Preparation of colloidal gold probes

Development and comparison of immunochromatographic strips with three nanomaterial labels: Colloidal gold, nanogold-polyaniline-nanogold microspheres (GPGs) and colloidal carbon for visual detection of salbutamol

In this study, the three nanomaterials: colloidal gold, nanogold-polyaniline-nanogold microspheres (GPGs) and colloidal carbon were respectively labeled with the antibody against salbutamol (SAL). We aimed to develop immunochromatographic strips with these nanomaterial labels and determine their performance in visual detection of SAL. For the colloidal gold-based strip, the detection limit of SAL was 1.0µgL(-1) in standard solution and 5.0µgkg(-1) in meat samples. For the GPG- and colloidal carbon-based strips, the limit of detection was 2.0µgL(-1) in standard solution and 10µgkg(-1) in meat samples. The results obtained using the test strips were found to be highly consistent with those obtained using a commercial kit, indicating the high accuracy of these strips. The three strips were also found to be stable up to 18 weeks under laboratory conditions. In terms of sensitivity, the colloidal gold-based strip was slightly better than the other two. For the GPG- and colloidal carbon-based strips, the difference between the results obtained for different batches was small (high consistency), and the stability was much better than that of the colloidal gold-based one. Our results indicate that colloidal carbon can be used as a label in immunochromatographic tests; it can also help reduce the cost involved and scale-up the production. The use of immunochromatographic test strips labeled with colloidal carbon can be a rapid and inexpensive method for SAL assays in on-site 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.

The role of Xgrip210 in gamma-tubulin ring complex assembly and centrosome recruitment

The gamma-tubulin ring complex (gammaTuRC), purified from the cytoplasm of vertebrate and invertebrate cells, is a microtubule nucleator in vitro. Structural studies have shown that gammaTuRC is a structure shaped like a lock-washer and topped with a cap. Microtubules are thought to nucleate from the uncapped side of the gammaTuRC. Consequently, the cap structure of the gammaTuRC is distal to the base of the microtubules, giving the end of the microtubule the shape of a pointed cap. Here, we report the cloning and characterization of a new subunit of Xenopus gammaTuRC, Xgrip210. We show that Xgrip210 is a conserved centrosomal protein that is essential for the formation of gammaTuRC. Using immunogold labeling, we found that Xgrip210 is localized to the ends of microtubules nucleated by the gammaTuRC and that its localization is more distal, toward the tip of the gammaTuRC-cap structure, than that of gamma-tubulin. Immunodepletion of Xgrip210 blocks not only the assembly of the gammaTuRC, but also the recruitment of gamma-tubulin and its interacting protein, Xgrip109, to the centrosome. These results suggest that Xgrip210 is a component of the gammaTuRC cap structure that is required for the assembly of the gammaTuRC.

Immunostructural evidence for the template mechanism of microtubule nucleation

Two opposing models have been proposed to explain how the gamma-tubulin ring complex (gammaTuRC) induces microtubule nucleation. In the 'protofilament' model, the gammaTuRC induces nucleation as a partially or completely straightened protofilament that is incorporated longitudinally into the wall of the nascent microtubule, whereas the 'template' model proposes that the gammaTuRC acts as a helical template that constitutes the base of the newly-formed polymer. Here we appraise these two models, using high-resolution structural and immunolocalization methods. We show that components of the gammaTuRC localize to a narrow zone at the extreme minus end of the microtubule and that these ends terminate in a pointed cap. Together, these results strongly favour the template model of microtubule nucleation.