Cytotoxicity, photoluminescence (PL) and bio-imaging properties of silicon nanoparticles prepared from nonpo-rous (LD) and porous (HD) silicon nanowires (SiNWs) have been investigated. Samples of LD-SiNWs and HD-SiNWs were formed by metal (silver)-assisted wet chemical etching of lowly and heavily boron-doped (100)-oriented single crystalline silicon substrates, respectively. The prepared silicon nanowires and its aqueous suspen-sions exhibit efficient room temperature photoluminescence (PL) in the spectral region of 600–1000 nm and it is explained by the radiative recombination of excitons confined within nanostructured sidewall of LD-SiNWs and volume of HD-SiNWs. For the first time, this work demonstrates bio-compatibility properties of such silicon nanostructures and their bio-imaging applications.