Hey Maria,

You are absolutely correct. It happens, once you change the solvent. Just remember that silver itself is hydrophobic and are not suppose to be in the colloid untill its srface has been modified. So, once you extracted with water, it means surface modified colloidal silver nanoparticles are in suspension. But once you add alcohal, there will be hydrophobic collapse of the metallic particles and you can not recover like that. Then you need to dissolve in organic solvent and then try to functionalize and bring back in the water phase.

My suggestion, make PBS extract and use that one, as this will not change the nanoparticle surface and they always will be in colloidal suspension.

In case if you are interested, you can see get an idea with gold np, little similar with your work.

Article Gold nanorod production by cyanobacteria—a green chemistry approach

Article Screening of different algae for green synthesis of gold nanoparticles

Maria,

Precipitation in alcoholic extract means the synthesized AgNPs are not stable in there. However, in water extract as they are stable. Several things are dependent to the synthesis of AgNPs. firstly, as you are making AgNPs colloids , the surface of the colloids has to be well protected and u need a surfactant stabiliser. Moreover, a number of research devoted in preparation of AgNPs in various synthetic condition such as PH, Temperature, amount of reducing agent etc. A little variation of each of this can result a large change in AgNPs size and shape. U can also estimate the size and shape of AgNPs by simple Mie calculation . For better understanding of the Topic I recommend you to read my paper synthsis of AgNPs in AOT RMs with green reducing agent l-ascorbic acid it will very help full for beginners...

Hi Maria,

Natural extracts have less capping capacity at room temp. Thats why it gets ppted. If you cap silver Nps with surfactants like SDS or saponin rich extract..results will be better! Try it!