Evaluation of photoluminescence, bio-imaging, cytotoxicity and sono-sensitizing properties of silicon nanoparticles (SiNPs) have been investigated. The prepared SiNPs exhibit efficient room temperature photoluminescence (PL) in the spectral region of 600–1000 nm. On the one hand in-vitro studies have demonstrated low cytotoxicity of SiNPs and possibilities of their bio-imaging applications. On the other hand, it has been found that SiNPs can act as efficient sensitizers of ultrasound induced suppression of the viability of Hep2 cancer cells. Listed modalities open new possibility of SiNP theranostic (therapy and diagnostic) applications.