Need Help: Beginner - Rendering with Eevee vs Cycles

Hey Blender Community!
Before I start I apologize already, as I am an absolute blender beginner and only teached myself a few things with tutorials so please be patient with me. Now for the Topic, I am currently trying to create a nice figure of some metallic nanoparticles wiht adorbed proteins on the surface inside of a blood vessel. I created the nanoparticle first and was very happy with the results, consecutive i created the blood vessel with the help of a tutorial, but as I was combining both I realized that I was only able to make one of them look good, the blood vessel with eevee and a not so shiny particle or a shiny particle but a terrible blood vessel with cycles as seen in the pictures. I am currently a little helpless why my blood vessel and blood cells look like this in cycles. So I hope you might be able to enlighten me.

And again sorry its my first post here, I hope I selected the right subforum.