Hierarchical Composite Nanoarchitectonics with a Graphitic Core, Dendrimer and Fluorocarbon Domains, and a Poly(ethylene glycol) Shell as O Reservoirs for Reactive Oxygen Species Production.

Graphene oxide (GO), single-walled carbon nanohorn (CNHox), and nitrogen-doped CNH (N-CNH) were functionalized with fluorinated poly(ethylene glycol) (-PEG) and/or with a fluorinated dendrimer (-DEN) to prepare a series of assembled nanocomposites (GO/-PEG, CNHox/-PEG, N-CNH/-PEG, N-CNH/-DEN, and N-CNH/-DEN/-PEG) that provide effective multisite O reservoirs. In all cases, the O uptake increased with time and saturated after 10-20 min. When graphitic carbons (GO and CNHox) were coated with -PEG, the O uptake doubled. The O loading was slightly higher in N-CNH compared to CNHox. Notably, coating N-CNH with -DEN or -PEG, or with both -DEN and -PEG, was more effective. The best performance was obtained with the N-CNH/-DEN/-PEG nanocomposite. The O uptake kinetics and mechanisms were analyzed in terms of the Langmuir adsorption equation based on a multibinding site assumption. This allowed the precise determination of multiple oxygen binding sites, including on the graphitic structure and in the dendrimer, -DEN, and -PEG. After an initial rapid, relatively limited release, the amount of O trapped in the nanomaterials remained high (>95%). This amount was marginally lower for the functionalized composites, but the oxygen stored was reserved for longer times. Finally, it is shown that these systems can generate singlet oxygen after irradiation by a light-emitting diode, and this production correlates with the amount of O loaded. Thus, it was anticipated that the present nanocomposites hierarchically assembled from components with different characters and complementary affinities for oxygen can be useful as O reservoirs for singlet oxygen generation to kill bacteria and viruses and to perform photodynamic therapy.