Vitaly Khanadeev

Analytical and Theranostic Applications of Gold Nanoparticles and Multifunctional Nanocomposites

Gold nanoparticles (GNPs) and GNP-based multifunctional nanocomposites are the subject of intensive studies and biomedical applications. This minireview summarizes our recent efforts in analytical and theranostic applications of engineered GNPs and nanocomposites by using plasmonic properties of GNPs and various optical techniques. Specifically, we consider analytical biosensing; visualization and bioimaging of bacterial, mammalian, and plant cells; photodynamic treatment of pathogenic bacteria; and photothermal therapy of xenografted tumors. In addition to recently published reports, we discuss new data on dot immunoassay diagnostics of mycobacteria, multiplexed immunoelectron microscopy analysis of Azospirillum brasilense, materno-embryonic transfer of GNPs in pregnant rats, and combined photodynamic and photothermal treatment of rat xenografted tumors with gold nanorods covered by a mesoporous silica shell doped with hematoporphyrin.

Nanocomposites Containing Silica-Coated Gold–Silver Nanocages and Yb–2,4-Dimethoxyhematoporphyrin: Multifunctional Capability of IR-Luminescence Detection, Photosensitization, and Photothermolysis

We describe novel composite nanoparticles consisting of a gold-silver nanocage core and a mesoporous silica shell functionalized with the photodynamic sensitizer Yb-2,4-dimethoxyhematoporphyrin (Yb-HP). In addition to the long-wavelength plasmon resonance near 750-800 nm, the composite particles exhibited a 400-nm absorbance peak and two fluorescence peaks, near 580 and 630 nm, corresponding to bound Yb-HP. The fabricated nanocomposites generated singlet oxygen under 630-nm excitation and produced heat under laser irradiation at the plasmon resonance wavelength (750-800 nm). In particular, we observed enhanced killing of HeLa cells incubated with nanocomposites and irradiated by 630-nm light. Furthermore, an additional advantage of fabricated conjugates was an IR-luminescence band (900-1060 nm), originating from Yb(3+) ions of bound Yb-HP and located in the long-wavelength part of the tissue transparency window. This modality was used to control the accumulation and biodistribution of composite particles in mice bearing Ehrlich carcinoma tumors in a comparative study with intravenously injected free Yb-HP molecules. Thus, these multifunctional nanocomposites seem an attractive theranostic platform for simultaneous IR-luminescence diagnostic and photodynamic therapy owing to Yb-HP and for plasmonic photothermal therapy owing to Au-Ag nanocages.

Gold nanorods with a hematoporphyrin-loaded silica shell for dual-modality photodynamic and photothermal treatment of tumors in vivo

AbstractNanocomposites (NCs) consisting of a gold nanorod core and a mesoporous silica shell doped with hematoporphyrin (HP) have been fabricated in order to improve the efficiency of cancer treatment by combining photothermal and photodynamic therapies (PDT + PTT) in vivo. In addition to the long-wavelength plasmon resonance near 810–830 nm, the fabricated NCs exhibited a 400-nm absorbance peak corresponding to bound HP, generated singlet oxygen under 633-nm excitation near the 632.5-nm Q-band, and produced heat under a 808-nm near-infrared (NIR) laser irradiation. These modalities were used for a combined PDT + PTT treatment of large (about 3 cm3) solid tumors in vivo with a xenorafted tumor rat model. NCs were directly injected into tumors and irradiated simultaneously with 633-nm and 808-nm lasers to stimulate the combined photodynamic and photothermal activities of NCs. The efficiency of the combined therapy was evaluated by optical coherence tomography, histological analysis, and by measurements of the tumor volume growth during a 21-day period. The NC-mediated PDT led to weak changes in tissue histology and to a moderate 20% decrease in the tumor volume. In contrast, the combined PDT + PTT treatment resulted in the large-area tumor necrosis and led to dramatic decrease in the tumor volume.

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 Stobers 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.

Gold nanoisland films as reproducible SERS substrates for highly sensitive detection of fungicides.

A wet-chemical approach is used to fabricate centimeter-scale gold nanoisland films (NIFs) with tunable morphology of islands and with strong electromagnetic coupling between them. The approach consists in a uniform seeding of small gold nanoparticles on a glass or silicon substrate, followed by controllable growth of the seeds into small nanoislands. A special technique for TEM sampling was developed to follow the gradual formation of larger-sized isolated nanoparticles, nanoislands of sintered overgrown seeds, and a complete gold layer with nanoscale cracks. The electromagnetic field distribution inside the fabricated NIFs was calculated by FDTD simulations applied to actual TEM images of the fabricated samples rather than to artificial models commonly used. SERS measurements with 1,4-aminothiophenol (ATP) molecules demonstrated the analytical enhancement factor about of 10(7) and the fundamental enhancement factor about of 10(8) for optimized substrates. These values were at least 1 order of magnitude higher than that for self-assembled arrays of gold nanostars and silver nanocubes. SERS spectra of independent samples demonstrated good sample-to-sample reproducibility in terms of the relative standard deviation (RSD) of the main peaks less than 20%. Additionally, Raman maps with 1 μm increment in X-Y directions of NIFs (800 spectral spots) demonstrated good point-to-point repeatability in the intensity of the main Raman vibration modes (RSD varied from 5% to 15% for 50 randomly selected points). A real-life application of the fabricated SERS substrates is exemplified by the detection of the thiram fungicide in apple peels within the 5-250 ppb linear detection range. Specifically, the NIF-based SERS technology detected thiram on apple peel down to level of 5 ng/cm(2).

Overgrowth of gold nanorods by using a binary surfactant mixture.

Seed-mediated surfactant-assisted growth is widely used as the most effective method for gold nanorod (NR) synthesis. Using prepared nanorods as seeds for further overgrowth can increase the dimensional tunability of the final particles. However, overgrowth in usual cetyltrimethylammonium bromide (CTAB) surfactant solutions leads to poor control of the final particle shape and size. In this work, we report an improved strategy to demonstrate the controllable overgrowth of gold NRs in the binary surfactant mixture sodium oleate (NaOL) + CTAB. This approach overcomes the difficulty of growing NR suspensions with small amounts of impurities. By controlling the total amount of added NR seeds, it is possible to tune the average length, diameter, and plasmon resonances of overgrown particles in a wide range. Together with the original NaOL + CTAB method developed by Murray and co-workers ( Nano Lett. 2013 , 13 , 555 ), this overgrowth approach expands the dimensional and plasmonic tunability of the fabrication technology without any decrease in the monodispersity and purity of samples.

Enhanced photoinactivation of Staphylococcus aureus with nanocomposites containing plasmonic particles and hematoporphyrin.

We fabricated composite nanoparticles consisting of a plasmonic core (gold nanorods or gold-silver nanocages) and a hematoporphyrin-doped silica shell. The dual photodynamic and photothermal activities of such nanoparticles against Staphylococcus aureus 209 P were studied and compared with the activities of reference solutions (hematoporphyrin or silica-coated plasmonic nanoparticles). Bacteria were incubated with nanocomposites or with the reference solutions for 15 min, which was followed by CW light irradiation with a few exposures of 5 to 30 min. To stimulate the photodynamic and photothermal activities of the nanocomposites, we used LEDs (405 and 625 nm) and a NIR laser (808 nm), respectively. We observed enhanced inactivation of S. aureus 209 P by nanocomposites in comparison with the reference solutions. By using fluorescence microscopy and spectroscopy, we explain the enhanced antimicrobial effect of hematoporphyrin-doped nanocomposites by their selective accumulation in the vicinity of the bacteria.

Tunable depolarized light scattering from gold and gold/silver nanorods

We combine the fabrication of Au and Au/Ag core/shell nanorods (NRs), as well as experimental measurements of vis-NIR extinction, unpolarized, and cross-polarized light scattering spectra, with T-matrix and separation-of-variables simulations, to gain insight into the relation between the morphology/composition of nanoparticles and their isotropic and anisotropic optical responses. Using several Au and Au/Ag core/shell NR samples, we present unambiguous experimental evidence of a tunable correlation between the longitudinal plasmon resonances of NRs and their spectral depolarization maxima. For gold NRs, the depolarization maxima follow the extinction plasmon resonances blue-shifted from 80 to 270 nm. In contrast, the depolarization maximum of Au/Ag NRs is located just near the longitudinal resonance, and the spectral shift of the depolarization maximum is about 10 to 20 nm. The experimental extinction and depolarization spectra of gold NRs are in good agreement with T-matrix simulations based on TEM-fitted models that account for the aspect ratio polydispersity and byproduct contributions. For composite Au/Ag NRs, the separation-of-variables simulations provide a calibration curve that correlates the relative spectral shift of the extinction resonance with the silver shell thicknesses and generates experimental data that are in good agreement with estimations based on the Ag/Au mass ratio.

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.

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.