Application of Nanogoid Probe Coupled with Silver Enhancement in Rapid cTnI Colorimetric Immunoassay

A rapid, inexpensive, reliable, and flexible quantitative immunoassay for cardiac troponin I （cTnI） based on the concepts of one-step dual monoclonal antibody “sandwich” principle. The low density protein array, the nanogold probe, and the silver enhancement on the gold particle were provided. The whole detection procedure of the assay could be fulfilled within 40 min with the pretreated colloidal gold-labeled detection antibody and supporting substrate. The assay showed good specific response to cTnI with very low cross-reactivity ratio to the skeletal isoforms of troponin I （sTnI）, cardiac troponin T （cTnT）, and myoglobin. 588 serum samples were assayed simultaneously by enzyme-linked immuno sorbent assay （ELISA） and this colloidal gold method to test the validity of the method and the data were analyzed using the statistical package SPSS version 11.0 （SPSS Inc.）. There was no significant difference between these two assays （P=0.66〉0.05）. The agreement between this method （〉 or 〈0.3 ng/mL） and ELISA was 86%.

Electrochemical Metalloimmunoassay Based on Enlargement of Gold Nanoparticle Label Treated with Ag Enhancement System

A novel sensitive electrochemical immunoassay with colloidal gold as the antibody labeling tag and subsequent signal amplification by silver enhancement is described. Colloidal gold was treated by a light-sensitive silver enhancement system which made silver deposit on the surface of colloidal gold(form Au/Ag core-shell structure), followed by the release of the metallic silver atoms anchored on the antibody by oxidative dissolution of them in an acidic solution and the indirect determination of the dissolved Ag + ions by anodic stripping voltammetry(ASV) at a carbon fiber microelectrode. The electrochemical signal is directly proportional to the amount of analyte(goat IgG) in the standard or a sample. The method was evaluated by means of a noncompetitive heterogeneous immunoassay of immunoglobulin G(IgG) with a concentration as low as 0.2 ng/mL. The high performance of the method is related to the sensitive ASV determination of silver(Ⅰ) at a carbon fiber microelectrode and to the release of a large number of Ag + ions from each silver shell anchored on the analyte(goat IgG).

EFFECT OF SOLVENT ON SURFACE ENHANCED RAMAN SCATTERING SPECTRA OF COLLOIDAL SILVER

The effect of solvent on surface enhanced Raman scattering [SERS) of colloidal silver has been studied. Experiments show that the intensity of SERS is related to the polarity and molecular constitution of the solvent. The influence of solvent is due to the change of the adsorption quantity and adsorption intensity.

THE CHARACTERIZATION OF SILVER SUBCOLLOID USED IN SURFACE ENHANCED RAMAN SPECTROSCOPY

A clear light-yellow silver sol which has the visible spectral absorption at 390 nm, when adsorbed phenylmercaptotetrazole(PMT) or mercaptobenzothiazole(MBT), has a new absorption at 510-550 nm. It was found that the adsorption of halide ions competes with PMT and MBT. However, halide ions have a completely different influence from PMT and MBT on the spectral absorption of the silver sol. The differences may result from the change of the properties of the surface of the silver subcolloidal particles and from the bond forms combining adsorbates with the substrates.

SURFACE ENHANCED RAMAN SPECTRA OF PHENYLMERCAPTOTETRAZOLE AND MERCAPTOBENZOTHIAZOLE ON SILVER

Normal Haman Spectra(NRS) of solid PMT (1-phenyl-5-mercaptotetrazole) and MBT (2-mercaptobenzothiazole) and their surface enhanced Raman spectra (SERS) adsorbed on the surface of the silver subcolloidal particles are reported and compared. It is supposed that PMT adsorbed on silver with both N and S atoms whereas MBT may be adsorbed on silver through S atom.

Hierarchical Nanogold Labels to Improve the Sensitivity of Lateral Flow Immunoassay

Lateral flow immunoassay(LFIA) is a widely used express method and offers advantages such as a short analysis time, simplicity of testing and result evaluation.However, an LFIA based on gold nanospheres lacks the desired sensitivity, thereby limiting its wide applications.In this study, spherical nanogold labels along with new types of nanogold labels such as gold nanopopcorns and nanostars were prepared, characterized, and applied for LFIA of model protein antigen procalcitonin. It was found that the label with a structure close to spherical provided more uniform distribution of specific antibodies on its surface, indicative of its suitability for this type of analysis.LFIA using gold nanopopcorns as a label allowed procalcitonin detection over a linear range of 0.5–10 ng mL^(-1) with the limit of detection of 0.1 ng mL^(-1), which was fivefold higher than the sensitivity of the assay with gold nanospheres. Another approach to improve the sensitivity of the assay included the silver enhancement method,which was used to compare the amplification of LFIA for procalcitonin detection. The sensitivity of procalcitonin determination by this method was 10 times better the sensitivity of the conventional LFIA with gold nanosphere as a label. The proposed approach of LFIA based on gold nanopopcorns improved the detection sensitivity without additional steps and prevented the increased consumption of specific reagents(antibodies).

Microanalysis of silver jewellery by laser-ablation laser-induced breakdown spectroscopy with enhanced sensitivity and minimal sample ablation

Laser-ablation laser-induced breakdown spectroscopy （LA-LIBS） based on single Nd：YAG laser is used to analyze copper impurity in silver jewellery with enhanced sensitivity and minimal sample ablation. 6-30 folds signal enhancement can be achieved under the re-excitation of the breakdown laser and the spatial resolution is only determined by the ablation laser. 50 ppm limit of detection of copper is achieved when the crater diameter is 17.2 μm under current experimental condition. This technique gives higher analysis sensitivity under the same sample ablation in comparison with single pulse （SP） LIBS. It is useful for high sensitive element mieroanalvsis of precious samples.