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Paper-based analytical devices (PADs) are very popular for point-of-care diagnostics, which provide a fast, cost-effective and possible multiplexed detection of a spectrum of molecules. They have been matching forward proudly to contribute to the modern analytical science and life science. Accompanying with their advantages and huge potentials, low detection sensitivity is continuing to challenge the application of PADs from bench to bedside. In order to improve the sensitivity and enhance the signal readout, variable signal amplification strategies have been investigated and applied for PADs. In this review, we have firstly classified formats of PADs according to the engineering design. Advances for improving sensitivity of PADs in recent five years are then summarised according to three popular types of signal amplification strategies (nanomaterial based, nucleic acid based, and engineering of PADs based). Pros and cons of each signal amplification approach have been discussed accordingly. Finally, the future perspectives of PADs are proposed. • Advances on signal amplification strategies to enhance sensitivity of paper based analytical devices (PADs) are outlined. • Three signal amplification strategies (nanomaterial, nucleic acid, and engineering of PADs based) are discussed. • The pros and cons of different signal amplification strategies are compared. • Future perspectives for signal amplification on PADs are proposed. [ABSTRACT FROM AUTHOR]

Rapid early diagnosis of Alzheimer's disease (AD) is critical for its effective and prompt treatment since the clinically available treatments can only relieve the symptoms or slow the disease progression. However, it is still a grand challenge to accurately diagnose AD at its early stage because of the indiscernible early symptoms and the lack of sensitive detection tools. Here, we develop a self-calibrating surface-enhanced Raman scattering (SERS)-lateral flow immunoassay (LFIA) biosensor for quantitative analysis of amyloid-β1-42 (Aβ1-42) biomarker in biofluids, enabling accurate AD diagnosis. The designed SERS-LFIA biosensor makes full use of the unique aspects of the LFIA format and the SERS technique to quantify the Aβ1-42 level in complex biofluids with high sensitivity, excellent anti-interference capability, low-cost, and operation simplicity. The key aspect of the design of this biosensor is that internal standard (IS)-SERS nanoparticles are embedded in the test line of the test strip as a self-calibration unit for correction of fluctuations of SERS signals caused by various external factors such as test parameters and sample heterogeneity. We demonstrate significant improvement of the detection performance of the SERS-LFIA biosensor for ratiometric quantification of Aβ1-42 owing to the built-in IS in the test line. We expect that the present IS-based biosensing strategy provides a promising tool for accurate AD diagnosis and longitudinal monitoring of therapeutic response with great promises for clinical translation. [ABSTRACT FROM AUTHOR]

This paper presents a lateral flow assay (LFA) for the quantitative, fluorescence-based detection of the cardiac biomarker troponin I (cTnI) that features an analytical strip made of cellulose filter paper. The results show that the wicking and test time are comparable to those obtained with conventional nitrocellulose (NC)-based LFAs. Further, the cellulose paper provides an excellent background with no auto-fluorescence that is very adequate in detecting fluorescent lines. While fluorescence that was generated with cellulose strips was lower when compared to that generated in NC strips, signals could be improved by layering carbon nanofibers (CNF) on the cellulose. A nonlinear behavior of the concentration–response relationship was observed for the LFA architectures with NC, cellulose, and cellulose-CNF in the 0 to 200 ng/mL cTnI concentration range. The measurements were consistent and characterized by coefficients of variation lower than 2.5%. Detection and quantitation limits that were in the range 1.28–1.40 ng/mL and 2.10–2.75 ng/mL were obtained for LFA with cellulose and cellulose CNF strips that are equivalent to the limits obtained with the standard NC LFA. Overall, we showed that commercially available filter paper can be used in the analytical strip of LFA.

Mycotoxins contamination is a global public health concern. Therefore, highly sensitive and selective techniques are needed for their on-site monitoring. Several approaches are conceivable for mycotoxins analysis, among which colorimetric methods are the most attractive for commercialization purposes thanks to their visual read-out, easy operation, cost-effectiveness, and rapid response. This review covers the latest achievements in the last five years for the development of colorimetric methods specific to mycotoxins analysis, with a particular emphasis on their potential for large-scale applications in food industries. Gathering all types of (bio)receptors, main colorimetric methods are critically discussed, including enzyme-linked assays, lateral flow-assays, microfluidic devices, and homogenous in-solution strategies. This special focus on colorimetry as a versatile transduction method for mycotoxins analysis is comprehensively reviewed for the first time.

Lateral flow assays (LFA) have been widely utilized as point-of-care testing devices in diverse fields. However, it is imperative to preprint costly bioreceptors onto the lateral flow nitrocellulose membrane at the control line. The complex manufacturing process and relatively limited detection capabilities of LFA have impeded their utilization in more challenging fields. Here, we propose a novel and simple strategy to simplify the manufacture of LFA while simultaneously improving the sensitivity by modifying the hydrogel line (HL). In our study, it was observed that the sensitivity of commercial LFA strips could be enhanced by 2-5-fold by incorporating an extra HL. Particularly, a universal control line was developed to accommodate multiple LFA detection modes by substituting the conventional antibody control line with a hydrogel control line (HCL). As a proof of concept, the HCL performance could be associated with the slowdown and interception effect toward fluid, which are dependent on the permeation and hydrophilicity of the hydrogel with varying concentrations in the nitrocellulose membrane. This new design builds the foundation to enhance the sensitivity and develop the simplified LFA sensing platform without additional complicated processes.

We present a lateral flow immunoassay (LFA) for the quantitative, fluorescence-based detection of the trauma brain injury (TBI) biomarker ubiquitin carboxyl-terminal hydrolase-L1 (UCH-L1) that features a layer of graphene oxide (GO) particles over the test zone of nitrocellulose (NC) strips. The introduction of 80 ng of GO at test lines increased fluorescence signals 2–3-fold. This was attributed to an increase in the immobilization of capture antibodies in the top layer of NC, which increased the density of recognition complexes at the surface and hence the signals reaching the reader used. A linear concentration–response relationship was observed in the 0–200 pg/mL UCH-L1 range with an inter assay CoV of 2.65 %. The LOD and LOQ values of 11.1 pg/mL and 33.5 pg/mL were compatible with threshold levels of UCH-L1. Finally, mock plasma samples with UCH-L1 levels characteristic of TBI patients with negative (60 pg/mL) and positive (130 pg/mL) CT scans were successfully analyzed. Storage stability testing further showed that GO did not affect the biological activity of the capture antibody. In summary, we demonstrate that the use of GO particles in the top layers of the test zone of NC strips improves signal intensity, which could potentially enhance the accuracy and efficiency of LFA-based diagnosis. • A new lateral flow immunoassay for the quantitative detection of TBI biomarker UCH-L1 is presented. • The LFA features a layer of graphene oxide particles over the test zone of nitrocellulose strips. • The introduction of GO particles increased fluorescence signals 2–3-fold. • The LFA exhibited a linear concentration-response relationship in the 0–200 pg/mL UCH-L1 range. • The LFA achieved LOD and LOQ values compatible with the threshold levels of UCH-L1. [ABSTRACT FROM AUTHOR]

The impact of malaria on global health has continually prompted the need to develop effective diagnostic strategies. In malaria endemic regions, routine diagnosis is hampered by technical and infrastructural challenges to laboratories. These laboratories lack standard facilities, expertise or diagnostic supplies; thus, therapy is administered based on clinical or self-diagnosis. There is the need for accurate diagnosis of malaria due to the continuous increase in the cost of medication, and the emergence and spread of drug resistant strains. However, the widely utilized Giemsa-stained microscopy and immunochromatographic tests for malaria are liable to several drawbacks, including inadequate sensitivity and false-positive outcomes. Alternative methods that offer improvements in performance are either expensive, have longer turnaround time or require a level of expertise that makes them unsuitable for point-of-care (POC) applications. These gaps necessitate exploration of more efficient detection techniques with the potential of POC applications, especially in resource-limited settings. This minireview discusses some of the recent trends and new approaches that are seeking to improve the clinical diagnosis of malaria. [ABSTRACT FROM AUTHOR]

Lateral flow assays (LFAs) have found widespread applications in biomedical fields, but improving their sensitivity remains challenging mainly due to the unclear convection-diffusion-reaction process. Therefore, we developed a 1D mathematical model to solve this process in LFAs. The model depicts the actual situation that one report particle may combine more than one target, which overcomes the deficiency of existing models where one report particle combines only one target. With this model, we studied the effect of report particle characteristics on LFAs, including binding site density, target analyte and report particle concentration. The model was qualitatively validated by reported experimental data and our designed experiments where the report particle with different accessible binding site (HIV-DP) densities is obtained by changing the ratio of HIV-DP and Dengue-DP in preparing AuNP-DP aggregates. The results indicate that a strong signal intensity can be obtained without consuming excess detector probe with the optimum binding site ( N = 30). A maximum normalized target concentration of 120 is obtained to prevent the false-negative result, while a minimum normalized report particle concentration of 0.015 is recommended to produce a strong signal. The developed model would serve as a powerful tool for designing highly effective LFAs. [ABSTRACT FROM AUTHOR]

Lateral flow assays (LFAs) have found applications in clinical diagnostics, veterinary medicine, food safety, environmental monitoring, bio-defence, drug abuse, etc . However, conventional LFAs with single test zone for one analyte (sLFA) show qualitative, positive/negative results (that are usually not so accurate for decision-making) and suffer from the hook effect (that easily induces false negative results). In this study, a modified LFA with multiple test zones for one analyte (mLFA) is developed for detection of nucleic acid showing two methods to interpret assay results. One is the sum of detection signals of test zones, which exhibits a stable and broader detection range compared with sLFA. The other is the pattern of test zones that is presented is correlated to the concentration of analyte, facilitating semi-quantitative detection without the aid of a reader or analyzer. [ABSTRACT FROM AUTHOR]

Point-of-care (POC) devices are rapid, simple, portable, inexpensive, and convenient, but typically they only deliver qualitative results when used in the form of a lateral flow assay (LFA). Electrochemical detection could improve their sensitivity and ensure quantitative detection; however, a breakthrough in material-based technology is needed. We demonstrate a new concept in which electrodes are directly embedded within the lateral flow, enabling flow-through and hence interaction with the entire sample. This is accomplished through laser-induced carbon nanofibers (LCNFs) made by electrospinning Matrimid into nanofiber mats with subsequent pyrolyzing of electrode structures through a CO 2 laser. Their highly porous 3D structure and superior graphene-like electrochemical properties are ideally suited for flow-through electrochemical LFA (EC-LFA), where the LCNFs are simply added in line with the other membranes. After optimization of the setup, biological binding assays typical for LFA diagnostics were successfully implemented, enabling the highly sensitive and quantitative detection of 137 pM DNA target sequences of a pathogenic organism that rivals the performance of pump-controlled microfluidic bioassays. This demonstrates that LCNF-based transducers can transform paper-based diagnostic tests to enable precise, quantitative analysis without reliance on cost-intensive read-out systems.

Severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) continues to threaten lives by evolving into new variants with greater transmissibility. Although lateral flow assays (LFAs) are widely used to self-test for coronavirus disease 2019 (COVID-19), these tests suffer from low sensitivity leading to a high rate of false negative results. In this work, a multiplexed lateral flow assay is reported for the detection of SARS-CoV-2 and influenza A and B viruses in human saliva with a built-in chemical amplification of the colorimetric signal for enhanced sensitivity. To automate the amplification process, the paper-based device is integrated with an imprinted flow controller, which coordinates the routing of different reagents and ensures their sequential and timely delivery to run an optimal amplification reaction. Using the assay, SARS-CoV-2 and influenza A and B viruses can be detected with ≈25x higher sensitivity than commercial LFAs, and the device can detect SARS-CoV-2-positive patient saliva samples missed by commercial LFAs. The technology provides an effective and practical solution to enhance the performance of conventional LFAs and will enable sensitive self-testing to prevent virus transmission and future outbreaks of new variants., (© 2023 Wiley-VCH GmbH.)

Neglected tropical diseases (NTDs) affect tropical and subtropical countries and are caused by viruses, bacteria, protozoa, and helminths. These kinds of diseases spread quickly due to the tropical climate and limited access to clean water, sanitation, and health care, which make exposed people more vulnerable. NTDs are reported to be difficult and inefficient to diagnose. As mentioned, most NTDs occur in countries that are socially vulnerable, and the lack of resources and access to modern laboratories and equipment intensify the difficulty of diagnosis and treatment, leading to an increase in the mortality rate. Portable and low-cost microfluidic systems have been widely applied for clinical diagnosis, offering a promising alternative that can meet the needs for fast, affordable, and reliable diagnostic tests in developing countries. This review provides a critical overview of microfluidic devices that have been reported in the literature for the detection of the most common NTDs over the past 5 years.

Lateral flow assays (LFAs) have attracted interest due to their friendly user formats, short assay times, little interferences, low costs, and being easy by operated by non-specialized personnel. This technique is based on biochemical interaction of antigen-antibody or probe DNA-target DNA hybridization. A lateral flow assay (LFA) is composed of four parts: a sample pad, which is the area on which sample is dropped; conjugate pad, on which labeled tags combined with biorecognition elements; reaction membrane containing test line and control line for target DNA-probe DNA hybridization or antigen-antibody interaction; and absorbent pad, which reserves waste. For the construction of LFAs gold nanoparticles, colored latex beads, carbon nanoparticles, quantum dots, and enzymes are used as a label for increasing the sensitivity. In this work, the principle of LFAs, biorecognition elements, analytical performances, limits of detection (LODs), linear ranges of developed LFAs in different fields are summarized. Future perspectives in this area are also discussed. [ABSTRACT FROM AUTHOR]

Remarkable efforts have been dedicated to paper-based chemosensors and biosensors over the last few years, mainly driven by the promise of reaching the best trade-off between performance, affordability and simplicity. Because of the low-cost and rapid prototyping of these sensors, recent research has been focused on providing affordable diagnostic devices to the developing world. The recent progress in sensitivity, multi-functionality and integration of microfluidic paper-based analytical devices (µPADs), increasingly suggests that this technology is not only attractive in resource-limited environments but it also represents a serious challenger to silicon, glass and polymer-based biosensors. This review discusses the design, chemistry and engineering aspects of these developments, with a focus on the past few years. [ABSTRACT FROM AUTHOR]

The combination of upconversion nanoparticles (UCNPs) and Lateral Flow Assays (LFAs) is becoming one of the most desirable quantitative assays for point-of-care testing (POCT) due to their excellent chemical and optical properties, which make them commercially viable as fast, sensitive and portable. We propose upconversion nanoparticle-based lateral flow assays (UCNP-LFAs) combined with computer vision for the instantaneous detection of small molecule targets in a commercial medical device. The device overcomes the traditional lengthy pre-processing and ambiguous qualitative results, where computer vision algorithms improve the sensitivity and robustness of quantitative results. Compared with the standard quantitative testing process, the accuracy of its quantitative test results was improved by 17.4%. The device detected and reported the quantitative results of Methamphetamine (MET) concentration with the lower limit of detection (LOD) of 0.1 ng/ml in 20 s in field tests. Its success demonstrated good sensitivity, repeatability, and robustness. Most importantly, the entire device measures only 100 mm * 120 mm* 74 mm and weighs 351.2 g, combining portability and immediacy and providing quantitative data for small molecule targets at a lower concentration. This makes our system an extraordinarily creative and attractive approach, especially for applications in complex field environments with chaotic personnel and special emergencies. [Display omitted] • A portable and ultra-sensitive upconversion fluorescent probe-based biosensor for in situ detection was designed. • A fluorescence intensity extraction-based image denoising algorithm is proposed to improve the sensitivity. • A waveform reconstruction algorithm based on Gaussian function is proposed to improve the sensitivity and robustness. • A complete and pervasive Internet of Things (IoT) solution based on UCNPs detection is established. [ABSTRACT FROM AUTHOR]

MicroRNAs (miRNA) are a kind of endogenous non-coding small molecule RNA, which are widely found in plants, animals, and viruses. miRNA can regulate the post-transcriptional cleavage of target message RNA or inhibit its translation process, and plays an important regulatory role in gene expression. Further studies have shown that miRNAs also play an important role in tumorigenesis and host-pathogen interactions. Given the important contribution of miRNAs in gene regulation and biological functions, rapid and accurate detection of miRNAs has become increasingly significant. Lateral flow assay is a detection method derived to achieve rapid detection in the field. It overcomes the problems of cumbersome, time-consuming, and high cost in traditional detection methods, and provides a good platform for accurate, sensitive, and immediate detection of target analytes. With the advantages convenient, cost-saving, and repaid result readout, the lateral flow test strips are now a recognized point-of-care testing (POCT) device and has been widely used in medical diagnosis, agriculture, food, and environmental safety. For the first time, we summarized the research progress of miRNA detection based on lateral flow methods, focusing on the strategies used in the lateral flow assays for miRNA detection and introducing some main experimental operation details, as well as providing an outlook on the future development direction of this field, aiming to provide a general guidance for colleagues preparing to conduct related research. [ABSTRACT FROM AUTHOR]

Microfluidics technology holds a special place in the field of biomedical and analytical chemistry thanks to its properties, such as low consumption of reagent, quick analysis time, and ease of integration. Nanotechnology makes significant progress towards high sensitive and selective detection of analytes. Compared to bulk materials, nanomaterials have distinctive properties which motivate the combination of nanoparticles with biosensors. Nanoparticle-based biosensors can bring a series of advantages in advancement high-throughput and ultrasensitive detection. In recent years, numerous studies have been done on the integration of nanomaterials with microfluidic systems. Given the scope of the nanoparticle-integrated biosensors, the purpose of this review is to provide an overview of various types of nanoparticle-integrated microfluidic biosensors. It mainly focuses on developed microfluidics-based on gold nanoparticles, graphene oxide , quantum dots, magnetic nanoparticles, carbon dots, silica nanoparticles, zinc oxide, and nanocomposites. This review summarizes the latest advancement of nanotechnology-assisted microfluidic biosensing on a smartphone for biochemical analysis. Also, the role of nanomaterials on the detection methods such as electrochemical, photoelectrochemical, electrochemiluminescent, optical piezoelectric, and so on was surveyed. In our opinion, the cooperation of microfluidic biodevices and nanoparticles is very beneficial and is expected to be effective in addressing the challenges related to microfluidic systems. [Display omitted] • Recent advances and limitations in nanotechnology-assisted microfluidic biosensing were discussed. • The analytical figures of merit of the developed methods are also evaluated. • Current improvements on the monitoring of biomarkers using microfluidic strategies were investigated. [ABSTRACT FROM AUTHOR]

Carbon nanoparticles (CNPs) labeled with reporter molecules can serve as signaling labels in rapid diagnostic assays as an alternative to gold, colored latex, silica, quantum dots, or up-converting phosphor nanoparticles. Detailed here is the preparation of biomolecule-labeled CNPs and examples of their use as a versatile label. CNPs can be loaded with a range of biomolecules, such as DNA, antibodies, and proteins (e.g., neutravidin or a fusion protein of neutravidin with an enzyme), and the resulting conjugates can be used to detect analytes of high or low molecular mass. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

MicroRNAs (miRNAs) are short RNA sequences found in eukaryotic cells and they are involved in several diseases pathogenesis including different types of cancers, metabolic and cardiovascular disorders. Thus, miRNAs circulating in serum, plasma, and other body fluids are employed as biomarkers for diagnostic and prognostic purposes and in assessment of drug response. Thus, various methods have been developed for detection of miRNAs including northern blotting, reverse transcriptase polymerase chain reaction (RT-PCR), next-generation sequencing, microarray, and isothermal amplification that are recognized as traditional methods. Considering the importance of early diagnosis and treatment of miRNAs-related diseases, development of simple, one-step, sensitive methods is of great interest. Nowadays developing technologies including lateral flow assay, biosensors (optical and electrochemical) and microfluidic systems which are simple fast responding, user-friendly, and are enabled with visible detection have gained considerable attention. This review briefly discusses miRNAs detection' methods, with a particular focus on lateral flow assay, biosensors, and microfluidic systems as novel and practical procedures. Schematic illustration of biogenesis of mature miRNAs and their detection using lateral flow assay, biosensors and microfluidic systems. [Display omitted] • MicroRNAs (miRNAs) are endogenous small non-coding RNAs with diverse biological roles in eukaryotic cells. • One of the most important applications of miRNAs assessment is early detection of some disease. • The methods of northern blotting, microarrays, next-generation sequencing, and RT-PCR are conventional methods for miRNAs. • Newly, point of care methods such as lateral flow assay, biosensors, and microfluidic are successfully developed for miRNAs. [ABSTRACT FROM AUTHOR]

The transmission of Tuberculosis (TB) is very rapid and the burden it places on health care systems is felt globally. The effective management and prevention of this disease requires that it is detected early. Current TB diagnostic approaches, such as the culture, sputum smear, skin tuberculin, and molecular tests are time-consuming, and some are unaffordable for low-income countries. Rapid tests for disease biomarker detection are mostly based on immunological assays that use antibodies which are costly to produce, have low sensitivity and stability. Aptamers can replace antibodies in these diagnostic tests for the development of new rapid tests that are more cost effective; more stable at high temperatures and therefore have a better shelf life; do not have batch-to-batch variations, and thus more consistently bind to a specific target with similar or higher specificity and selectivity and are therefore more reliable. Advancements in TB research, in particular the application of proteomics to identify TB specific biomarkers, led to the identification of a number of biomarker proteins, that can be used to develop aptamer-based diagnostic assays able to screen individuals at the point-of-care (POC) more efficiently in resource-limited settings. [ABSTRACT FROM AUTHOR]

Lateral flow assays (LFAs) are extensively used in qualitative detection because of their convenience, low cost, fast results, and ease of operation. However, the sample volume used in a lateral flow assay is usually determined experimentally. We test and find that the flow velocity is influenced by sample volume, using fluorescent microspheres as label particles, when analyte concentration is fixed in a sandwich LFA. A model is developed based on mass-action kinetics and advection-diffusion-reaction equation, combing the conjugate pad and nitrocellulose membrane. The model shows predictions from 10 to 120 μL, and predicts accurately the experimental results from 50 to 120 μL where the fluid can flow to the test line. Over all, the model can provide predictions over a wide range of sample volumes for sensitivity analysis. On the basis of the model, the sensitivity of the LFA can be improved according to the sample volume added in the experiment. [Display omitted] • A model is developed with a combination of conjugate pad and NC membrane. • The input flow rate of the model corresponds to the sample volume. • The signal intensity changes with the sample volume changing in a fixed analyte concentration both in model and experiments. • The model can provide a theoretical optimal sample volume prediction to obtain the optimal LFA sensitivity. [ABSTRACT FROM AUTHOR]

This paper presents a lateral flow assay (LFA) for the quantitative, fluorescence-based detection of the cardiac biomarker troponin I (cTnI) that features an analytical strip made of cellulose filter paper. The results show that the wicking and test time are comparable to those obtained with conventional nitrocellulose (NC)-based LFAs. Further, the cellulose paper provides an excellent background with no auto-fluorescence that is very adequate in detecting fluorescent lines. While fluorescence that was generated with cellulose strips was lower when compared to that generated in NC strips, signals could be improved by layering carbon nanofibers (CNF) on the cellulose. A nonlinear behavior of the concentration–response relationship was observed for the LFA architectures with NC, cellulose, and cellulose-CNF in the 0 to 200 ng/mL cTnI concentration range. The measurements were consistent and characterized by coefficients of variation lower than 2.5%. Detection and quantitation limits that were in the range 1.28–1.40 ng/mL and 2.10–2.75 ng/mL were obtained for LFA with cellulose and cellulose CNF strips that are equivalent to the limits obtained with the standard NC LFA. Overall, we showed that commercially available filter paper can be used in the analytical strip of LFA. [ABSTRACT FROM AUTHOR]

Mycotoxins contamination is a global public health concern. Therefore, highly sensitive and selective techniques are needed for their on-site monitoring. Several approaches are conceivable for mycotoxins analysis, among which colorimetric methods are the most attractive for commercialization purposes thanks to their visual read-out, easy operation, cost-effectiveness, and rapid response. This review covers the latest achievements in the last five years for the development of colorimetric methods specific to mycotoxins analysis, with a particular emphasis on their potential for large-scale applications in food industries. Gathering all types of (bio)receptors, main colorimetric methods are critically discussed, including enzyme-linked assays, lateral flow-assays, microfluidic devices, and homogenous in-solution strategies. This special focus on colorimetry as a versatile transduction method for mycotoxins analysis is comprehensively reviewed for the first time. [ABSTRACT FROM AUTHOR]

COVID-19 pandemic outbreak is the most astounding scene ever experienced in the XXI century. In this opinionated review, we underscore the crucial role of biosensing to handle with such situations. As a matter of fact, testing accelerates life-saving decisions on treatment and isolation of COVID-19 patients in an early stage, and thereby, decelerating or even preventing the spread of such emerging infectious diseases. Meanwhile, it is also proven that a timely and broad application of testing leads to lower mortality rates in countries like Germany or South Korea. Besides, biosensors are also powerful tools for effective assessment of clinical progress and to provide alertness on severity or critical trends of infection. In view hereof, we critically discuss the state-of-the-art biosensing devices for COVID-19 testing. We spot the urgent needs and highlight innovative diagnostic approaches for targeting various COVID-19 related biomarkers. Finally, we outline our recommendations on biosensors and biosensing-related issues towards pandemic outbreaks. Image 1 • The crucial role of diagnostics to handle with infectious diseases is highlighted. • Strengths and weaknesses of standard technologies targeting COVID-19 are discussed. • Novel biosensing devices for fighting the next pandemics are discussed. • COVID-19-related biomarkers are underscored. • Recommendations related to biosensing towards pandemic outbreaks are provided. [ABSTRACT FROM AUTHOR]

• Euroimmun ELISA IgG/IgA tests show higher overall sensitivity than Maglumi CLIA IgG/IgM tests. • Maglumi CLIA IgM test shows 100 % of specificity. • Lateral flow tests show similar overall performances than Euroimmun ELISA IgG/IgA and Maglumi CLIA IgG/IgM test. • The five immunoassays tested show equivalent performances and concordance after 14 days of the onset of symptoms. Several SARS-CoV-2 immunoassays have been developed recently. The purpose of this study was to assess the performance of five immunoassays for the detection of SARS-CoV-2 antibodies. Two quantitative automated immunoassays (Maglumi™2019-n-Cov IgG and IgM and Euroimmun Anti-SARS-CoV-2 IgG and IgA assays) and three lateral flow rapid tests were performed. This retrospective study included 200 residual sera from patients and healthy volunteers. Case serum samples (n = 128) were obtained from COVID-19 patients confirmed by RT-qPCR and CT-scan. Days since onset of symptoms was collected from their medical records. Control non-SARS-CoV-2 samples (n = 72) were obtained from anonymous stored residual serum samples. Maglumi™ IgG/IgM tests showed overall less sensitivity than Euroimmun IgG/IgA test (84.4 % versus 64.3 %). Both tests showed similar specificities of IgG at 99 % and 100 %, respectively. The results from the lateral flow assays were easily interpretable with unambiguous coloured reading bands. The overall sensitivity of the three tests was similar (around 70 %) without any significant differences. The sensitivity of the three lateral flow assays and also of the serological quantitative assays increased during the second week after symptom onset and all reached similar values (91 %–94 %) after 14 days. This study shows accurate and equivalent performance of the five serological antibody assays (ELISA, CLIA and three lateral flow tests) in detecting SARS-CoV-2 antibodies 14 days after the onset of COVID-19 symptoms. This is compatible with their application in specific clinical contexts and in determining epidemiological strategies for the COVID-19 pandemic. [ABSTRACT FROM AUTHOR]

Owing to their ease in operation and fast turnaround time, lateral flow assays (LFAs) are increasingly being used as point-of-care diagnostic tests for variety of analytes. In a majority of these LFAs, antibodies are used as a molecular recognition element. Antibodies have a number of limitations such as high batch-to-batch variation, poor stability, long development time, difficulty in functionalization and need for ethical approval and cold chain. All these factors pose a great challenge to scale up the antibody-based tests. In recent years, the advent of aptamer technology has made a paradigm shift in the point-of-care diagnostics owing to the various advantages of aptamers over antibodies that favour their adaptability on a variety of sensing platforms including the lateral flow. In this review, we have highlighted the advantages of aptamers over antibodies, suitability of aptamers for lateral flow platforms, different types of aptamer-based LFAs and various labels for aptamer-based LFAs. We have also provided a summary of the applications of aptamer technology in LFAs for analytical applications. [ABSTRACT FROM AUTHOR]

Readily deployable, low-cost point-of-care medical devices such as lateral flow assays (LFAs), microfluidic paper-based analytical devices (μPADs), and microfluidic thread-based analytical devices (μTADs) are urgently needed in resource-poor settings. Governed by the ASSURED criteria (affordable, sensitive, specific, user-friendly, rapid and robust, equipment-free, and deliverability) set by the World Health Organization, these reliable platforms can screen a myriad of chemical and biological analytes including viruses, bacteria, proteins, electrolytes, and narcotics. The Ebola epidemic in 2014 and the ongoing pandemic of SARS-CoV-2 have exemplified the ever-increasing importance of timely diagnostics to limit the spread of diseases. This review provides a comprehensive survey of LFAs, μPADs, and μTADs that can be deployed in resource-limited settings. The subsequent commercialization of these technologies will benefit the public health, especially in areas where access to healthcare is limited.

In recent years, advances in immunosensor device fabrication have significantly expanded the use of this technology in a broad range of applications including clinical diagnosis, food analysis, quality control, environmental studies and industrial monitoring. The most important aspect in fabrication is to obtain a design that provides a low detection limit. The utilization of nanomaterials as a label, catalyst and biosensing transducer is, perhaps, the most popular approach in ultrasensitive devices. This chapter reviews recent advances in immunosensor fabrication and summarizes the most recent studies. Strategies employed to significantly improve sensitivity and specificity of immunosensor technology and the advantages and limitations thereof are explored., (Copyright © 2021 Elsevier Inc. All rights reserved.)

• The multi-parameteric process of developing lateral flow assays (LFAs) is elucidated. • Novel capture/detector agent generation for improved target detection is presented. • Multiplexed detection is introduced, enabling increased throughput and efficiency. • Signal amplification methods bridge the performance of LFAs with lab techniques. • Prospects for more quantitative LFAs and broader applications are discussed. From a home-based pregnancy self-testing kit, lateral flow assays (LFAs) have proliferated and gained widespread utilization as point-of-care (POC) test kits. Their prevalence is due to their portability, rapid time-to-result, simplicity, stability, and cost-effectiveness. LFAs are well-suited for early detection of infectious diseases, which threatens public health and the economy, enabling timely medical intervention, and management of disease and treatment. This is vital for rural and resource-limited settings where well-equipped laboratories with well-trained personnel are scarce. Nevertheless, LFAs have certain limitations, such as moderate sensitivity and target throughput, as compared to lab-based technologies. Also, the development of LFA, although well-defined, is not straightforward. In this review article, we will elucidate the iterative process of LFA development, and discuss strategies for generating sensitive and specific capture/detector agents, multiplexed detection and signal amplification. An important starting point in LFA development is the clear definition/identification of design inputs and predicate. Newly engineered capture/detector agents, such as nanobodies and aptamers, should possess high binding affinity and functionality in body fluid samples for practical field application. Also, chemical methods, combined with engineering, have enabled multiplexing and signal amplification capabilities for higher target throughput and detection sensitivity. Furthermore, LFAs can be augmented or adapted to other platforms, such as smartphone, spectroscopy and electrochemistry, for quantitative measurements that can engender wider applications and adoption. Through these advances, LFA will transform into a genuinely versatile platform, capable of delivering accurate results that are similar to lab-based technologies, while retaining its advantage as a simple, portable, inexpensive and rapid test. [ABSTRACT FROM AUTHOR]

Advanced bisphenol A (BPA) lateral flow assays (LFAs) that use multiple nanosystems are reported. The assays use three nanosystems: gold nanostars, gold nanocubes, and gold nanorods, which are rarely applied in LFAs, compared with general gold nanoparticles that are referred to as gold nanospheres in this paper. These various nanosystems are bound to anti‐BPA antibodies and applied in LFAs to develop advanced BPA LFAs; the developed LFAs show differing BPA detection performance, as well as different visible colors, optical intensities, limits of detection, and application ranges. Advanced BPA LFAs that use multiple gold nano‐object shapes are successfully developed, and the geometry effects of diverse gold nanosystems coupled with anti‐BPA antibodies and the potential applications of regular BPA LFAs are explored. [ABSTRACT FROM AUTHOR]

Background: Lateral flow assays (LFA) play an increasingly important role in the rapid detection of various pathogens, pollutants, and toxins., Purpose: To overcome the drawbacks of low sensitivity and poor quantification in LFA, we developed a new calorimetric LFA (CLFA) using gold nanocages (GNCs) due to their high photothermal conversion efficiency, good stability of photophysical properties, and stronger penetrating ability of NIR light., Methods: Thiol-polyethylene glycol-succinyl imide ester (HS-PEG-NHS) was modified onto GNCs, and the complex was conjugated with an antibody. Subsequently, the antibody-conjugated GNCs were analyzed by UV/Vis spectrophotometer, transmission electron microscope, high-resolution transmission electron microscope with energy dispersive spectrometer, dynamic light scattering instrument, and Atom force microscope. The GNC-based CLFA of alpha-fetoprotein (AFP) and zearalenone (ZEN), a food toxin, required nitrocellulose strips, a NIR laser source, and an infrared camera., Results: The GNC-labeled CLFA platform technique exhibited detection sensitivity, qualitative specificity, and quantitative accuracy. The superior performance of the technique was evident both in sandwich format detection of biomacromolecules (eg, AFP protein) or competitive format detection of small molecules (eg, ZEN). After optimizing various test parameters, GNC-labeled CLFA provided ca . 5-6-fold enhanced sensitivity, higher correlativity ( R 2 >0.99), and more favorable recovery (82-115%) when compared with visual LFA., Conclusion: GNC-labeled CLFA may be a promising detection platform with high sensitivity, specificity, and precision., Competing Interests: Jiangshan Wan, Xiaole Peng, and Liyi Mai were employed by the C. Consum Pharmaceutical Group at the time of the study. The authors report no other conflicts of interest in this work., (© 2019 Hu et al.)

Lateral flow assays (LFAs) have been the pillar of rapid point-of-care (POC) diagnostics due to their simplicity, rapid process, and low cost. Recent advances in sensitivity, selectivity, and chemical stability enhancement have ensured the foothold of LFAs in commercial POC diagnostics. This paper reviews recent developments in labeling strategies and detection methods of LFAs. Moreover, vertical flow assays (VFAs) have emerged as an alternate paper-based assay due to faster detection time and unique multiplexing capabilities. Smartphones as LFA readers have been transformed into a universal integrated platform for imaging, data processing, and storage, providing quantitative results in low-resource settings. Commercial LFAs and VFAs products are evaluated with regards to their performance, market trends, and regulatory issues. The future outlook of the flow-based assays for POC diagnostics is also discussed., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)