Digital Microfluidic Platform to Maximize Diagnostic Tests with Low Sample Volumes from Newborns and Pediatric Patients

A capillary-aided microfiber Bragg grating pH sensor for hydrovoltaic technology

Hydrovoltaic is an emerging technology that aims to harvest energy from water flow and evaporation, in which the plasmonic hydrogen ions are generated by the interaction between water and hydrovoltaic device. However, the volume of the water sample for the interaction is usually ultra-small due to the compact size of hydrovoltaic device, making the quantification and characterization of the hydrogen ions in such water sample an elusive goal. To address this issue, a miniature fiber-optic pH probe is proposed using a unilaterally tapered-microfiber Bragg grating. The microfiber Bragg grating has an intrinsic Bragg reflection signal with a narrow linewidth. The fiber probe is functionalized by coating the sodium alginate, which can respond to the variation of pH mediated by the alteration of the hydrophilicity. The rigidity and robustness of microfiber Bragg grating facilitates the encapsulation of the sensor into a sampling capillary, allowing for the detection of trace aqueous sample less than 2 μL. The pH sensitivity of the tapered-μFBG-based sensor is 62.8 p.m./pH (R2 = 0.995) with a limit resolution of 0.096 pH. The sensor performed a practical application in the monitoring and characterization of the hydrovoltaic microdevice, which can generate microcurrent as soaked in the water. This work demonstrates a promising technology in the fields of materials, energy, biology and medicine, in which the detection of the microsamples is inevitable.

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.

Preliminary Investigation into the Prevalence of G6PD Deficiency in a Pediatric African American Population Using a Near-Patient Diagnostic Platform

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is prevalent in the African American population. We identified eighteen G6PD-deficient samples (9%) in a study of residual, de-identified whole blood specimens from 200 African American pediatric patients using a point-of-care instrument. This highlights the possibility of a rapid time to result for G6PD testing, which can be valuable in some clinical scenarios.

A Deep Reinforcement Learning Approach to Droplet Routing for Erroneous Digital Microfluidic Biochips

Digital microfluidic biochips (DMFBs), which are used in various fields like DNA analysis, clinical diagnosis, and PCR testing, have made biochemical experiments more compact, efficient, and user-friendly than the previous methods. However, their reliability is often compromised by their inability to adapt to all kinds of errors. Errors in biochips can be categorized into two types: known errors, and unknown errors. Known errors are detectable before the start of the routing process using sensors or cameras. Unknown errors, in contrast, only become apparent during the routing process and remain undetected by sensors or cameras, which can unexpectedly stop the routing process and diminish the reliability of biochips. This paper introduces a deep reinforcement learning-based routing algorithm, designed to manage not only known errors but also unknown errors. Our experiments demonstrated that our algorithm outperformed the previous ones in terms of the success rate of the routing, in the scenarios including both known errors and unknown errors. Additionally, our algorithm contributed to detecting unknown errors during the routing process, identifying the most efficient routing path with a high probability.

Electrokinetic Thin-Film Model for Electrowetting: The Role of Bulk Charges

The electrowetting behavior of a charge-carrying sessile droplet is relevant to applications such as point-of-care diagnostics. Often biomedical assays involve droplets that contain charged molecules such as dissolved ions, proteins, and DNA. In this work, we develop a reduced-order electrokinetic model for electrowetting of such a charge-carrying droplet under a parallel-plate electrode configuration. An inertial-lubrication model based on the weighted residual integral boundary layer (WRIBL) technique is used to obtain evolution equations that describe the spatiotemporal evolution of the fluid-air interface and the depth-integrated flow rate. The solutions to the evolution equations are obtained numerically by using the spectral collocation method. We investigate the role of domain and surface charges, characterized by the Debye length, on droplet wetting. Under low relaxation timescales, both droplet deformation and wetting alteration under an AC field are shown to be equivalent to that under a root-mean-square (RMS) DC field. We show that an electrolytic sessile droplet can exhibit a larger deformation in comparison to the two asymptotic limits of a perfect conductor and a perfect dielectric droplet, corresponding, respectively, to very low and high Debye lengths. The effects of several other parameters such as the inherent equilibrium wettability, permittivity ratio, and electric field strength are also investigated.

Engineering Innovative Interfaces for Point-of-Care Diagnostics

The ongoing Coronavirus disease 2019 (COVID-19) pandemic illustrates the need for sensitive and reliable tools to diagnose and monitor diseases. Traditional diagnostic approaches rely on centralized laboratory tests that result in long wait times to results and reduce the number of tests that can be given. Point-of-care tests (POCTs) are a group of technologies that miniaturize clinical assays into portable form factors that can be run both in clinical areas --in place of traditional tests-- and outside of traditional clinical settings --to enable new testing paradigms. Hallmark examples of POCTs are the pregnancy test lateral flow assay and the blood glucose meter. Other uses for POCTs include diagnostic assays for diseases like COVID-19, HIV, and malaria but despite some successes, there are still unsolved challenges for fully translating these lower cost and more versatile solutions. To overcome these challenges, researchers have exploited innovations in colloid and interface science to develop various designs of POCTs for clinical applications. Herein, we provide a review of recent advancements in lateral flow assays, other paper based POCTs, protein microarray assays, microbead flow assays, and nucleic acid amplification assays. Features that are desirable to integrate into future POCTs, including simplified sample collection, end-to-end connectivity, and machine learning, are also discussed in this review.

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.

Microfluidic systems in clinical diagnosis

The use of microfluidic devices is highly attractive in the field of biomedical and clinical assessments, as their portability and fast response time have become crucial in providing opportune therapeutic treatments to patients. The applications of microfluidics in clinical diagnosis and point-of-care devices are continuously growing. The present review article discusses three main fields where miniaturized devices are successfully employed in clinical applications. The quantification of ions, sugars, and small metabolites is examined considering the analysis of bodily fluids samples and the quantification of this type of analytes employing real-time wearable devices. The discussion covers the level of maturity that the devices have reached as well as cost-effectiveness. The analysis of proteins with clinical relevance is presented and organized by the function of the proteins. The last section covers devices that can perform single-cell metabolomic and proteomic assessments. Each section discusses several strategically selected recent reports on microfluidic devices successfully employed for clinical assessments, to provide the reader with a wide overview of the plethora of novel systems and microdevices developed in the last 5 years. In each section, the novel aspects and main contributions of each reviewed report are highlighted. Finally, the conclusions and future outlook section present a summary and speculate on the future direction of the field of miniaturized devices for clinical applications.

Integrating machine learning and digital microfluidics for screening experimental conditions

Digital microfluidics (DMF) has the signatures of an ideal liquid handling platform - as shown through almost two decades of automated biological and chemical assays. However, in the current state of DMF, we are still limited by the number of parallel biological or chemical assays that can be performed on DMF. Here, we report a new approach that leverages design-of-experiment and numerical methodologies to accelerate experimental optimization on DMF. The integration of the one-factor-at-a-time (OFAT) experimental technique with machine learning algorithms provides a set of recommended optimal conditions without the need to perform a large set of experiments. We applied our approach towards optimizing the radiochemistry synthesis yield given the large number of variables that affect the yield. We believe that this work is the first to combine such techniques which can be readily applied to any other assays that contain many parameters and levels on DMF.

Optimization of Electrode Patterns for an ITO-Based Digital Microfluidic through the Finite Element Simulation

Indium tin oxide (ITO)-based digital microfluidics (DMF) with unique optical and electrical properties are promising in the development of integrated, automatic and portable analytical systems. The fabrication technique using laser direct etching (LDE) on ITO glass has the advantages of being rapid, low cost and convenient. However, the fabrication resolution of LDE limits the minimum line width for patterns on ITO glasses, leading to a related wider lead wire for the actuating electrodes of DMF compared with photolithography. Therefore, the lead wire of electrodes could affect the droplet motion on the digital microfluidic chip due to the increased contact line with the droplet. Herein, we developed a finite element model of a DMF with improved efficiency to investigate the effect of the lead wire. An optimized electrode pattern was then designed based on a theoretical analysis and validated by a simulation, which significantly decreased the deformation of the droplets down to 0.012 mm. The performance of the optimized electrode was also verified in an experiment. The proposed simulation method could be further extended to other DMF systems or applications to provide an efficient approach for the design and optimization of DMF chips.

Comparison of a chemiluminescence immunoassay and an enzyme immunoassay for detection of IgM antibodies against measles, mumps, rubella, cytomegalovirus (CMV), Epstein Barr virus (EBV), and human herpes virus (HHV) -1 and -2 infections

PURPOSE

Outbreaks of vaccine-preventable viral diseases have been increasingly reported globally over the past few years. The burden of congenital viral infections, their impact on physical and mental development and the resulting economic loss to the family and the community are also well known. IgM antibody detection has been convenient in the diagnosis of acute viral infections, particularly in settings with limited resources where molecular tests are not feasible.

METHODS

This is a comparative study between a chemiluminescence immunoassay (Liaison, DiaSorin, Saluggia, Italy) and an enzyme linked immunosorbent assay (ELISA) (Euroimmun, Lubeck, Germany) for the detection of IgM antibody against measles, mumps, rubella, CMV, EBV and HHV-1 and -2 viruses using a total of 345 samples. Results are expressed as agreement using kappa statistics.

RESULTS

In this study, CLIA is perfectly comparable to ELISA for the detection of IgM antibodies against measles (0.86) and mumps (0.92) with a moderate agreement for rubella (0.52), CMV (0.57), EBV (0.50), and HHV-1 and -2 (0.47) assays. However, a PABAK (prevalence-adjusted bias-adjusted kappa) showed improved agreement for rubella (0.64), CMV (0.65), EBV (0.60), and HHV-1 and -2 (0.88) assays.

CONCLUSIONS

IgM antibody assays (CLIA and ELISA) against measles and mumps virus can be comparably used depending on the laboratory setup, throughput and expertise.

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.

Digital Microfluidic Hemagglutination Assays for Blood Typing, Donor Compatibility Testing, and Hematocrit Analysis

BACKGROUND

Blood typing, donor compatibility testing, and hematocrit analysis are common tests that are important in many clinical applications, including those found in high-stakes settings such as the trauma center. These tests are typically performed in centralized laboratories with sample batching; the minutes that are lost in this mode can lead to adverse outcomes, especially for critical-care patients. As a step toward providing rapid results at the bedside, we developed a point-of-care hemagglutination system relying on digital microfluidics (DMF) and a unique, automated readout tool, droplet agglutination assessment using digital microfluidics (DAAD).

METHODS

ABO and Rhesus blood grouping, donor crossmatching, and hematocrit assays were developed on a portable DMF platform that allowed for automated sample processing. The result of each assay could be determined by eye or automatically with the DAAD imaging tool.

RESULTS

DMF-DAAD was applied to 109 samples collected from different sources (including commercial samples, pinpricks from volunteers, and a hospital blood bank), with perfect fidelity to gold-standard results. Some of these tests were carried out by a nonexpert in a hospital trauma center. Proof-of-concept results were also collected from smaller sample sets for donor compatibility testing and hematocrit analysis.

CONCLUSION

DMF-DAAD shows promise for delivering rapid, reliable results in a format well suited for a trauma center and other settings where every minute counts.

Colorimetric Sensing with Gold Nanoparticles on Electrowetting-Based Digital Microfluidics

Digital microfluidic (DMF) has been a unique tool for manipulating micro-droplets with high flexibility and accuracy. To extend the application of DMF for automatic and in-site detection, it is promising to introduce colorimetric sensing based on gold nanoparticles (AuNPs), which have advantages including high sensitivity, label-free, biocompatibility, and easy surface modification. However, there is still a lack of studies for investigating the movement and stability of AuNPs for in-site detection on the electrowetting-based digital microfluidics. Herein, to demonstrate the ability of DMF for colorimetric sensing with AuNPs, we investigated the electrowetting property of the AuNPs droplets on the hydrophobic interface of the DMF chip and examined the stability of the AuNPs on DMF as well as the influence of evaporation to the colorimetric sensing. As a result, we found that the electrowetting of AuNPs fits to a modified Young–Lippmann equation, which suggests that a higher voltage is required to actuate AuNPs droplets compared with actuating water droplets. Moreover, the stability of AuNPs was maintained during the processing of electrowetting. We also proved that the evaporation of droplets has a limited influence on the detections that last several minutes. Finally, a model experiment for the detection of Hg²⁺ was carried out with similar results to the detections in bulk solution. The proposed method can be further extended to a wide range of AuNPs-based detection for label-free, automatic, and low-cost detection of small molecules, biomarkers, and metal ions.

Rapid quantitative assays for glucose-6-phosphate dehydrogenase (G6PD) and hemoglobin combined on a capillary-driven microfluidic chip

Rapid tests for glucose-6-phosphate dehydrogenase (G6PD) are extremely important for determining G6PD deficiency, a widespread metabolic disorder which triggers hemolytic anemia in response to primaquine and tafenoquine medication, the most effective drugs for the radical cure of malaria caused by Plasmodium parasites. Current point-of-care diagnostic devices for G6PD are either qualitative, do not normalize G6PD activity to the hemoglobin concentration, or are very expensive. In this work we developed a capillary-driven microfluidic chip to perform a quantitative G6PD test and a hemoglobin measurement within 2 minutes and using less than 2 μL of sample. We used a powerful microfluidic module to integrate and resuspend locally the reagents needed for the G6PD assay and controls. We also developed a theoretical model that successfully predicts the enzymatic reactions on-chip, guides on-chip reagent spotting and allows efficient integration of multiple assays in miniaturized formats with only a few nanograms of reagents.

Microsphere-Based Microfluidic Device for Plasma Separation and Potential Biochemistry Analysis Applications

The development of a simple, portable, and cost-effective plasma separation platform for blood biochemical analysis is of great interest in clinical diagnostics. We represent a plasma separation microfluidic device using microspheres with different sizes as the separation barrier. This plasma separation device, with 18 capillary microchannels, can extract about 3 μL of plasma from a 50 μL blood sample in about 55 min. The effects of evaporation and the microsphere barrier on the plasma biochemical analysis results were studied. Correction factors were applied to compensate for these two effects. The feasibility of the device in plasma biochemical analysis was validated with clinical blood samples.

Thin-film-transistor digital microfluidics for high value in vitro diagnostics at the point of need

The latest developments in thin-film-transistor digital-microfluidics (TFT-DMF, also known by the commercial name aQdrop™) are reported, and proof of concept application to molecular diagnostics (e.g. for coronavirus disease, COVID-19) at the point-of-need demonstrated. The TFT-DMF array has 41 thousand independently addressable electrodes that are capable of manipulating large numbers of droplets of any size and shape, along any pathway to perform multiple parallel reactions. Droplets are continually tracked and adjusted through closed-loop feedback enabled by TFT based sensors at each array element. The sample-to-answer molecular in vitro diagnostic (IVD) test for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) includes nucleic acid extractions from saliva, removal of dsDNA and quantitative reverse transcription polymerase chain reaction (RT-PCR). This proof of concept illustrates how the highly configurable TFT-DMF technology can perform many reactions in parallel and thus support the processing of a range of sample types followed by multiple complex multi-step assays.

Digital Microfluidics in Newborn Screening for Mucopolysaccharidoses: A Progress Report

Newborn screening (NBS) for mucopolysaccharidosis type I (MPS I, Hurler syndrome) is currently conducted in about two-fifths of the NBS programs in the United States and in a few other countries. Screening is performed by measurement of residual activity of the enzyme alpha-l-iduronidase in dried blood spots using either tandem mass spectrometry or digital microfluidic fluorometry (DMF). In this article, we focus on the development and practical experience of using DMF to screen for MPS I in the USA. By means of their responses to a questionnaire, we determined for each responding program that is screening for MPS I using DMF the screen positive rate, follow-up methods, and classification of confirmed cases as either severe or attenuated. Overall, the results show that at the time of reporting, over 1.3 million newborns in the US were screened for MPS I using DMF, 2094 (0.173%) of whom were screen positive. Of these, severe MPS I was confirmed in five cases, attenuated MPS I was confirmed in two cases, and undetermined phenotype was reported in one case. We conclude that DMF is an effective and economical method to screen for MPS I and recommend second-tier testing owing to high screen positive rates. Preliminary results of NBS for MPS II and MPS III using DMF are discussed.

A Low-Cost, Disposable and Portable Inkjet-Printed Biochip for the Developing World

Electrowetting on dielectric-based digital microfluidic platforms (EWOD-DMF) have a potential to impact point-of-care diagnostics. Conventionally, EWOD-DMF platforms are manufactured in cleanrooms by expert technicians using costly and time consuming micro-nanofabrication processes such as optical lithography, depositions and etching. However, such high-end microfabrication facilities are extremely challenging to establish in resource-poor and low-income countries, due to their high capital investment and operating costs. This makes the fabrication of EWOD-DMF platforms extremely challenging in low-income countries, where such platforms are most needed for many applications such as point-of-care testing applications. To address this challenge, we present a low-cost and simple fabrication procedure for EWOD-DMF electrode arrays, which can be performed anywhere with a commercial office inkjet printer without the need of expensive cleanroom facilities. We demonstrate the utility of our platform to move and mix droplets of different reagents and physiologically conductive buffers, thereby showing its capability to potentially perform a variety of biochemical assays. By combining our low-cost, inkjet-printed EWOD-DMF platform with smartphone imaging technology and a compact control system for droplet manipulation, we also demonstrate a portable and hand-held device which can be programmed to potentially perform a variety of biochemical assays.

Direct loading of blood for plasma separation and diagnostic assays on a digital microfluidic device

Finger-stick blood sampling is convenient for point of care diagnostics, but whole blood samples are problematic for many assays because of severe matrix effects associated with blood cells and cell debris. We introduce a new digital microfluidic (DMF) diagnostic platform with integrated porous membranes for blood-plasma separation from finger-stick blood volumes, capable of performing complex, multi-step, diagnostic assays. Importantly, the samples can be directly loaded onto the device by a finger "dab" for user-friendly operation. We characterize the platform by comparison to plasma generated via the "gold standard" centrifugation technique, and demonstrate a 21-step rubella virus (RV) IgG immunoassay yielding a detection limit of 1.9 IU mL-1, below the diagnostic cut-off. We propose that this work represents a critical next step in DMF based portable diagnostic assays-allowing the analysis of whole blood samples without pre-processing.

Current commercialization status of electrowetting-on-dielectric (EWOD) digital microfluidics

The emergence of electrowetting-on-dielectric (EWOD) in the early 2000s made the once-obscure electrowetting phenomenon practical and led to numerous activities over the last two decades. As an eloquent microscale liquid handling technology that gave birth to digital microfluidics, EWOD has served as the basis for many commercial products over two major application areas: optical, such as liquid lenses and reflective displays, and biomedical, such as DNA library preparation and molecular diagnostics. A number of research or start-up companies (e.g., Phillips Research, Varioptic, Liquavista, and Advanced Liquid Logic) led the early commercialization efforts and eventually attracted major companies from various industry sectors (e.g., Corning, Amazon, and Illumina). Although not all of the pioneering products became an instant success, the persistent growth of liquid lenses and the recent FDA approvals of biomedical analyzers proved that EWOD is a powerful tool that deserves a wider recognition and more aggressive exploration. This review presents the history around major EWOD products that hit the market to show their winding paths to commercialization and summarizes the current state of product development to peek into the future. In providing the readers with a big picture of commercializing EWOD and digital microfluidics technology, our goal is to inspire further research exploration and new entrepreneurial adventures.

Lab-on-a-Chip Technologies for the Single Cell Level: Separation, Analysis, and Diagnostics

In the last three decades, microfluidics and its applications have been on an exponential rise, including approaches to isolate rare cells and diagnose diseases on the single-cell level. The techniques mentioned herein have already had significant impacts in our lives, from in-the-field diagnosis of disease and parasitic infections, through home fertility tests, to uncovering the interactions between SARS-CoV-2 and their host cells. This review gives an overview of the field in general and the most notable developments of the last five years, in three parts: 1. What can we detect? 2. Which detection technologies are used in which setting? 3. How do these techniques work? Finally, this review discusses potentials, shortfalls, and an outlook on future developments, especially in respect to the funding landscape and the field-application of these chips.