Gas-phase molecular recognition on functional monolayers immobilized on a highly sensitive quartz-crystal microbalance

Abstract

Self-assembled monolayers of alkanethiols having functional groups (HS-(CH 2) 10-X X = -H, -COOH, -CONH 2, -NH 2, thymine and adenine bases) were immobilized on the Au electrode of a quartz-crystal microbalance (QCM), and binding kinetics of guest molecules from the gas phase were studied from time courses of frequency decreases (mass increases) of the QCM. A highly sensitive, 63-MHz overtone frequency of a conventional 9-MHz at AT-cut QCM was developed to detect monolayer adsorption of small molecules. When acetic acid was employed as guest molecules, it adsorbed onto the -CONH 2 membrane as a Langmuir-type monolayer and adsorbed as multilayers onto the -COOH and -NH 2 membranes, but hardly adsorbed onto the simple alkane membrane (-H membrane). When self-assembled monolayers bearing a thymine or adenine base as a terminal group were employed, selective binding processes of complementary guest molecules were observed: 2-aminopyridine (an adenine model) and γ-butyrolactam (a thymine model) selectively bound to the thyamine and adenine monolayers, respectively.