The influence of temperature and humidity on the growth rates of 1-octadecanethiol (ODT) and 16-mercaptohexadecanoic acid (MHA) monolayers deposited onto a gold substrate has been systematically studied
in the context of dip-pen nanolithography (DPN) experiments. By analyzing a statistically meaningful data
set, we conclude that for both inks the deposition rate increases with increasing temperature, and that this
temperature dependence is strongly affected by relative humidity, chemical nature of the ink and substrate,
and writing speed. We attribute these observations to the different solubilities of the ink molecules in water
(both the water in the meniscus and on the cantilever walls). In addition, we report a set of experiments that
demonstrate meniscus formation even at 0% relative humidity due to residual water that moves to the point
of contact between tip and sample.
Motile bacterial cell microarrays were fabricated by attaching Escherichia coli K-12 cells onto predesigned 16-mercaptohexadecanoic acid patterned microarrays, which were covalently functionalized with E. coli antibodies or poly-L-lysine. By utilizing 11-mercaptoundecyl-penta(ethylene glycol) or 11-mercapto-1-undecanol as passivating molecules, nonspecific binding of E. coli was significantly reduced. Microcontact printing and dip-pen nanolithography were used to prepare microarrays for bacterial adhesion, which was studied by optical fluorescence and atomic force microscopy. These data indicate that single motile E. coli can be attached to predesigned line or dot features and binding can occur via the cell body or the flagella of bacteria. Adherent bacteria are viable (remain alive and motile after adhesion to patterned surface features) for more than four hours. Individual motile bacterial cells can be placed onto predesigned surface features that are at least 1.3 microm in diameter or larger. The importance of controlling the adhesion of single bacterial cell to a surface is discussed with regard to biomotor design.
Water meniscus formation at the point of contact between an AFM tip and an atomically smooth NaCl substrate was experimentally studied as a function of atmospheric water content, from 70% relative humidity to ultrahigh vacuum (UHV). Meniscus formation was probed by measuring the pull-off point and evaluating the ability of the meniscus to dissolve the NaCl near the point-of-contact as a function of atmospheric water content. Hydrophilic and hydrophobic tips were studied, and although a decrease in meniscus size was observed for the hydrophobic tips, all data are consistent with both types of tips resulting in the formation of a meniscus even at 0% relative humidity.
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