Development of Time-Resolved Fluorescence Immunochromatographic Assays for Simultaneously Detecting Tylosin and Tilmicosin in Milk in Group-Screening Manner

Designing a size exclusion-based hapten and the development of a quantitative and visual time-resolved fluorescence immunochromatography assay strip for detecting dimethomorph and flumorph in a group-specific manner

Based on the size and surface properties of dimethomorph and flumorph, we used a computer simulation-assisted size exclusion hapten design strategy to develop group-specific monoclonal antibodies that can simultaneously recognize dimethomorph and flumorph. For this, we performed quantitative and visual semi-quantitative time-resolved fluorescence immunochromatography (TRFICA) to simultaneously detect dimethomorph and flumorph in potatoes and apples. In potato samples, the visual limit of detection (vLOD) for dimethomorph and flumorph was 4 ng/mL and 8 ng/mL, respectively, whereas the quantitative limit of detection (qLOD) for dimethomorph and flumorph was 0.26 and 0.33 ng/mL, respectively. The vLOD of dimethomorph and flumorph in apple samples was 8 ng/mL, whereas the qLOD of dimethomorph and flumorph was 0.17 and 0.38 ng/mL, respectively. The average recovery of potato and apple samples ranged from 77.5% to 121.7%, which indicated that the method can be used to rapidly detect dimethomorph and flumorph in food samples.

Development of a monoclonal antibody-based time-resolved fluorescence immunochromatographic assay strip for sensitively detecting florfenicol residues in milk and eggs: Theoretical chemical insights into unexpected high specificity

Florfenicol (FF), with its broad-spectrum antibacterial activity, is frequently abused in the livestock and poultry industries and has aroused the growing public concern. Owing to structural similarities and varying maximum residue limits between florfenicol and other chloramphenicol (CAP)-type antibiotics, including thiamphenicol (TAP) and chloramphenicol (CAP), there is an urgent need for a rapid and effective immunoassay method to distinguish them, in order to minimize the risk of false positives. Fortunately, a highly specific monoclonal antibody (mAb), named as SF11, has been developed using hybridoma technology. Molecular simulations have revealed that the mAb SF11's specificity in recognizing florfenicol stems from the π-π stacking interaction between florfenicol and the mAb SF11 binding pocket. Using this highly specific mAb, a sensitive time-resolved fluorescence immunochromatographic assay (TRFICA) strip for rapid florfenicol detection has been developed. Under optimal conditions, this TRFICA demonstrated good analytical performance for the detection of florfenicol in milk and eggs samples, with the half-maximal inhibition concentration (IC50) values of 1.89 and 2.86 ng mL-1, the limit of detection (LOD) of 0.23 and 0.48 ng mL-1, the cut-off values of 62.50 and 31.25 ng mL-1, and the testing time of approximately thirteen minutes. Spiked recoveries in the milk and eggs samples ranged from 104.7 % to 112.3 % and 95.3 % to 116.4 %, respectively, with no obvious cross-reactions with the other analogues observed. The TRFICA results correlated well with those of high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) for real samples, indicating that the developed TRFICA method was sensitive, accurate and adapted for the rapid determination of florfenicol in milk and egg samples.

Lateral Flow Immunoassay Based on Time-Resolved Fluorescence Microspheres for Rapid and Quantitative Screening CA199 in Human Serum

Carbohydrate antigen 199 (CA199) is a serum biomarker which has certain value and significance in the diagnosis, prognosis, treatment, and postoperative monitoring of cancer. In this study, a lateral flow immunoassay based on europium (III) polystyrene time-resolved fluorescence microspheres (TRFM-based LFIA), integrated with a portable fluorescence reader, has been successfully establish for rapid and quantitative analysis of CA199 in human serum. Briefly, time-resolved fluorescence microspheres (TRFMs) were conjugated with antibody I (Ab1) against CA199 as detection probes, and antibody II (Ab2) was coated as capture element, and a “TRFMs-Ab1-CA199-Ab2” sandwich format would form when CA199 was detected by the TRFM-based LFIA. Under the optimal parameters, the detection limit of the TRFM-based LFIA for visible quantitation with the help of an ultraviolet light was 4.125 U/mL, which was four times lower than that of LFIA based on gold nanoparticles. Additionally, the fluorescence ratio is well linearly correlated with the CA199 concentration (0.00–66.0 U/mL) and logarithmic concentration (66.0–264.0 U/mL) for quantitative detection. Serum samples from 10 healthy people and 10 liver cancer patients were tested to confirm the performances of the point-of-care application of the TRFM-based LFIA, 20.0 U/mL of CA199 in human serum was defined as the threshold for distinguishing healthy people from liver cancer patients with an accuracy of about 60%. The establishment of TRFM-based LFIA will provide a sensitive, convenient, and efficient technical support for rapid screening of CA199 in cancer diagnosis and prognosis.

Immunochromatographic assays based on three kinds of nanoparticles for the rapid and highly sensitive detection of tylosin and tilmicosin in eggs

Three kinds of immunochromatographic assays (ICAs) are proposed for the highly sensitive and rapid determination  of tylosin (TYL) and tilmicosin (TIM) in eggs based on colloidal gold (CG), latex microsphere (LM), and time-resolved fluorescent microsphere (TRFM). Three types of ICAs could tolerate the egg matrix via simple sample pretreatment and demonstrated high sensitivity for TYL and TIM with cut-off values of 6/6/3 μg/kg and 14/14/6 μg/kg, respectively. Furthermore, in a single-blind parallel study 20 egg samples were analyzed  by the three developed ICAs and confirmed by LC-MS/MS. The  results showed good consistency, and there were no false positive and false negative results in our three ICAs. Consequently, the proposed three ICAs offered rapid, highly sensitive, reliable, and selectable testing platforms for screening veterinary medicine or other small molecule contaminants.