ИСТИНА

Silicon nanoparticles (SiNPs) are very promising agents for nanodiagnostics and therapy due to their high biocompatibility and biodegradibility. They demonstrate intrinsic photoluminescence with quantum yield up to 20% in red and near infrared range (600-1000 nm), which is very convenient for in vivo diagnostics, since it is overlapped with optical transparency window of human body. They also can transfer energy to molecular oxygen exciting it to singlet state, which is useful for photodynamic therapy of cancer. Typically, SiNPs are prepared by electrochemical etching of silicon wafers (so-called porous silicon), but our research is based also on SiNPs, obtained by laser ablation in liquids and gases. Second approach allow us completely avoid usage of dangerous chemicals such as hydrofluoric or nitric acids, what potentially improves biocompatibility of SiNPs and eliminate unpredictable risks. However optical excitation meets serious limitations due to low penetration depth. Therefore ultrasonic (US) and radiofrequency (RF) irradiation were applied as deeper penetrating physical fields. Activation of SiNPs inside a tumor leads to significant enhancement of tumor growth suppression for both US and RF influences, while unactivated SiNPs do not demonstrate any remarkable effect. US activation is based on both hyperthermia enhancement and cavitation threshold lowering, while RF effect is provided by specific ionic environment surrounding SiNPs. Recently, remarkable contrasting by SiNPs in MRI was demonstrated, which is also in fact an interaction between SiNPs and RF field. We intentionally did not use any well-known magnetic contrast such as gadolinium or iron oxide, so it was provided by paramagnetic centers, i.e. dangling Si bonds or Pb-centers, created on the surface of SiNPs.