Light-induced assembly of living bacteria with honeycomb substrate.

Some bacteria are recognized to produce useful substances and electric currents, offering a promising solution to environmental and energy problems. However, applications of high-performance microbial devices require a method to accumulate living bacteria into a higher-density condition in larger substrates. Here, we propose a method for the high-density assembly of bacteria (106 to 107 cells/cm2) with a high survival rate of 80 to 90% using laser-induced convection onto a self-organized honeycomb-like photothermal film. Furthermore, the electricity-producing bacteria can be optically assembled, and the electrical current can be increased by one to two orders of magnitude simply by increasing the number of laser irradiations. This concept can facilitate the development of high-density microbial energy conversion devices and provide new platforms for unconventional environmental technology.

Preparation of patterned zinc oxide films by breath figure templating.

A large variety of microporous polymer films can be prepared by the breath figure technique. Here, we report on its use for the formation of microporous zinc oxide films. Zinc acetylacetonate, a zinc oxide precursor, is either dissolved in a polymer solution that is cast at high humidity to form microporous films or is vacuum evaporated onto a preformed microporous polymer film. Annealing leads to the pyrolysis of the organic material and the formation of zinc oxide films, which show increased photocatalytic activity as compared to unstructured films.

Preparation of an ordered array of cyanine complex microdomes by a simple dewetting method.

We demonstrate a simple method for fabricating a two-dimensional array of microdomes that consist of cyanine dye complexes. Investigation of the morphology and the fluorescence emission of microdomes was carried out before/after annealing. The principal of microdome formation is "dewetting," which is a self-organization phenomena. Generally, one can observe dewetting when a liquid film breaks spontaneously on a nonwettable substrate, leaving droplets or patterns on the substrate. A cyanine dye complex was prepared from a cationic cyanine dye and an anionic amphiphile, or vice versa, an anionic dye and a cationic amphiphile. When a chloroform solution of the cyanine complex was spread on a glass substrate by a roller, microdomes of the cyanine dye complex formed in dewetted films. The roller draws the three-phase line (the air-solid-liquid boundary of the droplet of the chloroform solution) with a constant rate. Thus dewetting can be controlled and leads to a two-dimensional ordered array of uniform sized microdomes. The diameter and height of microdomes decrease with increasing roller speed. Fluorescence microscopy shows that the cyanine dye complex formed J-aggregates. Annealing caused transformation of the dome morphology and a change of the fluorescence spectra. The microdome transformed into anisotropic crystals or became amorphous depending on the molecular structure of the cyanine dye.

Control of droplet size and spacing in micrometer-sized polymeric dewetting patterns.

When a polymer solution is cast on a flat substrate and the solvent is allowed to evaporate, dewetting might take place. Instead of a continuous film, the polymer forms micrometer-sized droplets. By controlling the solvent casting process with the help of a roller apparatus, the size and spacing of the polymer droplets can be adjusted. We investigated the effect of polymer concentration and roller speed on the pattern dimensions and found that higher concentrations lead to larger polymer droplets (from 1 to 11 microm), whereas faster roller speeds lead to a wider interdroplet spacing (from 4 to 130 microm).

Formation of ordered mesoscopic polymer arrays by dewetting.

It could be shown that by a simple casting process from solution two-dimensionally ordered arrays of mesoscopic (i.e., in the range of submicrometer to micrometer) polymer aggregates on solid substrates can be formed. Patterns were investigated by optical microscopy and atomic force microscopy. The pattern formation was observed in situ by optical and fluorescence microscopy and it was found that a "fingering instability" at the three-phase-line of a solution droplet is the crucial process for pattern formation. (c) 1999 American Institute of Physics.