Universal ink for microcontact printing.
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Biomedical subjects
Publications and source records attributed to Cees van der Marel.
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Poly(dimethylsiloxane) (PDMS) is the most widely used stamp material in microcontact printing. It has excellent properties with respect to versatility, chemical inertness, and mechanical stability. However, it has an inclination to contaminate printed substrates with low molecular weight siloxane fragments. In this study, it is shown, by a combination of lateral force microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy, that the extent of the PDMS-induced contamination is dependent on the nature of the ink used. The highest degree of contamination was found for relatively polar inks, whereas apolar alkanethiol inks were found to shield the substrate from contamination. This is interpreted in terms of the contaminating species being polar in nature.
The soft lithographic replication of patterns with a low filling ratio by microcontact printing (microCP) is problematic due to the poor mechanical stability of common elastomeric stamps. A recently described strategy to avoid this problem employs a modified patterning method, positive microcontact printing ((+)microCP), in which a stamp with a mechanically more stable inverted relief pattern is used. In contrast to conventional negative microCP ((-)microCP), in the contact areas a self-assembled monolayer (SAM) is printed of a "positive ink", which provides only minor etch protection, whereas the noncontacted areas are subsequently covered with a different, etch-resistant SAM, prior to development by chemical etching. With the aim to identify novel, highly versatile positive inks, the patterning of gold by (+)microCP with mercaptoalkyloligo(ethylene glycol)s (MAOEGs), the subsequent adsorption of octadecanethiol (ODT), and the final development by wet chemical etching have now been studied. A polydisperse mixture of mercaptoundecylocta(ethylene glycol) derivatives was found to provide the best patterning results. The surface spreading of the positive ink during stamping, the exchange of printed MAOEGs with ODT, and the choice of the right etching bath were identified as key parameters that influence the achievable pattern resolution and contrast. Due to the modular composition of functionalized alkyloligo(ethylene glycol) derivatives, (+)microCP with these positive inks has the potential for easy adaptation to a variety of materials and development conditions.