Spectroelectrochemical Sensing Based on Multimode Selectivity Simultaneously Achievable in a Single Device. 1. Demonstration of Concept with Ferricyanide

Abstract

A new type of spectroelectrochemical sensor that demonstrates three modes of selectivity (electrochemistry, spectroscopy, and selective partitioning) is demonstrated. The sensor consists of an optically transparent electrode (OTE) coated with a selective film. Sensing is based on the change in the attenuation of light passing through the OTE that accompanies an electrochemical reaction of the analyte at the electrode surface. Thus, for an analyte to be detected, it must partition into the selective coating and be electrolyzed at the potential applied to the electrode, and either the analyte or its electrolysis product must absorb light at the wavelength chosen. Selectivity for the analyte relative to other solution components is obtained by choice of coating material, electrolysis potential, and wavelength for optical monitoring. The sensor concept is demonstrated with an OTE consisting of an indium−tin oxide coating on glass that has been over-coated with a sol−gel-derived charge-selective thin film. Attenuated total reflection (ATR) is used as the optical detection mode. The selective coating was an anionically charge-selective sol−gel-derived PDMDAAC−SiO2 composite film, where PDMDAAC = poly(dimethyldiallylammonium chloride). Fe(CN)6 4- was used as a model analyte to demonstrate that the change in the transmittance of the ATR beam resulting from oxidation of Fe(CN)6 4- to Fe(CN)6 3- can be used to quantify an analyte. The unoptimized sensor exhibited the following characteristics: linear range, 8.0 × 10-6−5.0 × 10-5 M; sensitivity, 8.0 × 103ΔA/M; and detection limit, 8.0 × 10-6 M.

Waveguide surface plasmon resonance studies of surface reactions on gold electrodes

“…[18][19][20][21][22][23][24] In this configuration the planar waveguide behaves as an attenuated total reflection (ATR) structure in which the evanescent wave at the waveguide surface is used to measure the absorption of light by species present in solution within a couple of hundred nanometres of the electrode surface. If the waveguide is carefully designed it is possible to achieve very high sensitivity.…”

“…When used in this way the waveguide structure responds to changes in the imaginary part of the complex refractive index of the superstrate, in contrast to the planar waveguide surface plasmon resonance device which responds to changes in both the real and imaginary parts of the refractive index. For example, Piraud et al 21,22 have described an electrochemically regenerated chlorine sensor based on a lutetium phthalocyanine coated integrated waveguide structure, Dunphy et al 18,19 have used grating coupled step index slab waveguides to study adsorption of strongly coloured species at electrode surfaces, and Heineman et al 23,[25][26][27][28] have recently combined electrochemical modulation, selective adsorption into thin coatings, and planar waveguide optical measurements to develop highly sensitive and selective solution phase chemical sensors. In contrast a bare handful of papers describe SPR studies employing waveguide structures, despite the evident potential advantages of this approach.…”

A Novel Dye-Doped Sol–Gel Silica Sorbent for the Removal of Cobalt

“…(iii) It is a large molecule that can be entrapped securely inside the sol-gel pores. (iv) The reagent exhibits reasonable selectivity in analysis (Soylak et al 1997) and is readily available.…”

Design and Development of a New Hybrid Spectroelectrochemical Sensor

“…Ferrocyanide is part of a redox couple with well-defined, reversible electrochemistry that is accompanied by distinct spectral changes in the visible wavelength region (9). In this case, spectroelectrochemical modulation is accomplished by either scanning or stepping the potential from -0.3 V, at which no light is absorbed by ferrocyanide in the film, to +0.55 V at which light is absorbed (420nm maximum) by the electrogenerated ferricyanide in the film.…”