Elizaveta V. Panfilova

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 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).

Plasmonic nanopowders for photothermal therapy of tumors.

We describe a novel strategy for the fabrication of plasmonic nanopowders (dried gold nanoparticles) by using wet chemical nanoparticle synthesis, PEG-SH functionalization, and a standard freeze-drying technique. Our strategy is illustrated by successful fabrication of different plasmonic nanopowders, including gold nanorods, gold-silver nanocages, and gold nanospheres. Importantly, the dried nanoparticles can be stored for a long time under usual conditions and then can easily be dissolved in water at a desired concentration without such hard manipulations as sonication or heating. Redispersed samples maintain the plasmonic properties of parent colloids and do not form aggregates. These properties make pegylated freeze-dried gold nanoparticles attractive candidates for plasmonic photothermal therapy in clinical settings. In this work, redispersed gold nanorods were intravenously administered to mice bearing Ehrlich carcinoma tumors at doses of 2 and 8 mg (Au)/kg (animal). Particle biodistribution was measured by atomic absorption spectroscopy, and tumor hyperthermia effects were studied under laser NIR irradiation. Significant tumor damage was observed only at the higher dose of the nanorods.

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.

Multiplexed dot immunoassay using Ag nanocubes, Au/Ag alloy nanoparticles, and Au/Ag nanocages

AbstractWe report the first application of Ag nanocubes, Au/Ag alloy nanoparticles, and Au/Ag nanocages in a multiplexed dot immunoassay. The assay principle is based on the staining of analyte drops on a nitrocellulose membrane strip by using multicolor nanoparticles conjugated with biospecific probing molecules. Nanoparticles were prepared by a galvanic replacement reaction between the Ag atoms of silver nanocubes and Au ions of tetrachloroauric acid. Depending on the Ag/Au conversion ratio, the particle plasmon resonance was tuned from 450 to 700 nm and the suspension color changed from yellow to blue. The particles of yellow, red, and blue suspensions were functionalized with chicken, rat, and mouse immuno gamma globulin (IgG) molecular probes, respectively. The multiplex capability of the assay was illustrated by a proof-of-concept experiment involving simultaneous one-step determination of target molecules (rabbit anti-chicken, anti-rat, and anti-mouse antibodies) with a mixture of fabricated conjugates. Under naked eye examination, no cross-colored spots or nonspecific bioconjugate adsorption were observed, and the low detection limit was about 20 fmol.

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.

Site-Selective Surface-Enhanced Raman Detection of Proteins

Strategies for protein detection via surface-enhanced Raman spectroscopy (SERS) currently exploit the formation of randomly generated hot spots at the interfaces of metal colloidal nanoparticles, which are clustered together by intrusive chemical or physical processes in the presence of the target biomolecule. We propose a different approach based on selective and quantitative gathering of protein molecules at regular hot spots generated on the corners of individual silver nanocubes in aqueous medium at physiological pH. Here, the protein, while keeping its native configuration, experiences an intense local E-field, which boosts SERS efficiency and detection sensitivity. Uncontrolled signal fluctuations caused by variable molecular adsorption to different particle areas or inside clustered nanoparticles are circumvented. Advanced electron microscopy analyses and computational simulations outline a strategy relying on a site-selective mechanism with superior Raman signal enhancement, which offers the perspective of highly controlled and reproducible routine SERS detection of proteins.

New Types of Nanomaterials: Powders of Gold Nanospheres, Nanorods, Nanostars, and Gold-Silver Nanocages

We describe a new strategy for the fabrication of plasmonic nanopowders (dried gold or composite nanoparticles) by using wet chemical nanoparticle synthesis, PEG-SH functionalization, and freeze drying. This strategy is illustrated by the successful production of four plasmonic nanopowders, including gold nanorods, nanostars, gold-silver nanocages, and gold nanospheres. The dried nanoparticles can be stored for a long time under ordinary conditions and then easily dissolved in water at a desired concentration without heating, intense sonication, or other harsh treatments. According to the MTT assay with SPEV-2 cells, gold nanorod powder is not toxic at concentrations up to 100 mg/L. Redispersed samples maintain the plasmonresonant properties of the parent colloids and do not form aggregates. These properties make pegylated freeze-dried gold nanoparticles (GNPs) applicable in various fields of biomedicine.

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.

Composite multifunctional nanoparticles based on silica-coated gold-silver nanocages functionalized by Yb-hematoporphyrin

Composite nanoparticles consisting of gold-silver nanocages coated by mesoporous silicon dioxide and functionalized with a photodynamic sensitizer of the Yb-2,4-dimethoxyhematoporphyrin IX dipotassium salt (Yb-HP; about 70000 molecules per one particle) are obtained for the first time. The synthesis technology makes it possible to control the nanocage size in a range of 40–60 nm and the silica shell thickness from 20 to 100 nm. In addition to the known plasmon resonance near 750–800 nm, the composite nanoparticles exhibit an additional absorbance peak at about 400 nm, corresponding to free Yb-HP, and characteristic visible fluorescence bands near 580 and 630 nm, which correspond to the optical features of the bound Yb-HP. The presence of an additional IR luminescence band of the Yb3+ ion in the range of 900–1100 nm is used to control the accumulation and biodistribution of composite conjugates with the help of the IR luminescence method in the spectral window of the tissue. Comparative data on the biodistribution of free Yb-HP and Yb-HP luminescent conjugates are presented after intravenous injection in mice with grafted Ehrlich carcinoma tumors. The accumulation contrast in the tumors 24 h after injection is shown using the IR luminescence technique.