Mussel- and Diatom-Inspired Micropattern Generation of Silica on a Solid Substrate

Abstract

Biosilicification in diatoms and sponges potentially promises physiological, mild reaction conditions for controlling silica structures at the nanometer scale. Since Sumper et al. had isolated catalytic peptides (i.e., silaffins) from diatoms, a number of polymers bearing tertiary amine or ammonium groups have been used as a counterpart of silaffins to biomimetically synthesize silica structures. This biomimetic silicification has several advantages over conventional chemical methods. For instance, biomimetic silicification provides relatively uniform films over large areas under physiological reaction conditions without special equipment. Moreover, this method can be simply incorporated into conventional processes. As a result, recent years have witnessed a growing interest in the applications of biomimetic silicification, such as surface coating and patterning, sensors, (bio)catalysis, nanohybrids, and biotechnology. Especially, micropattern generation through biomimetic silicification has been of interest due to its potential applications in microelectronics. For example, Stone et al. generated sub-micrometer sized silica patterns by holographic two-photon-induced photopolymerization. In addition, Choi et al. reported the controlled pattern generation of silica on a solid substrate through atom-transfer radical polymerization and silicification. However, previous examples were performed on the limited kinds of materials due to the lack of versatility, and thus a versatile method of silica pattern generation has been required for wider applications. Very recently, a material-independent silica coating method was investigated by a combination of mussel-inspired polydopamine coating and subsequent diatom-inspired silicification. This method enabled us to achieve the silica coating of many diverse materials. Furthermore, it was successfully applied to the preparation of thermally stable silica/ polyethylene separators utilized in Li-ion batteries. The musseland diatom-inspired silica coating method has another advantage to use. It can be easily combined with a micromolding in capillaries (MIMIC) technique, which is a soft lithographic technique. In MIMIC technique, microchannels of poly(dimethylsiloxane) (PDMS) are filled with a solution, and the solution is then incubated for interfacial reaction onto surfaces. In the same manner, as the alkaline solution of dopamine is injected into the microchannels, polydopamine films are selectively deposited on the surface. Herein, we demonstrate a procedure for generating silica patterns by the above-mentioned method. Figure 1 shows the schematic description of the procedure. Briefly, MIMIC