Xuelan Chen

Quantum-DoT submicrobead-based immunochromatographic assay for quantitative and sensitive detection of zearalenone

Mycotoxin pollutants are commonly related to cereal products and cause fatal threats in food safety, and therefore require simple and sensitive detection. In this work, quantum-dot (QD) submicrobeads (QBs) were synthesized by encapsulating CdSe/ZnS QDs using the microemulsion technique. The resultant QBs, with approximately 2800 times brighter luminescence than the corresponding QDs, were explored as novel fluorescent probes in the immunochromatographic assay (ICA) for sensitive and quantitative detection of zearalenone (ZEN) in corns. Various parameters that influenced the sensitivity and stability of QB-based ICA (QB-ICA) were investigated and optimized. The optimal QB-ICA exhibits good dynamic linear detection for ZEN over the range of 0.125 ng/mL to 10 ng/mL with a median inhibitory concentration of 1.01±0.09 ng/mL (n=3). The detection limits for ZEN in a standard solution and real corn sample (dilution ratio of 1:30) are 0.0625 ng/mL and 3.6 µg/kg, respectively, which is much better than that of a previously reported gold nanoparticle-based ICA method. Forty-six natural corn samples are assayed using both QB-ICA and enzyme-linked immunosorbent assay. The two methods show a highly significant correlation (R(2)=0.92). Nine ZEN-contaminated samples were further confirmed with liquid chromatography-tandem mass spectrometry (LC-MS/MS), and the QB-ICA results also exhibited good agreement with LC-MS/MS method. In brief, this work demonstrates that QB-ICA is capable of rapid, sensitive screening of toxins in food analysis, and shows great promise for point-of-care testing of other analytes.

Ru(phen)32+ doped silica nanoparticle based immunochromatographic strip for rapid quantitative detection of β-agonist residues in swine urine

A Ru(phen)3(2+) doped silica nanoparticle based immunochromatographic strip was developed for the rapid and quantitative detection of five common β-agonist (salbutamol (SAL), cimbuterol, terbutaline, clenbuterol, and brombuterol) residues in swine urine. The broad spectrum monoclonal antibodies generated by immunizing BALB/c mice with salbutamol conjugated cationic bovine serum albumin. The fluorescence intensities (FIs) of the strip on the test line (FIT) and control line (FIC) were determined using a strip reader. Parameters that influenced the antibody and antigen interaction on the test strip were investigated by recording FIT and FIC values, and the concept of FIT/FIC ratio was used to offset the inherent heterogeneity of the test strips and the effect of the sample matrix. Under optimal conditions, the linear range for the quantitative detection of SAL was 0.6-5.0 ng/ml with a half maximal inhibitory concentration at 1.78 ng/ml. The limit of detection for real swine urine was 0.43 ng/ml. The recovery rates of the intraassay for spiked urine at SAL concentrations of 0.8, 1.5, and 3.5 ng/mL were 88.06%±3.75%, 95.77%±5.33%, and 94.06%±7.43%, whereas those for the interassay were 84.69%±5.0%, 95.06%±9.3%, and 88.34%±7.71%, respectively. The developed quantitative method exhibited excellent agreement with a commercially available competitive enzyme-linked immunosorbent assay kit for SAL-spiked urine samples, with a correlation of coefficient of 0.95 and a slope of 0.99 (n=36). The results indicated that the developed test strip enables sensitive, reproducible, and easily implementable screening for the rapid and quantitative detection of β-agonist residues in swine urine.

Monoclonal antibody-based enzyme-linked immunosorbent assay for detection of total malachite green and crystal violet residues in fishery products

A rapid easy-to-use trace level direct competitive enzyme-linked immunosorbent assay (dc-ELISA) detection of total residual malachite green (MG), crystal violet (CV) and their corresponding primary metabolites leucomalachite green (LMG) and leucocrystal violet (LCV) in fishery products in a single assay was developed. The monoclonal antibodies, anti-MG and anti-CV mAbs, were prepared using carboxyl-malachite green (CMG) and cationized bovine serum albumin (cBSA) conjugates as immunogen. The linear range for the quantitative detection of total MG, CV and their primary metabolites LMG and LCV was between 0.15 to 4.5 ng mL−1 with a half maximal inhibitory concentration (IC50) at 0.56 ± 0.04 ng mL−1 (n = 5). The anti-MG mAbs exhibited 98% cross-reactivity to CV, less than 0.1% cross-reactivity with LMG and LCV, and no cross-reactivity with chloramphenicol, enrofloxacin, sulfadiazine, and tetracycline. Application of the dc-ELISA in fish tissue samples gave a limit of detection (LOD) of 0.37 ng g−1. The improved total detection lead to a recovery of 74.60 ± 8.38% at 0.5 ng g−1 and 87.47 ± 12.83% at 2.0 ng g−1 that was better than existing techniques. The dc-ELISA showed total MG in 7 out of 44 field fish samples that were confirmed with LC-MS/MS. The easy-to-use, inexpensive, and rapid dc-ELISA for the detection of total MG, CV and their corresponding primary metabolites holds promise for field applications.

A sensitive chromatographic strip test for the rapid detection of enrofloxacin in chicken muscle

A sensitive colloidal gold immunochromatography assay using a specific monoclonal antibody was developed for the rapid detection of enrofloxacin (ENR) residues in chicken muscles. Anti‐ENR antibodies with high sensitivity and specificity are generated by immunising BALB/c mice with well‐characterised ENR‐bovine serum albumin conjugate. An orthogonal L9(3)3 test was designed, and various parameters that influenced the assay performance were investigated and optimised. Under the optimised conditions, the cut‐off limits of semi‐quantitative test strips for ENR were found to be 3 ng/mL in phosphate‐buffered saline and 8 µg/kg in chicken muscle. The ENR test strips showed a 6% cross‐reactivity with ciprofloxacin, 3% with norfloxacin, less than 1% with ofloxacin and sarafloxacin and 0.1% with the other eight fluoroquinolones including enoxacin, difloxacin, danofloxacin, pefloxacin, lomefloxacin, sparfloxacin, oxolinic acid and flumequine. Consistent results are produced from the parallel analysis of ENR‐contaminated chicken muscle extracts using test strips and ELISA.