When materials are synthesized/fabricated in very small dimensions, they exhibit physical properties different to their bulk properties. Properties such as extinction coefficient, conductivity, and catalytic activity can be tuned by controlling the size of the nanoparticles.

Nanoparticles, and especially silver nanoparticles, are increasingly used in industry for various applications ranging from sensors to food preservation, to bioelectronic wearables. At the moment, silver nanoparticles are commercially synthesized using sodium borohydride as the primary reductant and sodium citrate as the capping agent. However, sodium borohydride is caustic and difficult to completely purify from solution. One alternative route for synthesis is using biological reducing agents. For example, many works have demonstrated the ability to synthesize nanoparticles inside living organisms or with plant extracts. As promising as it seems, the lack of particle tunability produced "in vivo" and the complex process of nanoparticle separation from the living "soup" makes this route less attractive as it seemed to be in the first place. In our lab, we are examining specific biological molecules that can serve as reducing agents for silver nanoparticle synthesis. The motivation is to find cost-effective biologically abundant materials that can be used for silver nanoparticle production with the ability to control the particle size and their activity towards some specific biological function or catalysis.

Check out our recent paper here where we disprove a leading hypothesis that assumed a specific enzyme (nitrate reductase) was the main reducer of silver nanoparticles in vivo. Instead, we show that NADPH can act as the sole reducing agent of silver nitrate salt to form silver nanoparticles. In fact, the addition of nitrate reductase during the synthesis caused a decrease in reaction rate and broadened the size distribution of the particles.

We are currently focusing on other biological species and sugars to understand the broadness and applicability of these materials towards nanoparticle synthesis.