Noncovalent Interaction between Single-Walled Carbon Nanotubes and Pyrene-Functionalized Gold Nanoparticles in Water-Soluble Nanohybrids

The combination of different nanostructures in a multifunctional nanostructured hybrid is expected to improve their functionalities and lead to synergistic effects. In these regards, carbon nanotubes and gold colloids are well-studied building blocks with unique optical and electronic properties, which could be combined in a variety of optoelectronic applications. In this framework, we herein present an innovative approach to the preparation of water-soluble nanohybrids by noncovalent interaction between single-walled carbon nanotubes (SWCNTs) and gold nanoparticles (AuNPs) cofunctionalized with pyrenyl and choline residues. To this aim, we developed a procedure based on consecutive centrifugation steps, which allows straightforward isolation of the conjugates in their water-soluble form. Each step of the process was monitored by TEM and by UVvisNIR absorption spectroscopy to characterize the obtained nanohybrids and to confirm that the interaction of the pyrene residues of the cofunctionalized AuNPs with the nanotube walls is the only one responsible for the formation of the water-soluble nanohybrids. Further investigations including Raman spectroscopy and photoluminescence mapping confirm that the interaction between the AuNPs and the SWCNTs is arguably noncovalent and thus assures that the emission in the NIR region by the nanotubes is preserved. Measurements of the quenching of the fluorescence of pyrene by carbon nanotubes provide the association constants for complex formation between the cofunctionalized AuNPs and SWCNTs. The results reported herein provide the basis to novel strategies for the preparation of water-soluble nanohybrids between AuNPs and SWCNTs based on noncovalent interactions.