Development of a quantum dot-based immunochromatography test strip for rapid screening of oxytetracycline and 4-epi-oxytetracycline in edible animal tissues

Development of a Highly Specific Fluoroimmunoassay for the Detection of Doxycycline Residues in Water Environmental and Animal Tissue Samples

Doxycycline (DOX) and its metabolite residues in food and the environment pose a serious threat to human health and the ecological environment. In this work, a novel method, termed competitive fluoroimmunoassays (cFIA), based on monoclonal antibody (mAb) bio-conjugated CdSe/ZnS core-shell quantum dots (QDs), was developed for sensitive and rapid bioanalyses of DOX in natural water and commercial meats. After the optimization of the experimental conditions, 1 μg mL^-1 of coating antigen and 0.5 μg mL^-1 of QD-labeled mAb were used for the establishment of the cFIA. With this assay, the 50% inhibition concentration was found to be 0.35 ng mL^-1 of DOX in phosphate-buffered saline samples, and the limit of detection was 0.039 ng mL^-1 with minor cross-reactivity to other tetracycline members. The recoveries from natural water and commercial meats spiked with DOX concentrations of 10-600 ng mL^-1 were 81.3-109.8%, and standard deviation were all below 12%. Levels measured with the QD-cFIA for thirty authentic samples were confirmed by high-performance liquid chromatography with good correlations. These results indicate that QD-cFIA is sultable for the rapid and quantitative detection of DOX residue in environmental and food samples.

The Effects of Different Antigen-Antibody Pairs on the Results of 20 Min ELISA and 8 Min Chromatographic Paper Test for Quantitative Detection of Acetamiprid in Vegetables

To establish rapid, high-sensitive, quantitative detection of ACP residues in vegetables. A 1G2 cell clone was selected as the most sensitive for anti-ACP antibody production following secondary immunization, cell fusion, and screening. The affinity of the 1G2 antibody to each of the four coating agents (imidacloprid−bovine serum albumin [BSA], thiacloprid−BSA, imidaclothiz−BSA, and ACP-BSA) was determined using a 20 min enzyme-linked immunosorbent assay (ELISA). The half maximal inhibitory concentration (IC50) was 0.51−0.62 ng/mL, showing no significant difference in affinity to different antigens. However, we obtained IC50 values of 0.58 and 1.40 ng/mL on the linear regression lines for 1G2 anti-ACP antibody/imidacloprid−BSA and 1G2 anti-ACP antibody/thiacloprid−BSA, respectively, via quantum dot (QD)-based immunochromatography. That is, the 1G2 antibody/imidacloprid−BSA pair (the best combination) was about three times more sensitive than the 1G2 antibody/thiacloprid−BSA pair in immunochromatographic detection. The best combination was used for the development of an 8 min chromatographic paper test. With simple and convenient sample pretreatment, we achieved an average recovery of 75−117%. The coefficient of variation (CoV) was <25% for all concentrations tested, the false−positive rate was <5%, the false−negative rate was 0%, and the linear range of the method was 50−1800 μg/kg. These performance metrics met the ACP detection standards in China, the European Union (EU), and the United States (US). In summary, in this study, we established an 8 min QD-based immunochromatographic stripe for the rapid and accurate quantitative determination of ACP residues in vegetables.

A monoclonal antibody for identifying capsaicin congeners in illegal cooking oil and its applications

In this work, we studied the preparation of a high-affinity antibody and its immunochromatographic applications to simultaneously identify capsaicin(LJJ), dihydrocapsaicin(HLJ), nordihydrocapsaicin, homodihydrocapsaicin, and other congeners in illegal cooking oil. We used dihydrocapsaicin hapten-conjugated carrier protein BSA as the immunogen according to the formaldehyde method, and conjugated capsaicin and OVA as the coated detection antigen according to the formaldehyde method. We subsequently screened and cloned a hybridoma cell line 2B3 with the highest affinity, which could stably secrete monoclonal antibodies against compounds in the capsaicin family. We then established a capsaicin indirect ELISA standard curve, which was fitted using the linear regression equation R = 0.9987, curve y = -2.3x + 0.2, and IC₅₀ = 0.2 ng/mL. The cross-reaction rate for capsaicin was 100%, 116% for dihydrocapsaicin, 88% for homodihydrocapsaicin, and 94% for nordihydrocapsaicin. In the second application, we established a simple and accurate sample pretreatment method and a quantum dot-labeled test strip to quickly and quantitatively detect capsaicin family compounds in illegal cooking oil in 8 min. The average recovery rates for each spiked concentration were between 75% and 107.8%, and the coefficient of variation values for each spiked concentration were less than 15%. The high-affinity antibody we identified could simultaneously identify capsaicin, dihydrocapsaicin, nordihydrocapsaicin, homodihydrocapsaicin, and other congeners in illegal cooking oil, and the antibody could be quickly and accurately applied for the qualitative and quantitative detection of capsaicin family residues in illegal cooking oil.

Preparation of Monoclonal Antibody and Development of Indirect Competitive Enzyme-Linked Immunosorbent Assay and Fluorescence-Linked Immunosorbent Assay for Detecting 3-Amino-5-methylmorpholino-2-oxazolidinone (AMOZ) in Edible Animal Tissue

To monitor the illegal used of furaltadone, a highly sensitive indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) and fluorescence-linked immunosorbent assay (FLISA) based on a monoclonal antibody (mAb) were developed for the detection of 3-amino-5-methylmorpholino-2-oxazolidinone (AMOZ), the major metabolite of furaltadone in animal tissues. The highly specific mAb, which was very sensitive to a nitrophenyl derivative of AMOZ (2-NP-AMOZ) with IC50 values of 0.11 and 0.09 ng/mL for ic-ELISA and FLISA, respectively, was selected for the development of immunoassays. For both the ic-ELISA and FLISA for AMOZ-spiked experiments, acceptable recovery rates of 81.1-105.3% and coefficients of variation of 4.7-9.8% were obtained. In addition, results from both ic-ELISA and FLISA methods for spiked samples' data showed excellent correlation coefficients ranging from 0.9652 to 0.9927. Meanwhile, the proposed ic-ELISA and FLISA for thirty spiked samples were confirmed by standard LC-MS/MS with high correlation coefficients of 0.9911 and 0.9921, respectively. These results suggest that the developed ic-ELISA and FLISA are valid and cost-effective tools for high-throughput monitoring methods for AMOZ residues in animal tissues.

A quantum dot fluorescent microsphere based immunochromatographic strip for detection of brucellosis

BACKGROUND

Brucellosis is a serious zoonosis disease that frequently causes significant economic loss in animal husbandry and threatens human health. Therefore, we established a rapid, accurate, simple and sensitive fluorescent immunochromatographic strip test (ICST) based on quantum dots (QDs) for detection the antibodies of Brucella infection animals serum.

RESULTS

The test strips were successfully prepared by quantum dot fluorescent microspheres (QDFM) as tracers, which were covalently coupled to an outer membrane protein of Brucella OMP22. The outer membrane protein OMP28 and monoclonal antibodies of OMP22 were separately dispensed onto a nitrocellulose membrane as test and quality control lines, respectively. The critical threshold for determining negative or positive through the ratio of the fluorescent signal of the test line and the control line (H_T / H_C) is 0.0492. The repeatability was excellent with an overall average CV of 8.78%. Under optimum conditions, the limit of detection was 1.05 ng/mL (1:512 dilution). With regard to the detection of brucellosis in 150 clinical samples, the total coincidence rate of ICST and Rose Bengal plate test (RBPT) was 97.3%, the coincidence rate of positive samples was 98.8%, the coincidence rate of negative samples was 95.3%, the sensitivity of RBPT is 1:32, and no cross reaction with the sera of other related diseases was observed.

CONCLUSION

In our present study, the QDFM has promising application for on-site screening of brucellosis owing to its high detection speed, high sensitivity, high specificity and low cost.

Visual and fluorometric lateral flow immunoassay combined with a dual-functional test mode for rapid determination of tetracycline antibiotics

A fluorometric immunochromatographic assay (FICA) is described where ZnCdSe/ZnS quantum dots (QDs) act as fluorescent label and gold nanoparticles (AuNPs) act as quencher. The assay works in the "turn-on" mode, i.e. the fluorescent signal (best measured at excitation/emission wavelengths of 302/525 nm) increases with the increase of analyte concentration. This assay can detect tetracycline antibiotics including tetracycline, oxytetracycline, chlortetracycline, and doxycycline. It is not interfered by other veterinary drugs. The visual limits of detection (LODs) for the tetracycline antibiotics are 2 μg·L^-1 in buffer, 20 μg·L^-1 in milk, and 40 μg·kg^-1 in animal muscle tissue. The assay (including sample treatment) can be performed within 30 min. The FICA based on "turn on" mode is more sensitive than the colloidal gold-based immunochromatographic assay (CGICA) and quantum dot-based immunochromatographic assay (QDICA) based on "turn off" mode using either AuNPs or QDs as signal labels. One strip can simultaneously provide the fluorescent test results in the "turn on" mode on the basis of QD luminescence quenching under UV light. The colorimetric test is of the "turn off" mode based on the formation of a red coloration due to the use of AuNPs under natural light. The use of such a dual-functional test mode allows for rapid semi-quantitative determination of tetracycline antibiotics in milk and tissue samples. Graphical abstract Schematoc of a fluorometric immunochromatographic assay (FICA) based on fluorescence quenching of quantum dot (QD) by gold nanoparticle (AuNP) combined with a dual-functional test mode under UV light (turn on mode) and natural light (turn off mode) to visually detect tetracycline antibiotics.

A fluorescent immunochromatographic strip test using a quantum dot-antibody probe for rapid and quantitative detection of 1-aminohydantoin in edible animal tissues

A rapid, simple, and sensitive fluorescent immunochromatographic strip test (ICST) based on quantum dots (QDs) has been developed to detect 1-aminohydantoin (AHD), a major metabolite of nitrofurantoin in animal tissues. To achieve this, QD-labeled antibody conjugates, which consist of CdSe/ZnS QDs and monoclonal antibodies, were prepared by an activated ester method. Under optimal conditions, with the nitrophenyl derivative of AHD as the target, the ICST had a linear range from 0.1 to 100 ng/mL, with a correlation coefficient of 0.9656 and a 50% inhibitory concentration of 4.51 ng/mL. The limit of detection was 0.14 ng/g, which was below the minimum required performance limit of 1 μg/kg for AHD established by the European Commission. The recoveries for AHD ranged from 81.5% to 108.2%, with coefficients of variation below 13%, based on intraday and interday analysis. Furthermore, for AHD in real samples, the ICST showed high reliability and high correlation with liquid chromatography-tandem mass spectrometry (correlation coefficient of 0.9916). To the best of our knowledge, this is the first report of a novel and sensitive method based on a fluorescent ICST to detect AHD below the minimum required performance limit. The ICST demonstrated high reliability, and could be ideally suited for rapid, simple, and on-site screening of AHD contamination in animal tissues. Graphical abstract A rapid, simple, and sensitive fluorescent immunochromatographic strip test that is based on quantum dots was developed to detect 1-aminohydantoin (AHD), a major metabolite of nitrofurantoin in animal tissues. 2-NBA 2-nitrobenzaldehyde, NP nitrophenyl.

Development of monoclonal antibody-based ultrasensitive enzyme-linked immunosorbent assay and fluorescence-linked immunosorbent assay for 1-aminohydantoin detection in aquatic animals

Monitoring and rapid evaluation of nitrofurantoin metabolite, 1-aminohydantoin (AHD), are important for food safety and human health. Herein, we established the monoclonal antibody-based indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) and quantum dots (QDs)-fabricated fluorescence-linked immunosorbent assay (FLISA). Monoclonal antibody specific to nitrophenyl derivative of AHD was derived from hybridoma cell lines 3.2.4/5A8. For another, CdTe core QDs with emission wavelength of 605nm were also synthesized. The performances of the proposed ic-ELISA and FLISA were further examined and the corresponding results were also validated by standard LC-MS/MS analysis. The obtained results indicated that both ic-ELISA and FLISA exhibited good dynamic linear detection for NPAHD over the range from 0.1 to 3.0ngmL^-1. Meanwhile, proposed immunosorbent assays are characterized by satisfactory recovery rates of 81.5-113.7%. The experimental data suggested these two immunoassays could be facile, cost-effective and rapid tools for the prospective quantitative method for AHD analysis in food matrix.

A review of fluorescent signal-based lateral flow immunochromatographic strips

Fluorescent signal-based lateral flow immunochromatographic strips (FLFICS) have received great expectations since they combine the quantitative sensitivity of fluorescence analysis and the simplicity, rapidness, and portability of a common lateral flow immunochromatographic strip (LFICS).