Radiofrequency Hyperthermia of Cancer Cells Enhanced by Silicic Acid Ions Released during the Biodegradation of Porous Silicon Nanowires

The radiofrequency (RF) mild hyperthermia effect sensitized by biodegradable nanoparticles is a promising approach for therapy and diagnostics of numerous human diseases including cancer. Herein, we report the significant enhancement of local destruction of cancer cells induced by RF hyperthermia in the presence of degraded low-toxic porous silicon (PSi) nanowires (NWs). Proper selection of RF irradiation time (10 min), intensity, concentration of PSi NWs, and incubation time (24 h) decreased cell viability to 10%, which can be potentially used for cancer treatment. The incubation for 24 h is critical for degradation of PSi NWs and the formation of silicic acid ions H+ and H3SiO4- in abundance. The ions drastically change the solution conductivity in the vicinity of PSi NWs, which enhances the absorption of RF radiation and increases the hyperthermia effect. The high biodegradability and efficient photoluminescence of PSi NWs were governed by their mesoporous structure. The average size of pores was 10 nm, and the sizes of silicon nanocrystals (quantum dots) were 3-5 nm. Degradation of PSi NWs was observed as a significant decrease of optical absorbance, photoluminescence, and Raman signals of PSi NW suspensions after 24 h of incubation. Localization of PSi NWs at cell membranes revealed by confocal microscopy suggested that thermal poration of membranes could cause cell death. Thus, efficient photoluminescence in combination with RF-induced cell membrane breakdown indicates promising opportunities for theranostic applications of PSi NWs. © 2019 American Chemical Society

Photoluminescent porous silicon nanowires as contrast agents for bioimaging

Porous silicon nanowires (pSi NWs) have attracted considerable interest due to their unique structural, optical properties and biocompatibility. The most common method for their top-down synthesis is metal-assisted chemical etching (MACE) of crystalline silicon (c-Si) wafers using silver nanoparticles as a catalyst. However, the replacement of silver with bioinert gold nanoparticles (Au NPs) markedly improves the efficiency of pSi NWs in biomedical applications. The present study demonstrates the fabrication of porous pSi NWs arrays using Au NPs as the catalyst in MACE of c-Si wafers with a resistivity of 1–5 mOhm·cm. Using scanning electron microscopy (SEM), the formation of arrays of porous nanowires with a diameter of 50 nm that consist of small silicon nanocrystals (nc-Si) and pores was observed. Raman spectroscopy analysis determined the size of nc-Si is about 4 nm. The pSi NWs exhibit effective photoluminescence (PL) with a peak in the red spectrum, which is attributed to the quantum confinement effect occurred in small 4 nm nc-Si. In addition, the pSi NWs exhibit low toxicity towards MCF-7 cancer cells, and their PL characteristics allow them to be used as contrast agents for bioimagin

Influence of nanosized incoherent particles on dislocation annihilation in heterophase aluminum-matrix crystalline alloys

Using mathematical modeling, patterns of changing the densities of dislocation subsystem components in dispersion hardened materials have been revealed depending on the volume fraction and scale characteristics of the hardening phase at different deformation temperatures. It has been shown that in all examined materials with hardening particles of different sizes, the dislocation annihilation significantly decreases with the volume fraction of nanosized incoherent particles. It has been found that the dislocation density in prismatic loops is largely determined by the particle sizes and the volume fraction of the hardening phase

Doping nature of group V elements in ZnO single crystals grown from melts at high pressure

International audienceZnO single crystals doped with group-V elements have been grown from melt at high pressure. Dopants were introduced in several forms such as Sb2O3, P, As, Sb and Zn3X2 (X = P, As, Sb) in the high-pressure cell. Systematic studies of morphology were performed using optical microscopy and scanning electron microscopy. Crystal structure and lattice parameters were studied using X-ray diffraction and X-ray crystallography. Crystals exhibited distinct changes of size, shape and color compared to undoped ZnO melt-grown single crystals due to the dopants influence. X-ray photoelectron spectroscopy was used to determine valence states of group-V elements when incorporated in ZnO lattice. Photoluminescence, Raman spectroscopy and electron paramagnetic resonance spectroscopy were employed to investigate the nature of defects formed as the result of doping. Formation of VZn and VZn-complexes was confirmed and their concentrations were measured. Estimates of the number of VZn per one dopant atom showed that the ratio is noticeably higher than the one suggested for the shallow complex As(P, Sb)Zn-2VZn commonly regarded as responsible for acceptor properties in ZnO

Doping nature of group V elements in ZnO single crystals grown from melts at high pressure

ZnO single crystals doped with group-V elements have been grown from melt at high pressure. Dopants were introduced in several forms such as Sb2O3, P, As, Sb and Zn3X2 (X = P, As, Sb) in the high-pressure cell. Systematic studies of morphology were performed using optical microscopy and scanning electron microscopy. Crystal structure and lattice parameters were studied using X-ray diffraction and X-ray crystallography. Crystals exhibited distinct changes of size, shape and color compared to undoped ZnO melt-grown single crystals due to the dopants influence. X-ray photoelectron spectroscopy was used to determine valence states of group-V elements when incorporated in ZnO lattice. Photoluminescence, Raman spectroscopy and electron paramagnetic resonance spectroscopy were employed to investigate the nature of defects formed as the result of doping. Formation of VZn and VZn-complexes was confirmed and their concentrations were measured. Estimates of the number of VZn per one dopant atom showed that the ratio is noticeably higher than the one suggested for the shallow complex As(P, Sb)Zn-2VZn commonly regarded as responsible for acceptor properties in ZnO

Optical Monitoring of the Biodegradation of Porous and Solid Silicon Nanoparticles

Silicon nanoparticles (SiNP) are currently of great interest, especially in biomedicine, because of their unique physicochemical properties combined with biodegradability. SiNPs can be obtained in various ways and can have either a non-porous solid (sol-) or porous (por-) structure. In this work, we carry out detailed optical monitoring of sol- and por-SiNP biodegradation using Raman and photoluminescence (PL) micro-spectroscopy. SiNPs were obtained by ultrasound grinding of sol- or por-silicon nanowires, created by silver-assisted chemical etching of crystalline Si with different doping levels. In this case, sol-SiNPs consist of nanocrystals 30 nm in size, while por-SiNPs consist of small 3 nm nanocrystals and 16 nm pores. Both SiNPs show low in vitro cytotoxicity towards MCF-7 and HEK293T cells up to 800 μg/mL. The appearance of the F-band (blue–yellow) PL, as well as a decrease in the intensity of the Raman signal, indicate the gradual dissolution of the sol-SiNPs during 20 days of incubation. At the same time, the rapid dissolution of por-SiNP within 24 h is identified by the quenching of their S-band (red) PL and the disappearance of the Raman signal. The obtained results are important for development of intelligent biodegradable drug delivery systems based on SiNPs