CONSECUTIVE SELECTIVE ADSORPTION OF PENTAMIDINE AND PHOSPHATE BIOMOLECULES ON A SELF-ASSEMBLED LAYER - REVERSIBLE FORMATION OF A CHEMICALLYSELECTIVE COATING

In situ ellipsometric film thickness measurements, FT-IR external refl ectance spectroscopy, and potentiometric measurements indicated that t he amphiphile pentamidine (PAM), a bisbenzamidine, associated by self- assembly with a preformed self-assembled monolayer of a mercaptoalkano ic acid on gold, The structural properties of PAM and the nature of th e substrate were ideal for the formation of a densely packed monolayer , This process was fully reversible, as demonstrated by changing the p H of the surrounding medium, Thus, disassembly-reassembly occurred whe n the pH was cycled between 8.7 and 3, The bilayer structure, featurin g a positively charged amidinium surface, was subsequently used for se lective adsorption of phosphate biomolecules. Thus, selective binding of adenosine and inositol phosphates (K-a = 5 x 10(4) M(-1) for ATP) t o the surface, as well as strong binding of DNA-oligonucleotides, was monitored by in situ ellipsometry, This system suggests a new approach to chemical sensing, based on the reversible formation of a chemicall y selective coating.