Biomolecular immobilization on conducting polymers for biosensing applications.

A comprehensive overview is presented on the implication of silica-based organic-inorganic hybrid materials in electrochemical science. It involves composite materials of both class I (weak bonds between the organic and inorganic components) and class II (strong chemical bonds). Starting with a description of the common designs of electrodes modified with these hybrids, the review then reports their applications in the various fields of electrochemistry, illustrating the diversity of the organically modified silicates used for this purpose. The mild chemical conditions allowed by the sol-gel process provide very versatile access to these electrochemical devices. They have found many applications in electroanalysis, including preconcentration associated with voltammetric detection, permselective coatings, electrochemical sensors, electrocatalysis, and detectors for chromatography. They were also applied as redox and conducting polymers, as solid polymer electrolytes for batteries, for the design of spectroelectrochemical and electro-chemiluminescence devices, and in the field of electrochemical biosensors.

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Electrochemical Applications of Silica-Based Organic−Inorganic Hybrid Materials

The subject of sol−gel electrochemistry is introduced, starting with a brief account of milestones in its evolution. Then, the types of sol−gel materials that are useful for electrochemistry are presented, followed by a description of recent advances in the various fields of sol−gel electrochemistry. Modified electrodes, solid electrolytes, electrochromic devices, and corrosion protection coatings are described. Emerging fields such as RuO2 supercapacitors and electrochemical synthesis of sol−gel precursors are also addressed.

Sol−Gel Materials in Electrochemistry

The implications of organically-modified silica-based materials in electrochemical science is reviewed along with some selected recent trends in the field of functionalized and sol–gel silica electrochemistry. These recent trends include the electro-assisted generation of organosilica films on solid electrode surfaces, the preparation and applications of sol–gel derived composite (carbon, gold, nanotubes) electrodes, the electrochemical characterisation of mass transfer reactions in porous functionalized silicas, solid-state electrochemistry and gas sensors involving sol–gel materials, imprinted functionalized silica, and the electrochemical characterisation and applications of ordered mesoporous organosilicas.

Exciting new directions in the intersection of functionalized sol–gel materials with electrochemistry

Electrocatalytic oxidation of NAD(P) H at mediator-modified electrodes.

Electrochemical sensor for NADH based on Meldola's blue immobilized on silica gel modified with titanium phosphate

A new amperometric biosensor for salicylate based on salicylate hydroxylase immobilized on polipyrrole film doped with hexacyanoferrate

The voltammograms obtained with an electrode containing carbon paste with ferrocene immobilized on a titanium-oxide/silica gel material showed good response and stability in aqueous media. From pH 4 to 8 the electrode response remained almost constant, but a small shift in the midpoint potential towards more positive values was observed when the pH was decreased. The nature of the cation does not affect the voltammetric response. However, the nature of the anion affects the midpoint potential significantly. Cyclic voltammetry investigation showed that the electrode with immobilized glucose oxidase is an excellent biosensor. The mechanism of the electron transfer was proposed as being electron tunneling by the flavin of the enzyme to mediator, and the high current level is assigned to the high surface area of the silica matrix. The amperometric measurements showed a linear response in the range from 1.0 × 10−4 to 8.0 × 10−4 M. Above this range, saturation of the enzyme was observed. The response time was about 15 s. Determination of glucose in blood serum showed an excellent correlation when compared with Merck's Kit method. The immobilized material presented an excellent stability mantaining the same activity for at least six months.

Immobilized ferrocene and glucose oxidase on titanium(IV) oxide grafted onto a silica gel surface and its application as an amperometric glucose biosensor

A biosensor for salicylate was developed using a modified carbon paste electrode with silica gel coated with Meldola's Blue and salicylate hydroxylase. This biosensor detects the catechol produced in the enzymatic reaction through its electroxidation on the mediator. The influence of NADH/substrate ratio was verified and the biosensor presented response when this ratio was higher than 1.8. The pH of the medium significantly influences the results, requiring control within a narrow range of pH. The effect of the applied potential in the biosensor response showed that 200 mV vs SCE is the best potential to use in the measurements. The biosensor has a good linear response range of 10 to 60 μmol L−1, adjusted by the equation I = 11.7 (×1.3) + 6.78 (×0.03)[salicylate], with high sensitivity. The relative standard deviation for 6 measurements was 3.7%. The biosensor showed good stability for 20 days when used daily or for one month when stored in a refrigerator.

Benjamin G. Milagres

Papers

Electrochemical sensor for NADH based on Meldola's blue immobilized on silica gel modified with titanium phosphate

A new amperometric biosensor for salicylate based on salicylate hydroxylase immobilized on polipyrrole film doped with hexacyanoferrate

Immobilized ferrocene and glucose oxidase on titanium(IV) oxide grafted onto a silica gel surface and its application as an amperometric glucose biosensor

A Modified Carbon Paste Electrode with Silica Gel Coated with Meldola's Blue and Salicylate Hydroxylase as a Biosensor for Salicylate