Calixarene monolayers as quartz crystal microbalance sensing elements in aqueous solution

We have examined p-tert-butylcalix[4]arenetetrathiolate (BCAT) monolayers f or their potential use as molecular recognition elements for in situ aqueou s chemical sensors. Spectroscopic and wetting studies of BCAT monolayers on Au(lll) reveal that the calixarene molecules exist in monolayers, preferen tially oriented with their phenyl rings parallel to the surface normal axis . Using quartz crystal microbalance (QCM) sensors with gold-coated electrod es, the chemical specificity of monolayers and thin films to a variety of a romatic and aliphatic analytes in aqueous solution was examined. The respon se of BCAT sensors was compared to the responses of p-tert-butylcalix[4]are ne (BCA)- and decanethiolate (DT)-coated QCM electrodes. BCAT is very selec tive for alkylbenzenes, much more so than either its spray-coated thin-film analogue, BCA, or the highly ordered DT monolayer. From these measurements , the factors behind molecular differentiation in each film are explored. D rawing upon these findings, the roles of cavitation and film order in molec ular recognition for calixarene films are discussed.