Offering 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°C under relatively low nanoparticle concentrations (<1 mg/mL) and RF radiation intensities (1–5 W/cm2). 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 carcinoma 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.
Aqueous suspensions of porous silicon nanoparticles (NPs) with average size ∼100 nm and concentration ∼1 g/L undergo significant heating as compared with pure water under therapeutic ultrasonic (US) irradiation with frequencies of 1–2.5 MHz and intensities of 1–20 W/cm2. This effect is explained by taking into account the efficient absorption of US energy by NPs. The observed US-induced heating of biodegradable NPs is promising for applications in ultrasonic hyperthermia of tumors.
Silicon nanoparticles (SiNPs) obtained by mechanical grinding of porous silicon have been used for visualization of living cells in vitro. It was found that SiNPs could penetrate into the cells without any cytotoxic effect up to the concentration of 100 μg/ml. The cell cytoplasm was observed to be filled by SiNPs, which exhibited bright photoluminescence at 1.6 eV. SiNPs could also act as photosensitizers of the singlet oxygen generation, which could be used in the photodynamic therapy of cancer. These properties of SiNPs are discussed in view of possible applications in theranostics (both in therapy and in diagnostics).
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.
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