Droplet-based microfluidics offer great opportunities for applications in various fields, such as diagnostics, food sciences, and drug discovery. A droplet provides an isolated environment for performing a single reaction within a microscale-volume sample, allowing for a fast reaction with a high sensitivity, high throughput, and low risk of cross-contamination. Owing to several remarkable features, droplet-based microfluidic techniques have been intensively studied. In this review, we discuss the impact of droplet microfluidics, particularly focusing on drug screening and development. In addition, we surveyed various methods of device fabrication and droplet generation/manipulation. We further highlight some promising studies covering drug synthesis and delivery that were updated within the last 5 years. This review provides researchers with a quick guide that includes the most up-to-date and relevant information on the latest scientific findings on the development of droplet-based microfluidics in the pharmaceutical field.

In this study, a plastic microdevice based on loop-mediated isothermal amplification (LAMP) was fabricated for the amplification and on-chip fluorescence detection of multiple pathogens. Papers infused with LAMP reagents and specific primers were embedded inside the multiple reaction chambers of the microdevice. A solution containing the target pathogens was injected into the sample chamber, located in the center of the microdevice, and evenly distributed to the reaction chambers simultaneously via centrifugal force. For detection, fisetin, a plant-derived fluorophore, was used as the DNA-intercalating dye. Purified DNAs of Escherichia coli O157:H7 (E. coli O157:H7), Salmonella spp., Staphylococcus aureus (S. aureus), and Cochlodinium polykrikoides were successfully amplified and directly detected on the microdevice, where as low as 0.13 and 0.12 ng μL⁻¹ of the DNA of E. coli O157:H7 and S. aureus, respectively, were identified. In addition, the potential of this microdevice for point-of-care testing was further examined by incorporating on-chip sample purification module and testing using a real sample – milk spiked with Salmonella spp. The thermally lysed milk sample was filtered using polydopamine-coated paper embedded inside a sample chamber and seamlessly transported into the reaction chambers by centrifugal force for subsequent LAMP followed by direct on-chip detection inside the reaction chambers in which fisetin-soaked papers were embedded. The limit of detection for Salmonella spp. was determined to be approximately 1.7 × 10² CFU mL⁻¹ using the microdevice. This microdevice is safe, easy to use, selective, and sensitive enough for point-of-care testing to identify foodborne pathogens as well as environmentally harmful microorganisms.

In this study, we have developed a foldable microdevice fully integrating DNA purification, amplification, and detection processes for detecting multiple foodborne pathogens. Specifically, the loop-mediated isothermal amplification (LAMP) technique was combined with a fuchsin-based direct DNA colorimetric detection method. The microdevice was composed of three parts: a sample zone, reaction zone, and detection zone. A sealing film attached to the sample, reaction, and detection zones served as a bottom layer to make the microdevice foldable. The detection zone was made up of paper strips attached to the sticky side of the sealing film, and fuchsin-stained lines were drawn on the paper strips. The microdevice can be folded to directly transfer the DNA template solution from the sample chambers to the reaction chambers. In this manner, fluid manipulation was readily realized and the use of a bulky instrument such as a pump or rotator was completely dispensed with. After the LAMP reaction, the detection zone was folded so that the fuchsin-stained lines were completely soaked into the reaction chambers. Genomic DNAs of Salmonella spp. and Escherichia coli O157:H7 were first successfully purified from thermally-lysed milk using polydopamine-coated paper, amplified by LAMP, and directly identified by the naked eye using fuchsin within 65 min. Using this microdevice, approximately 10² CFU per mL of Salmonella spp. was detected. These results indicate the significant potential of this microdevice for the sample-in-answer-out genetic analysis of multiple foodborne pathogens in resource-limited environments.

Accurate and timely detection of infectious pathogens is urgently needed for disease treatment and control of possible outbreaks worldwide. Conventional methods for pathogen detection are usually time-consuming and labor-intensive. Novel strategies for the identification of pathogenic nucleic acids are necessary for practical application. The advent of microfluidic technology and microfluidic devices has offered advanced and miniaturized tools to rapidly screen microorganisms, improving many drawbacks of conventional nucleic acid amplification-based methods. In this review, we summarize advances in the microfluidic approach to detect pathogens based on nucleic acid amplification. We survey microfluidic platforms performing two major types of nucleic acid amplification strategies, namely, polymerase chain reaction (PCR) and isothermal nucleic acid amplification. We also provide an overview of nucleic acid amplification-based platforms including studies and commercialized products for SARS-CoV-2 detection. Technologically, we focus on the design of the microfluidic devices, the selected methods for sample preparation, nucleic acid amplification techniques, and endpoint analysis. We also compare features such as analysis time, sensitivity, and specificity of different platforms. The first section of the review discusses methods used in microfluidic devices for upstream clinical sample preparation. The second section covers the design, operation, and applications of PCR-based microfluidic devices. The third section reviews two common types of isothermal nucleic acid amplification methods (loop-mediated isothermal amplification and recombinase polymerase amplification) performed in microfluidic systems. The fourth section introduces microfluidic applications for nucleic acid amplification-based detection of SARS-CoV-2. Finally, the review concludes with the importance of full integration and quantitative analysis for clinical microbial identification.

Environmental pollution remains a major societal problem, leading to serious impacts on living organisms including humans. Human activities such as civilization, urbanization, and industrialization are major causes of pollution. Imposing stricter rules helps control environmental pollutant levels, creating a need for reliable pollutant monitoring in air, water, and soil. The application of traditional analytical techniques is limited in low-resource areas because they are sophisticated, expensive, and bulky. With the development of biosensors and microfluidics technology, environmental monitoring has significantly improved the analysis time, low cost, portability, and ease of use. This review discusses the fundamentals of portable devices, including microfluidics and biosensors, for environmental control. Recently, publications reviewing microfluidics and biosensor device applications have increased more than tenfold, showing the potential of emerging novel approaches for environmental monitoring. Strategies for enzyme-, immunoassay-, and molecular-based analyte sensing are discussed based on their mechanisms and applications. Microfluidic and biosensor platforms for detecting major pollutants, including metal ions, pathogens, pesticides, and antibiotic residues, are reviewed based on their working principles, advantages, and disadvantages. Challenges and future trends for the device design and fabrication process to improve performance are discussed. Miniaturization, low cost, selectivity, sensitivity, high automation, and savings in samples and reagents make the devices ideal alternatives for in-field detection, especially in low-resource areas. However, their operation with complicated environmental samples requires further research to improve the specificity and sensitivity. Although there is a wide range of devices available for environmental applications, their implementation in real-world situations is limited. This study provides insights into existing issues that can be used as references and a comparative analysis for future studies and applications.

This review first describes mechanisms of Fenton/Fenton-like reaction for colorimetric detection; then, recent advances in developing Fenton/Fenton-like reaction assisted by nanotechnology as well as nanomaterials are discussed.