Single-wall carbon nanotubes modified with organic dyes: Synthesis, characterization and potential cytotoxic effects

Abstract This work deals with the covalent functionalization of single-wall carbon nanotubes (SWNTs) with phenosafranine (PS) and Nile Blue (NB) dyes. These dyes can act as photosensitizers in energy and electron transfer reactions, with a potential to be applied in photodynamic therapy. Several changes in the characteristic Raman vibrational features of the dyes suggest that a covalent modification of the nanotubes with the organic dyes occurs. Specifically, the vibrational modes assigned to the NH 2 moieties of the dyes are seen to disappear in the SWNT–dye nanocomposites, corroborating the bond formation between amine groups in the dyes and carboxyl groups in the oxidized nanotubes. The X-ray absorption (XANES) data also show, that the intense band at 398.6 eV attributed to 1s → 2pπ* transition of the nitrogen of the aromatic PS ring, is shifted due to the bonding with the carbonic structure of the SWNTs. The cytotoxicity data of dyes-modified SWNT composites in the presence and absence of light shows that the SWNT–NB (4 μg/mL) composite presents a good photodynamic effect, namely a low toxicity in the dark, higher toxicity in the presence of light and also a reduced dye photobleaching by auto-oxidation.