The preparation of polyclonal antibody against chlordimeform and establishment of detection by indirect competitive ELISA

Objective: Chlordimeform is a chemical pesticide that is highly carcinogenic and toxic. The purpose of this study was to establish an enzyme-linked immunosorbent assay (ELISA) method for the detection of chlordimeform in aquaculture and fish farming.

METHODS

Chlordimeform was coupled with bovine serum albumin (BSA) and ovalbumin (OVA) as carrier proteins. A chlordimeform-BSA conjugate was used as an immunogen, and chlordimeform-OVA was used as a coating antigen. Chlordimeform-BSA was used to immunize rabbits, and a polyclonal antibody was prepared. An indirect competitive enzyme-linked immunosorbent assay (IC-ELISA) was established to detect chlordimeform.

RESULTS

The working range of the established IC-ELISA method for chlordimeform detection was 1-20 ng/mL. The IC₅₀ was 3.126 ng/mL, and the lower limit of detection (LOD) of chlordimeform was 0.637 ng/mL. The recovery of chlordimeform from spiked water samples ranged from 81% to 107%.

CONCLUSION

An anti-chlordimeform polyclonal antibody was successfully developed, and a novel IC-ELISA was established to detect chlordimeform in aquaculture.

The Preparation and Identification of a Monoclonal Antibody against Domoic Acid and Establishment of Detection by Indirect Competitive ELISA

Domoic acid (DA) is a potent toxin, marine biotoxin, and primarily produced by Pseudo-nitzschia. The DA hapten was coupled with bovine serum albumin (BSA), and ovalbumin (OVA) as carrier proteins. DA-BSA conjugate was used as immunogen and DA-OVA as coating antigen. Cell fusion between spleen cells and sp2/0 myeloma cells developed 1C3 hybridoma clone producing 1C3 monoclonal antibody (mAb). Hybridoma was injected into the mice to produce ascites, and further purified by caprylic acid/ammonium sulfate method. The mAb was of IgG3 subclass, and was specific to DA with high affinity (2.5 × 10⁸ L/mol). Moreover, western blot exhibited significant specificity to the DA antigens. Indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) showed DA working range of 0.006–0.2 ng/mL. The IC₅₀ was 0.03 ng/mL with low limit of detection (LOD) of 0.006 ng/mL. Average DA recovery from spiked shellfish extract was 100.56 ± 2.8% with the coefficient variation of 0.01–0.1%. Hence, mAb producing 1C3 hybridoma was successfully developed and could be used to detect DA in contaminated samples.

Use of biosensors as alternatives to current regulatory methods for marine biotoxins

Marine toxins are currently monitored by means of a bioassay that requires the use of many mice, which poses a technical and ethical problem in many countries. With the exception of domoic acid, there is a legal requirement for the presence of other toxins (yessotoxin, saxitoxin and analogs, okadaic acid and analogs, pectenotoxins and azaspiracids) in seafood to be controlled by bioassay, but other toxins, such as palytoxin, cyclic imines, ciguatera and tetrodotoxin are potentially present in European food and there are no legal requirements or technical approaches available to identify their presence. The need for alternative methods to the bioassay is clearly important, and biosensors have become in recent years a feasible alternative to animal sacrifice. This review will discuss the advantages and disadvantages of using biosensors as alternatives to animal assays for marine toxins, with particular focus on surface plasmon resonance (SPR) technology.

Detection of domoic acid in rat serum and brain by direct competitive enzyme-linked immunosorbent assay (cELISA)

In 1987 a large-scale incident of human poisoning in Canada was traced to commercial mussels contaminated with domoic acid (DOM). Since then, routine screening of shellfish domoic acid content has been carried out using a variety of assays, with liquid chromatography using ultraviolet absorbance detection (LC-UV) or mass spectrometric detection (LC-MS) being the currently accepted standard methodologies. Recently, a highly specific competitive enzyme-linked immunosorbent assay (cELISA) has been developed for the detection and analysis of DOM in commercial shellfish, but its accuracy relative to LC methods has not been independently verified in mammalian tissues. In this study we demonstrate that measurement of rat serum DOM concentration by cELISA gives a good correlation (r2 = 0.993) across a broad range of concentrations when compared to LC-MS analysis, with only a small (15%) overestimation of sample DOM content. In addition, we have developed an extraction method for analysis of DOM in rat brain by cELISA which yields complete recovery across a range of sample dilutions.

Surface plasmon resonance sensor for domoic acid based on grafted imprinted polymer

A molecularly imprinted polymer (MIP) film for domoic acid (DA) was synthesised by direct photo-grafting onto a gold chip suitable for a surface plasmon resonance (SPR) based bioanalytical instrument system, the BIAcore 3000. The gold surface was first functionalised with a self-assembled monolayer of 2-mercaptoethylamine and subsequent carbodiimide chemistry was performed for covalent attachment of the photoinitiator, 4,4'-azobis(cyanovaleric acid). This ensured that the formation of the MIP thin film, comprising 2-(diethylamino) ethyl methacrylate as functional monomer and ethylene glycol dimethacrylate as cross-linker, occurred only at the surface level. Optimisation and control over the grafting procedure were achieved using contact angle measurements and atomic force microscope (AFM) imaging. The surface grafting resulted in the formation of thin and homogeneous MIP film with thickness of 40 nm. A competitive binding assay was performed with free DA and its conjugate with horseradish peroxidase, which was used as a refractive label. The sensor was evaluated for its sensitivity, cross-reactivity, and robustness by using a BIAcore 3000. Likewise, monoclonal antibodies acting as natural receptors for the toxin were studied with the same BIAcore system. Results of a comparison between the artificial and natural receptors are reported. In contrast to monoclonal antibodies, the regeneration of MIP chip did not affect its recognition properties and continuous measurement was possible over a period of at least 2 months.