Rapid detection of Bacillus anthracis spores using a super-paramagnetic lateral-flow immunological detectionsystem

Use of Lateral Flow Assays in Forensics

Already for some decades lateral flow assays (LFAs) are 'common use' devices in our daily life. Also, for forensic use LFAs are developed, such as for the analysis of illicit drugs and DNA, but also for the detection of explosives and body fluid identification. Despite their advantages, including ease-of-use, LFAs are not yet frequently applied at a crime scene. This review describes (academic) developments of LFAs for forensic applications, focusing on biological and chemical applications, whereby the main advantages and disadvantages of LFAs for the different forensic applications are summarized. Additionally, a critical review is provided, discussing why LFAs are not frequently applied within the forensic field and highlighting the steps that are needed to bring LFAs to the forensic market.

Sensitive lateral flow immunoassay strips based on Fe3+-chelated polydopamine nanospheres for the detection of kanamycin

As kanamycin (KAN) residue in animal products is harmful to consumers, a rapid and sensitive method for KAN detection needs to be established. KAN monoclonal antibody (KAN-mAb, 1D11) with the half maximal inhibitory concentration of 1.16 ng/mL was prepared in this study. A one-pot method was used to synthesize Fe³⁺-chelated polydopamine nanospheres (Fe@PDANs) with excellent characteristics of strong light absorption. The novel label of Fe@PDANs and KAN-mAb was used to develop a lateral flow immunoassay (LFIA) for the sensitive detection of KAN. The limit of detection of the Fe@PDANs-based LFIA (Fe@PDANs-LFIA) for KAN was 0.0191 ng/mL, which was 2.75 times lower than PDANs-based LFIA. Furthermore, the Fe@PDANs-LFIA was successfully applied to detect KAN in pork, milk, and honey samples, with recoveries ranging from 93.75% to 113.80% (coefficient of variation < 10%). Therefore, Fe@PDANs have potential for the detection of analytes in LFIA.

Development and application of DETECTR-based rapid detection for pathogenic Bacillusanthracis

Bacillus anthracis (B. anthracis) is a gram-positive bacterium responsible for the acute disease anthrax. Rapid and reliable identification of pathogenic B. anthracis is important in the detection of natural infectious disease cases or bio-threats. Herein, a DNA endonuclease targeted CRISPR trans reporter (DETECTR) detection platform based on recombinase polymerase amplification (RPA) was studied. The DETECTR system targeted three sequences from B. anthracis (the BA_5345 chromosomal specific marker, the protective antigen gene pag A from pXO1 plasmid and the capsule-biosynthesis-related gene cap A from pXO2 plasmid). We developed a rapid (<40 min), easy-to-implement and accurate identification method for of B. anthracis nucleic acid with near two-copies sensitivity. The combination of tripartite primer sets is effective for the reliable identification of B. anthracis but also for fast screening of pathogenic strains. More importantly, DETECTR correctly detected simulated clinical blood samples and firstly detected positive samples collected from the location of world War-II site, preserved at north-east China (45°36'55.940″ N, 126°38'33.738″ E) with high sensitivity and specificity. Our study provides insight into the DETECTR-based detection of B. anthracis. We present a novel screening and diagnostic option for pathogenic B. anthracis that can be performed on a user-friendly portable device. Based on its proven reliability, sensitivity, specificity and simplicity, our proposed method can be readily adapted to detect pathogenic B. anthracis, anthrax and biothreats.

Plastic-based lateral flow immunoassay device for electrochemical detection of NT-proBNP

Here we report an easily fabricated, plastic-based lateral flow device for carrying out metalloimmunoassays. The device is called ocFlow to emphasize the open-channel design. We have shown that the ocFlow is capable of magnetic microbead (MμB)-based metalloimmunoassays for the detection of two types of immunoconjugates: a model composite (MC) and a sandwich immunoassay for the heart failure marker NT-proBNP. In both assays, Ag nanoparticles (AgNPs) were used as electrochemically detectable labels. NT-proBNP and MC concentrations as low as 750.0 pM and 10.0 pM, respectively, could be detected using the ocFlow device. Four key conclusions can be drawn from the results presented herein. First, immunoconjugates attached to the MμBs can be transported in the flow channel using combined hydrodynamic and capillary pressure passive pumping. Second, the ocFlow device is capable of on-chip storage, resolvation, and conjugate formation of both the MC and NT-proBNP composites. Third, electrochemical detection can be conducted on analytes suspended in serum by rinsing the electrodes with a wash buffer. Finally, and perhaps most significantly, the assay is quantitative and has a detection limit for NT-proBNP in the high picomolar range when the necessary reagents are stored on the device in a dry form.

Lateral flow immunoassay based on dual spectral-overlapped fluorescence quenching of polydopamine nanospheres for sensitive detection of sulfamethazine

Herein, we propose a lateral flow immunoassay (LFIA) based on the dual spectral-overlapped fluorescence quenching of polydopamine nanospheres (PDANs) caused by the inner filter effect to sensitively detect sulfamethazine (SMZ). The fluorescence quenching LFIA device consists of four parts: absorbent pad, polyvinyl chloride pad, sample pad, and nitrocellulose membrane. Compared with traditional quenchers such as gold nanoparticles (AuNPs) with single spectral-overlapped quenching ability, PDANs can quench the excitation light and emission light of three fluorescence donors (aggregation-induced emission fluorescent microsphere, AIEFM; fluorescent microsphere, FM; and quantum dot bead, QB). The fluorescence intensity changes (ΔF) are numerically larger for PDANs-LFIA (ΔF_AIEFM = 2315, ΔF_FM = 979, ΔF_QB = 910) than those for AuNPs-LFIA (ΔF_AIEFM = 1722, ΔF_FM = 833, ΔF_QB =;520). AIEFM-based PDANs-LFIA exhibits a large ΔF (2315) in response to the changes in the SMZ concentration, and produces a high signal-to-noise ratio. The limit of detection (LOD) and visual LOD of LFIA based on PDANs quenching AIEFM for the detection of SMZ in chicken are 0.043 and 0.5 ng/mL, respectively. The results confirm that the proposed method can be used for the detection of hazardous materials in practical applications.

Biosensors for the Detection of Bacillus anthracis

Bacillus anthracis, present in two forms of vegetative cells and spores, is a pathogen that infects humans through contact with infected animals or contaminated animal products and is also maliciously used in terrorist acts. Therefore, a rapid and sensitive test for B. anthracis is necessary but challenging. The challenge comes from the following aspects: an accurate distinction of B. anthracis from other Bacillus species due to their high genomic similarity and the horizontal gene transfer between Bacillus members; direct detection of the B. anthracis spores without damaging them for component extraction to avoid the risk of spore atomization; and the rapid detections of B. anthracis in complex samples, such as soil and suspicious powders, without sample pretreatments and expensive large-scale equipment. Although culturing B. anthracis from samples is the conventional method for the detection of B. anthracis, it is time-consuming and the detection results would not be easy to interpret because many Bacillus species share similar phenotypic features such as a lack of motility and hemolysis, resistance to gamma phages, and so on. Intensive and extensive effort has been expended to develop reliable detection technologies, among which biosensors exhibit comprehensive advantages in terms of sensitivity, specificity, and portability. Here, we briefly review the research progress, providing highlights of the latest achievements and our own practice and experience. The contents can be summarized in three aspects: the discovery of detection targets, including genes, toxins, and other components; the creation of molecular recognition elements, such as monoclonal antibodies, single-chain antibody fragments, specific peptides, and aptamers; and the design and construction of biosensing systems by the integration of appropriate molecular recognition elements and transducer devices. These sensor devices have their own characteristics and different principles. For example, the surface plasmon resonance biosensor and quartz crystal microbalance biosensor are very sensitive, while the multiplex PCR-on-a-chip can detect multitargets. Biosensors for direct spore detection are highly recommended because they are not only fast but also avoid contamination from aerosol-containing spores. The introduction of nanotechnology has significantly improved the performance of biosensors. Superparamagnetic nanoparticles and phage-displayed gold nanoparticle ligand peptides have made the results of spore detection visible to the naked eye. Because of space constraints, many advanced biosensors for B. anthracis are not described in detail but are cited as references. Although biosensors provide a variety of options for various application scenarios, the challenges have not been fully addressed, which leaves room for the development of more advanced and practical B. anthracis detection means.

Highly sensitive protein detection using recombinant spores and lateral flow immunoassay

Lateral flow immunoassays (LFIs) can be used to detect intact bacteria or spores; when gold nanoparticles (AuNPs) are used as the signal reporters, the detection limits are very low. Spore-based surface display has been widely studied for enzyme immobilization and live-nontoxic oral vaccines. In this study, recombinant spores were used to improve the sensitivity of a LFI. We developed a test kit that combines streptavidin-displayed spores with a LFI assay for rapid protein detection. The recombinant spores served as a signal amplifier and AuNPs were used as the signal reporters. For detection of β-galactosidase, which was used as the model protein, the detection limit was about 10^-15 mol, while that of the conventional LFI is about 10^-12 mol. In both methods, nanogold was used as the colorimetric signal and could be observed with the naked eye. This method improved LFI sensitivity without sacrificing its advantages. Furthermore, enhanced green fluorescent protein (eGFP) was also displayed on the surface of the streptavidin-displayed spores. Without AuNPs, the fluorescent recombinant spores acted as the signal, which could be detected by a fluorescence detector, such as a fluorescence microscope. The detection limit was 10^-16 mol under fluorescence microscopy whose magnification was 25-fold. Therefore, in conclusion, in this proof of concept study, the detection limits of both proposed methods were far superior to those of traditional LFI assay.

Development of a visible loop mediated isothermal amplification assay for rapid detection of Bacillus anthracis

Distressing effects on animal and human health with lethal progression, being used as bioweapon and shared features with non-pathogenic bacteria demands sensitive, specific, safe, cost effective and rapid detection methods for anthrax causing organisms. Conventional microbiology based diagnostics for anthrax are time consuming and need sophisticated equipment, while molecular diagnostics require less time and labor. The Loop mediated isothermal amplification assay (LAMP) is rapid, sensitive and specific assay and requires no specialized equipment. In the present study, we developed a LAMP assay for rapid as well as specific detection of Bacillus anthracis. The optimized assay produced positive results with the Sterne strain and one field isolate of B. anthracis and, negative results with other bacteria of the same and different genera within 2 h. Sensitivity was 500 fg of total DNA of B. anthracis, which was 100 times more sensitive than conventional PCR. The present study also demonstrated that the simple method of total DNA extraction by repeated boiling and freezing will not adversely affect the LAMP results. In conclusion, the optimized LAMP assay is a promising tool for the specific, sensitive, less time-consuming diagnosis for anthrax causing bacteria and also, for detecting the virulence of suspected B. anthracis cultures.

A simple and rapid immunochromatography test based on readily available filter paper modified with chitosan to screen for 13 sulfonamides in milk

In this study, we developed a novel, simple, rapid, and low-cost colloidal gold-based immunochromatography method, with filter paper replacing nitrocellulose membrane as the substrate. To obtain adequately immobilized protein, chitosan was used to functionalize the filter paper. After conditions and parameters were optimized, the novel immunochromatography method was applied for detection of sulfonamide residues in milk. Quantitative detection was accomplished using a smartphone and Photoshop software (Adobe Inc., San Jose, CA), allowing us to screen 13 sulfonamides with a limit of detection ranging from 0.42 to 8.64 μg/L and recovery ranging from 88.2 to 116.9% in milk. The proposed novel method performed similarly to the conventional method that uses a nitrocellulose membrane as the transport medium, and it had lower cost and better usability because of the inexpensive and easily available filter paper.

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.

Molecular Imprinted Based Quartz Crystal Microbalance Sensors for Bacteria and Spores

A molecular imprinting strategy was combined with mass-sensitive transducers to generate robust and reliable biomimetic sensor systems for the detection of bioparticles. The patterning of polymers with bioanalytes enabled us to detect Escherichia coli (E. coli) bacteria with quartz crystal microbalance (QCM). The QCM sensor results were compared with direct Atomic Force Microscopy (AFM) measurements—bacteria cells adhering to the sensor coatings were counted. The recognition sites generated by Bacillus subtilis (B. subtilis) spores could successfully and reversibly recognize the template analyte and ensured rapid sensing. Cross sensitive measurements clearly showed the advantage of the molecular imprinting strategy, by which spores of Bacillus species (subtilis and thuringiensis) could easily be differentiated and selectively detected. The growth of B. subtilis from its spores was observed at 42 °C in appropriate nutrient solution of glucose and ammonium sulfate over a period of 15 h. Moreover, the growth of B. subtilis bacteria from its respective spores was studied by increasing the glucose concentration until saturation effect of the sensor. The polymeric sensor coatings were patterned to fix the B. subtilis in order to investigate osmotic effects according to a frequency response of 400 Hz by altering the ionic strength of 0.1 M.

High throughput detection of antibiotic residues in milk by time-resolved fluorescence immunochromatography based on QR code

Herein, we have successfully established a novel, rapid, and simple lateral-flow immunoassay based on time-resolved fluorescence and biotin-streptavidin to detect the residues of various antibiotics in milk. The fluorescence signal and sensitivity of immunochromatography were enhanced through biotinylated antibody coupled with streptavidin europium microspheres. Moreover, due to the use of a QR Code and fluorescent reader, quantitative detection and real-time data uploading can be achieved. Under the optimal conditions, the various antibiotic residues were detected in the milk samples. The results showed that the limits of detection of tylosin, lincomycin and doxycycline were 0.10, 0.06, and 0.27 ng/mL, respectively. The recoveries of the spiked milk samples were 88.9%~127%, with coefficients of variation less than 11%, and the test strip can be stored at room temperature for 12 months. This study shows that the proposed time-resolved fluorescence immunoassay is sensitive, rapid and reliable, and has the potential to be used for detection of veterinary antibiotic residues in food safety fields.

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.

Hybrid paper and 3D-printed microfluidic device for electrochemical detection of Ag nanoparticle labels

In the present article we report a new hybrid microfluidic device (hyFlow) comprising a disposable paper electrode and a three-dimensional (3D) printed plastic chip for the electrochemical detection of a magnetic bead-silver nanoparticle (MB-AgNP) bioconjugate. This hybrid device evolved due to the difficulty of incorporating micron-scale MBs into paper-only fluidic devices. Specifically, paper fluidic devices can entrap MB-containing conjugates within their cellulose or nitrocellulose fiber matrix. The hyFlow system was designed to minimize such issues and transport MB conjugates more efficiently to the electrochemical detection zone of the device. The hyFlow system retains the benefit of fluid transport by pressure-driven flow, however, no pump is required for its operation. The hyFlow device is capable of detecting either pre-formed MB-AgNP conjugates or conjugates formed in situ. The detection limit of AgNPs using this device is 12 pM, which represents just 22 AgNPs per MB.

A fluorescence immunoassay based on CdTe : Zn/ZnS quantum dots for the rapid detection of bacteria, taking Delftia tsuruhatensis CM’13 as an example

A fluorescence immunoassay has been widely applied in different fields due to its high sensitivity, simple operations, and high accuracy.

Lateral flow biosensors based on the use of micro- and nanomaterials: a review on recent developments

This review (with 187 refs.) summarizes the progress that has been made in the design of lateral flow biosensors (LFBs) based on the use of micro- and nano-materials. Following a short introduction into the field, a first section covers features related to the design of LFBs, with subsections on strip-based, cotton thread-based and vertical flow- and syringe-based LFBs. The next chapter summarizes methods for sample pretreatment, from simple method to membrane-based methods, pretreatment by magnetic methods to device-integrated sample preparation. Advances in flow control are treated next, with subsections on cross-flow strategies, delayed and controlled release and various other strategies. Detection conditionst and mathematical modelling are briefly introduced in the following chapter. A further chapter covers methods for reliability improvement, for example by adding other validation lines or adopting different detection methods. Signal readouts are summarized next, with subsections on color-based, luminescent, smartphone-based and SERS-based methods. A concluding section summarizes the current status and addresses challenges in future perspectives. Graphical abstractRecent development and breakthrough points of lateral flow biosensors.

Development of a highly sensitive magneto-enzyme lateral flow immunoassay for dengue NS1 detection

Background

Dengue infection represents a global health issue of growing importance. Dengue non-structural protein 1 (NS1) plays a central role in the early detection of the disease. The most common method for NS1 detection is testing by lateral flow immunoassays (LFIAs) with varying sensitivity. In this study, we present a highly sensitive magneto-enzyme LFIA for prompt diagnosis of dengue.

Methods

We have demonstrated the development of a magneto-enzyme LFIA combining super-paramagnetic nanoparticles as labels and Biotin–Streptavidin signal amplification strategy to detect dengue NS1. Factors affecting the test performance including antibody pair, super-paramagnetic nanoparticle size, nitrocellulose membrane type, amounts of detection and capture antibodies, and amounts of Streptavidin-polyHRP were optimized. Analytical sensitivity and cross-reactivity were determined. Clinical performance of the novel assay was evaluated using a panel of 120 clinical sera.

Results

This newly developed assay could detect NS1 of all four serotypes of dengue virus (DENV). The limit of detection (LOD) was found to be as low as 0.25 ng ml⁻¹ for DENV-1 and DENV-3, 0.1 ng ml⁻¹ for DENV-2, and 1.0 ng ml⁻¹ for DENV-4. The LOD for DENV-2 was a 50-fold improvement over the best values previously reported. There was an absence of cross-reactivity with Zika NS1, Hepatitis B virus, Hepatitis C virus, and Japanese encephalitis virus. The sensitivity and specificity of the novel assay were 100% when tested on clinical samples.

Conclusions

We have successfully developed a magneto-enzyme LFIA, allowing rapid and highly sensitive detection of dengue NS1, which is essential for proper management of patients infected with DENV.

Calorimetric lateral flow immunoassay detection platform based on the photothermal effect of gold nanocages with high sensitivity, specificity, and accuracy

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.

Direct vs Mediated Coupling of Antibodies to Gold Nanoparticles: The Case of Salivary Cortisol Detection by Lateral Flow Immunoassay

Stable and efficient conjugates between antibodies and gold nanoparticles (GNP-Ab) are sought to develop highly sensitive and robust biosensors with applications in medicine, toxicology, food safety controls, and targeted drug delivery. Several strategies have been proposed for directing the antibody attachment to GNPs thus preserving antibody activity, including covalently coupling the antibody to a polymer grafted on GNP surface and exploiting the high affinity of bioreceptors as mediators for the binding. Both approaches also allow for shielding GNPs with a protective layer that guarantees the robustness of the conjugate. Notwithstanding, antibodies freely adsorb to GNP with high binding efficiency. The nonspecific adsorption is far more simple, fast, and inexpensive than any mediated coupling. Therefore, it is preferred for most applications, although it is considered to produce GNP-Ab with a limited activity. In this work, we compared three strategies for producing GNP-Ab, such as (i) covalent coupling mediated by a chemical layer, (ii) affinity-based binding mediated by a biomolecular layer composed of Staphylococcal protein A, and (iii) direct attachment via adsorption. The so-prepared GNP-Ab were employed as probes in a colorimetric lateral flow immunoassay (LFIA) for measuring salivary cortisol as a model biosensor that relies on the use of active GNP-Ab conjugates. Unexpectedly, the biosensors fabricated using the three probes were completely comparable in terms of their ability to measure salivary cortisol. Furthermore, we observed that the sensitivity of the LFIA primarily depended on the amount of the antibody bound to GNPs rather than on the method by which it was bound. The probes prepared using both the direct adsorption approach and mediated coupling via the biochemical mediator enabled development of point-of-care devices for the fast, sensitive, and reliable measurement of human salivary cortisol.

Magnetic immunochromatographic test for histamine detection in wine

Histamine, a biogenic amine, is abundant in fermented foods and beverages, notably wine. A high intake of this monoamine may produce adverse reactions in humans, which may be severe in individuals with a reduced capacity to catabolise extrinsic histamine. Thus, control of histamine concentration during wine production and before distribution is advisable. Simple, rapid, point-of-use bioanalytical platforms are needed because traditional methods for the detection and quantification of histamine are expensive and time-consuming. This work applies the lateral flow immunoassay technique to histamine detection. Superparamagnetic particle labels, and an inductive sensor designed to read the test line in the immunoassay, enable magnetic quantification of the molecule. The system is calibrated with histamine standards in the interval of interest for wine production. A commercial optical strip reader is used for comparison measurements. The lateral flow system has a limit of detection of 1.2 and 1.5 mg/L for the inductive and optical readers, respectively. The capability of the inductive system for histamine quantification is demonstrated for wine samples at different processing points (at the end of alcoholic fermentation, at the end of malolactic fermentation, in freshly bottled wine, and in reserve wine). The results are validated by ultra-high-performance liquid chromatography. Graphical abstract.

Simple and rapid extracellular vesicles quantification via membrane biotinylation strategy coupled with fluorescent nanospheres-based lateral flow assay

Extracellular vesicles (EVs) are cell-excreted membrane particles existing in a variety of biological fluids. As potential noninvasive biomarkers, EVs have received wide attention in recent years. However, usual EVs assays are complex, time-consuming and costly, thus limiting their clinical utility. Simple and rapid EVs quantification within biological fluids remains challenging. Here, we developed a simple, rapid strategy for EVs quantification, which combined with lateral flow assay and membrane biotinylation strategy. By utilizing biotin-functionalized phosphatidylethanolamine (DSPE-PEG-Biotin), the membrane of EVs could be successfully modified with biotin under strong hydrophobic interactions. Subsequently, based on the high affinity between streptavidin and biotin, quantification assay was achieved by lateral flow assay with fluorescent nanospheres (FNs) as a reporter. Biotinylation of biogenic EVs could be reached to 85%. This proposed method enables sensitive detection of 2.0 × 10³ particles/μL. The whole procedure time was within 1 h. Furthermore, this approach was used to detect EVs in biological samples, demonstrating potential clinical applications.

Inorganic Complexes and Metal-Based Nanomaterials for Infectious Disease Diagnostics

Infectious diseases claim millions of lives each year. Robust and accurate diagnostics are essential tools for identifying those who are at risk and in need of treatment in low-resource settings. Inorganic complexes and metal-based nanomaterials continue to drive the development of diagnostic platforms and strategies that enable infectious disease detection in low-resource settings. In this review, we highlight works from the past 20 years in which inorganic chemistry and nanotechnology were implemented in each of the core components that make up a diagnostic test. First, we present how inorganic biomarkers and their properties are leveraged for infectious disease detection. In the following section, we detail metal-based technologies that have been employed for sample preparation and biomarker isolation from sample matrices. We then describe how inorganic- and nanomaterial-based probes have been utilized in point-of-care diagnostics for signal generation. The following section discusses instrumentation for signal readout in resource-limited settings. Next, we highlight the detection of nucleic acids at the point of care as an emerging application of inorganic chemistry. Lastly, we consider the challenges that remain for translation of the aforementioned diagnostic platforms to low-resource settings.

Invited review: Advancements in lateral flow immunoassays for screening hazardous substances in milk and milk powder

Dairy-related food safety outbreaks, such as food-borne pathogen contamination, mycotoxin contamination, and veterinary drug contamination, sometimes happen and have been reported all over the world, affecting human health and, in some cases, leading to death. Thus, rapid yet robust detection methods are needed to monitor milk and milk powder for the presence of hazardous substances. The lateral flow immunoassay (LFI) is widely used in onsite testing because of its rapidity, simplicity, and convenience. In this review, we describe some traditional LFI used to detect hazardous substances in milk and milk powder. Furthermore, we discuss recent advances in LFI that aim to improve sensitivity or detection efficiency. These advances include the use of novel label materials, development of signal amplification systems, design of multiplex detection systems, and the use of nucleic acid-based LFI.

Machine Learning Approach to Enhance the Performance of MNP-Labeled Lateral Flow Immunoassay

The use of magnetic nanoparticle (MNP)-labeled immunochromatography test strips (ICTSs) is very important for point-of-care testing (POCT). However, common diagnostic methods cannot accurately analyze the weak magnetic signal from ICTSs, limiting the applications of POCT. In this study, an ultrasensitive multiplex biosensor was designed to overcome the limitations of capturing and normalization of the weak magnetic signal from MNPs on ICTSs. A machine learning model for sandwich assays was constructed and used to classify weakly positive and negative samples, which significantly enhanced the specificity and sensitivity. The potential clinical application was evaluated by detecting 50 human chorionic gonadotropin (HCG) samples and 59 myocardial infarction serum samples. The quantitative range for HCG was 1-1000 mIU mL^-1 and the ideal detection limit was 0.014 mIU mL^-1, which was well below the clinical threshold. Quantitative detection results of multiplex cardiac markers showed good linear correlations with standard values. The proposed multiplex assay can be readily adapted for identifying other biomolecules and also be used in other applications such as environmental monitoring, food analysis, and national security.

Staining Traditional Colloidal Gold Test Strips with Pt Nanoshell Enables Quantitative Point-of-Care Testing with Simple and Portable Pressure Meter Readout

Traditional immunochromatographic test strips based on colloidal gold are effective devices for portable and low-cost point-of-care (POC) testing. Nevertheless, they still suffer from the limitation of qualitative or semiquantitative tests via naked-eye detection. Replacement of gold with other signal entities, such as magnetic particles or fluorescent particles, requires professional instrumentation to obtain quantitative results. A pressure-based assay with platinum nanoparticles (PtNPs) can provide quantitative results using a portable pressure meter but is also hampered by the long-term instability of PtNPs. Consequently, we developed a Pt-staining method based on test strips to create platinum nanoshells on the surface of colloidal gold. This method not only preserves the original advantages of colloidal gold with easy synthesis and decoration but also introduces PtNPs with excellent catalytic activity as signal labels to achieve sensitive quantitative detection. Myoglobin was tested as a model target, and the limit of detection was 5.47 ng/mL in 20% diluted serum samples, which satisfies the requirements for clinical monitoring of acute myocardial infarction. In addition, the two most common colloidal gold strips available in the marketplace were applied to demonstrate the compatibility of Pt-staining. Taking advantage of low cost, user-friendliness, compatibility, simplicity, and stability, colloidal gold test strips with Pt-staining are expected to satisfy the need for quantitative POC testing of biomarkers, especially in resource-limited regions.

A two-dimensional mathematical model for analyzing the effects of capture probe properties on the performance of lateral flow assays

Lateral flow assays (LFAs) are promising candidates in biomedical diagnosis fields due to their rapid, low-cost, and portable features.

Colorimetric-Fluorescent-Magnetic Nanosphere-Based Multimodal Assay Platform for Salmonella Detection

Rapid and sensitive foodborne pathogen detection assay, which can be applied in multiple fields, is essential to timely diagnosis. Herein, we proposed a multisignal readout lateral flow immunoassay for Salmonella typhimurium ( S. typhi) detection. The assay employs colorimetric-fluorescent-magnetic nanospheres (CFMNs) as labels, which possess multifunctional target separation and enrichment, multisignal readout, and two formats of quantitation. The assay for S. typhi detection involves magnetic separation and chromatography. First, the S. typhi were separated and enriched from matrix by antibody labeled CFMNs, and then the S. typhi-containing suspension is added onto the sample pad to flow up the test strip. The introduction of magnetic separation enhances anti-interference ability and 10-fold sensitivity, making the assay possible for practical application. The assay has realized naked eye detection of 1.88 × 10⁴ CFU/mL S. typhi, and 3.75 × 10³ CFU/mL S. typhi can be detected with a magnetic assay reader, which is 2-4 orders of magnitude lower than other label-based LFIAs, with a quantitation range of 1.88 × 10⁴ to 1.88 × 10⁷ CFU/mL by measuring the fluorescence intensity and magnetic signal. Moreover, the successful detection of S. typhi in complex matrix (tap water, milk, fetal bovine serum, and whole blood) indicated its potential application in real samples.

Detecting Biothreat Agents: From Current Diagnostics to Developing Sensor Technologies

Although a fundamental understanding of the pathogenicity of most biothreat agents has been elucidated and available treatments have increased substantially over the past decades, they still represent a significant public health threat in this age of (bio)terrorism, indiscriminate warfare, pollution, climate change, unchecked population growth, and globalization. The key step to almost all prevention, protection, prophylaxis, post-exposure treatment, and mitigation of any bioagent is early detection. Here, we review available methods for detecting bioagents including pathogenic bacteria and viruses along with their toxins. An introduction placing this subject in the historical context of previous naturally occurring outbreaks and efforts to weaponize selected agents is first provided along with definitions and relevant considerations. An overview of the detection technologies that find use in this endeavor along with how they provide data or transduce signal within a sensing configuration follows. Current "gold" standards for biothreat detection/diagnostics along with a listing of relevant FDA approved in vitro diagnostic devices is then discussed to provide an overview of the current state of the art. Given the 2014 outbreak of Ebola virus in Western Africa and the recent 2016 spread of Zika virus in the Americas, discussion of what constitutes a public health emergency and how new in vitro diagnostic devices are authorized for emergency use in the U.S. are also included. The majority of the Review is then subdivided around the sensing of bacterial, viral, and toxin biothreats with each including an overview of the major agents in that class, a detailed cross-section of different sensing methods in development based on assay format or analytical technique, and some discussion of related microfluidic lab-on-a-chip/point-of-care devices. Finally, an outlook is given on how this field will develop from the perspective of the biosensing technology itself and the new emerging threats they may face.

Lateral flow assay with pressure meter readout for rapid point-of-care detection of disease-associated protein

Paper-based assays such as lateral flow assays are good candidates for portable diagnostics owing to their user-friendly format and low cost. In terms of analytical detection, lateral flow assays usually require dedicated instruments to obtain quantitative results. Here we demonstrate a lateral flow assay with handheld pressure meter readout for the rapid detection of disease-related protein with high sensitivity and selectivity. Based on the pressure change produced by the catalytic reaction of Pt nanoparticles related to the concentration of the target, a quantitative reaction platform was established. During the lateral flow assay, the Pt nanoparticles are aggregated in the test line to form a gray band by biomolecular recognition and finally convert the recognition signal into highly sensitive pressure readout for quantitative analysis. Without sophisticated instrumentation and complicated operations, the whole detection process can be completed within 20 minutes. The limit of detection for myoglobin (2.9 ng mL^-1 in diluted serum samples) meets the requirements of clinical monitoring. With the advantages of low cost, ease of operation, high sensitivity and selectivity, the method represents a versatile platform for point-of-care testing of disease biomarkers.

Enhancement of lateral flow assay performance by electromagnetic relocation of reporter particles

Lateral flow assays (LFAs) are a widely-used point-of care diagnostic format, but suffer from limited analytical sensitivity, especially when read by eye. It has recently been reported that LFA performance can be improved by using magnetic reporter particles and an external magnetic field applied at the test line. The mechanism of sensitivity/performance enhancement was suggested to be concentration/retardation of reporter particles at the test line. Here we demonstrate an additional mechanism of particle relocation where reporter particles from the lower depths of the translucent LFA strip relocate to more-visible locations nearer to the top surface, producing a more visible signal. With a magnetic field we observed an improvement in sensitivity of human chorionic gonadotropin (hCG) detection from 1.25 ng/mL to 0.31 ng/mL. We also observed an increase of the color intensity per particle in test lines when the magnetic field was present.

Recent advances in nanoparticle-based lateral flow immunoassay as a point-of-care diagnostic tool for infectious agents and diseases

Recent advances in lateral flow immunoassay-based devices as a point-of-care analytical tool for the detection of infectious diseases are reviewed.

Development of a rapid lateral flow immunoassay test for detection of exosomes previously enriched from cell culture medium and body fluids

Exosomes are cell-secreted nanovesicles (40–200 nm) that represent a rich source of novel biomarkers in the diagnosis and prognosis of certain diseases. Despite the increasingly recognized relevance of these vesicles as biomarkers, their detection has been limited due in part to current technical challenges in the rapid isolation and analysis of exosomes. The complexity of the development of analytical platforms relies on the heterogeneous composition of the exosome membrane. One of the most attractive tests is the inmunochromatographic strips, which allow rapid detection by unskilled operators. We have successfully developed a novel lateral flow immunoassay (LFIA) for the detection of exosomes based on the use of tetraspanins as targets. We have applied this platform for the detection of exosomes purified from different sources: cell culture supernatants, human plasma and urine. As proof of concept, we explored the analytical potential of this LFIA platform to accurately quantify exosomes purified from a human metastatic melanoma cell line. The one-step assay can be completed in 15 min, with a limit of detection of 8.54×10⁵ exosomes/µL when a blend of anti-CD9 and anti-CD81 were selected as capture antibodies and anti-CD63 labelled with gold nanoparticles as detection antibody. Based on our results, this platform could be well suited to be used as a rapid exosome quantification tool, with promising diagnostic applications, bearing in mind that the detection of exosomes from different sources may require adaptation of the analytical settings to their specific composition.

Rapid and sensitive detection of HIV-1 p24 antigen by immunomagnetic separation coupled with catalytic fluorescent immunoassay

In this study, a system of magnetic beads (MBs) coupled with catalytic fluorescent immunoassay for rapid and sensitive determination of HIV-1 capsid antigen p24 was developed. p24 was captured by antibody immobilized MBs, and the detection antibody was linked to horseradish peroxidase (HRP) through biotin-streptavidin recognition, catalyzing the oxidation of o-phenylenediamine (OPD) and hydrogen peroxide to produce a fluorescent product. This is the first reported utilization of the fluorescence of OPD oxidation product catalyzed by HRP for immunoassay. Optimization of conditions afforded a low detection limit of 0.5 pg/mL (3σ) for p24 with a linear range of 1.4-90.0 pg/mL. The assay exhibited good reproducibility with a relative standard deviation (RSD) of 4.4 %, 4.7 %, and 5.0 % for detecting 1.4 pg/mL, 22.5 pg/mL, and 45.0 pg/mL p24, respectively. The assay can be completed in less than 90 min. Moreover, the proposed method was successfully applied to detect p24 in spiked serum. This method overcomes the interference of MBs to the fluorescence signal and demonstrated higher sensitivity for detection of p24 than conventional ELISA kits. The system could be applied for detecting other antigens with high sensitivity, rapidity, specificity, and simple operation. Graphical Abstract A rapid and sensitive biosensing method coupling immunomagnetic separation and catalytic fluorescence for determination of HIV-1 p24 has been developed.

Surface-enhanced Raman scattering based lateral flow immunochromatographic assay for sensitive influenza detection

A novel sensitive SERS-lateral flow immunochromatographic integration system using Raman active molecule-coated gold nanostar as reporters for influenza virus detection is reported. Qualitative and quantitative SERS signal detection can be achieved.

Silver and gold enhancement methods for lateral flow immunoassays

Sensitivity is the main concern at the development of rapid test by lateral flow immunoassays. On the other hand, low limits of detection are often required at medical diagnostics and other field of analysis. To overcome this drawback, several enhancement protocols have been described. In this paper, we have selected different silver enhancement methods and one dual gold conjugation, and we critically compared the amplification produced when applied to a gold-nanoparticle based lateral flow immunoassay for the detection of prostate specific antigen (PSA). The highest amplification was obtained by using an immersion method based on a solution of silver nitrate and hydroquinone/citrate buffer in proportion 1:1. Under these conditions, the system is capable of detecting PSA within 20 min at levels as low as 0.1 ng/mL, with a 3-fold sensitivity improvement.

Rapid detection and quantification of the marine toxic algae, Alexandrium minutum, using a super-paramagnetic immunochromatographic strip test

The dinoflagellates of Alexandrium genus are known to be producers of paralytic shellfish toxins that regularly impact the shellfish aquaculture industry and fisheries. Accurate detection of Alexandrium including Alexandrium minutum is crucial for environmental monitoring and sanitary issues. In this study, we firstly developed a quantitative lateral flow immunoassay (LFIA) using super-paramagnetic nanobeads for A. minutum whole cells. This dipstick assay relies on two distinct monoclonal antibodies used in a sandwich format and directed against surface antigens of this organism. No sample preparation is required. Either frozen or live cells can be detected and quantified. The specificity and sensitivity are assessed by using phytoplankton culture and field samples spiked with a known amount of cultured A. minutum cells. This LFIA is shown to be highly specific for A. minutum and able to detect reproducibly 10(5)cells/L within 30min. The test is applied to environmental samples already characterized by light microscopy counting. No significant difference is observed between the cell densities obtained by these two methods. This handy super-paramagnetic lateral flow immnunoassay biosensor can greatly assist water quality monitoring programs as well as ecological research.

Rapid and quantitative detection of C-reactive protein based on quantum dots and immunofiltration assay

Convenient and rapid immunofiltration assays (IFAs) enable on-site "yes" or "no" determination of disease markers. However, traditional IFAs are commonly qualitative or semi-quantitative and are very limited for the efficient testing of samples in field diagnostics. Here, we overcome these limitations by developing a quantum dots (QDs)-based fluorescent IFA for the quantitative detection of C-reactive proteins (CRP). CRP, the well-known diagnostic marker for acute viral and bacterial infections, was used as a model analyte to demonstrate performance and sensitivity of our developed QDs-based IFA. QDs capped with both polyethylene glycol (PEG) and glutathione were used as fluorescent labels for our IFAs. The presence of the surface PEG layer, which reduced the non-specific protein interactions, in conjunction with the inherent optical properties of QDs, resulted in lower background signal, increased sensitivity, and ability to detect CRP down to 0.79 mg/L with only 5 µL serum sample. In addition, the developed assay is simple, fast and can quantitatively detect CRP with a detection limit up to 200 mg/L. Clinical test results of our QD-based IFA are well correlated with the traditional latex enhance immune-agglutination aggregation. The proposed QD-based fluorescent IFA is very promising, and potentially will be adopted for multiplexed immunoassay and in field point-of-care test.