Detection of calcium ions using gold-coated micro-cantilever sensors using upper- and lower-rim functionalized calix[4]arenes

The use of a bimodal calix[4]arene 2, was investigated as a potential host/guest sensing layer for microcantilever sensors for detecting selected ions in dilute aqueous solutions. It was found that the sensing layers gave the highest microcantilever sensitivity when microcantilevers coated with 5 nm of Inconel and 40 nm of Au were incubated for 1 h in a 1.0 μM dichloromethane:ethanol (1:9) solution of calix[4]arene 2. This calix[4]arene 2 was observed to form well-ordered self-assembled monolayers (SAM) on Au-coated substrates with no sign of bare areas or etch pits. Microcantilever sensor measurements showed that the calix[4]arene 2-functionalized cantilevers were able to detect Ca2+ ions in aqueous solutions of CaCl2 at concentrations as low as 10−12 M. Although this receptor was shown to have a high affinity for CaCl2 in aqueous solutions, it was also found to be able to detect other ionic compounds, however only producing microcantilever deflections ranging from 10% to 30% of those obtained for CaCl2.