Gold immunochromatographic assay for trimethoprim in milk and honey samples based on a heterogenous monoclonal antibody

Development of an Open Droplet Microchannel-Based Magnetosensor for Immunofluorometric Assay of Trimethoprim in Chicken and Pork Samples with a Wide Linear Range

Trimethoprim (TMP), functioning as a synergistic antibacterial agent, is utilized in diagnosing and treating diseases affecting livestock and poultry. Human consumption of the medication indirectly may lead to its drug accumulation in the body and increase drug resistance due to its prolonged metabolic duration in livestock and poultry, presenting significant health hazards. Most reported immunoassay techniques, such as ELISA and immunochromatographic assay (ICA), find it challenging to achieve the dual advantages of high sensitivity, simplicity of operation, and a wide detection range. Consequently, an open droplet microchannel-based magnetosensor for immunofluorometric assay (OMM-IFA) of trimethoprim was created, featuring a gel imager to provide a signal output derived from the highly specific antibody (Ab) targeting trimethoprim. The method exhibited high sensitivity in chicken and pork samples, with LODs of 0.300 and 0.017 ng/mL, respectively, and a wide linear range, covering trimethoprim's total maximum residue limits (MRLs). Additionally, the spiked recoveries in chicken and pork specimens varied between 81.6% and 107.9%, maintaining an acceptable variation coefficient below 15%, aligning well with the findings from the ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) technique. The developed method achieved a much wider linear range of about 5 orders of magnitude of 10-2-103 levels with grayscale signals as the output signal, which exhibited high sensitivity, excellent applicability and simple operability based on magnetic automation.

A simple and rapid immunochromatography test based on readily available filter paper modified with chitosan to screen for 13 sulfonamides in milk

In this study, we developed a novel, simple, rapid, and low-cost colloidal gold-based immunochromatography method, with filter paper replacing nitrocellulose membrane as the substrate. To obtain adequately immobilized protein, chitosan was used to functionalize the filter paper. After conditions and parameters were optimized, the novel immunochromatography method was applied for detection of sulfonamide residues in milk. Quantitative detection was accomplished using a smartphone and Photoshop software (Adobe Inc., San Jose, CA), allowing us to screen 13 sulfonamides with a limit of detection ranging from 0.42 to 8.64 μg/L and recovery ranging from 88.2 to 116.9% in milk. The proposed novel method performed similarly to the conventional method that uses a nitrocellulose membrane as the transport medium, and it had lower cost and better usability because of the inexpensive and easily available filter paper.

Influence of Small Molecular Property on Antibody Response

Antibodies with high titer and affinity to small molecules are critical in the field of vaccines against drugs of abuse, antidotes to toxins, and immunoassays for compounds. However, little is known regarding how properties of small molecules have influence and which molecular descriptors could indicate the degree of the antibody response. On the basis of our previous study, we designed and synthesized two groups of hapten molecules with varied hydrophobicity to investigate the relationship between the properties of the small molecules and the antibody response in terms of titer and affinity. We found that the magnitude of the antibody response was positively correlated with the degree of molecular hydrophobicity and related descriptors. This study provides insight into the immunological characteristics of small molecules themselves and useful clues to produce high-quality antibodies against small molecules.

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.

Generic Hapten Synthesis, Broad-Specificity Monoclonal Antibodies Preparation, and Ultrasensitive ELISA for Five Antibacterial Synergists in Chicken and Milk

An antibody with broad specificity and principally depending on hapten structure and size is a key reagent for developing a class-selective immunoassay. In the present study, three new generic haptens of antibacterial synergists (ASGs) were proposed using trimethoprim as the starting molecule. These haptens contained carboxyl groups on the meta position of trimethoxybenzene for conjugating to protein, while, the common moiety of ASGs, i.e., diaminopyrimidine, was intentionally and maximally exposed to the immune system in animals in order to induce antibodies with broad specificity against ASGs. Five monoclonal antibodies (mAbs) were finally obtained, and 5C4 from the hapten with a short spacer arm, named Hapten A, showed not only uniform broad specificity but also high affinity to all five ASGs. We further determined the possible recognition mechanism of mAbs in terms of conformational and electronic aspects. An indirect competitive ELISA (icELISA)-based 5C4 was established and exhibited IC₅₀ values of 0.067-0.139 μg L^-1 with cross-reactivity of 48.2%-418.7% for the five ASGs in buffer under optimal conditions. The calculated limits of detection of the icELISA for chicken and milk were 0.06-0.8 μg kg^-1 and 0.05-0.6 μg L^-1, respectively. The recoveries in spiked chicken and milk samples were 75.2%-101.4% with a coefficient of variation less than 14.3%. In summary, we have developed, for the first time, a rapid and reliable icELISA for ASGs with significantly improved sensitivity and class selectivity.