Atomic force microscopy characterization of a microcontact printed, self-assembled thiol monolayer for use in biosensors

This paper describes friction experiments and pull-off force measurements using atomic force microscopy (AFM), between a nonfunctionalized silicon probe and a 2.5 μm diameter CH and COOH terminated thiol self-assembled monolayer pattern. The pattern is microcontact printed onto a gold-coated silicon wafer, in air, at room temperature, with a relative humidity around 30%, and used to examine probe-monolayer interactions. Atomic force microscopy imaging reveals that the patterns have been successfully reproduced on the substrate surface. We obtained force values of (8.67±2.60)·10 N, (2.68±1.09)·10 N, and (4.60±0.24)·10 N for CH terminated alkyl-thiol, COOH terminated thiol, and gold substrate respectively. Normalizing these values with the tip radius we obtained (0.87±0.27) N/m for CH terminated alkyl-thiol, (2.68±1.10) N/m for COOH terminated thiol, and (4.60±2.50) N/m for bare gold. These interactions are discussed in terms of the chemical affinity between the probe and the substrate. Copyright © Taylor & Francis Group, LLC