Subnanometer Thick Carbon-Layer-Encapsulated Silver Nanoparticles Selectively Neutralizing Human Cancer Cells and Pathogens through Controlled Release of Ag+ Ions

Abstract

We present the excellent and selective activity against human cancer cells and pathogens by double-layer carbon-encapsulated silver nanoparticles (C@AgNPs) and monolayer carbon-encapsulated silver nanoparticles (AC@AgNPs). C@AgNPs were synthesized via a modified solvothermal approach, whereas AC@AgNPs were prepared by exfoliation of the outer carbon layer of C@AgNPs. The physicochemical structures and properties of the C@AgNPs and AC@AgNPs are thoroughly examined; the carbon layer is found to ensure the needful release of Ag+ ions from the core Ag nanoparticles, and improve the biocompatibility and selectivity of NPs to kill the cancer cells. Hence, the C@AgNPs and AC@AgNPs are substantiated to be beneficial for controlling the overtoxicity caused by unstable bare AgNPs and achieving the targeted actions. The Ag+ ions exhibit their toxic effects against cancer cells or pathogens chiefly through the reactive oxygen species (ROS) generation. The Ag+-ion release and ROS generation of the AC@AgNPs are found greater than those of the C@AgNPs because of the synergistic effect of the reduced thickness of carbon layer and increased specific surface area. The C@AgNPs and AC@AgNPs were applied against cancer cells (K562 and Hep3B), normal cells (LO2), and pathogens in vitro. The AC@AgNPs exhibit greater dose- and time-dependent late apoptosis of cancer cells than the C@AgNPs, and reduce the viability of cancer cells more effectively than the C@AgNPs. The crystal violet assay explicitly displays that the as-prepared samples exhibit preferential attack on cancer cells. In the analysis of apoptosis associated proteins, caspase-3 and PARP as markers, the protein expression was visible only for the cancer cells asserting that the prepared C@AgNPs and AC@AgNPs act selectively, invading only the cancer cells. Moreover, the AC@AgNPs exhibit a larger linear inhibition zone than the C@AgNPs against both Gram negative and Gram positive pathogenic bacterial stains in bactericidal activity probes.