Aim: We aim to develop a facile strategy for assembling nanoparticles within cross-linked polymer micelles that enables tuning of their overall hydrodynamic size and surface charge and to mitigate toxicity. Materials & Methods: Hydrophobic nanoparticles and amphiphilic co-polymers self-assembled upon solvent-selective precipitation. Size-tunability of the assembled nanostructure was achieved by controlling both the nanoparticle and polymer ratio and the kinetics of the assembly process. Results & Conclusion: We were successful in creating polymer shells on the surface of inorganic nanoparticles. The shell thickness could be tuned, and protect the nanoparticles from environmental degradation and minimize the cytotoxicity of inorganic nanoparticles. This strategy provides a method to engineer the interactions of nanoparticles with biological systems, including their targeted delivery to diseased tissues and their safety of use without significantly altering their original materials properties.