A novel protocol for the seedless synthesis of gold nanorods (AuNRs) using dopamine as a reductant has been developed. We report that the concentration of CTAB can be reduced to 22 mM and that the AuNRs' longitudinal surface plasmon resonance (LSPR) can be tuned from 700 to 1050 nm. The size of the AuNRs can also be tuned from 7 × 30 nm to 20 × 100 nm. The amphiphilicity and the cationic structure of the protonated dopamine enable it to interact favorably with the CTAB bilayer and lead to a high-yield synthesis of AuNRs (80–95%). LSPR peaks, size, and aspect ratio of the synthesized AuNRs can be tuned by adjusting the concentration and ratio of silver ions, CTAB, and dopamine. In addition, this reaction is much faster than previously reported methods requiring only 30 minutes to complete.

While gold nanorods have been extensively studied and used in many biological, plasmonics, and sensing applications, their conventional seed-mediated synthesis still presents a number of limitations. Its high sensitivity to the concentration of the reducing agent (ascorbic acid) leads to problems with reliability as well as extremely poor yield of ionic-to-metallic gold conversion, which is only ∼15%. In addition, the synthesis of high purity nanorods with longitudinal surface plasmon resonance (LSPR) peak higher than 1000 nm is particularly difficult utilizing this technique. This report demonstrates the use of hydroquinone for the synthesis of gold nanorods which addresses these two major limitations. By replacing ascorbic acid with a large excess of hydroquinone, rods with LSPR up to 1230 nm can be synthesized with a high degree of purity, reliability, and near quantitative conversion of gold ions to metallic gold. The growth of the rods is tracked by TEM utilizing a thiolation reaction to halt their growth. Finally, the effect of changing various parameters including hydroquinone, seed, gold, and silver concentration is examined, demonstrating the tunability of the procedure over the broad range of attainable LSRPs from 770 to 1230 nm.Keywords: anisotropic crystal growth; gold nanorods; hydroquinone; surface functionalization);

Recently, branched and star-shaped gold nanoparticles have received significant attention for their unique optical and electronic properties, but most examples of such nanoparticles have a zero-dimensional shape with varying numbers of branches coming from a quasi-spherical core. This report details the first examples of higher-order penta-branched gold particles including rod-, wire-, and platelike particles which contain a uniquely periodic starfruitlike morphology. These nanoparticles are synthesized in the presence of silver ions by a seed-mediated approach based on utilizing highly purified pentahedrally twinned gold nanorods and nanowires as seed particles. The extent of the growth can be varied, leading to shifts in the plasmon resonances of the particles. In addition, the application of the starfruit rods for surface-enhanced Raman spectroscopy (SERS) is demonstrated.

The fabrication of highly optically active supercrystals of anisotropic nanorods exploiting the electric field concentration and the nanoantenna effects provides a new family of optical sensors with the potential to maximize the SERS signal and thereby the possibility of detecting and quantifying the disease markers with low SERS cross-sections at ultralow concentrations. The capabilities of the new self-assembled nanorod SERS substrates have been demonstrated for real-time sensing of prions in real blood. It may also be possible to functionalize the top layers of supercrystals with specific recognition molecules for sensing many other disease markers, or even its integration into on-line devices, for the ultrasensitive screening of analytical targets relevant to medical science, environment, and homeland security.Graphical abstractHighlights► Description of the application of gold nanorod supercrystals as optical antennas for SERS detection. ► The advantages of SERS as ultrasensitive analytical technique are described. ► Gold nanorods can self-assemble into supercrystals and generate intense fields. ► The resulting nanoplasmonic platform has been applied for prion detection in blood.

Highly organized supercrystals of Au nanorods with plasmonic antennae enhancement of electrical field have made possible fast direct detection of prions in complex biological media such as serum and blood. The nearly perfect three-dimensional organization of nanorods render these systems excellent surface enhanced Raman scattering spectroscopy substrates with uniform electric field enhancement, leading to reproducibly high enhancement factor in the desirable spectral range.

We report on the structure, uniaxial orientation, and photoluminescent properties of CdS nanorods that form stable nanocomposites with smectic C hydrogen-bonded polymers from the family of poly(4-(n-acryloyloxyalkoxy)benzoic acids. TEM analysis of microtomed films of nanocomposites reveals that CdS nanorods form small domains that are homogeneously distributed in the LC polymer matrix. They undergo long-range orientation with the formation of one-dimensional aggregates of rods when the composite films are uniaxially deformed. The Stokes photoluminescence was observed from CdS NRs/LC polymer composites with emission peak located almost at the same wavelength as that of NRs solution in heptane. An anti-Stokes photoluminescence (ASPL) in polymer nanocomposites was found under the excitation below the nanoparticles ground state. The mechanism of ASPL was interpreted in terms of thermally populated states that are involved in the excitation process. These nanocomposites represent an unusual material in which the optical properties of anisotropic semiconductor nanostructures can be controlled by mechanical deformation of liquid-crystalline matrix.

We report on the plasmonic properties of 6 nm gold nanoparticles that form highly stable solutions in the nematic liquid crystal 4-cyano-4-n-pentylbiphenyl (5CB). The nanoparticles were covalently functionalized with 4-sulfanylphenyl-4-[4-(octyloxy)phenyl]benzoate, which resembles the structure of the 5CB molecules. The solubility of these nanoparticles in 5CB was significantly higher than that of conventional alkanethiol-terminated nanoparticles. An 8 nm shift of the surface plasmon resonance was observed when the gold nanoparticles were dissolved in the nematic phase of 5CB, as compared to the isotropic solution in methylene chloride. Good agreement of the experimental surface plasmon resonance shift with Mie calculations using an adjusted dielectric function for a reduced electron mean free path in small nanoparticles confirmed that the gold nanoparticles are solvated by the liquid crystal molecules. The stability of this composite was verified by repeated temperature cycling between the isotropic and nematic phases. We also investigated the nematic-to-isotropic phase transition temperature and the threshold voltage for the Freedericksz transition in gold-nanoparticle-doped and undoped liquid crystal devices.

Stabförmige Nanokristalle ordnen sich üblicherweise parallel an – eine Folge ihrer anisometrischen Form und Steife. In ihrer Zuschrift auf S. 2245 ff. berichten E. R. Zubarev und B. P. Khanal über die spontane Selbstorganisation von polymerumhüllten Metallnanostäben zu ringförmigen Anordnungen (siehe Bild). Die Bildung dieser Überstrukturen – „Ringen aus Nanostäben“ – wird durch Wassertropfen ausgelöst, die auf der Oberfläche nichtpolarer Lösungsmittel kondensieren, und verläuft innerhalb von Sekunden nahezu quantitativ.

Rodlike nanocrystals typically pack in a parallel fashion as dictated by their anisometric shape and stiffness. In their Communication on page 2195 ff., E. R. Zubarev and B. P. Khanal report the spontaneous self-organization of polymer-coated metallic nanorods into circular arrays (see picture). These superstructures—“rings of nanorods”—are templated by water microdroplets that condense on the surface of nonpolar organic solvents and can be produced in near-quantitative yield in a matter of seconds.

This review will first look at the various covalent strategies that have been developed to attach drugs to gold nanoparticles as well as the strengths and limitations of such strategies. After examining general strategies for the synthesis of gold nanoparticles and their subsequent covalent functionalization, this review will focus on nanoparticle conjugates for gene therapy, antibacterial, and anticancer applications including the use of gold nanoparticles with intrinsically therapeutic properties. The effects of targeting and cellular uptake of gold nanoparticles will also be discussed.Download high-res image (497KB)Download full-size image