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The selectivity of an optical sensor can be improved by combining optical detection with electrochemical oxidation or
reduction of the target analyte to change its spectral properties. The changing signal can distinguish the analyte from
interferences with similar spectral properties that would otherwise interfere. The analyte is detected by measuring the
intensity of the electrochemically modulated signal. In one form this spectroelectrochemical sensor consists of an
optically transparent electrode (OTE) coated with a film that preconcentrates the target analyte. The OTE functions as
an optical waveguide for attenuated total reflectance (ATR) spectroscopy, which detects the analyte by absorption.
Sensitivity relies in part on a large change in molar absorptivity between the two oxidation states used for
electrochemical modulation of the optical signal. A critical part of the sensor is the ion selective film. It should
preconcentrate the analyte and exclude some interferences. At the same time the film must not interfere with the
electrochemistry or the optical detection. Therefore, since the debut of the sensor’s concept one major focus of our group
has been developing appropriate films for different analytes. Here we report the development of a series of quaternized
poly(vinylpyridine)-co-styrene (QPVP-co-S) anion exchange films for use in spectroelectrochemical sensors to enable
sensitive detection of target anionic analytes in complex samples. The films were either 10% or 20% styrene and were
prepared with varying degrees of quaternized pyridine groups, up to 70%. Films were characterized with respect to
thickness with spectroscopic ellipsometry, degree of quaternization with FTIR, and electrochemically and
spectroelectrochemically using the anions ferrocyanide and pertechnetate.
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