Chih-Cheng Chou

The disruption of bacterial membrane integrity through ROS generation induced by nanohybrids of silver and clay.

Nanohybrids, synthesized via silver nitrate reduction in the presence of silicate clay, exhibit a high potency against bacterial growth. The plate-like clay, due to its anionic surface charges and a large surface area, serves as the support for the formation of silver nanoparticles (AgNPs) approximately 30 nm in diameter. The nanohybrid consisting of Ag/silicate at a 7/93 weight ratio inhibited the growth of dermal pathogens including Staphylococcus aureus (S. aureus), Pseudomonas aeruginosa and Streptococcus pyrogens, as well as the methicillin- and oxacillin-resistant S. aureus (MRSA and ORSA). Scanning electron microscope revealed that these nanohybrids were adherent on the surface of individual bacteria. The thin silicate plates provide a surface for immobilizing AgNPs in one highly concentrated area but prevent them from entering the cell membrane. Subsequent cytotoxicity studies indicated that surface contact with the reduced AgNPs on clay is sufficient to initiate cell death. This toxicity is related to a loss in membrane integrity due to reactive oxygen species (ROS) generation. The hybridization of AgNPs on clay surface is viable for generating a new class of nanohybrids exhibiting mild cytotoxicity but high efficacy for battling drug-resistant bacteria.

Synthesis of immobilized silver nanoparticles on ionic silicate clay and observed low-temperature melting

Silver nanoparticles (AgNPs) of narrow size distribution and low melting point were synthesized from the reduction of silver nitrate in the presence of inorganic silicate clays. The natural clays with a lamellar geometric shape provided a high surface area for immobilizing AgNPs with nanometer diameter in the range of 17–88 nm. At a 1/1 equivalent ratio of Ag+ to clay counter ions, the generated particles had a narrow size distribution (polydispersity of Dw/Dn = 1.2 at 26 nm Dn by SEM) and a UV absorption at 420 cm−1. Without organic dispersants, the colloidal clays could complex with Ag+ in the initial stage of mixing and subsequently stabilized the generated Ag0 particles. It seems that the high surface area stabilizes the clay rather than the Ag metal intercalation into the layered structure since the basal spacing was only slightly enlarged (12.0 A versus 13.9 A by XRD). The resulting AgNPs were highly stable and maintained their particle size after several cycles of drying at 80 °C and re-dispersion in water. Moreover, the AgNPs on the clay surface melted at a low temperature (110 °C), observed by SEM. Such AgNPs may have potential applications for fabricating silver arrays or conductors at low temperature.