Production of the broad specific monoclonal antibody against sarafloxacin for rapid immunoscreening of 12 fluoroquinolones in meat

Simple dual-readout immunosensor based on phosphate-triggered and potassium permanganate for visual detection of fenitrothion

Multicolor-based visual immunosensor is a promising tool for rapid analysis without the use of bulky instruments. Herein, an anti-fenitrothion nanobody-alkaline phosphatase fusion protein (VHHjd8-ALP) was employed to develop a multicolor visual immunosensor (MVIS) and a ratiometric fluorescence MVIS (RFMVIS, respectively). After one-step competitive immunoassay, the VHHjd8-ALP bound to microplate catalyzed phenyl phosphate disodium salt (ArP) into phenol. Under high alkaline condition (pH 12), the phenol reduced KMnO4 to intermediate (K2MnO4) and further to MnO2 in alkaline condition (pH 12), accompanied by a visible color transition of purple-green-yellow, which can be used for semiquantitative visual analysis or qualitative detection by measuring RGB value. RFMVIS was proposed on the basis of MVIS to further improve sensitivity. The CdTe quantum dot and fluorescein were used as signal probes to develop the fluorescent immunosensor. The CdTe dots with red emission (644 nm) was quenched by oxidation of KMnO4, whereas the fluorescein with green emission (520 nm) remained constant, accompanied by a fluorescent color transition of green-yellow-red. By measuring the ratio of the fluorescence intensity (I644/I520), the ratiometric fluorescence immunosensor was developed for qualitative analysis. The two visual immunosensors were sensitive and simple, and they showed good accuracy and practicability in the recovery test, thus are ideal tools for rapid screening.

Preparation of Anti-Aristolochic Acid I Monoclonal Antibody and Development of Chemiluminescent Immunoassay and Carbon Dot-Based Fluoroimmunoassay for Sensitive Detection of Aristolochic Acid I

Aristolochic acid (AA) toxicity has been shown in humans regarding carcinogenesis, nephrotoxicity, and mutagenicity. Monitoring the AA content in drug homologous and healthy foods is necessary for the health of humans. In this study, a monoclonal antibody (mAb) with high sensitivity for aristolochic acid I (AA-I) was prepared. Based on the obtained mAb, a chemiluminescent immunoassay (CLEIA) against AA-I was developed, which showed the 50% decrease in the RLU_max (IC₅₀) value of 1.8 ng/mL and the limit of detection (LOD) of 0.4 ng/mL. Carbon dots with red emission at 620 nm, namely rCDs, were synthesized and employed in conventional indirect competitive enzyme-linked immunosorbent assay (icELISA) to improve the assay sensitivity of a fluoroimmunoassay (FIA). Oxidized 3,3'',5,5''-tetramethylbenzidine dihydrochloride (oxTMB) can quench the emission of the rCDs through the inner-filter effect; therefore, the fluorescence intensity of rCDs can be regulated by the concentration of mAb. As a result, the assay sensitivity of FIA was improved by five-fold compared to CLEIA. A good relationship between the results of the proposed assays and the standard ultra-high performance liquid chromatography-triple quadrupole mass spectrometer (UPLC-QQQ-MS/MS) of real samples indicated good accuracy and practicability of CLEIA and FIA.

The Most Active Oxidase-Mimicking Mn2 O3 Nanozyme for Biosensor Signal Generation

Oxidase-mimicking nanozymes are more desirable than peroxidase-mimicking ones since H₂ O₂ can be omitted. However, only a few nanomaterials are known for oxidase-like activities. In this work, we compared the activity of Mn₂ O₃ , Mn₃ O₄ and MnO₂ and found that Mn₂ O₃ had the highest oxidase activity. Interestingly, the activity of Mn₂ O₃ was even inhibited by H₂ O₂ . The oxidase-like activity of Mn₂ O₃ was not much affected by the presence of proteins such as bovine serum albumin (BSA), but the physisorption of antibodies to Mn₂ O₃ was not strong enough to withstand the displacement by BSA. We then treated Mn₂ O₃ with 3-aminopropyltriethoxysilane to graft an amine group, which was used to conjugate antibodies using glutaraldehyde as a crosslinker. A one-step indirect competitive ELISA (icELISA) was developed for the detection of isocarbophos, and an IC₅₀ of 261.7 ng/mL was obtained, comparable with the results of the standard two-step assay using horseradish peroxidase (HRP)-labeled antibodies. This assay has the advantage of significant timesaving for rapid detection of large amounts of samples. This work has discovered a highly efficient oxidase-mimicking nanozyme useful for various nano- and analytical applications.

Effect of proteins on the oxidase-like activity of CeO2 nanozymes for immunoassays

Protein adsorption inhibits the oxidase-like activity of CeO₂ nanoparticles. Coating a partial shell of silica on CeO₂ and subsequent conjugation of antibodies allow highly sensitive and selective detection of fenitrothion.

Ciprofloxacin and Clinafloxacin Antibodies for an Immunoassay of Quinolones: Quantitative Structure⁻Activity Analysis of Cross-Reactivities

A common problem in the immunodetection of structurally close compounds is understanding the regularities of immune recognition, and elucidating the basic structural elements that provide it. Correct identification of these elements would allow for select immunogens to obtain antibodies with either wide specificity to different representatives of a given chemical class (for class-specific immunoassays), or narrow specificity to a unique compound (mono-specific immunoassays). Fluoroquinolones (FQs; antibiotic contaminants of animal-derived foods) are of particular interest for such research. We studied the structural basis of immune recognition of FQs by antibodies against ciprofloxacin (CIP) and clinafloxacin (CLI) as the immunizing hapten. CIP and CLI possess the same cyclopropyl substituents at the N1 position, while their substituents at C7 and C8 are different. Anti-CIP antibodies were specific to 22 of 24 FQs, while anti-CLI antibodies were specific to 11 of 26 FQs. The molecular size was critical for the binding between the FQs and the anti-CIP antibody. The presence of the cyclopropyl ring at the N1 position was important for the recognition between fluoroquinolones and the anti-CLI antibody. The anti-CIP quantitative structure–activity relationship (QSAR) model was well-equipped to predict the test set (pred_R² = 0.944). The statistical parameters of the anti-CLI model were also high (R² = 0.885, q² = 0.864). Thus, the obtained QSAR models yielded sufficient correlation coefficients, internal stability, and predictive ability. This work broadens our knowledge of the molecular mechanisms of FQs’ interaction with antibodies, and it will contribute to the further development of antibiotic immunoassays.

Rapid and Simple Determination of Sarafloxacin and Difloxacin in Beef by Capillary Electrophoresis Coupled with Solid-Phase Extraction

A simple and rapid capillary electrophoresis method with diode array detector was developed for determination of sarafloxacin and difloxacin in beef. In this study, the experimental parameters affecting the determination were systematically optimized, including wavelength, buffer system, pH and concentration, and separation temperature and voltage. Under the optimal conditions, sarafloxacin and difloxacin could be quantified within 4 min using H₃BO₃/Na₂B₄O₇ buffer (35 mmol/L, pH 8.8) as background electrolyte, 25 kV as separation voltage, and 22°C as the column temperature. The linear range of the method was 1-20 μg/mL with LOD 0.8 μg/mL for sarafloxacin and 0.5-20 μg/mL with LOD 0.3 μg/mL for difloxacin. The RSDs for the peak area of 8 μg/mL sarafloxacin were 4.8% (intraday) and 7.8% (interday), respectively. The proposed method has been applied to determine the residue of sarafloxacin and difloxacin in beef samples with the satisfactory recovery.

Production and Directional Evolution of Antisarafloxacin ScFv Antibody for Immunoassay of Fluoroquinolones in Milk

A recombinant antisarafloxacin ScFv antibody was produced by direct transformation of its gene into Rosetta-gami(DE3) for expression, and then its recognition mechanisms for 12 fluoroquinolones were studied using the molecular docking method. On the basis of the results of virtual mutation, the ScFv antibody was evolved by directional mutagenesis of contact amino acid residue Tyr99 to His. The ScFv mutant showed highly increased affinity for the 12 drugs with up to sevenfold improved sensitivity. Finally, the mutant was used to develop an indirect competitive enzyme linked immunosorbent assay for determination of the 12 drugs in milk. The limits of detection were in the range of 0.3-8.0 ng/mL; the ties were in the range of 5-106%, and the recoveries from the standard fortified blank milk were in the range of 62.0-89.3%. This is the first study reporting the evolution of an ScFv antibody using a directional mutagenesis strategy based on virtual mutation.

Magnetic nanoparticle based purification and enzyme-linked immunosorbent assay using monoclonal antibody against enrofloxacin

Monoclonal anti-enrofloxacin antibody was prepared for a direct competitive enzyme-linked immunosorbent assay (ELISA) and purification system using monoclonal antibody (mAb) coupled magnetic nanoparticles (MNPs). The IC₅₀ values of the developed mAb for enrofloxacin (ENR), ciprofloxacin, difloxacin, sarafloxacin, pefloxacin, and norfloxacin were 5.0, 8.3, 9.7, 21.7, 36.0, and 63.7 ng/mL, respectively. The lowest detectable level of ENR was 0.7 ng/mL in the prepared ELISA system. To validate the developed ELISA in the food matrix, known amounts of ENR were spiked in meat and egg samples at 10, 20 and 30 ng/mL. Recoveries for ENR ranged from 72.9 to 113.16% with a coefficient of variation (CV) of 2.42 to 10.11%. The applicability of the mAb-MNP system was verified by testing the recoveries for ENR residue in three different matrices. Recoveries for ENR ranged from 75.16 to 86.36%, while the CV ranged from 5.08 to 11.53%. Overall, ENR-specific monoclonal antibody was prepared and developed for use in competitive to ELISAs for the detection of ENR in animal meat samples. Furthermore, we suggest that a purification system for ENR using mAb-coupled MNPs could be useful for determination of ENR residue in food.

Enzyme-linked immunosorbent assay for the determination of five organophosphorus pesticides in camellia oil

A matrix solid-phase dispersion and direct competitive enzyme-linked immunosorbent assay (MSPD-ELISA) was developed for five organophosphorus pesticides (OPs) in camellia oil. Seven haptens with different substituents in the aromatic ring were used to prepare different competitors; the ELISA showed highest sensitivity and specificity to OPs when the competitor had moderate heterology to the immunizing hapten. Several assay conditions were optimized to increase the ELISA sensitivity. The optimized ELISA for five OPs had 50% inhibitory concentrations of 6.3 ng/ml (parathion), 18.9 ng/ml (methyl parathion), 120.7 ng/ml (fenitrothion), 110.4 ng/ml (fenthion), and 20.7 ng/ml (phoxim). The average recoveries of five OPs in camellia oil ranged from 75.7 to 105.3%, with the interassay coefficient of variations ranging from 6.0 to 13.4%. Compared with the results previously reported, the ELISA that was developed in the present study showed a much higher sensitivity. Additionally, MSPD was used in the sample preparation to minimize the matrix effect. Recoveries from the method developed here were in agreement with those obtained by gas chromatography, which indicated that the detection performance of the MSPD-ELISA could meet the regulatory requirements of different governments and international organizations.