. The electromagnets produced a magnetic force of 15 milliTesla, demonstrating precise immobilization of magnetic beads. We show the potential of PhageBox for bacteriophage research through three initial protocols: a universal framework for PCR, T7 bacteriophage restriction enzyme digestion, and concentrating ϕX174 RF genomic DNA.

CONCLUSION

Our work presents an open-source hardware and software extension for digital microfluidics devices. This extension integrates temperature and electromagnetic modules, demonstrating efficacy in biomedical applications and potential for bacteriophage research.

SIGNIFICANCE

We developed PhageBox to be accessible: the components are off-the-shelf at a low cost ( ≤ $200), and the hardware designs and software code are open-source. With the long aim of ensuring reproducibility and accelerating collaboration, we also provide a DIY-build document.

A microfluidic cover converts a standard 96-well plate into a mass-transport-controlled immunoassay system

96-well microtiter plates, widely used in immunoassays, face challenges such as prolonged assay time and limited sensitivity due to the lack of analyte transport control. Orbital shakers, commonly employed to facilitate mass transport, offer limited improvements and can introduce assay inconsistencies. While microfluidic devices offer performance enhancements, their complexity and incompatibility with existing platforms limit their wide adoption. This study introduces a novel microfluidic 96-well cover designed to convert a standard 96-well plate to a mass-transport-controlled surface bioreactor. The cover employs microfluidic methods to enhance the diffusion flux of analytes toward the receptors immobilized on the well bottom. Both simulation and experimental results demonstrated that the cover significantly enhances the capture rate of analyte molecules, resulting in increased signal strength for various detection methods and a lower detection limit. The cover serves as an effective add-on to standard 96-well plates, offering enhanced assay performance without requiring modifications to existing infrastructure or reagents. This innovation holds promise for improving the efficiency and reliability of microtiter plate based immunoassays.

Digital microfluidics with distance-based detection - a new approach for nucleic acid diagnostics

There is great enthusiasm for using loop-mediated isothermal amplification (LAMP) in point-of-care nucleic acid amplification tests (POC NAATs), as an alternative to PCR. While isothermal amplification techniques like LAMP eliminate the need for rapid temperature cycling in a portable format, these systems are still plagued by requirements for dedicated optical detection apparatus for analysis and manual off-chip sample processing. Here, we developed a new microfluidic system for LAMP-based POC NAATs to address these limitations. The new system combines digital microfluidics (DMF) with distance-based detection (DBD) for direct signal readout. This is the first report of the use of (i) LAMP or (ii) DMF with DBD - thus, we describe a number of characterization steps taken to determine optimal combinations of reagents, materials, and processes for reliable operation. For example, DBD was found to be quite sensitive to background signals from low molecular weight LAMP products; thus, a Capto™ adhere bead-based clean-up procedure was developed to isolate the desirable high-molecular-weight products for analysis. The new method was validated by application to detection of SARS-CoV-2 in saliva. The method was able to distinguish between saliva containing no virus, saliva containing a low viral load (104 genome copies per mL), and saliva containing a high viral load (108 copies per mL), all in an automated system that does not require detection apparatus for analysis. We propose that the combination of DMF with distance-based detection may be a powerful one for implementing a variety of POC NAATs or for other applications in the future.

Advanced design and applications of digital microfluidics in biomedical fields: An update of recent progress

Significant breakthroughs have been made in digital microfluidic (DMF)-based technologies over the past decades. DMF technology has attracted great interest in bioassays depending on automatic microscale liquid manipulations and complicated multi-step processing. In this review, the recent advances of DMF platforms in the biomedical field were summarized, focusing on the integrated design and applications of the DMF system. Firstly, the electrowetting-on-dielectric principle, fabrication of DMF chips, and commercialization of the DMF system were elaborated. Then, the updated droplets and magnetic beads manipulation strategies with DMF were explored. DMF-based biomedical applications were comprehensively discussed, including automated sample preparation strategies, immunoassays, molecular diagnosis, blood processing/testing, and microbe analysis. Emerging applications such as enzyme activity assessment and DNA storage were also explored. The performance of each bioassay was compared and discussed, providing insight into the novel design and applications of the DMF technology. Finally, the advantages, challenges, and future trends of DMF systems were systematically summarized, demonstrating new perspectives on the extensive applications of DMF in basic research and commercialization.

Immunity of Canadians and risk of epidemics workshop - Conference report

On November 18-19, 2019, the Immunity of Canadians and Risk of Epidemics (iCARE) Network convened a workshop in Toronto, Ontario, Canada. The objectives of the workshop were to raise the profile of sero-epidemiology in Canada, discuss best practice and methodological innovations, and strategize on the future direction of sero-epidemiology work in Canada. In this conference report, we describe the presentations and discussions from the workshop, and comment on the impact of the COVID-19 pandemic on serosurveillance initiatives, both in Canada and abroad.

Disposable Device for Bacterial Vaginosis Detection

Due to the increasing demand for clinical testing of infectious diseases at the point-of-care, the global market claims alternatives for rapid diagnosis tools such as disposable biosensors, avoiding the need for specialized laboratories and skilled personnel. Bacterial vaginosis (BV) is an infectious disease that commonly affects reproductive-age women and predisposes the infection of sexually transmitted diseases. Especially in asymptomatic cases, BV can lead to pelvic inflammatory conditions, postpartum endometritis, and preterm labor. Conventionally, BV diagnosis involves the microscopic analysis of vaginal swab samples; it thus requires highly trained personnel. In response, we report a novel microfluidic paper-based analytical device for BV diagnosis. Sialidase, a biomarker overexpressed in BV, was detected by exploiting an immunosensing mechanism previously discovered by our team. This technology employs a graphene oxide-coated surface as a quencher of fluorescence; the fluorescence of the immunoprobes that do not experiment immunoreactions (antibody-antigen) are deactivated by graphene oxide via non-radiative energy transfer, whereas those immunoprobes undergoing immunoreactions preserve their photoluminescence due to the distance and the low affinity between the immunocomplex and the graphene oxide-coated surface. Our paper-based test was typically carried out within 20 min, and the sample volume was 6 μL. Besides, it was tested with 14 vaginal swabs specimens to discriminate clinical samples of women with normal microbiota from those with BV. Our disposable device represents a new tool to prevent the consequences of BV.

Rapid, low-cost fabrication of electronic microfluidics via inkjet-printing and xurography (MINX)

Microfluidics has shown great promise for point-of-care assays due to unique chemical and physical advantages that occur at the micron scale. Furthermore, integration of electrodes into microfluidic systems provides additional capabilities for assay operation and electronic readout. However, while these systems are abundant in biological and biomedical research settings, translation of microfluidic devices with embedded electrodes are limited. In part, this is due to the reliance on expensive, inaccessible, and laborious microfabrication techniques. Although innovative prior work has simplified microfluidic fabrication or inexpensively patterned electrodes, low-cost, accessible, and robust methods to incorporate all these elements are lacking. Here, we present MINX, a low-cost <1 USD and rapid (∼minutes) fabrication technique to manufacture microfluidic device with embedded electrodes. We characterize the structures created using MINX, and then demonstrate the utility of the approach by using MINX to implement an electrochemical bead-based biomarker detection assay. We show that the MINX technique enables the scalable, inexpensive fabrication of microfluidic devices with electronic sensors using widely accessible desktop machines and low-cost materials.

Enhanced absorbance detection system for online bacterial monitoring in digital microfluidics

We report a fully integrated digital microfluidic absorbance detection system with an enhanced sensitivity for online bacterial monitoring. Through a 100 μm gap in the chip, our optical detection system has a detection sensitivity for a BCA protein concentration of 0.1 mg mL-1. The absorbance detection limit of our system is 1.4 × 10-3 OD units, which is one order of magnitude better than that of the existing studies. The system's linear region is 0.1-7 mg mL-1, and the dynamic range is 0-25 mg mL-1. We measured the growth curves of wild-type and E. coli transformed with resistance plasmids and mixed at different ratios on chip. We sorted out the bacterial species including highly viable single cells based on the difference in absorbance data of growth curves. We explored the changes in the growth curves of E. coli under different concentrations of resistant media. In addition, we successfully screened for the optimal growth environment of the bacteria, in which the growth rate of PET30a-DH5α (in a medium with 33 μg mL-1 kanamycin resistance) was significantly higher than that of a 1 mg mL-1 resistance medium. In conclusion, the enhanced digital microfluidic absorbance detection system exhibits exceptional sensitivity, enabling precise bacterial monitoring and growth curve analysis, while also laying the foundation for DMF-based automated bioresearch platforms, thus advancing research in the life sciences.

Prospects of Microfluidic Technology in Nucleic Acid Detection Approaches

Conventional diagnostic techniques are based on the utilization of analyte sampling, sensing and signaling on separate platforms for detection purposes, which must be integrated to a single step procedure in point of care (POC) testing devices. Due to the expeditious nature of microfluidic platforms, the trend has been shifted toward the implementation of these systems for the detection of analytes in biochemical, clinical and food technology. Microfluidic systems molded with substances such as polymers or glass offer the specific and sensitive detection of infectious and noninfectious diseases by providing innumerable benefits, including less cost, good biological affinity, strong capillary action and simple process of fabrication. In the case of nanosensors for nucleic acid detection, some challenges need to be addressed, such as cellular lysis, isolation and amplification of nucleic acid before its detection. To avoid the utilization of laborious steps for executing these processes, advances have been deployed in this perspective for on-chip sample preparation, amplification and detection by the introduction of an emerging field of modular microfluidics that has multiple advantages over integrated microfluidics. This review emphasizes the significance of microfluidic technology for the nucleic acid detection of infectious and non-infectious diseases. The implementation of isothermal amplification in conjunction with the lateral flow assay greatly increases the binding efficiency of nanoparticles and biomolecules and improves the limit of detection and sensitivity. Most importantly, the deployment of paper-based material made of cellulose reduces the overall cost. Microfluidic technology in nucleic acid testing has been discussed by explicating its applications in different fields. Next-generation diagnostic methods can be improved by using CRISPR/Cas technology in microfluidic systems. This review concludes with the comparison and future prospects of various microfluidic systems, detection methods and plasma separation techniques used in microfluidic devices.

Large-Area Electronics-Enabled High-Resolution Digital Microfluidics for Parallel Single-Cell Manipulation

Large-area electronics as switching elements are an ideal option for electrode-array-based digital microfluidics. With support of highly scalable thin-film semiconductor technology, high-resolution digital droplets (diameter around 100 μm) containing single-cell samples can be manipulated freely on a two-dimensional plane with programmable addressing logic. In addition, single-cell generation and manipulation as foundations for single-cell research demand ease of operation, multifunctionality, and accurate tools. In this work, we reported an active-matrix digital microfluidic platform for single-cell generation and manipulation. The active device contained 26,368 electrodes that could be independently addressed to perform parallel and simultaneous droplet generation and achieved single-cell manipulation. We demonstrate a high-resolution digital droplet generation with a droplet volume limit of 500 pL and show the continuous and stable movement of droplet-contained cells for over 1 h. Furthermore, the success rate of single droplet formation was higher than 98%, generating tens of single cells within 10 s. In addition, a pristine single-cell generation rate of 29% was achieved without further selection procedures, and the droplets containing single cells could then be tested for on-chip cell culturing. After 20 h of culturing, about 12.5% of the single cells showed cell proliferation.

Integrated Digital Microfluidics NMR Spectroscopy: A Key Step toward Automated In Vivo Metabolomics

Toxicity testing is currently undergoing a paradigm shift from examining apical end points such as death, to monitoring sub-lethal toxicity in vivo. In vivo nuclear magnetic resonance (NMR) spectroscopy is a key platform in this endeavor. A proof-of-principle study is presented which directly interfaces NMR with digital microfluidics (DMF). DMF is a "lab on a chip" method allowing for the movement, mixing, splitting, and dispensing of μL-sized droplets. The goal is for DMF to supply oxygenated water to keep the organisms alive while NMR detects metabolomic changes. Here, both vertical and horizontal NMR coil configurations are compared. While a horizontal configuration is ideal for DMF, NMR performance was found to be sub-par and instead, a vertical-optimized single-sided stripline showed most promise. In this configuration, three organisms were monitored in vivo using ¹H-¹³C 2D NMR. Without support from DMF droplet exchange, the organisms quickly showed signs of anoxic stress; however, with droplet exchange, this was completely suppressed. The results demonstrate that DMF can be used to maintain living organisms and holds potential for automated exposures in future. However, due to numerous limitations of vertically orientated DMF, along with space limitations in standard bore NMR spectrometers, we recommend future development be performed using a horizontal (MRI style) magnet which would eliminate practically all the drawbacks identified here.

3D-printed capillaric ELISA-on-a-chip with aliquoting

Sandwich immunoassays such as the enzyme-linked immunosorbent assay (ELISA) have been miniaturized and performed in a lab-on-a-chip format, but the execution of the multiple assay steps typically requires a computer or complex peripherals. Recently, an ELISA for detecting antibodies was encoded structurally in a chip thanks to the microfluidic chain reaction (Yafia et al. Nature, 2022, 605, 464-469), but the need for precise pipetting and intolerance to commonly used surfactant concentrations limit the potential for broader adoption. Here, we introduce the ELISA-on-a-chip with aliquoting functionality that simplifies chip loading and pipetting, accommodates higher surfactant concentrations, includes barrier channels that delay the contact between solutions and prevent undesired mixing, and that executed a quantitative, high-sensitivity assay for the SARS-CoV-2 nucleocapsid protein in 4×-diluted saliva. Upon loading the chip using disposable pipettes, capillary flow draws each reagent and the sample into a separate volumetric measuring reservoir for detection antibody (70 μL), enzyme conjugate (50 μL), substrate (80 μL), and sample (210 μL), and splits washing buffer into 4 different reservoirs of 40, 40, 60, and 20 μL. The excess volume is autonomously drained via a structurally encoded capillaric aliquoting circuit, creating aliquots with an accuracy of >93%. Next, the user click-connects the assay module, comprising a nitrocellulose membrane with immobilized capture antibodies and a capillary pump, to the chip which triggers the step-by-step, timed flow of all aliquoted solutions to complete the assay in 1.5 h. A colored precipitate forming a line on a nitrocellulose strip serves as an assay readout, and upon digitization, yielded a binding curve with a limit of detection of 54 and 91 pg mL^-1 for buffer and diluted saliva respectively, vastly outperforming rapid tests. The ELISA chip is 3D-printed, modular, adaptable to other targets and assays, and could be used to automate ELISA in the lab; or as a diagnostic test at the point of care with the convenience and form factor of rapid tests while preserving the protocol and performance of central laboratory ELISA.

Digital microfluidic platform assembled into a home-made studio for sample preparation and colorimetric sensing of S-nitrosocysteine

Digital microfluidics (DMF) is a versatile lab-on-a-chip platform that allows integration with several types of sensors and detection techniques, including colorimetric sensors. Here, we propose, for the first time, the integration of DMF chips into a mini studio containing a 3D-printed holder with previously fixed UV-LEDs to promote sample degradation on the chip surface before a complete analytical procedure involving reagent mixture, colorimetric reaction, and detection through a webcam integrated on the equipment. As a proof-of-concept, the feasibility of the integrated system was successfully through the indirect analysis of S-nitrosocysteine (CySNO) in biological samples. For this purpose, UV-LEDs were explored to perform the photolytic cleavage of CySNO, thus generating nitrite and subproducts directly on DMF chip. Nitrite was then colorimetrically detected based on a modified Griess reaction, in which reagents were prepared through a programable movement of droplets on DMF devices. The assembling and the experimental parameters were optimized, and the proposed integration exhibited a satisfactory correlation with the results acquired using a desktop scanner. Under the optimal experimental conditions, the obtained CySNO degradation to nitrite was 96%. Considering the analytical parameters, the proposed approach revealed linear behavior in the CySNO concentration range between 12.5 and 400 μmol L^-1 and a limit of detection equal to 2.8 μmol L^-1. Synthetic serum and human plasma samples were successfully analyzed, and the achieved results did not statistically differ from the data recorded by spectrophotometry at the confidence level of 95%, thus indicating the huge potential of the integration between DMF and mini studio to promote complete analysis of lowmolecular weight compounds.

Digital microfluidics for biological analysis and applications

Digital microfluidics (DMF) is an emerging liquid-handling technology based on arrays of microelectrodes for the precise manipulation of discrete droplets. DMF offers the benefits of automation, addressability, integration and dynamic configuration ability, and provides enclosed picoliter-to-microliter reaction space, making it suitable for lab-on-a-chip biological analysis and applications that require high integration and intricate processes. A review of DMF bioassays with a special emphasis on those actuated by electrowetting on dielectric (EWOD) force is presented here. Firstly, a brief introduction is presented on both the theory of EWOD actuation and the types of droplet motion. Subsequently, a comprehensive overview of DMF-based biological analysis and applications, including nucleic acid, protein, immunoreaction and cell assays, is provided. Finally, a discussion on the strengths, challenges, and potential applications and perspectives in this field is presented.

Antifouling Properties of Pluronic and Tetronic Surfactants in Digital Microfluidics

Fouling at liquid-solid interfaces is a pernicious problem for a wide range of applications, including those that are implemented by digital microfluidics (DMF). There are several strategies that have been used to combat surface fouling in DMF, the most common being inclusion of amphiphilic surfactant additives in the droplets to be manipulated. Initial studies relied on Pluronic additives, and more recently, Tetronic additives have been used, which has allowed manipulation of complex samples like serum and whole blood. Here, we report our evaluation of 19 different Pluronic and Tetronic additives, with attempts to determine (1) the difference in antifouling performance between the two families, (2) the structural similarities that predict exceptional antifouling performance, and (3) the mechanism of the antifouling behavior. Our analysis shows that both Pluronic and Tetronic additives with modest molar mass, poly(propylene oxide) (PPO) ≥50 units, poly(ethylene oxide) (PEO) mass percentage ≤50%, and hydrophilic-lipophilic balance (HLB) ca. 13-15 allow for exceptional antifouling performance in DMF. The most promising candidates, P104, P105, and T904, were able to support continuous movement of droplets of serum for more than 2 h, a result (for devices operating in air) previously thought to be out of reach for this technique. Additional results generated using device longevity assays, intrinsic fluorescence measurements, dynamic light scattering, asymmetric flow field flow fractionation, supercritical angle fluorescence microscopy, atomic force microscopy, and quartz crystal microbalance measurements suggest that the best-performing surfactants are more likely to operate by forming a protective layer at the liquid-solid interface than by complexation with proteins. We propose that these results and their implications are an important step forward for the growing community of users of this technique, which may provide guidance in selecting surfactants for manipulating biological matrices for a wide range of applications.

Combining sensors and actuators with electrowetting-on-dielectric (EWOD): advanced digital microfluidic systems for biomedical applications

The concept of digital microfluidics (DMF) enables highly flexible and precise droplet manipulation at a picoliter scale, making DMF a promising approach to realize integrated, miniaturized "lab-on-a-chip" (LOC) systems for research and clinical purposes. Owing to its simplicity and effectiveness, electrowetting-on-dielectric (EWOD) is one of the most commonly studied and applied effects to implement DMF. However, complex biomedical assays usually require more sophisticated sample handling and detection capabilities than basic EWOD manipulation. Alternatively, combined systems integrating EWOD actuators and other fluidic handling techniques are essential for bringing DMF into practical use. In this paper, we briefly review the main approaches for the integration/combination of EWOD with other microfluidic manipulation methods or additional external fields for specified biomedical applications. The form of integration ranges from independently operating sub-systems to fully coupled hybrid actuators. The corresponding biomedical applications of these works are also summarized to illustrate the significance of these innovative combination attempts.

Colorimetric and Raman dual-mode lateral flow immunoassay detection of SARS-CoV-2 N protein antibody based on Ag nanoparticles with ultrathin Au shell assembled onto Fe3O4 nanoparticles

Serological antibody tests are useful complements of nuclei acid detection for SARS-CoV-2 diagnosis, which can significantly improve diagnostic accuracy. However, antibody detection in serum or plasma remains challenging to do with high sensitivity. In this study, Ag nanoparticles with ultra-thin Au shells embedded with 4-mercaptobenzoic acid (MBA) (Ag^MBA@Au) were manufactured and then assembled onto Fe₃O₄ surface by electrostatic interaction to construct the Fe₃O₄-Ag^MBA@Au nanoparticles (NPs) with magnetic-Raman-colorimetric properties. Based on the composite nanoparticles, a colorimetric and Raman dual-mode lateral flow immunoassay (LFIA) for ultrasensitive identification of SARS-CoV-2 nucleocapsid (N) protein antibody was constructed. The magnetic nanoparticles (Fe₃O₄ NPs) were acted as the core and coated a layer of Ag^MBA@Au particles on the surface by electrostatic interaction to prepare Fe₃O₄-Ag^MBA@Au NPs, which can amplify the SERS signal due to multiple Ag^MBA@Au particles concentrated on a single magnetic nanoparticle. Moreover, the Fe₃O₄-Ag^MBA@Au NPs facilitated pre-purifying sample using magnetic separation, and complex matrix interference would be greatly decreased in the detection. The Fe₃O₄-Ag^MBA@Au NPs modified with N protein recognized and bound with N protein antibodies, which were trapped on the T-line, forming color band for observing detection. Under optimal conditions, the N protein antibodies could be qualitatively detected in colorimetric mode with the visual limit of 10^-8 mg/mL and quantitatively detected by SERS signals between 10^-6 and 10^-10 mg /mL with 0.08 pg/mL detection limit. The coefficients variations (CV) of intra-assay was 8.0%, whereas of inter-assay was 11.7%, confirming of good reproducibility. Finally, this approach was able to discriminate between positive, negative, and weakly positive samples when detecting 107 clinical serum samples. The process enables highly sensitive quantitative assays that are valuable for evaluating disease processes and guiding treatment. Colorimetric and Raman dual-mode LFIA detection of SARS-CoV-2 N protein antibody based on Fe₃O₄-Ag^MBA@Au nanoparticles.

Use of a rapid digital microfluidics-powered immunoassay for assessing measles and rubella infection and immunity in outbreak settings in the Democratic Republic of the Congo

The Democratic Republic of the Congo (DRC) has a high measles incidence despite elimination efforts and has yet to introduce rubella vaccine. We evaluated the performance of a prototype rapid digital microfluidics powered (DMF) enzyme-linked immunoassay (ELISA) assessing measles and rubella infection, by testing for immunoglobulin M (IgM), and immunity from natural infection or vaccine, by testing immunoglobulin G (IgG), in outbreak settings. Field evaluations were conducted during September 2017, in Kinshasa province, DRC. Blood specimens were collected during an outbreak investigation of suspected measles cases and tested for measles and rubella IgM and IgG using the DMF-ELISA in the field. Simultaneously, a household serosurvey for measles and rubella IgG was conducted in a recently confirmed measles outbreak area. DMF-ELISA results were compared with reference ELISA results tested at DRC's National Public Health Laboratory and the US Centers for Disease Control and Prevention. Of 157 suspected measles cases, rubella IgM was detected in 54% while measles IgM was detected in 13%. Measles IgG-positive cases were higher among vaccinated persons (87%) than unvaccinated persons (72%). In the recent measles outbreak area, measles IgG seroprevalence was 93% overall, while rubella seroprevalence was lower for children (77%) than women (98%). Compared with reference ELISA, DMF-ELISA sensitivity and specificity were 82% and 78% for measles IgG; 88% and 89% for measles IgM; 85% and 85% for rubella IgG; and 81% and 83% for rubella IgM, respectively. Rubella infection was detected in more than half of persons meeting the suspected measles case definition during a presumed measles outbreak, suggesting substantial unrecognized rubella incidence, and highlighting the need for rubella vaccine introduction into the national schedule. The performance of the DMF-ELISA suggested that this technology can be used to develop rapid diagnostic tests for measles and rubella.

A chemical timer approach to delayed chemiluminescence

Although the onset time of chemical reactions can be manipulated by mechanical, electrical, and optical methods, its chemical control remains highly challenging. Herein, we report a chemical timer approach for manipulating the emission onset time of chemiluminescence (CL) reactions. A mixture of Mn²⁺, NaHCO₃, and a luminol analog with H₂O₂ produced reactive oxygen species (ROS) radicals and other superoxo species (superoxide containing complex) with high efficiency, accompanied by strong and immediate CL emission. Surprisingly, the addition of thiourea postponed CL emission in a concentration-dependent manner. The delay was attributed to a slow-generation-scavenging mechanism, which was found to be generally applicable not only to various types of CL reagents and ROS radical scavengers but also to popular chromogenic reactions. The precise regulation of CL kinetics was further utilized in dynamic chemical coding with improved coding density and security. This approach provides a powerful platform for engineering chemical reaction kinetics using chemical timers, which is of application potential in bioassays, biosensors, CL microscopic imaging, microchips, array chips, and informatics.

Translating diagnostics and drug delivery technologies to low-resource settings

Diagnostics and drug delivery technologies engineered for low-resource settings aim to meet their technical design specifications using strategies that are compatible with limited equipment, infrastructure, and operator training. Despite many preclinical successes, very few of these devices have been translated to the clinic. Here, we identify factors that contribute to the clinical success of diagnostics and drug delivery systems for low-resource settings, including the need to engage key stakeholders at an early stage, and provide recommendations for the clinical translation of future medical technologies.

Technologies for Frugal and Sensitive Point-of-Care Immunoassays

Immunoassays are a powerful tool for sensitive and quantitative analysis of a wide range of biomolecular analytes in the clinic and in research laboratories. However, enzyme-linked immunosorbent assay (ELISA)-the gold-standard assay-requires significant user intervention, time, and clinical resources, making its deployment at the point-of-care (POC) impractical. Researchers have made great strides toward democratizing access to clinical quality immunoassays at the POC and at an affordable price. In this review, we first summarize the commercially available options that offer high performance, albeit at high cost. Next, we describe strategies for the development of frugal POC assays that repurpose consumer electronics and smartphones for the quantitative detection of analytes. Finally, we discuss innovative assay formats that enable highly sensitive analysis in the field with simple instrumentation.

A Digital Microfluidic Device Integrated with Electrochemical Impedance Spectroscopy for Cell-Based Immunoassay

The dynamic immune response to various diseases and therapies has been considered a promising indicator of disease status and therapeutic effectiveness. For instance, the human peripheral blood mononuclear cell (PBMC), as a major player in the immune system, is an important index to indicate a patient's immune function. Therefore, establishing a simple yet sensitive tool that can frequently assess the immune system during the course of disease and treatment is of great importance. This study introduced an integrated system that includes an electrochemical impedance spectroscope (EIS)-based biosensor in a digital microfluidic (DMF) device, to quantify the PBMC abundance with minimally trained hands. Moreover, we exploited the unique droplet manipulation feature of the DMF platform and conducted a dynamic cell capture assay, which enhanced the detection signal by 2.4-fold. This integrated system was able to detect as few as 104 PBMCs per mL, presenting suitable sensitivity to quantify PBMCs. This integrated system is easy-to-operate and sensitive, and therefore holds great potential as a powerful tool to profile immune-mediated therapeutic responses in a timely manner, which can be further evolved as a point-of-care diagnostic device to conduct near-patient tests from blood samples.

All-in-One Digital Microfluidics System for Molecular Diagnosis with Loop-Mediated Isothermal Amplification

In this study, an “all-in-one” digital microfluidics (DMF) system was developed for automatic and rapid molecular diagnosis and integrated with magnetic bead-based nucleic acid extraction, loop-mediated isothermal amplification (LAMP), and real-time optical signal monitoring. First, we performed on- and off-chip comparison experiments for the magnetic bead nucleic acid extraction module and LAMP amplification function. The extraction efficiency for the on-chip test was comparable to that of conventional off-chip methods. The processing time for the automatic on-chip workflow was only 23 min, which was less than that of the conventional methods of 28 min 45 s. Meanwhile, the number of samples used in on-chip experiments was significantly smaller than that used in off-chip experiments; only 5 µL of E. coli samples was required for nucleic acid extraction, and 1 µL of the nucleic acid template was needed for the amplification reaction. In addition, we selected SARS-CoV-2 nucleic acid reference materials for the nucleic acid detection experiment, demonstrating a limit of detection of 10 copies/µL. The proposed “all-in-one” DMF system provides an on-site “sample to answer” time of approximately 60 min, which can be a powerful tool for point-of-care molecular diagnostics.

Portable sample processing for molecular assays: application to Zika virus diagnostics

This paper introduces a digital microfluidic (DMF) platform for portable, automated, and integrated Zika viral RNA extraction and amplification. The platform features reconfigurable DMF cartridges offering a closed, humidified environment for sample processing at elevated temperatures, as well as programmable control instrumentation with a novel thermal cycling unit regulated using a proportional integral derivative (PID) feedback loop. The system operates on 12 V DC power, which can be supplied by rechargeable battery packs for remote testing. The DMF system was optimized for an RNA processing pipeline consisting of the following steps: 1) magnetic-bead based RNA extraction from lysed plasma samples, 2) RNA clean-up, and 3) integrated, isothermal amplification of Zika RNA. The DMF pipeline was coupled to a paper-based, colorimetric cell-free protein expression assay for amplified Zika RNA mediated by toehold switch-based sensors. Blinded laboratory evaluation of Zika RNA spiked in human plasma yielded a sensitivity and specificity of 100% and 75% respectively. The platform was then transported to Recife, Brazil for evaluation with infectious Zika viruses, which were detected at the 100 PFU mL^-1 level from a 5 μL sample (equivalent to an RT-qPCR cycle threshold value of 32.0), demonstrating its potential as a sample processing platform for miniaturized diagnostic testing.

Development of an Aptamer-Based Electrochemical Microfluidic Device for Viral Vaccine Quantitation

Global deployment of vaccines poses significant challenges in the distribution and use of the accompanying immunoassays, one of the standard methods for quality control of vaccines, particularly when establishing assays in countries worldwide to support testing/release upon importation. This work describes our effort toward developing an integrated, portable device to carry out affinity assays for viral particles quantification in viral vaccines by incorporating (i) aptamers, (ii) microfluidic devices, and (iii) electrochemical detection. We generated and characterized more than eight aptamers against multiple membrane proteins of cytomegalovirus (CMV), which we used as a model system and designed and fabricated electrochemical microfluidic devices to measure CMV concentrations in a candidate vaccine under development. The aptamer-based assays provided a half maximal effective concentration, EC₅₀, of 12 U/mL, comparable to that of an ELISA using a pair of antibodies (EC₅₀ 60 U/mL). The device measured relative CMV concentrations accurately (within ±10% bias) and precisely (11%, percent relative standard deviation). This work represents the critical first steps toward developing simple, affordable, and robust affinity assays for global deployment without the need for sensitive equipment and extensive analyst training.

Novel Field-Based Protein Detection Method Using Light Transmission Spectroscopy and Antibody Functionalized Gold Nanoparticles

Protein detection is a universal tool critical to many applications in medicine, agriculture, and biotechnology. We developed a novel protein detection method combining light transmission spectroscopy and particle-size analysis of gold nanospheres monovalently functionalized with polyclonal antibodies and applied it to an emerging challenge for such technologies─the monitoring of environmental proteins (eProteins) present in natural aquatic systems. These are an underreported source of pollution and include the pseudopersistent Cry toxins that enter aquatic ecosystems from surrounding genetically engineered crops. The assay is capable of detecting proteins in complex matrices, such as water samples collected in the field, making it a competitive assay for eProtein detection. It is sensitive, reaching 1.25 ng mL^-1, and we demonstrate its application to the detection of Cry1Ab from subsurface tile-drain and streamwater samples from agricultural waterways. The assay can also be quickly adapted for other protein detection applications in the future.

Digital Microfluidics-Powered Real-Time Monitoring of Isothermal DNA Amplification of Cancer Biomarker

We introduce a digital microfluidics (DMF) platform specifically designed to perform a loop-mediated isothermal amplification (LAMP) of DNA and applied it to a real-time amplification to monitor a cancer biomarker, c-Myc (associated to 40% of all human tumors), using fluorescence microscopy. We demonstrate the full manipulation of the sample and reagents on the DMF platform, resulting in the successful amplification of 90 pg of the target DNA (0.5 ng/µL) in less than one hour. Furthermore, we test the efficiency of an innovative mixing strategy in DMF by employing two mixing methodologies onto the DMF droplets-low frequency AC (alternating current) actuation as well as back-and-forth droplet motion-which allows for improved fluorescence readouts. Fluorophore bleaching effects are minimized through on-chip sample partitioning by DMF processes and sequential droplet irradiation. Finally, LAMP reactions require only 2 µL volume droplets, which represents a 10-fold volume reduction in comparison to benchtop LAMP.

Field validation of the performance of paper-based tests for the detection of the Zika and chikungunya viruses in serum samples

In low-resource settings, resilience to infectious disease outbreaks can be hindered by limited access to diagnostic tests. Here we report the results of double-blinded studies of the performance of paper-based diagnostic tests for the Zika and chikungunya viruses in a field setting in Latin America. The tests involved a cell-free expression system relying on isothermal amplification and toehold-switch reactions, a purpose-built portable reader and onboard software for computer vision-enabled image analysis. In patients suspected of infection, the accuracies and sensitivities of the tests for the Zika and chikungunya viruses were, respectively, 98.5% (95% confidence interval, 96.2–99.6%, 268 serum samples) and 98.5% (95% confidence interval, 91.7–100%, 65 serum samples) and approximately 2 aM and 5 fM (both concentrations are within clinically relevant ranges). The analytical specificities and sensitivities of the tests for cultured samples of the viruses were equivalent to those of the real-time quantitative PCR. Cell-free synthetic biology tools and companion hardware can provide de-centralized, high-capacity and low-cost diagnostics for use in low-resource settings.

Dual-detection fluorescent immunochromatographic assay for quantitative detection of SARS-CoV-2 spike RBD-ACE2 blocking neutralizing antibody

The global effort against the COVID-19 pandemic dictates that routine quantitative detection of SARS-CoV-2 neutralizing antibodies is vital for assessing immunity following periodic revaccination against new viral variants. Here, we report a dual-detection fluorescent immunochromatographic assay (DFIA), with a built-in self-calibration process, that enables rapid quantitative detection of neutralizing antibodies that block binding between the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein and the angiotensin-converting enzyme 2 (ACE2). Thus, this assay is based on the inhibition of binding between ACE2 and the RBD of the SARS-CoV-2 spike protein by neutralizing antibodies, and the affinity of anti-human immunoglobulins for these neutralizing antibodies. Our self-calibrating DFIA shows improved precision and sensitivity with a wider dynamic linear range, due to the incorporation of a ratiometric algorithm of two-reverse linkage signals responding to an analyte. This was evident by the fact that no positive results (0/14) were observed in verified negative samples, while 22 positives were detected in 23 samples from verified convalescent plasma. A comparative analysis of the ability to detect neutralizing antibodies in 266 clinical serum samples including those from vaccine recipients, indicated that the overall percent agreement between DFIA and the commercial ELISA kit was 90.98%. Thus, the proposed DFIA provides a more reliable and accurate rapid test for detecting SARS-CoV-2 infections and vaccinations in the community. Therefore, the DFIA based strategy for detecting biomarkers, which uses a ratiometric algorithm based on affinity and inhibition reactions, may be applied to improve the performance of immunochromatographic assays.

Blood Group Testing

Red blood cell (RBC) transfusion is one of the most frequently performed clinical procedures and therapies to improve tissue oxygen delivery in hospitalized patients worldwide. Generally, the cross-match is the mandatory test in place to meet the clinical needs of RBC transfusion by examining donor-recipient compatibility with antigens and antibodies of blood groups. Blood groups are usually an individual's combination of antigens on the surface of RBCs, typically of the ABO blood group system and the RH blood group system. Accurate and reliable blood group typing is critical before blood transfusion. Serological testing is the routine method for blood group typing based on hemagglutination reactions with RBC antigens against specific antibodies. Nevertheless, emerging technologies for blood group testing may be alternative and supplemental approaches when serological methods cannot determine blood groups. Moreover, some new technologies, such as the evolving applications of blood group genotyping, can precisely identify variant antigens for clinical significance. Therefore, this review mainly presents a clinical overview and perspective of emerging technologies in blood group testing based on the literature. Collectively, this may highlight the most promising strategies and promote blood group typing development to ensure blood transfusion safety.

Digital Microfluidic qPCR Cartridge for SARS-CoV-2 Detection

Point-of-care (POC) tests capable of individual health monitoring, transmission reduction, and contact tracing are especially important in a pandemic such as the coronavirus disease 2019 (COVID-19). We develop a disposable POC cartridge that can be mass produced to detect the SARS-CoV-2 N gene through real-time quantitative polymerase chain reaction (qPCR) based on digital microfluidics (DMF). Several critical parameters are studied and improved, including droplet volume consistency, temperature uniformity, and fluorescence intensity linearity on the designed DMF cartridge. The qPCR results showed high accuracy and efficiency for two primer-probe sets of N1 and N2 target regions of the SARS-CoV-2 N gene on the DMF cartridge. Having multiple droplet tracks for qPCR, the presented DMF cartridge can perform multiple tests and controls at once.

Determination of blood lithium-ion concentration using digital microfluidic whole-blood separation and preloaded paper sensors

Existing microfluidic technologies for blood tests have several limitations, including difficulties in integrating the sample preparation steps, such as blood dilution, and precise metering of tiny samples (microliter) for accurate downstream analyses on a chip. Digital microfluidics (DMF) is a liquid manipulation technique that can provide precise volume control of micro or nano-liter liquid droplets. Without using sensitive but complex detection methods for tiny droplets involving fluorescence, luminescence, and electrochemistry, this article presents a DMF device with embedded paper-based sensors to detect blood lithium-ion (Li⁺) concentration by colorimetry. Dielectrophoresis on the DMF device between two parallel planar electrodes separates plasma droplets (from tens to hundreds of nanoliters in volume) from undiluted whole blood (a few microliters) within 4 min with an efficiency exceeding 90%. The embedded paper sensors contain a detection reagent to absorb the DMF-transported plasma droplets. These droplets change the color of the paper sensors in accordance with the Li⁺ concentration. Subsequently, colorimetry is used to reveal the Li⁺ concentration via image analysis. The proposed method meets the detection-sensitivity requirement for clinical diagnosis of bipolar disorder, making the DMF device a potential therapeutic tool for rapid whole-blood Li⁺ detection.