Weakening Circular Dichroism of Plasmonic Nanospirals Induced by Surface Grafting with Alkyl Ligands.

Silver nanospirals with strong chiroptical activity (characterized by circular dichroism) are grafted with achiral alkyl ligands, resulting in a weakening of the chiroptical activity. The chiroptical weakening is exacerbated with increasing bond energy of the Ag-ligand contacts, which is ascribed to the effective medium screening effect and electron withdrawal toward the alkyl ligands.

Ballistic glancing angle deposition of inclined Ag nanorods limited by adatom diffusion.

The growth dynamics of 1D nanorods (NRs) composed of noble metals is ambiguous during glancing angle deposition (GLAD). The continuum equation (CE) model describes ballistic deposition limited by adatom diffusion, not verified in GLAD of noble metal NRs. In this work, GLAD is operated at Ts (substrate temperature) below room temperature to create inclined Ag NRs, and the CE fits the growth orientation of NRs with deposition angles at fixed Ts well. The CE fitting evaluates the diffusion activation energy (Ed) as 0.23 eV, showing that Ag NRs are poly-crystalline with dominant (111), as confirmed by XRD. This work introduces an effective approach to study the growth thermodynamics of 1D nanostructures and evaluate the Ed of adatoms with relatively low melting points.

Extracellular Nanomatrix-Induced Self-Organization of Neural Stem Cells into Miniature Substantia Nigra-Like Structures with Therapeutic Effects on Parkinsonian Rats.

Substantia nigra (SN) is a complex and critical region of the brain wherein Parkinson's disease (PD) arises from the degeneration of dopaminergic neurons. Miniature SN-like structures (mini-SNLSs) constructed from novel combination of nanomaterials and cell technologies exhibit promise as potentially curative cell therapies for PD. In this work, a rapid self-organization of mini-SNLS, with an organizational structure and neuronal identities similar to those of the SN in vivo, is achieved by differentiating neural stem cells in vitro on biocompatible silica nanozigzags (NZs) sculptured by glancing angle deposition, without traditional chemical growth factors. The differentiated neurons exhibit electrophysiological activity in vitro. Diverse physical cues and signaling pathways that are determined by the nanomatrices and lead to the self-organization of the mini-SNLSs are clarified and elucidated. In vivo, transplantation of the neurons from a mini-SNLS results in an early and progressive amelioration of PD in rats. The sculptured medical device reported here enables the rapid and specific self-organization of region-specific and functional brain-like structures without an undesirable prognosis. This development provides promising and significant insights into the screening of potentially curative drugs and cell therapies for PD.

Metal enhanced fluorescence improved protein and DNA detection by zigzag Ag nanorod arrays.

As metal nano-arrays show great potential on metal enhanced fluorescence (MEF) than random nanostructures, MEF of Ag zigzag nanorod (ZNR) arrays made by oblique angle deposition has been studied for biomolecule-protein interaction and DNA hybridization. By changing the folding number and the deposition substrate temperature, a 14-fold enhancement factor (EF) is obtained for biotin-neutravidin detection. The optimal folding number is decided as Z=7, owing to the high scattering intensity of Ag ZNRs. The substrate temperature T=25°C and 0°C slightly alters the morphology of Ag ZNRs but has no big difference in EF. Further, Ag ZNRs deposited on a layer of Ag film have been introduced to the DNA hybridization and a significant signal enhancement has been observed through the fluorescence microscope. Through a detailed quantitative EF analysis, which excludes the enhancing effect from the increased surface area of ZNRs and only considers the contribution of MEF, an EF of 28 is achieved for the hybridization of two single-stranded oligonucleotides with 33 bases. Furthermore, a limit of detection is determined as 0.01pM. We believe that the Ag ZNR arrays can serve as a universal and sensitive bio-detection platform.