| In this study, surface plasmon resonance (SPR) was used to investigate the adsorption of MUA (11-mercapto-undecanoic acid), MPA (3-mercapto-propionic acid) and MHX (6-mercapto-1-hexanol) onto a gold SPR sensor surface. MUA, MPA, and MHX were dissolved in phosphate buffers of ionic strengths varying from 0.1 mM to 1 M and at pH values between 2 and 11, and monolayer formation experiments were performed. Our results illustrate how the adsorption of these charged and neutral alkanethiols depends on solution ionic strength and pH. Results indicate that, for single-component MUA or MPA layers, low pH and elevated solution ionic strength may promote denser layer formation. For binary MUA-MHX monolayers, potentiostatic control was important to establish reproducible SAM formation. Surprisingly, for 0.00 V potentiostatic depositions from mixed MUA-MHX solutions, MUA was substantially incorporated into the monolayer only at pH 3; whereas, at pH 7 and 11, MHX strongly predominated in the monolayer phase. |
