Very stable and bright emitting amine-terminated Si nanoparticles (NPs) with different alkyl chain lengths between the Si core and amine end-group are synthesized. The obtained NPs have a spherical shape and homogeneous size distribution (1.57 ± 0.24 nm). Their emission can be tuned from the UV to the blue spectral region, in a controllable fashion, by only changing the alkyl spacer length. The emission quantum yields are ∼12% for all synthesized Si NPs. Excited state lifetimes are in the ns range and point to a direct band gap excitation. NH2-terminated Si NPs exhibit an exceptional stability over a wide pH range (1–13) and high temperatures (120 °C). The diffusion coefficient of prepared Si NPs is determined by fluorescence correlation spectroscopy (FCS) to be 3.3 × 10−10 m2 s−1. The derived size of Si NPs from mobility corresponds to 1.4 nm which is in a good agreement with the size obtained by transmission electron microscopy (TEM). Prepared Si NPs are shown to be highly suitable for bioimaging studies as they are readily taken up by BV2 cells. Si NPs are located in the cells cytosol. Proliferation of stained BV2 cells is observed and showed that newly formed cells are also stained with Si NPs, indicating their minimal toxicity. By using Si NPs it is possible to stain multiple cell generations by only staining the mother cells.