Bonding Strategies for Thermoplastics Applicable for Bioanalysis and Diagnostics

Microfluidics is a multidisciplinary science that includes physics, chemistry, engineering, and biotechnology. Such microscale systems are receiving growing interest in applications such as analysis, diagnostics, and biomedical research. Thermoplastic polymers have emerged as one of the most attractive materials for microfluidic device fabrication owing to advantages such as being optically transparent, biocompatible, cost-effective, and mass producible. However, thermoplastic bonding is a key challenge for sealing microfluidic devices. Given the wide range of bonding methods, the appropriate bonding approach should be carefully selected depending on the thermoplastic material and functional requirements. In this review, we aim to provide a comprehensive overview of thermoplastic fabricating and bonding approaches, presenting their advantages and disadvantages, to assist in finding suitable microfluidic device bonding methods. In addition, we highlight current applications of thermoplastic microfluidics to analyses and diagnostics and introduce future perspectives on thermoplastic bonding strategies.

Green synthesis of carbon quantum dots and their environmental applications

Green synthesis of scalable, high-quality, fluorescent carbon quantum dots (CQDs) from natural biomass remains attractive due to their outstanding environmental application. CQDs are an emerging class of zero-dimensional carbon nanomaterials (<10 nm) that have recently attracted much attention due to their strong optical properties, biocompatibility, nontoxicity, uniform particle size, high photostability, low-cost synthesis, and highly tunable photoluminescence. The unique properties of CQDs possess a broad range of prospective applications in a number of fields such as metal ions detection, photocatalysis, sensing, medical diagnosis, bioimaging, and drug delivery. CQD nanostructures are synthesized using various techniques such as hydrothermal method, laser ablation, microwave irradiation, electrochemical oxidation, reflux method, and ultrasonication. However, this type of fabrication approach requires several chemical reactions including oxidation, carbonization, and pyrolysis. Green synthesis of CQDs has several advantages such as the use of low-cost and non-toxic raw materials, renewable resources, simple operations, and being environment-friendly. This review article will discuss the physicochemical properties of CQDs techniques used in the production of CQDs, and the stability of CQDs along with their applications in wastewater treatment and biomedical fields.

Colorimetric detection of viable antibiotic resistant Enterococcus mediated by cordless operation of reverse transcription loop-mediated isothermal amplification

In this study, we applied a tube-based reverse transcription loop-mediated isothermal amplification technique using preloaded amplification and detection reagents for simple screening of viable vancomycin-resistant Enterococcus in a cordless manner. We adopted an mRNA-based approach to detect live Enterococcus in vancomycin-treated cultures. We used agarose to preload and store all reagents for amplification and detection inside the tube, which could achieve on-site isothermal nucleic acid amplification and detection in less than 1 h without using sophisticated instruments. Moreover, the use of a portable insulated water tumbler eliminated the need for electricity, which is usually important in nucleic acid amplification-based assays. The water tumbler acted as a heat source to supply a stable heat required for the amplification reaction, which could last up to 45 min. In addition, colorimetric detection was realized using pH-based methods. The detection was triggered by shaking the tube so that the amplified solution was reacted with phenolphthalein embedded in the tube cap. The introduced one-pot strategy has many advantages such as easy and cordless operation, low cost, disposability, and less chance of contamination because the amplification and detection occur in a closed system. The system could have a great impact on nucleic acid analyses in instrument-free and low-resource areas.

Recent advances in airborne pathogen detection using optical and electrochemical biosensors

The world is currently facing an adverse condition due to the pandemic of airborne pathogen SARS-CoV-2. Prevention is better than cure; thus, the rapid detection of airborne pathogens is necessary because it can reduce outbreaks and save many lives. Considering the immense role of diverse detection techniques for airborne pathogens, proper summarization of these techniques would be beneficial for humans. Hence, this review explores and summarizes emerging techniques, such as optical and electrochemical biosensors used for detecting airborne bacteria (Bacillus anthracis, Mycobacterium tuberculosis, Staphylococcus aureus, and Streptococcus pneumoniae) and viruses (Influenza A, Avian influenza, Norovirus, and SARS-CoV-2). Significantly, the first section briefly focuses on various diagnostic modalities applied toward airborne pathogen detection. Next, the fabricated optical biosensors using various transducer materials involved in colorimetric and fluorescence strategies for infectious pathogen detection are extensively discussed. The third section is well documented based on electrochemical biosensors for airborne pathogen detection by differential pulse voltammetry, cyclic voltammetry, square-wave voltammetry, amperometry, and impedance spectroscopy. The unique pros and cons of these modalities and their future perspectives are addressed in the fourth and fifth sections. Overall, this review inspected 171 research articles published in the last decade and persuaded the importance of optical and electrochemical biosensors for airborne pathogen detection.

A Rotatable Paper Device Integrating Reverse Transcription Loop-Mediated Isothermal Amplification and a Food Dye for Colorimetric Detection of Infectious Pathogens

In this study, we developed a rotatable paper device integrating loop-mediated isothermal amplification (RT-LAMP) and a novel naked-eye readout of the RT-LAMP results using a food additive, carmoisine, for infectious pathogen detection. Hydroxyl radicals created from the reaction between CuSO₄ and H₂O₂ were used to decolor carmoisine, which is originally red. The decolorization of carmoisine can be interrupted in the presence of DNA amplicons produced by the RT-LAMP reaction due to how DNA competitively reacts with the hydroxyl radicals to maintain the red color of the solution. In the absence of the target DNA, carmoisine is decolored, owing to its reaction with hydroxyl radicals; thus, positive and negative samples can be easily differentiated based on the color change of the solution. A rotatable paper device was fabricated to integrate the RT-LAMP reaction with carmoisine-based colorimetric detection. The rotatable paper device was successfully used to detect SARS-CoV-2 and SARS-CoV within 70 min using the naked eye. Enterococcus faecium spiked in milk was detected using the rotatable paper device. The detection limits for the SARS-CoV-2 and SARS-CoV targets were both 10³ copies/µL. The rotatable paper device provides a portable and low-cost tool for detecting infectious pathogens in a resource-limited environment.

Emerging bismuth-based direct Z-scheme photocatalyst for the degradation of organic dye and antibiotic residues

Organic dye and antibiotic residues are some of the key substances that can contaminate the environment due to their wide usage in various industries and modern medicine. The degradation of these substances present in waterbodies is essential while contemplating human health. Photocatalysts (PSs) are promising materials that develop highly reactive species instantly by simple solar energy conversion for degrading the organic dye and antibiotic residues and converting them into nontoxic products. Among numerous semiconductors, the bismuth (Bi)-containing PS has received great attention due to its strong sunlight absorption, facile preparation, and high photostability. Owing to the technology advancement and demerits of the traditional methods, a Bi-containing direct Z-scheme PS has been developed for efficient photogenerated charge carrier separation and strong redox proficiency. In this review, a synthetic Bi-based Z-scheme heterojunction that mimics natural photosynthesis is described, and its design, fabrication methods, and applications are comprehensively reviewed. Specifically, the first section briefly explains the role of various semiconductors in the environmental applications and the importance of the Bi-based materials for constructing the Z-scheme photocatalytic systems. In the successive section, overview of Z-scheme PS are concisely discussed. The fourth and fifth sections extensively explain the degradation of the organic dyes and antibiotics utilizing the Bi-based direct Z-scheme heterojunction. Eventually, the conclusions and future perspectives of this emerging research field are addressed. Overall, this review is potentially useful for the researchers involved in the environmental remediation field as a collection of up-to-date research articles for the fabrication of the Bi-containing direct Z-scheme PS.

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.

Adsorptive removal of organic pollutant methylene blue using polysaccharide-based composite hydrogels

Methylene blue (MB) is categorized as an organic dye (OD) released as effluents after various industrial activities and is one of the most abundant pollutants in the aquatic environment. Significantly, because of its potential toxicity, removing MB from wastewater has been a matter of necessity in recent times. Numerous analytical techniques have been applied, among which polysaccharide-based composite hydrogels appear as the most favorable for MB removal because of their large surface area, excellent mechanical properties, swelling capability, and large-scale production. In this review, the first section gives adequate information about the ODs' adverse effects on the environment and the contribution of polysaccharide-based hydrogels for OD removal, especially MB. Next, various mechanisms such as electrostatic interactions, π-π interactions, hydrogen bonding, hydrophobic interaction, van der Waals force, and coordination interaction involved in the adsorption technique are investigated. The third section extensively describes the MB removal by incorporation of various materials such as monomers, metal oxides, magnetic nanoparticles, and clay into the polysaccharide matrix to produce composite hydrogels. Finally, the current limitations and future perspectives of the polysaccharide-based composite hydrogel techniques are addressed. Overall, this review acknowledged the vital role of polysaccharide-based composite hydrogels for MB adsorption by surveying 110 research articles published in the past five years (2015-2021).

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.

Quantitative proteomic analysis comparing grades ICRS1 and ICRS3 in patients with osteoarthritis

Osteoarthritis (OA), which is caused by joint damage, is the most common form of arthritis, affecting millions of people worldwide. This damage can accumulate over time, which is why aging is one of the main contributors to joint damage associated with OA. The OA-related proteins that have been reported to date have been identified by the comparative analysis of OA patients with normal controls, following surgical or pharmacological treatment. For the first time, the present study analyzed OA-related proteins in patients with OA according to the International Cartilage Repair Society (ICRS) scale. Changes in protein expression can be observed during the OA process. The present study demonstrated differential protein expression patterns in articular cartilage from ICRS1- and ICRS3-graded OA patients. ICRS grade-matched OA knee samples from 12 OA patients, 6 ICRS grade 1 patients and 6 ICRS3 patients were subjected to proteomic analysis using the LTQ-Orbitrap mass spectrometry system. A total of 231 unique proteins were identified as expressed across the ICRS1 and ICRS3 OA patient groups. Relative differences in protein expression associated with the following classifications were observed: Biological adhesion, cell killing, cellular process, development process and molecular function. Although some of these proteins have been previously reported to be associated with rheumatoid arthritis, including cartilage oligomeric matrix protein, collagen types, angiogenin, complement C5 and CD59 glycoprotein, numerous additional proteins were newly identified, which may further help our understanding of disease pathogenesis. These findings suggested that these proteins may be used to develop novel therapeutic targets for OA.

Polydopamine aggregation: A novel strategy for power-free readout of loop-mediated isothermal amplification integrated into a paper device for multiplex pathogens detection

Loop-mediated isothermal amplification (LAMP) has been widely used for detecting pathogens. However, power-free and clear visualization of results still remain challenging. In this study, we developed a paper device integrated with power-free DNA detection strategy realized by polydopamine aggregation. In the presence of DNA amplicons, the polymerization of dopamine into aggregated polydopamine was hindered, while in the absence of DNA amplicons, polydopamine aggregation is facilitated. The porosity of the paper enabled the capillary flow of dispersed polydopamine for positive sample, while aggregated polydopamine remained at the bottom of the paper strip due to large size of the aggregates for negative sample. Based on this mechanism, we fabricated a slidable paper device integrating LAMP with dopamine polymerization for the naked-eye detection, operated in a seamless manner. Moreover, the introduced paper device was successfully used to detect DNA extracted from Escherichia coli O157:H7 and SARS-CoV-2 within 25 min, as well as Enterococcus faecium within 35 min. The detection limits of both Escherichia coli O157:H7 and SARS-CoV-2 were 10^-4 ng/μL. The introduced paper device can be used as a simple and sensitive tool for detecting multiple infectious pathogens, making it an ideal tool particularly for resource-limited environment.

Ferrowax microvalves for fully automated serial dilution on centrifugal microfluidic platforms

We herein describe a centrifugal microfluidic system to accomplish a fully automated serial dilution. The liquid flow on the disc was regulated by utilizing ferrowax microvalves systematically integrated into the channels within specially designed metering structures. By opening the differently positioned microvalves through irradiation of IR laser to allow metering, the same amount of diluent was serially eluted to the dilution chamber from the same diluent chamber. After dilution, the diluted samples were automatically delivered to the respective final product chambers by appropriately opening or closing the microvalves in the connecting channels, followed by rotating the disc. Based on this unique design principle, six consecutive two-fold and 10-fold dilutions were successfully achieved, yielding excellent accuracy in a wide dynamic range up to six orders of magnitude. Very importantly, the overall serial dilution process, including the diluent addition, mixing, and product transfer steps, was completed very rapidly within 5 min, due to the minimized procedures enabled by the automated actuation of the ferrowax microvalves at the rationally designed positions. We expect our centrifugal microfluidic system would serve as a powerful elemental tool to realize fully automated diagnostic microsystems involving the serial dilution process.

Spinning and Fully Integrated Microdevice for Rapid Screening of Vancomycin-Resistant Enterococcus

This study introduces a spinning and fully integrated paper-based microdevice that can perform multiple functions, including DNA extraction, amplification, and colorimetric detection, for monitoring two major vancomycin-resistant Enterococci (VREs), which carry the vanA and vanB genes. The spinning microdevice is composed of a stationary part and a spinning part. The square-shaped stationary part has two zones: the lysis and reaction zones. The spinning part, which has a spin wheel-like shape, was inserted perpendicularly into the stationary part so that its two semicircles remained on the upper and lower parts. Sodium hydroxide-treated glass microfiber filter discs, inserted in the upper semicircle, were soaked in the lysis chambers by folding them toward the lysis zone to capture DNA in the lysis chambers. The captured DNA was transferred to the reaction chambers by folding the discs toward the reaction chambers. Water was added to the sodium hydroxide-treated glass microfiber filter discs to elute purified DNA into the reaction chambers. The upper semicircle was then unfolded, and the reaction chambers were sealed for subsequent loop-mediated isothermal amplification (LAMP) for 45 min. After the reaction, the spinning part was spun in the lysis zone direction to bring the lower semicircle, inserted with phenolphthalein-treated glass microfiber filter discs, toward the upper part of the stationary part. By folding it toward the reaction chambers, the lower semicircle came into contact with them and the phenolphthalein-treated glass microfiber filter discs were soaked in the reaction chambers and expressed color after 30 s. Based on the pH change during the LAMP reaction, the phenolphthalein-treated discs remained pink in the absence of target DNA, while those in contact with the positive samples turned colorless. A sensitive detection with a VRE limit of detection of 10² CFU/mL for tap water spiked with VRE carrying the vanA gene was achieved using this microdevice. Both VREs, carrying vanA and vanB genes, were successfully identified from tap water and contaminated equipment surfaces within 75 min. The introduced microdevice demonstrated a rapid, accurate, and sensitive performance for the environmental assessment of VRE contamination in resource-limited regions.

Increased salivary syndecan-1 level is associated with salivary gland function and inflammation in patients with Sjögren's syndrome

Objectives: Syndecan-1 (SDC-1), a transmembrane heparin sulphate proteoglycan predominantly expressed on epithelial cells, also exists in a soluble form through ectodomain shedding. SDC-1 expression and shedding may be modulated in the inflammatory milieu of primary Sjögren's syndrome (SS). We investigated SDC-1 expression in minor salivary glands (MSGs) and analysed the association between salivary or plasma levels of SDC-1 and clinical parameters in SS.Method: We measured salivary and plasma SDC-1 levels via an enzyme-linked immunosorbent assay and assessed the salivary flow rates (SFRs) in 70 patients with SS and 35 healthy subjects. Disease activity indices, serological markers, salivary gland scintigraphy, and MSG biopsy were evaluated in patients with SS.Results: SDC-1 expression was upregulated on ductal epithelial cells in inflamed salivary glands. Salivary SDC-1 levels in patients significantly exceeded those in healthy subjects [median (interquartile range) 49.0 (20.7-79.1) vs 3.7 (1.7-6.3) ng/mL, p < 0.001] and inversely correlated with SFRs (r = -0.358, p = 0.032) and ejection fractions of the parotid (r = -0.363, p = 0.027) and submandibular (r = -0.485, p = 0.002) glands in salivary gland scintigraphy. Plasma SDC-1 levels were significantly correlated with the EULAR Sjögren's Syndrome Disease Activity Index (r = 0.507, p < 0.001) and EULAR Sjögren's Syndrome Patient Reported Index (r = 0.267, p = 0.033). Focus scores were correlated with salivary SDC-1 levels (r = 0.551, p = 0.004).Conclusion: Salivary and plasma SDC-1 levels may constitute potential biomarkers for salivary gland function and disease activity, respectively, in SS.

Recent progress in smartphone-based techniques for food safety and the detection of heavy metal ions in environmental water

Emerging smartphone-based point-of-care tests (POCTs) are cost-effective, precise, and easy to implement in resource-limited areas. Thus, they are considered a potential alternative to conventional diagnostic testing. This review explores food safety and the detection of metal ions in environmental water based on unprecedented smartphone technology. Specifically, we provide an overview of various methods used for target analyte detection (antibiotics, enzymes, mycotoxins, pathogens, pesticides, small molecules, and metal ions), such as colorimetric, fluorescence, microscopic imaging, and electrochemical methods. This paper performs a comprehensive review of smartphone-based POCTs developed in the last three years (2018-2020) and evaluates their relative advantages and limitations. Moreover, we discuss the imperative role of new technology in the progress of POCTs. Sensor materials (metal nanoparticles, carbon dots, quantum dots, organic substrates, etc.) and detection techniques (paper-based, later flow assay, microfluidic platform, etc.) involved in POCTs based on smartphones, and the challenges faced by these techniques, are addressed.

Incidence and Distribution of the Pathogens Causing Central Nervous System Infections at the University Hospital of Korea

BACKGROUND

The pathogens involved in central nervous system (CNS) infections are various, such as viruses, bacteria, and fungi, so a syndromic approach can be required. In addition, since their rapid and accurate detection is very crucial, molecular diagnostics using cerebrospinal fluid is becoming the emerging standard method.

METHODS

The study was conducted retrospectively to identify the incidence and distribution patterns of the pathogens according to gender, age, season, and month and to analyze their codetection from August 2017 to July 2020. It was also conducted to investigate turn-around times (TATs) according to the detection method. The detection methods were FilmArray® Meningitis/Encephalitis (M/E) method (FilmArray), Cepheid® Xpert EV assay (Xpert), and Multiplex PCR method for five species of bacteria.

RESULTS

The overall incidence for at least one pathogen was 13.9% (346/2,496). The highest incidence was shown in age group 4 (3 - 6 years), with 27.4%. The detection rates by FilmArray, Xpert, and Multiplex PCR method were 39.8%, 41.7%, and 0.4%, respectively. Enterovirus (EV) showed the highest incidence rate, which accounted for 37.0%. The distribution of the pathogens according to the age groups were the highest in age group 4, with 47.5% (168/354), followed by 27.4% (97/354) in age group 5. Of the ten cases in which bacteria were detected, S. agalactiae accounted for 60.0% (6/10), most of which occurred in age group 1. E. coli K1, L. monocytogenes, and N. meningitidis were not detected. In the viral distribution, EV accounted for the highest proportion in all age groups. The overall proportion of EV accounted for 87.6% (310/354), followed by human parechovirus with 2.8% (10/354). The most commonly detected season was summer, comprising 75.1%. A total of eight cases of co-detection with two pathogens accounted for 1.6% (8/507) in FilmArray. In FilmArray, all TATs were found to be shorter than Xpert.

CONCLUSIONS

The information on the incidence and distribution patterns of the pathogens causing CNS infections and their rapid detection are critically important to clinicians in the management of immunocompromised patients, elderly, and children. The expeditious molecular diagnostics for these pathogens would be valuable in medical decisions by clinicians.

Development of a highly sensitive sensor chip using optical diagnostic based on functionalized plasmonically active AuNPs

Measuring solution concentration plays an important role in chemical, biochemical, clinical diagnosis, environmental monitoring, and biological analyses. In this work, we develop a transmission-mode localized surface plasmon resonance sensor chip system and convenient method which is highly efficient, highly sensitive for detection sensing using multimode fiber. The plasmonically active sensor's surface AuNPs with high-density NPs were decorated onto 1 cm sensing length of various clad-free fiber in the form of homogeneous monolayer utilizing a self-assembly process for immobilization of the target molecule. The carboxyl bond is formed through a functional reaction on the sensor head. Using the significance in the refractive index difference and numerical aperture, which is caused by a variation in the concentration of measuring bovine serum albumin (BSA) protein which can be accurately measured by the output signal. The refractive index variation of the medium analyte layer can be converted to signal output power change at the He-Ne wavelength of 632.8 nm. The sensor detection limit was estimated to be 0.075 ng ml^-1for BSA protein which shows high sensitivity compared to other types of label-free optical biosensors. This also leads to a possibility of finding the improvement in the sensitivity label-free biosensors. The conventional method should allow multimode fiber biosensors to become a possible replacement for conventional biosensing techniques based on fluorescence.

Nucleic acid amplification-based microfluidic approaches for antimicrobial susceptibility testing

Because of the global spread of antimicrobials, there is an urgent need to develop rapid and effective tools for antimicrobial susceptibility testing to help clinicians prescribe accurate and appropriate antibiotic doses sooner. The conventional methods for antimicrobial susceptibility testing are usually based on bacterial culture methods, which are time-consuming, complicated, and labor-intensive. Therefore, other approaches are needed to address these issues. Recently, microfluidic technology has gained significant attention in infection management due to its advantages including rapid detection, high sensitivity and specificity, highly automated assay, simplicity, low cost, and potential for point-of-care testing in low-resource areas. Microfluidic advances for antimicrobial susceptibility testing can be classified into phenotypic (usually culture-based) and genotypic tests. Genotypic antimicrobial susceptibility testing is the detection of resistant genes in a microorganism using methods such as nucleic acid amplification. This review (with 107 references) surveys the different forms of nucleic acid amplification-based microdevices used for genotypic antimicrobial susceptibility testing. The first section reviews the serious threat of antimicrobial-resistant microorganisms and the urgent need for fast check-ups. Next, several conventional antimicrobial susceptibility testing methods are discussed, and microfluidic technology as a promising candidate for rapid detection of antimicrobial-resistant microorganisms is briefly introduced. The next section highlights several advancements of microdevices, with an emphasis on their working principles and performance. The review concludes with the importance of fully integrated microdevices and a discussion on future perspectives.

A paper-based colorimetric chemosensor for rapid and highly sensitive detection of sulfide for environmental monitoring

In this study, we report on paper-based colorimetric detection of sulfide using a newly synthesized chemical acting as a chemosensor, based on the deprotonation mechanism. Paper strips were also fabricated and incorporated with the chemosensor for on-site monitoring. The presence of sulfide induced deprotonation of a hydroxyl group of the chemosensor, which eventually resulted in a distinct spectral change in the tube as well as a visible color change on a paper strip. The chemosensor showed a highly selective colorimetric response to sulfide by changing its color from colorless to yellow without any interference from a mixture containing other anions. Moreover, the chemosensor effectively differentiated sulfide from other thiols, including cysteine and glutathione. The chemosensor colorimetrically detected sulfide with a fast response time of 10 s under physiological conditions. Practically, the paper test strip enabled colorimetric visualization of as low as 30 μM sulfide and a good recovery in quantitative analysis in water samples. The introduced paper-based chemosensor is a promising colorimetric strategy with rapid, selective, and sensitive sensing abilities for sulfide monitoring in environmental water samples.

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.

Ultraviolet-induced in situ gold nanoparticles for point-of-care testing of infectious diseases in loop-mediated isothermal amplification

The present study investigated ultraviolet-induced in situ gold nanoparticles (AuNPs) coupled with loop-mediated isothermal amplification (LAMP) for the point-of-care testing (POCT) of two major infectious pathogens, namely, Coronavirus (COVID-19) and Enterococcus faecium (E. faecium spp.). In the process, gold ions in a gold chloride (HAuCl4) solution were reduced using trisodium citrate (Na3Ct), a reducing agent, and upon UV illumination, red-colored AuNPs were produced in the presence of LAMP amplicons. The nitrogenous bases of the target deoxyribonucleic acid (DNA) acted as a physical support for capturing gold ions dissolved in the sample. The high affinity of gold with the nitrogenous bases enabled facile detection within 10 min, and the detection limit of COVID-19 plasmid DNA was as low as 42 fg μL-1. To ensure POCT, we designed a portable device that contained arrays of reagent chambers and detection chambers. In the portable device, colorimetric reagents such as HAuCl4 and Na3Ct were contained in the reagent chambers; these reagents were subsequently transferred to the detection chambers where LAMP amplicons were present and thus allowed convenient sample delivery and multiplex detection. Owing to the high sensitivity of the in situ AuNPs, simplicity of portable device fabrication, and rapid colorimetric detection, we strongly believe that the fabricated portable device could serve as a kit for rapid POCT for instantaneous detection of infectious diseases, and could be readily usable at the bedside.