Interaction of Tris with DNA molecules and carboxylic groups on self-assembled monolayers of alkanethiols measured with surface plasmon resonance

Functional materials employing organic coatings on inorganic substrates are perceived as potential platforms for applications in a variety of fields. Therefore, the investigation of interactions of such systems with the microenvironment has become an important research direction in surface science. Herein, we study the interaction of one of the buffers most commonly used in biological studies, Tris buffer, with self-assembled monolayers (SAMs) of alkanethiols and short DNAs using a surface plasmon resonance (SPR) biosensor. We show that the interaction between Tris and carboxylic groups of SAMs is a complex multiphasic process. We demonstrate that Tris base binds to the protonated carboxylic groups. When those groups become deprotonated, Tris base dissociates and Tris acid is attracted, which results in the formation of a diffuse layer over the charged surface. In addition, we show that the interaction of Tris with the immobilized DNA molecules biases the determination of surface concentrations of the immobilized DNA molecules and thus also the determination of hybridization efficiencies