A new technique has been developed that combines evanescent-field optical sensing with electrochem. control of surface adsorption processes. This new technique, termed \"electrochem. optical wave-guide lightmode spectroscopy\" (EC-OWLS), proved efficient in monitoring mol. surface adsorption and layer thickness changes of an adsorbed polymer layer examd. in situ as a function of potential applied to a waveguide in a pilot study. For optical sensing, a layer of indium tin oxide (ITO) served as both a high-refractive-index waveguide and a conductive electrode. In addn., an electrochem. flow-through fluid cell was provided, which incorporated working, ref., and counter electrodes, and was compatible with the constraints of optical sensing. Poly(L-lysine)-grafted-poly(ethylene glycol) (PLL-g-PEG) served as a model, polycation adsorbate. Adsorption of PLL-g-PEG from aq. buffer soln. increased from 125 to 475 ng/cm2 along a sigmoidal path as a function of increasing potential between 0 and 1.5 V vs. the Ag ref. electrode. Upon buffer rinse, adsorption was partially reversible when a potential of >=0.93 V was maintained on the ITO waveguide. However, reducing the applied potential back to 0 V before rinsing resulted in irreversible polymer adsorption. PLL-g-PEG modified with biotin demonstrated similar adsorption characteristics, but subsequent streptavidin binding was independent of biotin concn. Applying pos. potentials resulted in increased adsorbed mass, presumably due to polymer chain extension and reorganization in the mol. adlayer. [on SciFinder (R)]