This chapter discusses different designs for the preparation and application of composite polymer colloids, mainly focusing on their optical properties and surface-enhanced Raman scattering (SERS)-based sensing. It shows advances related to the encapsulation of gold nanoparticles using amphiphilic polymers (based on hydrophobic interactions), the use of polymer beds as nanoparticles carriers (by electrostatic interactions) and composites comprising smart polymers, as examples of the progress of the field. All these polymer structures show unique properties that derive in novel optical and structural features, which allow their use for SERS sensing in combination with other applications such as drug delivery, imaging or catalysis. A particular attention is paid to the development of bright contrast agents for SERS (bio)imaging, which offer advantages such as long term stability, true multiplexing or response in the near-IR (biological transparency windows), which will lead to breakthroughs in biomedical imaging and understanding of complex biological systems such as tumors or the brain.