Cation sensing by patterned self-assembled monolayers on gold

X-Ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) have been used to study the interactions between self-assembled monolayers (SAMs) of crown ether adsorbates and metal ions. Both analytical techniques confirmed the selectivities of the 12-crown-4 and 15-crown-5 SAMs that had previously been determined by electrochemical impedance spectroscopy. AFM has also been used to characterize microcontact-printed crown ether monolayers. The electrochemical patterning of monolayers on gold allowed the design of a dual sensor for the electrochemical detection of cations. However, due to cross-contamination of both monolayers during the patterning process a significant selectivity reduction of the layers was observed. Nevertheless, the remaining Na+ selectivity of the 12-crown-4 SAM and the K+ selectivity of the 15-crown-5 SAM allowed the unambiguous discrimination between both metal ions.