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.

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

Scientific and practical applications of supported lipid-protein bilayers are described. Membranes can be covalently coupled to or separated from solids by ultrathin layers of water or soft polymer cushions. The latter systems maintain the structural and dynamic properties of free bilayers, forming a class of models of biomembranes that allow the application of a manifold of surface-sensitive techniques. They form versatile models of low-dimensionality complex fluids, which can be used to study interfacial forces and wetting phenomena, and enable the design of phantom cells to explore the interplay of lock-and-key forces (such as receptor-ligand binding) and universal forces for cell adhesion. Practical applications are the design of (highly selective) receptor surfaces of biosensors on electrooptical devices or the biofunctionalization of inorganic solids.

https://science.sciencemag.org/content/sci/271/5245/43.full.pdf

Supported Membranes: Scientific and Practical Applications

The adhesion force between the tip of an atomic force microscope cantilever derivatized with avidin and agarose beads functionalized with biotin, desthiobiotin, or iminobiotin was measured Under conditions that allowed only a limited number of molecular pairs to interact, the force required to separate tip and bead was found to be quantized in integer multiples of 160 +/- 20 piconewtons for biotin and 85 +/- 15 piconewtons for iminobiotin The measured force quanta are interpreted as the unbinding forces of individual molecular pairs

https://science.sciencemag.org/content/sci/264/5157/415.full.pdf

Adhesion forces between individual ligand-receptor pairs.

Molecular mechanisms associated with adhesion and contact angle hysteresis of monolayer surfaces

Synchrotron x-ray diffraction results of phospholipid monolayers at an air/water interface are reported and compared with fluorescence microscopic observations of the fluid-gel lipid phase transition. The pressure-induced transition to an orientationally ordered phase occurs at a pressure ${\ensuremath{\pi}}_{c}$ which is by more than 15 mN/m below a pressure ${\ensuremath{\pi}}_{s}$ where a transition to a positionally ordered phase occurs. Hence there exists an intermediate phase with long-range orientational and short-range positional order.

/pdf/ordering-in-lipid-monolayers-studied-by-synchrotron-x-ray-3eua83p5ex.pdf

Ordering in lipid monolayers studied by synchrotron x-ray diffraction and fluorescence microscopy.

Colloidal gold adsorbed onto positively charged substrates forms a two-dimensional layer with a maximum coverage of 1 colloid/1000 nm2 as shown by optical absorption spectroscopy, small-angle X-ray scattering, and atomic force microscopy. Positively charged substrates are obtained by either chemisorption of end-group-functionalized silanes or by polycation adsorption. Bulk diffusion controls the gold adsorption; thus lower coverages can also be achieved. The optical spectra not only contain information on single colloids but also on their mutual interactions, as well as on the polymeric and solvent environments. Absorption spectra based on Mie and Maxwell−Garnett theory are calculated. The films remain stable on exchange of the external solvent. The local dielectric environment is shown to not only influence the position of the absorption band but also, more drastically, the intensity (by a factor of 2.5), in agreement with theoretical predictions (±15%). Particle aggregation induced by branched polycatio...

Preparation and Optical Properties of Colloidal Gold Monolayers

Synchrotron X-ray diffraction and reflection studies of arachidic acid monolayers at the air−water interface

The distance dependent interaction between polyelectrolyte-covered mica surfaces in aqueous solution was investigated with the surface forces apparatus. We find the following:  (i) The surface charge changes sign, when an oppositely charged polyelectrolyte from a concentrated polyelectrolyte solution is adsorbed. (ii) Tails and loops of the adsorbed polyions dangle into the bulk phase, inducing a small steric force. If polycations and poyanions are adsorbed on top of each other, a strong short range attractive force is seen due to ion-pair formation after crossing a large repulsive electrostatic/steric barrier. (iii) Obviously, after polyelectrolyte adsorption, there are still nonoccupied binding places (point charges) on the substrate. We show that these adsorption properties regulate the build-up of polyelectrolyte multilayers:  Ion pairs between oppositely charged polyion segments and the substrate are formed, until the surface charge is inversed. The electrostatic barrier limits the adsorbed amount, g...

Christiane A. Helm

Papers

Molecular mechanisms associated with adhesion and contact angle hysteresis of monolayer surfaces

Ordering in lipid monolayers studied by synchrotron x-ray diffraction and fluorescence microscopy.

Preparation and Optical Properties of Colloidal Gold Monolayers

Synchrotron X-ray diffraction and reflection studies of arachidic acid monolayers at the air−water interface

Molecular Mechanisms Controlling the Self-Assembly Process of Polyelectrolyte Multilayers