Organized arrays of anisotropic nanoparticles show electronic and optical properties that originate from the coupling of shape-dependent properties of the individual nanorods. The organization of nanorods in a controllable and predictable way provides a route to the fabrication of new materials and functional devices. So far, significant progress has been achieved in the self-assembly of nanorod arrays, yet the realization of a range of different structures requires changing the surface chemistry of the nanoparticles. We organized metal nanorods in structures with varying geometries by using a striking analogy between amphiphilic ABA triblock copolymers and the hydrophilic nanorods tethered with hydrophobic polymer chains at both ends. The self-assembly was tuneable and reversible and it was achieved solely by changing the solvent quality for the constituent blocks. This approach provides a new route to the organization of anisotropic nanoparticles by using the strategies that are established for the self-assembly of block copolymers.

Photothermally driven volume transitions in polymer microgels have promising applications for site-specific drug delivery and photodynamic therapy. We studied the temperature-induced volume phase transitions for a series of thermoresponsive microgels of various compositions to find a system with a sharp transition in the physiologically relevant range spanning 38-41 degrees C in 0.01 M phosphate-buffered saline solution (pH = 7.4). We found that the poly(N-isopropylacrylamide-maleic acid) microgels showed an 8-fold decrease in size under the aforementioned conditions. These microgels were loaded with gold nanorods designed to absorb in the near-IR spectral range. Following irradiation at lambda = 809 nm, the microgels underwent a large, reversible, photothermally triggered change in volume. We believe that this microgel system is a promising candidate for photothermally controlled drug release.

We report a predefined self-organization of gold nanorods (NRs) end-terminated with multiple polymer arms ("pom-poms") in higher-order structures. The assembly of polymer-tethered NRs was controlled by changing the structure of the polymer pom-poms. We show that the variation in the molecular weight of the polymer molecules and their relative location with respect to the long side of the NRs resulted in two competing association modes of the nanorods, that is, their side-by-side and end-to-end assembly, and produced bundles, chains, rings, and bundled chains of the NRs. The superposition of the two variables controlling the organization of NRs allowed us to create a map showing the variation in the longitudinal plasmonic bands of the NRs achieved by their self-assembly.

Self-assembly of nanoparticles is one of the fascinating subjects of nanoscience. Controlled organization of nanoparticles in ordered or hierarchical structures allows for the coupling of their size-and shape-dependent properties, and makes them potentially useful in optoelectronics, sensing and imaging, and biomedical applications. [1][2][3] A broad range of targeted self-assembled structures can be produced by organizing nanoparticles with compositional heterogeneity, [4][5][6][7] which is realized either by synthesizing nanoparticles from several different materials or by selectively attaching organic molecules to the different sites of the nanoparticles. [8,9] Compositional heterogeneity makes nanoparticles conceptually similar to amphiphilic molecules (e.g., surfactants or block copolymers) and allows the use of thermodynamic approaches to the self-assembly of the ''colloidal molecules'' in energetically favorable structures. These strategies are particularly useful in the assembly of polymer-tethered inorganic nanorods (NRs), which in addition to the compositional heterogeneity possess an asymmetric structure and the associated shape-dependent properties. The organization of NRs in organized arrays provides an additional degree of freedom in tuning their properties by the coupling of the optical and electronic properties of the adjacent individual NRs.Experimental and theoretical studies of the organization of polymer-tethered inorganic NRs show that they can be organized in a range of structures which include bundles, tubes and sheets, [10] lamella and spherical micelles, [11] and rings, chains, and spheres. [12,13] Thermodynamic approaches favorably complement other methods for the engineered NR assembly which include the template-driven assembly, [10,11,[14][15][16] the interactions between the ligands stabilizing NRs, [17] assembly induced by using external fields, [18,19] and the organization of NRs by using controlled solvent evaporation. [20] Recently, a ''block copolymer'' paradigm was proposed for the self-assembly of gold nanorods coated with a bilayer of cetyl trimethyl ammonium bromide (CTAB) and terminated with polystyrene molecules at both ends.[12] (Later in the text these polymer-tethered NRs are referred to as ''triblocks''.) The proposed strategy used the analogy between pom-pom block copolymers, in which multiple polymer chains are attached to the ends of the linear block, [21] and amphiphilic triblocks comprising a hydrophilic central metal block and two hydrophobic polymer end blocks. The triblocks were dispersed in dimethylformamide, N,N-dimethyl formamide (DMF; a good solvent for both the metal block and PS) or tetrahydrofuran (THF; a poor solvent for the CTAB-coated metal block and a good solvent for PS). The self-assembly of the triblocks was achieved by adding water to the solution of polymer-terminated NRs, thus changing the quality of solvent for the hydrophilic and hydrophobic blocks. Organization of triblocks in the DMF/water mixture yielded chains of nanorods, characterized by...

Herein we demonstrate the photothermally-triggered self-assembly of poly(N-isopropylacrylamide)-functionalized gold nanorods in one-dimensional structures.