I've synthesized CeNPs from bacteria using the extracellular method and coated them using polymers. Both the coated and uncoated NPs do not possess any activity in the bioactivity assays I have tested them in - antimicrobial and even DPPH antioxidant assay. Also purchased cerium (iv) oxide from Sigma to assess bioactivity. According to the literature, these chem-CeNPs possess antimicrobial as well as antioxidant activity but I am not getting any data. What am I doing wrong?