Integrated microfluidic systems with sample preparation and nucleic acid amplification

Advances in biomacromolecule-functionalized magnetic particles for phytopathogen detection

Due to the increasing crop losses caused by common and newly emerging phytopathogens, there is a pressing need for the development of rapid and reliable methods for phytopathogen detection and analysis. Leveraging advancements in biochemical engineering technologies and nanomaterial sciences, researchers have put considerable efforts on utilizing biofunctionalized magnetic micro- and nanoparticles (MPs) to develop rapid and reliable systems for phytopathogen detection. MPs facilitate the rapid, high-throughput analysis and in-field applications, while the biomacromolecules, which play key roles in the biorecognitions, interactions and signal amplification, determine the specificity, sensitivity, reliability, and portability of pathogen detection systems. The integration of MPs and biomacromolecules provides dimensionality- and composition-dependent properties, representing a novel approach to develop phytopathogen detection systems. In this review, we summarize and discuss the general properties, synthesis and characterization of MPs, and focus on biomacromolecule-functionalized MPs as well as their representative applications for phytopathogen detection and analysis reported over the past decade. Extensively studied bioreceptors, such as antibodies, phages and phage proteins, nucleic acids, and glycans that are involved in the recognitions and interactions, are covered and discussed. Additionally, the integration of MPs-based detection system with portable microfluidic devices to facilitate their in-field applications is also discussed. Overall, this review focuses on biomacromolecule-functionalized MPs and their applications for phytopathogen detection, aiming to highlight their potential in developing advanced biosensing systems for effective plant protection.

Implementation of Rapid Nucleic Acid Amplification Based on the Super Large Thermoelectric Cooler Rapid Temperature Rise and Fall Heating Module

In the rapid development of molecular biology, nucleic acid amplification detection technology has received more and more attention. The traditional polymerase chain reaction (PCR) instrument has poor refrigeration performance during its transition from a high temperature to a low temperature in the temperature cycle, resulting in a longer PCR amplification cycle. Peltier element equipped with both heating and cooling functions was used, while the robust adaptive fuzzy proportional integral derivative (PID) algorithm was also utilized as the fundamental temperature control mechanism. The heating and cooling functions were switched through the state machine mode, and the PCR temperature control module was designed to achieve rapid temperature change. Cycle temperature test results showed that the fuzzy PID control algorithm was used to accurately control the temperature and achieve rapid temperature rise and fall (average rising speed = 11 °C/s, average falling speed = 8 °C/s) while preventing temperature overcharging, maintaining temperature stability, and achieving ultra-fast PCR amplification processes (45 temperature cycle time < 19 min). The quantitative results show that different amounts of fluorescence signals can be observed according to the different concentrations of added viral particles, and an analytical detection limit (LoD) as low as 10 copies per μL can be achieved with no false positive in the negative control. The results show that the TEC amplification of nucleic acid has a high detection rate, sensitivity, and stability. This study intended to solve the problem where the existing thermal cycle temperature control technology finds it difficult to meet various new development requirements, such as the rapid, efficient, and miniaturization of PCR.

Sample preparation and detection methods in point-of-care devices towards future at-home testing

Timely and accurate diagnosis is critical for effective healthcare, yet nearly half the global population lacks access to basic diagnostics. Point-of-care (POC) testing offers partial solutions by enabling low-cost, rapid diagnosis at the patient's location. At-home POC devices have the potential to advance preventive care and early disease detection. Nevertheless, effective sample preparation and detection methods are essential for accurate results. This review surveys recent advances in sample preparation and detection methods at POC. The goal is to provide an in-depth understanding of how these technologies can enhance at-home POC devices. Lateral flow assays, nucleic acid tests, and virus detection methods are at the forefront of POC diagnostic technology, offering rapid and sensitive tools for identifying and measuring pathogens, biomarkers, and viral infections. By illuminating cutting-edge research on assay development for POC diagnostics, this review aims to accelerate progress towards widely available, user-friendly, at-home health monitoring tools that empower individuals in personalized healthcare in the future.

Gravity-driven flow control in a fully integrated microfluidic cartridge for molecular point-of-care testing

Molecular point-of-care testing (POCT) system is crucial for the timely prevention and control of infectious diseases. We recently proposed a gravity-driven microfluidic cartridge for molecular POCT detection, without the need for external sources or actuators, demonstrating the advantages in terms of the reduced cartridge size and low development costs. How to achieve precise control of liquid flow behavior is challenging for the gravity-driven cartridge. In this work, we explored the underlying mechanism of flow control in the cartridge and offered optimized solutions for our cartridge design to achieve precise control of dynamic flow rates and enhance pumping efficiency significantly. Through the computational fluid dynamics simulations, we demonstrated that adopting an asymptotic contraction chamber geometry design and a closed-loop air flow channel design with the cartridge inlet can facilitate stable laminar flow of the liquid in our microfluidic cartridge, enabling precise control of flow velocity. We further optimized the microchannel diameter and the contact angle of the liquid with the microchannel wall. The effectiveness of the optimized cartridge for POCT detection was well validated by the accurate detection of the human papillomavirus type 16 virus in the 120 clinical swab samples.

Integrated High-Throughput Centrifugal Microfluidic Chip Device for Pathogen Detection On-Site

An integrated and high-throughput device for pathogen detection is crucial in point-of-care testing (POCT), especially for early diagnosis of infectious diseases and preventing the spread of infection. We developed an on-site testing platform that utilizes a centrifugal microfluidic chip and automated device to achieve high-throughput detection. The low-power (<32 W), portable (220 mm × 220 mm × 170 mm, 4 kg) device can complete bacterial lysis, nucleic acid extraction and purification, loop-mediated isothermal amplification (LAMP) reaction, and real-time fluorescence detection. Magnetic beads for nucleic acid adsorption can be mixed by applying electromagnetic fields and centrifugal forces, and the efficiency of nucleic acid extraction is improved by 60% compared to the no-mixing group. The automated nucleic acid extraction process achieves equivalent nucleic acid extraction efficiency in only 40% of the time consumed using the kit protocol. By designing the valve system and disc layout, the maximum speed required for the centrifugal microfluidic chip is reduced to 1500 rpm, greatly reducing the equipment power consumption and size. In detecting E. coli, our platform achieves a limit of detection (LOD) of 102 CFU/mL in 60 min. In summary, our active centrifugal microfluidic platform provides a solution for the integration of complex biological assays on turntables, with great potential in the application of point-of-care diagnosis.

A highly integrated digital PCR system with on-chip heating for accurate DNA quantitative analysis

Digital polymerase chain reaction (dPCR) is extensively used for highly sensitive disease diagnosis due to its single-molecule detection ability. However, current dPCR systems require intricate DNA sample distribution, rely on cumbersome external heaters, and exhibit sluggish thermal cycling, hampering efficiency and speed of the dPCR process. Herein, we presented the development of a microwell array based dPCR system featuring an integrated self-heating dPCR chip. By utilizing hydrodynamic and electrothermal simulations, the chip's structure is optimized, resulting in improved partitioning within microwells and uniform thermal distribution. Through strategic hydrophilic/hydrophobic modifications on the chip's surface, we effectively secured the compartmentalization of sample within the microwells by employing an overlaying oil phase, which renders homogeneity and independence of samples in the microwells. To achieve precise, stable, uniform, and rapid self-heating of the chip, the ITO heating layer and the temperature control algorithm are deliberately designed. With a capacity of 22,500 microwells that can be easily expanded, the system successfully quantified EGFR plasmid solutions, exhibiting a dynamic linear range of 105 and a detection limit of 10 copies per reaction. To further validate its performance, we employed the dPCR platform for quantitative detection of BCR-ABL1 mutation gene fragments, where its performance was compared against the QuantStudio 3D, and the self-heating dPCR system demonstrated similar analytical accuracy to the commercial dPCR system. Notably, the individual chip is produced on a semiconductor manufacturing line, benefiting from mass production capabilities, so the chips are cost-effective and conducive to widespread adoption and accessibility.

A point-of-care testing platform for on-site identification of genetically modified crops

Genetically modified (GM) food is still highly controversial nowadays. Due to the disparate policies and attitudes worldwide, demands for a rapid, cost-effective and user-friendly GM crop identification method are increasingly significant for import administration, market supervision, etc. However, as the most-recognized methods, nucleic acid-based identification approaches require bulky instruments, long turn-around times and trained personnel, which are only suitable in laboratories. To fulfil the urgent needs of on-site testing, we develop a point-of-care testing platform that is able to identify 12 types of GM crops in less than 40 minutes without using laboratory settings. Our system integrates sample pre-treatment modules in a microfluidic chip, performs DNA amplification via a battery-powered portable kit, and presents results via eye-recognized colorimetric change. A paraffin-based reflow method and a slip plate-based fluid switch are developed to encapsulate and release amplification primers in individual microwells on demand, thus enabling identification of varied targets simultaneously. Our system offers an efficient, affordable and convenient tool for GM crop identification, thus it will not only benefit customs and market administration bureaus, but also satisfy demands of numerous consumers.

A portable all-in-one microfluidic device with real-time colorimetric LAMP for HPV16 and HPV18 DNA point-of-care testing

Screening for high-risk human papillomavirus (HPV) infection is one of the most important preventative measures for cervical cancer. However, fast, convenient, and low-cost HPV detection remains challenging, especially in resource-limited settings. Here, we report a portable all-in-one device (PAD) for point-of-care testing (POCT) for HPV16 and HPV18 DNA in cervical swabs. The PAD was engineered to integrate modules for extraction-free sample lysis, loop-mediated isothermal amplification (LAMP) with lyophilized reagent beads, and real-time colorimetric signal sensing into a single miniaturized device, considerably shortening the sample-to-result time to 15 min. The precision liquid handling in the completely sealed microfluidic chip is achieved by a uniquely designed pressure-balanced automatic liquid flow mechanism, thereby eliminating the need for manual manipulation of liquids and thus the risk of biohazards. The PAD employs an improved real-time colorimetric LAMP (rcLAMP) assay with a limit of detection (LOD) of 1 copy/μL, enabled by enhanced assay chemistry to maximize the reaction kinetics. To validate this device for clinical application, we tested 206 clinical cervical swab samples and obtained a sensitivity of 92.1% and a specificity of 99.0%. This custom PAD enabled by microfluidic and electronic engineering techniques can be configured for the simultaneous detection of HPV16 and HPV18 or other pathogens in point-of-care applications.

Combination-Lock SlipChip Integrating Nucleic Acid Sample Preparation and Isothermal LAMP Amplification for the Detection of SARS-CoV-2

Nucleic acid analysis with an easy-to-use workflow, high specificity and sensitivity, independence of sophisticated instruments, and accessibility outside of the laboratory is highly desirable for the detection and monitoring of infectious diseases. Integration of laboratory-quality sample preparation on a hand-held system is critical for performance. A SlipChip device inspired by the combination lock can perform magnetic bead-based nucleic acid extraction with several clockwise and counterclockwise rotations. A palm-sized base station was developed to assist sample preparation and provide thermal control of isothermal nucleic acid amplification without plug-in power. The loop-mediated isothermal amplification reaction can be performed with a colorimetric method and directly analyzed by the naked eye or with a mobile phone app. This system achieves good bead recovery during the sample preparation workflow and has minimal residue carryover from the lysis and elution buffers. Its performance is comparable to that of the standard laboratory protocol with real-time qPCR amplification methods. The entire workflow is completed in less than 35 min and the device can achieve 500 copies/mL sensitivity. Thirty clinical nasal swab samples were collected and tested with a sensitivity of 95% and a specificity of 100% for SARS-CoV-2. This combination-lock SlipChip provides a promising fast, easy-to-use nucleic acid test with bead-based sample preparation that produces laboratory-quality results for point-of-care settings, especially in home use applications.

Rapid detection methods for foodborne pathogens based on nucleic acid amplification: Recent advances, remaining challenges, and possible opportunities

This article presents a review of recent advancements in the utilization of NAA-based techniques for detecting foodborne pathogens in food products, focusing on studies conducted within the past five years. This review revealed that recent research efforts have primarily aimed at enhancing sensitivity and specificity by improving sample pre-treatment/preparation, DNA isolation, and readout methods. Isothermal-based amplification methods, such as LAMP, RPA, RAA, and RCA, have emerged as promising approaches, providing rapid results within one h and often demonstrating comparable or superior sensitivity to conventional or qPCR methods. However, the attention paid to specific pathogens varies, with Salmonella spp., Listeria spp., E. coli, and V. parahaemolyticus receiving more focus than norovirus and other similar pathogens. NAA-based methods have the potential to significantly contribute to food safety and public health protection. However, further advancements are necessary to fully realize their benefits.

Sample-to-answer sensing technologies for nucleic acid preparation and detection in the field

Efficient sample preparation and accurate disease diagnosis under field conditions are of great importance for the early intervention of diseases in humans, animals, and plants. However, in-field preparation of high-quality nucleic acids from various specimens for downstream analyses, such as amplification and sequencing, is challenging. Thus, developing and adapting sample lysis and nucleic acid extraction protocols suitable for portable formats have drawn significant attention. Similarly, various nucleic acid amplification techniques and detection methods have also been explored. Combining these functions in an integrated platform has resulted in emergent sample-to-answer sensing systems that allow effective disease detection and analyses outside a laboratory. Such devices have a vast potential to improve healthcare in resource-limited settings, low-cost and distributed surveillance of diseases in food and agriculture industries, environmental monitoring, and defense against biological warfare and terrorism. This paper reviews recent advances in portable sample preparation technologies and facile detection methods that have been / or could be adopted into novel sample-to-answer devices. In addition, recent developments and challenges of commercial kits and devices targeting on-site diagnosis of various plant diseases are discussed.

Droplet magnetic-controlled microfluidic chip integrated nucleic acid extraction and amplification for the detection of pathogens and tumor mutation sites

Traditional nucleic acid extraction and detection is based on open operation, which may cause cross-contamination and aerosol formation. This study developed a droplet magnetic-controlled microfluidic chip integrated nucleic acid extraction, purification and amplification. The reagent is sealed in oil to form a droplet, and the nucleic acid is extracted and purified by controlling the movement of the magnetic beads (MBs) through a permanent magnet, ensuring a closed environment. This chip can automatically extract nucleic acid from multiple samples within 20 min, and can be directly placed in the in situ amplification instrument for amplification without further transfer of nucleic acid, characterized by simple, fast, time-saving and labor-saving. The results showed that the chip was able to detect <10 copies/test SARS-CoV-2 RNA, and EGFR exon 21 L858R mutations were detected in H1975 cells as low as 4 cells. In addition, on the basis of the droplet magnetic-controlled microfluidic chip, we further developed a multi-target detection chip, which used MBs to divide the nucleic acid of the sample into three parts. And the macrolides resistance mutations A2063G and A2064G, and the P1 gene of mycoplasma pneumoniae (MP) were successfully detected in clinical samples by the multi-target detection chip, providing the possibility for future application in the detection of multiple pathogens.

A portable, high-throughput real-time quantitative PCR device for point-of-care testing

Nucleic acids detection has become essential in the identification of many infectious diseases and tumors. Conventional qPCR instruments are not suitable for point-of-care Moreover, current miniaturized nucleic acid detection equipment has limited throughput and multiplex detection capabilities, typically allowing the detection of a limited number of samples. Here, we present an affordable, portable, and high-throughput nucleic acid detection device for point-of-care detection. This portable device is approximately 220×165×140 mm in size and about 3 kg in weight. It can provide stable and accurate temperature control and analyze two fluorescent signals (FAM and VIC) and run 16 samples simultaneously. As a proof of concept, we used the two purified DNA samples from Bordetella pertussis and Canine parvovirus and the results showed good linearity and coefficient of variation. Moreover, this portable device can detect as low as 10 copies and has good specificity. Therefore, our device can provide advantages in real-time diagnosis of high-throughput nucleic acid detection in the field, especially for resource-limited conditions.

Trends in Molecular Diagnosis of Nosocomial Pneumonia Classic PCR vs. Point-of-Care PCR: A Narrative Review

Nosocomial pneumonia is one of the most frequent hospital-acquired infections. One of the types of nosocomial pneumonia is ventilator-associated pneumonia, which occurs in endotracheally intubated patients in intensive care units (ICU). Ventilator-associated pneumonia may be caused by multidrug-resistant pathogens, which increase the risk of complications due to the difficulty in treating them. Pneumonia is a respiratory disease that requires targeted antimicrobial treatment initiated as early as possible to have a good outcome. For the therapy to be as specific and started sooner, diagnostic methods have evolved rapidly, becoming quicker and simpler to perform. Polymerase chain reaction (PCR) is a rapid diagnostic technique with numerous advantages compared to classic plate culture-based techniques. Researchers continue to improve diagnostic methods; thus, the newest types of PCR can be performed at the bedside, in the ICU, so-called point of care testing-PCR (POC-PCR). The purpose of this review is to highlight the benefits and drawbacks of PCR-based techniques in managing nosocomial pneumonia.

Advances in point-of-care genetic testing for personalized medicine applications

Breakthroughs within the fields of genomics and bioinformatics have enabled the identification of numerous genetic biomarkers that reflect an individual's disease susceptibility, disease progression, and therapy responsiveness. The personalized medicine paradigm capitalizes on these breakthroughs by utilizing an individual's genetic profile to guide treatment selection, dosing, and preventative care. However, integration of personalized medicine into routine clinical practice has been limited-in part-by a dearth of widely deployable, timely, and cost-effective genetic analysis tools. Fortunately, the last several decades have been characterized by tremendous progress with respect to the development of molecular point-of-care tests (POCTs). Advances in microfluidic technologies, accompanied by improvements and innovations in amplification methods, have opened new doors to health monitoring at the point-of-care. While many of these technologies were developed with rapid infectious disease diagnostics in mind, they are well-suited for deployment as genetic testing platforms for personalized medicine applications. In the coming years, we expect that these innovations in molecular POCT technology will play a critical role in enabling widespread adoption of personalized medicine methods. In this work, we review the current and emerging generations of point-of-care molecular testing platforms and assess their applicability toward accelerating the personalized medicine paradigm.

Taking the microfluidic approach to nucleic acid analysis in forensics: Review and perspectives

Forensic laboratories are universally acknowledged as being overburdened, underfunded, and in need of improved analytical methods to expedite investigations, decrease the costs associated with nucleic acid (NA) analysis, and perform human identification (HID) at the point of need (e.g., crime scene, booking station, etc.). In response, numerous research and development (R&D) efforts have resulted in microfluidic tools that automate portions of the forensic genetic workflow, including DNA extraction, amplification, and short tandem repeat (STR) typing. By the early 2000 s, reports from the National Institute of Justice (NIJ) anticipated that microfluidic 'swab-in-profile-out' systems would be available for use at the crime scene by 2015 and the FBI's 2010 'Rapid DNA' Initiative, approved by Congress in 2017, directed this effort by guiding the development and implementation of maturing systems. At present, few fully-automated microfluidic DNA technologies are commercially available for forensic HID and their adoption by agencies interested in identification has been limited. In practice, the integration of complex laboratory processes to produce one autonomous unit, along with the highly variable nature of forensic input samples, resulted in systems that are more expensive per sample and not comparable to gold-standard identification methods in terms of sensitivity, reproducibility, and multiplex capability. This Review and Perspective provides insight into the contributing factors to this outcome; namely, we focus on the complications associated with the tremendous undertaking that is developing a sample-in-answer-out platform for HID. For context, we also describe the intricate forensic landscape that contributes to a nuanced marketplace, not easily distilled down to cases of simple supply and demand. Moving forward and considering the trade-offs associated with developing methods to compete, sometimes directly, with conventional ones, we recommend a focus shift for microfluidics developers toward the creation of innovative solutions for emerging applications in the field to increase the bandwidth of the forensic investigative toolkit. Likewise, we urge case working personnel to reframe how they conceptualize the currently available Rapid DNA tools; rather than comparing these microfluidic methods to gold-standard procedures, take advantage of their rapid and integrated modes for those situations requiring expedited identifications in an informed manner.

Handheld Purification-Free Nucleic Acid Testing Device for Point-of-Need Detection of Malaria from Whole Blood

World Health Organization's aim to eliminate malaria from developing/resource-limited economies requires easy access to low-cost, highly sensitive, and specific screening. We present a handheld nucleic acid testing device with on-chip automated sample preparation to detect malaria (Plasmodium falciparum) infection from a whole blood sample as a feasibility study. We used a simple two-reagent-based purification-free protocol to prepare the whole blood sample on a piezo pump pressure-driven microfluidic cartridge. The cartridge includes a unique mixing chamber for sample preparation and metering structures to dispense a predetermined volume of the sample lysate mixture into four chambers containing a reaction mix. The parasite genomic DNA concentration can be estimated by monitoring the fluorescence generated from the loop-mediated isothermal amplification reaction in real time. We achieved a sensitivity of ∼0.42 parasite/μL of whole blood, sufficient for detecting asymptomatic malaria parasite carriers.

Sensitive and Quantitative Point-of-Care HIV Viral Load Quantification from Blood Using a Power-Free Plasma Separation and Portable Magnetofluidic Polymerase Chain Reaction Instrument

Point-of-care (POC) HIV viral load (VL) tests are needed to enhance access to HIV VL testing in low- and middle-income countries (LMICs) and to enable HIV VL self-testing at home, which in turn have the potential to enhance the global management of the disease. While methods based on real-time reverse transcription-polymerase chain reaction (RT-PCR) are highly sensitive and quantitatively accurate, they often require bulky and expensive instruments, making applications at the POC challenging. On the other hand, although methods based on isothermal amplification techniques could be performed using low-cost instruments, they have shown limited quantitative accuracies, i.e., being only semiquantitative. Herein, we present a sensitive and quantitative POC HIV VL quantification method from blood that can be performed using a small power-free three-dimensional-printed plasma separation device and a portable, low-cost magnetofluidic real-time RT-PCR instrument. The plasma separation device, which is composed of a plasma separation membrane and an absorbent material, demonstrated 96% plasma separation efficiency per 100 μL of whole blood. The plasma solution was then processed in a magnetofluidic cartridge for automated HIV RNA extraction and quantification using the portable instrument, which completed 50 cycles of PCR in 15 min. Using the method, we achieved a limit of detection of 500 HIV RNA copies/mL, which is below the World Health Organization's virological failure threshold, and a good quantitative accuracy. The method has the potential for sensitive and quantitative HIV VL testing at the POC and at home self-testing.

Nucleic acid amplification-based strategy to detect foodborne pathogens in milk: a review

Milk contaminated with trace amounts of foodborne pathogens can considerably threaten food safety and public health. Therefore, rapid and accurate detection techniques for foodborne pathogens in milk are essential. Nucleic acid amplification (NAA)-based strategies are widely used to detect foodborne pathogens in milk. This review article covers the mechanisms of the NAA-based detection of foodborne pathogens in milk, including polymerase chain reaction (PCR), loop-mediated isothermal amplification (LAMP), recombinase polymerase amplification (RPA), rolling circle amplification (RCA), and enzyme-free amplification, among others. Key factors affecting detection efficiency and the advantages and disadvantages of the above techniques are analyzed. Potential on-site detection tools based on NAA are outlined. We found that NAA-based strategies were effective in detecting foodborne pathogens in milk. Among them, PCR was the most reliable. LAMP showed high specificity, whereas RPA and RCA were most suitable for on-site and in-situ detection, respectively, and enzyme-free amplification was more economical. However, factors such as sample separation, nucleic acid target conversion, and signal transduction affected efficiency of NAA-based strategies. The lack of simple and effective sample separation methods to reduce the effect of milk matrices on detection efficiency was noteworthy. Further research should focus on simplifying, integrating, and miniaturizing microfluidic on-site detection platforms.

Magnetophoresis in Centrifugal Microfluidics at Continuous Rotation for Nucleic Acid Extraction

Centrifugal microfluidics enables fully automated molecular diagnostics at the point-of-need. However, the integration of solid-phase nucleic acid extraction remains a challenge. Under this scope, we developed the magnetophoresis under continuous rotation for magnetic bead-based nucleic acid extraction. Four stationary permanent magnets are arranged above a cartridge, creating a magnetic field that enables the beads to be transported between the chambers of the extraction module under continuous rotation. The centrifugal force is maintained to avoid uncontrolled spreading of liquids. We concluded that below a frequency of 5 Hz, magnetic beads move radially inwards. In support of magnetophoresis, bead inertia and passive geometrical design features allow to control the azimuthal bead movement between chambers. We then demonstrated ferrimagnetic bead transfer in liquids with broad range of surface tension and density values. Furthermore, we extracted nucleic acids from lysed Anopheles gambiae mosquitoes reaching comparable results of eluate purity (LabDisk: A260/A280 = 1.6 ± 0.04; Reference: 1.8 ± 0.17), and RT-PCR of extracted RNA (LabDisk: Ct = 17.9 ± 1.6; Reference: Ct = 19.3 ± 1.7). Conclusively, magnetophoresis at continuous rotation enables easy cartridge integration and nucleic acid extraction at the point-of-need with high yield and purity.

CRISPR-Cas-based techniques for pathogen detection: Retrospect, recent advances, and future perspectives

BACKGROUND

Early detection of pathogen-associated diseases are critical for effective treatment. Rapid, specific, sensitive, and cost-effective diagnostic technologies continue to be challenging to develop. The current gold standard for pathogen detection, polymerase chain reaction technology, has limitations such as long operational cycles, high cost, and high technician and instrumentation requirements.

AIM OF REVIEW

This review examines and highlights the technical advancements of CRISPR-Cas in pathogen detection and provides an outlook for future development, multi-application scenarios, and clinical translation.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Approaches enabling clinical detection of pathogen nucleic acids that are highly sensitive, specific, cheap, and portable are necessary. CRISPR-Cas9 specificity in targeting nucleic acids and "collateral cleavage" activity of CRISPR-Cas12/Cas13/Cas14 show significant promise in nucleic acid detection technology. These methods have a high specificity, versatility, and rapid detection cycle. In this paper, CRISPR-Cas-based detection methods are discussed in depth. Although CRISPR-Cas-mediated pathogen diagnostic solutions face challenges, their powerful capabilities will pave the way for ideal diagnostic tools.

A Salmonella Microfluidic Chip Combining Non-Contact Eddy Heater and 3D Fan-Shaped Mixer with Recombinase Aided Amplification

Foodborne pathogenic bacteria have become a worldwide threat to human health, and rapid and sensitive bacterial detection methods are urgently needed. In this study, a facile microfluidic chip was developed and combined with recombinase-aided amplification (RAA) for rapid and sensitive detection of Salmonella typhimurium using a non-contact eddy heater for dynamic lysis of bacterial cells and a 3D-printed fan-shaped active mixer for continuous-flow mixing. First, the bacterial sample was injected into the chip to flow through the spiral channel coiling around an iron rod under an alternating electromagnetic field, resulting in the dynamic lysis of bacterial cells by this non-contact eddy heater to release their nucleic acids. After cooling to ~75 °C, these nucleic acids were continuous-flow mixed with magnetic silica beads using the fan-shaped mixer and captured in the separation chamber using a magnet. Finally, the captured nucleic acids were eluted by the eluent from the beads to flow into the detection chamber, followed by RAA detection of nucleic acids to determine the bacterial amount. Under the optimal conditions, this microfluidic chip was able to quantitatively detect Salmonella typhimurium from 1.1 × 10² to 1.1 × 10⁵ CFU/mL in 40 min with a detection limit of 89 CFU/mL and might be prospective to offer a simple, low-cost, fast and specific bacterial detection technique for ensuring food safety.

Development of amplification system for point-of-care test of nucleic acid

Nucleic acid testing (NAT) has been widely used in many fields such as medical diagnosis, food safety testing and forensic identification. However, it can only be carried out in professional laboratory because the test process is complicated and rigorous. In this paper, a nucleic acid amplification system based on polymerase chain reaction (PCR) was developed to meet the requirements of point-of-care testing (POCT) for nucleic acids. Firstly, the mechanical structure and electronic control system were designed and constructed. Secondly, an integral separation PID algorithm for temperature control and an intelligent temperature compensation method based on support vector regression (SVR) were proposed. Finally, temperature measurement and biological experiments were performed to prove the stability and availability of the nucleic acid amplification system. The results showed that the system achieved a rapid temperature change velocity of 4.5 °C/s, and the steady-state error was within ± 0.5 °C. The nucleic acids in samples of different concentrations were well amplified, the system can be used for quantitative detection of nucleic acid with the help of a fluorescence detection system, and has higher sensitivity than Tianlong PCR instrument.

Detection of SARS-CoV-2 RNA through tandem isothermal gene amplification without reverse transcription

Diagnosis of SARS-CoV-2 infection through rapid, accurate, and sensitive testing is the most important and fundamental step in coping with the COVID-19 epidemic. We have developed a sensitive fluorometric assay to detect SARS-CoV-2 viral RNA without thermal cycling. This assay system, based on tandem isothermal gene amplification (TIGA), is composed of ternary rolling circle amplification (t-RCA) and subsequent strand displacement amplification (SDA) coupled with G-quadruplex-generating RCA (SDA/GQ-RCA). Without the need to convert viral RNA into cDNA, viral RNA forms a ternary complex composed of hairpin primer (HP) and dumbbell padlock DNA during the t-RCA process. t-RCA generates a long chain of single-stranded DNA (ssDNA) with tandemly repeated hairpin structures that are subjected to SDA. SDA produces multiple short ssDNAs from t-RCA products, which then serve as primers for the second RCA reaction. A long ssDNA harboring repeated copies of the G-quadruplex is produced in the second round of RCA. Emission of enhanced fluorescence by thioflavin T, which intercalates into the G-quadruplex, allows fluorometric detection of amplified viral genes. This fluorometric analysis sensitively detected SARS-CoV-2 RNA as low as 5.9 aM, with a linear range between 0.2 fM and 200 fM within 1 h. Hence, this isothermal gene amplification method without reverse transcription of viral RNA can be applied to diagnose COVID-19 with high sensitivity and accuracy as an alternative to current PCR-based diagnosis.

Development of a proof-of-concept microfluidic portable pathogen analysis system for water quality monitoring

Waterborne diseases cause millions of deaths worldwide, especially in developing communities. The monitoring and rapid detection of microbial pathogens in water is critical for public health protection. This study reports the development of a proof-of-concept portable pathogen analysis system (PPAS) that can detect bacteria in water with the potential application in a point-of-sample collection setting. A centrifugal microfluidic platform is adopted to integrate bacterial cell lysis in water samples, nucleic acid extraction, and reagent mixing with a droplet digital loop mediated isothermal amplification assay for bacteria quantification onto a single centrifugal disc (CD). Coupled with a portable "CD Driver" capable of automating the assay steps, the CD functions as a single step bacterial detection "lab" without the need to transfer samples from vial-to-vial as in a traditional laboratory. The prototype system can detect Enterococcus faecalis, a common fecal indicator bacterium, in water samples with a single touch of a start button within 1 h and having total hands-on-time being less than 5 min. An add-on bacterial concentration cup prefilled with absorbent polymer beads was designed to integrate with the pathogen CD to improve the downstream quantification sensitivity. All reagents and amplified products are contained within the single-use disc, reducing the opportunity of cross contamination of other samples by the amplification products. This proof-of-concept PPAS lays the foundation for field testing devices in areas needing more accessible water quality monitoring tools and are at higher risk for being exposed to contaminated waters.

Microfluidics-based strategies for molecular diagnostics of infectious diseases

Traditional diagnostic strategies for infectious disease detection require benchtop instruments that are inappropriate for point-of-care testing (POCT). Emerging microfluidics, a highly miniaturized, automatic, and integrated technology, are a potential substitute for traditional methods in performing rapid, low-cost, accurate, and on-site diagnoses. Molecular diagnostics are widely used in microfluidic devices as the most effective approaches for pathogen detection. This review summarizes the latest advances in microfluidics-based molecular diagnostics for infectious diseases from academic perspectives and industrial outlooks. First, we introduce the typical on-chip nucleic acid processes, including sample preprocessing, amplification, and signal read-out. Then, four categories of microfluidic platforms are compared with respect to features, merits, and demerits. We further discuss application of the digital assay in absolute nucleic acid quantification. Both the classic and recent microfluidics-based commercial molecular diagnostic devices are summarized as proof of the current market status. Finally, we propose future directions for microfluidics-based infectious disease diagnosis.

Recent advances and application of whole genome amplification in molecular diagnosis and medicine

Whole genome amplification (WGA) is a technology for non-selective amplification of the whole genome sequence, first appearing in 1992. Its primary purpose is to amplify and reflect the whole genome of trace tissues and single cells without sequence bias and to provide sufficient DNA template for subsequent multigene and multilocus analysis, along with comprehensive genome research. WGA provides a method to obtain a large amount of genetic information from a small amount of DNA and provides a valuable tool for preserving limited samples in molecular biology. WGA technology is especially suitable for forensic identification and genetic disease research, along with new technologies such as next-generation sequencing (NGS). In addition, WGA is also widely used in single-cell sequencing. Due to the small amount of DNA in a single cell, it is often unable to meet the amount of samples needed for sequencing, so WGA is generally used to achieve the amplification of trace samples. This paper reviews WGA methods based on different principles, summarizes both amplification principle and amplification quality, and discusses the application prospects and challenges of WGA technology in molecular diagnosis and medicine.

Powerful CRISPR-Based Biosensing Techniques and Their Integration With Microfluidic Platforms

In the fight against the worldwide pandemic coronavirus disease 2019 (COVID-19), simple, rapid, and sensitive tools for nucleic acid detection are in urgent need. PCR has been a classic method for nucleic acid detection with high sensitivity and specificity. However, this method still has essential limitations due to the dependence on thermal cycling, which requires costly equipment, professional technicians, and long turnover times. Currently, clustered regularly interspaced short palindromic repeats (CRISPR)-based biosensors have been developed as powerful tools for nucleic acid detection. Moreover, the CRISPR method can be performed at physiological temperature, meaning that it is easy to assemble into point-of-care devices. Microfluidic chips hold promises to integrate sample processing and analysis on a chip, reducing the consumption of sample and reagent and increasing the detection throughput. This review provides an overview of recent advances in the development of CRISPR-based biosensing techniques and their perfect combination with microfluidic platforms. New opportunities and challenges for the improvement of specificity and efficiency signal amplification are outlined. Furthermore, their various applications in healthcare, animal husbandry, agriculture, and forestry are discussed.

A fully integrated SNP genotyping system for hereditary hearing-loss detection

Hereditary hearing loss is one of the most common human neurosensory disorders, and there is a great need for early intervention methods such as genetically screening newborns. Single nucleotide polymorphisms (SNPs) are the major genetic targets for hearing-loss screening. In this study, a fully integrated SNP genotyping system was constructed to identify hereditary hearing loss-related genetic markers from human whole blood. The entire detection process, including blood cell lysis, nucleic acid extraction, the reaction mixture distribution, the chambers sealing and the two-colour multiplex competitive allele-specific polymerase chain reaction (KASP), can be automatically conducted in a self-contained cassette within 3 hours. To critically evaluate the performance of the system, its specificity, sensitivity and stability were assessed. Then, 13 clinical samples were genotyped with this fluidic cassette system to detect seven hotspot deafness-associated mutations in three genes (MT-RNR1, GJB2 and SLC26A4). The detection results of the cassette system were 100% concordant with those obtained by Sanger sequencing, proving its accuracy in the genetic screening of inherited hearing loss.

Bridging the gap between development of point-of-care nucleic acid testing and patient care for sexually transmitted infections

The incidence rates of sexually transmitted infections (STIs), including the four major curable STIs - chlamydia, gonorrhea, trichomoniasis and, syphilis - continue to increase globally, causing medical cost burden and morbidity especially in low and middle-income countries (LMIC). There have seen significant advances in diagnostic testing, but commercial antigen-based point-of-care tests (POCTs) are often insufficiently sensitive and specific, while near-point-of-care (POC) instruments that can perform sensitive and specific nucleic acid amplification tests (NAATs) are technically complex and expensive, especially for LMIC. Thus, there remains a critical need for NAAT-based STI POCTs that can improve diagnosis and curb the ongoing epidemic. Unfortunately, the development of such POCTs has been challenging due to the gap between researchers developing new technologies and healthcare providers using these technologies. This review aims to bridge this gap. We first present a short introduction of the four major STIs, followed by a discussion on the current landscape of commercial near-POC instruments for the detection of these STIs. We present relevant research toward addressing the gaps in developing NAAT-based STI POCT technologies and supplement this discussion with technologies for HIV and other infectious diseases, which may be adapted for STIs. Additionally, as case studies, we highlight the developmental trajectory of two different POCT technologies, including one approved by the United States Food and Drug Administration (FDA). Finally, we offer our perspectives on future development of NAAT-based STI POCT technologies.

Visible-light and near-infrared fluorescence and surface-enhanced Raman scattering point-of-care sensing and bio-imaging: a review

This review article deals with the concepts, principles and applications of visible-light and near-infrared (NIR) fluorescence and surface-enhanced Raman scattering (SERS) in in vitro point-of-care testing (POCT) and in vivo bio-imaging. It has discussed how to utilize the biological transparency windows to improve the penetration depth and signal-to-noise ratio, and how to use surface plasmon resonance (SPR) to amplify fluorescence and SERS signals. This article has highlighted some plasmonic fluorescence and SERS probes. It has also reviewed the design strategies of fluorescent and SERS sensors in the detection of metal ions, small molecules, proteins and nucleic acids. Particularly, it has provided perspectives on the integration of fluorescent and SERS sensors into microfluidic chips as lab-on-chips to realize point-of-care testing. It has also discussed the design of active microfluidic devices and non-paper- or paper-based lateral flow assays for in vitro diagnostics. In addition, this article has discussed the strategies to design in vivo NIR fluorescence and SERS bio-imaging platforms for monitoring physiological processes and disease progression in live cells and tissues. Moreover, it has highlighted the applications of POCT and bio-imaging in testing toxins, heavy metals, illicit drugs, cancers, traumatic brain injuries, and infectious diseases such as COVID-19, influenza, HIV and sepsis.

Recombinase polymerase amplification integrated with microfluidics for nucleic acid testing at point of care

Nucleic acid testing (NAT) implemented on a portable, miniaturized, and integrated device with rapid and sensitive results readout is highly demanded for pathogen detection or genetic screening at resource-limited settings, especially after the outbreak of coronavirus disease 2019 (COVID-19). The integration of recombinase polymerase amplification (RPA) with emerging microfluidics, classified by paper-based microfluidics and chip-based microfluidics, shows great potential to perform laboratory independent NAT assays at point of care with minimal labor, time and energy consumption. This review summarizes the state-of-the-art of RPA integrated with paper-based microfluidics and chip-based microfluidics, and discusses their pros and cons. Finally, existing challenges and possible ways for optimization of microfluidics-based RPA are proposed.

A finger-driven disposable micro-platform based on isothermal amplification for the application of multiplexed and point-of-care diagnosis of tuberculosis

Tuberculosis (TB) remains the high-risk infectious pathogen that caused global pandemic and high mortality, particularly in the areas lack in health resources. Clinical TB screening and diagnosis are so far mainly conducted on limited types of commercial platforms, which are expensive and require skilled personnel. In this work, we introduced a low-cost and portable finger-driven microfluidic chip (named Fd-MC) based on recombinase polymerase amplification (RPA) for rapid on-site detection of TB. After injection of the pre-treated sample solution, the pre-packaged buffer was driven by the pressure generated by the finger-actuated operation to accomplish sequential processes of diagnosis in a fully isolated microchannel. An in-situ fluorescence strategy based on FAM-probe was implemented for on-chip results read-out though a hand-held UV lamp. Hence, the Fd-MC proved unique advantageous for avoiding the risk of infection or environmental contamination. In addition, the Fd-MC was designed for multiplexed detection, which is able to not only identify TB/non-TB infection, but also differentiate between human Mycobacterium tuberculosis and Mycobacterium bovis. The platform was verified in 37 clinical samples, statistically with 100% specificity and 95.2% sensitivity as compared to commercial real-time RPA. Overall, the proposed platform eliminates the need on external pumps and skilled personnel, holding promise to POC testing in the resource-limited area.

DCD-chip designed for the digital and ultraprecise quantification of copy number variation

The progress of CNV detection in DCD-chip.

Micro and Nanoscale Technologies for Diagnosis of Viral Infections

Viral infection is one of the leading causes of mortality worldwide. The growth of globalization significantly increases the risk of virus spreading, making it a global threat to future public health. In particular, the ongoing coronavirus disease 2019 (COVID-19) pandemic outbreak emphasizes the importance of devices and methods for rapid, sensitive, and cost-effective diagnosis of viral infections in the early stages by which their quick and global spread can be controlled. Micro and nanoscale technologies have attracted tremendous attention in recent years for a variety of medical and biological applications, especially in developing diagnostic platforms for rapid and accurate detection of viral diseases. This review addresses advances of microneedles, microchip-based integrated platforms, and nano- and microparticles for sampling, sample processing, enrichment, amplification, and detection of viral particles and antigens related to the diagnosis of viral diseases. Additionally, methods for the fabrication of microchip-based devices and commercially used devices are described. Finally, challenges and prospects on the development of micro and nanotechnologies for the early diagnosis of viral diseases are highlighted.

Microfluidic Systems for Cancer Diagnosis and Applications

Microfluidic devices have led to novel biological advances through the improvement of micro systems that can mimic and measure. Microsystems easily handle sub-microliter volumes, obviously with guidance presumably through laminated fluid flows. Microfluidic systems have production methods that do not need expert engineering, away from a centralized laboratory, and can implement basic and point of care analysis, and this has attracted attention to their widespread dissemination and adaptation to specific biological issues. The general use of microfluidic tools in clinical settings can be seen in pregnancy tests and diabetic control, but recently microfluidic platforms have become a key novel technology for cancer diagnostics. Cancer is a heterogeneous group of diseases that needs a multimodal paradigm to diagnose, manage, and treat. Using advanced technologies can enable this, providing better diagnosis and treatment for cancer patients. Microfluidic tools have evolved as a promising tool in the field of cancer such as detection of a single cancer cell, liquid biopsy, drug screening modeling angiogenesis, and metastasis detection. This review summarizes the need for the low-abundant blood and serum cancer diagnosis with microfluidic tools and the progress that has been followed to develop integrated microfluidic platforms for this application in the last few years.

Integrated Microfluidic-Based Platforms for On-Site Detection and Quantification of Infectious Pathogens: Towards On-Site Medical Translation of SARS-CoV-2 Diagnostic Platforms

The rapid detection and quantification of infectious pathogens is an essential component to the control of potentially lethal outbreaks among human populations worldwide. Several of these highly infectious pathogens, such as Middle East respiratory syndrome (MERS) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), have been cemented in human history as causing epidemics or pandemics due to their lethality and contagiousness. SARS-CoV-2 is an example of these highly infectious pathogens that have recently become one of the leading causes of globally reported deaths, creating one of the worst economic downturns and health crises in the last century. As a result, the necessity for highly accurate and increasingly rapid on-site diagnostic platforms for highly infectious pathogens, such as SARS-CoV-2, has grown dramatically over the last two years. Current conventional non-microfluidic diagnostic techniques have limitations in their effectiveness as on-site devices due to their large turnaround times, operational costs and the need for laboratory equipment. In this review, we first present criteria, both novel and previously determined, as a foundation for the development of effective and viable on-site microfluidic diagnostic platforms for several notable pathogens, including SARS-CoV-2. This list of criteria includes standards that were set out by the WHO, as well as our own "seven pillars" for effective microfluidic integration. We then evaluate the use of microfluidic integration to improve upon currently, and previously, existing platforms for the detection of infectious pathogens. Finally, we discuss a stage-wise means to translate our findings into a fundamental framework towards the development of more effective on-site SARS-CoV-2 microfluidic-integrated platforms that may facilitate future pandemic diagnostic and research endeavors. Through microfluidic integration, many limitations in currently existing infectious pathogen diagnostic platforms can be eliminated or improved upon.

Digital Hybridization Human Papillomavirus Assay with Attomolar Sensitivity without Amplification

Detection of nucleic acid without amplification can avoid problems associated with thermal cycling such as labor-intensiveness and aerosol pollution. Here we develop a droplet-based digital microfluidic hybridization assay for nucleic acid detection with attomolar sensitivity. This assay provides a clinically useful sensitivity for detecting human papillomavirus (HPV) without amplification. The sensitivity is accomplished using femtoliter-sized droplet microfluidics for concentrating enzyme-catalyzed fluorescent products into a detectable signal and magnetic beads for accelerating reaction time. Meanwhile, using magnetic beads and droplet microfluidic chips, we can improve the sampling efficiency over conventional methods. We characterized the sensitivity, selectivity, detection range, stability, and accuracy of our assay. Our assay is 50-fold more sensitive than the traditional hybrid capture assay. The assay without amplification avoids problems of complex handling procedures and aerosol pollution. The direct and sensitive detection of nucleic acid using a droplet microfluidic system provides an early disease diagnosis tool.

An integrated microfluidic detection system for the automated and rapid diagnosis of high-risk human papillomavirus

Human papillomavirus (HPV) causes the prevalent sexually transmitted infection that accounts for the majority of cervical cancer incidences. Therefore, the development of a rapid, accurate, automatic and affordable nucleic acid detection strategy is urgently required for HPV tests, among which microfluidic chip is a promising diagnostic method. In this work, we developed a microfluidic detection system consisting of a microfluidic chip and the corresponding detection equipment to diagnose high-risk HPV. The proposed method integrates nucleic acid purification, isothermal amplification and real-time fluorescence detection into one device. Moreover, it demonstrates good detection performance such as high specificity of primer sets (100%) and exceptional stability (coefficient of variation <6%) among five HPV genotypes. Besides, the microfluidic loop-mediated isothermal amplification (LAMP) assay is accurate (specificity of 91.7% and sensitivity of 100%) and fast (average time threshold = 10.56 minutes) when considering the conventional qPCR assay as the gold standard. The integrated microfluidic detection system offers automated and rapid diagnosis within 40 minutes and shows broad potential to deliver point-of-care detection in resource-limited circumstances owing to its simplicity and affordability.

Nucleic Acid Tests for Clinical Translation

Nucleic acids, including deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), are natural biopolymers composed of nucleotides that store, transmit, and express genetic information. Overexpressed or underexpressed as well as mutated nucleic acids have been implicated in many diseases. Therefore, nucleic acid tests (NATs) are extremely important. Inspired by intracellular DNA replication and RNA transcription, in vitro NATs have been extensively developed to improve the detection specificity, sensitivity, and simplicity. The principles of NATs can be in general classified into three categories: nucleic acid hybridization, thermal-cycle or isothermal amplification, and signal amplification. Driven by pressing needs in clinical diagnosis and prevention of infectious diseases, NATs have evolved to be a rapidly advancing field. During the past ten years, an explosive increase of research interest in both basic research and clinical translation has been witnessed. In this review, we aim to provide comprehensive coverage of the progress to analyze nucleic acids, use nucleic acids as recognition probes, construct detection devices based on nucleic acids, and utilize nucleic acids in clinical diagnosis and other important fields. We also discuss the new frontiers in the field and the challenges to be addressed.

Tumor-Induced Inflammatory Cytokines and the Emerging Diagnostic Devices for Cancer Detection and Prognosis

Chronic inflammation generated by the tumor microenvironment is known to drive cancer initiation, proliferation, progression, metastasis, and therapeutic resistance. The tumor microenvironment promotes the secretion of diverse cytokines, in different types and stages of cancers. These cytokines may inhibit tumor development but alternatively may contribute to chronic inflammation that supports tumor growth in both autocrine and paracrine manners and have been linked to poor cancer outcomes. Such distinct sets of cytokines from the tumor microenvironment can be detected in the circulation and are thus potentially useful as biomarkers to detect cancers, predict disease outcomes and manage therapeutic choices. Indeed, analyses of circulating cytokines in combination with cancer-specific biomarkers have been proposed to simplify and improve cancer detection and prognosis, especially from minimally-invasive liquid biopsies, such as blood. Additionally, the cytokine signaling signatures of the peripheral immune cells, even from patients with localized tumors, are recently found altered in cancer, and may also prove applicable as cancer biomarkers. Here we review cytokines induced by the tumor microenvironment, their roles in various stages of cancer development, and their potential use in diagnostics and prognostics. We further discuss the established and emerging diagnostic approaches that can be used to detect cancers from liquid biopsies, and additionally the technological advancement required for their use in clinical settings.

An integrated microfluidic platform for detection of ovarian clear cell carcinoma mRNA biomarker FXYD2

In this work we developed an integrated microfluidic system for automatically detecting the ovarian clear cell carcinoma (OCCC) biomarker FXYD2. Dealing with ascites from ovarian cancer patients, capture of cancer cells, isolation of messenger RNA, and quantitative reverse-transcription polymerase chain reaction were integrated into a single microfluidic chip and carried out on-chip automatically. OCCC is a subtype of ovarian cancer with a high mortality risk, and a high FXYD2 gene expression level was shown to be closely associated with OCCC. The lowest limit of quantification using a benchtop protocol of this system could be as low as 100 copies per sample. By normalizing the expression to a housekeeping gene, GAPDH, a simple cycle threshold ratio index could distinguish high FXYD2 expression cells from the low-expression ones. This developed platform may therefore facilitate future OCCC diagnosis and/or prognosis.

Microfluidic formation of crystal-like structures

Crystal-like structures find application in several fields ranging from biomedical engineering to material science. For instance, droplet crystals are critical for high throughput assays and material synthesis, while particle crystals are important for particles and cell encapsulation, Drop-seq technologies, and single-cell analysis. Formation of crystal-like structures relies entirely on the possibility of manipulating with great accuracy the micrometer-size objects forming the crystal. In this context, microfluidic devices offer versatile tools for the precise manipulation of droplets and particles, thus enabling fabrication of crystal-like structures that form due to hydrodynamic interactions among droplets or particles. In this review, we aim at providing an holistic representation of crystal-like structure formation mediated by hydrodynamic interactions in microfluidic devices. We also discuss the physical origin of these hydrodynamic interactions and their relation to parameters such as device geometry, fluid properties, and flow conditions.

Recent Advances in Microfluidic Devices for Contamination Detection and Quality Inspection of Milk

Milk is a necessity for human life. However, it is susceptible to contamination and adulteration. Microfluidic analysis devices have attracted significant attention for the high-throughput quality inspection and contaminant analysis of milk samples in recent years. This review describes the major proposals presented in the literature for the pretreatment, contaminant detection, and quality inspection of milk samples using microfluidic lab-on-a-chip and lab-on-paper platforms in the past five years. The review focuses on the sample separation, sample extraction, and sample preconcentration/amplification steps of the pretreatment process and the determination of aflatoxins, antibiotics, drugs, melamine, and foodborne pathogens in the detection process. Recent proposals for the general quality inspection of milk samples, including the viscosity and presence of adulteration, are also discussed. The review concludes with a brief perspective on the challenges facing the future development of microfluidic devices for the analysis of milk samples in the coming years.