Hydroxyl-Functionalized and N-Doped Multiwalled Carbon Nanotubes Decorated with Silver Nanoparticles Preserve Cellular Function

Abstract

The present study aims to investigate biocompatibility of silver nanoparticles (Ag-NPs) anchored to different types of multiwalled carbon nanotubes (MWNTs). The MWNTs were decorated with Ag-NPs via a novel chemical route without using any sulfur containing reagent. Three different MWNTs were used as substrate materials for anchoring Ag-NPs: MWNTs-Ag (pure carbon), COx-MWNTs-Ag (carboxyl functionalized), and CNx-MWNTs-Ag (nitrogen-doped). The Ag-NPs, synthesized without thiol capping groups, and which were strongly anchored to the nanotubes surfaces, exhibit an average size of 7 ± 1, 10 ± 1, and 12 ± 1 nm in MWNTs, COx-MWNTs, and CNx-MWNTs, respectively. To determine biocompatibility of these three types of novel hybrid Ag-nanotube materials, cellular function and immune response were evaluated in the human keratinocyte cell line (HaCaT). Cellular assays revealed marginal toxicity after 24 h, and full cellular recovery was observed at 48 h based on an MTS assay for cellular viability. Therefore, Ag-nanotube systems appear to be very different from isolated dispersed Ag-NPs, and due to the strong interactions between the Ag-NPs and the doped nanotube surfaces, they make the Ag particles less toxic because they are not released easily to the cells. Pure carbon MWNTs appear to start releasing Ag-NPs at periods longer than 1 week by an observed decrease in cell proliferation. However, the use of N- and COx-doped MWNTs do not appear to release Ag-NPs to the cells due to the strong binding to the tube surfaces caused by the doped sites. We envisage the use of COx-MWNTs, and CNx-MWNTs anchored with Ag-NP as efficient drug delivery carriers and biosensors.