Adv. Funct. Mater. 2011, 21, 4668–4676

Matthias Karg ,* Thomas Hellweg , and Paul Mulvaney

Abstract:

Understanding and controlling 3D nanocrystal self-assembly is a fundamental challenge in materials science. Assembly enables the unique optical and electronic properties of nanocrystals to be exploited in macroscopic materials, and also opens up the possibility to couple the optical response of nanocrystals to the optical modes of the superlattice. To date, assembly of such nanocrystal superlattices (NCSL) has focussed on fi xed, close packed structures with particle separations of just 1–3 nm. To achieve highly crystalline structures with tunable optical response, the nanocrystal interparticle separation needs to be precise and easily variable but >  50 nm. Here, we show the preparation of nanocrystal superlattices with spacings of 50–500 nm assembled from gold-poly- N   isopropylacrylamide core-shell particles and the characterization of their fascinating diffraction behavior by means of UV-vis spectroscopy. These nanocrystal superlattices exhibit pronounced diffraction in the visible (440-560 nm) with peak half-widths of the order of 10 nm. The position of the Bragg peak is simply tuned by adjusting the particle volume fraction. Due to the thermoresponsive nature of the polymer shell, temperature is used to initiate crystallization or melting of the superlattice. Heating and cooling cycles cause highly reversible melting/recrystallization in less than a minute.

dx.doi.org/10.1021/la2032829 | Langmuir

Enrico Della Gaspera,† Matthias Karg,‡ Julia Baldauf,‡ Jacek Jasieniak,§ Gianluigi Maggioni,|| and Alessandro Martucci*,†

†Dipartimento di Ingegneria Meccanica Settore Materiali, Universita di Padova, Via Marzolo, 9, 35131 Padova, Italy

‡School of Chemistry & Bio21 Institute, University of Melbourne, Parkville, VIC, 3010, Australia

§CSIRO Materials Science and Engineering, Ian Wark Laboratory, Bayview Avenue, Clayton 3168, Australia

||Dipartimento di Fisica, Universita di Padova c/o INFN Legnaro National Laboratories, Viale dell'Universita, 2 35020 Legnaro (Pd) Italy

Abstract:

In this work, we provide a detailed study of the influence of thermal annealing on submonolayer Au nanoparticle deposited on functionalized surfaces as standalone films and those that are coated with sol gel NiO and TiO2  thin films. The systems are characterized through the use of UV vis absorption, X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and spectroscopic ellipsometry. The surface plasmon resonance peak of the Au nanoparticles was found to red-shift and increase in intensity with increasing surface coverage, an observation that is directly correlated to the complex refractive index properties of Au nanoparticle layers. The standalone Au nanoparticles sinter at 200 C, and a relationship between the optical properties and the annealing temperature is presented.When overcoated with sol gel metal oxide films (NiO, TiO2 ), the optical properties of the Au nanoparticles are strongly aff ected by the metal oxide, resulting in an intense red shift and broadening of the plasmon band; moreover, the temperature-driven sintering is strongly limited by the metal oxide layer. Optical sensing tests for ethanol vapor are presented as one possible application, showing reversible sensing dynamics and confirming the effect of Au nanoparticles in increasing the sensitivity and in providing a wavelength dependent response, thus confirming the potential use of such materials as optical probes.

small 2011, 7, No. 22, 3113–3127

Feng Zhang , Emma Lees , Faheem Amin , Pilar Rivera_Gil , Fang Yang , Paul Mulvaney , * and Wolfgang J. Parak *

Abstract:

Water solubilization of nanoparticles is a fundamental prerequisite for many biological applications. To date, no single method has emerged as ideal, and several different approaches have been successfully utilized. These ‘phase-transfer’ strategies are reviewed, indicating key advantages and disadvantages, and a discussion of conjugation strategies is presented. Coating of hydrophobic nanoparticles with amphiphilic polymers provides a generic pathway for the phase transfer of semiconductor, magnetic, metallic, and upconverting nanoparticles from nonpolar to polar environments. Amphiphilic polymers that include maleimide groups can be readily functionalized with chemical groups for specifi c applications. In the second, experimental part, some of the new chemical features of such polymer-capped nanoparticles are demonstrated. In particular, nanoparticles to which a pH sensitive fluorophore has been attached are described, and their use for intracellular pH-sensing demonstrated. It is shown that the properties of analyte-sensitive fl uorophores can be tuned by using interactions with the underlying nanoparticles.

Coupling modes of gold trimer superstructures

AM Funston, TJ Davis, C Novo, P Mulvaney

An experimental and theoretical examination of the coupling modes within superstructures of gold nanorod trimers is presented. The experimentally determined spectrum of the nanorod trimers is reported and the modes are elucidated using an electrostatic eigenmode method based on the coupling of evanescent electric fields. The theory is able to reproduce the experimental spectrum well, and the nature of the modes and interactions are discussed.

ABSTRACT:

We present experimental data on the light scattering properties of linear chains of gold nanoparticles with up to six nanoparticles and an interparticle spacing of 1 nm. A red shift of the surface plasmon resonance with increasing chain length is observed. An exponential model applied to the experimental data allows determination of an asymptotic maximum resonance at a chain length of 10!12 particles. The
optical data are compared with analytical and numerical calculation methods (EEM and BEM).

KEYWORDS: Surface plasmon, waveguide, nanoparticle, coupling, DNA, assembly

J. Mater. Chem., 2011, 21, 13074

Alessandro Antonello,a Enrico Della Gaspera,a Julia Baldauf,b Giovanni Matteic and Alessandro Martucci*a

Received 3rd June 2011, Accepted 14th June 2011

DOI: 10.1039/c1jm12537k

Abstract:

Au nanorods have shown high potential applications due to strong and aspect ratio dependent surface plasmon resonances. A major limitation in the use of such nanostructures is related to their tendency to transform into the most thermodynamically stable spherical shape under heat or radiation exposure. In this work, we propose a method to delay the rod to sphere transformation, stabilizing the cylindrical shape up to 400 C. This has been accomplished by using photosensitive-layered titanates, which can be densified and stiffened by UV irradiation. Au nanorods dispersed in titanate films were deposited by spin coating and treated by both UV irradiation and thermal annealing at different temperatures. By properly combining UV curing and thermal annealing, this method allows to obtain Au nanorods covered by crystalline TiO2 rigid shells and to retain their shape and peculiar optical properties. Finally, the effect of interaction with specific gas analytes on the plasmon resonances of Au nanorods in TiO2 anatase films has been exploited for optical gas sensing applications.

Anthony J. Morfa,*,† Nicholas Kirkwood,† Matthias Karg,† Th. B. Singh,‡ and Paul Mulvaney†

†School of Chemistry & Bio21 Institute, University of Melbourne, Parkville, 3010, Victoria, Australia

‡CSIRO Division of Materials Science and Engineering, Clayton, 3169, Victoria, Australia

ABSTRACT: The effects of ZnO crystal defects and the ubiquitous defect fluorescence on the electronic properties of nanocrystal thin-films were determined. Films were prepared from particles prepared in DMSO with controllable defect fluorescence. Particles were determined to range in size from 5 to 12 nm on average, with little bearing on the electronic properties. Thin film electron mobilities were found to decrease from 0.04 cm2 V^1 s^1 to 0.008 cm2 V^1 s^1 with decreasing defect fluorescence, indicating crystal defects are pivotal to high- mobility ZnO nanoparticle films. The threshold voltage of ZnO nanoparticle FET devices was found to decrease from 120 to 40 V while the resistivity increased 100-fold with decreasing defect fluorescence. These results are found to be in excellent agreement with theory and greatly improve our understanding of ZnO nanoparticle conduction.

Zhengwei Mao,^,† Regis Cartier,^,† Anja Hohl,† Maura Farinacci,‡ Anca Dorhoi,‡ Tich-Lam Nguyen,§ Paul Mulvaney,§ John Ralston,|| Stefan H. E. Kaufmann,‡ Helmuth M␣ohwald,† and Dayang Wang*,†,||

†Max Planck Institute of Colloids and Interfaces, D-14424, Potsdam, Germany

‡Max Planck Institute for Infection Biology, Department of Immunology, 10117, Berlin, Germany

§School of Chemistry and Bio21 Institute, University of Melbourne, VIC 3010, Australia

Ian Wark Research Institute, University of South Australia, Adelaide, SA 5095, Australia

ABSTRACT: Biocompatibility is of paramount importance for drug delivery, tumor labeling, and in vivo application of nanoscale bioprobes. Until now, biocompatible surface proces- sing has typically relied on PEGylation and other surface coatings, which, however, cannot minimize clearance by macro- phages or the renal system but may also increase the risk of chemical side e␣ects. Cell membranes provide a generic and far more natural approach to the challenges of encapsulation and delivery in vivo. Here we harness for the ␣rst time living cells as “factories” to manufacture cell membrane capsules for encap- sulation and delivery of drugs, nanoparticles, and other biolabels. Furthermore, we demonstrate that the built-in protein channels of the new capsules can be utilized for controlled release of encapsulated reagents.

KEYWORDS: Drug delivery, encapsulation, nanoparticles, cell membranes, nanostructures