Silver nanoparticles are emerging as one of the fastest growing nanomaterials with wide applications. Because of their unique quantum size effects, nanoparticles present vastly different properties from those of bulk materials including enhanced reactivity and greater ability to penetrate cell membranes. Currently, little is known about the adverse effects of silver nanoparticles to human health and their fate in ecological systems. Nitrification involving ammonium oxidation to nitrite and nitrate is an important biological process in both natural and engineered systems, and nitrifying bacteria could serve as potential environmental health indicators because of their extreme sensitivity to metal toxins. In view of the above considerations and building on their experience in nitrification and fluorescence microscopy, the investigators are proposing an exploratory experimental research on nitrification inhibition by silver nanomaterials. In this research, silver nanoparticles will be prepared by chemical reduction and characterized via UV/Vis spectrophotometry and electron microscopy. The detrimental effects of the nanoparticles on nitrification kinetics and microbial energetics at various silver concentrations will be quantified using extant respirometry. The size- and shape-dependent luminescent behavior of silver nanoparticles and their extracellular and/or intracellular location will be analyzed by two-photon laser scanning fluorescence microscopy. Cell membrane integrity will be evaluated based on nucleic acid staining and surface-enhanced fluorescence in the presence of silver nanoparticles. With the support from NSF, this exploratory research will lead to a better understanding of nanoparticle-microbe interactions and shed light on the fundamental mechanisms of nitrification inhibition by emerging metallic nanomaterials.
