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A quantum dot-based lateral flow immunoassay system (QD-LFIAS) was developed to simultaneously detect both influenza A virus subtypes H5 and H9. Water-soluble carboxyl-functionalized quantum dots (QDs) were used as fluorescent tags. The QDs were conjugated to specific influenza A virus subtype H5 and H9 antibodies via an amide bond. When influenza A virus subtype H5 or H9 was added to the QD-LFIAS, the QD-labeled antibodies specifically bound to the H5 or H9 subtype viruses and were then captured by the coating antibodies at test line 1 or 2 to form a sandwich complex. This complex produced a bright fluorescent band in response to 365 nm ultraviolet excitation. The intensity of fluorescence can be detected using an inexpensive, low-maintenance instrument, and the virus concentration directly correlates with the fluorescence intensity. The detection limit of the QD-LFIAS for influenza A virus subtype H5 was 0.016 HAU, and the detection limit of the QD-LFIAS for influenza A virus subtype H9 was 0.25 HAU. The specificity and reproducibility were good. The simple analysis step and objective results that can be obtained within 15 min indicate that this QD-LFIAS is a highly efficient test that can be used to monitor and prevent both Influenza A virus subtypes H5 and H9., (Copyright © 2015 Elsevier B.V. All rights reserved.)

A novel strip test system combining immunomagnetic separation with lateral flow immunoassay (LFIA) was established for the accurate detection of Listeria monocytogenes. In this system, a pair of matched monoclonal antibodies was used to construct a sandwich immunoassay, in which superparamagnetic particles were coupled with one of the antibodies as a labeled antibody to capture the target bacteria, while the other antibody was immobilized on the detection zone. After a 20-min reaction, the strips were analyzed by a novel instrument which could detect the magnetic signal of the immunocomplex in a magnetic field. Sensitivity evaluation showed that the limit of detection (LOD) of the superparamagnetic LFIA system for L. monocytogenes was 10(4) CFU/mL, which was at least one log lower than conventional LFIA. No cross-reaction was observed when Salmonella, Escherichia coli O157:H7, or three types of harmless Listeria strains were tested. Further evaluation with actual food samples indicated that the superparamagnetic LFIA system showed 100 % concordance with real-time PCR. Therefore, this novel superparamagnetic LFIA system could be used as a rapid, sensitive, and specific method for the detection of L. monocytogenes.

Superparamagnetic Fe3O4/poly(St-co-MPS)/SiO2 composite particles with the average size of 140 nm were functionalized with carboxyl group by emulsion polymerization. Functionalized particles with carboxyl contents of 13.6 and 136 micromol/mL were prepared by changing the amount of acrylic acid monomer used in the polymerization. After conjugation with human chorionic gonadotrophin (hCG) antibody, the particles were used to construct lateral flow immunoassays (LFIA) for the detection of hCG in solution. The quantitative analysis could be finished in 20 min by using the magnetic particles as labels. The detection limit of LFIA was determined to be 1 and 5 IU/L respectively for the magnetic particles with carboxyl contents of 13.6 and 136 micromol/mL.

The pandemic of new coronary pneumonia caused by the COVID-19 virus continues to ravage the world. Large-scale population testing is the key to controlling infection and related mortality worldwide. Lateral flow immunochromatographic assay (LFIA) is fast, inexpensive, simple to operate, and easy to carry, very suitable for detection sites. This study developed a COVID-19 N protein detect strip based on p-toluenesulfonyl modified rare earth fluorescent microspheres. The p-toluenesulfonyl-activated nanomaterials provide reactive sulfonyl esters to covalently attach antibodies or other ligands containing primary amino or sulfhydryl groups to the nanomaterial surface. Antibodies are immobilized on these nanomaterials through the Fc region, which ensures optimal orientation of the antibody, thereby increasing the capture rate of the target analyte. The use of buffers with high ionic strength can promote hydrophobic binding; in addition, higher pH could promote the reactivity of the tosyl group. The detection limit of the prepared COVID-19 N protein strips can reach 0.01 ng/mL, so it has great application potential in large-scale population screening. [ABSTRACT FROM AUTHOR]

Aflatoxin B1 (AFB1) is one of the major mycotoxins, which naturally occurs in food and agricultural products. In this study, a cyclic peptide (CVPSKPGLC) mimicking AFB1 was used to develop a biotinylated peptide–based immunoassay (bp-ELISA) for AFB1 determination. This cyclic peptide was isolated from a commercially available phage-displayed random 7-mer cyclic peptide library, and then synthesized chemically. Instead of phage particles, the peptide was biotinylated and used to detect AFB1 by bp-ELISA, with an IC50 of 0.92 ng/mL, which was approximately 60-fold better than that of phage ELISA. Good recoveries (83–102%) were obtained in spiked rice and corn samples, which were further validated by high-performance liquid chromatography-fluorescence detector. As better sensitivities (0.92–1.21 ng/mL) were obtained by bp-ELISA even using selected anti-AFB1 antibodies prepared previously in laboratory, this cyclic peptide is suitable as a substitute for synthetic competitive AFB1 antigens in food contamination monitoring. [ABSTRACT FROM AUTHOR]

Early prevention and monitoring of Ralstonia solanacearum (Rs) on nightshade is extremely critical for potent prevention and treatment of bacterial wilt disease. We developed two kinds of lateral flow immunochromatographic strip (LFICS) using gold nanoparticles (GNPs) and fluorescein isothiocyanate (FITC) for rapid diagnosis of plant bacterial wilt, caused by Ralstonia solanacearum (Rs), which both were based on double antibody sandwich method. Three monoclonal antibodies (McAb) highly specific to Rs were obtained by cell fusion and screening after four times of immunization with the strain GIM 1.76. Under optimized conditions, the limit of detection (LOD) with GNPs and FITC were 104 colony forming units per millilitre (CFU/mL) and 106 CFU/mL respectively, then the range detection correspondingly were 104-109 CFU/mL and 106-109 CFU/mL. On top of that, the developed immunoassay could be used for spot and point-of-care testing Rs on tomato seed, ginger seed, casuarina seed and display no cross-reaction with 43 other phytopathogenic strains that also could infect plants so as to cause plants diseases. These results demonstrated that we sucessfully developed two simple, effective and sensitive strips for monitoring bacterial wilt infection. Meanwhile, this is the first report about LFICS labelled by FITC for rapid detection of Rs, and it is the first time conformed that the sensitive of the LFICS with GNPs is significantly higher than FITC. [ABSTRACT FROM AUTHOR]

Mycotoxins are the toxic secondary metabolites produced by fungi and they are a worldwide public health concern. A VHH antibody (or nanobody) is the smallest antigen binding entity and is produced by heavy chain only antibodies. Compared with conventional antibodies, VHH antibodies overcome many pitfalls typically encountered in clinical therapeutics and immunodiagnostics. Likewise, VHH antibodies are particularly useful for monitoring mycotoxins in food and feedstuffs, as they are easily genetic engineered and have superior stability. In this review, we summarize the efforts to produce anti-mycotoxins VHH antibodies and associated assays, presenting VHH as a potential tool in mycotoxin analysis. [ABSTRACT FROM AUTHOR]

• The monoclonal antibodies against S protein of COVID-19 have cross-reaction with HCoV-OC43, HCoV-NL63 and HCoV-HKU1. • The N protein Ag-mAb system is more specific and accurate, suitable for immunoassay. • N protein strips we prepared can quickly and easily screen the swab samples within 11 min with 93.33 % accuracy rate. The SARS-CoV-2 virus responsible for coronavirus 2019 (COVID-19) poses a significant challenge to healthcare systems worldwide. According to the World Health Organization (WHO), the outbreak of COVID-19 has been a pandemic that infected more than 25.32 million people and caused more than 848.25 thousand deaths worldwide at the time of 1st September 2020. Despite governmental initiatives aimed to contain the spread of the disease, several countries are experiencing unmanageable increases in medical equipment and larger testing capacity. The current diagnosis based on nuclear acid requires specialized instruments, time-consuming, and laborious, the low-cost and convenient technologies were still urgently needed. Both spike and nucleocapsid are key structural proteins of COVID-19 with good immunogenicity, can serve as primary targets for immunoassay. After comparative research, we certified nucleocapsid antigen-monoclonal antibody (mAbs) system was more suitable for the COVID-19 immunodetection. Subsequently, we designed a rapid test strip based on it that can be used in large-scale screening of COVID-19 in population and more suitable for some remote and special needs areas were restricted by a medical condition or for quick and large quantities of screenings. [ABSTRACT FROM AUTHOR]

Abstract: A multiplexed immunoassay biosensor for detecting serum biomarkers was developed by using photoluminescent (PL) aqueous CdSe/ZnS quantum dots (QDs) with high efficiency and stability as fluorescence labels and carboxyl functionalized microporous nylon membrane as a matrix. Two main biomarkers of Down Syndrome (DS), β-human chorionic gonadotrophin (β-HCG) and α-fetal protein (AFP), were selected for detection in this biosensor system. For specific detection of DS, antibody-immobilized microporous nylon membrane first captured the targeted antigens from the physiological samples and formed immunocomplexes (antibody–antigen) on the membrane surface. Then the immunocomplexes continued to react with QDs conjugated antibodies (labeled antibodies), and formed triplex “sandwich” structure, which was confirmed by AFM and confocal microscopy. Quantitative detection of β-HCG and AFP was also realized, the detectable level of this new biosensor was as low as 1×10−6 IU/L for β-HCG and 1ng/mL for AFP in a relatively short assay time without any enrichment. [Copyright &y& Elsevier]

Abstract: Au/Ag core-shell nanoparticles labeled by monoclonal antibody and surface-enhanced Raman scattering (SERS) probes were used for immunoassay analysis. Mouse polyclonal antibodies against hepatitis B surface antigen (mouse Anti-HBsAg PAb) were covalently immobilized on the silicon chips modified by a self-assembled monolayer of (3-amino-propyl) trimethoxysilane via glutaraldehyde (GA) activation. The Au/Ag core-shell nanoparticles were labeled by the mouse monoclonal antibody against hepatitis B surface antigen (mouse Anti-HBsAg MAb) and the probe molecule, p-mercaptobenzoic acid (MBA). Immunoreactions between the labeled Au/Ag core-shell nanoparticles and the corresponding antigens captured by the Anti-HBsAg PAb on the silicon chips were investigated by SERS. [Copyright &y& Elsevier]