Electrochemical sensors for saccharide

James has prepared a ferrocene monoboronic acid 64 and diboronic acid 65 as electrochemical saccharide sensors. The monoboronic acid system 64 has also been prepared and proposed as an electrochemical sensor for saccharides by Norrild and Sotofte. The electrochemical saccharide sensor 65 contains two boronic acid units (saccharide selectivity), one ferrocene unit (electrochemical read out), and a hexamethylene linker unit (for D-glucose selectivity). The electrochemical sensor 65 displays enhanced D-glucose (40 times) and D-galactose (17 times) selectivity when compared to the monoboronic acid 64. 

Nakashima has prepared a phenylboronic acid terminated redox active self-assembled monolayer on a gold electrode as an electrochemical sensor for saccharides. Self-assembled monolayers of 89, a phenylboronic acid terminated viologen alkyl disulfide, function as a sensitive saccharide sensor in aqueous soluhon [168]. 

Using a different approach, the research gronps of Fabre and Freund have synthesized boronate-functionalized conjugated polymers, which serve as electrochemical sensors. For example, a conjugated redox-active film of polypyrrole (174) was electrodeposited onto a platinum electrode from acetonitrile solution. Addition of fluoride anions led to a new redox system that showed an anodic shift relative to polypyrrole itself, which was attributed to fluoride binding to the boronate group. A related poly(aniline boronic acid) (175) was also reported and studied for saccharide detection. " ... 

Recently, Fabre et al. [31] and Freund et al. [7, 8] used electro-chemically deposited, self-doped, boronic-acid-substituted, conducting polymers for saccharide and fluoride detection. Freund et al. prepared a potentiometric sensor for saccharides using self-doped PABA [7, 8]. The transduction mechanism in that system is reportedly the change in pKa of polyaniline that accompanies complexation, and the resulting change in the electrochemical potential. Sensors produced with this approach exhibit reversible responses with selectivity to various saccharides and 1,2-diols (Figure 3.22) that reflect their binding constants with phenylboronic acid observed in bulk solutions. The sensitivity... 

Boronic acid-based biosensors to detect saccharides The recognition of saccharides, especially o-glucose, is of particular interest, owing to their correlation to diabetes and human cancers. The specific recognition of boronic acid for -diols provides a sensing selectivity. In the sugar sensors based on boronic acids (Figure 8), fluorescent, colorimetric, or electrochemical methods can be used as readout units. 

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