Authors: J.P. Bearinger, J. Vörös, N.D. Spencer, J.A. Hubbell and M. Textor
Affilation: ETH Zürich/ Lawrence Livermore National Laboratory, United States
Pages: 48 - 51
Keywords: polymer, interfaces, electrochemical, biotechnology
A new technique has been developed that combines evanescent-field optical sensing with electrochemical control of surface adsorption processes. This technique, termed Electrochemical Optical Waveguide Lightmode Spectroscopy (EC-OWLS), proved efficient in monitoring molecular surface adsorption and layer thickness changes of an adsorbed polymer layer examined in situ as a function of potential applied to a waveguide. For optical sensing, a layer of indium tin oxide (ITO) served as both a high refractive index waveguide and a conductive electrode, an electrochemical flow-through fluid cell incorporated working, reference and counter electrodes. Poly(L-lysine)-grafted-poly(ethylene glycol) (PLL-g-PEG) served as a model, polycation adsorbate. PLL-g-PEG adsorption from aqueous buffer solution increased from 125 to 475 ng/cm2 along a sigmoidal path as a function of increasing potential between 0 and 1.5 V versus the Ag reference electrode. Upon buffer rinse, adsorption was partially reversible when a potential 0.93 V or greater was maintained on the ITO waveguide. Reducing applied potential back to 0 V before rinsing resulted in irreversible adsorption. PLL-g-PEG modified with biotin demonstrated similar adsorption characteristics, but subsequent streptavidin binding was independent of biotin concentration. Applying positive potentials resulted in increased adsorbed mass, presumably due to polymer chain extension and reorganization in the molecular adlayer.