RESUMO
Many interactions drive the adsorption of molecules on surfaces, all of which can result in a measurable change in surface stress. This article compares the contributions of various possible interactions to the overall induced surface stress for cantilever-based sensing applications. The surface stress resulting from adsorption-induced changes in the electronic density of the underlying surface is up to 2-4 orders of magnitude larger than that resulting from intermolecular electrostatic or Lennard-Jones interactions. We reveal that the surface stress associated with the formation of high quality alkanethiol self-assembled monolayers on gold surfaces is independent of the molecular chain length, supporting our theoretical findings. This provides a foundation for the development of new strategies for increasing the sensitivity of cantilever-based sensors for various applications.
RESUMO
Coverage defects in alkylthiol self-assembled monolayers (SAMs) are critically important to function related to electron transfer from soluble redox probes. There is therefore a need for an accurate and direct measurement of the number and type of coverage defect in a range of SAMs. Ferrocenyldodecanethiol (FcC(12)SH) has been assessed as an electrochemically-addressable label of coverage defects. It is shown that short time exposure of a SAM to FcC(12)SH leads to a quantifiable Fc coverage (Gamma(Fc)), with Gamma(Fc) < 1% readily measurable. The voltammetric signature of FcC(12)SH label is also able to differentiate types of defect in a given SAM. A number of SAM preparation conditions are assessed for the density and type of coverage defect. This labeling method therefore will be a useful tool for research into SAM property-function relationships.