Development of an indirect competitive ELISA for simultaneous detection of enrofloxacin and ciprofloxacin

Development of a Sensitive Monoclonal Antibody-Based Colloidal Gold Immunochromatographic Strip for Lomefloxacin Detection in Meat Products

Lomefloxacin (LOM), an antibiotic crucial for preventing various animal diseases in animal husbandry, can pose serious health risks when found in excessive amounts in meat products. The development of highly specific and sensitive colloidal gold immunochromatographic test strips is essential for the accurate detection of this class of antibiotics. Our study utilized a monoclonal antibody (mAb) assay and immunochromatographic strips to detect lomefloxacin residues in meat products. The results showed minimal cross-reactivity with other structural analogs, with a maximum half inhibitory concentration (IC50) of 0.93 ng/mL and a linear range of 0.38 to 2.3 ng/mL for the indirect competitive enzyme-linked immunosorbent assay (ic-ELISA). The recovery of LOM was 80% to 120%, with an average coefficient of variation below 5%. The immunochromatographic strip test results showed a visual detection limit of 2.5 ng/g, meeting the market requirements for the test. This study highlights the significance of specific and sensitive testing methods for detecting lomefloxacin, ensuring consumers' safety and health.

Development of a highly sensitive immunoassay for detecting aminopyrine abuse in herbal tea

With the popularity of herbal tea in China, many food fraudsters have added illegal drugs to herbal tea to enhance its functions, among which aminopyrine is widely abused as an antipyretic and analgesic. Presently, there is no immunoassays for aminopyrine, and it is difficult to achieve real-time detection in the field. Based on a polyclonal antibody of aminopyrine with high specificity and sensitivity, an optimal combination of coating antigen/antibody was obtained by screening different coating antigens. On this basis, a sensitive ic-ELISA method was established to detect aminopyrine in herbal tea. The detection limit of the ic-ELISA was 0.18 ng mL^-1, which was much lower than the 100 ng mL^-1 required as a standard. The method had good consistency with LC-MS in the detection of actual samples and could be used as a reliable method for the detection of aminopyrine in herbal tea.

Immunoinformatics Design and Assessment of a Multiepitope Antigen (OvMCBL02) for Onchocerciasis Diagnosis and Monitoring

Onchocerciasis is a Neglected Tropical Disease that has a significant socioeconomic impact, especially in Sub-Saharan Africa. Numerous reports indicate that the Expanded Special Project for the Elimination of Neglected Tropical Diseases needs novel diagnostic tools before achieving its goal of successful elimination of onchocerciasis in Africa. The current diagnostic tests are either invasive, insensitive, or not applicable in the field and about 25% of persons infected cannot mount immune responses against the single antigen used in the only approved Ov-16 serological test. In the quest to identify novel biomarkers that can be used to certify that a patient is free from the disease, evaluate the progress of elimination programmes, and conduct post elimination surveillances, mass spectrometric analysis of Onchocerca volvulus crude extract revealed that 1392 proteins are expressed in the adult and microfilariae stages of the parasite. Computational analysis predicted six of the proteins as O. volvulus potential diagnostic targets. Linear B-epitopes were predicted from the six proteins and used to construct a multiepitope antigen (OvMCBL02). Serological analysis revealed that the OvMCBL02 test significantly differentiated between serum samples of onchocerciasis patients from the Kombone Health Area in the South West Region of Cameroon (n = 63) and control serum samples from Rwanda (n = 29) and Europe (n = 26) as well as between serum samples from the onchocerciasis hyperendemic region of Kombone Health Area (n = 63) and the hypoendemic region of Bandjoun Health District (n = 54). Interestingly, the test did not cross-react with serum samples from patients suffering from related nematode infections, thereby suggesting that further characterization of the OvMCBL02 multiepitope antigen will render it an additional member of the diagnostic toolbox for the elimination of onchocerciasis.

Development of a new dual electrochemical immunosensor for a rapid and sensitive detection of enrofloxacin in meat samples

A novel dual electrochemical immunosensor was fabricated for the rapid and sensitive detection of enrofloxacin (EF) antibiotic in meat. Anti-quinolone antibody was immobilized onto screen-printed dual carbon electrodes via carbodiimide coupling. A new electrochemical probe was synthesized by conjugating difloxacin and aminoferrocene, whose oxidation was measured at + 0.2 V vs. Ag/AgCl by differential pulse voltammetry. The detection principle was based on the competitive binding of this conjugate and free EF on immobilized antibodies. The proposed immunosensor allowed detection of EF at concentrations ranging from 0.005 µg.mL^-1 to 0.01 µg.mL^-1 with a detection limit of 0.003 µg.mL^-1. The immunosensor was stable for at least 1 month at 4 °C and displayed a good specificity for other fluoroquinolones. The new dual electrode design offered an improved accuracy as one electrode was used as negative control. The efficiency of the sensor and the adequacy of the extraction process were finally validated by detecting EF in different meat samples.

Immunochromatographic assays for ultrasensitive and high specific determination of enrofloxacin in milk, eggs, honey, and chicken meat

Enrofloxacin, a veterinary antibiotic that persists in food, poses a risk to human health. Here, a monoclonal antibody against enrofloxacin, 1H12, was prepared based on the hapten ENR-1, and showed excellent sensitivity with a 50% inhibitory concentration (IC₅₀) of 0.03 ng/mL. Using this antibody, 2 lateral-flow immunochromatographic assays were developed for determination of enrofloxacin in egg, milk, honey, and chicken meat samples. The detection ranges (IC₂₀-IC₈₀) were 0.16-0.82 ng/g, 0.24-1.8 ng/g, 0.25-3.6 ng/g, and 0.61-3.9 ng/g by colloidal gold-immunochromatographic sensor (CG-ICS) analysis, and 0.022-0.42 ng/g, 0.054-0.42 ng/g, 0.069-1.4 ng/g, and 0.19-2.2 ng/g by Eu-fluorescence-immunochromatographic sensor (EF-ICS) analysis. The intraassay and interassay recovery rates were 88.9 to 108.5% with coefficients of variation of 1.3 to 7.0% by CG-ICS analysis, and 88.6 to 113.6% with coefficients of variation of 1.3 to 8.1% by EF-ICS analysis. Thus, our newly developed ICS are sensitive and reliable, providing an option for rapid quantitative detection of enrofloxacin in food samples.

Preparation and Directed Evolution of Anti-Ciprofloxacin ScFv for Immunoassay in Animal-Derived Food

An immunized mouse phage display scFv library with a capacity of 3.34 × 10⁹ CFU/mL was constructed and used for screening of recombinant anti-ciprofloxacin single-chain antibody for the detection of ciprofloxacin (CIP) in animal-derived food. After four rounds of bio-panning, 25 positives were isolated and identified successfully. The highest positive scFv-22 was expressed in E. coli BL21. Then, its recognition mechanisms were studied using the molecular docking method. The result showed the amino acid residue Val160 was the key residue for the binding of scFv to CIP. Based on the results of virtual mutation, the scFv antibody was evolved by directional mutagenesis of contact amino acid residue Val160 to Ser. After the expression and purification, an indirect competitive enzyme-linked immunosorbent assay (IC-ELISA) based on the parental and mutant scFv was established for CIP, respectively. The IC50 value of the assay established with the ScFv mutant was 1.58 ng/mL, while the parental scFv was 26.23 ng/mL; this result showed highly increased affinity, with up to 16.6-fold improved sensitivity. The mean recovery for CIP ranged from 73.80% to 123.35%, with 10.46% relative standard deviation between the intra-assay and the inter-assay. The RSD values ranged between 1.49% and 9.81%. The results indicate that we obtained a highly sensitive anti-CIP scFv by the phage library construction and directional evolution, and the scFv-based IC-ELISA is suitable for the detection of CIP residue in animal-derived edible tissues.

Colorimetric detection of ciprofloxacin in aqueous solution based on an unmodified aptamer and the aggregation of gold nanoparticles

A colorimetric method is described for detection of the antibiotic ciprofloxacin (CIP) in aqueous solutions based on an unmodified CIP-aptamer and gold nanoparticles (AuNPs), which are regarded as a probe and an indicator, respectively. In the absence of CIP, aptamers can hybridize with poly dimethyl diallyl ammonium chloride (PDDA) to form a 'duplex' structure through electrostatic interactions, and AuNPs remain dispersed in solution, leading to a red solution and an obvious absorption peak at 520 nm. Contrarily, the CIP-aptamer can specifically bind to CIP after the introduction of CIP into the solution. Then PDDA is thus free to aggregate AuNPs. The solution turns blue from red accordingly, presenting a strong absorption at 650 nm. Hence, the concentration of CIP can be quantified through the changes of the absorption. This sensitive and selective colorimetric method for CIP detection has a good linear response (R = 0.9935) in the 20 to 300 nM CIP concentration range, with a limit of detection (LOD) of 0.215 nM. Importantly, the proposed aptasensor demonstrates great application potential in CIP determination in aqueous samples.

Fluorescence Polarization Immunoassay for Determination of Enrofloxacin in Pork Liver and Chicken

Enrofloxacin (ENR) is a widely used fluoroquinolone (FQ) antibiotic for antibacterial treatment of edible animal. In this study, a rapid and highly specific fluorescence polarization immunoassay (FPIA) was developed for monitoring ENR residues in animal foods. First, ENR was covalently coupled to bovine serum albumin (BSA) to produce specific polyclonal antibodies (pAbs). Three fluorescein-labeled ENR tracers (A, B, and C) with different spacers were synthesized and compared to obtain higher sensitivity. Tracer C with the longest arm showed the best sensitivity among the three tracers. The developed FPIA method showed an IC₅₀ (50% inhibitory concentration) of 21.49 ng·mL⁻¹ with a dynamic working range (IC₂₀–IC₈₀) of 4.30–107.46 ng·mL⁻¹ and a limit of detection (LOD, IC₁₀) of 1.68 ng·mL⁻¹. The cross-reactivity (CR) of several structurally related compounds was less than 2%. The recoveries of spiked pork liver and chicken samples varied from 91.3% to 112.9%, and the average coefficients of variation were less than 3.83% and 5.13%, respectively. The immunoassay took only 8 min excluding sample pretreatment. This indicated that the established method had high sensitivity, specificity, and the advantages of simplicity. Therefore, the proposed FPIA provided a useful screening method for the rapid detection of ENR residues in pork liver and chicken.

Rapid screening and quantification of multi-class antibiotic pollutants in water using a planar waveguide immunosensor

Antibiotics are commonly used in livestock-related agriculture and aquaculture, but they also remain in water and potentially threaten human health. Immunosensors are attractive tools for the rapid detection of antibiotics in water due to their high sensitivity and low costs. However, the simultaneous detection of multi-class antibiotics remains a challenge due to the limited number of detection sites on the immunochip. Also, matrix effects hinder the practical application of these sensors. This paper presents a method for multi-class antibiotic detection in real water using a planar waveguide immunosensor (PWI). We integrate the screening and quantitive detection sites on the same immunochip, and a single screening detection site could detect multi-class antibiotics from the same family, increasing the detection types of analytes. In addition, to eliminate the matrix effects, we develop a testing buffer for real water detection, so that complex pretreatments of the samples can be omitted. Using our sensor and testing buffer, we detect 14 different antibiotics in real water. Lincomycin can be detected with a detection limit of 0.01 μg L-1, and 13 quinolones can be screened in a single assay. These results demonstrate that this planar waveguide immunosensor is capable of simultaneous screening and quantification of multi-class antibiotic pollutants and is expected to be applied for practical environmental monitoring.

Four Hapten Spacer Sites Modulating Class Specificity: Nondirectional Multianalyte Immunoassay for 31 β-Agonists and Analogues

Immunoassay methods are important for monitoring β-agonists illegally used for reducing animal fat deposition in livestock. However, there is no simultaneous screening surveillance immunoassay for detecting various β-agonist chemicals that are possibly present in food. In this study, through the use of an R-(-)-salbutamol derivative as the immunizing hapten, an antibody recognizing 31 β-agonists and analogues was generated for the first time. Three-dimensional quantitative structure-activity relationship (3D QSAR) revealed that strong steric and hydrophobic fields around the hapten spacer near C-2, as well as a chirality at C-1', dominantly modulated the class specificity of the raised antibody. However, a hapten spacer linked at C-2' or C-1 would lead to a narrow specificity, and the spacer charge at C-6 could affect the raised antibody specificity spectrum. A class specificity competitive indirect enzyme-linked immunosorbent assay (ciELISA) was established with an ideal recovery ranging from 81.8 to 118.3% based on the obtained antibody. With a good agreement to the HPLC/MS method, the proposed ciELISA was confirmed to be reliable for the rapid surveillance screening assay of β-agonists in urine. This investigation will contribute to the rational design and control of the immunoassay specificity.

Simplified approach for in-vitro production and purification of cell derived Cancer Antigen 15-3

Cancer antigen 15-3 (CA15-3) is a key biomarker, currently used for understanding the onset and prognosis of breast cancer. In present investigation, CA15-3 has been purified from the culture supernatant of breast cancer T47-D cell line with 76% yield and 3350 fold purification. Isolated CA15-3 was analyzed by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE), immunoblotting (western blotting), chemiluminescence immunoassay (CLIA) and Fourier-transform infrared spectroscopy (FTIR). CA15-3 is a monomeric protein with an apparent molecular mass in between ∼250-350kDa. The FTIR spectroscopy revealed similar profiles of T47-D derived CA15-3 and commercially available CA15-3 protein. With the easy availability of T47-D cell line and a simple purification approach described here will support for the large scale production of CA15-3 to be used for various clinical and diagnostic applications.

Construction and sequencing analysis of scFv antibody fragment derived from monoclonal antibody against norfloxacin (Nor155)

Norfloxacin belongs to the group of fluoroquinolone antibiotics which has been approved for treatment in animals. However, its residues in animal products can pose adverse side effects to consumer. Therefore, detection of the residue in different food matrices must be concerned. In this study, a single chain variable fragment (scFv) that recognizes norfloxacin antibiotic was constructed. The cDNA was synthesized from total RNA of hybridoma cells against norfloxacin. Genes encoding VH and VL regions of monoclonal antibody against norfloxacin (Nor155) were amplified and size of VH and VL fragments was 402 bp and 363 bp, respectively. The scFv of Nor155 was constructed by an addition of (Gly4Ser)3 as a linker between VH and VL regions and subcloned into pPICZαA, an expression vector of Pichia pastoris. The sequence of scFv Nor155 (GenBank No. AJG06891.1) was confirmed by sequencing analysis. The complementarity determining regions (CDR) I, II, and III of VH and VL were specified by Kabat method. The obtained recombinant plasmid will be useful for production of scFv antibody against norfloxacin in P. pastoris and further engineer scFv antibody against fluoroquinolone antibiotics.

Four Specific Hapten Conformations Dominating Antibody Specificity: Quantitative Structure-Activity Relationship Analysis for Quinolone Immunoassay

Antibody-based immunoassay methods have been important tools for monitoring drug residues in animal foods. However, because of limited knowledge about the quantitative structure-activity relationships between a hapten and its resultant antibody specificity, antibody production with the desired specificity is still a huge challenge. In this study, the three-dimensional quantitative structure-activity relationship (3D QSAR) was analyzed in accordance with the cross-reactivity of quinolone drugs reacting with the antibody raised by pipemidic acid as the immunizing hapten and compared with the reported cross-reactivity data and their hapten structures. It was found that the specificity of a quinolone antibody was strongly related to the conformation of the hapten used and that hapten conformations shaped like the letters "I", "P", and "Φ" were essential for the desired high specificity with low cross-reactivity, but that the hapten conformation shaped like the letter "Y" led to an antibody with broad specificity and high cross-reactivity. Almost all of the antibodies against quinolones could result from these four hapten conformations. It was first found that the concrete conformations dominated the specificity of the antibody to quinolone, which will be of significance for the accurate hapten design, predictable antibody specificity, and better understanding the recognition mechanism between haptens and the antibodies for immunoassays.

Detecção de resíduos de enrofloxacina por ensaio imunoenzimático e cromatografia líquida acoplada à espectrometria de massas em ovos comerciais de galinha após tratamento

A enrofloxacina é um dos antimicrobianos mais utilizados na avicultura industrial, e a deposição de resíduos em produtos avícolas, como os ovos, são de grande importância para a saúde pública. Na legislação brasileira não existe padronização do período de carência para o seu uso na produção avícola e não há Limite Máximo de Resíduo (LMR) fixado para enrofloxacina em ovos. Neste estudo, foi utilizado o kit de ELISA comercial (Bioo Scientific(r)) e a LC-MS/MS na pesquisa de enrofloxacina em ovos de 30 galinhas tratadas previamente via água de bebida, com 10mg/kg de enrofloxacina, durante cinco dias. Seis ovos foram coletados diariamente e analisados durante o tratamento e após a sua suspensão, durante 15 dias. A deposição de resíduos obteve níveis máximos no quinto dia de tratamento das aves, declinando gradativamente até não ser detectada a partir do nono dia de suspensão do tratamento. Considerando como base o LMR de 100µg/kg fixado pelo Brasil para tecidos comestíveis de aves e pela União Europeia para músculo, gordura e pele, após seis dias de suspensão do tratamento, os níveis de resíduos foram inferiores a esse limite, tendo como médias 37,43µg/kg na LC-MS/MS e 14,731µg/kg no ELISA. Dentro das condições deste estudo, um período de carência de seis dias seria mais adequado para utilização dos ovos para consumo humano. Foram detectados valores de resíduos nos ovos menores no ELISA em relação à LC-MS/MS para a mesma amostra, mas os dois métodos apresentaram concordância estatística entre si. A LC-MS/MS é o teste recomendado pela legislação brasileira para a análise de resíduos em alimentos; entretanto, pelos resultados obtidos, o kit de ELISA utilizado também pode ser aplicado na detecção de resíduos de enrofloxacina em ovos, com as vantagens de rapidez e simplicidade.

Development of indirect competitive ELISA for quantification of mitragynine in Kratom (Mitragyna speciosa (Roxb.) Korth.)

Monoclonal antibody (MAb) against mitragynine (MG), an analgesic alkaloid from Kratom leaves (Mitragyna speciosa), was produced. MG was coupled to carrier proteins employing either 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide (EDC/NHS), a zero-length cross linker or a 5-carbon length glutaraldehyde cross linker. To confirm the immunogenicity, the hapten numbers were determined using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Preparation of the MAb was accomplished by the electrofusion method. Hybridoma 1A6 that was constructed from the fusion between splenocytes of EDC/NHS conjugate immunized mice and SP2/0-Ag14 myeloma cells was selected, cloned twice and expanded. The cross-reactivities (CRs) of this MAb 1A6 with a series of indole alkaloids were 30.54%, 24.83% and 8.63% for speciogynine, paynantheine and mitraciliatine, respectively. Using this MAb, an indirect competitive enzyme-linked immunosorbent assay (icELISA) was developed with a measurement range of 32.92-250 μg/mL. Quantitative analysis of the MG contents in plant samples by icELISA correlated well with the standard high performance liquid chromatography method (R(2)=0.994). The MAb against mitragynine provided a tool for detection of MG in Kratom preparations.

Optimization of condition for conjugation of enrofloxacin to enzymes in chemiluminescence enzyme immunoassay

In this study, in order to find out a proper method for conjugation of enrofloxacin to label enzymes, two methods were compared and carbodiimide condensation was proved to be better. The results showed that the binding ratio of enrofloxacin and alkaline phosphatase (ALP) was 8:1 and that of enrofloxacin and horseradish peroxidase (HRP) was 5:1. This indicated that conjugate synthesized by carbodiimide condensation was fit for chemiluminescence enzyme immunoassay (CLEIA). Furthermore, data revealed that dialysis time was an important parameter for conjugation and 6days was best. Buffer to dilute conjugate had little effect on CLEIA. The storage condition for conjugates was also studied and it was shown that the conjugate was stable at 4°C with no additive up to 30days. These data were valuable for establishing CLEIA to quantify enrofloxacin.

Development of an enzyme-linked immunosorbent assay for detection of chicken osteocalcin and its use in evaluation of perch effects on bone remodeling in caged White Leghorns

Osteocalcin (OC) is a sensitive biochemical marker for evaluating bone turnover in mammals. The role of avian OC is less clear because of the need for a chicken assay. Our objectives were to develop an assay using indirect competitive ELISA for detecting chicken serum OC and use the assay to examine the effects of perches on bone remodeling in caged hens. Anti-chicken OC polyclonal antibody was produced by immunization of rabbits with a recombinant OC from Escherichia coli. Chicken OC extracted from bone was used as a coated protein, and purified chicken OC was used for calibration. The limit of detection of the developed OC ELISA was 0.13 ng/mL. The intra- and interassay CV were <7 and <12%, respectively. The sensitivity of the developed OC ELISA was compared with a commercial Rat-Mid OC ELISA in laying hens housed in conventional cages with or without perches. Serum samples were collected from 71-wk-old White Leghorn hens subjected to 4 treatments. Treatment 1 was control chickens that never had access to perches during their life cycle. Treatment 2 chickens had perches during the pullet phase (0 to 16.9 wk of age), whereas treatment 3 chickens had perches only during the egg-laying phase of the life cycle (17 to 71 wk of age). Treatment 4 chickens always had access to perches (0 to 71 wk of age). Correlation between the 2 assays was 0.62 (P < 0.0001). Levels of serum OC using the developed chicken ELISA were higher than that detected using the Rat-Mid ELISA (P < 0.0001). Results from the chicken ELISA assay showed that hens with perch access had higher concentrations of serum OC than hens without perches during egg laying (P = 0.04). Pullet access to perches did not affect serum OC levels in 71-wk-old hens (P = 0.15). In conclusion, a chicken OC ELISA has been validated that is sensitive and accurate with adequate discriminatory power for measuring bone remodeling in chickens.

Fluorescent Ru(phen)3(2+)-doped silica nanoparticles-based ICTS sensor for quantitative detection of enrofloxacin residues in chicken meat

A Ru(phen)3(2+)-doped silica fluorescent nanoparticle (FN)-based immunochromatographic test strip (ICTS) sensor was developed for rapid, high sensitivity, easy to use, and low cost quantitative detection of enrofloxacin (ENR) residues in chicken meat. The fluorescence signal intensity of the FNs at the test line (FI(T)) and control line (FI(C)) was determined with a prototype of a portable fluorescent strip reader. Unique properties of Ru(phen)3(2+) doped silica nanoparticles (e.g., large Stokes shift, high emission quantum yield, and long fluorescence lifetime) were combined with the advantages of ICTS and an easy to make portable fluorescent strip reader. The signal was based on FI(T)/FI(C) ratio to effectively eliminate strip to strip variation and matrix effects. Various parameters that influenced the strip were investigated and optimized. Quantitative ENR detection with the FNs ICTS sensor using 80 μL sample took only 20 min, which is faster than the commercial ELISA kit (that took 90 min). The linear range of detection in chicken extract was established at 0.025-3.500 ng/mL with a half maximal inhibitory concentration at 0.22 ± 0.02 ng/mL. Using the optimized parameters, the limit of detection (LOD) for ENR using the FNs ICTS sensor was recorded at 0.02 ng/mL in chicken extract. This corresponds to 0.12 μg/kg chicken meat which is two (2) orders of magnitude better that the maximum residue limits (MRLs) imposed in Japan (10 μg/kg) and three (3) orders of magnitude better than those imposed in China. The intra- and inter-assay coefficient of variations (CVs) were 6.04% and 12.96% at 0.5 ng/mL, 6.92% and 12.61% at 1.0 ng/mL, and 6.66% and 11.88% at 2.0 ng/mL in chicken extract, respectively. The recoveries using the new FNs ICTS sensor from fifty (50) ENR-spiked chicken samples showed a highly significant correlation (R(2) = 0.9693) with the commercial enzyme-linked immunosorbent assay (ELISA) kit. The new FNs ICTS sensor is a simple, rapid, sensitive, accurate, and inexpensive quantitative detection of ENR residues in chicken meat and extracts.

Development of a class-specific polyclonal antibody-based indirect competitive ELISA for detecting fluoroquinolone residues in milk

Modified 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) method was employed to synthesize the artificial antigen of norfloxacin (NOR), and New Zealand rabbits were used to produce anti-NOR polyclonal antibody (pAb). Based on the checkerboard titration, an indirect competitive enzyme-linked immunosorbent assay (icELISA) standard curve was established. This assay was sensitive and had a working range from 0.12 to 68.40 ng/ml, with the half maximal inhibitory concentration (IC(50)) and limit of detection (LOD) values of 2.7 ng/ml and 0.06 ng/ml, respectively. The produced pAb exhibited high cross-reactivity to fluoroquinolones (FQs) tested, and the IC(50) values to enoxacin, ciprofloxacin, and pefloxacin were 3.1, 3.4, and 4.1 ng/ml, respectively. It also indicated that the concentrations of NaOH and methanol in assay buffer should not be higher than 10% and 30%. When spiked in milk at 5, 20, and 50 ng/ml, the recoveries for NOR, enoxacin, ciprofloxacin, and pefloxacin ranged 90.5%-98.0%, 84.0%-95.2%, 94.0%-106.0%, and 89.5%-100.0%, respectively. The results suggest that this class-specific pAb-based icELISA could be utilized for the primary screening of FQ residues in animal-original products.