Colorimetric Nucleic Acid Detection on Paper Microchip Using Loop Mediated Isothermal Amplification and Crystal Violet Dye

Nanohybrid nanozyme based colourimetric immunosensor for porcine gelatin

Enzyme mimicking nanomaterials, nanozymes, have gained considerable interest in the scientific community because of their superior properties compared to natural enzymes, including their high stability at extreme conditions, cheaper availability, and ease of synthesis. Herein, we report novel colloidal gold nanoparticles - graphene nanoplatelets - chitosan (CS) with peroxidase mimicking properties used to carry out highly sensitive and selective immunoassay for porcine gelatin detection. The interaction between anti-gelatin antibody conjugated nanozyme with porcine gelatin proteins produced an ultrasensitive immunoassay response in the form of a colourimetric signal directly proportional to the porcine gelatin protein concentration. The nanozyme produced a colourimetric response in the presence of its substrate, 3,3',5,5'-tetramethylbenzidine (TMB) and hydrogen peroxide (H2O2), demonstrating its peroxidase mimicking properties. The results revealed that the nanozyme exhibited remarkable selectivity and sensitivity in the assay, detecting proteins at concentrations as low as 86.42 pg/mL. Additionally, the immunosensor demonstrated a broad linear detection range spanning from 200 pg/mL to 2 ng/mL.

Isothermal amplification-based microfluidic devices for detecting foodborne pathogens: a review

The gold standard for nucleic acid amplification-based diagnosis is the polymerase chain reaction (PCR). The PCR recognizes the targets such as foodborne pathogens by amplifying their specific genes. The integration of nucleic acid amplification-based assays on microfluidic platforms represents a highly promising solution for convenient, cheap, and effective control of foodborne pathogens. However, the application of the PCR is limited to on-site detection because the method requires sophisticated equipment for temperature control, which makes it complicated for microfluidic integration. Alternatively, isothermal amplification methods are promising tools for integrating microfluidic platforms for on-site detection of foodborne pathogens. This review summarized advances in isothermal amplification-based microfluidic devices for detecting foodborne pathogens. Different nucleic acid extraction approaches and the integration of these approaches in microfluidic platforms were first reviewed. Microfluidic platforms integrated with three common isothermal amplification methods including loop-mediated isothermal amplification, recombinase polymerase amplification, and recombinase-aided amplification were then described and discussed.

Low-tech vs. high-tech approaches in μPADs as a result of contrasting needs and capabilities of developed and developing countries focusing on diagnostics and point-of-care testing

Paper-based analysis has captivated scientists' attention in the field of analytical chemistry and related areas for the last two decades. Arguably no other area of modern chemical analysis is so broad and diverse in its approaches spanning from simple 'low-tech' low-cost paper-based analytical devices (PADs) requiring no or simple instrumentation, to sophisticated PADs and microfluidic paper-based analytical devices (μPADs) featuring elements of modern material science and nanomaterials affording high selectivity and sensitivity. Correspondingly diverse is the applicability, covering resource-limited scenarios on the one hand and most advanced approaches on the other. Herein we offer a view reflecting this diversity in the approaches and types of devices. The core idea of this article rests in dividing μPADs according to their type into two groups: A) instrumentation-free μPADs for resource-limited scenarios or developing countries and B) instrumentation-based μPADs as futuristic POC devices for e-diagnostics mainly aimed at developed countries. Each of those two groups is presented and discussed with the view of the main requirements in the given area, the most common targets, sample types and suitable detection approaches either implementing high-tech elements or low-tech low-cost approaches. Finally, a socioeconomic perspective is offered in discussing the fabrication and operational costs of μPADs, and, future perspectives are offered.

Tuning Hydrophobicity of Paper Substrates for Effective Colorimetric detection of Glucose and Nucleic acids

This study investigated the colorimetric response of standard glucose, serum glucose, and nucleic acid assays on various paper surfaces with different wettability, including hydrophilic, hydrophobic, and nearly superhydrophobic surfaces. Water contact angles (WCA) formed by water droplets on each surface were measured using ImageJ software. The hydrophilic surface showed no contact angle, while the hydrophobic and nearly superhydrophobic surfaces exhibited contact angles of 115.667° and 133.933°, respectively. The colorimetric sensitivity of the standard glucose assay was analyzed on these surfaces, revealing enhanced sensitivity on the nearly superhydrophobic surface due to the high molecular crowding effect owing to its non-wetting behavior and eventually confined reaction product at the sample loading zone. The hydrophobic nature of the surface restricts the spreading and diffusion of the reaction product, leading to a controlled and localized concentration of the assay product leading to moderate colorimetric intensity. On the other hand, the hydrophilic surface showed the least enhancement in colorimetric sensitivity; this is attributed to the high wettability of the hydrophilic surface causing the reaction product to spread extensively, resulting in a larger area of dispersion and consequently a lower colorimetric intensity. The measured limit of detection (LOD) for nucleic acid on nearly superhydrophobic surfaces was found to be 16.15 ng/µL, which was almost four-fold lower than on hydrophilic surfaces (60.08 ng/µL). Additionally, the LODs of standard glucose and clinical serum samples were two-fold lower on nearly superhydrophobic surfaces compared to hydrophilic surfaces. Our findings clearly highlight the promising potential of utilizing superhydrophobic surfaces to significantly enhance colorimetric sensitivity in paper-based diagnostic applications. This innovative approach holds promise for advancing point-of-care diagnostics and improving disease detection in resource-limited settings.

Plasmonic Cross-Linking Colorimetric PCR for Simple and Sensitive Nucleic Acid Detection

Simple, low-cost, and accurate nucleic acid assay platforms hold great promise for point-of-care (POC) pathogen detection, disease surveillance, and control. Plasmonic photothermal polymerase chain reaction (PPT-PCR) is a powerful and efficient nucleic acid amplification technique, but it lacks a simple and convenient analysis method for POC applications. Herein, we propose a novel plasmonic cross-linking colorimetric PCR (PPT-ccPCR) assay by integrating plasmonic magnetic nanoparticle (PMN)-based PPT-PCR with gold nanoparticle (AuNP)-based cross-linking colorimetry. AuNPs form assembled structures with the PMNs in the presence of amplicons and collect in a magnetic field, resulting in color changes to the supernatant. Target DNA with concentrations as low as 5 copies/μL can be visually detected within 40 min. The achieved limit of detection was 1.8 copies/μL based on the absorption signals. This simple and sensitive strategy needs no expensive instrumentation and demonstrates high potential for POC detection while enabling further applications in clinical diagnostics.

Overview of Optical Biosensors for Early Cancer Detection: Fundamentals, Applications and Future Perspectives

Conventional cancer detection and treatment methodologies are based on surgical, chemical and radiational processes, which are expensive, time consuming and painful. Therefore, great interest has been directed toward developing sensitive, inexpensive and rapid techniques for early cancer detection. Optical biosensors have advantages in terms of high sensitivity and being label free with a compact size. In this review paper, the state of the art of optical biosensors for early cancer detection is presented in detail. The basic idea, sensitivity analysis, advantages and limitations of the optical biosensors are discussed. This includes optical biosensors based on plasmonic waveguides, photonic crystal fibers, slot waveguides and metamaterials. Further, the traditional optical methods, such as the colorimetric technique, optical coherence tomography, surface-enhanced Raman spectroscopy and reflectometric interference spectroscopy, are addressed.

Sensitive colorimetric detection of antibiotic resistant Staphylococcus aureus on dairy farms using LAMP with pH-responsive polydiacetylene

Rapidly and accurately detecting antibiotic-resistant pathogens in agriculture and husbandry is important since these represent a major threat to public health. While much attention has been dedicated to detecting now-common resistant bacteria, such as methicillin-resistant Staphylococcus aureus, fewer methods have been developed to assess resistance against macrolides in Staphylococcus aureus (SA). Here, we report a visual on-site detection system for macrolide resistant SA in dairy products. First, metagenomic sequencing in raw milk, cow manure, water and aerosol deposit collected from dairy farms around Tianjin was used to identify the most abundant macrolide resistance gene, which was found to be the macB gene. In parallel, SA housekeeping genes were screened to allow selective identification of SA, which resulted in the selection of the SAOUHSC_01275 gene. Next, LAMP assays targeting the above-mentioned genes were developed and interpreted by agarose gel electrophoresis. For on-site application, different pH-sensitive colorimetric LAMP indicators were compared, which resulted in selection of polydiacetylene (PDA) as the most sensitive candidate. Additionally, a semi-quantitative detection could be realized by analyzing the RGB information via smartphone with a LOD of 1.344 × 10-7 ng/μL of genomic DNA from a milk sample. Finally, the proposed method was successfully carried out at a real farm within 1 h from sample to result by using freeze-dried reagents and portable devices. This is the first instance in which PDA is used to detect LAMP products, and this generic read-out system can be expanded to other antibiotic resistant genes and bacteria.

Paper-Based Biosensors for the Detection of Nucleic Acids from Pathogens

Paper-based biosensors are microfluidic analytical devices used for the detection of biochemical substances. The unique properties of paper-based biosensors, including low cost, portability, disposability, and ease of use, make them an excellent tool for point-of-care testing. Among all analyte detection methods, nucleic acid-based pathogen detection offers versatility due to the ease of nucleic acid synthesis. In a point-of-care testing context, the combination of nucleic acid detection and a paper-based platform allows for accurate detection. This review offers an overview of contemporary paper-based biosensors for detecting nucleic acids from pathogens. The methods and limitations of implementing an integrated portable paper-based platform are discussed. The review concludes with potential directions for future research in the development of paper-based biosensors.

LAMP-Based Point-of-Care Biosensors for Rapid Pathogen Detection

Seeking optimized infectious pathogen detection tools is of primary importance to lessen the spread of infections, allowing prompt medical attention for the infected. Among nucleic-acid-based sensing techniques, loop-mediated isothermal amplification is a promising method, as it provides rapid, sensitive, and specific detection of microbial and viral pathogens and has enormous potential to transform current point-of-care molecular diagnostics. In this review, the advances in LAMP-based point-of-care diagnostics assays developed during the past few years for rapid and sensitive detection of infectious pathogens are outlined. The numerous detection methods of LAMP-based biosensors are discussed in an end-point and real-time manner with ideal examples. We also summarize the trends in LAMP-on-a-chip modalities, such as classical microfluidic, paper-based, and digital LAMP, with their merits and limitations. Finally, we provide our opinion on the future improvement of on-chip LAMP methods. This review serves as an overview of recent breakthroughs in the LAMP approach and their potential for use in the diagnosis of existing and emerging diseases.

Portable Electrochemical Biosensors Based on Microcontrollers for Detection of Viruses: A Review

With the rise of zoonotic diseases in recent years, there is an urgent need for improved and more accessible screening and diagnostic methods to mitigate future outbreaks. The recent COVID-19 pandemic revealed an over-reliance on RT-PCR, a slow, costly and lab-based method for diagnostics. To better manage the pandemic, a high-throughput, rapid point-of-care device is needed for early detection and isolation of patients. Electrochemical biosensors offer a promising solution, as they can be used to perform on-site tests without the need for centralized labs, producing high-throughput and accurate measurements compared to rapid test kits. In this work, we detail important considerations for the use of electrochemical biosensors for the detection of respiratory viruses. Methods of enhancing signal outputs via amplification of the analyte, biorecognition of elements and modification of the transducer are also explained. The use of portable potentiostats and microfluidics chambers that create a miniature lab are also discussed in detail as an alternative to centralized laboratory settings. The state-of-the-art usage of portable potentiostats for detection of viruses is also elaborated and categorized according to detection technique: amperometry, voltammetry and electrochemical impedance spectroscopy. In terms of integration with microfluidics, RT-LAMP is identified as the preferred method for DNA amplification virus detection. RT-LAMP methods have shorter turnaround times compared to RT-PCR and do not require thermal cycling. Current applications of RT-LAMP for virus detection are also elaborated upon.

Dicationic styryl dyes for colorimetric and fluorescent detection of nucleic acids

Nucleic acid staining dyes are important tools for the analysis and visualizing of DNA/RNA in vitro and in the cells. Nevertheless, the range of commercially accessible dyes is still rather limited, and they are often very costly. As a result, finding nontoxic, easily accessible dyes, with desirable optical characteristics remains important. Styryl dyes have recently gained popularity as potential biological staining agents with many appealing properties, including a straightforward synthesis procedure, excellent photostability, tunable fluorescence, and high fluorescence quantum yield in the presence of nucleic acid targets with low background fluorescence signals. In addition to fluorescence, styryl dyes are strongly colored and exhibit solvatochromic properties which make them useful as colorimetric stains for low-cost and rapid testing of nucleic acids. In this work, novel dicationic styryl dyes bearing quaternary ammonium groups are designed to improve binding strength and optical response with target nucleic acids which contain a negatively charged phosphate backbone. Optical properties of the newly synthesized styryl dyes have been studied in the presence and absence of nucleic acid targets with the aim to find new dyes that can sensitively and specifically change fluorescence and/or color in the presence of nucleic acid targets. The binding interaction and optical response of the dicationic styryl dyes with nucleic acid were superior to the corresponding monocationic styryl dyes. Applications of the developed dyes for colorimetric detection of DNA in vitro and imaging of cellular nucleic acids are also demonstrated.

A CRISPR-Cas12a integrated SERS nanoplatform with chimeric DNA/RNA hairpin guide for ultrasensitive nucleic acid detection

Background: CRISPR-Cas12a has been integrated with nanomaterial-based optical techniques, such as surface-enhanced Raman scattering (SERS), to formulate a powerful amplification-free nucleic acid detection system. However, nanomaterials impose steric hindrance to limit the accessibility of CRISPR-Cas12a to the narrow gaps (SERS hot spots) among nanoparticles (NPs) for producing a significant change in signals after nucleic acid detection. Methods: To overcome this restriction, we specifically design chimeric DNA/RNA hairpins (displacers) that can be destabilized by activated CRISPR-Cas12a in the presence of target DNA, liberating excessive RNA that can disintegrate a core-satellite nanocluster via toehold-mediated strand displacement for orchestrating a promising "on-off" nucleic acid biosensor. The core-satellite nanocluster comprises a large gold nanoparticle (AuNP) core surrounded by small AuNPs with Raman tags via DNA hybridization as an ultrabright Raman reporter, and its disassembly leads to a drastic decrease of SERS intensity as signal readouts. We further introduce a magnetic core to the large AuNPs that can facilitate their separation from the disassembled nanostructures to suppress the background for improving detection sensitivity. Results: As a proof-of-concept study, our findings showed that the application of displacers was more effective in decreasing the SERS intensity of the system and attained a better limit of detection (LOD, 10 aM) than that by directly using activated CRISPR-Cas12a, with high selectivity and stability for nucleic acid detection. Introducing magnetic-responsive functionality to our system further improves the LOD to 1 aM. Conclusion: Our work not only offers a platform to sensitively and selectively probe nucleic acids without pre-amplification but also provides new insights into the design of the CRISPR-Cas12a/SERS integrated system to resolve the steric hindrance of nanomaterials for constructing biosensors.

Rotational diffusometric sensor with isothermal amplification for ultra-sensitive and rapid detection of SARS-CoV-2 nsp2 cDNA

In the wake of a pandemic, the development of rapid, simple, and accurate molecular diagnostic tests can significantly aid in reducing the spread of infections. By combining particle imaging with molecular assays, a quick and highly sensitive biosensor can readily identify a pathogen at low concentrations. Here, we implement functionalized particle-enabled rotational diffusometry in combination with loop-mediated isothermal amplification for the rapid detection of the SARS-CoV-2 nsp2 gene in the recombinant plasmid as a proof of concept for COVID-19 diagnostics. By analyzing the images of blinking signals generated by these modified particles, the change in micro-level viscosity due to nucleic acid amplification was measured. The high sensitivity of rotational diffusometry enabled facile detection within 10 min, with a limit of detection of 70 ag/μL and a sample volume of 2 μL. Tenfold higher detection sensitivity was observed for rotational diffusometry in comparison with real-time PCR. In addition, the system stability and the effect of temperature on rotational diffusometric measurements were studied and reported. These results demonstrated the utility of a rotational diffusometric platform for the rapid and sensitive detection of SARS-CoV-2 cDNA fragments.

Quantitative isothermal amplification on paper membranes using amplification nucleation site analysis

Quantitative nucleic acid amplification tests (qNAATs) are critical in treating infectious diseases, such as in HIV viral load monitoring or SARS-CoV-2 testing, in which viral load indicates viral suppression or infectivity. Quantitative PCR is the gold standard tool for qNAATs; however, there is a need to develop point-of-care (POC) qNAATs to manage infectious diseases in outpatient clinics, low- and middle-income countries, and the home. Isothermal amplification methods are an emerging tool for POC NAATs as an alternative to traditional PCR-based workflows. Previous works have focused on relating isothermal amplification bulk fluorescence signals to input copies of target nucleic acids for sample quantification with limited success. In this work, we show that recombinase polymerase amplification (RPA) reactions on paper membranes exhibit discrete fluorescent amplification nucleation sites. We demonstrate that the number of nucleation sites can be used to quantify HIV-1 DNA and viral RNA in less than 20 minutes. An image-analysis algorithm quantifies nucleation sites and determines the input nucleic acid copies in the range of 67-3000 copies per reaction. We demonstrate a mobile phone-based system for image capture and onboard processing, illustrating that this method may be used at the point-of-care for qNAATs with minimal instrumentation.

Naked-eye detection strategies coupled with isothermal nucleic acid amplification techniques for the detection of human pathogens

Nucleic acid amplification-based techniques have gained acceptance by the scientific, and general, community as reference methodologies for many different applications. Since the development of the gold standard of these techniques, polymerase chain reaction (PCR), back in the 1980s many improvements have been made, and alternative techniques emerged reporting improvements over PCR. Among these, isothermal amplification approaches resulted of particular interest as could overcome the need of specialized equipment to accurately control temperature changes, but it was after year 2000 that these techniques have flourished in a huge number of novel alternatives with many different degrees of complexities and requirements. An added value is their possibility to be combined with many different naked-eye detection strategies, simplifying the resources needed, allowing to reduce cost, and serving as the basis for novel developments of lab-on-chip systems, and miniaturized devices, for point-of-care testing. In this review, we will go over different types of naked-eye detection strategies, combined with isothermal amplification. This will provide the readers up-to-date information for them to select the most appropriate strategies depending on the particular needs and resources for their experimental setup.

Micro/nanofluidic devices for DNA/RNA detection and separation

The development and research have ramped up at a greater speed than ever in the field of diseases diagnosis. Still there is struggle in developing early detection techniques which uses complex biomolecules like RNA, DNA and proteins in order to detect diseases caused by bacteria, viruses or fungi. Until now separation techniques used before detection rely on traditional techniques like electrophoresis etc. which often require centralized services. Although efforts are made in developing devices that is capable enough on carrying out separation and detection based on microfluidic (MF) and nanofluidic (NF) or lab on chip. Hence, in this chapter, we have discussed about the advancement, limitations and future steps that needs to be taken to flourish the field of NF and MF for the detection and separation of nucleic acid.

Quantitative Isothermal Amplification on Paper Membranes using Amplification Nucleation Site Analysis

Quantitative nucleic acid amplification tests (qNAATs) are critical in treating infectious diseases, such as in HIV viral load monitoring or SARS-CoV-2 testing, in which viral load indicates viral suppression or infectivity. Quantitative PCR is the gold standard tool for qNAATs; however, there is a need to develop point-of-care (POC) qNAATs to manage infectious diseases in outpatient clinics, low- and middle-income countries, and the home. Isothermal amplification methods are an emerging tool for POC NAATs as an alternative to traditional PCR-based workflows. Previous works have focused on relating isothermal amplification bulk fluorescence signals to input copies of target nucleic acids for sample quantification with limited success. In this work, we show that recombinase polymerase amplification (RPA) reactions on paper membranes exhibit discrete fluorescent amplification nucleation sites. We demonstrate that the number of nucleation sites can be used to quantify HIV-1 DNA and RNA in less than 20 minutes. An image-analysis algorithm quantifies nucleation sites and determines the input nucleic acid copies in the range of 67-3,000 copies per reaction. We demonstrate a mobile phone-based system for image capture and onboard processing, illustrating that this method may be used at the point-of-care for qNAATs with minimal instrumentation.

LAMP-H+-responsive electrochemical ratiometric biosensor with minimized background signal for highly sensitive assay of specific short-stranded DNA

Herein, the sequence-specific short-stranded biomarker DNA (hDNA, 21-nt) is acted as targeting out-primer to implement the loop-mediated isothermal amplification for releasing hydrogen ions (LAMP-H⁺). Using LAMP-H⁺ as signaling transducer, we report a highly sensitive electrochemical ratiometric biosensor for hDNA with minimized background signal, which is achieved via magnetic separation using AuNPs-modified Fe₃O₄ (Au@Fe₃O₄) as micro-reactor. In Au@Fe₃O₄, a double-stranded complex of a pH-responsible strand (I*) and a substrate strand (S*) is bound via Au-N bonds, where the treatment with LAMP-H⁺ leads to I* folding into i-motif conformation and S* dehybridization. The S* further hybridizes a catalytic strand (C*) to assemble Mg²⁺-DNAzymes that are cleaved by Mg²⁺, releasing C* for repeated formation and robust nicking of Mg²⁺-DNAzymes. The resultant output fuel strands (F*) are introduced in a modified electrode to drive the strand displacement of two hairpins individually labeled with two electron mediators. Through F*-mediated recycled amplification, the ratio of their electrochemical currents changed in opposite is highly sensitive to the varied hDNA down to 2.1 fM. By integrating LAMP-H⁺-stimulated i-motif switching with Mg²⁺-DNAzyme cleavage, this logic transduction of LAMP-H⁺(i-motif/Mg²⁺-DNAzyme)F* efficiently minimizes the inherent background of traditional LAMP-based assays. Resultantly, our electrochemical ratiometric strategy would be applicable to diverse short-stranded DNAs or even RNAs as targeting primers of LAMP.

A paper-based colorimetric molecular test for SARS-CoV-2 in saliva

Herein, we describe the development of a paper-based device to detect nucleic acids of pathogens of interest in complex samples using loop-mediated isothermal amplification (LAMP) by producing a colorimetric response visible to the human eye. To demonstrate the utility of this device in emerging public health emergencies, we developed and optimized our device to detect SARS-CoV-2 in human saliva without preprocessing. The resulting device was capable of detecting the virus within 60 min and had an analytical sensitivity of 97% and a specificity of 100% with a limit of detection of 200 genomic copies/μL of patient saliva using image analysis. The device consists of a configurable number of reaction zones constructed of Grade 222 chromatography paper separated by 20 mil polystyrene spacers attached to a Melinex® backing via an ARclean® double-sided adhesive. The resulting device is easily configurable to detect multiple targets and has the potential to detect a variety of pathogens simply by changing the LAMP primer sets.

Co-Quenching Effect between Lanthanum Metal-Organic Frameworks Luminophore and Crystal Violet for Enhanced Electrochemiluminescence Gene Detection

Exploring new electrochemiluminescence (ECL) luminophores to construct high-efficiency sensing systems is always a hot direction for developing ECL sensors. Compared with other luminophores, metal-organic frameworks (MOFs) exhibit high mass transfer ability for accelerating the reactivity in its pore channels, which is conducive to improving the performance of ECL sensors. In this work, La³⁺ -BTC MOFs (LaMOFs) are prepared as the highly active reactor and novel ECL luminophore. On this basis, a novel co-quenching effect mechanism is proposed based on double-stranded DNA (dsDNA) triggered cooperation between LaMOFs and crystal violet (CV) molecules. Under the confined pore channels of LaMOFs, CV can play an important role as the photon-acceptor due to the matched absorption spectrum with the ECL spectrum of LaMOFs, and the electron-acceptor on account of its lowest unoccupied molecular orbital level. Based on the proposed co-quenching effect mechanism, a constructed ECL gene sensor shows good assay performance toward p53 gene in the detection range of 1 pm to 100 nm with a detection limit of 0.33 pm. The co-quenching effect integrating LaMOFs with CV is expected to be a versatile approach in the construction of ECL gene sensor, which has good prospect in expanding the application range of ECL technology.

Passively driven microfluidic device with simple operation in the development of nanolitre droplet assay in nucleic acid detection

Since nucleic acid amplification technology has become a vital tool for disease diagnosis, the development of precise applied nucleic acid detection technologies in point-of care testing (POCT) has become more significant. The microfluidic-based nucleic acid detection platform offers a great opportunity for on-site diagnosis efficiency, and the system is aimed at user-friendly access. Herein, we demonstrate a microfluidic system with simple operation that provides reliable nucleic acid results from 18 uniform droplets via LAMP detection. By using only micropipette regulation, users are able to control the nanoliter scale of the droplets in this valve-free and pump-free microfluidic (MF) chip. Based on the oil enclosure method and impermeable fabrication, we successfully preserved the reagent inside the microfluidic system, which significantly reduced the fluid loss and condensation. The relative standard deviation (RSD) of the fluorescence intensity between the droplets and during the heating process was < 5% and 2.0%, respectively. Additionally, for different nucleic acid detection methods, the MF-LAMP chip in this study showed good applicability to both genome detection and gene expression analysis.

All-in-one in situ colorimetric RT-LAMP assay for point-of-care testing of SARS-CoV-2

The ongoing outbreaks of the coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have resulted in unprecedented challenges to global health. To effectively contain the COVID-19 transmission, rapid tests for detecting existing SARS-CoV-2 infections and assessing virus spread are critical. To address the huge need for ever-increasing tests, we developed a facile all-in-one nucleic acid testing assay by combining Si-OH activated glass bead (aGB)-based viral RNA fast extraction and in situ colorimetric reverse transcription loop-mediated isothermal amplification (RT-LAMP) detection in a single tube. aGBs demonstrate a strong ability to capture viral RNA in a guanidinium-based lysis buffer, and the purified aGBs/RNA composite, without RNA elution step, could be directly used to perform RT-LAMP assay. The assay was well characterized by using a novel SARS-CoV-2-like coronavirus GX/P2V, and showed a limit of detection (LOD) of 15 copies per μL in simulated clinical samples within 50 min. We further demonstrated our assay by testing simulated SARS-CoV-2 pseudovirus samples, showing an LOD of 32 copies per μL and high specificity without cross-reactivity with the most closely related GX/P2V or host DNA/RNA. The all-in-one approach developed in this study has the potential as a simple, scalable, and time-saving alternative for point-of-care testing of SARS-CoV-2 in low-income regions, as well as a promising tool for at-home testing.

G-Quadruplex-Probing CRISPR-Cas12 Assay for Label-Free Analysis of Foodborne Pathogens and Their Colonization In Vivo

Foodborne pathogen infection is a key issue of food safety. Herein, we developed a label-free assay for Salmonella enterica (S. enterica) detection based on the G-quadruplex-probing CRISPR-Cas12 system (termed G-CRISPR-Cas), allowing highly sensitive detection of S. enterica and investigation of their colonization in chickens. The introduction of the G-quadruplex probe serving as the substrate of Cas 12a realized a label-free analysis for foodborne pathogens. Due to the amplification process induced by loop-mediated isothermal amplification (LAMP), G-CRISPR-Cas assay can detect S. enterica as low as 20 CFU. Specificity for pathogenic gene detection was guaranteed by the dual recognition process via LAMP primers and Cas 12a-guided RNA binding. The G-CRISPR-Cas assay was applied to explore S. enterica colonization in the intestinal tract and organs of chickens and showed the risk of S. enterica infection outside of the intestinal tract. The G-CRISPR-Cas assay is promising for on-site diagnosis of the infection or contamination of foodborne pathogens outside the laboratories, such as abattoirs and markets.

Loop-Mediated Isothermal Amplification Detection of SARS-CoV-2 and Myriad Other Applications

As the second year of the COVID-19 pandemic begins, it remains clear that a massive increase in the ability to test for SARS-CoV-2 infections in a myriad of settings is critical to controlling the pandemic and to preparing for future outbreaks. The current gold standard for molecular diagnostics is the polymerase chain reaction (PCR), but the extraordinary and unmet demand for testing in a variety of environments means that both complementary and supplementary testing solutions are still needed. This review highlights the role that loop-mediated isothermal amplification (LAMP) has had in filling this global testing need, providing a faster and easier means of testing, and what it can do for future applications, pathogens, and the preparation for future outbreaks. This review describes the current state of the art for research of LAMP-based SARS-CoV-2 testing, as well as its implications for other pathogens and testing. The authors represent the global LAMP (gLAMP) Consortium, an international research collective, which has regularly met to share their experiences on LAMP deployment and best practices; sections are devoted to all aspects of LAMP testing, including preanalytic sample processing, target amplification, and amplicon detection, then the hardware and software required for deployment are discussed, and finally, a summary of the current regulatory landscape is provided. Included as well are a series of first-person accounts of LAMP method development and deployment. The final discussion section provides the reader with a distillation of the most validated testing methods and their paths to implementation. This review also aims to provide practical information and insight for a range of audiences: for a research audience, to help accelerate research through sharing of best practices; for an implementation audience, to help get testing up and running quickly; and for a public health, clinical, and policy audience, to help convey the breadth of the effect that LAMP methods have to offer.

Multifunctional nanoscale lanthanide metal-organic framework based ratiometric fluorescence paper microchip for visual dopamine assay

Dopamine (DA) plays a significant role in the human body and cerebral nervous system, and the accurate and rapid assay of DA is essential for the diagnosis of related diseases. Herein, we proposed a turn-on ratiometric fluorescent DA assay strategy by integrating a specific DA-resorcinol chemical reaction with a multifunctional lanthanide metal-organic framework (Ln-MOF). First, Eu-BTC (1,3,5-benzenetricarboxylic acid) was synthesized and further modified to obtain Cu@Eu-BTC, which simultaneously plays multiple roles such as fluorescence internal standard, nanoreactor, cooperative catalysis effect and color shift enhancement. The Cu@Eu-BTC dispersion-based method exhibits ultra-sensitive (limit of detection, LOD is 0.01 μM) and wide-range linear response (0.04-30 μM) to DA in real serum. More importantly, it has excellent selectivity for DA, even in the presence of epinephrine and norepinephrine analogs. Thus, this method realizes the accurate and precise quantification of DA in serum (recoveries: 98.1%-110.1%, relative standard deviation RSD < 4.6%). Next, Cu@Eu-BTC was prepared into paper microchip, which has good storage stability (RSD < 3.5%, n = 3) in four weeks and achieves point-of-care visual DA assay coupled with smartphone-assisted portable detection device. The MOF paper microchip-based method shows low sample consumption (30 μL), high accuracy and precision for the quantification of DA in serum (recovery of 92.9%-106.2%, RSD < 5.3%), and gets the same assay results as the MOF dispersion-based method (relative error ≤ 6.83%). To our knowledge, this is the first time to propose the catalytic fluorescence turn-on detection strategy of DA based on a MOF paper microchip.

Point-of-care diagnostics for infectious diseases: From methods to devices

The current widespread of COVID-19 all over the world, which is caused by SARS-CoV-2 virus, has again emphasized the importance of development of point-of-care (POC) diagnostics for timely prevention and control of the pandemic. Compared with labor- and time-consuming traditional diagnostic methods, POC diagnostics exhibit several advantages such as faster diagnostic speed, better sensitivity and specificity, lower cost, higher efficiency and ability of on-site detection. To achieve POC diagnostics, developing POC detection methods and correlated POC devices is the key and should be given top priority. The fast development of microfluidics, micro electro-mechanical systems (MEMS) technology, nanotechnology and materials science, have benefited the production of a series of portable, miniaturized, low cost and highly integrated POC devices for POC diagnostics of various infectious diseases. In this review, various POC detection methods for the diagnosis of infectious diseases, including electrochemical biosensors, fluorescence biosensors, surface-enhanced Raman scattering (SERS)-based biosensors, colorimetric biosensors, chemiluminiscence biosensors, surface plasmon resonance (SPR)-based biosensors, and magnetic biosensors, were first summarized. Then, recent progresses in the development of POC devices including lab-on-a-chip (LOC) devices, lab-on-a-disc (LOAD) devices, microfluidic paper-based analytical devices (μPADs), lateral flow devices, miniaturized PCR devices, and isothermal nucleic acid amplification (INAA) devices, were systematically discussed. Finally, the challenges and future perspectives for the design and development of POC detection methods and correlated devices were presented. The ultimate goal of this review is to provide new insights and directions for the future development of POC diagnostics for the management of infectious diseases and contribute to the prevention and control of infectious pandemics like COVID-19.

In Situ Nucleic Acid Amplification and Ultrasensitive Colorimetric Readout in a Paper-Based Analytical Device Using Silver Nanoplates

A rapid, highly sensitive, and quantitative colorimetric paper-based analytical device (PAD) based on silver nanoplates (AgNPls) and loop-mediated isothermal amplification (LAMP) is presented. It is shown that cauliflower-like concatemer LAMP products can mediate crystal etching of AgNPls, with a threefold signal enhancement versus linear dsDNA. Methicillin-resistant Staphylococcus aureus (MRSA), an antimicrobial resistant bacterium that poses a formidable risk with persistently high mortality, is used as a model pathogen. Due to the excellent color contrast provided by AgNPls, the PAD allows qualitative analysis by the naked eye and quantitative analysis using a smartphone camera, with detection limits down to a single copy in just 30 min, and a linear response from 1 to 10⁴ copies (R² = 0.994). The entire assay runs in situ on the paper surface, which drastically simplifies operation of the device. This is the first demonstration of single copy detection using a colorimetric readout, and the developed PAD shows great promise for translation into an ultrasensitive gene-based point-of-care test for any infectious disease target, via modification of the LAMP primer set.

Fluorometric Paper-Based, Loop-Mediated Isothermal Amplification Devices for Quantitative Point-of-Care Detection of Methicillin-Resistant Staphylococcus aureus (MRSA)

Loop-mediated isothermal amplification (LAMP) has been widely used to detect many infectious diseases. However, minor inconveniences during the steps of adding reaction ingredients and lack of simple color results hinder point-of-care detection. We therefore invented a fluorometric paper-based LAMP by incorporating LAMP reagents, including a biotinylated primer, onto a cellulose membrane paper, with a simple DNA fluorescent dye incubation that demonstrated rapid and accurate results parallel to quantitative polymerase chain reaction (qPCR) methods. This technology allows for instant paper strip detection of methicillin-resistant Staphylococcus aureus (MRSA) in the laboratory and clinical samples. MRSA represents a major public health problem as it can cause infections in different parts of the human body and yet is resistant to commonly used antibiotics. In this study, we optimized LAMP reaction ingredients and incubation conditions following a central composite design (CCD) that yielded the shortest reaction time with high sensitivity. These CCD components and conditions were used to construct the paper-based LAMP reaction by immobilizing the biotinylated primer and the rest of the LAMP reagents to produce the ready-to-use MRSA diagnostic device. Our paper-based LAMP device could detect as low as 10 ag (equivalent to 1 copy) of the MRSA gene mecA within 36-43 min, was evaluated using both laboratory (individual cultures of MRSA and non-MRSA bacteria) and clinical blood samples to be 100% specific and sensitive compared to qPCR results, and had 35 day stability under 25 °C storage. Furthermore, the color readout allows for quantitation of MRSA copies. Hence, this device is applicable for point-of-care MRSA detection.

Fantastic Downy Mildew Pathogens and How to Find Them: Advances in Detection and Diagnostics

Downy mildews affect important crops and cause severe losses in production worldwide. Accurate identification and monitoring of these plant pathogens, especially at early stages of the disease, is fundamental in achieving effective disease control. The rapid development of molecular methods for diagnosis has provided more specific, fast, reliable, sensitive, and portable alternatives for plant pathogen detection and quantification than traditional approaches. In this review, we provide information on the use of molecular markers, serological techniques, and nucleic acid amplification technologies for downy mildew diagnosis, highlighting the benefits and disadvantages of the technologies and target selection. We emphasize the importance of incorporating information on pathogen variability in virulence and fungicide resistance for disease management and how the development and application of diagnostic assays based on standard and promising technologies, including high-throughput sequencing and genomics, are revolutionizing the development of species-specific assays suitable for in-field diagnosis. Our review provides an overview of molecular detection technologies and a practical guide for selecting the best approaches for diagnosis.

A highly selective electron affinity facilitated H2S sensor: the marriage of tris(keto-hydrazone) and an organic field-effect transistor

Conjugated polymers (CPs) are emerging as part of a promising future for gas-sensing applications. However, some of their limitations, such as poor specificity, humidity sensitivity and poor ambient stability, remain persistent. Herein, a novel combination of a polymer-monomer heterostructure, derived from a CP (PDVT-10) and a newly reported monomer [tris(keto-hydrazone)] has been integrated in an organic field-effect transistor (OFET) platform to sense H₂S selectively. The hybrid heterostructure shows an unprecedented sensitivity (525% ppm^-1) and high selectivity toward H₂S gas. In addition, we demonstrated that the PDVT-10/tris(keto-hydrazone) OFET sensor has the lowest limit of detection (1 ppb), excellent ambient stability (∼5% current degradation after 150 days), good response-recovery behavior, and exceptional electrical behavior and gas response reproducibility. This work can help pave the way to incorporate futuristic gas sensors in a multitude of applications.

Public health management during COVID-19 and applications of point-of-care based biomolecular detection approaches

The emergence of the novel human coronavirus, characterized as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has led to a worldwide pandemic. The outbreak of SARS-CoV-2 was first reported at a local wet market in the city of Wuhan in the Hubei province of China at a local wet market. This virus is highly contagious, which gives it the potential for rapid transmission across the world. The transmission of SARS-CoV-2 can be triggered via respiratory droplets in the air from an infected individual to a healthy individual. Thus, to restrict the transmission of the virus, proper public health management and early diagnosis of infected individual is extremely essential. Considering this, the development of various point-of-care (POC) biomolecular assays lead to the importance of early diagnoses at a larger scale during this pandemic situation. Detecting a minimum level of specific target analytes to a particular disease with less instrumentation and minimum reagents, as well as immidiate outcomes, has appeared a challenging path for researchers. Apart from early-stage diagnosis, public awareness is also important to prevent the spread of the virus. Proper intensive care units, isolation rooms, maintaining hygiene, and wearing masks in public areas are necessary. In this chapter, we have discussed the public health management steps and current clinical diagnostics processes and various advanced technology including, molecular, serological, and nanobiosensing approaches for SARS-CoV-2 detection. Furthermore, we have highlighted the various challenges and limitations associated with health management and early diagnostics technologies during SARS-CoV-2 pandemic. Additionally, we have summarized various technical aspects of the development of such POC strategies including biomarkers selections, sensing platforms, unit fabrication, and device incorporation.

Updated insight into COVID-19 disease and health management to combat the pandemic

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes COVID-19 disease in humans and is the responsible viral agent for the currently ongoing pandemic. Early cases of COVID-19 were reported from Wuhan, Hubei province of China, the likely birthplace of this outbreak. Currently, over 92 million people in the globe are actively battling this virus, and over 2 million individuals have already succumbed to the disease. The high human-to-human transmission capacity of the virus is among the primary causes for such a rapid global spread of COVID-19. In humans, it causes acute to severe respiratory distress in the form of pneumonia. The presentation of clinical features of the disease ranges from mild in healthy adults to severe among individuals with weakened or immunocompromised immune systems and the elderly. Thus, increasing patient cases of COVID-19 warrants a growing demand for medical attention that is eventually overburdening our health care systems. Rapid detection of COVID-19 in suspected individuals and isolation are among the crucial intervention norms in health management strategies to control the COVID-19 pandemic, in addition to strict observance of public hygienic practices such as reduced public gathering, use of facial masks, and practicing of social distancing. This chapter provides an overview of the epidemiology of COVID-19 and the current classical health management strategies and issues to tackle this pandemic. It particularly highlights the role of standard as well as novel biomolecular diagnostic techniques as a tool for successful implementation of such public safety measures issued by medical policy makers and the governing bodies.

Lab-on-a-Chip Zika Detection With Reverse Transcription Loop-Mediated Isothermal Amplification-Based Assay for Point-of-Care Settings

CONTEXT.—

Zika virus (ZIKV) infection, primarily transmitted by mosquitoes, causes various neurologic disorders. To differentiate ZIKV from other arboviruses, such as dengue, chikungunya, and yellow fever viruses, a highly specific, sensitive, and automated detection system is needed for point-of-care (POC) settings.

OBJECTIVE.—

To detect ZIKV at POC settings, we have developed a fully automated lab-on-a-chip microfluidic platform for rapid disease detection by using reverse transcription loop-mediated isothermal amplification.

DESIGN.—

The developed setup consists of a microfluidic chip, a platform for magnetic actuation, and a heater along with the sensor to precisely control the temperature for the target amplification. The platform accurately controls the movement of the magnetic beads that enable the isolation and purification of the target nucleotides adhered to their surface for the amplification and disease detection on the microfluidic chip.

RESULTS.—

Within 40 minutes, change in color due to the presence of ZIKV amplicons was visually observed with the spiked plasma samples in the end point analysis. Also, we have accurately and specifically identified ZIKV in a small number of de-identified clinical samples.

CONCLUSIONS.—

All-inclusive, the developed fully automated POC ZIKV diagnostic chip is rapid, simple, easy to use, inexpensive, and suitable for the areas where facilities are limited.

Loop-mediated isothermal amplification technique: principle, development and wide application in food safety

Food safety is a major and enduring challenge and has a profound impact on the quality of human life. Loop-mediated isothermal amplification (LAMP) is a relatively novel gene amplification method under isothermal conditions with rapidity, simplicity and high specificity. This review will describe the principles and development of the LAMP technique along with its advantages and disadvantages, such as LAMP integrated on classical microfluidic chips, paper-chips, electrochemical devices, nanomaterials and digital devices. Moreover, we will systematically and comprehensively review its applications in the field of food safety, such as in the detection of foodborne pathogens, allergens and organophosphorus pesticides and genetically modified organisms; finally its development trends in food safety will be discussed.

Dual platform based sandwich assay surface-enhanced Raman scattering DNA biosensor for the sensitive detection of food adulteration

Surface enhanced Raman scattering (SERS) DNA biosensing is an ultrasensitive, selective, and rapid detection technique with the ability to produce molecule-specific distinct fingerprint spectra. It supersedes the long amplicon based PCR assays, the fluorescence and spectroscopic techniques with their quenching and narrow spectral bandwidth, and the electrochemical detection techniques using multiplexing. However, the performance of the SERS DNA biosensor relies on the DNA probe length, platform composition, both the presence and position of Raman tags and the chosen sensing strategy. In this context, we herein report a SERS biosensor based on dual nanoplatforms with a uniquely designed Raman tag (ATTO Rho6G) intercalated short-length DNA probe for the sensitive detection of the pig species Sus scrofa. In the design of the signal probe (SP), a Raman tag was incorporated adjacent to the spacer arm, followed by a terminal thiol modifier, which consequently had a strong influence on the SERS signal enhancement. The detection strategy involves the probe-target DNA hybridization mediated coupling of the two platforms, i.e., the graphene oxide-gold nanorod (GO-AuNR) functionalized capture probe (CP) and SP-conjugated gold nanoparticles (AuNPs), consequently enhancing the SERS intensity by both the electromagnetic hot spots generated at the junctions or interstices of the two platforms and the chemical enhancement between the AuNPs and the adsorbed intercalated Raman tag. This dual platform based SERS DNA biosensor exhibited outstanding sensitivity in detecting pork DNA with a limit of detection (LOD) of 100 aM validated with DNA extracted from a pork sample (LOD 1 fM). Moreover, the fabricated SERS biosensor showed outstanding selectivity and specificity for differentiating the DNA sequences of six closely related non-target species from the target DNA sequences with single and three nucleotide base-mismatches. Therefore, the developed short-length DNA linked dual platform based SERS biosensor could replace the less sensitive traditional methods of pork DNA detection and be adopted as a universal detection approach for the qualitative and quantitative detection of DNA from any source.

Microfluidic devices for detection of RNA viruses

There is a long way to go before the coronavirus disease 2019 (Covid‐19) outbreak comes under control. qRT‐PCR is currently used for the detection of severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2), the causative agent of Covid‐19, but it is expensive, time‐consuming, and not as sensitive as it should be. Finding a rapid, easy‐to‐use, and cheap diagnostic method is necessary to help control the current outbreak. Microfluidic systems provide a platform for many diagnostic tests, including RT‐PCR, RT‐LAMP, nested‐PCR, nucleic acid hybridization, ELISA, fluorescence‐Based Assays, rolling circle amplification, aptamers, sample preparation multiplexer (SPM), Porous Silicon Nanowire Forest, silica sol‐gel coating/bonding, and CRISPR. They promise faster, cheaper, and easy‐to‐use methods with higher sensitivity, so microfluidic devices have a high potential to be an alternative method for the detection of viral RNA. These devices have previously been used to detect RNA viruses such as H1N1, Zika, HAV, HIV, and norovirus, with acceptable results. This paper provides an overview of microfluidic systems as diagnostic methods for RNA viruses with a focus on SARS‐CoV‐2.

Optimization of isothermal amplification method for Mycobacteriumtuberculosisdetection and visualization method for fieldwork

Background/aim

Tuberculosis is still one of the most contagious diseases around the world. Key factors of tuberculosis control are rapid diagnostic, efficient treatment, and prevention of contamination by surveillance and monitoring. However, culture is the gold standard method for laboratory diagnosis of tuberculosis; the results are several weeks to obtain. In order to prevent contamination of tuberculosis, diagnosis must be made in short time and treatment should be started as soon as possible. The aim of this study is to optimize the loop-mediated isothermal amplification (LAMP) method, which provides a much faster and more sensitive result than the polymerase chain reaction (PCR) method and allows the replication of target nucleic acid sequences under isothermal conditions without the need for laboratory infrastructure.

Materials and methods

Sputum samples were homogenized with 5% trypsin solution in CaCl2 to obtain DNA. DNA was purified using QIAGEN QIAamp DNA mini kit. LAMP primers were design using Primer explorer V5 program according to IS6110 gene of Mycobacterium tuberculosis. NEB Bst 3.0 DNA polymerase kit was used for LAMP reactions. Besides, LAMP reactions were compared with TaqMan based RT-PCR method using NEB’s Taq polymerase kit. Finally, for visualization of LAMP products, lateral flow dipsticks that produced by Milenia Biotec, colorimetric 2X LAMP master mix that produced by NEB and 2% w/v agarose gel electrophoresis methods were used.

Results

Optimum amplification temperature for LAMP was found to be 71.4 °C. The detection limit of the method was 102 CFU/mL and sensitivity was determined 100% compared to five different Mycobacterium species.

Conclusion

The current study indicated that the LAMP-LFD and colorimetric LAMP protocol optimized with sputum samples can be reliable used as a rapid, sensitive and specific assay in the diagnosis of tuberculosis in the field.

End-point dual specific detection of nucleic acids using CRISPR/Cas12a based portable biosensor

A CRISPR/Cas12a based portable biosensor (Cas12a-PB) was developed to simultaneously visually detect CaMV35S promoter and Lectin gene from genetically modified (GM) soybean powders (Roundup Ready@). The Cas12a-PB, mainly made of polymethylmethacrylate (PMMA) and PMMA tape, has a connection structure, three channels and three detection chambers. The CRISPR/Cas12a detection reagents were preloaded in detection chambers and the reaction tube was connected to the connection structure by screw threads. After amplification, the amplicons were gone into three detection chambers by swinging the Cas12a-PB to conduct dual detection. Positive samples would produce green fluorescence while negative samples were black under the irradiation of 490 nm LED light. In this study, the Cas12a-PB successively combined with ordinary PCR, rapid PCR and loop-mediated isothermal amplification (LAMP) to achieve dual detection, which made detection process more convenient and portable. As low as 0.1% transgenic ingredients in soybean powders could be detected and the specificity of Cas12a-PB was confirmed with GM maize powders (MON810, GA21), GM soybean powders (DP305423), non-GM peanut and rice as targets. In the end, an amplification chamber combining with Cas12a-PB on a PMMA chip was further designed to eliminate the use of reaction tube and mineral oil, which made operation simpler. The established Cas12a-PB would provide a new reliable solution for multiple targets detection in clinic diagnostics, food safety, etc.

Correction pen based paper fluidic device for the detection of multiple gene targets of Leptospira using Loop Mediated Isothermal Amplification

Paper-based nucleic acid testing techniques are increasingly in demand. Hence, we have developed a simple and cheap paper fluidic device to detect multiple gene targets in Leptospira. Fluidic channels of the penta-clover device are drawn using a correction pen on Whatman filter paper 1. The fluid blocks the pores of the paper, avoiding leakage and ensuring the equal flow of sample to the reaction pads. The target genes are amplified by performing Loop-Mediated Isothermal Amplification (LAMP) with dry reaction components. Thecolor change of leuco crystal violetallows real-time monitoring of a positive amplification. The difference in color intensity is captured with a smartphone and analyzed using image processing software. The device amplifies the target within 15 min, detects the pathogen at a concentration as low as 50 attogram μL^-1, detects Leptospira in blood samples without prior treatment and differentiates the Leptospira species even after 21 days of storage at room temperature.

Applications of paper as a support material in biomedical sciences: A decadal review

In human history, the paper has long been used as a platform to record and preserve information. However, over the decades, paper has found its application in Biomedical Sciences, too. Both paper-based microfluidic devices (μPADs) and paper-based cultures and scaffolds have shown immense potential to be used as a sensor as well as a supporting material for in vitro tissue engineering. μPADs can be used to perform low-cost and fast biomolecular assays at Point-Of-Care (POC). They are being used to detect various biomarkers like viral proteins, metabolites, oncogenes, and antigens; and conditions like Venous Thromboembolism (VTE). On the other hand, the paper has also been used to develop paper-based 3D cultures and scaffolds to test drugs, and monitor cytotoxic effects in vitro cell microenvironments and also as implantable tissues. In this review, we intend to enumerate the development in the field of μPADs, paper-based cell cultures, and paper-based scaffolds and their plethora of applications over the last decade.

Current analytical methods for porcine identification in meat and meat products

Authentication of meat products is critical in the food industry. Meat adulteration may lead to religious apprehensions, financial gain and food-toxicities such as meat allergies. Thus, empirical validation of the quality and constituents of meat is paramount. Various analytical methods often based on protein or DNA measurements are utilized to identify meat species. Protein-based methods, including electrophoretic and immunological techniques, are at times unsuitable for discriminating closely related species. Most of these methods have been replaced by more accurate and sensitive detection methods, such as DNA-based techniques. Emerging technologies like DNA barcoding and mass spectrometry are still in their infancy when it comes to their utilization in meat detection. Gold nanobiosensors have shown some promise in this regard. However, its applicability in small scale industries is distant. This article comprehensively reviews the recent developments in the field of analytical methods used for porcine identification.

Paper-based microfluidics for rapid diagnostics and drug delivery

Paper is a common material that is promising for constructing microfluidic chips (lab-on-a-paper) for diagnostics and drug delivery for biomedical applications. In the past decade, extensive research on paper-based microfluidics has accumulated a large number of scientific publications in the fields of biomedical diagnosis, food safety, environmental health, drug screening and delivery. This review focuses on the recent progress on paper-based microfluidic technology with an emphasis on the design, optimization and application of the technology platform, in particular for medical diagnostics and drug delivery. Novel advances have concentrated on engineering paper devices for point-of-care (POC) diagnostics, which could be integrated with nucleic acid-based tests and isothermal amplification experiments, enabling rapid sample-to-answer assays for field testing. Among the isothermal amplification experiments, loop-mediated isothermal amplification (LAMP), an extremely sensitive nucleic acid test, specifically identifies ultralow concentrations of DNA/RNA from practical samples for diagnosing diseases. We thus mainly focus on the paper device-based LAMP assay for the rapid infectious disease diagnosis, foodborne pathogen analysis, veterinary diagnosis, plant diagnosis, and environmental public health evaluation. We also outlined progress on paper microfluidic devices for drug delivery. The paper concludes with a discussion on the challenges of this technology and our insights into how to advance science and technology towards the development of fully functional paper devices in diagnostics and drug delivery.

LAMP-generated H+ ions-induced dimer i-motif as signal transducer for ultrasensitive electrochemical detection of DNA

Herein, an ultrasensitive electrochemical biosensor is proposed for the quantification of the Flu A virus biomarker DNA (fDNA), and is based on loop-mediated isothermal amplification-generated hydrogen ions (LAMP-H+) which induce the formation of the dimer i-motif structure (DiMS) for signal transduction, coupled with exonuclease III (ExoIII)-assisted DNA walking for signal dual-amplification.

Background-Free Quantitative Surface Enhanced Raman Spectroscopy Analysis Using Core–Shell Nanoparticles with an Inherent Internal Standard

Surface enhanced Raman spectroscopy (SERS) is an ultrasensitive label-free analytical technique that can provide unique chemical and structural fingerprint information. However, gaining reliable quantitative analysis with SERS remains a huge challenge because of poor reproducibility and the instability of nanostructured SERS active surfaces. Herein, an effective strategy of coating Au nanoparticles (NPs) with ultrathin and uniform Prussian blue (PB) shell (Au@PB NPs) was developed for quantitative detection of dopamine (DA) concentrations in blood serum and crystal violet (CV) contaminants in lake water. The only intense PB Raman signal at 2155 cm^-1 served as an ideal and interference-free internal standard (IS) for correcting fluctuations in the Raman intensities of analytes. Also, the stability of Au@PB NPs was investigated, exhibiting good functionality in strong acid solutions and thermal stability at 100 °C. This work demonstrates a convenient and fast quantitative SERS technique for detecting analyte concentrations in complex systems and has a great number of potential applications for use in analytical chemistry.