One-shot high-resolution melting curve analysis for KRAS point-mutation discrimination on a digital microfluidics platform

Programmable DNA barcode-encoded exponential amplification reaction for the multiplex detection of miRNAs

Multiple analysis of miRNAs is essential for the early diagnosis and monitoring of diseases. Here, a programmable, multiplex, and sensitive approach was developed for one-pot detection of miRNAs by melting temperature encoded sequences and exponential isothermal amplification (E-EXPAR). In the presence of target miRNAs, the corresponding templates initiate the cycles of nicking and polymerization/displacement, generating numerous barcode strands with unique encoding sequences. Subsequently, generated barcode strands hybridize with fluorescent probes and quench the fluorophore by a triplet of G base through a photo-induced electron transfer mechanism. Finally, a melting curve analysis is performed to quantify miRNAs by calculating the rate of fluorescence change at the corresponding melting temperature. Based on this, miRNA-21, miRNA-9, and miRNA-122 were detected with the detection limits of 3.3 fM, 2.9 fM, and 1.7 fM, respectively. This E-EXPAR was also employed to simultaneously detect three miRNAs in biological samples, showing consistent results with RT-qPCR. Overall, this study provides a programmable and universal platform for multiplex analysis of miRNAs, and holds great promise as an alternative to the multiplex analysis in clinical diagnostics and prognostics for nucleic acid detection.

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.

Sub-5-Minute Ultrafast PCR using Digital Microfluidics

The development of a rapid and reliable polymerase chain reaction (PCR) method for point-of-care (POC) diagnosis is crucial for the timely identification of pathogens. Microfluidics, which involves the manipulation of small volumes of fluidic samples, has been shown to be an ideal approach for POC analysis. Among the various microfluidic platforms available, digital microfluidics (DMF) offers high degree of configurability in manipulating μL/nL-scale liquid and achieving automation. However, the successful implementation of ultrafast PCR on DMF platforms presents challenges due to inherent system instability. In this study, we developed a robust and ultrafast PCR in 3.7-5 min with a detection sensitivity comparable to conventional PCR. Specifically, the implementation of the pincer heating scheme homogenises the temperature within a drop. The utilization of a μm-scale porous hydrophobic membrane suppresses the formation of bubbles under high temperatures. The design of a groove around the high-temperature zone effectively mitigates the temperature interference. The integration of a soluble sensor into the droplets provides an accurate and instant in-drop temperature sensing. We envision that the fast, robust, sensitive, and automatic DMF system will empower the POC testing for infectious diseases.

EWOD Chip with Micro-Barrier Electrode for Simultaneous Enhanced Mixing during Transportation

Digital microfluidic platforms have been extensively studied in biology. However, achieving efficient mixing of macromolecules in microscale, low Reynolds number fluids remains a major challenge. To address this challenge, this study presents a novel design solution based on dielectric electro-wetting (EWOD) by optimizing the geometry of the transport electrode. The new design integrates micro-barriers on the electrodes to generate vortex currents that promote mixing during droplet transport. This design solution requires only two activation signals, minimizing the number of pins required. The mixing performance of the new design was evaluated by analyzing the degree of mixing inside the droplet and quantifying the motion of the internal particles. In addition, the rapid mixing capability of the new platform was demonstrated by successfully mixing the sorbitol solution with the detection solution and detecting the resulting reaction products. The experimental results show that the transfer electrode with a micro-barrier enables rapid mixing of liquids with a six-fold increase in mixing efficiency, making it ideal for the development of EWOD devices.

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.

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.