Synthesis of stable and monodisperse bare nanoparticles in solution has been highly sought for better understanding their fundamental properties and exploring a variety of potential applications, including design of nanophotonic probes for imaging and diagnosis in vivo. We have synthesized (11.3 ± 2.3) nm silver (Ag) nanoparticles and used a simple approach to prepare optically uniform (75-99%), stable and purified bare Ag nanoparticles. We found that single Ag nanoparticles resist photodecomposition and blinking, allowing to be continuously monitored for hours. Utilizing size-dependent localized-surface-plasmon-resonance-spectra of individual nanoparticles, we can identify the nanoparticle size in vivo in real-time and use the identical size of nanoparticles to simultaneously probe multiple nano-environments in living embryos, to probe their diffusion, transport mechanism and biocompatibility in living embryos in real time, and to investigate the embryonic fluids (e.g., viscosity) at nm spatial resolution in real time. Our study demonstrates new approaches to prepare and use uniform single nanoparticle optics for simultaneous imaging multiple events in vivo in real-time. The detailed experimental design and prospective applications will be discussed in this presentation.