Rapid screening method for halofuginone residues in poultry eggs and liver using time-resolved fluorometry combined with the all-in-one dry chemistry assay concept

Binding affinity-guided design of a highly sensitive noncompetitive immunoassay for small molecule detection

Small molecules are immunochemically classified as hapten that lacking of at least two epitopes, usually using competitive format for establishing immunoassays. However, theoretically, noncompetitive immunoassay format is more sensitive and has a wider analytical range. In the present study, a novel hapten of halofuginone was synthesized and used to produce a monoclonal antibody (mAb). By analyzing the binding kinetics, we found that the affinity of analyte-enzyme to mAb was much greater than that of analyte, which could result in a low sensitivity of competitive assay format. Based on this, we established a novel noncompetitive immunoassay by using a replacement approach. The noncompetitive format has obvious advantages in sensitivity and analytical range, which promoted approximately 3.5- and 5-fold, respectively, compared to the competitive immunoassay. Ultimately, the newly designed noncompetitive immunoassay in this work will provide insights as well as alternative method to traditional small molecule competitive assays.

Development and validation of a multi-residue liquid chromatography-tandem mass spectrometry confirmatory method for eleven coccidiostats in eggs

A confirmatory method for the determination of residues of eleven coccidiostats including ionophore antibiotics: lasalocid, maduramycin, monensin, narasin, salinomycin, semduramycin and chemical coccidiostats: decoquinate, diclazuril, halofuginone, nicarbazin and robenidine in poultry eggs was developed and validated. The sample was extracted with acetonitrile, defatted with hexane and cleaned-up on a silica SPE cartridge. The analytes were identified and quantified by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The method performance characteristics required by Commission Decision 2002/657/EC were estimated adopting a more flexible and simple validation design. In this alternative approach the experimental study focuses on a larger dynamic range with progressively increasing validation levels. Each of them presents equal concentrations of all the analytes. On the contrary the classical Decision plan investigates a restricted concentration range necessarily different for each analyte being determined by the individual permitted limit (0.5-1.5 times the permitted limit). As a consequence each validation level involves the simultaneous fortification with complex mixtures containing different concentrations of each analyte. Adopting this alternative strategy the validation of several substances with significantly different permitted limits is considerably simplified and a deeper knowledge of the method is achieved. The results proved that the method enables the confirmation of regulated coccidiostats in eggs at the levels required in the official control of residues (CCα in the range of 2.2-174 μg kg(-1), depending on the coccidiostat). The repeatability (CV(r) in the range of 1.1-19%) and within-laboratory reproducibility (CV(Rw) in the range of 1.8-30%) are also acceptable. The procedure was successfully verified in the proficiency test and implemented in the national residue control plan.

Light-chain shuffling from an antigen-biased phage pool allows 185-fold improvement of an anti-halofuginone single-chain variable fragment

Halofuginone is an antiprotozoal drug used in the treatment of coccidiosis in poultry, a contagious enteric disease caused by parasites of the Eimeria spp. To ensure that food is free from any halofuginone residues and safe for human consumption, a rapid method to detect these residues below the maximum residue limits (MRLs) in a variety of matrices is necessary. To address this need, we constructed an immune single-chain variable fragment (scFv) library from the RNA of a halofuginone-immunized chicken and selected halofuginone-specific scFv by phage display. The best clone isolated from the library had a limit of detection of 30 ng/ml as determined by enzyme-linked immunosorbent assay (ELISA). However, the minimum MRL for halofuginone in certain foodstuffs can be as low as 1 ng/ml, well below the sensitivity of the selected antibody. The selected antibody was then affinity maturated by light-chain shuffling to further improve the antibody's assay performance. The halofuginone-specific heavy-chain pool of the biopanned library was assembled with the light-chain repertoire amplified from the original prepanned library. This resulted in a heavy-chain-biased library from which an scFv with the potential to detect halofuginone residues as low as 80 pg/ml was isolated, a 185-fold improvement over the original scFv. This new chain-shuffled scFv was incorporated into a validated ELISA (according to Commission Regulation 2002/657/EC) for the sensitive detection of halofuginone in spiked processed egg samples.

Comparison of time-resolved fluoroimmunoassay for determining hexoestrol residues in chicken muscle tissues based on polyclonal antibodies with liquid chromatography and tandem mass spectrometry

A time-resolved fluoroimmunoassay (TR-FIA) was developed for the determination of hexoestrol (HES) residues in animal tissues. The limit of detection (LOD) was determined to be 0.02 ng g(-1) and the limit of quantification (LOQ) was less than 0.12 ng g(-1). The results obtained by the TR-FIA and ELISA showed a good correlation. The established TR-FIA was validated for the determination of market chicken muscle tissues and confirmed by high-performance liquid chromatography and tandem mass spectrometry (LC-MS-MS). This proposed technique could be applied to routine residue analysis.

Time-resolved fluoroimmunoassay for ractopamine in swine tissue

This study describes the development and validation of a time-resolved fluoroimmunoassay (TR-FIA) for screening ractopamine (RAC) in swine tissue. The method is based on the direct competitive-type immunoassay using europium-labeled anti-RAC monoclonal antibody as a tracer and RAC-ovalbumin as a solid-phase antigen. When RAC was spiked at levels of 1-10 microg kg(-1), recoveries ranged from 88.2 to 118.5% for swine liver and muscle with coefficients of variation from 7.1 to 20.5%. The detection limit was 0.1 microg kg(-1). The proposed TR-FIA method was applied to the determination of RAC in an actual residue study and the applicability was confirmed by liquid chromatography-tandem mass spectrometry.

A monoclonal antibody-based time-resolved fluoroimmunoassay for chloramphenicol in shrimp and chicken muscle

A time-resolved fluoroimmunoassay (TR-FIA) for determination of chloramphenicol (CAP) in shrimp and chicken muscle was developed. The method was based on a direct competitive immunoassay using europium-labeled anti-CAP monoclonal antibody (MAb) and CAP-ovalbumin as coated antigen. The limit of detection was 0.05 ng g(-1) and limit of quantification was 0.1 ng g(-1). Recoveries ranged from 101.2 to 112.5% for shrimp and 104.9 to 115.3% for chicken muscle at spiked levels of 0.1-5 ng g(-1), with intra-assay and inter-assay variations 8.7-14.6 and 9.6-17.8%, respectively. The results obtained by the TR-FIA and ELISA correlated well. The established TR-FIA was validated for the determination of incurred shrimp samples and confirmed by gas chromatography with microcell electron capture detector (GC-microECD).