Rapid detection of Shiga toxin type II using lateral flow immunochromatography test strips of colorimetry and fluorimetry

Advantages of aggregation-induced luminescence microspheres compared with fluorescent microspheres in immunochromatography assay with sandwich format

Organic fluorescein dye-embedded fluorescent microspheres (FMs) are currently the most established commercially fluorescent markers, and they have been widely used to improve the sensitivity of immunochromatography assay (ICA). However, these FMs have natural defects, such as the aggregation-caused quenching effect and small Stokes shift, which are not conducive to improving the detection performance of ICA. Herein, two green emitted FMs, namely aggregation-induced emission FMs (AIEFMs) and fluorescein isothiocyanate FMs (FITCFMs), were prepared by swelling the AIE luminogens and FITC dyes into the carboxyl group-modified polystyrene microspheres. The average diameters of AIEFMs and FITCFMs were 350 and 450 nm, respectively. Compared with FITCFMs, the AIEFMs exhibited stronger fluorescence intensity and a larger Stokes shift. These two FMs were used as the labeling markers of ICA for procalcitonin (PCT) detection with the sandwich format. Among them, AIEFM-ICA showed dynamic linear detection of PCT from 7.6 pg mL^-1 to 125 ng mL^-1 with the limit of detection (LOD) at 3.8 pg mL^-1. These values were remarkably superior to those of FITCFM-ICA (linear range from 61 pg mL^-1 to 62.5 ng mL^-1 and LOD value at 60 pg mL^-1). Furthermore, the average recoveries of the intra- and inter-assays of AIEFM-ICA ranged from 86% to 112%, with coefficients of variation ranging from 1.2% to 8.8%, indicating accuracy and precision for PCT quantitative detection. Additionally, the reliability of the developed AIEFM-ICA was further assessed by analyzing 30 real serum samples from systemic inflammatory response by infectious diseases, and the results showed good agreement with the chemiluminescence immunoassay. In conclusion, compared with traditional FITCFMs, green emitted AIEFMs as a novel fluorescent label, exhibits greater potential to enhance the detection performance of the ICA platform.

Recent advances in immunoassay technologies for the detection of human coronavirus infections

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is the seventh coronavirus (CoV) that has spread in humans and has become a global pandemic since late 2019. Efficient and accurate laboratory diagnostic methods are one of the crucial means to control the development of the current pandemic and to prevent potential future outbreaks. Although real-time reverse transcription-polymerase chain reaction (rRT-PCR) is the preferred laboratory method recommended by the World Health Organization (WHO) for diagnosing and screening SARS-CoV-2 infection, the versatile immunoassays still play an important role for pandemic control. They can be used not only as supplemental tools to identify cases missed by rRT-PCR, but also for first-line screening tests in areas with limited medical resources. Moreover, they are also indispensable tools for retrospective epidemiological surveys and the evaluation of the effectiveness of vaccination. In this review, we summarize the mainstream immunoassay methods for human coronaviruses (HCoVs) and address their benefits, limitations, and applications. Then, technical strategies based on bioinformatics and advanced biosensors were proposed to improve the performance of these methods. Finally, future suggestions and possibilities that can lead to higher sensitivity and specificity are provided for further research.

Recent advances in detection technologies for COVID-19

Corona Virus Disease 2019 (COVID-19) is a highly infectious respiratory illness that was caused by the SARS-CoV-2. It spread around the world in just a few months and became a worldwide pandemic. Quick and accurate diagnosis of infected patients is very important for controlling transmission. In addition to the commonly used Real-time reverse-transcription polymerase chain reaction (RT-PCR) detection techniques, other diagnostic techniques are also emerging endlessly. This article reviews the current diagnostic methods for COVID-19 and discusses their advantages and disadvantages. It provides an important reference for the diagnosis of COVID-19.

Multi-Quantum Dots-Embedded Silica-Encapsulated Nanoparticle-Based Lateral Flow Assay for Highly Sensitive Exosome Detection

Exosomes are attracting attention as new biomarkers for monitoring the diagnosis and prognosis of certain diseases. Colorimetric-based lateral-flow assays have been previously used to detect exosomes, but these have the disadvantage of a high limit of detection. Here, we introduce a new technique to improve exosome detection. In our approach, highly bright multi-quantum dots embedded in silica-encapsulated nanoparticles (M–QD–SNs), which have uniform size and are brighter than single quantum dots, were applied to the lateral flow immunoassay method to sensitively detect exosomes. Anti-CD63 antibodies were introduced on the surface of the M–QD–SNs, and a lateral flow immunoassay with the M–QD–SNs was conducted to detect human foreskin fibroblast (HFF) exosomes. Exosome samples included a wide range of concentrations from 100 to 1000 exosomes/µL, and the detection limit of our newly designed system was 117.94 exosome/μL, which was 11 times lower than the previously reported limits. Additionally, exosomes were selectively detected relative to the negative controls, liposomes, and newborn calf serum, confirming that this method prevented non-specific binding. Thus, our study demonstrates that highly sensitive and quantitative exosome detection can be conducted quickly and accurately by using lateral immunochromatographic analysis with M–QD–SNs.

Sensitive Lateral Flow Immunoassay for the Residues of Imidocarb in Milk and Beef Samples

Based on the successful derivation of a hapten, we prepared and optimized a murine monoclonal antibody against imidocarb, with an IC₅₀ of 2.22 ng/mL and a limit of detection (LOD) of 0.45 ng/mL. Cross-experiment results showed that the cross-over rate for 4,4'-dinitrocarbanilide was 18.12%, and the cross-reactivity with other analogues when using the ic ELISA was less than 0.1%. We used the developed ic-ELISA to detect the addition and recovery of imidocarb in milk and beef samples, and values were 86.0-93.5 and 84.5-101.2%, respectively. The preparation of an immunochromatographic test strip based on gold nanoparticles was used for the rapid identification of imidocarb in milk and beef samples. When assessed by the naked eye, the visual LOD for imidocarb in milk and beef samples was 5 and 10 ng/mL, and the cut-off values were 20 and 50 ng/mL, respectively. Because of its high sensitivity, specificity, and simplicity, the test strip can be used for on-site testing and rapid screening of imidocarb in food samples.

Point-of-Care Diagnoses and Assays Based on Lateral Flow Test

Analytical devices for point-of-care diagnoses are highly desired and would improve quality of life when first diagnoses are made early and pathologies are recognized soon. Lateral flow tests (LFTs) are such tools that can be easily performed without specific equipment, skills, or experiences. This review is focused on the use of LFT in point-of-care diagnoses. The principle of the assay is explained, and new materials like nanoparticles for labeling, new recognition molecules for interaction with an analyte, and new additional instrumentation like signal scaling by a smartphone camera are described and discussed. Advantages of the LFT devices as well as their limitations are described and discussed here considering actual papers that are properly cited.

Sensitive Immunochromatographic Assay Using Highly Luminescent Quantum Dot Nanobeads as Tracer for the Detection of Cyproheptadine Hydrochloride in Animal-Derived Food

Cyproheptadine hydrochloride (CYP), used as human and veterinary drug, has been used illegally as feed additive for food-producing animals, which could remain in food and jeopardize human health. There is a need for on-site detection of CYP residue in animal-derived food. In this study, a hapten was designed, and a specific monoclonal antibody (mAb) was developed to detect CYP with an IC50 of 1.38 ng/mL and negligible cross-reactivity (CR) for other analogs. Forthermore, a high sensitive immunochromatographic assay (QBs-ICA) was developed using quantum dot nanobeads as reporters. The assay showed the linear detection range (IC20-IC80) of 0.03-0.52 ng/mL, the limit of detection (LOD) and visual detection limit (VDL) reached to 0.01 and 0.625 ng/mL, respectively. Spiked recovery study in pig urine and pork confirmed that the QBs-ICA was applicable for on-site testing. This assay showed better sensitivity and speedy than the reported instrumental analysis and immunoassays.

Rapid Detection of IgM Antibodies against the SARS-CoV-2 Virus via Colloidal Gold Nanoparticle-Based Lateral-Flow Assay

Last year, the novel coronavirus disease (COVID-19) emerged in Wuhan, and it has rapidly spread to many other countries and regions. COVID-19 exhibits a strong human-to-human transmission infectivity and could cause acute respiratory diseases. Asymptomatic carriers are able to infect other healthy persons, and this poses a challenge for public health; the World Health Organization (WHO) has already announced COVID-19 as a global pandemic. Nucleic acid testing, considered as the current primary method for diagnosing COVID-19, might lead to false negatives and is difficult to be applied for every suspected patient because of the existence of asymptomatic carriers. Meanwhile, detecting specific antibodies in blood, such as the IgM antibody, against the SARS-CoV-2 virus is another choice for COVID-19 diagnosis, as it is widely accepted that IgM is an important indicator in the acute infection period. In this study, a colloidal gold nanoparticle-based lateral-flow (AuNP-LF) assay was developed to achieve rapid diagnosis and on-site detection of the IgM antibody against the SARS-CoV-2 virus through the indirect immunochromatography method. For preparing AuNP-LF strips, the SARS-CoV-2 nucleoprotein (SARS-CoV-2 NP) was coated on an analytical membrane for sample capture, and antihuman IgM was conjugated with AuNPs to form the detecting reporter. Optimization of AuNP-LF assay was carried out by altering the pH value and the amount of antihuman IgM. The performance of AuNP-LF assay was evaluated by testing serum samples of COVID-19 patients and normal humans. The results were compared with the real-time polymerase chain reaction. The sensitivity and specificity of AuNP-LF assay were determined to be 100 and 93.3%, respectively, and an almost perfect agreement was exhibited by Kappa statistics (κ coefficient = 0.872). AuNP-LF assay showed outstanding selectivity in the detection of IgM against the SARS-CoV-2 virus with no interference from other viruses such as severe fever with thrombocytopenia syndrome virus (SFTSV) and dengue virus (DFV). AuNP-LF assay was able to achieve results within 15 min and needed only 10-20 μL serum for each test. As a whole, in the light of its advantages such as excellent specificity and stability, easy operation, low cost, and being less time-consuming, AuNP-LF assay is a feasible method for the diagnosis of COVID-19 in primary hospitals and laboratories, especially in emergency situations in which numerous samples need to be tested on time.

Rapid Detection of IgM Antibodies against the SARS-CoV-2 Virus via Colloidal Gold Nanoparticle-Based Lateral-Flow Assay

Last year, the novel coronavirus disease (COVID-19) emerged in Wuhan, and it has rapidly spread to many other countries and regions. COVID-19 exhibits a strong human-to-human transmission infectivity and could cause acute respiratory diseases. Asymptomatic carriers are able to infect other healthy persons, and this poses a challenge for public health; the World Health Organization (WHO) has already announced COVID-19 as a global pandemic. Nucleic acid testing, considered as the current primary method for diagnosing COVID-19, might lead to false negatives and is difficult to be applied for every suspected patient because of the existence of asymptomatic carriers. Meanwhile, detecting specific antibodies in blood, such as the IgM antibody, against the SARS-CoV-2 virus is another choice for COVID-19 diagnosis, as it is widely accepted that IgM is an important indicator in the acute infection period. In this study, a colloidal gold nanoparticle-based lateral-flow (AuNP-LF) assay was developed to achieve rapid diagnosis and on-site detection of the IgM antibody against the SARS-CoV-2 virus through the indirect immunochromatography method. For preparing AuNP-LF strips, the SARS-CoV-2 nucleoprotein (SARS-CoV-2 NP) was coated on an analytical membrane for sample capture, and antihuman IgM was conjugated with AuNPs to form the detecting reporter. Optimization of AuNP-LF assay was carried out by altering the pH value and the amount of antihuman IgM. The performance of AuNP-LF assay was evaluated by testing serum samples of COVID-19 patients and normal humans. The results were compared with the real-time polymerase chain reaction. The sensitivity and specificity of AuNP-LF assay were determined to be 100 and 93.3%, respectively, and an almost perfect agreement was exhibited by Kappa statistics (κ coefficient = 0.872). AuNP-LF assay showed outstanding selectivity in the detection of IgM against the SARS-CoV-2 virus with no interference from other viruses such as severe fever with thrombocytopenia syndrome virus (SFTSV) and dengue virus (DFV). AuNP-LF assay was able to achieve results within 15 min and needed only 10-20 μL serum for each test. As a whole, in the light of its advantages such as excellent specificity and stability, easy operation, low cost, and being less time-consuming, AuNP-LF assay is a feasible method for the diagnosis of COVID-19 in primary hospitals and laboratories, especially in emergency situations in which numerous samples need to be tested on time.

Development of a lateral flow immunoassay strip for rapid detection of IgG antibody against SARS-CoV-2 virus

Rapid and simple LFIA strips based on Au NPs provide a preliminary test result for physicians to make the correct diagnosis of SARS-CoV-2 infections along with alternative testing methods.