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 sensinglayers gave the highest microcantilever sensitivity when microcantilevers coated with 5 nm of Inconel and40 nm of Au were incubated for 1 h in a 1.0 mu M 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-coatedsubstrates with no sign of bare areas or etch pits. Microcantilever sensor measurements showed that thecalix[ 4] arene 2-functionalized cantilevers were able to detect Ca2+ ions in aqueous solutions of CaCl2atconcentrations as low as 10-12M. Although this receptor was shown to have a high affinity for CaCl2inaqueous solutions, it was also found to be able to detect other ionic compounds, however only producingmicrocantilever deflections ranging from 10% to 30% of those obtained for CaCl2. (C) 2014 Elsevier B. V. All rights reserved.