Thermally Reduced Graphene Oxide Nanohybrids of Chiral Functional Naphthalenediimides for Prostate Cancer Cells Bioimaging

Abstract

This study reports on the supramolecular assemblies formed between planar carbon systems (PCSs) such as thermally reduced graphene oxide (TRGO) and its small‐molecule model system coronene and a series of d‐ and l‐α amino acid derivatized naphthalenediimides (NDIs) where the halogen substituents (X = F, Cl, Br, I) are varied systematically. Confocal fluorescence microscopy of NDIs, NDI•coronene, and NDI•TRGO complexes is performed proving the uptake and stability of such complexes in the cellular environment and suggesting their potential as prostate cancer imaging agents. 1H NMR and UV–vis spectroscopy studies support the formation of charge transfer complexes whereby the increasing polarizability and general electronegativity of the aryl halide substituted at the NDI periphery influence the magnitude of the association constants in the ground state between NDI and coronene. Complexation between NDIs and PCSs also results in stable photoexcited assemblies within the solution (coronene) as well as the dispersed phased (TRGO). Fluorescence emission titrations and 2‐photon time correlated single photon counting measurements suggest the existence of dynamic quenching mechanisms upon the excitation of the fluorophore in the presence of the carbon substrates, as these methods are sensitive proves for the subtle changes in the NDI environment. The series of halogenated species used exerts supramolecular control over the degree of surface assembly on the TRGO and over the interactions with the coronene molecule, and this is of relevance to the assembly of future biosensing platforms as these materials can both be viewed as congeners of graphene. Finally, MTT assays carried out in PC‐3 cells demonstrate that the stable noncovalent functionalization of TRGO and coronene with either l or d NDIs remarkably improves the cellular viability in the presence of such graphene‐like materials. These phenomena are of particular relevance for the understanding of the direct donor–acceptor interactions in solutions which govern the design of nanomaterials with future biosensing and bioimaging applications.

Synthesis, Radiolabelling and In Vitro Imaging of Multifunctional Nanoceramics

“…A minor and longer second component (τ2=3216.5 ps, a2=11.8%) was also detected. As previously reported, the presence of a second longer component may suggest the presence of NP aggregates in suspension . However, the percentage of such secondary component, although significant, remains lower (11.8%) than that previously reported for nanocomposite materials (31.1%) .…”

“…Adapting the methods established by Wu et al . and Jacinto et al ., the fluorophores were incorporated hereby using a rapid and simple one‐step microemulsion method. TEM micrographs of such NPs are illustrated in Fig.…”

Fluorescence‐Lifetime Imaging and Super‐Resolution Microscopies Shed Light on the Directed‐ and Self‐Assembly of Functional Porphyrins onto Carbon Nanotubes and Flat Surfaces

“…In agreement to the observations for the single‐photon excitation mechanism, the covalent functionalisation of SWNTs results in a more significant lifetime shortening. The appearance of a second longer minor component suggests instead the presence of unquenched species free in solid state (free‐based or zinc porphyrins) or their supramolecular self‐assembled structures …”

“…We have recently reported that these changes in lifetime upon complexation, particularly the presence of a shorter lifetime component, may account for a photo‐induced excited‐state energy transfer occurring between the closely bound donor–acceptor aromatic chromophores and planar carbon‐based materials . Therefore, it is reasonable to conclude that a Förster resonance energy transfer (FRET) occurs in these systems, in which the porphyrins act as FRET donors and the SWNTs as the corresponding FRET acceptors …”

“…We characterised these materials in a thin film environment using fluorescence lifetime measurements via time‐correlated single photon counting (TCSPC) combined with multi‐photon laser scanning confocal microscopy; this allows us to gain detailed information on the environment of the fluorophore upon immobilisation within the nanomaterial hybrid and estimate the influence of the different linking strategies on the emerging materials′ optical properties by observing their quenching characteristics in solution and in the solid state …”