Method and apparatus to study biological molecules or biological components at or in self-assembled monolayers (SAMs) on metal surfaces (2) such as gold in aqueous environments (6) using attenuated total internal reflection Fourier transform infra-red (ATR-FTIR) spectroscopy are described. Said method may be used for e.g. the screening for effective substances suitable as agonists or antagonists or - if performed time resolved - for studying kinetics of interactions of e.g. biological molecules adsorption and desorption processes or for the development of materials and surfaces for biological or medical applications.