A solid-phase dot assay using silica/gold nanoshells

The usage of phage mini-antibodies as a means of detecting ferritin concentration in animal blood serum

Mini-antibodies that have specific ferritin response have been produced for the first time using sheep's phage libraries (Griffin.1, Medical Research Council, Cambridge, UK). Produced phage antibodies were used for the first time for the development of diagnostic test kits for ferritin detection in the blood of cattle. The immunodot assay with secondary biospecific labeling is suggested as means of ferritin detection in cow blood serum (antiferritin phage antibodies and rabbit antiphage antibodies conjugated with different labels). Сolloidal gold, gold nanoshells, and horse reddish peroxidase used as labels have shown a similar response while detecting concentration of ferritin (0.2 mg/mL). It is shown that the method of solid-phase immunoassay with a visual view of the results allows determination of the minimum concentration of ferritin in the blood of cows at 0.225 g/mL.

Gold nanoparticles in biomedical applications: recent advances and perspectives

Gold nanoparticles (GNPs) with controlled geometrical, optical, and surface chemical properties are the subject of intensive studies and applications in biology and medicine. To date, the ever increasing diversity of published examples has included genomics and biosensorics, immunoassays and clinical chemistry, photothermolysis of cancer cells and tumors, targeted delivery of drugs and antigens, and optical bioimaging of cells and tissues with state-of-the-art nanophotonic detection systems. This critical review is focused on the application of GNP conjugates to biomedical diagnostics and analytics, photothermal and photodynamic therapies, and delivery of target molecules. Distinct from other published reviews, we present a summary of the immunological properties of GNPs. For each of the above topics, the basic principles, recent advances, and current challenges are discussed (508 references).

Quantitative cell bioimaging using gold-nanoshell conjugates and phage antibodies

The authors describe a quantitative evaluation of the efficacy of cell labeling with plasmon-resonant light-scattering nanoparticles used as contrast agents for dark-field microscopy imaging. The experimental model is based on the biospecific labeling of pig embryo kidney (SPEV) cells with primary phage antibodies, followed by the dark-field microscopic visualization using conjugates of silica/gold nanoshells with secondary rabbit antiphage antibodies. To quantify nanoparticle binding, the authors introduce the labeling-efficacy factor (LEF) which is equal to the ratio of the bound-particle pixels per cell to the total number of pixels occupied by the cell. The LEF is calculated by an imaging-analysis algorithm based on the freely available ImageJ Java-based processing code. In terms of the LEF, a distinct difference was found between intact, nonspecifically labeled, and biospecifically labeled cells.

Template Route to Chemically Engineering Cavities at Nanoscale: A Case Study of Zn(OH)(2) Template

A size-controlled Zn(OH)(2) template is used as a case study to explain the chemical strategy that can be executed to chemically engineering various nanoscale cavities. Zn(OH)(2) octahedron with 8 vertices and 14 edges is fabricated via a low temperature solution route. The size can be tuned from 1 to 30 μm by changing the reaction conditions. Two methods can be selected for the hollow process without loss of the original shape of Zn(OH)(2) template. Ion-replacement reaction is suitable for fabrication of hollow sulfides based on the solubility difference between Zn(OH)(2) and products. Controlled chemical deposition is utilized to coat an oxide layer on the surface of Zn(OH)(2) template. The abundant hydroxyl groups on Zn(OH)(2) afford strong coordination ability with cations and help to the coating of a shell layer. The rudimental Zn(OH)(2) core is eliminated with ammonia solution. In addition, ZnO-based heterostructures possessing better chemical or physical properties can also be prepared via this unique templating process. Room-temperature photoluminescence spectra of the heterostructures and hollow structures are also shown to study their optical properties.

Fabrication of color changeable polystyrene spheres decorated by gold nanoparticles and their label-free biosensing

A novel and simple method for gold nanoshell synthesis with controllable core and shell sizes is reported here. A new 'tree-shape' surfactant bis(amidoethyl-carbamoylethyl) octadecylamine (C18N3) was synthesized and used as the glue for the fast combination of gold nanoparticles and the subsequent gold shell outside. The functionalized polystyrene (PS) cores were covered by a surfactant (PS@C18N3) bilayer. The presence of the surfactant double layer played the role of 'glue' in this method, so that upon controlling the amount of surfactant, it was possible to achieve: the manipulation of gold seed density on the PS@C18N3 spheres, the preparation of PS@Au hybrid structures, and a red-shift in the extinction absorption from 520 to 750 nm. Besides, the as-prepared PS@Au composites supported on a glass substrate exhibited excellent effectiveness in the molecular recognition of human-immunoglobulin G (h-IgG) and goat anti-human-immunoglobulin G (goat anti-h-IgG), showing a rapid response within 20 min with a low detection limit of 10 ng ml(-1). This demonstrates that PS@Au prepared and assembled using our method is potentially useful as a nanosensor platform for immunoassay.

Nanometer Sized Silver Particles Embedded Silica Particles-Spray Method

Spherical shaped, nanometer to micro meter sized silica particles were prepared in a homogeneous nature by spray technique. Silver nanoparticles were produced over the surface of the silica grains in a harmonized manner. The size of silver and silica particles was effectively controlled by the precursors and catalysts. The electrostatic repulsion among the silica spheres and the electro static attraction between silica spheres and silver particles make the synchronized structure of the synthesized particles and the morphological images are revealed by transmission electron microscope. The silver ions are reduced by sodium borohydride. Infra red spectroscopy and X-ray photoelectron spectroscopy analysis confirm the formation of silver-silica composite particles. Thermal stability of the prepared particles obtained from thermal analysis ensures its higher temperature applications. The resultant silver embedded silica particles can be easily suspended in diverse solvents and would be useful for variety of applications.

Enhanced solid-phase immunoassay using gold nanoshells: effect of nanoparticle optical properties

Plasmon-resonant nanoparticle-labeled immunoassays provide a simple, low-cost and effective way of detecting target molecules in solutions. The optical mechanisms behind their efficiency, however, have not been addressed until now. We present the first theoretical description of nanoparticle-labeled dot immunoassay and its experimental verification with functionalized 15 nm colloidal gold nanospheres and silica/gold nanoshells (GNs). Three types of GNs, with silica core diameters of 100, 140 and 180 nm and a gold shell thickness of about 15 nm, were studied in our experiments. The fabricated markers were characterized by electron and atomic-force microscopy, UV-vis spectroscopy and dynamic light scattering. A normal rabbit serum (the target IgG molecules) and sheep antirabbit antibodies (the probing molecules) were used as a biospecific model. The minimal detection limit for IgG target molecules was about 15 ng in the case of a standard dot-assay protocol based on 15 nm colloidal gold particles conjugated with probing molecules. In contrast to this observation, a simple replacement of 15 nm gold labels by GN conjugates resulted in a drastic increase in detection sensitivity of up to 0.25 ng in the case of 180/15 nm GNs and of up to 0.5-1 ng for 100/15 and 140/15 GNs. By using the theory developed, we explained the dependences of the low detection limit, the maximal-color intensity and the probe-load saturation limit on the particle parameters.

Determination of the size, concentration, and refractive index of silica nanoparticles from turbidity spectra

The size and concentration of silica cores determine the size and concentration of silica/gold nanoshells in final preparations. Until now, the concentration of silica/gold nanoshells with Stober's silica core has been evaluated through the material balance assumption. Here, we describe a method for simultaneous determination of the average size and concentration of silica nanospheres from turbidity spectra measured within the 400-600 nm spectral band. As the refractive index of silica nanoparticles is the key input parameter for optical determination of their concentration, we propose an optical method and provide experimental data on a direct determination of the refractive index of silica particles n = 1.475 +/- 0.005. Finally, we exemplify our method by determining the particle size and concentration for 10 samples and compare the results with transmission electron microscopy (TEM), atomic force microscopy (AFM), and dynamic light scattering data.