AVS 54th International Symposium | |
Biomaterial Interfaces | Thursday Sessions |
Session BI-ThP |
Session: | Biomaterial Interfaces Poster Session |
Presenter: | S.E. Creager, Clemson University |
Authors: | K.P. Fears, Clemson University S.E. Creager, Clemson University R.A. Latour, Clemson University |
Correspondent: | Click to Email |
Alkanethiol self-assembled monolayers (SAMs) are widely used as model surfaces because they form very well-characterized monolayers over a broad range of surface chemistries. An important property for SAMs with ionizable functional groups is the surface dissociation constant (pKd), which defines the charge-density for a given pH solution. Using surface plasmon resonance (SPR) spectroscopy, we developed a method for the direct measurement of the pKd of COOH and NH2-SAMs by combining the ability of SPR to detect the changes in mass concentration close to a surface and the shift in ion concentration over the surface as a function of surface charged density. An analytical study was first performed to theoretically predict the general shape of the expected SPR plots by calculating the excess mass of salt ions over the SAMs as a function of the difference between the solution pH and surface pKd. SPR studies were then conducted to measure the shift in salt concentration as a function of bulk pH, with the resulting data being used to determine the pKd for HS-(CH2)11-COOH SAMs to be 7.4 ± 0.2 (N=4, mean ± 95% C.I.) and 6.5 ± 0.4 (N=4, mean ± 95% C.I.) for HS-(CH2)11-NH2 SAMs . These methods present a way to calculate the pKd for charged SAM surfaces that is non-disruptive and minimally interactive with the surface, thus providing an accurate and direct measure of the pKd of the surface.