Designs, formats and applications of lateral flow assay: A literature review

Ru(bpy)32+ -Loaded Mesoporous Silica Nanoparticles as Electrochemiluminescent Probes of a Lateral Flow Immunosensor for Highly Sensitive and Quantitative Detection of Troponin I

The lateral flow immunosensor (LFI) is a widely used diagnostic tool for biomarker detection; however, its sensitivity is often insufficient for analyzing targets at low concentrations. Here, an electrochemiluminescent LFI (ECL-LFI) is developed for highly sensitive detection of troponin I (TnI) using Ru(bpy)₃²⁺ -loaded mesoporous silica nanoparticles (RMSNs). A large amount of Ru(bpy)₃²⁺ is successfully loaded into the mesoporous silica nanoparticles with excellent loading capacity and shows strong ECL signals in reaction to tripropylamine. Antibody-immobilized RMSNs are applied to detect TnI by fluorescence and ECL analysis after a sandwich immunoassay on the ECL-LFI strip. The ECL-LFI enables the highly sensitive detection of TnI-spiked human serum within 20 min at femtomolar levels (≈0.81 pg mL^-1 ) and with a wide dynamic range (0.001-100 ng mL^-1 ), significantly outperforming conventional fluorescence detection (>3 orders of magnitude). Furthermore, TnI concentrations in 35 clinical serum samples across a low range (0.01-48.31 ng mL^-1 ) are successfully quantified with an excellent linear correlation (R²  = 0.9915) using a clinical immunoassay analyzer. These results demonstrate the efficacy of this system as a high-performance sensing strategy capable of capitalizing on future point-of-care testing markets for biomolecule detection.

Monoclonal antibodies with subnanomolar affinity to tenofovir for monitoring adherence to antiretroviral therapies: from hapten synthesis to prototype development

Approximately 32 million people have died of HIV infection since the beginning of the outbreak, and 38 million are currently infected. Among strategies adopted by the Joint United Nations Programme on HIV/AIDS to end the AIDS global epidemic, the treatment, diagnosis, and viral suppression of the infected subjects are considered crucial for HIV prevention and transmission. Although several antiretroviral (ARV) drugs are successfully used to manage HIV infection, their efficacy strictly relies on perfect adherence to the therapy, which is seldom achieved. Patient supervision, especially in HIV-endemic, low-resource settings, requires rapid, easy-to-use, and affordable analytical tools, such as the enzyme-linked immunosorbent assay (ELISA) and especially the lateral flow immunoassay (LFIA). In this work, high-affinity monoclonal antibodies were generated to develop ELISA and LFIA prototypes for monitoring tenofovir (TFV), an ARV drug present in several HIV treatments. TFV was functionalized by inserting a carboxylated C5-linker at the phosphonic group of the molecule, and the synthetic derivative was conjugated to proteins for mice immunization. Through a rigorous screening strategy of hybridoma supernatants, a panel of monoclonal antibodies strongly binding to TFV was obtained. Following antibody characterization for affinity and selectivity by competitive ELISA, a LFIA prototype was developed and tentatively applied to determine TFV in simulated urine. The point-of-care test showed ultra-high detectability (the visual limit of detection was 2.5 nM, 1.4 ng mL^-1), excellent selectivity, and limited proneness to matrix interference, thus potentially making this rapid method a valuable tool for the on-site assessment of patient adherence to ARV therapy.

Nucleic Acid and Immunological Diagnostics for SARS-CoV-2: Processes, Platforms and Pitfalls

Accurate diagnosis at an early stage of infection is essential for the successful management of any contagious disease. The coronavirus disease 2019 (COVID-19), caused by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) virus is a pandemic that has affected 214 countries affecting more than 37.4 million people causing 1.07 million deaths as of the second week of October 2020. The primary diagnosis of the infection is done either by the molecular technique of RT-qPCR by detecting portions of the RNA of the viral genome or through immunodiagnostic tests by detecting the viral proteins or the antibodies produced by the host. As the demand for the test increased rapidly many naive manufacturers entered the market with novel kits and more and more laboratories also entered the diagnostic arena making the test result more error-prone. There are serious debates globally and regionally on the sensitivity and specificity of these tests and about the overall accuracy and reliability of the tests for decision making on control strategies. The significance of the test is also complexed by the presence of asymptomatic carriers, re-occurrence of infection in cured patients as well as by the varied incubation periods of the infection and shifting of the viral location in the host tissues. In this paper, we review the techniques available for SARS-CoV-2 diagnosis and probable factors that can reduce the sensitivity and specificity of the different test methods currently in vogue. We also provide a checklist of factors to be considered to avoid fallacious practices to reduce false positive and false negative results by the clinical laboratories.

Detection of ochratoxin A by quantum dots-based fluorescent immunochromatographic assay

Ochratoxin A (OTA) is a toxic metabolite produced mainly by Aspergillus and Penicillium species. A quantitative method was developed for the rapid, simple, and sensitive detection of OTA in corn by quantum dots-based fluorescent immunochromatographic assay (QDs-ICA). The CdSe/ZnS QDs-labelled anti-OTA monoclonal antibody (mAb) conjugates were designed as the fluorescent signal probe. The QDs-ICA included the designation of test line (T line) and control line (C line), which were sprayed with optimal concentrations of the OTA-OVA and staphylococcal protein-A (SPA), respectively. Under the optimal experimental conditions, the QDs-ICA exhibited excellent specificity and good accuracy and precision. For qualitative detection, the cut-off value for the T line of the visual detection method was 2.5 ng/mL. For quantitative detection, the linear regression equation of the standard curve was y = 0.366x + 0.514 with a reliable correlation coefficient (R² = 0.992). Moreover, the 50% inhibition value (IC₅₀) of the QDs-ICA was 0.91 ng/mL, the limit of detection (LOD) was 0.07 ng/mL, and the detection range was 0.05 to 10 ng/mL. In addition, the recovery rates ranged from 91.82 to 100.35% with a coefficient of variation (CV) below 3% for intra-assay, whereas the recovery rates for inter-assay changed from 94.29 to 104.62% with a CV below 10%. These results indicate that the QDs-ICA can serve as a potential large-scale preliminary device for rapid determination of OTA. Using CdSe/ZnS QDs as the fluorescent signal for quantum dots-based fluorescent immunochromatographic assay, the QDs-ICA provided a novel method for the rapid simultaneous qualitative and quantitative determination of OTA.

New insights into the role of nanotechnology in microbial food safety

Today, the role of nanotechnology in human life is undeniable as a broad range of industries, particularly food and medicine sectors, have been dramatically influenced. Nanomaterials can contribute to food safety by forming new nano-sized ingredients with modified physicochemical characteristics. Nanotechnologies can inhibit the growth of food spoilage microorganisms by recruiting novel and unique agents that are involved in removal of microbes from foods or prevent adhesion of microbial cells to food surfaces. Hence, nanotechnology could be considered as a high-potential tool in food packaging, safety, and preservation. Moreover, the prevention of biofilm formation by disturbing the attachment of bacteria to the food surface is another useful nanotechnological approach. Recently, nanoparticle-based biosensors have been designed and developed to detect the food-borne pathogens and hazardous substances through complicated mechanisms. During the past half-century, many methods such as freeze-drying and spray drying have been employed for increasing the viability in food industries; however, the other novel approaches such as encapsulation methods have also been developed. Admittedly, some beneficial bacteria such as probiotics bring diverse benefits for human health if only they are in a sufficient number and viability in the food products and gastrointestinal tract (GI). Encapsulation of these valuable microbial strains by nanoparticles improves the survival of probiotics under harsh conditions such as extreme levels of temperature, pH, and salinity during the processing of food products and within the GIT tract. The survival and effectiveness of encapsulated microorganisms depends on different factors including function of cell wall components in bacteria and type of coating materials. This review aims to broadly explore the potential of different aspects of nanotechnology in food industry, especially for packaging, preservation, safety, and viability.

Development of rapid gold nanoparticles based lateral flow assays for simultaneous detection of Shigella and Salmonella genera

Salmonella and Shigella genera are common pathogens that contaminate foods and beverages. Lateral flow assays (LFA) are commonly used to detect these pathogens. However, most of the developed LFAs are for single detection. Simultaneous detection of pathogens is required to reduce cost and time. In this work, 40 nm gold nanoparticles (AuNPs) were synthesized using the seeding growth method as labeling agent. The AuNPs were characterized and conjugated with mouse anti-Gram negative endotoxin antibody. The nitrocellulose membrane HF135 was immobilized with anti-mouse IgG antibody as a control line and two separate test lines with either anti-Shigella or anti-Salmonella antibody, respectively. Color intensity of test lines was observed for positive samples. A milk sample was used as proof of concept to mimic actual contamination. The limit of detection of the LFA was 3.0 × 10⁶ CFU/mL for multiplex detection of Shigella flexneri and Salmonella Typhi and for both single detections. The result was comparable with the enzyme-linked immunosorbent assay (ELISA) analysis. The produced LFA could differentiate between Shigella flexneri, Shigella boydii, Salmonella Enteritidis, and Salmonella Typhi. The developed LFA was able to identify Shigella flexneri and Salmonella Typhi with good sensitivity in milk samples, thus, beneficial to ensure the safety of food before entering the market.

Quantitative hematocrit measurement of whole blood in a point-of-care lateral flow device using a smartphone flow tracking app

We present a rapid and quantitative point-of-care (PoC) system based on a smartphone application that is capable of accurately tracking the flow of red blood cells (RBCs) through a no-reaction lateral flow assay (nrLFA) device. Utilizing only the camera feed from the smartphone and built-in image processing, the nrLFA is identified and RBC fluid flow distances and rates are recorded in parallel with the test without the need of any custom hardware or enclosure. We demonstrated the application by first measuring and then calculating hematocrit (Hct) values of whole blood samples with nominal content of 28%, 35%, 40%, and 45% Hct on the nrLFA platform. The PoC system was able to accurately measure (to within 1% Hct of nominal values) whole blood Hct in ~10-20 s after sample dispensing.

Analysis of pressure-driven membrane preconcentration for point-of-care assays

Point-of-care diagnostic devices for both physicians and patients themselves are now ubiquitous, but often not sensitive enough for highly dilute analytes (e.g., pre-symptomatic viral detection). Two primary methods to address this challenge include (1) increasing the sensitivity of molecular recognition elements with greater binding affinity to the analyte or (2) increasing the concentration of the analyte being detected in the sample itself (preconcentration). The latter approach, preconcentration, is arguably more attractive if it can be made universally applicable to a wide range of analytes. In this study, pressure-driven membrane preconcentration devices were developed, and their performance was analyzed for detecting target analytes in biofluids in the form of point-of-care lateral-flow assays (LFAs). The demonstrated prototypes utilize negative or positive pressure gradients to move both water and small interferents (salt, pH) through a membrane filter, thereby concentrating the analyte of interest in the remaining sample fluid. Preconcentration up to 33× is demonstrated for influenza A nucleoprotein with a 5 kDa pore polyethersulfone membrane filter. LFA results are obtained within as short as several minutes and device operation is simple (very few user steps), suggesting that membrane preconcentration can be preferable to more complex and slow conventional preconcentration techniques used in laboratory practice.

Collocation of avian and mammal antibodies to develop a rapid and sensitive diagnostic tool for Russell's Vipers Snakebite

Russell's vipers (RVs) envenoming is an important public health issue in South-East Asia. Disseminated intravascular coagulopathy, systemic bleeding, hemolysis, and acute renal injury are obvious problems that develop in most cases, and neuromuscular junction blocks are an additional problem caused by western RV snakebite. The complex presentations usually are an obstacle to early diagnosis and antivenom administration. Here, we tried to produce highly specific antibodies in goose yolks for use in a paper-based microfluidic diagnostic kit, immunochromatographic test of viper (ICT-Viper), to distinguish RVs from other vipers and even cobra snakebite in Asia. We used indirect ELISA to monitor specific goose IgY production and western blotting to illustrate the interaction of avian or mammal antibody with venom proteins. The ICT-Viper was tested not only in prepared samples but also in stored patient serum to demonstrate its preliminary efficacy. The results revealed that specific anti-Daboia russelii IgY could be raised in goose eggs effectively without inducing adverse effects. When it was collocated with horse anti-Daboia siamensis antibody, which broadly reacted with most of the venom proteins of both types of Russell's viper, the false cross-reactivity was reduced, and the test showed good performance. The limit of detection was reduced to 10 ng/ml in vitro, and the test showed good detection ability in clinical snake envenoming case samples. The ICT-Viper performed well and could be combined with a cobra venom detection kit (ICT-Cobra) to create a multiple detection strip (ICT-VC), which broadens its applications while maintaining its detection ability for snake envenomation identification. Nonetheless, the use of the ICT-Viper in the South-East Asia region is pending additional laboratory and field investigations and regional collaboration. We believe that the development of this practical diagnostic tool marks the beginning of positive efforts to face the global snakebite issue.

Alginate Hydrogel-Embedded Capillary Sensor for Quantitative Immunoassay with Naked Eye

We have developed an alginate hydrogel-embedded capillary sensor (AHCS) for naked eye-based quantification of immunoassay. Alkaline phosphatase (ALP) can modulate gel-sol transformation to increase the permeability of Cu²⁺-cross-linked alginate hydrogel film in the AHCS, followed by solution exchange into the capillary. Through measuring the length of the liquid phase of the microfluidics in the capillary at a given time, the concentration of the ALP could be quantified with the naked eye. Since ALP is widely applied as a signal reporter for immunoassays, the AHCS could easily accommodate conventional immune sensing platforms. We justify the practicality of AHCS with hepatitis B virus surface antigen (HBsAg) in serum samples and got comparable results with commercialized immunoassay. This AHCS is easy to make and use, effective in cost, and robust in quantification with the naked eye, showing great promise for next generation point-of-care testing.

Lateral flow assay modified with time-delay wax barriers as a sensitivity and signal enhancement strategy

The ease of use, low cost and quick operation of lateral flow assays (LFA) have made them some of the most common point of care biosensors in a variety of fields. However, their generally low sensitivity has limited their use for more challenging applications, where the detection of low analytic concentrations is required. Here we propose the use of soluble wax barriers to selectively and temporarily accumulate the target and label nanoparticles on top of the test line (TL). This extended internal incubation step promotes the formation of the immune-complex, generating a 51.7-fold sensitivity enhancement, considering the limit of quantification, and up to 96% signal enhancement compared to the conventional LFA for Human IgG (H-IgG) detection.

Scalable COVID-19 Detection Enabled by Lab-on-Chip Biosensors

Introduction

The emergence of a novel coronavirus, SARS-CoV-2, has highlighted the need for rapid, accurate, and point-of-care diagnostic testing. As of now, there is not enough testing capacity in the world to meet the stated testing targets, which are expected to skyrocket globally for broader testing during reopening

Aim

This review focuses on the development of lab-on-chip biosensing platforms for diagnosis of COVID-19 infection.

Results

We discuss advantages of utilizing lab-on-chip technologies in response to the current global pandemic, including their potential for low-cost, rapid sample-to-answer processing times, and ease of integration into a range of healthcare settings. We then highlight the development of magnetic, colorimetric, plasmonic, electrical, and lateral flow-based lab-on-chip technologies for the detection of SARS-CoV-2, in addition to other viruses. We focus on rapid, point-of-care technologies that can be deployed at scale, as such devices could be promising alternatives to the current gold standard of reverse transcription-polymerase chain reaction (RT-PCR) diagnostic testing.

Conclusion

This review is intended to provide an overview of the current state-of-the-field and serve as a resource for innovative development of new lab-on-chip assays for COVID-19 detection.

Synthesis and Initial Evaluation of a Novel Fluorophore for Selective FMDV 3C Protease Detection

The development and evaluation of a Boc-AL(Boc)Q(Trt)-AMC fluorophore to detect 3C Protease, produced by Foot and Mouth Disease Virus (FMDV) is reported, with a view to a potential use as a rapid screen for FMDV infected livestock The peptide-linked conjugate fluorophore is evaluated in vitro for sensitivity, specificity, stability and rapidity and shows statistically significant increases in fluorescence when exposed to physiologically relevant concentrations of 3C Protease and selectivity when compared with other common proteases likely to be located, typically in the absence of FMDV. The stability of deprotected Boc-AL(Boc)Q(Trt)-AMC is reported as a limitation of this probe.

Wicking in Paper Strips under Consideration of Liquid Absorption Capacity

Paper-based microfluidic devices have the potential of being a low-cost platform for diagnostic devices. Electrical circuit analogy (ECA) model has been used to model the wicking process in paper-based microfluidic devices. However, material characteristics such as absorption capacity cannot be included in the previous ECA models. This paper proposes a new model to describe the wicking process with liquid absorption in a paper strip. We observed that the fluid continues to flow in a paper strip, even after the fluid reservoir has been removed. This phenomenon is caused by the ability of the paper to store liquid in its matrix. The model presented in this paper is derived from the analogy to the current response of an electric circuit with a capacitance. All coefficients in the model are fitted with data of capillary rise experiments and compared with direct measurement of the absorption capacity. The theoretical data of the model agrees well with experimental data and the conventional Washburn model. Considering liquid absorption capacity as a capacitance helps to explain the relationship between material characteristics and the wicking mechanism.

Newly developed diagnostic methods for SARS-CoV-2 detection

The emergence of SARS-CoV-2, responsible for COVID-19 disease, has caused a substantial worldwide pandemic and has become a significant public health problem. World Health Organization (WHO) has declared COVID-19 as a devastating health emergency for all countries. Public health officials continue to monitor the situation closely to control this new virus-related outbreak. In order to continue to manage this pandemic, a fast and sensitive diagnosis of COVID-19 is attempted. Emerging tests have become an essential part of the management of the COVID-19 crisis. This review article aims to provide a detailed explanation of ongoing and new diagnostic technologies for SARS-CoV-2 and a summary of method principles. Examples of new diagnostic methods for providing efficient and rapid diagnostic tests for managing the SARS-CoV-2 outbreak are also mentioned.

Liposome-Based Bioassays

This review highlights the potential of using liposomes in bioassays. Liposomes consist of nano- or micro-sized, synthetically constructed phospholipid vesicles. Liposomes can be loaded with a number of reporting molecules that allow a dramatic amplification of the detection threshold in bioassays. Liposome-based sensors bind or react with the biological components of targets through the introduction of properly tailored vectors anchored on their external surface. The use of liposome-based formulations allows the set-up of bioassays that are rapid, sensitive, and often suitable for in-field applications. Selected applications in the field of immunoassays, as well as recognition/assessment of corona proteins, nucleic acids, exosomes, bacteria, and viruses are surveyed. The role of magnetoliposomes is also highlighted as an additional tool in the armory of liposome-based systems for bioassays.

A plasmonic fiberoptic absorbance biosensor for mannose-capped lipoarabinomannan based tuberculosis diagnosis

Tuberculosis (TB) is a resurgent infectious disease affecting a large number of people in the developing countries. An on-site, affordable diagnostic screening at an early-stage for an immediate anti-TB treatment is known to tremendously minimize the high mortality rates. Lipoarabinomannan (LAM), a surface glycolipid, has been identified as a potential TB biomarker present in urine at ultra-low concentrations of a few fg/mL. Here, we report a plasmonic fiber optic absorbance biosensor (P-FAB) strategy for mannosylated LAM (Man-LAM or Mtb LAM) detection down to attomolar concentrations. It involves a plasmonic sandwich immunoassay on a U-bent fiber optic probe with gold plasmonic (AuNP) labels functionalized with anti-Mtb LAM immunoglobulin M (IgM) and anti-Mtb LAM IgG respectively. The Mtb LAM is quantified in terms of absorption of light passing through the fiber probe using a green LED and a photodetector. The choice of fiber optic probes (fused silica versus polymer), the optimum size (20, 40, 60 and 80 nm) and concentration (2 × , 10 × , and 20 × ) of AuNP labels were investigated to obtain high sensitivity and lower limits of analyte detection (LoD). P-FAB with a simple LED-photodetector pair, 200 μm fused silica U-bent fiber probe and 60 nm (20 × ) AuNP labels gave LoDs down to 1 fg/mL and 10 fg/mL in the buffer and synthetic urine respectively. Moreover, the anti-Mtb LAM IgM bound sensor probes and the AuNP reagent stored at 4 °C were stable up to 45 days. P-FAB based Mtb LAM sensor demonstrates its potential for an on-site TB diagnosis.

A Two-Dimensional Affinity Capture and Separation Mini-Platform for the Isolation, Enrichment, and Quantification of Biomarkers and Its Potential Use for Liquid Biopsy

Biomarker detection for disease diagnosis, prognosis, and therapeutic response is becoming increasingly reliable and accessible. Particularly, the identification of circulating cell-free chemical and biochemical substances, cellular and subcellular entities, and extracellular vesicles has demonstrated promising applications in understanding the physiologic and pathologic conditions of an individual. Traditionally, tissue biopsy has been the gold standard for the diagnosis of many diseases, especially cancer. More recently, liquid biopsy for biomarker detection has emerged as a non-invasive or minimally invasive and less costly method for diagnosis of both cancerous and non-cancerous diseases, while also offering information on the progression or improvement of disease. Unfortunately, the standardization of analytical methods to isolate and quantify circulating cells and extracellular vesicles, as well as their extracted biochemical constituents, is still cumbersome, time-consuming, and expensive. To address these limitations, we have developed a prototype of a portable, miniaturized instrument that uses immunoaffinity capillary electrophoresis (IACE) to isolate, concentrate, and analyze cell-free biomarkers and/or tissue or cell extracts present in biological fluids. Isolation and concentration of analytes is accomplished through binding to one or more biorecognition affinity ligands immobilized to a solid support, while separation and analysis are achieved by high-resolution capillary electrophoresis (CE) coupled to one or more detectors. When compared to other existing methods, the process of this affinity capture, enrichment, release, and separation of one or a panel of biomarkers can be carried out on-line with the advantages of being rapid, automated, and cost-effective. Additionally, it has the potential to demonstrate high analytical sensitivity, specificity, and selectivity. As the potential of liquid biopsy grows, so too does the demand for technical advances. In this review, we therefore discuss applications and limitations of liquid biopsy and hope to introduce the idea that our affinity capture-separation device could be used as a form of point-of-care (POC) diagnostic technology to isolate, concentrate, and analyze circulating cells, extracellular vesicles, and viruses.

Carbon-Coated Superparamagnetic Nanoflowers for Biosensors Based on Lateral Flow Immunoassays

Superparamagnetic iron oxide nanoflowers coated by a black carbon layer (Fe3O4@C) were studied as labels in lateral flow immunoassays. They were synthesized by a one-pot solvothermal route, and they were characterized (size, morphology, chemical composition, and magnetic properties). They consist of several superparamagnetic cores embedded in a carbon coating holding carboxylic groups adequate for bioconjugation. Their multi-core structure is especially efficient for magnetic separation while keeping suitable magnetic properties and appropriate size for immunoassay reporters. Their functionality was tested with a model system based on the biotin-neutravidin interaction. For this, the nanoparticles were conjugated to neutravidin using the carbodiimide chemistry, and the lateral flow immunoassay was carried out with a biotin test line. Quantification was achieved with both an inductive magnetic sensor and a reflectance reader. In order to further investigate the quantifying capacity of the Fe3O4@C nanoflowers, the magnetic lateral flow immunoassay was tested as a detection system for extracellular vesicles (EVs), a novel source of biomarkers with interest for liquid biopsy. A clear correlation between the extracellular vesicle concentration and the signal proved the potential of the nanoflowers as quantifying labels. The limit of detection in a rapid test for EVs was lower than the values reported before for other magnetic nanoparticle labels in the working range 0-3 × 107 EVs/μL. The method showed a reproducibility (RSD) of 3% (n = 3). The lateral flow immunoassay (LFIA) rapid test developed in this work yielded to satisfactory results for EVs quantification by using a precipitation kit and also directly in plasma samples. Besides, these Fe3O4@C nanoparticles are easy to concentrate by means of a magnet, and this feature makes them promising candidates to further reduce the limit of detection.

Sensitive and rapid lateral-flow assay for early detection of subclinical mammary infection in dairy cows

Detection of subclinical mastitis (SCM) in its initial stage can save great economic losses, improve milk quality and animal welfare. We have developed a semiquantitative lateral flow assay for the detection of SCM in dairy cows targeting myeloperoxidase (MPO) enzyme of milk neutrophils. A competitive immunoassay format was used, and colloidal gold nanoparticles (GNP) were prepared and used as a labelling agent. Monoclonal anti-MPO antibodies were used and assessed for its quality by enzyme-linked immunosorbent assay and dot blot. Conjugation method for GNP and anti-MPO antibodies was standardised, and the conjugate was placed over the conjugate pad. MPO coupled with a carrier protein (OVA) and the species-specific secondary antibodies were placed on test and control lines, respectively. The developed assay was verified with 75 milk samples collected from healthy, SCM and clinical mastitis cows. It displayed a high sensitivity as it could detect MPO as low as 1.5 ng/ml, an accuracy greater than 97% and showed no crossreactivity when crosschecked with other milk proteins. The developed assay can be used as an alternative for SCM diagnostic tests where lab structure are available for obtaining the lysate of milk SCC.

[Seroprevalence and SARS-CoV-2 testing in healthcare occupations]

The SARS-CoV‑2 causes a disease spectrum that includes asymptomatic and mildly symptomatic infections with subclinical manifestations but which can nevertheless still be potentially contagious. Evidence from SARS-CoV‑2 infected macaque monkeys and from studies with seasonal coronaviruses suggests that the infection is likely to produce an immunity that is protective for a certain period of time. Available test methods enable a high degree of reliability, e.g. if high-quality serological methods are combined. Although individual test results have to be interpreted with caution, serosurveillance in a tertiary eye care center and large eye research institute can reduce anxiety and provide clarity regarding the actual number of (unreported) SARS-CoV‑2 infections.

4D synchrotron microtomography and pore-network modelling for direct in situ capillary flow visualization in 3D printed microfluidic channels

Powder-based 3D printing was employed to produce porous, capillarity-based devices suitable for passive microfluidics. Capillary imbibition in such devices was visualized in situ through dynamic synchrotron X-ray microtomography performed at the European Synchrotron Radiation Facility (ESRF) with sub-second time resolution. The obtained reconstructed images were segmented to observe imbibition dynamics, as well as to compute the system effective contact angle and to generate a pore-network to model capillary imbibition. A contact angle gradient was observed resulting in a preferential wicking direction, with the central portion of the microfluidic channel filling faster than the edge areas. The contact angle analysis and the pore-network model results suggest that this is due to spatial variations in the material surface properties arising from both the 3D printing and the subsequent drying processes.

Aptamer-gold nanozyme based competitive lateral flow assay for rapid detection of CA125 in human serum

For several decades, point-of-care technology (POCT) has proven its potential regarding swift and cost-efficient detection of analytes. Lateral flow assay is a highly popular POC technology that needs improvisation to increase its sensitivity, cost effectiveness and quantification so that it becomes more user friendly and affordable technology. In this context, the present study has investigated the use of aptamers and nanozymes together for the first time in developing an Aptamer-nanozyme lateral flow assay (ALFA). The present study uses a specific aptamer for CA125 as capture reagent and peroxidase mimetic gold nanoparticles as label for detection of CA125 in human serum through developed competitive ALFA. The assay was specific and has a limit of detection of 3.71 U/mL. The ALFA test was in house validated for its precision, recovery and showed a significant correlation with established CA125 chemiluminiscent ELISA with P-value<0.0001. In summary, this assay quantitatively detects an analyte by using an aptamer and peroxidase mimetic gold nanoparticles that ensures circumventing the use of antibodies and incorporating enzyme mimetic activity in assay systems.

Preparation of ELISA and Lateral Flow Kits for rapid Diagnosis of Mycoplasma gallisepticum in Poultry

Avian mycoplasmas were mainly the cause of poultry industry economic losses; reduced meat and egg production and increases the antibiotic treatment cost. Mycoplasma gallisepticum (MG) infection is designated as infectious sinusitis of turkeys and chronic respiratory disease of chickens (gasping, depression, semi closed eyes, infraorbital sinuses edema and decrease in egg production). This study aimed to prepare, evaluate and Compare in-house ELISA kits and lateral flow assay (LFA) from a local strain of MG with commercial ELISA kits and PCR consequently. A total of 54 samples (27 tracheal swabs, 10 trachea and 17 lung) and 50 serum samples collected from birds suffering from chronic respiratory disease were tested by prepared in-house ELISA, commercial ELISA kits, PCR and LFA; a high correlation coefficient between in-house ELISA using whole antigen or sonicated antigen and commercial kit was recorded. Lateral Flow assay (LFA) performance indicate a low sensitivity (77.5%) but maintain a high specificity (92%) compared to PCR. The in-house ELISA kits and LFA prepared could be used as a fast diagnostic technique for detection of MG in Egypt. According to the available knowledge the prepared LFA for diagnosis of MG infection in chickens was developed for the first time in Egypt.

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.

A lateral flow-based portable platform for determination of reproductive status of cattle

Our objective was to develop and validate a tool integrating a disposable fluorescence-based lateral flow immunoassay (LFIA) coupled with a portable imaging device for estimating circulating plasma concentrations of progesterone (P4). First, we developed and optimized a competitive LFIA test strip to measure P4 in bovine plasma. The LFIA design included a sample pad, a conjugate pad that stores R-phycoerythrin-anti-P4 conjugates, a glass-fiber spacer pad, a nitrocellulose membrane with printed test and control lines, and a cellulose-fiber absorbent pad. To perform a test, 20 µL of plasma and 50 µL of running buffer were added on the sample pad. After 3 min, 45 µL of running buffer was added to initiate sample flow. After allowing 15 min to stabilize the colorimetric signal, strips were introduced in an LFIA portable reader wirelessly linked to a laptop to determine P4 concentration based on test-to-control-line signal (T/C ratio). In a series of experiments (n = 6), the ability of the LFIA to differentiate plasma samples with ≥1 or <1 ng/mL of P4 was evaluated. For each experiment, a calibration curve was constructed using plasma with known concentrations of P4 (0.1 to 3.7 ng/mL; n = 5). The resulting linear equation was then used to determine a T/C ratio cutoff to differentiate samples with ≥1 or <1 ng/mL of P4. In addition, to evaluate the ability of the platform to assign samples to P4 concentration groups without a calibration curve for individual batches, we performed a receiver operating characteristic analysis to identify a single cutoff value for T/C ratio that could potentially be used for all batches. Overall, calibration curves showed a linear relationship between T/C ratio and P4 levels (mean coefficient of determination = 0.74; range 0.42 to 0.99). Next, plasma samples from lactating dairy cows (n = 58) were tested in triplicate to determine the ability of the LFIA system to differentiate plasma samples with ≥1 or <1 ng/mL of P4 using a RIA for P4 as reference test. Overall, the LFIA assay correctly classified 90% of the samples, with 97% sensitivity, 83% specificity, 85% positive predictive value, and 96% negative predictive value. Agreement between the tests was substantial (kappa = 0.79; 95% confidence interval 0.64 to 0.95). When using a single cutoff value for T/C ratio selected by receiver operating characteristic analysis, sensitivity and specificity to determine CL presence were 97 (95% confidence interval 82 to 99) and 79% (95% confidence interval 60 to 92), respectively. These data suggest that the developed portable LFIA system can accurately differentiate plasma samples with ≥1 or <1 ng/mL of P4.

Recent progress, challenges, and prospects of fully integrated mobile and wearable point-of-care testing systems for self-testing

The rapid growth of research in the areas of chemical and biochemical sensors, lab-on-a-chip, mobile technology, and wearable electronics offers an unprecedented opportunity in the development of mobile and wearable point-of-care testing (POCT) systems for self-testing. Successful implementation of such POCT technologies leads to minimal user intervention during operation to reduce user errors; user-friendly, easy-to-use and simple detection platforms; high diagnostic sensitivity and specificity; immediate clinical assessment; and low manufacturing and consumables costs. In this review, we discuss recent developments in the field of highly integrated mobile and wearable POCT systems. In particular, aspects of sample handling platforms, recognition elements and sensing methods, and new materials for signal transducers and powering devices for integration into mobile or wearable POCT systems will be highlighted. We also summarize current challenges and future prospects for providing personal healthcare with sample-in result-out mobile and wearable POCT.

Bioorthogonal Reactions Amplify Magnetic Nanoparticles Binding and Assembly for Ultrasensitive Magnetic Resonance Sensing

Conventional transverse relaxation time (T₂)-mediated magnetic resonance sensors (MRS) that utilizing the target-induces state change of magnetic nanoparticles (MNPs) mainly suffer from low sensitivity. Recent T₂-MRS that based on target-induced amount change of MNPs can achieve a higher sensitivity, but these sensors can hardly accommodate small molecules. We herein develop an ultrasensitive T₂-MRS that enable the detection of small molecules based on cascade bioorthogonal reactions (BRs)-realized MNPs binding and assembly. Benefiting from rapid and highly selective cascade BRs, a single small molecule target can not only increase MNPs binding but also assembly MNPs, which greatly amplifies T₂ signal for sensing based on both the state and amount change of MNPs for the first time. Our strategy is capable of sensing chlorpyrifos with a liner range of 0.1 ng/mL to 1000 ng/mL. We justify the practicability of our assay by detecting chlorpyrifos in apple and cabbage samples, whose accuracy is higher than that of enzyme linked immunosorbent assay. Our assay provides a cascade BRs-mediated MRS that can greatly broaden the use of T₂-based MRS for ultrasensitive sensing trace small molecules in complex samples.

Aerosol jet printing of biological inks by ultrasonic delivery

Printing is a promising method to reduce the cost of fabricating biomedical devices. While there have been significant advancements in direct-write printing techniques, non-contact printing of biological reagents has been almost exclusively limited to inkjet printing. Motivated by this lacuna, this work investigated aerosol jet printing (AJP) of biological reagents onto a nonfouling polymer brush to fabricate in vitro diagnostic (IVD) assays. The ultrasonication ink delivery process, which had previously been reported to damage DNA molecules, caused no degradation of printed proteins, allowing printing of a streptavidin-biotin binding assay with sub-nanogram ml-1 analytical sensitivity. Furthermore, a carcinoembryogenic antigen IVD was printed and found to have sensitivities in the clinically relevant range (limit of detection of approximately 0.5 ng ml-1 and a dynamic range of approximately three orders of magnitude). Finally, the multi-material printing capabilities of the aerosol jet printer were demonstrated by printing silver nanowires and streptavidin as interconnected patterns in the same print job without removal of the substrate from the printer, which will facilitate the fabrication of mixed-material devices. As cost, versatility, and ink usage become more prominent factors in the development of IVDs, this work has shown that AJP should become a more widely considered technique for fabrication.

Algorithms for immunochromatographic assay: review and impact on future application

Lateral flow immunoassay (LFIA) is a critical choice for applications of point-of-care testing (POCT) in clinical and laboratory environments because of its excellent features and versatility. To obtain authentic values of analyte concentrations and reliable detection results, the relevant research has featured the application of a diversity of methods of mathematical analysis to technical analysis to allow for use with a small quantity of data. Accordingly, a number of signal and image processing strategies have also emerged for the application of gold immunochromatographic and fluorescent strips to improve sensitivity and overcome the limitations of correlative hardware systems. Instead of traditional methods to solve the problem, researchers nowadays are interested in machine learning and its more powerful variant, deep learning technology, for LFIA detection. This review emphasizes different models for the POCT of accurate labels as well as signal processing strategies that use artificial intelligence and machine learning. We focus on the analytical mechanism, procedural flow, and the results of the assay, and conclude by summarizing the advantages and limitations of each algorithm. We also discuss the potential for application of and directions of future research on LFIA technology when combined with Artificial Intelligence and deep learning.

Emerging Designs of Electronic Devices in Biomedicine

A long-standing goal of nanoelectronics is the development of integrated systems to be used in medicine as sensor, therapeutic, or theranostic devices. In this review, we examine the phenomena of transport and the interaction between electro-active charges and the material at the nanoscale. We then demonstrate how these mechanisms can be exploited to design and fabricate devices for applications in biomedicine and bioengineering. Specifically, we present and discuss electrochemical devices based on the interaction between ions and conductive polymers, such as organic electrochemical transistors (OFETs), electrolyte gated field-effect transistors (FETs), fin field-effect transistor (FinFETs), tunnelling field-effect transistors (TFETs), electrochemical lab-on-chips (LOCs). For these systems, we comment on their use in medicine.

A multicolor multiplex lateral flow assay for high-sensitivity analyte detection using persistent luminescent nanophosphors

Incorporating two persistent luminescent nanophosphors (PLNPs), green-emitting SrAl2O4:Eu2+,Dy3+ (SAO) and blue-emitting (Sr0.625Ba0.375)2MgSi2O7:Eu2+,Dy3+ (SBMSO), in a single lateral flow assay (LFA) establishes a luminescence-based, multiplex point-of-need test capable of simultaneously detecting two different analytes in a single sample. The advantages of this system are the high sensitivity and photostability of PLNPs, while only requiring access to minimal hardware and a smartphone for signal detection. The PLNPs were obtained by first wet milling bulk synthesized phosphor powders, followed by fractionation using differential centrifugal sedimentation to obtain monodisperse nanoparticles. A modified Stöber process was then employed to encapsulate the nanoparticles in a water-stable silica shell followed by attaching antibodies to the particles' surfaces using reductive amination chemistry. The resulting PLNPs were incorporated in an LFA to concurrently detect two independent model analytes, prostate-specific antigen (PSA) and human chorionic gonadotropin (hCG). The multicolor-multiplex PLNP-based assays were finally imaged using a smartphone-based imaging system with excellent detection limits (0.1 ng mL-1 of PSA and 1 ng mL-1 of hCG) that are competitive with commercially available LFAs.

A plasmonic thermal sensing based portable device for lateral flow assay detection and quantification

Point-of-care testing (POCT) is widely used for early diagnosis and monitoring of diseases. Lateral flow assay (LFA) is a successfully commercial tool for POCT. However, LFA often suffers from a lack of quantification and analytical sensitivity. To solve these drawbacks, we have previously developed a thermal LFA using plasmonic gold nanoparticles for thermal contrast into a portable device. Although this methodology significantly improves the analytical sensitivity compared with conventional visual detection, quantification problems are still remaining. In this study, we optimized the operating conditions for the device using conduction and radiation thermal sensing modes allowing the quantification of LFA. The limit of detection of the strips merely containing nanoparticles was decreased by 5-fold (conduction mode) and 12-fold (radiation mode) compared to traditional visual detection. The effect of the ambient temperature was studied for both methods of detection showing that the radiation mode was more affected by the ambient temperature than the conduction mode. To validate the thermal sensing method, human chorionic gonadotropin (HCG) biomarker was quantified using our LFA strips, obtaining a detection limit of 2.8 mIU/mL when using the radiation method of detection.

Recent advances in high-sensitivity detection methods for paper-based lateral-flow assay

Paper-based lateral-flow assays (LFAs) have achieved considerable commercial success and continue to have a significant impact on medical diagnostics and environmental monitoring. Conventional LFAs are typically performed by examining the color changes in the test bands by naked eye. However, for critical biochemical markers that are present in extremely small amounts in the clinical specimens, this readout method is not quantitative, and does not provide sufficient sensitivity or suitable detection limit for a reliable assay. Diverse technologies for high-sensitivity LFA detection have been developed and commercialization efforts are underway. In this review, we aim to provide a critical and objective overview of the recent progress in high-sensitivity LFA detection technologies, which involve the exploitation of the physical and chemical responses of transducing particles. The features and biomedical applications of the technologies, along with future prospects and challenges, are also discussed.

Application of aptamers as molecular recognition elements in lateral flow assays

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.

Combining bacteriophage engineering and linear dichroism spectroscopy to produce a DNA hybridisation assay

Nucleic acid detection is an important part of our bio-detection arsenal, with the COVID-19 pandemic clearly demonstrating the importance to healthcare of rapid and efficient detection of specific pathogenic sequences. As part of the drive to establish new DNA detection methodologies and signal read-outs, here we show how linear dichroism (LD) spectroscopy can be used to produce a rapid and modular detection system for detecting quantities of DNA from both bacterial and viral pathogens. The LD sensing method exploits changes in fluid alignment of bionanoparticles (bacteriophage M13) engineered with DNA stands covalently attached to their surfaces, with the read-out signal induced by the formation of complementary duplexes between DNA targets and two M13 bionanoparticles. This new sandwich assay can detect pathogenic material down to picomolar levels in under 1 minute without amplification, as demonstrated by the successful sensing of DNA sequences from a plant virus (Potato virus Y) and an ampicillin resistance gene, ampR.

A novel DNA sensing method based on LD spectroscopy and using bionanoparticle scaffolds is described, as demonstrated by the rapid detection of DNA strands associated with bacterial and viral pathogens.

Development and optimization of thermal contrast amplification lateral flow immunoassays for ultrasensitive HIV p24 protein detection

Detection of human immunodeficiency virus (HIV) p24 protein at a single pg/ml concentration in point-of-care (POC) settings is important because it can facilitate acute HIV infection diagnosis with a detection sensitivity approaching that of laboratory-based assays. However, the limit of detection (LOD) of lateral flow immunoassays (LFAs), the most prominent POC diagnostic platform, falls short of that of laboratory protein detection methods such as enzyme-linked immunosorbent assay (ELISA). Here, we report the development and optimization of a thermal contrast amplification (TCA) LFA that will allow ultrasensitive detection of 8 pg/ml p24 protein spiked into human serum at POC, approaching the LOD of a laboratory test. To achieve this aim, we pursued several innovations as follows: (a) defining a new quantitative figure of merit for LFA design based on the specific to nonspecific binding ratio (BR); (b) using different sizes and shapes of gold nanoparticles (GNPs) in the systematic optimization of TCA LFA designs; and (c) exploring new laser wavelengths and power regimes for TCA LFA designs. First, we optimized the blocking buffer for the membrane and running buffer by quantitatively measuring the BR using a TCA reader. The TCA reader interprets the thermal signal (i.e., temperature) of GNPs within the membrane when irradiated by a laser at the plasmon resonance wavelength of the particle. This process results in higher detection and quantitation of GNPs than in traditional visual detection (i.e., color intensity). Further, we investigated the effect of laser power (30, 100, 200 mW), GNP size and shape (30 and 100 nm gold spheres, 150 nm gold-silica shells), and laser wavelength (532, 800 nm). Applying these innovations to a new TCA LFA design, we demonstrated that 100 nm spheres with a 100 mW 532 nm laser provided the best performance (i.e., LOD = 8 pg/ml). This LOD is significantly better than that of the current colorimetric LFA and is in the range of the laboratory-based p24 ELISA. In summary, this TCA LFA for p24 protein shows promise for detecting acute HIV infection in POC settings.

Current and emerging trends in point-of-care urinalysis tests

Introduction: The development of point-of-care testing (POCT) has made clinical diagnostics available, affordable, rapid, and easy to use since the 1990s.The significance of this platform rests on its potential to empower patients to monitor their own health status more frequently, in the convenience of their home, so that diseases can be diagnosed at the earliest possible time-point. Recent advances have expanded traditional formats such as qualitative or semi-quantitative dipsticks and lateral flow immunoassays to newer platforms such as microfluidics and paper-based assays where signals can be measured quantitatively using handheld devices.Areas covered: This review discusses: (1) working principles and operating mechanisms of both existing and emerging POCT platforms, (2) urine analytes measured using POCT in comparison to the laboratory or clinical 'gold standard,' and (3) limitations of existing POCT and expectations of emerging POCT in urinalysis.Expert opinion: Currently, a variety of biological samples such as urine, saliva, serum, plasma, and other fluids can be applied to POCT for quick diagnosis, especially in resource-limited settings. Emerging platforms will increasingly empower individuals to monitor their health status through frequent urine analysis even from their homes. The impact of these emerging technologies on healthcare is likely to be transformative.

Developing Gold Nanoparticles-Conjugated Aflatoxin B1 Antifungal Strips

Lateral flow immunochromatographic assays are a powerful diagnostic tool for point-of-care tests, based on their simplicity, specificity, and sensitivity. In this study, a rapid and sensitive gold nanoparticle (AuNP) immunochromatographic strip is produced for detecting aflatoxin B1 (AFB1) in suspicious fungi-contaminated food samples. The 10 nm AuNPs were encompassed by bovine serum albumin (BSA) and AFB1 antibody. Thin-layer chromatography, gel electrophoresis and nuclear magnetic resonance spectroscopy were employed for analysing the chemical complexes. Various concentrations of AFB1 antigen (0-16 ng/mL) were tested with AFB1 antibody-BSA-AuNPs (conjugated AuNPs) and then analysed by scanning electron microscopy, ultraviolet-visible spectroscopy, and Zetasizer. The results showed that the AFB1 antibody was coupled to BSA by the N-hydroxysuccinimide ester method. The AuNPs application has the potential to contribute to AFB1 detection by monitoring a visible colour change from red to purple-blue, with a detection limit of 2 ng/mL in a 96-well plate. The lateral flow immunochromatographic strip tests are rapid, taking less than 10 min., and they have a detection capacity of 10 ng/g. The smartphone analysis of strips provided the results in 3 s, with a detection limit of 0.3 ng/g for AFB1 when the concentration was below 10 ng/g. Excellent agreement was found with AFB1 determination by high-performance liquid chromatography in the determination of AFB1 among 20 samples of peanuts, corn, rice, and bread.

A highly sensitive and specific lateral flow aptasensor for the detection of human osteopontin

The rapid determination of human osteopontin (OPN) protein, a potential cancer biomarker, holds substantial promise for point-of-care diagnostics and biomedical applications. To date, most reported platforms for OPN detection are apparatus-dependent, time-consuming, and expensive. Herein, we established a lateral flow biosensor (LFB) for OPN detection. A biotinylated aptamer was used for OPN pre-capture from samples, an antibody for OPN was immobilized on the test line for a second specific target identification, and streptavidin-modified gold nanoparticles were sprayed on the conjugation pad for color detection. This LFB achieved as low as 0.1 ng mL^-1 OPN sensitivity with a good dynamic detection between 10 and 500 ng mL^-1 within 5 min. Intriguingly, the LFB allowed a qualitative and semi-quantitative detection of OPN in serum at clinically cut-off levels as in cancer patients, and can discriminate OPN from interfering proteins with high specificity. Thus, it is a promising alterative approach for point-of-care OPN screening and detection.