A feedback-controlling digital microfluidic fluorimetric sensor device for simple and rapid detection of mercury (II) in costal seawater

Recent advances and trends in innovative biosensor-based devices for heavy metal ion detection in food

Low-cost, reliable, and efficient biosensors are crucial in detecting residual heavy metal ions (HMIs) in food products. At present, based on distance-induced localized surface plasmon resonance of noble metal nanoparticles, enzyme-mimetic reaction of nanozymes, and chelation reaction of metal chelators, the constructed optical sensors have attracted wide attention in HMIs detection. Besides, based on the enrichment and signal amplification strategy of nanomaterials on HMIs and the construction of electrochemical aptamer sensing platforms, the developed electrochemical biosensors have overcome the plague of low sensitivity, poor selectivity, and the inability of multiplexed detection in the optical strategy. Moreover, along with an in-depth discussion of these different types of biosensors, a detailed overview of the design and application of innovative devices based on these sensing principles was provided, including microfluidic systems, hydrogel-based platforms, and test strip technologies. Finally, the challenges that hinder commercial application have also been mentioned. Overall, this review aims to establish a theoretical foundation for developing accurate and reliable sensing technologies and devices for HMIs, thereby promoting the widespread application of biosensors in the detection of HMIs in food.

Microfluidics in environmental analysis: advancements, challenges, and future prospects for rapid and efficient monitoring

Microfluidic devices have emerged as advantageous tools for detecting environmental contaminants due to their portability, ease of use, cost-effectiveness, and rapid response capabilities. These devices have wide-ranging applications in environmental monitoring of air, water, and soil matrices, and have also been applied to agricultural monitoring. Although several previous reviews have explored microfluidic devices' utility, this paper presents an up-to-date account of the latest advancements in this field for environmental monitoring, looking back at the past five years. In this review, we discuss devices for prominent contaminants such as heavy metals, pesticides, nutrients, microorganisms, per- and polyfluoroalkyl substances (PFAS), etc. We cover numerous detection methods (electrochemical, colorimetric, fluorescent, etc.) and critically assess the current state of microfluidic devices for environmental monitoring, highlighting both their successes and limitations. Moreover, we propose potential strategies to mitigate these limitations and offer valuable insights into future research and development directions.

Microfluidic Devices for Heavy Metal Ions Detection: A Review

The contamination of air, water and soil by heavy metal ions is one of the most serious problems plaguing the environment. These metal ions are characterized by a low biodegradability and high chemical stability and can affect humans and animals, causing severe diseases. In addition to the typical analysis methods, i.e., liquid chromatography (LC) or spectrometric methods (i.e., atomic absorption spectroscopy, AAS), there is a need for the development of inexpensive, easy-to-use, sensitive and portable devices for the detection of heavy metal ions at the point of interest. To this direction, microfluidic and lab-on-chip (LOC) devices fabricated with novel materials and scalable microfabrication methods have been proposed as a promising approach to realize such systems. This review focuses on the recent advances of such devices used for the detection of the most important toxic metal ions, namely, lead (Pb), mercury (Hg), arsenic (As), cadmium (Cd) and chromium (Cr) ions. Particular emphasis is given to the materials, the fabrication methods and the detection methods proposed for the realization of such devices in order to provide a complete overview of the existing technology advances as well as the limitations and the challenges that should be addressed in order to improve the commercial uptake of microfluidic and LOC devices in environmental monitoring applications.

Deep learning with microfluidics for on-chip droplet generation, control, and analysis

Droplet microfluidics has gained widespread attention in recent years due to its advantages of high throughput, high integration, high sensitivity and low power consumption in droplet-based micro-reaction. Meanwhile, with the rapid development of computer technology over the past decade, deep learning architectures have been able to process vast amounts of data from various research fields. Nowadays, interdisciplinarity plays an increasingly important role in modern research, and deep learning has contributed greatly to the advancement of many professions. Consequently, intelligent microfluidics has emerged as the times require, and possesses broad prospects in the development of automated and intelligent devices for integrating the merits of microfluidic technology and artificial intelligence. In this article, we provide a general review of the evolution of intelligent microfluidics and some applications related to deep learning, mainly in droplet generation, control, and analysis. We also present the challenges and emerging opportunities in this field.

Research progress of electrode shapes in EWOD-based digital microfluidics

Digital microfluidics (DMF) is an innovative technology used for precise manipulation of liquid droplets. This technology has garnered significant attention in both industrial applications and scientific research due to its unique advantages. Among the key components of DMF, the driving electrode plays a role in facilitating droplet generation, transportation, splitting, merging, and mixing. This comprehensive review aims to present an in-depth understanding of the working principle of DMF particularly focusing on the Electrowetting On Dielectric (EWOD) method. Furthermore, it examines the impact of driving electrodes with varying geometries on droplet manipulation. By analyzing and comparing their characteristics, this review offers valuable insights and a fresh perspective on the design and application of driving electrodes in DMF based on the EWOD approach. Lastly, an assessment of the development trend and potential applications of DMF concludes the review, providing an outlook for future prospects in the field.

Automated study on kinetics and biosensing of glow-type luminescence reaction via digital microfluidics-chemiluminescence

Automated manipulation of discrete droplets by digital microfluidics (DMF) combined with chemiluminescence (CL) is promising to achieve automated and sensitive biosensing and bioanalysis. Herein, a DMF-CL device was built to automatically study CL kinetics and biosensing of a glow-type CL reaction. Copper-cysteine nanoparticles (Cu/CysNP) were synthesized as a new CL catalyst to extend the CL reaction of luminol-H₂O₂ to more than 10 min. The automated manipulation of droplets reduced reagent costs and manual errors, leading to real-time, automated, and reliable study of CL kinetics. The CL kinetics curve collected by the DMF-CL integration device is in accordance with that of a commercial CL analyser. The long-lasting luminescence ensured automated, sensitive, and reliable detection of H₂O₂ as a direct or indirect analyte of the cascade catalytic reaction. Moreover, an innovative asymmetrical splitting method is proposed to quickly and precisely generate daughter droplets to ensure uniformity of the droplets and good repeatability of the DMF-CL measurements. Therefore, the DMF-CL analysis holds great potential for achieving online and automatic analysis and biosensing.

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.

Artificial intelligence-powered microfluidics for nanomedicine and materials synthesis

Artificial intelligence (AI) is an emerging technology with great potential, and its robust calculation and analysis capabilities are unmatched by traditional calculation tools. With the promotion of deep learning and open-source platforms, the threshold of AI has also become lower. Combining artificial intelligence with traditional fields to create new fields of high research and application value has become a trend. AI has been involved in many disciplines, such as medicine, materials, energy, and economics. The development of AI requires the support of many kinds of data, and microfluidic systems can often mine object data on a large scale to support AI. Due to the excellent synergy between the two technologies, excellent research results have emerged in many fields. In this review, we briefly review AI and microfluidics and introduce some applications of their combination, mainly in nanomedicine and material synthesis. Finally, we discuss the development trend of the combination of the two technologies.

Microfluidics and materials for smart water monitoring: A review

Water quality monitoring of drinking, waste, fresh and seawaters is of great importance to ensure safety and wellbeing for humans, fauna and flora. Researchers are developing robust water monitoring microfluidic devices but, the delivery of a cost-effective, commercially available platform has not yet been achieved. Conventional water monitoring is mainly based on laboratory instruments or sophisticated and expensive handheld probes for on-site analysis, both requiring trained personnel and being time-consuming. As an alternative, microfluidics has emerged as a powerful tool with the capacity to replace conventional analytical systems. Nevertheless, microfluidic devices largely use conventional pumps and valves for operation and electronics for sensing, that increment the dimensions and cost of the final platforms, reducing their commercialization perspectives. In this review, we critically analyze the characteristics of conventional microfluidic devices for water monitoring, focusing on different water sources (drinking, waste, fresh and seawaters), and their application in commercial products. Moreover, we introduce the revolutionary concept of using functional materials such as hydrogels, poly(ionic liquid) hydrogels and ionogels as alternatives to conventional fluidic handling and sensing tools, for water monitoring in microfluidic devices.

Instrumentation-Compact Digital Microfluidic Reaction Interface-Extended Loop-Mediated Isothermal Amplification for Sample-to-Answer Testing of Vibrio parahaemolyticus

Vibrio parahaemolyticus is usually spread via consumption of contaminated seafood and causes vibriosis. By combination of digital microfluidic (DMF) and loop-mediated isothermal amplification (LAMP), we provided an automated instrumentation-compact DMF-LAMP device for sample-to-answer detection of V. parahaemolyticus. For the first time, how much the proper mixing might facilitate the DMF-LAMP process is explored. The results illustrated that increasing the number of flow configurations and decreasing the fluid-reversibility will extend the interfacial surface available for diffusion-based mass transfer within a droplet microreactor, thus contributing to the overall amplification reaction rate. Noticeably, the DMF-LAMP amplification plateau time is shortened by proper mixing, from 60 min in static mixing and traditional bulk LAMP to 30 min in 2-electrode mixing and 15 min in 3-electrode mixing. The device achieved much higher detection sensitivity (two copies per reaction) than previously reported devices. V. parahaemolyticus from spiked shrimps is detected by Q-tip sampling associated with 3-electrode mixing DMF-LAMPs. The detectable signal occurs within only 3 min at a higher concentration and, at most, is delayed to 18 min, with a detection limit of <0.23 × 10³ CFU/g. Thus, the developed DMF-LAMP device demonstrates potential for being used as a sample-to-answer system with a quick analysis time, high sensitivity, and sample-to-answer format.

A Review of Microfluidic Detection Strategies for Heavy Metals in Water

Heavy metal pollution of water has become a global issue and is especially problematic in some developing countries. Heavy metals are toxic to living organisms, even at very low concentrations. Therefore, effective and reliable heavy metal detection in environmental water is very important. Current laboratory-based methods used for analysis of heavy metals in water require sophisticated instrumentation and highly trained technicians, making them unsuitable for routine heavy metal monitoring in the environment. Consequently, there is a growing demand for autonomous detection systems that could perform in situ or point-of-use measurements. Microfluidic detection systems, which are defined by their small size, have many characteristics that make them suitable for environmental analysis. Some of these advantages include portability, high sample throughput, reduced reagent consumption and waste generation, and reduced production cost. This review focusses on developments in the application of microfluidic detection systems to heavy metal detection in water. Microfluidic detection strategies based on optical techniques, electrochemical techniques, and quartz crystal microbalance are discussed.

An integrated digital microfluidic bioreactor for fully automatic screening of microalgal growth and stress-induced lipid accumulation

Algae are the promising feedstock of biofuel. The screening of competent species and proper fertilizer supply is of the most important tasks. To accelerate this rather slow and laborious step, we developed an integrated high-throughput digital microfluidic (DMF) system that uses a discrete droplet to serve as a microbioreactor, encapsulating microalgal cells. On the basis of fundamental understanding of various droplet hydrodynamics induced by the existence of different sorts of ions and biological species, incorporation of capacitance-based position estimator, electrode-saving-based compensation, and deterministic splitting approach, was performed to optimize the DMF bioreactor. Thus, it enables all processes (e.g., nutrient gradient generation, algae culturing, and analyzing of growth and lipid accumulation) occurring automatically on-chip especially in a high-fidelity way. The ability of the system to compare different microalgal strains on-chip was investigated. Also, the Chlorella sp. were stressed by various conditions and then growth and oil accumulation were analyzed and compared, which demonstrated its potential as a powerful tool to investigate microalgal lipid accumulation at significantly lower laborites and reduced time.

Microenvironment-Controlled Micropatterned Microfluidic Model (MMMM) for Biomimetic In Situ Studies

Attachment of trophozoites to the intestine is an indispensable step for Giardia's survival and pathogenicity in almost 280 million infections worldwide each year. However, the analysis of the attachment mechanism is difficult due to the lack of methods that can create a favorable microaerobic atmosphere. Herein, we developed an osmotic-pressure, pH, excretion, nutrition, gas, ionic-strength, flow-rate, and temperature microenvironment-controlled micropatterned microfluidic model to simulate the in vivo microenvironment to study in situ the stress applied to Giardia in the intestinal tract. We designed three nonbiological surfaces with stagger arrangement manners and integrated them with a resistance microfluidic network to split Giardia-attaching forces ingeniously and developed the term "attaching contribution rate" (ACR) to describe their corresponding contributions. Our study shows that the total attaching force measured is 49.58 Pa, with three components being 22.66 Pa (suction force), 12.52 Pa (clutching force), and 14.4 Pa (combined electrostatic and van der Waals force), respectively, with ACRs being 46%, 25%, and 29%, respectively. By decomposing the attaching force and analyzing each force component and their structure and composition basis, whole profiles of the attachment mechanisms were revealed. Our method enables the analysis of the surface attachment mechanisms and their ACRs for Giardia.