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 5nm of Inconel and 40nm of Au were incubated for 1h in a 1.0μM 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 10−12M. 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.