Why are metal nanoparticles used more than polymer nanoparticles in biological (green) nanoparticles?

There are lots of reason for choosing metal over polymer nanoparticles. some of them are:-

1. Shape and size of metal nanoparticles can be easily controlled and synthesized
2. Some metal being inherently magnetic in nature can be used for targeted and controlled drug delivery application
3. Most of the metal intrinsically photoactive can be used in for photoactivated degradation of some specific cell which is not possible in a pure polymer
4. polymer has a large molecular weight and controlling for an application is difficult when compared to metal NPs.

Reference: https://www.quora.com/Why-are-metal-nanoparticles-used-more-than-polymer-nanoparticles-in-biological-green-nanoparticles