Gold nanorods exhibit rich surface-plasmon-resonance (SPR)derived properties, which have made discrete nanorods useful for many interesting applications such as optical data storage, [1] submicrometer metallic barcodes, [2] sensing, [3] biological imaging, [4] and controlled gene delivery. [5] Future scientific and technological applications of Au nanorods require the capability to assemble into complex one-, two-, or even three-dimensional (3D) functional architectures. The assembly of Au nanorods also allows for the utilization of their collective properties that result from the coupling of the optical and electronic properties between neighboring individual nanorods. Several approaches have been developed for the assembly of Au nanorods in either end-to-end (EE) or side-by-side (SS) orientations. They include i) assembly through electrostatic interactions, hydrogen bonding, or covalent bonding, [6] ii) antibody/antigen and streptavidin/biotin biorecognitions, [7] iii) use of carbon nanotubes and silica nanofibers as templates, [8] and iv) interactions between functionalized polymers in selective solvents. [9] Au nanorods assembled by these approaches are generally difficult to disassemble. Even though significant progress has been made in the organization of nanomaterials, reversible assembly and disassembly of Au nanorods in either EE or SS orientations has remained a big challenge. So far, reversible aggregation of spherical Au nanoparticles has been demonstrated by functionalizing them with thiol-modified DNA oligomers. [10] Here, we report on a robust strategy for the reversible assembly and disassembly of Au nanorods in both EE and SS fashion. Thiol-containing bifunctional molecules are selectively bound to the end or side surface of individual Au nanorods. The bound molecules induce the assembly of Au nanorods if the pH of the nanorod solution is adjusted within an optimal range. Outside the optimal pH range, Au nanorods are disassembled. This pH-controlled assembly and disassembly is reversible and can be repeated many times. Moreover, the distances between assembled nanorods are estimated to vary from 0.080 to 1.8 nm for different assembling molecules and assembly orientations.As-prepared Au nanorods are stabilized in 0.1 M aqueous cetyltrimethylammonium bromide (CTAB) solutions with pH ¼ 3.5. Their ensemble transverse and longitudinal plasmon wavelengths are 515 and 780 nm, respectively. The ensemble extinction values at the two plasmon peaks are 1.0 and 3.7, respectively, suggesting a high yield of Au nanorods. The nanorod concentration is estimated to be %0.8 nM according to previously determined molar extinction coefficients. [11] The average length, diameter, and aspect ratio, determined from %500 nanorods on transmission electron microscopy (TEM) images, are 38 AE 4 nm, 11 AE 1 nm, and 3.6 AE 0.5 nm, respectively. The used bifunctional molecules include 3-mercaptopropionic acid (MPA), 11-mercaptoundecanoic acid (MUA), glutathione (GSH), and cysteine (CYS). Their concentrations in nanorod so...

Hybrid nanostructures of organic dyes and inorganic gold nanorods are constructed using the layer-by-layer assembly method via electrostatic interactions. Strong coupling is observed between the molecular resonance of dyes and the plasmonic resonance of gold nanorods when their spectra overlap strongly. The coupling strength is tuned by choosing gold nanorods with longitudinal plasmon wavelengths varying from 570 to 870 nm. The resonance coupling-induced plasmon shift is found to be strongly dependent on the dye concentration and the spacing between the dye and nanorod. Moreover, the resonance coupling can be switched off by laser illumination to decompose adsorbed dyes. We believe this is the first time that the coupling between molecular and plasmonic resonances is observed for freestanding hybrid nanostructures constructed out of dyes and colloidal gold nanorods. These results will be helpful in understanding the fundamental interactions between molecular and plasmonic resonances and useful for the design of resonance coupling-based chemical and biological sensors.

Conducting hydrogels provide great potential for creating designer shape-morphing architectures for biomedical applications owing to their unique solid-liquid interface and ease of processability. Here, a novel nanofibrous hydrogel with significant enzyme-like activity that can be used as "ink" to print flexible electrochemical devices is developed. The nanofibrous hydrogel is self-assembled from guanosine (G) and KB(OH) with simultaneous incorporation of hemin into the G-quartet scaffold, giving rise to significant enzyme-like activity. The rapid switching between the sol and gel states responsive to shear stress enables free-form fabrication of different patterns. Furthermore, the replication of the G-quartet wires into a conductive matrix by in situ catalytic deposition of polyaniline on nanofibers is demonstrated, which can be directly printed into a flexible electrochemical electrode. By loading glucose oxidase into this novel hydrogel, a flexible glucose biosensor is developed. This study sheds new light on developing artificial enzymes with new functionalities and on fabrication of flexible bioelectronics.

Manufacturing V(2)O(5) in a 3D periodic highly interconnected gyroid structure on the 10 nm length scale is shown to lead to a significant electrochromic performance enhancement. The structured devices surpass previous inorganic electrochromic materials in all relevant parameters: the switching speed, coloration contrast, and composite coloration efficiency. In particular, the 85 ms switching speed lies within a factor of two of video rate. Enhanced ion intercalation into the gyroid morphology can be extended to other transition-metal oxides and is therefore promising for lithium ion batteries, supercapacitors, and sensors.

Plasmonic gold nanorods (Au NRs)-copper sulfide heterostructures have recently attracted much attention owing to the synergistically enhanced photothermal properties. However, the facile synthesis and interface tailoring of Au NRs-copper sulfide heterostructures remain a formidable challenge. In this study, the rational design and synthesis of Au NRs-Cu S heterostructures via a one-pot hydrothermal process is reported. Specifically, core-shell and dumbbell-like Au NRs-Cu S heterostructures are obtained with well-controlled interfaces by employing the Au NRs with different aspect ratios. Both core-shell and dumbbell-like Au NRs-Cu S have proven effective as photothermal therapy agents, which offer both high photothermal stability and significant photothermal conversion efficiency up to 62%. The finite-difference time domain simulation results confirm the coupling effect that leads to the enhanced local field as well as the optical absorption at the heterostructure interface. Importantly, these Au NRs-Cu S heterostructures can be compatibly used as an 808 nm laser-driven photothermal therapy agents for the efficient photothermal therapy of cancer cells in vitro. This study will provide new insight into the design of other noble metal-semiconductor heterostructures for a broad range of applications utilizing surface plasmon resonance enhancement phenomena.