Book excerpt: Engineered nanoparticles provide a powerful scaffold for interfacing with proteins. The nanoparticle surface can be tailored to present recognition elements, providing surface complementarity to interact with protein surfaces. In this thesis, I have explored both the fundamental and the applied aspects of this interaction. On the fundamental side, I have co-engineered the nanoparticles and the proteins to generate robust dyads with strong binding affinity even at high salt concentration. Fluorescence titrations and docking studies were carried out to quantify the binding properties of the nanoparticles and proteins. Those studies revealed the prospect of tuning the affinity between the nanoparticles and proteins by co-engineering. On the application side, I have employed nanoparticle-protein interaction to fabricate self-assembled nanostructures to be used as intracellular protein delivery tools. In the first segment, nanoparticles and proteins were assembled to form nanoparticle stabilized capsules (NPSCs) for nuclear trafficking of proteins. The first non-peptide synthetic nuclear localization signal based on boronate was discovered, as well, using NPSC delivery platform. In the second segment, proteins and nanoparticles were co-engineered to self-assemble into hierarchical multi-layered nanostructures. These nanostructures were employed to deliver encapsulated proteins into cell cytosol, establishing a general strategy for protein delivery. Using this technology, I have delivered CRISPR/Cas9-ribonucleoprotein that resulted in highly efficient gene editing. Further, I have created an integrated nanotechnology/biology approach to engineer macrophages in vitro, thus, greatly enhancing their ability to phagocytose tumor cells, providing a new immunotherapeutic strategy for cancer therapy.