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Latent fingerprints are made visible in a single step by in situ growth of gold nanoparticles on ridge patterns. The chemicals, among the essential components of human sweat, found responsible for the formation and assembly of gold nanoparticles are screened and used as ink to write invisible patterns, using common ball pen and inkjet printer, which are then developed by selectively growing gold nanoparticles by soaking them in gold salt solution.

Aggregation of gold nanoparticles into soluble spherical assemblies using bi-functional ligands i.e., dithiols has recently been demonstrated but with limited control over the size of such assemblies. Herein, we report a new approach to further control the size of water dispersible spherical assemblies by confining gold nanoparticles in tiny oil droplets in water (oil-in-water emulsions) followed by their cross-linking with alkanedithiols. By controlling the size of the oil droplets and the concentration of nanoparticles, the size of spherical aggregates can be controlled from 20 to 400 nm. Cryo-TEM micrographs confirm the formation of covalently-linked soluble spherical nanoparticle assemblies within the oil emulsions in water. Such size-controlled nanoparticle assemblies may have several potential applications including those in gas sensors, controlled delivery, and optical coatings., (Copyright 2010 Elsevier Inc. All rights reserved.)

The synthesis of fluorescent water-soluble gold nanoparticles by the reduction of a gold salt in the presence of a designed polymer ligand is described, the size and fluorescence of the particles being controlled by the polymer to gold ratio; the most fluorescent nanomaterial has a 3% quantum yield, a 1.1 nm gold core and a 6.9 nm hydrodynamic radius.

A new methodology is described for the one-step aqueous preparation of highly monodisperse gold nanoparticles with diameters below 5 nm using thioether- and thiol-functionalized polymer ligands. The particle size and size distribution was controlled by subtle variation of the polymer structure. It was shown that poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA) were the most effective stabilizing polymers in the group studied and that relatively low molar mass ligands (approximately 2500 g/mol) gave rise to the narrowest particle size distributions. Particle uniformity and colloidal stability to changes in ionic strength and pH were strongly affected by the hydrophobicity of the ligand end group. "Multidentate" thiol-terminated ligands were produced by employing dithiols and tetrathiols as chain-transfer agents, and these ligands gave rise to particles with unprecedented control over particle size and enhanced colloidal stability. It was found throughout that dynamic light scattering (DLS) is a very useful corroboratory technique for characterization of these gold nanoparticles in addition to optical spectroscopy and TEM.