Fabrication of Well-Defined Microdomains Composed of Aldehyde- and Carboxy-Terminated Self-Assembled Monolayers

Coplanar microdomains consisting of two organosilane self-assembled monolayers (SAMs) terminated with chemically reactive functional groups (e.g., aldehyde-[CHO] and carboxy-[COOH] groups) were prepared on Si substrates covered with native oxide (SiO(2)/Si). A SAM of triethoxysilylundecanal (TESUD) molecules was prepared by chemical vapor deposition on the SiO(2)/Si surfaces. A few of these samples were exposed to 172 nm vacuum-ultraviolet (UV) radiation for 5 similar to 60 min at 10(5) Pa. Various experimental techn ques including water-contact angle measurements, ellipsometry, attenuated total reflection Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and atomic force microscopy confirmed that CHO terminal groups of the SAM have been photochemically converted to COOH groups. Based on this result, site-selective photoirradiation of the TESUD-SAM with the same radiation source was performed using a photomask. Lateral force microscopy images revealed that well-ordered microstructures of 5 x 5 mu m(2) square-shaped features are formed on the substrate. The difference in chemical reactivity was characterized by fluorescence microscopy using specific bonding between biotin hydrazide and streptavidin-conjugated quantum dots (QDs). The fluorescence microscopy images revealed that biotin hydrazide immobilized site-selectively on the masked CHO-terminated regions and not on the vacuum-UV irradiated regions. However, the latter regions showed chemical reactivity to biotin hydrazide after activation treatments using N-hydroxysuccinimide and 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride, and well-defined QDs patterns can be obtained within these regions. This suggests that the surface CHO groups of the vacuum-UV irradiated regions were transformed to COOH groups, and the activation treatments lead to the formation of active N-hydroxysuccinimidyl esters, which are reactive toward amine groups of biotin hydrazide.