Sol-Gel Encapsulation of Reactive Species

2 Sol-Gel Encapsulation of Reactive Species Another new and attractive route for tailoring electrode surfaces involves the low-temperature encapsulation of recognition species within sol-gel films (41,42). Such ceramic films are prepared by the hydrolysis of an alkoxide precursor such as, Si(OCH3)4 under acidic or basic condensation, followed by polycondensation of the hydroxylated monomer to form a three-dimensional interconnected porous network. The resulting porous glass-like material can physically retain the desired modifier but permits its interaction with the analyte that diffuses into the matrix. Besides their ability to entrap the modifier, sol-gel processes offer tunability of the physical characteristics 

FIGURE 4-15 Cyclic voltanimograms for 1.5 x 10 libose (a), glucose (b), galactose (c), and fructose (d) recorded at a Ru02-modified carbon-paste electrode. Dotted lines were obtained in carbohydrate-free solutions. (Reproduced with permission from reference 50.) 

Practical examples of using preconcentrating CMEs include the use of a mixed 2,9-dimethyl-1,10-phenantln oline/cai bon-paste electrode for trace measurements of copper (55), the use of clay-containing cai bon pastes for voltammetric measurements of non (56), the use of polyelecfrolyte coatings for the uptake and 

FIGURE 4-17 Preconcentrating surfaces based on covalent binding of the ligand to a polymer backbone. Q = charge A = electrode area F = surface coverage. (Reproduced with permission from reference 52.) 

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