Priyanka Dey

Self assembly of plasmonic core–satellite nano-assemblies mediated by hyperbranched polymer linkers

The morphology of plasmonic nano-assemblies has a direct influence on optical properties, such as localised surface plasmon resonance (LSPR) and surface enhanced Raman scattering (SERS) intensity. Assemblies with core-satellite morphologies are of particular interest, because this morphology has a high density of hot-spots, while constraining the overall size. Herein, a simple method is reported for the self-assembly of gold NPs nano-assemblies with a core-satellite morphology, which was mediated by hyperbranched polymer (HBP) linkers. The HBP linkers have repeat units that do not interact strongly with gold NPs, but have multiple end-groups that specifically interact with the gold NPs and act as anchoring points resulting in nano-assemblies with a large (∼48 nm) core surrounded by smaller (∼15 nm) satellites. It was possible to control the number of satellites in an assembly which allowed optical parameters such as SPR maxima and the SERS intensity to be tuned. These results were found to be consistent with finite-difference time domain (FDTD) simulations. Furthermore, the multiplexing of the nano-assemblies with a series of Raman tag molecules was demonstrated, without an observable signal arising from the HBP linker after tagging. Such plasmonic nano-assemblies could potentially serve as efficient SERS based diagnostics or biomedical imaging agents in nanomedicine.

Hyperbranched Polymer–Gold Nanoparticle Assemblies: Role of Polymer Architecture in Hybrid Assembly Formation and SERS Activity

Plasmonic gold nanoassemblies that self-assemble with the aid of linking molecules or polymers have the potential to yield controlled hierarchies of morphologies and consequently result in materials with tailored optical (e.g., localized surface plasmon resonances (LSPR)) and spectroscopic properties (e.g., surface-enhanced Raman scattering (SERS)). Molecular linkers that are structurally well-defined are promising for forming hybrid nanoassemblies which are stable in aqueous solution and are increasingly finding application in nanomedicine. Despite much ongoing research in this field, the precise role of molecular linkers in governing the morphology and properties of the hybrid nanoassemblies remains unclear. Previously we have demonstrated that branched linkers, such as hyperbranched polymers, with specific anchoring end groups can be successfully employed to form assemblies of gold NPs demonstrating near-infrared SPRs and intense SERS scattering. We herein introduce a tailored polymer as a versatile molecular linker, capable of manipulating nanoassembly morphologies and hot-spot density. In addition, this report explores the role of the polymeric linker architecture, specifically the degree of branching of the tailored polymer in determining the formation, morphology, and properties of the hybrid nanoassemblies. The degree of branching of the linker polymer, in addition to the concentration and number of anchoring groups, is observed to strongly influence the self-assembly process. The assembly morphology shifts primarily from 1D-like chains to 2D plates and finally to 3D-like globular structures, with increase in degree of branching of the macromolecular linker. Insights have been gained into how the morphology influences the SERS performance of these nanoassemblies with respect to hot-spot density. These findings supplement the understanding of the morphology determining nanoassembly formation and pave the way for the possible application of these nanoassemblies as SERS biosensors for medical diagnostics.

Mixed Polymer-Coated Magnetic Nanoparticles as Forward Osmosis Draw Agents of Tuned Hydrophilicity

We recently reported a polymer-coated magnetic nanoparticle (MNP) draw agent for the forward osmosis (FO) water desalination process. The water flux was found to increase when the polymer poly(sodium acrylate) (PSA) was anchored to the MNP surface as compared to the polymer (or polyelectrolyte solution) alone, due to the polymer chains being stretched out and most of the hydrophilic groups on the polymer contributing to water flux. We herein report the use of a secondary polymer poly(N-isopropylacrylamide) PNIPAM to manipulate the PSA polymer conformation and influence inter- and intrachain interactions to enhance the efficiency of the FO draw agent. These PSA-PNIPAM-coated MNPs generated a much higher water flux of ∼11.66 LMH when compared to the 100 % PSA-coated MNPs featuring a value of ∼5.32 LMH under identical FO conditions. The osmotic pressure and water flux driven by the mixed polymer-coated MNPs were found to be a strong function of the net polymer coverage on MNPs, that is, net available hydrophilic groups. Our new draw agent demonstrates potential for use in the water industry due to its improved efficiency and cost effectiveness as it uses only ∼0.062 % (w/v) of the draw agent solution.