Sol-gel-derived thick-film amperometric immunosensors.

Sol-gel processing is used for the first time for the preparation of electrochemical immunosensors. One-step sensor fabrication, based on the coupling of sol-gel and screen-printing technologies, is employed. A low-temperature cured ink is prepared by dispersion of rabbit immunoglobulin G (RIgG), graphite powder, and a binder in the sol-gel solution. The enzyme-labeled antibody can readily diffuse toward the encapsulated antigen, which retains its binding properties, and the association reaction is easily detected at the dispersed graphite surface. Use of anti-RIgG labeled with alkaline phosphatase, naphthyl phosphate as the substrate, and amperometric detection at +400 mV (vs Ag/AgCl) results in a low detection limit of 5 ng/mL (32 pM) for the solution antigen. Tailoring the porosity of the ceramic-carbon matrix can be used for tuning the assay performance. The high sensitivity, low cost, durability, and simplicity of the new single-use immunosensors make them well suited for various on-site applications.

Overoxidized poly(pyrrole-co-[3-(pyrrol-1-yl)-propanesulfonate])-coated platinum electrodes for selective detection of catecholamine neurotransmitters.

The cation-exchange and anion-exclusion properties of the poly¿pyrrole-co-[3-(pyrrol-1-yl)propanesulfonate]¿-(PPy-PS) copolymer are exploited for imparting higher selectivity to measurements of primary neurotransmitters in the presence of ascorbic acid. Such incorporation of ionizable sulfonated groups in the pyrrole ring prior to its electropolymerization leads to effective rejection of the anionic ascorbate species and preferential collection of the cationic dopamine and norepinephrine. Overoxidized PPy-PS films thus offer better discrimination against ascorbic acid than Nafion or overoxidized polypyrrole coatings. Experimental variables influencing the permselective behavior of the PPy-PS layer, including the electropolymerization time and solution pH, were explored. The selectivity and sensitivity improvements associated with the increased electrostatic character of overoxidized polypyrrole films hold promise for neurochemical electrochemical studies.

Sol-gel carbon composite electrode as an amperometric detector for liquid chromatography.

The performance characteristics of an electrochemical detector for liquid chromatography based on a sol-gel carbon composite working electrode in a wall-jet configuration are described. The new detector combines the versatility of sol-gel processes with several favorable characteristics, including fast electron-transfer kinetics, mechanical rigidity and renewability. Factors influencing the amperometric response are explored and optimized. Detection limits of 58-170 pg are reported for various neurotransmitters. Repetitive injections yield peak heights with relative standard deviations of 2.6-3.7%. The prospects of using sol-gel derived electrochemical detectors are discussed.

Sol-gel-derived gold composite electrodes.

The preparation, characterization, and analytical utility of sol-gel-derived gold composite electrodes is described. The new metal-ceramic electrodes are comprised of gold powder homogeneously dispersed in a modified silica matrix. They couple the favorable electron-transfer kinetics common to gold surfaces with the regeneration, bulk modification, and versatility features of sol-gel-derived composite materials. The voltammetric characteristics of the composite gold-silica electrodes are explored and compared with conventional gold electrodes. Sol-gel-derived gold biosensors have been prepared by incorporating an oxidase enzyme within the sol-gel gold solution. Analogous thick-film enzyme strips, based on a new screen-printable gold biogel ink, have also been fabricated. To our knowledge, the above represent the first examples of metal-ceramic sensing electrodes and of bulk modification of metallic working electrodes.

Screen-printable sol-gel enzyme-containing carbon inks.

Enzymes usually cannot withstand the high-temperature curing associated with the thick-film fabrication process and require a separate immobilization step in connection with the production of single-use biosensors. We report on the development of sol-gel-derived enzyme-containing carbon inks that display compatibility with the screen-printing process. Such coupling of sol-gel and thick-film technologies offers a one-step fabrication of disposable enzyme electrodes, as it obviates the need for thermal curing. The enzyme-containing sol-gel carbon ink, prepared by dispersing the biocatalyst, along with the graphite powder and a binder, within the sol-gel precursors, is cured very rapidly (10 min) at low temperature (4 °C). The influence of the ink preparation conditions is explored, and the sensor performance is evaluated in connection with the incorporation of glucose oxidase or horseradish peroxidase. The resulting strips are stable for at least 3 months. Such sol-gel-derived carbon inks should serve as hosts for other heat-sensitive biomaterials in connection with the microfabrication of various thick-film biosensors.

Disposable screen-printed electrodes for monitoring hydrazines.

Disposable amperometric sensors for hydrazines have been fabricated by a judicious tailoring of the surface of screen-printed electrodes. Strong electrocatalytic action towards the oxidation of hydrazines is achieved by incorporating cobalt phthalocyanine within the carbon inks or by covering the printed surface with a mixed valent ruthenium cyanide coating. The electrocatalytic behavior, sensor optimization and analytical performance are reported. The new sensor strips should facilitate on-site environmental and industrial monitoring of hydrazine compounds.