There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Although gold is the subject of one of the most ancient themes of investigation in science, its renaissance now leads to an exponentially increasing number of publications, especially in the context of emerging nanoscience and nanotechnology with nanoparticles and self-assembled monolayers (SAMs). We will limit the present review to gold nanoparticles (AuNPs), also called gold colloids. AuNPs are the most stable metal nanoparticles, and they present fascinating aspects such as their assembly of multiple types involving materials science, the behavior of the individual particles, size-related electronic, magnetic and optical properties (quantum size effect), and their applications to catalysis and biology. Their promises are in these fields as well as in the bottom-up approach of nanotechnology, and they will be key materials and building block in the 21st century. Whereas the extraction of gold started in the 5th millennium B.C. near Varna (Bulgaria) and reached 10 tons per year in Egypt around 1200-1300 B.C. when the marvelous statue of Touthankamon was constructed, it is probable that “soluble” gold appeared around the 5th or 4th century B.C. in Egypt and China. In antiquity, materials were used in an ecological sense for both aesthetic and curative purposes. Colloidal gold was used to make ruby glass 293 Chem. Rev. 2004, 104, 293−346

Gold nanoparticles: assembly, supramolecular chemistry, quantum-size-related properties, and applications toward biology, catalysis, and nanotechnology.

Molecular self-assembly is the spontaneous association of molecules under equilibrium conditions into stable, structurally well-defined aggregates joined by noncovalent bonds. Molecular self-assembly is ubiquitous in biological systems and underlies the formation of a wide variety of complex biological structures. Understanding self-assembly and the associated noncovalent interactions that connect complementary interacting molecular surfaces in biological aggregates is a central concern in structural biochemistry. Self-assembly is also emerging as a new strategy in chemical synthesis, with the potential of generating nonbiological structures with dimensions of 1 to 10(2) nanometers (with molecular weights of 10(4) to 10(10) daltons). Structures in the upper part of this range of sizes are presently inaccessible through chemical synthesis, and the ability to prepare them would open a route to structures comparable in size (and perhaps complementary in function) to those that can be prepared by microlithography and other techniques of microfabrication.

Molecular self-assembly and nanochemistry: A chemical strategy for the synthesis of nanostructures

12.2.2. Four-Wave Mixing (FWM) 4849 12.2.3. Dye Aggregation 4850 12.2.4. Optoelectronic Nanodevices 4850 12.3. Sensor 4851 12.3.1. Chemical Sensor 4851 12.3.2. Biological Sensor 4851 12.4. Catalysis 4852 13. Conclusion and Perspectives 4852 14. Abbreviations 4853 15. Acknowledgements 4854 16. References 4854 * Corresponding author E-mail: tpal@chem.iitkgp.ernet.in. † Raidighi College. § Indian Institute of Technology. 4797 Chem. Rev. 2007, 107, 4797−4862

Interparticle Coupling Effect on the Surface Plasmon Resonance of Gold Nanoparticles: From Theory to Applications

Nanomaterials, such as metal or semiconductor nanoparticles and nanorods, exhibit similar dimensions to those of biomolecules, such as proteins (enzymes, antigens, antibodies) or DNA. The integration of nanoparticles, which exhibit unique electronic, photonic, and catalytic properties, with biomaterials, which display unique recognition, catalytic, and inhibition properties, yields novel hybrid nanobiomaterials of synergetic properties and functions. This review describes recent advances in the synthesis of biomolecule-nanoparticle/nanorod hybrid systems and the application of such assemblies in the generation of 2D and 3D ordered structures in solutions and on surfaces. Particular emphasis is directed to the use of biomolecule-nanoparticle (metallic or semiconductive) assemblies for bioanalytical applications and for the fabrication of bioelectronic devices.

Integrated Nanoparticle–Biomolecule Hybrid Systems: Synthesis, Properties, and Applications

We developed a simple method for highly ordered assemblies of gold nanoparticles (AuNPs) along DNA molecules on substrates, and achieved assemblies with well-aligned and long-range order by using well-stretched DNA templates. In addition, oxidized aniline-capped AuNPs (AN−AuNPs) prepared in this study were strongly attached to DNA. Two different assembly methods were carried out, and consequently continuous depositions and necklace-like depositions of AN−AuNPs along DNA molecules were achieved.

Highly Ordered Assemblies of Au Nanoparticles Organized on DNA

Review: Micro- and nanosized molecularly imprinted polymers for high-throughput analytical applications

A humidity-sensitive composite film has been synthesized that consists of soluble polyaniline (PAn) and poly(vinyl alcohol) (PVA). PAn gave a percolation threshold where the electrical conductivity rose sharply at a volume fraction of 0.1%. This value is very small compared with that (about 5 vol%) reported in general for composite films consisting of conducting and non-conducting polymers, indicating that the two polymers used in this study were mixing completely. The conductivity of the PAn–PVA composite was proportional to the relative humidity, and the linearity was valid from 3×10–5 to 1.5×10–1 S cm–1 . The response time of the composite for the humidity change was 45 s and 9 min for moistening and desiccating steps, respectively. The conductivity of the composite film varied depending on the doping level of PAn, which was affected by the concentration of water molecules surrounding the conducting polymer. At high humidity, the PAn was in the form of an emeraldine salt, and transformed into a non-conducting base with decreasing environmental humidity.

The humidity dependence of the electrical conductivity of a solublepolyaniline–poly(vinyl alcohol) composite film

A label-free high-resolution DNA sensing technique using a nanogapped gold particle film is presented to acquire nucleotide polymorphism information, which can be read by electronic protocols.

Label-free electronic detection of DNA-hybridization on nanogapped gold particle film.

A convenient "one step" preparation process of molecularly imprinted overoxidized-polypyrrole (oPPy) colloids by chemical polymerization and their high uptake ability and enantioselectivity are described. Since an oxidizing agent gives a different standard redox potential and rate of polymerization, the property of the resulting oPPy colloid can be controlled by the kind and concentration of the oxidizing agent. At higher concentrations of (NH4)2S2O8 (0.3 M), the overoxidation of PPy colloid automatically occurred. The extraction of L-lactate as a dopant has created a shape-complementary cavity on the surface of the oPPy colloid through overoxidation following polymerization. The oPPy colloid exhibited an excellent selectivity not only on the alanine enantiomer but also on the difference in the side-chain size of amino acids. The uptake of oPPy colloid towards L-alanine over D-alanine was 11.3 micromol/g-colloid against 3.6 micromol/g. The molecularly imprinted cavity can also recognize the existences of the OH or CH3 substituents.

Hiroshi Shiigi

Papers

Highly Ordered Assemblies of Au Nanoparticles Organized on DNA

Review: Micro- and nanosized molecularly imprinted polymers for high-throughput analytical applications

The humidity dependence of the electrical conductivity of a solublepolyaniline–poly(vinyl alcohol) composite film

Label-free electronic detection of DNA-hybridization on nanogapped gold particle film.

Highly selective molecularly imprinted overoxidized polypyrrole colloids: one-step preparation technique.