Digital Chip Research Articles

Fully Integrated Microfluidic Digital Chip for Simple and Highly Quantitative Detection of Norovirus.

The prevalence of foodborne illnesses is a significant global concern, resulting in numerous illnesses, deaths, and substantial economic losses annually. Traditional detection methods for foodborne pathogens are often slow, limited, and impractical for field use, underscoring the need for rapid, sensitive, and portable assays. Microfluidic technology has emerged as a promising solution for sample preparation, reaction, and detection on a small scale. Our study introduces a novel microfluidic digital loop-mediated isothermal amplification (LAMP) assay platform, which employs digital microfluidic chips for absolute quantitative analysis of nucleic acids. This portable chip utilizes LAMP technology to achieve ultrasensitive detection of target nucleic acids within 30 min and reduces the detection limit to 1 fM without the need for complex instrumentation. By digitizing amplification signals directly from the target sample, our platform offers simplicity, affordability, portability, and quantitative molecular readouts. This innovation represents a crucial step toward the on-site detection of foodborne pathogens, thereby enhancing food safety and mitigating disease outbreaks.

Microcavity Array-Based Digital SERS Chip for Rapid and Accurate Label-free Quantitative Detection of Live Bacteria.

In this study, we developed a novel digital surface-enhanced Raman spectroscopy (SERS) chip that integrates an inverted pyramid microcavity array, a microchannel cover plate, and a multilayer gold nanoparticle (AuNP) SERS substrate. This innovative design exploits the synergistic effects of the microcavity array and the microchannel to enable rapid and large-scale digital discretization of bacterial suspensions. The concentration effect of the picoliter cavities, combined with the superior Raman enhancement effect of the multilayer AuNP SERS substrate, allows for the precise identification of live bacteria within the microcavities through in situ and label-free SERS testing after a short incubation period. By counting the resulting positive or negative signals, the concentration of the target analyte can be directly determined via Poisson statistics. Experimental results demonstrate that this method enables the accurate quantification of Escherichia coli (E. coli) BL21 within a 4-h incubation period. Compared with traditional analog SERS detection methods, our proposed digital SERS detection strategy reduces the impact of signal intensity fluctuations, thereby significantly improving detection efficiency and accuracy. We believe that this digital SERS chip has great application prospects in the fields of bacterial detection, antibiotic resistance analysis, and cellular dynamics monitoring.

Digital microfluidic chip with photopatterned reactive sites for direct biomolecules immobilization and magnetic beads-free immunoassay

Digital microfluidics (DMF), as an emerging liquid-handling technology, is widely recognized as an ideal platform for enzyme-linked immunosorbent assay (ELISA). However, current DMF-based ELISA methods are highly dependent on magnetic beads (MBs), which usually involves tedious modification of MBs, complex peripherals for MBs control, and impairs the parallel processing capability of DMF. To address these issues, we herein developed a photopatterned reactive sites-integrated DMF chip (PRS-DMF) for MBs-free immunoassay. By taking advantage of click chemistry between N-(allyloxycarbonyloxy) succinimide and thiol-ene substrate, the preparation of PRS is very simple, and leaves the reactive N-hydroxysuccinimide (NHS) ester groups on the surface. This enables direct biomolecules immobilization without any surface modification/activation processes. Moreover, the patterned micropillar array can notably increase the specific surface area, and promote the liquid mixing and immunoreaction. As a consequence, highly sensitive and MBs-free ELISA can be readily achieved on PRS-DMF, with a proof-of-concept H5N1 assay having been successfully demonstrated herein, which offers a low limit of detection (LOD) of 147 pg/mL. This also avoids the use of complex magnetic peripherals, and thus, contributing to the instrument miniaturization into a very compact form. It is therefore reasonably expected that the proposed PRS-DMF may serve as a promising platform for a variety of biological and biomedical applications, especially in the field of point-of-care testing (POCT).

Current disturbance compensation of continuous model predictive control scheme for PMSMs

During the operation of a permanent magnet synchronous motor, limitations imposed by digital chips inevitably result in certain delays. Additionally, external environmental factors introduce variations in motor parameters. This study aims to comprehensively analyze these issues. Firstly, the control delay and disturbances caused by motor parameter changes are transformed into current disturbances using a uniform approach. Secondly, various sliding mode model predictive controllers are designed to effectively suppress the current disturbances arising from aforementioned reasons. Moreover, considering controller implementation aspects, this paper thoroughly discusses the influence of core controller parameters on current disturbances and their adaptability towards different parameter mismatches. Furthermore, extensive examination is conducted on global stability conditions for controller realization. Finally, experimental results validate that the proposed methods successfully optimize current disturbances originating from aforementioned causes.

Coupling digital microfluidics with mass spectrometry

AbstractDigital microfluidics enables the electrical actuation of microliter‐sized droplets on a planar surface, facilitating precise control and digitization of chemical processes. It is typically operated in a closed chip format, preventing evaporation and contamination which also complicates chemical analysis of the trapped droplets. Thus, subsequent analytics are usually carried out offline or with simple optical methods. A new method including a chip‐integrated microspray hole now allows on‐the‐fly mass spectrometry analysis on a digital microfluidics chip.

A high-performance digital polymerase chain reaction chip integrated with nanorods-decorated microchannel plate

Abstract In this paper, we report on a digital PCR chip integrated with microchannel plate (MCP) for the quantification of DNA molecules. MCP, a highly porous glass membrane, is employed here as microreactors. The density of the microreactors reaches up to 1600 mm−2 with a total number of 40,000 chambers each in 100 pL volumes embedded in a 5 × 5 mm2 MCP, which is 100 times larger than that of the conventional microfabricated chips. In addition, the MCP is functionalized with ZnO nanorods to enhance the fluorescence signal. The dynamic range is noted as 105 and the detection limit of λDNA is determined to be 1.4 copies/μL.

High Frequency and Addressable Impedance Measurement System for On-Site Droplet Analysis in Digital Microfluidics

Digital microfluidics is a novel technique for manipulating discrete droplets with the advantages of programmability, small device size, low cost, and easy integration. The development of droplet sensing methods advances the automation control of digital microfluidics. Impedance measurement emerges as a promising technique for droplet localization and characterization due to its non-invasive nature, high sensitivity, simplicity, and cost-effectiveness. However, traditional impedance measurement approaches in digital microfluidics based on the high-voltage actuating signal are limited in sensing accuracy in practical applications. In this paper, we propose a novel droplet impedance sensing system for digital microfluidics by introducing a low-voltage and addressable measurement circuit, which enables impedance measurement over a wide frequency range. The proposed measurement system has also been used for detecting the droplet composition, size, and position in a digital microfluidic chip. The improved impedance sensing method can also promote the applications of the digital microfluidic, which requires high accuracy, real-time, and contactless sensing with automatic sample pretreatment.

Integrated Droplet-Based Digital Loop-Mediated Isothermal Amplification Microfluidic Chip with Droplet Generation, Incubation, and Continuous Fluorescence Detection.

This study integrated sample partition, incubation, and continuous fluorescence detection on a single microfluidic chip for droplet-based digital Loop-Mediated Isothermal Amplification (LAMP) of nucleic acids. This integration eliminated the need to transfer reactions between different platforms, avoiding sample contamination and loss. Prior to the reaction, filling the channels with an oil phase and adding a glass cover slip on top of the chip overcame the problem of bubble generation in the channels during the LAMP reaction due to heating. Additionally, using two fluorescence intensity thresholds enabled simultaneous detection and counting of positive and negative droplets within a single fluorescence detection channel. The chip can partition approximately 6000 droplets from a 5 µL sample within 10 min, with a droplet diameter of around 110 µm and a coefficient of variation (CV) value of 0.82%. Staphylococcus aureus was quantified via the proposed platform. The results demonstrated a highly accurate correlation coefficient (R = 0.9998), and the detection limit reached a concentration of 1.7 × 102 copies/µL. The entire process of the droplet digital LAMP reaction, from droplet generation to incubation to quantitative results, took a maximum of 70 min.

Advances in electrowetting-on-dielectric digital microfluidics technology for disease diagnosis and prevention applications

Rapid and accurate diagnostic technologies are crucial for early detection and diagnosis of diseases. Electrowetting-on-dielectric digital microfluidics, with its high-precision detection and high-throughput screening capabilities, significantly enhances the accuracy and efficiency in early disease diagnosis and personalized treatment, enabling swift disease detection and widespread screening. This article provides a comprehensive review of the working principles and fabrication processes of digital microfluidic chips based on electrowetting on dielectric method. It details the latest research progress in the areas of nucleic acids, proteins, and cells, organizes the commercialization of digital microfluidics technology, and finally discusses the current challenges and future directions of digital microfluidic chips.

Rapid and portable quantification of HIV RNA via a smartphone-enabled digital CRISPR device and deep learning

For the 29.8 million people in the world living with HIV/AIDS and receiving antiretroviral therapy, it is crucial to monitor their HIV viral loads. To this end, rapid and portable diagnostic tools that can quantify HIV RNA are critically needed. We report herein a rapid and quantitative digital CRISPR-assisted HIV RNA detection assay that has been implemented within a portable smartphone-based device as a potential solution. Specifically, we first developed a fluorescence-based reverse transcription recombinase polymerase amplification (RT-RPA)-CRISPR assay that can efficiently detect HIV RNA at 42 °C. We then implemented this assay within a commercial stamp-sized digital chip, where RNA molecules were quantified as strongly fluorescent digital reaction wells. The isothermal reaction condition and the strong fluorescence in the digital chip simplified the design of thermal and optical modules, allowing us to engineer a palm-size device measuring 70 × 115 × 80 mm and weighing less than 0.6 kg. We also capitalized the smartphone by developing a custom app to control the device, perform the digital assay, and capture fluorescence images throughout the assay using the smartphone's camera. Moreover, we trained and verified a deep learning-based algorithm for analyzing fluorescence images and identifying positive digital reaction wells with high accuracy. Using our smartphone-enabled digital CRISPR device, we successfully detected as low as 75 copies of HIV RNA in just 15 min, showing its potential toward monitoring of HIV viral loads and aiding the global effort to combat the HIV/AIDS epidemic.

Clinical Performance of the Line Immunoassay and Digital Liquid Chip Method for Detecting Autoimmune Liver Disease Autoantibodies.

The identification of autoantibodies associated with autoimmune liver disease (ALD) is crucial for diagnosis and management. Various laboratory methods have been introduced to detect autoantibody profiles. However, the variable performance of these assays may create challenges for clinicians and patients. To investigate the concordance rates and diagnostic performance of 2 commercially available assays, line immunoassay (LIA) and digital liquid chip method (DLCM), in patients with ALD. A total of 291 serum samples were collected, consisting of 180 sera from patients with ALD and 111 sera from controls. The samples were detected through LIA and DLCM. The agreement and diagnostic performance of each assay were analyzed. There was substantial to almost perfect agreement among prevalent autoantibodies (anti-mitochondrial antibody M2, antibodies against gp210, Sp100, and Ro52). Nevertheless, the Cohen κ coefficient of some uncommon autoantibodies (anti-LKM-1, anti-LC-1, and anti-SLA/LP) between the 2 methods was not ideal. LIA showed slightly better sensitivity, accuracy, and negative predictive value, while DLCM exhibited slightly higher specificity and positive predictive value. LIA and DLCM demonstrated comparable performance for the detection of common ALD-related autoantibodies. LIA seemed to be more sensitive, while DLCM displayed more specificity. However, standardization of ALD autoantibody detection still faces challenges between these diverse detection systems. Comprehensive interlaboratory validation is essential to mitigate potential misunderstanding and confusion among patients and clinicians.

Simulation analysis and experimental verification of thermodynamic characteristics of integrated droplet digital PCR chip

Simulation analysis and experimental verification of thermodynamic characteristics of integrated droplet digital PCR chip

Detection of Interleukin-1 β (IL-1β) in Single Human Blastocyst-Conditioned Medium Using Ultrasensitive Bead-Based Digital Microfluidic Chip and Its Relationship with Embryonic Implantation Potential.

The implantation of human embryos is a complex process involving various cytokines and receptors expressed by both endometrium and embryos. However, the role of cytokines produced by a single embryo in successful implantation is largely unknown. This study aimed to investigate the role of IL-1β expressed in a single-embryo-conditioned medium (ECM) in embryo implantation. Seventy samples of single ECM were analyzed by a specially designed magnetic-beads-based microfluidic chip from 15 women. We discovered that IL-1β level increased as the embryo developed, and the difference was significant. In addition, receiver operator characteristic (ROC) curves analysis showed a higher chance of pregnancy when the IL-1β level on day 5 ECM was below 79.37 pg/mL and the difference between day 5 and day 3 was below 24.90 pg/mL. Our study discovered a possible association between embryonic proteomic expression and successful implantation, which might facilitate single-embryo transfer in the future by helping clinicians identify the embryo with the greatest implantation potential.

AM-DMF-SCP: Integrated Single-Cell Proteomics Analysis on an Active Matrix Digital Microfluidic Chip.

Single-cell proteomics offers unparalleled insights into cellular diversity and molecular mechanisms, enabling a deeper understanding of complex biological processes at the individual cell level. Here, we develop an integrated sample processing on an active-matrix digital microfluidic chip for single-cell proteomics (AM-DMF-SCP). Employing the AM-DMF-SCP approach and data-independent acquisition (DIA), we identify an average of 2258 protein groups in single HeLa cells within 15 min of the liquid chromatography gradient. We performed comparative analyses of three tumor cell lines: HeLa, A549, and HepG2, and machine learning was utilized to identify the unique features of these cell lines. Applying the AM-DMF-SCP to characterize the proteomes of a third-generation EGFR inhibitor, ASK120067-resistant cells (67R) and their parental NCI-H1975 cells, we observed a potential correlation between elevated VIM expression and 67R resistance, which is consistent with the findings from bulk sample analyses. These results suggest that AM-DMF-SCP is an automated, robust, and sensitive platform for single-cell proteomics and demonstrate the potential for providing valuable insights into cellular mechanisms.

Photothermal-Based Multiplex Nested Digital PCR System for Rapid Detection of Foodborne Pathogens.

The rapid and sensitive detection of foodborne pathogens is crucial for ensuring food safety. Among virus testing methods, polymerase chain reaction (PCR) has served as the gold-standard technique in most food safety regulation organizations. However, to enhance the speed and efficiency of PCR, novel approaches are continually being explored. In this work, leveraging the photothermal effects and high thermal conductivity of gold nanoparticles, we have significantly improved the heating and cooling rates of thermal cycles, enabling ultra-fast PCR detection. Specifically, we present a pre-degassing multiplex digital PCR chip integrated with gold nanoparticles. We further developed a portable system with a light source for photothermal heating cycling, along with an optoelectronic sensor to analyze PCR amplification products after rapid thermal cycling. As proof of concept, the proposed chip and portable device was applied for the on-site detection of several types of foodborne pathogens, including Escherichia coli, Listeria monocytogenes, Staphylococcus aureus, and Salmonella. The whole system could distinguish those pathogens within 20 min, showing good potential for the rapid detection of multiple types of foodborne pathogens.

Digital microfluidics methods for nucleic acid detection: A mini review.

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

Complete Prevention of Bubbles in a PDMS-Based Digital PCR Chip with a Multifunction Cavity.

In a chamber-based digital PCR (dPCR) chip fabricated with polydimethylsiloxane (PDMS), bubble generation in the chambers at high temperatures is a critical issue. Here, we found that the main reason for bubble formation in PDMS chips is the too-high saturated vapor pressure of water at an elevated temperature. The bubbles should be completely prevented by reducing the initial pressure of the system to under 13.6 kPa to eliminate the effects of increased-pressure water vapor. Then, a cavity was designed and fabricated above the PCR reaction layer, and Parylene C was used as a shell covering the chip. The cavity was used for the negative generator in sample loading, PDMS degassing, PCR solution degassing in the digitization process and water storage in the thermal reaction process. The analysis was confirmed and finally achieved a desirable bubble-free, fast-digitization, valve-free and no-tubing connection dPCR.

Novel Digital SERS-Microfluidic Chip for Rapid and Accurate Quantification of Microorganisms.

In this work, we present a simple and novel digital surface-enhanced Raman spectroscopy (SERS)-microfluidic chip designed for the rapid and accurate quantitative detection of microorganisms. The chip employs a high-density inverted pyramid microcavity (IPM) array to separate and isolate microbial samples. The presence or absence of target microorganisms is determined by scanning the IPM array using SERS and identifying the characteristic Raman bands. This approach allows for the "digitization" of the SERS response of each IPM, enabling quantification through the application of mathematical statistical techniques. Significantly, precise quantitative detection of yeast was achieved within a concentration range of 106-109 cells/mL, with the maximum relative standard deviation from the concentration calibrated by the cultivation method being 5.6%. This innovative approach efficiently addresses the issue of irregularities in SERS quantitative detection, which arises due to fluctuations in SERS intensity and poor reproducibility. We strongly believe that this digital SERS-microfluidic chip holds immense potential for diverse applications in the rapid detection of various microorganisms, including pathogenic bacteria and viruses.

Improved Teflon lift-off for droplet microarray generation and single-cell separation on digital microfluidic chips.

Droplet microarrays (DMAs) leveraging wettability differences are instrumental in digital immunoassays, single-cell analysis, and high-throughput screening. This study introduces an enhanced Teflon lift-off process to fabricate hydrophilic-hydrophobic patterns on a digital microfluidic (DMF) chip, thereby integrating DMAs with DMF technology. By employing DMF for droplet manipulation and utilizing wettability differences, the automated generation of high-throughput DMAs was achieved. The volume of the microdroplets ranged from picoliters to nanoliters. For droplets with a diameter of 150 μm, the array density reached up to 1282 cm-2. We systematically investigated the influence of various DMF parameters on the formation of DMAs and applied this technique to particle distribution, achieving a single-cell isolation rate of approximately 30%. We believe that this method will be a potent tool to enhance the capabilities of DMAs and DMF technology and extend their applicability across more fields.

Laser-induced graphene-based digital microfluidics (gDMF): a versatile platform with sub-one-dollar cost.

Digital microfluidics (DMF), is an emerging liquid-handling technology, that shows promising potential in various biological and biomedical applications. However, the fabrication of conventional DMF chips is usually complicated, time-consuming, and costly, which seriously limits their widespread applications, especially in the field of point-of-care testing (POCT). Although the paper- or film-based DMF devices can offer an inexpensive and convenient alternative, they still suffer from the planar addressing structure, and thus, limited electrode quantity. To address the above issues, we herein describe the development of a laser-induced graphene (LIG) based digital microfluidics chip (gDMF). It can be easily made (within 10 min, under ambient conditions, without the need of costly materials or cleanroom-based techniques) by a computer-controlled laser scribing process. Moreover, both the planar addressing DMF (pgDMF) and vertical addressing DMF (vgDMF) can be readily achieved, with the latter offering the potential of a higher electrode density. Also, both of them have an impressively low cost of below $1 ($0.85 for pgDMF, $0.59 for vgDMF). Experiments also show that both pgDMF and vgDMF have a comparable performance to conventional DMF devices, with a colorimetric assay performed on vgDMF as proof-of-concept to demonstrate their applicability. Given the simple fabrication, low cost, full function, and the ease of modifying the electrode pattern for various applications, it is reasonably expect that the proposed gDMF may offer an alternative choice as a versatile platform for POCT.