A yeast-based biosensor for silver nanoparticle accumulation and cellular dissolution

Silver nanoparticles (AgNPs) are now being increasingly applied in many fields, thus it is critical to quantify these nanoparticles as well as their cellular dissolution for biological assessment. In this study, we developed a novel technique to quantify the concentration of ultra-small AgNPs based principally on the finding that dissolved Ag⁺ decreased the Zn²⁺ directed fluorescence increase of an adenine deficient yeast [Ade(−) yeast]. To obtain the highest sensitivity to AgNPs, the biomass and addition of Zn²⁺ were optimized to be 0.005 and 0.05 μM, respectively. The lowest detectable Ag⁺ dissolved from the internalized AgNPs was 3.77 ng Ag/μg P. The lowest detectable concentration of AgNPs (7 nm) was 8.9 μg/L, while the bio-response induced by larger AgNPs (20 nm) did not change with increasing AgNPs concentration. Thus, Ade(−) yeast selectively collected the ambient ultra-small AgNPs and acted as a screener to differentiate small AgNPs (4.5–9 nm) and large ones (16–26 nm). The method was further employed to determine the cellular dissolution of these ultra-small AgNPs once they were internalized by the yeast cells. Over 78% of the internalized 7 nm-AgNPs was dissolved to Ag⁺. Our study provided a novel biosensing system using Ade(−) yeast in screening ultra-small AgNPs from the large ones and monitoring the cellular dissolution processes of these ultra-small AgNPs.