Adenosine-Monophosphate-Assisted Homogeneous Silica Coating of Silver Nanoparticles in High Yield.

In this study, we propose a novel approach for the silica coating of silver nanoparticles based on surface modification with adenosine monophosphate (AMP). Upon AMP stabilization, the nanoparticles can be transferred into 2-propanol, promoting the growth of silica on the particle surfaces through the standard Stöber process. The obtained silica shells are uniform and homogeneous, and the method allows a high degree of control over shell thickness while minimizing the presence of uncoated NPs or the negligible presence of core-free silica NPs. In addition, AMP-functionalized AgNPs could be also coated with a mesoporous silica shell using cetyltrimethylammonium chloride (CTAC) as a template. Interestingly, the thickness of the mesoporous silica coating could be tightly adjusted by either the silica precursor concentration or by varying the CTAC concentration while keeping the silica precursor concentration constant. Finally, the influence of the silica coating on the antimicrobial effect of AgNPs was studied on Gram-negative bacteria (R. gelatinosus and E. coli) and under different bacterial growth conditions, shedding light on their potential applications in different biological environments.

Silver and Copper Acute Effects on Membrane Proteins and Impact on Photosynthetic and Respiratory Complexes in Bacteria.

Silver (Ag+) and copper (Cu+) ions have been used for centuries in industry, as well as antimicrobial agents in agriculture and health care. Nowadays, Ag+ is also widely used in the field of nanotechnology. Yet, the underlying mechanisms driving toxicity of Ag+ ions in vivo are poorly characterized. It is well known that exposure to excess metal impairs the photosynthetic apparatus of plants and algae. Here, we show that the light-harvesting complex II (LH2) is the primary target of Ag+ and Cu+ exposure in the purple bacterium Rubrivivax gelatinosus Ag+ and Cu+ specifically inactivate the 800-nm absorbing bacteriochlorophyll a (B800), while Ni2+ or Cd2+ treatment had no effect. This was further supported by analyses of CuSO4- or AgNO3-treated membrane proteins. Indeed, this treatment induced changes in the LH2 absorption spectrum related to the disruption of the interaction of B800 molecules with the LH2 protein. This caused the release of B800 molecules and subsequently impacted the spectral properties of the carotenoids within the 850-nm absorbing LH2. Moreover, previous studies have suggested that Ag+ can affect the respiratory chain in mitochondria and bacteria. Our data demonstrated that exposure to Ag+, both in vivo and in vitro, caused a decrease of cytochrome c oxidase and succinate dehydrogenase activities. Ag+ inhibition of these respiratory complexes was also observed in Escherichia coli, but not in Bacillus subtilisIMPORTANCE The use of metal ions represents a serious threat to the environment and to all living organisms because of the acute toxicity of these ions. Nowadays, silver nanoparticles are one of the most widely used nanoparticles in various industrial and health applications. The antimicrobial effect of nanoparticles is in part related to the released Ag+ ions and their ability to interact with bacterial membranes. Here, we identify, both in vitro and in vivo, specific targets of Ag+ ions within the membrane of bacteria. This include complexes involved in photosynthesis, but also complexes involved in respiration.

Enhancement of Ag cluster mobility on Ag surfaces by chloridation.

To understand the role of chlorine in the stability and the observed fragmentation of Ag dendritic nanostructures, we have studied computationally two model systems using density functional theory. The first one relates to diffusion of Ag(n) and Ag(n)Cl(m) (n = 1-4) clusters on an Ag(111) surface, and the second demonstrates interaction strength of (Ag(55))(2) dimers with and without chloridation. Based on our calculated energy barriers, Ag(n)Cl(m) clusters are more mobile than Ag(n) clusters for n = 1-4. The binding energy between two Ag(55) clusters is significantly reduced by surface chloridation. Bond weakening and enhanced mobility are two important mechanisms underlying corrosion and fragmentation processes.