Fabrication of Polymerase Chain Reaction Plastic Lab-on-a-Chip Device for Rapid Molecular Diagnoses

Rapid Prototyping of Multi-Functional and Biocompatible Parafilm®-Based Microfluidic Devices by Laser Ablation and Thermal Bonding

In this paper, we report a simple, rapid, low-cost, biocompatible, and detachable microfluidic chip fabrication method for customized designs based on Parafilm^®. Here, Parafilm^® works as both a bonding agent and a functional membrane. Its high ultimate tensile stress (3.94 MPa) allows the demonstration of high-performance actuators such as microvalves and micropumps. By laser ablation and the one-step bonding of multiple layers, 3D structured microfluidic chips were successfully fabricated within 2 h. The consumption time of this method (~2 h) was 12 times less than conventional photolithography (~24 h). Moreover, the shear stress of the PMMA-Parafilm^®-PMMA specimens (0.24 MPa) was 2.13 times higher than that of the PDMS-PDMS specimens (0.08 MPa), and 0.56 times higher than that of the PDMS-Glass specimens (0.16 MPa), showing better stability and reliability. In this method, multiple easily accessible materials such as polymethylmethacrylate (PMMA), PVC, and glass slides were demonstrated and well-incorporated as our substrates. Practical actuation devices that required high bonding strength including microvalves and micropumps were fabricated by this method with high performance. Moreover, the biocompatibility of the Parafilm^®-based microfluidic devices was validated through a seven-day E. coli cultivation. This reported fabrication scheme will provide a versatile platform for biochemical applications and point-of-care diagnostics.

Rapid on-site nucleic acid testing: On-chip sample preparation, amplification, and detection, and their integration into all-in-one systems

As nucleic acid testing is playing a vital role in increasingly many research fields, the need for rapid on-site testing methods is also increasing. The test procedure often consists of three steps: Sample preparation, amplification, and detection. This review covers recent advances in on-chip methods for each of these three steps and explains the principles underlying related methods. The sample preparation process is further divided into cell lysis and nucleic acid purification, and methods for the integration of these two steps on a single chip are discussed. Under amplification, on-chip studies based on PCR and isothermal amplification are covered. Three isothermal amplification methods reported to have good resistance to PCR inhibitors are selected for discussion due to their potential for use in direct amplification. Chip designs and novel strategies employed to achieve rapid extraction/amplification with satisfactory efficiency are discussed. Four detection methods providing rapid responses (fluorescent, optical, and electrochemical detection methods, plus lateral flow assay) are evaluated for their potential in rapid on-site detection. In the final section, we discuss strategies to improve the speed of the entire procedure and to integrate all three steps onto a single chip; we also comment on recent advances, and on obstacles to reducing the cost of chip manufacture and achieving mass production. We conclude that future trends will focus on effective nucleic acid extraction via combined methods and direct amplification via isothermal methods.

Fabrication of Ultrafine, Highly Ordered Nanostructures Using Carbohydrate-Inorganic Hybrid Block Copolymers

Block copolymers (BCPs) have garnered considerable interest due to their ability to form microphase-separated structures suitable for nanofabrication. For these applications, it is critical to achieve both sufficient etch selectivity and a small domain size. To meet both requirements concurrently, we propose the use of oligosaccharide and oligodimethylsiloxane as hydrophilic and etch-resistant hydrophobic inorganic blocks, respectively, to build up a novel BCP system, i.e., carbohydrate-inorganic hybrid BCP. The carbohydrate-inorganic hybrid BCPs were synthesized via a click reaction between oligodimethylsiloxane with an azido group at each chain end and propargyl-functionalized maltooligosaccharide (consisting of one, two, and three glucose units). In the bulk state, small-angle X-ray scattering revealed that these BCPs microphase separated into gyroid, asymmetric lamellar, and symmetric lamellar structures with domain-spacing ranging from 5.0 to 5.9 nm depending on the volume fraction. Additionally, we investigated microphase-separated structures in the thin film state and discovered that the BCP with the most asymmetric composition formed an ultrafine and highly oriented gyroid structure as well as in the bulk state. After reactive ion etching, the gyroid thin film was transformed into a nanoporous-structured gyroid SiO₂ material, demonstrating the material’s promising potential as nanotemplates.

Fabrication of Wearable PDMS Device for Rapid Detection of Nucleic Acids via Recombinase Polymerase Amplification Operated by Human Body Heat

Pathogen detection by nucleic acid amplification proved its significance during the current coronavirus disease 2019 (COVID-19) pandemic. The emergence of recombinase polymerase amplification (RPA) has enabled nucleic acid amplification in limited-resource conditions owing to the low operating temperatures around the human body. In this study, we fabricated a wearable RPA microdevice using poly(dimethylsiloxane) (PDMS), which can form soft-but tight-contact with human skin without external support during the body-heat-based reaction process. In particular, the curing agent ratio of PDMS was tuned to improve the flexibility and adhesion of the device for better contact with human skin, as well as to temporally bond the microdevice without requiring further surface modification steps. For PDMS characterization, water contact angle measurements and tests for flexibility, stretchability, bond strength, comfortability, and bendability were conducted to confirm the surface properties of the different mixing ratios of PDMS. By using human body heat, the wearable RPA microdevices were successfully applied to amplify 210 bp from Escherichia coli O157:H7 (E. coli O157:H7) and 203 bp from the DNA plasmid SARS-CoV-2 within 23 min. The limit of detection (LOD) was approximately 500 pg/reaction for genomic DNA template (E. coli O157:H7), and 600 fg/reaction for plasmid DNA template (SARS-CoV-2), based on gel electrophoresis. The wearable RPA microdevice could have a high impact on DNA amplification in instrument-free and resource-limited settings.

Pressure-Free Assembling of Poly(methyl methacrylate) Microdevices via Microwave-Assisted Solvent Bonding and Its Biomedical Applications

Poly(methyl methacrylate) (PMMA) has become an appealing material for manufacturing microfluidic chips, particularly for biomedical applications, because of its transparency and biocompatibility, making the development of an appropriate bonding strategy critical. In our research, we used acetic acid as a solvent to create a pressure-free assembly of PMMA microdevices. The acetic acid applied between the PMMA slabs was activated by microwave using a household microwave oven to tightly merge the substrates without external pressure such as clamps. The bonding performance was tested and a superior bond strength of 14.95 ± 0.77 MPa was achieved when 70% acetic acid was used. Over a long period, the assembled PMMA device with microchannels did not show any leakage. PMMA microdevices were also built as a serpentine 2D passive micromixer and cell culture platform to demonstrate their applicability. The results demonstrated that the bonding scheme allows for the easy assembly of PMMAs with a low risk of clogging and is highly biocompatible. This method provides for a simple but robust assembly of PMMA microdevices in a short time without requiring expensive instruments.

A newly developed paper embedded microchip based on LAMP for rapid multiple detections of foodborne pathogens

BACKGROUND

Microfluidic chip detection technology is considered a potent tool for many bioanalytic applications. Rapid detection of foodborne pathogens in the early stages is imperative to prevent the outbreak of foodborne diseases, known as a severe threat to human health. Conventional bacterial culture methods for detecting foodborne pathogens are time-consuming, laborious, and lacking in pathogen diagnosis. To overcome this problem, we have created an embedded paper-based microchip based on isothermal loop amplification (LAMP), which can rapidly and sensitively detect foodborne pathogens.

RESULTS

We embed paper impregnated with LAMP reagent and specific primers in multiple reaction chambers of the microchip. The solution containing the target pathogen was injected into the center chamber and uniformly distributed into the reaction chamber by centrifugal force. The purified DNA of Escherichia coli O157:H7, Salmonella spp., Staphylococcus aureus, and Vibrio parahaemolyticus has been successfully amplified and directly detected on the microchip. The E. coli O157:H7 DNA was identified as low as 0.0134 ng μL- 1. Besides, the potential of this microchip in point-of-care testing was further tested by combining the on-chip sample purification module and using milk spiked with Salmonella spp.. The pyrolyzed milk sample was filtered through a polydopamine-coated paper embedded in the inside of the sample chamber. It was transported to the reaction chamber by centrifugal force for LAMP amplification. Then direct chip detection was performed in the reaction chamber embedded with calcein-soaked paper. The detection limit of Salmonella spp. in the sample measured by the microchip was approximately 12 CFU mL- 1.

CONCLUSION

The paper embedded LAMP microchip offers inexpensive, user-friendly, and highly selective pathogen detection capabilities. It is expected to have great potential as a quick, efficient, and cost-effective solution for future foodborne pathogen detection.

Advances in Plant Disease Detection and Monitoring: From Traditional Assays to In-Field Diagnostics

Human activities significantly contribute to worldwide spread of phytopathological adversities. Pathogen-related food losses are today responsible for a reduction in quantity and quality of yield and decrease value and financial returns. As a result, “early detection” in combination with “fast, accurate, and cheap” diagnostics have also become the new mantra in plant pathology, especially for emerging diseases or challenging pathogens that spread thanks to asymptomatic individuals with subtle initial symptoms but are then difficult to face. Furthermore, in a globalized market sensitive to epidemics, innovative tools suitable for field-use represent the new frontier with respect to diagnostic laboratories, ensuring that the instruments and techniques used are suitable for the operational contexts. In this framework, portable systems and interconnection with Internet of Things (IoT) play a pivotal role. Here we review innovative diagnostic methods based on nanotechnologies and new perspectives concerning information and communication technology (ICT) in agriculture, resulting in an improvement in agricultural and rural development and in the ability to revolutionize the concept of “preventive actions”, making the difference in fighting against phytopathogens, all over the world.

Poly(acrylic acid) as an adhesion promoter for UV-assisted thermoplastic bonding: Application for the in vitro construction of human blood vessels

In this study, we introduced a novel adhesion bonding method for fabricating thermoplastic microdevices using poly(acrylic acid) (PAA) as a UV-assisted adhesion promoter. The bonding mechanism was based on the covalent cross-links between poly(methyl methacrylate) (PMMA) and PAA via the free radicals in their carbon backbone generated under UV irradiation. The water contact angle and Fourier-transformed infrared (FTIR) analysis were performed to analyze the surface characteristics of the PAA-coated PMMA. PMMAs were bonded under UV treatment for 60 s with the highest bond strength of around 1.18 MPa. The PMMA microdevice was leak-proof for over 200 h. Besides, clog-free PMMA microdevices with various-sizes microchannels were performed to demonstrate such a high applicable bonding method for microdevice fabrication. Moreover, PMMAs were bonded with other thermoplastics with a bond strength of around 0.5 MPa. Notably, collagen was easily coated inside the PMMA microchannels via electrostatic interaction between PAA and collagen which is beneficial for on-device cell culture. As a result, a layered co-culture model of smooth muscle cells (SMCs) and human umbilical vein endothelial cells (HUVECs) was realized inside simple straight microchannels mimicking human blood vessel wall. Therefore, the introduced bonding method could pave the way for fabricating microdevice for cell-related applications.

Chitosan-polydopamine hydrogel complex: a novel green adhesion agent for reversibly bonding thermoplastic microdevice and its application for cell-friendly microfluidic 3D cell culture

Owing to biocompatible characteristics and supporting cell growth capability, hydrogels have been widely used for scaffold fabrication and surface coating for cell culture. To employ the advantages of hydrogels, in the present study, we introduce a biocompatible chitosan (CS)-polydopamine (pDA) hydrogel complex as a green adhesion agent for the reversible bonding of thermoplastics assisted by UV irradiation. Poly(methyl methacrylate) (PMMA) substrates were bonded due to the covalent bond network formed between the amine groups of either CS or pDA in the hydrogel complex and the aldehyde groups of the oxidized PMMA surface via the Schiff-base reaction during the UV irradiation. Furthermore, the introduced method allowed for reversible bonding, which is highly appropriate for the fabrication of microdevices for cell-related applications. Surface characterizations such as water contact angle measurement, scanning electron microscopy analysis (SEM), atomic force microscopy analysis (AFM), and Fourier-transform infrared microscopy analysis (FTIR) were performed to confirm the successful coating of the hydrogel complex on the PMMA surface. Moreover, the bonding between two PMMAs or PMMA with other thermoplastics was successfully investigated with high bond strengths ranging from 0.4 to 0.7 MPa. The potential for reversible bonding of this method was verified by repeating the bonding/debonding cycle of the bonded PMMAs for three times, which maintained the bond strength at approximately 0.5 MPa. The compatibility of the bonding method in biological applications was examined by culturing mesenchymal stem cells (MSCs) inside a microchannel where multiple uniform-sized MSC spheroids were successfully formed. Then, spheroids were harvested for off-chip experiments enabled by the reversibility of the introduced bonding strategy. The bonding strategy employing a green hydrogel complex as a cell-friendly and eco-friendly adhesion agent could have a high impact on the fabrication of microdevices suitable for advanced organ-on-a-chip studies.

The highly sensitive determination of serotonin by using gold nanoparticles (Au NPs) with a localized surface plasmon resonance (LSPR) absorption wavelength in the visible region

The development of improved methods for the synthesis of monodisperse gold nanoparticles (Au NPs) is of high priority because they can be used as substrates for surface-enhanced Raman scattering (SERS) applications relating to biological lipids. Herein, Au NPs have been successfully synthesized via a seed-mediated growth method. The LSPR peak is controlled via adjusting the gold nanoseed component, and different fabrication methods were studied to establish the effect of sonication time on NP size. The simple, facile, and room-temperature method is based on a conventional ultrasonic bath, which leads to ultrasonic energy effects on the size and morphology of the Au NPs. This research offers new opportunities for the production of highly monodispersed spherical Au NPs without the use of a magnetic stirrer method, as evidenced by ultraviolet-visible reflectance spectra and scanning electron microscopy (SEM) analysis. SEM images indicate that the spherical Au NP colloidal particles are stable and reliable, which paves the way for their use as a nanostructured biosensor platform that can be exploited for multiple applications, for example, in materials science, sensing, catalysis, medicine, food safety, biomedicine, etc. The highest enhancement factor that could be achieved in terms of the SERS enhancement activity of these Au NP arrays was determined using 10-9 M serotonin (5-hydroxytryptamine, 5-HT) as the Raman probe molecules.

All-in-one microfluidic nucleic acid diagnosis system for multiplex detection of sexually transmitted pathogens directly from genitourinary secretions

Sexually transmitted infections are a serious public health concern worldwide, especially in young people. More than 30 pathogens can cause sexually transmitted diseases and co-infection often occurs. Therefore, the development of fast, low-cost and easy-to-use diagnostic screening methods is urgently needed for disease prevention and control. Herein, we established an all-in-one microfluidic nucleic acid diagnosis system, which could simultaneously detect Chlamydia trachomatis, Neisseria gonorrhoeae, Mycoplasma hominis and Ureaplasma urealyticum directly from genitourinary secretions with minimal manual manipulations. This system integrated nucleic acid extraction, amplification, and detection on a single microfluidic chip and could be automatically performed in an integrated detection device. This novel diagnosis tool showed good detection limits, stability (coefficient of variation <6%), specificity (no cross-reaction with 23 other pathogens for each target) and resistance to interference by other substances and the diagnostic efficacy was similar to that of PCR. The turn-around time was reduced to 50 min from sample to answer with automated testing steps. This novel diagnosis tool has the advantages of highly integrated, automated, sample-to-answer detection, and could thus replace the traditional method. This could significantly improve the prevention and control of sexually transmitted diseases.

Rapid Fabrication of Poly(methyl methacrylate) Devices for Lab-on-a-Chip Applications Using Acetic Acid and UV Treatment

In the present study, we introduce a new approach for rapid bonding of poly(methyl methacrylate) (PMMA)-based microdevices using an acetic acid solvent with the assistance of UV irradiation. For the anticipated mechanism, acetic acid and UV irradiation induced free radicals on the PMMA surfaces, and acrylate monomers subsequently formed cross-links to create a permanent bonding between the PMMA substrates. PMMA devices effectively bonded within 30 s at a low pressure using clamps, and a clogging-free microchannel was achieved with the optimized 50% acetic acid. For surface characterizations, contact angle measurements and bonding performance analyses were conducted using predetermined acetic acid concentrations to optimize bonding conditions. In addition, the highest bond strength of bonded PMMA was approximately 11.75 MPa, which has not been reported before in the bonding of PMMA. A leak test was performed over 180 h to assess the robustness of the proposed method. Moreover, to promote the applicability of this bonding method, we tested two kinds of microfluidic device applications, including a cell culture-based device and a metal microelectrode-integrated device. The results showed that the cell culture-based application was highly biocompatible with the PMMA microdevices fabricated using an acetic acid solvent. Moreover, the low pressure required during the bonding process supported the integration of metal microelectrodes with the PMMA microdevice without any damage to the metal films. This novel bonding method holds great potential in the ecofriendly and rapid fabrication of microfluidic devices using PMMA.

Heat and pressure-resistant room temperature irreversible sealing of hybrid PDMS–thermoplastic microfluidic devices via carbon–nitrogen covalent bonding and its application in a continuous-flow polymerase chain reaction

In this study, we have introduced a facile room-temperature strategy for irreversibly sealing polydimethylsiloxane to various thermoplastics using (3-aminopropyl)triethoxysilane (APTES) and [2-(3,4-epoxycyclohexyl)ethyl]trimethoxysilane (ECTMS).

Fabrication of a polycarbonate microdevice and boronic acid-mediated surface modification for on-chip sample purification and amplification of foodborne pathogens

In this study, we integrated sample purification and genetic amplification in a seamless polycarbonate microdevice to facilitate foodborne pathogen detection. The sample purification process was realized based on the increased affinity of the boronic acid-modified surface toward the cis-diol group present on the bacterial outer membrane. The modification procedure was conducted at room temperature using disposable syringe. The visible color and fluorescence signals of alizarin red sodium were used to confirm the success of the surface modification process. Escherichia coli O157:H7 containing green fluorescence protein (GFP) and Staphylococcus aureus were chosen as the microbial models to demonstrate the nonspecific immobilization using the microdevice. Bacterial solutions of various concentrations were injected into the microdevice at three flow rates to optimize the operation conditions. This microdevice successfully amplified the 384-bp fragment of the eaeA gene of the captured E. coli O157:H7 within 1 h. Its detection limit for E. coli O157:H7 was determined to be 1 × 10³ colony-forming units per milliliter (CFU mL^-1). The proposed microdevice serves as a monolithic platform for facile and on-site identification of major foodborne pathogens.

A foldable isothermal amplification microdevice for fuchsin-based colorimetric detection of multiple foodborne pathogens

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.

A rapid and eco-friendly isothermal amplification microdevice for multiplex detection of foodborne pathogens

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.

Analysis of PCR Kinetics inside a Microfluidic DNA Amplification System

In order to analyze the DNA amplification numerically with integration of the DNA kinetics, three-dimensional simulations, including flow and thermal fields, and one-dimensional polymerase chain reaction (PCR) kinetics are presented. The simulated results are compared with experimental data that have been applied to the operation of a continuous-flow PCR device. Microchannels fabricated by Micro Electro-Mechanical Systems (MEMS) technologies are shown. Comprehensive simulations of the flow and thermal fields and experiments measuring temperatures during thermal cycling are presented first. The resultant velocity and temperature profiles from the simulations are introduced to the mathematical models of PCR kinetics. Then kinetic equations are utilized to determine the evolution of the species concentrations inside the DNA mixture along the microchannel. The exponential growth of the double-stranded DNA concentration is investigated numerically with the various operational parameters during PCR. Next a 190-bp segment of Bartonella DNA is amplified to evaluate the PCR performance. The trends of the experimental results and numerical data regarding the DNA amplification are similar. The unique architecture built in this study can be applied to a low-cost portable PCR system in the future.