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.

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 (LSPR) peak of GNRs in the CD response is much more apparent than that of the transverse LSPR. The CD responses of individual CYS-attached GNRs and CYS-assembled gold nanoparticles (GNPs) substantiate that the form of assembly and the shape of building blocks are significant not only for the intensity but for the line shape of the CD signals.

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.

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.

Inorganic nanocrystal (NC) superstructures, which exhibit unique collective properties that are different to those of both the individual NCs and bulk materials, are of much scientific and technological interest. [1][2][3][4][5] For noble-metal NCs, the collective oscillation of free electrons, that is, the so-called plasmon resonance in the superstructures, provides a feasible way to realize light concentration and manipulation on a small scale.[6] Such plasmon resonance gives rise to many potential applications of noble-metal NC superstructures in different fields, for example, optical waveguides, [7] superlensing, [8] photon detection, [9] and surface-enhanced Raman scattering (SERS). Among these applications, the SERS effect based on noble-metal NC superstructures is of particular interest because of its extraordinary advantages in the highly sensitive detection of trace chemical or biological species. [10,11] The SERS effect originates from the dramatic amplification of electromagnetic fields in the NC superstructures. When the superstructures are irradiated at the wavelength that couples with the plasmon resonance of the inner NCs, the junction regions among the adjacent NCs function as "hotspots" and the local electromagnetic fields in the superstructure are amplified.[12] As a result, the Raman scattering of the detected species located at these junctions will be remarkably enhanced. Evidently, the intensity of SERS in the superstructures is determined not only by the type, shape, and size of the single NC units, but also by the inter-NC distance and arrangement pattern. Although many reports have shown that the 1D, 2D, and 3D assemblies of noble-metal NCs can be used as efficient substrates for SERS, [13] the corresponding studies on the NC superstructures are rare because of the difficulties in synthesis of monodispersed NCs that have different shapes, as well as the controlled organization of NCs on a large scale. In order to understand and maximize the SERS effect, large-scale NC superstructures with controllable morphologies are highly desirable. Herein we report how three types of Au NCs with identical sizes but different shapes can be used as building blocks to prepare superstructures on several different substrates. We demonstrate that both the structures and morphologies of the superstructures are highly dependent on the shapes of the NC units, and furthermore, that these superstructures exhibit obvious differences in their SERS properties. Both the formation mechanism and the SERS properties of the different Au NC superstructures are explored in detail.The seed-mediated growth method was used to synthesize single-crystalline rhombic dodecahedral (RD), octahedral, and cubic Au NCs by manipulating the growth kinetics of the NCs (see the Experimental Section). As reported in our previous study, RD, octahedral, and cubic Au NCs are bounded by twelve (110) planes, eight (111) planes, and six (100) planes, respectively.[14] The three types of Au NCs, with an average size of around 70 nm, have well-def...

This report shows that a nanovector composed of peptide-based nanofibrous hydrogel can condense DNA to result in strong immune responses against HIV. This nanovector can strongly activate both humoral and cellular immune responses to a balanced level rarely reported in previous studies, which is crucial for HIV prevention and therapy. In addition, this nanovector shows good biosafety in vitro and in vivo. Detailed characterizations show that the nanofibrous structure of the hydrogel is critical for the dramatically improved immune responses compared to existing materials. This peptide-based nanofibrous hydrogel shows great potential for efficacious HIV DNA vaccines and can be potentially used for delivering other vaccines and drugs.

Sizing up QDs: CdTe or CdSe quantum dots (QDs) stabilized by chiral biomolecules show size‐dependent circular dichroism (CD) characteristics in the visible light region. Theoretical calculations reveal that the origin of this CD is the combination of the weak optical activity of the biomolecules and the large enhancement effects from the strong absorption of QDs.

his help with the characterization of optical properties of NC superstructures. SERS = surface-enhanced Raman scattering.Supporting information for this article is available on the WWW under http://dx.