I have my research in green synthesis of nanoparticles, and I wants to know that why nanoparticles synthesized through green synthesis method are biocompatible need reference papers.
at the same time, the answer on your question is both simple and complicate.
From one point of view, typically used reagents for obtained of NPs by "green" synthesis are plant or microbial origin. And taking into account that such substances are both reducer and stabilizer then natural origin substances that adsorbted on the NPs surface facilitate interaction of metallc part and biological structures.
From the other hand, natural substances during the synthesis will be oxidized and can form some uncertain products that may be toxic in some cases. That is why researcher must be very careful in the experiments and obtained products.