Nanocarriers encapsulating gold nanoparticles (AuNPs) hold tremendous promise for numerous biomedical applications. So far only a few fabrication strategies have been investigated and efficient processes for the manufacturing of gold nanohybrids (AuNHybs) are still missing. We encapsulated a tetrachloroaurate/citrate mixture within nanocarriers and initiated the AuNP formation after self assembly of the nanomaterial by a temperature shift. This nanoreactor approach was successfully combined with the film rehydration, nanoprecipitation, or microfluidics method. Different nanomaterials were validated including phospholipids and copolymers and the process was optimized towards encapsulation efficiency and physico chemical homogeneity of AuNHybs. Our nanoreactor technology is versatile, efficient, and highly reproducible. Dynamic light scattering and electron microscopy techniques confirmed that generated lipid and polymer based AuNHybs were of uniform size below 130 nm and contained a single AuNP. The AuNHyb solutions had a deep red color and exhibited the specific surface plasmon absorption of AuNPs. The unique optical properties of AuNHybs were used to visualize cellular uptake of nanocarriers in vitro demonstrating the promising applicability of AuNHybs as bioimaging tool.