Generally this will be difficult to do as your fungal biomass does not have defined purity as would any other reducing agent (e.g. hydrogen, borohydride, hydrazine hydrate).

Supporting Dr. Alan F Rawle's comment who is absolutely correct regarding the factors that effect the synthesis and stabilization of nano particles, any reducing agent or barrier may have impacts on nano particle synthesis. Biological sub-cellular environment is such an example. So, you have to standardize with both the concentration of the metal ions and biomass to get the desired size of particles. Increased cell mass at an optimum concentration of metal ion may reduce it to your desired size.

Previous experts are right. Only synthesis in shaped emulsions allows us to plan the synthesis of nanoparticles of a certain size in a certain size of a nano reactor.

See for example

Article Relationship between size of cadmium sulfide nanoparticles a...

If it is Saccharomyces or Aspergillus, NADH dependent nitrate reductase is responsible for the reduction. You can control the the size if you can estimate the concentration of this specific enzyme in the aqueous solution of suspended biomass.

I agree with Abhishek Bhattacharya