Spontaneous elongation from nanorod to nanowire in the presence of an amine is reported for nanocrystals of cadmium sulfide and silver sulfide (cation exchanged from CdS). Elongation occurs instantaneously where the final aspect ratio is a controllable multiple of the original nanorod length.Transmission electron microscopy (TEM) data and kinetic modeling reveal the influential factors on the attachment process are the concentration of amine, duration and temperature of the reaction. The elongated nanorods are further characterized by X-Ray diffraction (XRD), photoluminescence (PL), ultraviolet-visible spectroscopy (UV-Vis) and X-ray photoelectron spectroscopy (XPS). A mechanism of oriented attachment is evidenced by the doubling in length of asymmetrically gold tipped CdS nanorods with the corresponding absence of elongation in symmetrically tipped nanorods.1

The gene for the alpha polypeptide chain (alpha s) of the heterotrimeric G protein Gs can be activated to the putative oncogene gsp by specific point mutations at codons 201 and 227. Such mutations have been reported in 40% of human growth hormone-secreting pituitary adenomas and in a single autonomously functioning thyroid adenoma. We examined an archival series of 45 differentiated human thyroid tumors by polymerase chain reaction amplification and oligonucleotide hybridization to identify point mutations at each of the affected codons. Successful amplification was achieved in 38 cases, and activating mutations were identified in 5 of 13 (38%) autonomously functioning adenomas, but in none of 16 nonfunctioning adenomas, six papillary carcinomas, or three follicular carcinomas. Our results confirm that the gsp oncogene is involved in the pathogenesis of autonomously functioning tumors but do not support a role in other thyroid tumors.

A facile spin cast process is used for the instantaneous asymmetric formation of gold tips on perpendicularly aligned CdS nanorod superlattices. Tip size varies as a function of precursor solution concentration and growth time. A single uniform tip occurs on the end facets of each nanorod in the array when an optimised gold chloride solution is used , with multiple tipping 10 occuring with variations in precursor concentration. HRTEM shows that the gold tip growth does not always occur centro-symmetrically on the nanorods, with growth occuring on the (101) or the (001) facet of the wurtzite nanocrystal depending on the rod shape. X -ray diffraction confirms that the gold tips are crystalline with a 60% lattice mismatch with the wurtzite CdS nanocrystal suggesting strain relief may be a factor in tip formation. The gold tipped nanorods are further 15 characterised by photoluminescence spectroscopy.

Gold tip size and multiplicity is controlled in hybrid gold-semiconductor nanorods (CdS-Au, CdSe-Au and CdTe-Au) in fast reaction times of less than 2 minutes by optimising precursor type, concentration, and temperature. Controllable gold tips up to as large as 40 nm on a rod diameter of 7 nm are reported with the tip size shown to be directly related to the redox potentials of the 10 dangling atoms on the nanorod and the gold chloride precursors (mono or trivalent). The preference for symmetric (both ends) over asymmetric (single end) is achieved by simply elevating the reaction temperature to 80ºC without changing the reaction time. TEM and XRD analysis were preformed to verify both the gold nanoparticle size and crystallinity of the hybrid nanostructures. Increased quenching of nanorod emission is observed as the size of the gold tip increases 15 suggesting optimisation of charge transfer between the semiconductor and the metal .

Publication informationNanoscale, 3 (11): 4580-4583 Publisher RSC publicationsLink to online version http://dx