A plasmonic core/satellite heterostructure is synthesized through an electrostatic self-assembly protocol. The heterostructure comprises C-coated Ag nanoparticles known as Ag@C shell-isolated nanoparticles (SHINs) acting as satellite particles and a C-coated Fe3O4 dielectric particle core (Fe3O4@C). The enhanced electromagnetic field generated from the hierarchical nanoscale gaps found among the particles makes high-quality Raman spectra possible. As a result, shell-isolated-nanoparticle-enhanced Raman spectroscopy (SHINERS) based on this heterostructure is successfully applied for in-situ trace-amount detection of perylene in water. There is potential for its use in ultrasensitive detection in the liquid phase with real-time monitoring. This work offers a new strategy for developing SHINs to improve the performance of SHINERS.