: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Gold nanorods have been receiving extensive attention owing to their extremely attractive applications in biomedical technologies, plasmon-enhanced spectroscopies, and optical and optoelectronic devices. The growth methods and plasmonic properties of Au nanorods have therefore been intensively studied. In this review, we present a comprehensive overview of the flourishing field of Au nanorods in the past five years. We will focus mainly on the approaches for the growth, shape and size tuning, functionalization, and assembly of Au nanorods, as well as the methods for the preparation of their hybrid structures. The plasmonic properties and the associated applications of Au nanorods will also be discussed in detail.

Gold nanorods and their plasmonic properties

Chemical methods developed over the past two decades enable preparation of colloidal nanocrystals with uniform size and shape. These Brownian objects readily order into superlattices. Recently, the range of accessible inorganic cores and tunable surface chemistries dramatically increased, expanding the set of nanocrystal arrangements experimentally attainable. In this review, we discuss efforts to create next-generation materials via bottom-up organization of nanocrystals with preprogrammed functionality and self-assembly instructions. This process is often driven by both interparticle interactions and the influence of the assembly environment. The introduction provides the reader with a practical overview of nanocrystal synthesis, self-assembly, and superlattice characterization. We then summarize the theory of nanocrystal interactions and examine fundamental principles governing nanocrystal self-assembly from hard and soft particle perspectives borrowed from the comparatively established fields of micro...

Self-Assembly of Colloidal Nanocrystals: From Intricate Structures to Functional Materials

Diagnostics and Therapy Guanying Chen,‡,† Indrajit Roy,†,§ Chunhui Yang,*,‡ and Paras N. Prasad*,† †Institute for Lasers, Photonics, and Biophotonics and Department of Chemistry, University at Buffalo, State University of New York, Buffalo, New York 14260, United States ‡School of Chemical Engineering and Technology, Harbin Institute of Technology, Harbin, Heilongjiang 150001, China Department of Chemistry, University of Delhi, Delhi 110007, India

Nanochemistry and Nanomedicine for Nanoparticle-based Diagnostics and Therapy

Anisotropic gold nanoparticles (AuNPs) have attracted the interest of scientists for over a century, but research in this field has considerably accelerated since 2000 with the synthesis of numerous 1D, 2D, and 3D shapes as well as hollow AuNP structures. The anisotropy of these nonspherical, hollow, and nanoshell AuNP structures is the source of the plasmon absorption in the visible region as well as in the near-infrared (NIR) region. This NIR absorption is especially sensitive to the AuNP shape and medium and can be shifted towards the part of the NIR region in which living tissue shows minimum absorption. This has led to crucial applications in medical diagnostics and therapy ("theranostics"), especially with Au nanoshells, nanorods, hollow nanospheres, and nanocubes. In addition, Au nanowires (AuNWs) can be synthesized with longitudinal dimensions of several tens of micrometers and can serve as plasmon waveguides for sophisticated optical devices. The application of anisotropic AuNPs has rapidly spread to optical, biomedical, and catalytic areas. In this Review, a brief historical survey is given, followed by a summary of the synthetic modes, variety of shapes, applications, and toxicity issues of this fast-growing class of nanomaterials.

Anisotropic gold nanoparticles: synthesis, properties, applications, and toxicity

Reversible plasmonic circular dichroism (CD) responses are realized for the first time based on temperature-dependent assembly and disassembly of Au nanorod (Au NR) and DNA hybrids. Compared with the conventional UV-vis absorption spectra, the changes in both intensity and line shape of plasmonic CD signals are much more pronounced, leading to a preliminary detection limit of DNA as low as 75 nM. The mechanism and influence factors of reversible plasmonic CD responses are explored.

Reversible Plasmonic Circular Dichroism of Au Nanorod and DNA Assemblies

Keeping in shape: The shapes of gold nanocrystals determine their self-assembly behavior—rhombic dodecahedral nanocrystals form triangular multilayers (see picture), whereas cubic and octahedral nanocrystals form monolayers or multilayers without well-defined contours. The three superstructures exhibit different optical properties, and the rhombic dodecahedral gold nanocrystals display strong anisotropic SERS effects.

Superstructures and SERS Properties of Gold Nanocrystals with Different Shapes

The manipulation of the chirality and corresponding optical activity in the visible–near-infrared (NIR) light region is significant to realize applications in the fields of chemical sensing, enantioselective separation, chiral nanocatalysis, and optical devices. We studied the plasmon-induced circular dichroism (CD) response by one-dimensional (1D) assembly of cysteine (CYS) and gold nanorods (GNRs). Typically, GNRs can form end-to-end assembly through the electrostatic attraction of CYS molecules preferentially attached on the ends of different GNRs. CD responses are observed at both the UV and visible–NIR light region in the 1D assembly, which are assigned to the CYS molecules and the GNRs, respectively. In addition, the wavelength of the CD responses can be manipulated from 550 nm to more than 900 nm through altering the aspect ratios of GNRs in 1D assembly. Anisotropic enhancement of optical activity is discovered, suggesting that the enhancement of the longitudinal localized surface plasmon resonance...

Manipulation of collective optical activity in one-dimensional plasmonic assembly.

The design and fabrication of chiral nanostructures is a promising approach to realize enantiomeric recognition and separation. In our work, gold nanorod@chiral mesoporous silica core–shell nanoparticles (GNR@CMS NPs) have been successfully synthesized. This novel material exhibits strong and tunable circular dichroism signals in the visible and near-infrared regions due to the optical coupling between the CMS shells and the GNR cores. When chiral cysteine molecules are loaded in the porous shells, the corresponding surface enhanced Raman scattering spectroscopy demonstrates a distinct chiral recognition effect, which can be used to semiquantitatively measure the composition of chiral enantiomers. A detailed sensing mechanism has been disclosed by density functional theory calculations.

Gold nanorod@chiral mesoporous silica core-shell nanoparticles with unique optical properties.

Assemblies of chiral cysteine (CYS) and Au nanorods (GNRs) are constructed in two typical patterns, end-to-end and side-by-side. Impressively, side-by-side assembled GNRs with CYS show obviously stronger plasmonic circular dichrosim (CD) response compared with the end-to-end assemblies. The corresponding theoretical calculation elucidates the intrinsic relationship among geometric structure, electromagnetic interaction, and induced plasmonic CD of the assemblies. This work will significantly benefit the design and application of plasmonic nanodevices with controllable chiroptical responses.

Zhening Zhu

Papers

Reversible Plasmonic Circular Dichroism of Au Nanorod and DNA Assemblies

Superstructures and SERS Properties of Gold Nanocrystals with Different Shapes

Manipulation of collective optical activity in one-dimensional plasmonic assembly.

Gold nanorod@chiral mesoporous silica core-shell nanoparticles with unique optical properties.

Conformation Modulated Optical Activity Enhancement in Chiral Cysteine and Au Nanorod Assemblies