Disclosed herein are embodiments of composites and compositions that can be used for therapeutic applications in vivo and/or in vitro. The disclosed composites can comprise cores having magnetic nanoparticles, quantum dots, or combinations thereof and zwitterionic polymeric coatings that facilitate solubility and bioconjugation. The compositions disclosed herein can comprise the composites and one or more biomolecules, drugs, or combinations thereof. Also disclosed herein are methods of making the composites, composite components, and methods of making quantum dots for use in the composites.