SELF-ASSEMBLED MONOLAYERS FOR CHEMICAL SENSORS - MOLECULAR RECOGNITION BY IMMOBILIZED SUPRAMOLECULAR STRUCTURES

We have studied the applicability of two different self-assembling mon olayer systems as chemically sensitive coatings for quartz microbalanc es. The first consists of a monolayer of substituted resorcin[4]arenes and serves as a gas sensing device, The second is based on a modified peptide antigen embedded in a hydroxyundecanethiol-monolayer and serv es as a liquid sensing device to monitor antibodies. Both monolayer sy stems are coupled to gold surfaces via S-Au bonds. Quartz microbalance s (QMB) are employed as mass sensitive transducers and allow for sensi tive detection of the molecular recognition process. Information about the orientation and structure of resorcin[4]arene monolayers as well as their interactions with organic molecules were obtained from angle- resolved X-ray photoelectron spectroscopy (AR-XPS) and thermal desorpt ion spectroscopy (TDS). The latter technique makes it possible to dete rmine experimentally binding energies of the molecule/resorcin[4]arene -'key-lock' interaction. Several different organic molecules were dete cted in the gas phase, By far the most pronounced sensor response and hence highest selectivity was observed for tetrachloroethene (C2Cl4) T he modified synthetic peptide was deposited on the electrodes of a QMB by self-assembly. The quartz crystals were mounted into a flow-throug h cell with only one side exposed to the liquid. The successful immuno logical reaction between the immobilized antigen and the antibody in s olution could be monitored on-line with a QMB. The sensitive coating o f the QMB could be regenerated for its successive use as a mass sensit ive biosensor.