Nanoparticles can be used for a wide range of applications. Especially if used in the medical field they need to be free from toxic chemicals, which are used in the conventional way of nanoparticle formation. Therefore, our goal is to use synthetic biology to create a way of generating environmentally friendly nanoparticles. Our Escherichia coli take up metal ions like iron, copper, silver or ... [Show full abstract] gold ions to accumulate them in the periplasm and the cytoplasm. To prevent metal ion export, several genes need to be silenced. Besides using knock-out strains, which are created using CRISPR/Cas9, we aim to introduce a two-plasmid system working with siRNA to ensure a essential minimal expression of some genes. In addition, our E. coli they have several optimized mechanisms against the toxicity of metal ions. Within the cell the ions get accumulated and reduced to nanoparticles. These nanoparticles will be isolated from the cells and could be used in different way. Our proof of concept will be the printing of electric curcuits for electronic tattoos out of nanoparticle ink consisting mainly of our self-produced nanoparticles.