Liquid phase sensors based on chemically functionalized GaAs/AlGaAs heterostructures

We report on surface-near two-dimensional electron gases in GaAs/AlGaAs heterostructures for application in potential chemical or biochemical sensors in liquid environment. GaAs cap layers of the heterostructures were coated with self-assembled monolayers of 4′-substituted 4-mercaptobiphenyls (MBP), showing stable device performance in physiological (aqueous) buffers. Deposition of MBP with different 4′-substituents led to systematic changes in the lateral resistance, which can be correlated to the electrical potential drop across the established surface dipole layers. Furthermore, the lateral resistance showed a clear dependency on organic solvents with different polarities, suggesting its high sensitivity to the polarity of physisorbed molecules.