Monolayer-protected Au, Ag, and Au:Ag alloy nanoclusters have been synthesized using octanethiol and octadecanethiol as capping agents. The particle-size distribution is narrow with an average core size of 3-4 nm. Optical nonlinearity induced by 35 ps pulses at 532 nm has been investigated in these samples using the Z-scan technique. It is found that in general, they behave either as saturable absorbers or reverse saturable absorbers depending on the intensity of excitation. Au and Ag clusters show nearly the same efficiency for optical limiting, but the alloy clusters are found to be less efficient in limiting and are less photostable. The observed effects are explained in terms of the electron dynamics of the excited-state species.

We report here a multistep route for the immobilization of DNA and proteins on chemically modified gold substrates using fourth-generation NH(2)-terminated poly(amidoamine) dendrimers supported by an underlying amino undecanethiol (AUT) self-assembled monolayer (SAM). Bioactive ultrathin organic films were prepared via layer-by-layer self-assembly methods and characterized by fluorescence microscopy, variable angle spectroscopic ellipsometry, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and attenuated total internal reflection Fourier transform infrared spectroscopy (ATR-FTIR). The thickness of the AUT SAM base layer on the gold substrates was determined to be 1.3 nm from ellipsometry. Fluorescence microscopy and AFM measurements, in combination with analyses of the XPS/ATR-FTIR spectra, confirmed the presence of the dendrimer/biopolymer molecules on the multilayer sensor surfaces. Model proteins, including streptavidin and rabbit immunoglobulin proteins, were covalently attached to the dendrimer layer using linear cross-linking reagents. Through surface plasmon resonance measurements, we found that sensor surfaces containing a dendrimer layer displayed an increased protein immobilization capacity, compared to AUT SAM sensor surfaces without dendrimer molecules. Other SPR studies also revealed that the dendrimer-based surfaces are useful for the sensitive and specific detection of DNA-DNA interactions. Significantly, the multicomponent films displayed a high level of stability during repeated regeneration and hybridization cycles, and the kinetics of the DNA-DNA hybridization process did not appear to be influenced by surface mass transport limiting effects.

Alkanethiol-protected silver clusters of average diameter 4.0 ( 0.5 nm form single-phase superlattice solids, and their X-ray powder diffractograms have been fully indexed to single cubic unit cells. Whereas alkanethiols with five or more carbon atoms form superlattices, the corresponding cluster with four carbons yield only separated clusters. The superlattice solids can be recrystallized from nonpolar solvents. No such superlattices are seen for the corresponding gold clusters. The superlattice collapses upon heating, but the solid retains the structure even at 398 K, much above the melting point of crystalline alkanes and the corresponding self-assembled monolayer. In situ variable-temperature X-ray diffraction investigations did not show any solid-state phase transitions in the superlattice. Temperature-dependent infrared spectroscopy reveals the melting of the alkyl chain, and it is seen that the chain as a whole achieves rotational freedom prior to the collapse of the superlattice. Calorimetric investigations show distinct monolayer and superlattice melting transitions. The chemical nature of the cluster-molecule interaction is similar to that of the previously investigated gold and silver systems, as revealed by NMR, mass, infrared, and X-ray photoelectron spectroscopies and thermogravimetry analyses. Conductivity measurements clearly manifest the superlattice melting transition. Diffusion constants in solution measured by NMR show that the relative decrease in the diffusion constant with increasing monolayer chain length is smaller for silver than for gold, suggested to be a signature of intercluster interaction even in solution. Corroborative evidence is provided by the variable-temperature UV/vis investigations of the clusters.

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Insufficient cell proliferation, cell migration, and angiogenesis are among the major causes for nonhealing of chronic diabetic wounds. Incorporation of cerium oxide nanoparticles (nCeO2) in wound dressings can be a promising approach to promote angiogenesis and healing of diabetic wounds. In this paper, we report the development of a novel nCeO2 containing electrospun poly­(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) membrane for diabetic wound healing applications. In vitro cell adhesion studies, chicken embryo angiogenesis assay, and in vivo diabetic wound healing studies were performed to assess the cell proliferation, angiogenesis, and wound healing potential of the developed membranes. The experimental results showed that nCeO2 containing PHBV membranes can promote cell proliferation and cell adhesion when used as wound dressings. For less than 1% w/w of nCeO2 content, human mammary epithelial cells (HMEC) were adhered parallel to the individual fibers of PHBV. For higher than 1% w/w of nCeO2 content, cells started to flatten and spread over the fibers. In ovo angiogenic assay showed the ability of nCeO2 incorporated PHBV membranes to enhance blood vessel formation. In vivo wound healing study in diabetic rats confirmed the wound healing potential of nCeO2 incorporated PHBV membranes. The study suggests that nCeO2 incorporated PHBV membranes have strong potential to be used as wound dressings to enhance cell proliferation and vascularization and promote the healing of diabetic wounds.

Growth mechanism from nano-ordered clusters to nanocrystals in a deeply undercooled melt of Zr-Ni-Ti metallic glass Dependence of Al layer growth mode on Cr underlayer thickness in molecular-beam epitaxy of (001) Al/Cr superlattices J.Melting of crystalline solids ͑superlattices͒ of octadecanethiol and octanethiol protected silver clusters has been studied with x-ray powder diffraction ͑XRD͒, differential scanning calorimetry ͑DSC͒, and infrared ͑IR͒ spectroscopy. These solids have been compared with the silver thiolate layered compounds in view of their similarity in alkyl chain packing and x-ray diffraction patterns. Superlattice melting is manifested in XRD around 400 K as the complete disappearance of all the low angle reflections; only bulk silver reflections due to the cluster cores are seen at 423 K. The superlattice structure is regained upon cooling from a temperature close to its melting point. However, cooling from a higher temperature of 473 K does not regain the superlattice order, whereas thiolate melting is repeatedly reversible even at these temperatures. Transmission electron microscopy suggests aggregation of clusters during heating/cooling cycles. DSC shows two distinct transitions, first corresponding to alkyl chain melting and the second corresponding to superlattice melting. Only alkyl chain melting is observed in variable temperature IR and increased order is manifested upon repeated heating/cooling cycles. Alkyl chain assembly shows strong interchain coupling leading to factor group splitting in cluster superlattices upon annealing. In thiolates only one melting feature is seen in DSC and it produces gauche defects, whereas significant increase in defect structures is not seen in superlattices. Repeated heating/cooling cycles increase interchain interactions within a cluster and the superlattice order collapses.

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