Insightful Analysis of Phenomena Arising at the Metal|Polymer Interphase of Au-Ti Based Non-Enzymatic Glucose Sensitive Electrodes Covered by Nafion

Abstract

This paper focuses on the examination of glucose oxidation processes at an electrode material composed of gold nanoparticles embedded in a titanium template. Three different conditions were investigated: the chloride content in the electrolyte, its ionic conductivity and the presence of a Nafion coating. The impact of the provided environment on the oxidation reaction was evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Two models, namely: chemisorption and incipient hydrous oxide/adatom mediator (IHOAM), were applied to explain the complex voltammetric responses of the electrodes exposed to solutions of varied glucose concentrations. Three different phenomena were observed for the studied cases. The first is related to the transition between the dominant mechanism of glucose oxidation from the IHOAM model to the chemisorption model. This happens only in an electrolyte containing chlorides after exceeding a certain amount of glucose. The second effect exhibits a bottleneck nature resulting from the presence of Nafion on the electrode’s surface. In this case, mass transport through the semi-permeable polymer is hampered, due to the blocking of channels and physical internal cross-linking. This leads to a preconcentration of glucose inside the pores resulting in an increase in both the material sensitivity and the linear range of the calibration curve. Lastly, the third effect is manifested in a low concentration of the supporting electrolyte. It is based on the fact that mass transport of hydroxyl ions is governed not only by diffusion, but also by migration. These three effects have a tremendous impact on the glucose oxidation mechanism and reveal its very complex nature.

Tailoring Diffusional Fields in Zwitterion/Dopamine Copolymer Electropolymerized at Carbon Nanowalls for Sensitive Recognition of Neurotransmitters

“…The first sensitivity value is very close to the slope measured in 1× Tris. This behavior suggests a transition to a different sensing mechanism, presumably due to interactions of dopamine with proteins. In higher dopamine concentrations, it can spontaneously bind to tryptophan and tyrosine residues of albumins by hydrogen bonding (DA–albumin). , As a result, the chemical moiety being sensed in BSA is not pure DA but DA–albumin.…”

Simple synthesis route for fabrication of protective photo‐crosslinked poly(zwitterionic) membranes for application in non‐enzymatic glucose sensing

“…The presence of an inflection point at 2 mM might be connected with the change of the dominant oxidation mechanism discussed in depth in our previous work. 47 However, in the logarithmic scale, the linear range is significantly wider, that is, 0.4-12 mM with sensitivity equal to 36.8 μA cm À2 mM À1 (Figure S6). This range is sufficient to cover concentration ranges in most physiological fluids.…”

“…45 In other words, the microenvironment of the solution inside the polymer and the tendency to swelling seen by the naked eye strictly correlate with the changes of the dielectric constant and, therefore, the double-layer capacitance. Considering the low values of n parameters, the resulting C dl data can be quantitative and incorrect, 46,47 although it can still provide qualitative information.…”

“…It is worth remembering that our studies are performed in 0.1 Â PBS containing at least 13 mM of chloride with pH = 7.4, not in 0.1 M NaOH, where the formation of hydroxide is much more facilitated due to the larger amount of adsorbed electrocatalytic AuOH ads species. 47 Figure 7b shows the glucose oxidation current density in 0.1 Â PBS containing 5 mM of glucose on increasing the number of bending cycles in the preliminary testing. One can see that even after 1,000 bends, the current density stays roughly the same, indicating that Nafion-co-PZ maintains integrity, and therefore, the response is considered stable.…”

Advances in nanostructured material-based non-enzymatic electrochemical glucose sensors

“…Reducing the working potential and adding the polymer membrane are both effective means. 33,34 They are generally realized via the selection and regulation of catalysts and polymers.…”