V.Y. Timoshenko

Laser-synthesized oxide-passivated bright Si quantum dots for bioimaging.

Crystalline silicon (Si) nanoparticles present an extremely promising object for bioimaging based on photoluminescence (PL) in the visible and near-infrared spectral regions, but their efficient PL emission in aqueous suspension is typically observed after wet chemistry procedures leading to residual toxicity issues. Here, we introduce ultrapure laser-synthesized Si-based quantum dots (QDs), which are water-dispersible and exhibit bright exciton PL in the window of relative tissue transparency near 800 nm. Based on the laser ablation of crystalline Si targets in gaseous helium, followed by ultrasound-assisted dispersion of the deposited films in physiological saline, the proposed method avoids any toxic by-products during the synthesis. We demonstrate efficient contrast of the Si QDs in living cells by following the exciton PL. We also show that the prepared QDs do not provoke any cytoxicity effects while penetrating into the cells and efficiently accumulating near the cell membrane and in the cytoplasm. Combined with the possibility of enabling parallel therapeutic channels, ultrapure laser-synthesized Si nanostructures present unique object for cancer theranostic applications.

Numerical methods for calculation of optical properties of layered structures

Three methods, namely 2×2 and 4×4 transfer matrix methods as well as scattering matrix method, for simulation of the transmission and reflection spectra of the layered structures are described in this paper. The advantages of each of these methods for simulation of the optical spectra of one-dimensional photonic crystals are analyzed. The modified 2×2 transfer matrix method is suggested for calculation of the reflection and transmission coefficients of the layered structures in situation when the incident light beam has a cone-like shape.

Methods for increasing the efficiency of nonlinear optical interactions in nanostructured semiconductors

Methods for increasing the efficiency of the optical second-and third-harmonic generation in gallium phosphide and silicon nanostructures formed by electrochemical etching of crystalline semiconductors are discussed. The efficiency of nonlinear optical interactions can be increased by using phase matching in anisotropic nanostructured semiconductors that exhibit form birefringence or by increasing the local field, as in scattering in macroporous semiconductors. The efficiencies of third-harmonic generation in porous silicon and of second-harmonic generation in porous gallium phosphide are found to increase by more than an order of magnitude.

Silicon Nanoparticles as Amplifiers of the Ultrasonic Effect in Sonodynamic Therapy

The possibility of using mesoporous silicon nanoparticles as amplifiers (sensitizers) of therapeutic ultrasonic exposure were studied experimentally in vitro and in vivo. The combination of nanoparticles and ultrasound led to a significant inhibition of Hep-2 cancer cell proliferation and Lewis lung carcinoma growth in mice. These results indicated good prospects of using silicon nanoparticles as sensitizers for sonodynamic therapy of tumors.

Nonlinear optical properties of silicon carbide (SiC) nanoparticles by carbothermal reduction

SiC nanoparticles by carbothermal reduction show promising properties in terms of second harmonic and multiphoton excited luminescence. In particular, we estimate a nonlinear efficiency < d < = 17 pm/V, as obtained by Hyper Rayleigh Scattering. We also present results of cell labelling to demonstrate the potential use of SiC nanoparticles for nonlinear bioimaging by simultaneous detection of second harmonic and luminescence.

Optical spectra of two-dimensional photonic crystal bars based on macroporous Si

Two-dimensional (2D) photonic crystal (PC) bars with 6 and 21 periods were fabricated by simultaneous photoelectrochemical etching of macropores and trenches in a pre-patterned silicon wafer. The structures had square lattice of cylindrical pores and were terminated by nonmodulated silicon pre-layers. The infrared reflection spectra of the PC bars have been simulated using scattering matrix method. In order to take into account the roughness of pore inner surface an additional silicon layer around the pores was introduced with a fitted complex refractive index. A comparison between the simulated refection spectra and those obtained experimentally demonstrates a satisfactory agreement in the region of secondary photonic band gaps.

Spatially nanostructured silicon for optical applications

We report on a strong intrinsic optical anisotropy of silicon induced by its dielectric nanopatterning. As a result, an in-plane birefringence for nanostructured (110) Si surfaces is found to be 105 times stronger than that observed in bulk silicon crystals. A difference in the main values of the anisotropic refractive index exceeds that one of any natural birefringent crystals. The anisotropy parameters are found to be strongly dependent on the typical size of the silicon nanowires assembling the layers. The value of birefringence is dependent also on the dielectric surrounding of silicon nanoparticles assembling these layers. We show that stacks of layers having alternative refractive indices act as a distributed Bragg reflectors or optical microcavities. Dichroic reflection/transmission behavior of these structures sensitive to the polarization of the incident linearly polarized light is demonstrated. These findings open the possibility of an application of optical devices based on birefringent silicon layers in a wide spectral range.

Si nanoparticles as sensitizers for radio frequency-induced cancer hyperthermia

We review our recently obtained data on the employment of Si nanoparticles as sensitizers of radiofrequency (RF) - induced hyperthermia for mild cancer therapy tasks. Such an approach makes possible the heating of aqueous suspensions of Si nanoparticles by tens of degrees Celsius under relatively low intensities (1–5 W/cm2) of 27 MHz RF radiation. The heating effect is demonstrated for nanoparticles synthesized by laser ablation in water and mechanical grinding of porous silicon, while laser-ablated nanoparticles demonstrate a remarkably higher heating rate than porous silicon-based ones for the whole range of the used concentrations. The observed RF heating effect can be explained in the frame of a model considering the polarization of Si NPs and electrolyte in the external oscillating electromagnetic field and the corresponding release of heat by electric currents around the nanoparticles. Our tests evidence relative safety of Si nanostructures and their efficient dissolution in physiological solutions, suggesting potential clearance of nanoparticles from a living organism without any side effects. Profiting from Si nanoparticle-based heating, we finally demonstrate an efficient treatment of Lewis Lung carcinoma in vivo. The obtained data promise a breakthrough in the development of mild, non-invasive methods for cancer therapy.

Form anisotrophy influence on properties of cubic susceptibility tensor in birefrigent porous silicon

The cubic susceptibility tensor properties in (100) porous silicon with strong in-plane birefringence caused by form anisotropy is considered. Polarization-sensitive third-harmonic generation in such media reveals a modification in the cubic susceptibility tensor.

Optical anisotropy of nanostructured silicon films studied by Fourier transform infrared spectroscopy

Electrochemically nanostructured Si films with surface orientation (110) prepared at different current density were investigated by Fourier transform infrared spectroscopy. The spectra exhibit beats of interference fringes arisen from the summation of intensities of ordinary and extraordinary waves which interfere in the film. The investigated films are shown to exhibit properties of a negative uniaxial crystal (no > ne) with optical axis lying in the surface plane along [001] direction. The value of birefringence reaches 18% for nanostructured Si films with porosity of 80%. Experimental data agree with calculations based on the effective media approximation for anisotropically spaced Si nanocrystals.