Salt Mediated Self-Assembly of Poly(ethylene glycol)-Functionalized Gold Nanorods

BODIPY directed one-dimensional self-assembly of gold nanorods

The assembly of anisotropic nanomaterials into ordered structures is challenging. Nevertheless, such self-assembled systems are known to have novel physicochemical properties and the presence of a chromophore within the nanoparticle ensemble can enhance the optical properties through plasmon-molecule electronic coupling. Here, we report the end-to-end assembly of gold nanorods into micrometer-long chains using a linear diamino BODIPY derivative. The preferential binding affinity of the amino group and the steric bulkiness of BODIPY directed the longitudinal assembly of gold nanorods. As a result of the linear assembly, the BODIPY chromophores positioned themselves in the plasmonic hotspots, which resulted in efficient plasmon-molecule coupling, thereby imparting photothermal properties to the assembled nanorods. This work thus demonstrates a new approach for the linear assembly of gold nanorods resulting in a plasmon-molecule coupled system, and the synergy between self-assembly and electronic coupling resulted in an efficient system having potential biomedical applications.

Two-dimensional assembly of gold nanoparticles grafted with charged-end-group polymers

HYPOTHESIS

Introducing charged terminal groups to polymers that graft nanoparticles enable Coulombic control over their assembly by tuning the pH and salinity of their aqueous suspensions.

EXPERIMENTS

Gold nanoparticles (AuNPs) are grafted with poly (ethylene glycol) (PEG) terminated with (charge-neutral), (negatively charged) or groups (positively charged), and characterized with dynamic light scattering, ζ-potential, and thermal gravimetric analysis. Liquid surface X-ray reflectivity (XR) and grazing incidence small-angle X-ray scattering (GISAXS) are used to determine the density profile and in-plane structure of the AuNPs assembly at the aqueous surface.

FINDINGS

Assembly of PEG-AuNPs at the liquid/vapor interface is tunable by adjusting pH or salinity for COOH but less for terminals. The distinct assembly behaviors are attributed to the overall charge of PEG-AuNPs as well as PEG conformation. COOH-PEG corona is more compact than those of the other terminal groups, leading to a crystalline structure with a smaller superlattice. The net charge per particle depends not only on the PEG terminal groups but also on the cation sequestration of PEG and the intrinsic negative charge of the AuNP surface. [1] The closeness to overall charge neutrality, and hydrogen bonding in play, brought by -PEG, drive -PEG-AuNPs to assembly and crystallinity without additives to the suspensions.

Methylene Blue-Loaded Mesoporous Silica-Coated Gold Nanorods on Graphene Oxide for Synergistic Photothermal and Photodynamic Therapy

Photo-nanotheranostics integrates near-infrared (NIR) light-triggered diagnostics and therapeutics, which are combined into a novel all-in-one phototheranostic nanomaterial that holds great promise for the early detection and precise treatment of cancer. In this study, we developed methylene blue-loaded mesoporous silica-coated gold nanorods on graphene oxide (MB-GNR@mSiO₂-GO) as an all-in-one photo-nanotheranostic agent for intracellular surface-enhanced Raman scattering (SERS) imaging-guided photothermal therapy (PTT)/photodynamic therapy (PDT) for cancer. Amine functionalization of the MB-GNR@mSiO₂ surfaces was performed using 3-aminopropyltriethoxysilane (APTES), which was well anchored on the carboxyl groups of graphene oxide (GO) nanosheets uniformly, and showed a remarkably higher photothermal conversion efficiency (48.93%), resulting in outstanding PTT/PDT for cancer. The in vitro photothermal/photodynamic effect of MB-GNR@mSiO₂-GO with laser irradiation showed significantly reduced cell viability (6.32%), indicating that MB-GNR@mSiO₂-GO with laser irradiation induced significantly more cell deaths. Under laser irradiation, MB-GNR@mSiO₂-GO showed a strong SERS effect, which permits accurate cancer cell detection by SERS imaging. Subsequently, the same Raman laser can focus on highly detected MDA-MB-23l cells for a prolonged time to perform PTT/PDT. Therefore, MB-GNR@mSiO₂-GO has great potential for precise SERS imaging-guided synergistic PTT/PDT for cancer.

Effect of Polymer Chain Length on the Superlattice Assembly of Functionalized Gold Nanoparticles

We report on the assembly of gold nanoparticle (AuNPs) superlattices at the liquid/vapor interface and in the bulk of their suspensions. Interparticle distances in the assemblies are achieved on multiple length scales by varying chain lengths of surface grafted AuNPs by polyethylene glycol (PEG) with molecular weights in the range 2000-40,000 Da. Crystal structures and lattice constants in both 2D and 3D assemblies are determined by synchrotron-based surface-sensitive and small-angle X-ray scattering. Assuming knowledge of grafting density, we show that experimentally determined interparticle distances are adequately modeled by spherical brushes close to the θ point (Flory-Huggins parameter, χ≈12) for 2D superlattices at a liquid interface and a nonsolvent (χ = ∞) for the 3D dry superlattices.

Near-Infrared-Triggered Photothermal Aggregation of Polymer-Grafted Gold Nanorods in a Simulated Blood Fluid

Gold nanorods were decorated with thermoresponsive copolymers of tailored architecture and constructed from N-isopropyl acrylamide and acrylamide. The copolymers were prepared via reversible addition-fragmentation chain transfer polymerization (RAFT) and immobilized on the gold nanorod surface taking advantage of the aurophilicity of its inherently formed trithiocarbonate groups. The topology as well as the average molecular weight of the copolymers was altered using either a monofunctional or 3-arm star RAFT agent. Two-dimensional arrays of the self-assembled core-shell nanostructures were fabricated by drop-casting showing tunable interparticle spacings. In a simulated blood fluid, the lower critical solution temperature of the nanohybrids could be modified over a significant temperature range around body temperature by adjusting the copolymer composition, the architecture, and/or the size of the polymer. The intrinsic photothermal properties of the gold nanorods were utilized to trigger particle aggregation by irradiation at 808 nm in the optical window of human tissues. In effect, a new nanohybrid system with remotely controllable aggregation via an external NIR-light stimulus for nanomedical applications was developed.

The Effects of Temperature on the Assembly of Gold Nanoparticle by Interpolymer Complexation

Using synchrotron-based small-angle X-ray scattering techniques, we demonstrate that poly(ethylene glycol)-functionalized gold nanoparticles (PEG-AuNPs) are assembled into close-packed structures that include short-range order with face-centered cubic structure, where crystalline qualities are varied by controlling the electrolyte concentration, pH, and temperature of the suspensions. We show that interpolymer complexation with poly(acrylic acid) (PAA) is induced by lowering the pH level of the PEG-AuNPs suspensions, and furthermore, increasing the temperature of the suspension strengthens interparticle attraction, leading to improved supercrystal structures. Our results indicate that this strategy creates robust nanoparticle superlattices with high thermal stability. The effects of PAA and PEG chain lengths on the assemblies are also investigated, and their optimal conditions for creating improved superlattices are discussed.

Self-Assembly of Polymer End-Tethered Gold Nanorods into Two-Dimensional Arrays with Tunable Tilt Structures

We demonstrated a facile yet effective strategy for self-assembly of polymer end-tethered gold nanorods (GNRs) into tunable two-dimensional (2D) arrays with the assistance of supramolecules of hydrogen bonded poly(4-vinyl pyridine) (P4VP) and 3-n-pentadecylphenol (PDP). Well-ordered 2D arrays with micrometer size were obtained by rupturing the assembled supramolecular matrix with a selective solvent. The formation of long-range ordered 2D arrays during a drying process was observed via small-angle X-ray scattering. Interestingly, the packing structure of the ordered arrays strongly depends on the molecular weight (M_w) of the polymer ligands and the size of the GNRs. By increasing M_w of the polymer ligands, tilted arrays can be obtained. The average angle between GNRs and the surface normal direction of the layered 2D arrays changes from 0 to 37° with the increase in M_w of the polymer ligands. A mechanism for assembly behavior of dumbbell shapes with a soft shell structure has been proposed. The resulting GNR arrays with different orientations showed anisotropic surface-enhanced Raman scattering (SERS) performance. We showed that the vertically ordered GNR arrays exhibited ∼3 times higher SERS signals than the tilt ordered arrays. The results prove that the polymer end-tethered GNRs can be used as a building block for preparing the tilted 2D arrays with tunable physicochemical properties, which could have a wide range of potential applications in photonics, electronics, plasmonics, etc.

Cytotoxicity and genotoxicity of gold nanorods assisted photothermal therapy against Ehrlich carcinoma in-vivo

AIM

Preparation of pegylated gold nanorods (PEG-AuNRs) that are capable of converting near infrared (NIR) light into heat. Evaluation of cancer therapeutic efficacy and long-term toxicity of the proposed photothermal therapy in comparison with other conventional modalities.

MATERIALS AND METHODS

Prepared PEG-AuNRs were characterized by measuring their absorption spectra, zeta potential, and transmission electron microscope (TEM). Cancer therapeutic efficacy was assessed by monitoring tumor growth, measuring DNA damage and superoxide dismutase (SOD) and malondialdehyde (MDA) levels in addition to examining tumor histopathology. Further analysis concerning the toxicity of all the proposed treatment modalities was also assessed by evaluating the cytotoxicity and genotoxicity in liver and kidney tissues.

KEY FINDINGS

The results demonstrated that both photothermal therapy (PEG-AuNRs + NIR laser) and chemotherapy (cisplatin) have higher efficacy in diminishing Ehrlich tumor growth with significance DNA damage over the other treatment modalities. Concerning the biosafety issue, mice treated photothermally exhibited lower MDA level and higher SOD activity in liver and kidney tissues compared with other treated groups. DNA damage represented by tail moment and olive moment of kidney tissues exhibited lower values for photothermal treated group and higher values for cisplatin treated group.

SIGNIFICANCE

Photothermal therapy (PEG-AuNRs + NIR laser) potentiates higher efficacy in treating Ehrlich tumor with minimum toxicity in comparison with other conventional treatment modalities.