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

Low-Load Metal-Assisted Catalytic Etching Produces Scalable Porosity in Si Powders

The recently discovered low-load metal-assisted catalytic etching (LL-MACE) creates nanostructured Si with controllable and variable characteristics that distinguish this technique from the conventional high-load variant. LL-MACE employs 150 times less metal catalyst and produces porous Si instead of Si nanowires. In this work, we demonstrate that some of the features of LL-MACE cannot be explained by the present understanding of MACE. With mechanistic insight derived from extensive experimentation, it is demonstrated that (1) the method allows the use of not only Ag, Pd, Pt, and Au as metal catalysts but also Cu and (2) judicious combinations of process parameters such as the type of metal, Si doping levels, and etching temperatures facilitate control over yield (0.065−88%), pore size (3−100 nm), specific surface area (20−310 m2·g−1), and specific pore volume (0.05−1.05 cm3·g−1). The porous structure of the product depends on the space-charge layer, which is controlled by the Si doping and the chemical identity of the deposited metal. The porous structure was also dependent on the dynamic structure of the deposited metal. A distinctive comet-like structure of metal nanoparticles was observed after etching with Cu, Ag, Pd, and, in some cases, Pt; this structure consisted of 10−50 nm main particles surrounded by smaller (\u3c5 nm) nanoparticles. With good scalability and precise control of structural properties, LL-MACE facilitates Si applications in photovoltaics, energy storage, biomedicine, and water purification

Modeling of Heat Release in Aqueous Suspensions of Solid-State Nanoparticles under Electromagnetic Radio-Frequency Irradiation

Conference on Synthesis and Photonics of Nanoscale Materials XIII, San Francisco, CA, FEB 15-17, 2016International audienceWe examine absorption of electromagnetic radio-frequency (RF) radiation in aqueous suspensions of semiconductor (silicon) and metal (gold) nanoparticles (NPs) and theoretically investigate the heat release in these systems. The absorption of RF radiation is considered in both bulk electrolyte and the region around the NPs. Simulations show a strong dependence of the heating rate on electrical conductivity of the electrolyte rather than on that of NPs properties. The obtained results indicate that NPs can act as sensitizers of the RF induced hyperthermia for biomedical applications

Toward Controlled Photothermal Treatment of Single Cell: Optically Induced Heating and Remote Temperature Monitoring In Vitro through Double Wavelength Optical Tweezers

Cancer treatment based on hyperthermia (HT) relies on exposing the malignant cells to elevated local temperature. Although the procedure has been successfully applied in clinics, the fundamental aspects of HT are not yet fully understood. In order to verify the susceptibility of single cells in vitro to raised temperature, we have developed novel nano- and microtools. In particular, an optical double-trap system utilizing combined galvano-mirror scanning and spatial light phase modulator was devised to manipulate several micron-sized objects simultaneously. The manipulation comprised both optical trapping and translocating, on demand photoactivated heating, and simultaneous remote temperature readout of living cells, infrared activated heaters and optical thermometers, respectively. Mesoporous silicon microparticles were used as an infrared absorber to generate an increased temperature of about 100 °C with 0.4 W laser power. The optical micron-sized thermometer was based on up-converting Yb–Er codoped nanocrystalline particles encapsulated in amorphous silica shells produced with yeast cells as the templates. These hybrid particles displayed a relative sensitivity of 0.28%/K, an accuracy of 0.1 °C (at 32 °C), spatial resolution of <10 μm, and a temporal response of 50 ms/acquisition to record the temperature changes in specified areas in real time. The system was utilized in monitoring the stepwise cell death of individual diffuse large B-cell lymphoma (DLBCL) cells due to locally induced excessive heating induced by the absorber localized in the vicinity of the cell

Nano Air Seeds Trapped in Mesoporous Janus Nanoparticles Facilitate Cavitation and Enhance Ultrasound Imaging

The current contrast agents utilized in ultrasound (US) imaging are based on microbubbles which suffer from a short lifetime in systemic circulation. The present study introduces a new type of contrast agent for US imaging based on bioresorbable Janus nanoparticles (NPs) that are able to generate microbubbles <i>in situ</i> under US radiation for extended time. The Janus NPs are based on porous silicon (PSi) that was modified via a nanostopper technique. The technique was exploited to prepare PSi NPs which had hydrophobic pore walls (inner face), while the external surfaces of the NPs (outer face) were hydrophilic. As a consequence, when dispersed in an aqueous solution, the Janus NPs contained a substantial amount of air trapped in their nanopores. The specific experimental setup was developed to prove that these nano air seeds were indeed acting as nuclei for microbubble growth during US radiation. Using the setup, the cavitation thresholds of the Janus NPs were compared to their completely hydrophilic counterparts by detecting the subharmonic signals from the microbubbles. These experiments and the numerical simulations of the bubble dynamics demonstrated that the Janus NPs generated microbubbles with a radii of 1.1 μm. Furthermore, the microbubbles generated by the NPs were detected with a conventional medical ultrasound imaging device. Long systemic circulation time was ensured by grafting the NPs with two different PEG polymers, which did not affect adversely the microbubble generation. The present findings represent an important landmark in the development of ultrasound contrast agents which possess the properties for both diagnostics and therapy

Scalable Synthesis of Biodegradable Black Mesoporous Silicon Nanoparticles for Highly Efficient Photothermal Therapy

Porous silicon (PSi) has attracted wide interest as a potential material for various fields of nanomedicine. However, until now, the application of PSi in photothermal therapy has not been successful due to its low photothermal conversion efficiency. In the present study, biodegradable black PSi (BPSi) nanoparticles were designed and prepared via a high-yield and simple reaction. The PSi nanoparticles possessed a low band gap of 1.34 eV, a high extinction coefficient of 13.2 L/g/cm at 808 nm, a high photothermal conversion efficiency of 33.6%, good photostability, and a large surface area. The nanoparticles had not only excellent photothermal properties surpassing most of the present inorganic photothermal conversion agents (PCAs) but they also displayed good biodegradability, a common problem encountered with the inorganic PCAs. The functionality of the BPSi nanoparticles in photothermal therapy was verified in tumor-bearing mice in vivo. These results showed clearly that the photothermal treatment was highly efficient to inhibit tumor growth. The designed PCA material of BPSi is robust, easy to prepare, biocompatible, and therapeutically extremely efficient and it can be integrated with several other functionalities on the basis of simple silicon chemistry

Comparison between fluorescence imaging and elemental analysis to determine biodistribution of inorganic nanoparticles with strong light absorption

Abstract Black porous silicon nanoparticles (BPSi NPs) are known as highly efficient infrared light absorbers that are well-suitable for photothermal therapy (PTT) and photoacoustic imaging (PAI). PTT and PAI require a sufficient number of effectively light-absorbing NPs to be accumulated in tumor after intravenous administration. Herein, biodistribution of PEGylated BPSi NPs with different sizes (i.e., 140, 200, and 300 nm in diameter) is investigated after intravenous administration in mice. BPSi NPs were conjugated with fluorescent dyes Cy5.5 and Cy7.5 to track them in vitro and in vivo, respectively. Optical imaging with an in vivo imaging system (IVIS) was found to be an inadequate technique to assess the biodistribution of the dye-labeled BPSi NPs in vivo because the intrinsic strong absorbance of the BPSi NPs interfered fluorescence detection. This challenge was resolved via the use of inductively coupled plasma optical emission spectrometry to analyze ex vivo the silicon content in different tissues and tumors. The results indicated that most of the polyethylene glycol-coated BPSi NPs were found to accumulate in the liver and spleen after intravenous injection. The smallest 140 nm particles accumulated the most in tumors at an amount of 9.5 ± 3.4% of the injected dose (concentration of 0.18 ± 0.08 mg/mL), the amount known to produce sufficient heat for cancer PTT. Furthermore, the findings from the present study also suggest that techniques other than optical imaging should be considered to study the organ biodistribution of NPs with strong light absorbance properties

Radio frequency radiation-induced hyperthermia using Si nanoparticle-based sensitizers for mild cancer therapy

International audienceOffering mild, non-invasive and deep cancer therapy modality, radio frequency (RF) radiation-induced hyperthermia lacks for efficient biodegradable RF sensitizers to selectively target cancer cells and thus avoid side effects. Here, we assess crystalline silicon (Si) based nanomaterials as sensitizers for the RF-induced therapy. Using nanoparticles produced by mechanical grinding of porous silicon and ultraclean laser- ablative synthesis, we report efficient RF-induced heating of aqueous suspensions of the nanoparticles to temperatures above 45-50 degrees C under relatively low nanoparticle concentrations (< 1 mg/mL) and RF radiation intensities (1-5 W/cm(2)). For both types of nanoparticles the heating rate was linearly dependent on nanoparticle concentration, while laser-ablated nanoparticles demonstrated a remarkably higher heating rate than porous silicon-based ones for the whole range of the used concentrations from 0.01 to 0.4 mg/mL. The observed effect is explained by the Joule heating due to the generation of electrical currents at the nanoparticle/water interface. Profiting from the nanoparticle-based hyperthermia, we demonstrate an efficient treatment of Lewis lung carcinomain in vivo. Combined with the possibility of involvement of parallel imaging and treatment channels based on unique optical properties of Si-based nanomaterials, the proposed method promises a new landmark in the development of new modalities for mild cancer therapy