Inter-laboratory studies for the evaluation of ELISA kits for the detection of chloramphenicol residues in milk and muscle

Sensitive immunoenzyme assay for the detection of antibiotic flumequine in honey

Fluoroquinolone antibiotics are used to cure and protect bees and apiaries from infections. Consequently, they may contaminate honey and other products of beekeeping. In this study, a highly sensitive immunoenzyme assay (EIA) was for the first time developed for the determination of a fluoroquinolone flumequine (FLU) in honey. The EIA was carried out in an indirect competitive format with colorimetric detection. The analysis was characterized by a low limit of detection of 30 pg mL-1. The polyclonal antibodies used showed no cross-reactivity with 24 other (fluoro)quinolones; the assay was highly specific only toward FLU. Different coating FLU-protein conjugates were tested to achieve the most sensitive competitive immunodetection. A highly simplified and rapid (3-5 min) sample preparation was proposed based on the 100-300 times dilution of honey by a buffer. The developed EIA has been tested to detect FLU in honey of different origins, namely acacia, flower, buckwheat, chestnut, and linden honey. It has been demonstrated that 76.2-115.9% of FLU could be determined by the assay. The versatility, simplicity, and rapidity of the EIA enable us to propose this method as an effective tool to control the contamination of honey.

Pretreatment-Integration for Milk Protein Removal and Device-Facilitated Immunochromatographic Assay for 17 Items

Accurate and comprehensive immunochromatographic assay (ICA) data are urgently required in the daily supervision of plants, schools, testing institutions, and law-enforcing departments. Through pretreatment-integration and device-facilitated operation, a quantitative ICA with high sensitivity and throughput was realized on the basis of a commercialized semi-quantitative ICA strip. Three pretreatment methods, namely, acid base, heavy metal salt, and organic solvent methods, have less than three steps. The pretreatment was established for protein removal. A total of 17 pretreated ICA items in milk were considered for the identification of the most suitable pretreatment method. The items are composed of six items pretreated by the acid-base method, six by the heavy salt method, and five by the organic solvent method. Then, the ICA results with pretreatment were compared with those without pretreatment. After pretreatment, the signal intensity increased by 39%, the detection limit decreased to 12%, the half maximal inhibitory concentration decreased to 18%, and the detection range increased fourfold. A device with mixing and centrifugation functions was designed for the pretreatment-related operations. A pre-incubation sampling device was used to facilitate incubation in batch and high-throughput detection. An ICA reader was used. The detection throughput reached 8 samples per batch or 32 samples per hour. The designed devices were printed through 3D printing and rapid prototyping.

Flexible freestanding graphene paper-based potentiometric enzymatic aptasensor for ultrasensitive wireless detection of kanamycin

Flexible sensing devices have drawn tremendous attention in the past decades due to their potential applications in future hand-held, potable consumer, and wearable electronics. Here, we firstly developed an ultrasensitive wireless potentiometric aptasensor based on flexible freestanding graphene paper for kanamycin detection. Flexible graphene paper made from a simple vacuum filtration method was used as a biocompatible platform for effective immobilization of aptamer. A nuclease-assisted amplification strategy was introduced into this potentiometric biosensing system in order to significantly improve the detection sensitivity through a classic catalytic recycling reaction of target induced by the nuclease (DNase I). As expected, an ultra-low detection limit of 30.0 fg/mL for kanamycin was achieved. Furthermore, the developed potentiometric enzymatic aptasensor exhibits high selectivity, favorable flexibility, excellent stability and reproducibility, which holds great promising for its routine sensing application.

Development of in-house ELISA for detection of chloramphenicol in bovine milk with subsequent confirmatory analysis by LC-MS/MS

This study was undertaken to develop and validate direct competitive ELISA for the determination of chloramphenicol residues in bovine milk. Antisera and an enzyme-tracer for chloramphenicol were prepared and used to develop an ELISA with inhibition concentrations, IC₂₀ and IC₅₀, of 0.09 and 0.44 ng mL^-1, respectively. Milk samples were spiked with standards equivalent to 0, 0.2, 0.3, 0.5, 1.0 & 1.5 ng mL^-1 and extracted in methanol. The mean recoveries were found to be 73-100% with coefficient of variance 7-11%. The decision limit (CCα) and detection capability (CCβ) were calculated as 0.10 and 0.12 ng mL^-1, respectively. The results were found comparable with the commercial ELISA, having recoveries of 87 to 100%, CCα 0.09 ng mL^-1 and CCβ 0.12 ng mL^-1. As per Commission Decision 2002/657/EC, in-house ELISA was further validated by using LC-MS/MS. Mass spectral acquisition was done by using electrospray ionization in the negative ion mode applying single reaction monitoring of the diagnostic transition reaction for CAP (m/z 152, 194 and 257). The calibration curve showed good linearity in concentrations from 0.025 to 1.6 ng mL^-1 with correction coefficient 0.9902. The mean recoveries were found to be 88 to 100%. The CCα was calculated as 0.057 ng mL^-1 and CCβ 0.10 ng mL^-1. Since CCα and CCβ are less than half of the MRPL (0.15 ng mL^-1), the test was found suitable for screening and quantification of CAP residues in bovine milk samples. Results of surveillance studies indicated that out of 31 analyzed milk samples, 12.9% samples were found with CAP residues but only 3.2% samples were declared positive with maximum concentration 0.31 ng mL^-1, slightly above the MRPL.

Simultaneous determination of chloramphenicol and aflatoxin M1 residues in milk by triple quadrupole liquid chromatography-tandem mass spectrometry

A reliable, rapid, and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for simultaneous determination of chloramphenicol and aflatoxin M(1) in milk has been developed. This method includes simple extraction of sample with acetonitrile, separation on a MGIII-C(18) column using 5 mM ammonium acetate aqueous solution/methanol (60:40, v/v) as mobile phase, and MS/MS detection using multiple reaction monitoring mode. The method was validated according to Commission Decision 2002/657/EC. The limits of detection (LODs) were 0.05 μg/kg for chloramphenicol and 0.005 μg/kg for aflatoxin M(1.) The limits of quantification (LOQs) were 0.2 μg/kg for chloramphenicol and 0.02 μg/kg for aflatoxin M(1). The recovery values ranged from 88.8% to 100.6%, with relative standard deviation lower than 15% in all cases, when samples were fortified at three different concentrations. The decision limits (CCα) and detection capability (CCβ) of the method were also reported. This method has been successfully applied for simultaneous analysis of chloramphenicol and aflatoxin M(1) residues in milk from local supermarkets in China.

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).