Self-assembly is a process in which components, either separate or linked, spontaneously form ordered aggregates. Self-assembly can occur with components having sizes from the molecular to the macroscopic, provided that appropriate conditions are met. Although much of the work in self-assembly has focused on molecular components, many of the most interesting applications of self-assembling processes can be found at larger sizes (nanometers to micrometers). These larger systems also offer a level of control over the characteristics of the components and over the interactions among them that makes fundamental investigations especially tractable.

ATR-FTIR spectroscopy is useful in investigating the lateral organization of Stratum corneum (SC) lipids in full-thickness skin. Based on studies of the thermotropic phase transitions in n-tricosane and in excised human skin, the temperature dependence of the CH2 scissoring bandwidth emerged as a measure of the extent of orthorhombic and hexagonal phases. This dependence provides a simpler measure of the lateral order in lipid assemblies than the common spectroscopic approaches based on difference spectra, curve fitting of the CH2 scissoring region, and the position of the CH2 stretching vibrations. It has the advantages of ease of determination, relatively low variability, and high discriminative power for the type of lateral intermolecular chain packing. A comparison of the lateral organization of the lipids at the SC surface of mammalian skin using the scissoring bandwidth revealed considerable differences between human abdominal skin (containing mostly orthorhombic phases), porcine ear skin (containing mostly hexagonal phases), and reconstructed human epidermis (containing mostly disordered phases). This parameter also correctly described the different effects of propylene glycol (minimally disturbing) and oleic acid (formation of a highly disordered phase) on the SC lipids in excised human skin. The procedure described here is applicable to in vivo studies in the areas of dermatology, transdermal drug delivery, and skin biophysics.

Modifying colloidal gold particles with DNA is a new interesting approach in the development of genetic biosensors. Normally the modification is designed to consist of a covalent gold−sulfur bond mediated by a thiol group on one end of a single-stranded oligonucleotide. Here we investigate to what extent the binding actually consists of only the sulfur bridge or if some other nonspecific binding mechanism is present as well. We report on an electrophoresis study showing high amounts of strong, non-thiol-mediated (nonspecific) binding of both single- and double-stranded DNA to gold nanoparticles. Interestingly, even the double strands, lacking interacting groups from the exposed bases of single-stranded DNA, interact nonspecifically with the gold particles. We suggest the mechanism for this to be ion-induced dipole dispersive interactions, where the negatively charged phosphate groups on the DNA induce dipoles in the highly polarizable gold particles. Moreover, we show that particles with nonspecifically adsorbed DNA can be separated from the specifically modified and unmodified ones by gel electrophoresis.

Nitrite is a signaling molecule and regulator of gene expression in mammalian tissues. Nat Chem Biol 1:290-7 Bryan NS, Rassaf T, Maloney RE, Rodriguez CM, Saijo F, Rodriguez JR et al. (2004) Cellular targets and mechanisms of nitros(yl)ation: an insight into their nature and kinetics in vivo. Proc Natl Acad Sci USA 101:4308-13 Butler AR, Ridd JH (2004) Formation of nitric oxide from nitrous acid in ischemic tissue and skin. Nitric Oxide 10:20-4 Cape JL, Hurst JK (2009) The role of nitrite ion in phagocyte function-perspectives and puzzles. Arch Biochem Biophys 484:190-6 Feelisch M, Rassaf T, Mnaimneh S, Singh N, Bryan NS, Jourd'heuil D et al. (2002) Concomitant S-, N-, and heme-nitros(yl)ation in biological tissues and fluids: implications for the fate of NO in vivo. FASEB J 16:1775-85 Gribbe O, Gustafsson LE, Wicklund NP (2008) Transdermally administered nitric oxide by application of acidified nitrite increases blood flow in rat epigastric island skin flaps.

Self-assembly-the spontaneous generation of order in systems of components-is ubiquitous in chemistry; in biology, it generates much of the functionality of the living cell. Self-assembly is relatively unused in microfabrication, although it offers opportunities to simplify processes, lower costs, develop new processes, use components too small to be manipulated robotically, integrate components made using incompatible technologies, and generate structures in three dimensions and on curved surfaces. The major limitations to the self-assembly of micrometer-to millimeter-sized components (mesoscale self-assembly) do not seem to be intrinsic, but rather operational: selfassembly can, in fact, be reliable and insensitive to small process variations, but fabricating the small, complex, functional components that future applications may require will necessitate the development of new methodologies. Proof-of-concept experiments in mesoscale self-assembly demonstrate that this technique poses fascinating scientific and technical challenges and offers the potential to provide access to hard-to-fabricate structures.