N. G. Khlebtsov

Laser-induced tissue hyperthermia mediated by gold nanoparticles: toward cancer phototherapy

We describe an application of plasmonic silica/gold nanoshells to produce a controllable laser hyperthermia in tissues with the aim of the enhancement of cancer photothermal therapy. Laser irradiation parameters are optimized on the basis of preliminary experimental studies using a test-tube phantom and laboratory rats. Temperature distributions on the animal skin surface at hypodermic and intramuscular injection of gold nanoparticle suspensions and affectations by the laser radiation are measured in vivo with a thermal imaging system. The results of temperature measurements are compared with tissue histology.

Photoacoustic flow cytometry: principle and application for real-time detection of circulating single nanoparticles, pathogens, and contrast dyes in vivo

The goal of this work is to develop in vivo photoacoustic (PA) flow cytometry (PAFC) for time-resolved detection of circulating absorbing objects, either without labeling or with nanoparticles as PA labels. This study represents the first attempt, to our knowledge, to demonstrate the capability of PAFC with tunable near-infrared (NIR) pulse lasers for real-time monitoring of gold nanorods, Staphylococcus aureus and Escherichia coli labeled with carbon nanotubes (CNTs), and contrast dye Lymphazurin in the microvessels of mouse and rat ears and mesenteries. PAFC shows the unprecedented threshold sensitivity in vivo as one gold nanoparticle in the irradiated volume and as one bacterium in the background of 10(8) of normal blood cells. The CNTs are demonstrated to serve as excellent new NIR high-PA contrast agents. Fast Lymphazurin diffusion in live tissue is observed with rapid blue coloring of a whole animal body. The enhancement of the thermal and acoustic effects is obtained with clustered, multilayer, and exploded nanoparticles. This novel combination of PA microscopy/spectroscopy and flow cytometry may be considered as a new powerful tool in biological research with the potential of quick translation to humans, providing ultrasensitive diagnostics of pathogens (e.g., bacteria, viruses, fungi, protozoa, parasites, helminthes), metastatic, infected, inflamed, stem, and dendritic cells, and pharmacokinetics of drug, liposomes, and nanoparticles in deep vessels (with focused transducers) among other potential applications.

Optical Properties and Biomedical Applications of Nanostructures Based on Gold and Silver Bioconjugates

We discuss optical properties of single and aggregated colloidal gold and silver conjugates that can be fabricated by adsorption of a biopolymer onto nanoparticle surfaces. We start with a discussion of two-layer and multilayer optical models for colloidal gold and silver nanoparticle conjugates that consist of a metal core and a polymer shell formed by recognizing and target molecules. The point at issue is the core-size optimization of conjugate-based nanosensors as elementary transducers of molecular binding events into optical signals. We present a detailed discussion of optical properties of various aggregated conjugate-based structures such as bispheres, linear chains, plane arrays on a rectangular lattice, compact and porous clusters embedded on a cubic body-centerd lattice, and random fractal aggregates. Our attention is focused on the following topics: (1) statistical and orientation averaging of optical observables; (2) dependence of extinction and scattering spectra on the optical binary coupling of conjugates; (3) optical effects related to the chain-like structures; (4) effects of polymer coating, interparticle spacing, and cluster structure; (5) simulation of kinetic changes in the optical properties of aggregated sols formed during biospecific binding. Finally, we discuss experimental data and biomedical applications of metal nanoparticles and their biospecific conjugates in various biomedical studies.

Silver nanocubes and gold nanocages: Fabrication and optical and photothermal properties

The paper presents experimental data on fabrication, optical, and photothermal properties of silver nanocubes and gold-silver nanostructures based on silver cube templates. The silver cubes were obtained using polyol synthesis with a sulfide-mediated reduction of silver nitrate by ethylene glycol in the presence of poly(vinyl pyrrolidone). A galvanic replacement method was used to fabricate gold-silver nanoparticles of various structures, starting from silver-gold alloy particles and ending by target gold nanocages. The gold nanocages formation was controlled by shifts of the extinction and differential light scattering plasmon resonances, the transmission and scanning electron microscopy, the electronic-spectroscopy analysis (ESI), the dark-field microscope light scattering, and by visual inspection of colloid colors. The comparative experimental data on the laser heating kinetics are presented for three particle types: gold nanorods, silica/gold nanoshells, and gold nanocages. For suspensions with equal optical density at the laser heating wavelength (near plasmon resonances at 800 nm), all three particle types revealed close photothermal parameters. However, the specific photothermal efficiency per metal particle mass was maximal for gold nanocages followed by gold nanorods and silica/gold nanoshells. A coupled dipole spheres method was used to calculate the extinction and absorption spectra of randomly oriented particles by an analytical solution for random orientation averaging. The nanoparticles were modeled by arrays of interacting spheres with small intersection and polarizability calculated through the first Mie coefficient. The measured and calculated extinction spectra of silver cubes and gold nanocages are in good agreement.

Study of polyol synthesis reaction parameters controlling high yield of silver nanocubes

The influence of the parameters and conditions of sodium sulfide-induced reaction of polyol synthesis of silver nanoparticles on the yield of cube-shaped particles and the optical properties of colloids is studied. The protocol proposed by Skrabalak et al. for the synthesis of nanocubes in small volumes (Nature Protocols, 2007, vol. 2, p. 2182) is taken as an initial variant for optimization. The effects of the reagent concentrations, degree of ethylene glycol oxygenation, the presence of impurities, reaction time, and temperature are studied. Suspensions containing nanoparticles with different shapes and sizes, including polydisperse particles of irregular shapes, silver nanocubes with a yield of 0 to 97%, nanoprisms, and nanorods, can be produced by varying the synthesis parameters. The key parameters controlling the yield of nanocubes are the degree of ethylene glycol oxygenation and the presence of trace amounts of ions of other metals (not silver). It is established that variations in the reaction time make it possible to vary the sizes of nanocubes in the range of 30–60 nm. Suspensions with high contents of cube-shaped particles are shown to exhibit three maxima in the plasmon extinction resonance spectrum at wavelengths of 350, 390, and, depending on the particle size, 435–470 nm.

Anisotropic properties of plasmonic nanoparticles: depolarized light scattering, dichroism, and birefringence

The properties of gold and silver nanorods and nanodisks with geometric parameters typical of wet chemical fabrication protocols were investigated. With an extended-precision T-matrix code, a representative set of simulations for extinction, light scattering, and depolarization ratio spectra of randomly oriented particles and for dichroism and birefringence spectra of particles with an arbitrary predominant orientation with respect to incident linearly polarized light were obtained. The appearance of ultra-depolarized light scattering from random ensembles was elucidated by several 3D maps illustrating the dependence of the depolarization ratio on particular orientations of rods and disks. A simple dipole model sufficed to explain the orientation dependence of dichroism and birefringence and the unusual invariant spectral localization of the depolarization ratio maxima. Reasonable agreement was obtained with experimental data on depolarized light scattering from gold nanorods.

Penetration of Pegylated Gold Nanoparticles Through Rat Placental Barrier

Penetration of pegylated (enveloped in polyethylene glycol) gold nanoparticles 5 and 30 nm in diameter through the placental barrier was studied in pregnant rats injected intravenously with these particles in a dose of about 0.8 mg Au/kg on day 10 of gestation. The particles were visualized in tissues by silver nitrate autometallography; the total content of gold in the fetuses was evaluated by atomic adsorption spectroscopy. Gold nanoparticles were detected in the fetal liver macrophages and in the spleens; high total content of gold in the fetuses was demonstrated for particles of both sizes. The data suggest that gold nanoparticles penetrate through rat placental barrier in vivo. No morphological changes were detected in the liver, kidneys, spleen, and brain of fetuses.

Attenuation, scattering, and depolarization of light by gold nanorods with silver shells

Gold nanoparticles with silver nanoshells are obtained by synthesizing gold nanorods in a growing solution containing cetyltrimethylammonium bromide, subsequent separation in a concentration gradient of glycerol, and reduction of silver nitrate by ascorbic acid under alkaline conditions in the presence of polyvinylpyrrolidone. The formation of silver nanoshells was monitored by the shift of plasmon resonances of extinction and differential light scattering, by the appearance of characteristics peaks of silver in the energy dispersive X-ray (EDX) spectra of samples, by the data of transmission electron microscopy, and by visual changes in the color of colloids. The spectrum of the intensity ratio of the co- and cross-polarized compo- nents of light scattered by gold-silver nanorods is measured for the first time, and it is observed that the maximum is shifted by 80–100 nm compared to previously published spectra of gold nanorods (Khlebtsov et al., J. Phys. Chem. C 112, 12760 (2008)). The extinction and light scattering spectra are calculated by the method of separation of variables using the model of a confocal two-layer spheroid and these calculations are found to agree with spectral measurements. A method for determining the thickness of a silver nanolayer by the spectral shift of an extinction longitudinal resonance is described. The obtained data of optical spectroscopy and transmission electron microscopy and estimations of the mass of the deposited metal show that the aver-age thickness of the silver layer varies from 0.12 to 4 nm as the Ag/Au ratio changes from 2/80 to 90/80 μg/μg.

Biodistribution and toxicity of gold nanoparticles

This paper reviews data on the biodistribution and toxicity of five types of gold nanoparticles (GNPs) (atomic clusters and colloidal particles with diameters of 1 to 200 nm, gold nanorods (GNRs), silica/gold nanoshells (GNSs), hollow GNSs, and nanowires) in in vivo and in vitro experiments. Published data from 1995 to March 2010 are systematized according to the types and parameters of particles, their surface functionalization, models (cell or animal), examined organs, applied doses, administration routes, duration of experiments, and methods used for assessing the toxicity and concentration of GNPs in organs and their distribution between cells. A critical analysis of the data suggests some general conclusions on the key parameters of nanoparticles; methods for modifying their surface; and the doses that determine the type and kinetics of biodistribution, cytotoxicity, and toxicity at the body level.

Surface-enhanced raman scattering platforms on the basis of assembled gold nanorods

This study investigates the surface-enhanced Raman scattering (SERS) of rhodamine 6G (R6G) on the surface of gold nanorods (GNRs) assembled on silicon. Two samples of GNRs were synthesized, notably, GNR-670 and GNR-810, with the average (length × thickness) dimensions of 64 × 23 and 45 × 11 nm and with plasmon resonances at 670 and 810 nm, respectively. Three types of substrates were fabricated, namely, a low-density monolayer (S1), a densely packed monolayer with regions of the side-by-side assembly of nanorods (S2), and a fractal film (S3). The extinction spectra of densely packed substrates showed the appearance of new maxima and the broadening and the red-shift of plasmon resonances, as was consistent with the typical behavior of plasmonic particles interacting at an interparticle distance of about 1–3 nm (data of transmission electron microscopy). The intensities of SERS peaks of the rhodamine 6G increased for substrates S1, S2, and S3 as 1: 6: 260, respectively. There was no significant difference in the SERS efficiency of the substrates based on GNR-670 and GNR-810 rods. The average enhancement of the signal over an area of 400 μm was about 105 with a reproducibility error of ±10%, thus making the obtained substrates promising platforms for sensitive SERS chemical and biological sensors.