Combinatorial electrochemistry: A highly parallel, optical screening method for discovery of better electrocatalysts

Combinatorial screening of electrochemical catalysts by current-voltage methods can be unwieldy for large sample sizes. By converting the ions generated in an electrochemical half-cell reaction to a fluorescence signal, the most active compositions in a large electrode array have been identified. A fluorescent acid-base indicator was used to image high concentrations of hydrogen ions, which were generated in the electrooxidation of methanol. A 645-member electrode array containing five elements (platinum, ruthenium, osmium, iridium, and rhodium), 80 binary, 280 ternary, and 280 quaternary combinations was screened to identify the most active regions of phase space. Subsequent "zoom" screens pinpointed several very active compositions, some in ternary and quaternary regions that were bounded by rather inactive binaries. The best catalyst, platinum(44)/ruthenium(41)/osmium(10)/iridium(5) (numbers in parentheses are atomic percent), was significantly more active than platinum(50)/ruthenium(50) in a direct methanol fuel cell operating at 60 degreesC, even though the latter catalyst had about twice the surface area of the former.

An improved model for bacterial encrustation studies.

A comparative evaluation of various biomaterials for their resistance to bacterial colonization and encrustation in infected urine is an important area in urological biomaterials research. This article describes an in vitro dynamic perfusion system that allows four reactors containing 24 1-in. catheter samples (6 per reactor) to be simultaneously perfused at a constant flow rate by synthetic urine. A common urease-producing urinary pathogen, Proteus mirabilis, was maintained at a level of 10(6) colony-forming units/mL for 7 days in the dynamic perfusion reactors. The pH and bacterial population were monitored every 24 h and the percentage of encrustation on latex and hydrogel-coated commercial catheter materials gave reproducible results in three different runs, 15.2 +/- 3.65% and 13.8 +/- 2.58%, respectively. A major issue of inlet clogging due to ascending bacteria or ammonia has been rectified using a dismountable inlet assembly. An incubator coupled with a cooling system allowed accurate temperature maintenance of 37 degrees C in all four reactors. Results from scanning electron microscopy of some latex samples are also presented.

In vitro and in vivo testing of an electrocatalytic glucose sensor.

A prerequisite for the development of an implantable artificial pancreas is the availability of a stable, long-life glucose sensor. Platinum (Pt) catalyzed electrodes have been demonstrated in vitro to show high sensitivity to glucose and long cycle life but are more sensitive to co-reactants compared with enzymatic methods. The authors developed a special data processing method (compensated net charge ratio, or CNCR) in which the measured electrode response is very sensitive to glucose, completely insensitive to urea, and only moderately sensitive to amino acids. Other endogenous and exogenous co-reactants show only minor interferences. The CNCR method involves the determination of the ratio of net oxidation charge to total charge during one complete cycle of a cyclic voltammogram. Prototype electrodes tested in vitro in spiked plasma have shown typical sensitivities of greater than 2 x 10(-4) CNCR units per 1 mg/dl change in glucose concentration, with linear response up to 400 mg/dl. For in vivo testing, a modified 5 F vascular catheter with membrane covered surface mounted electrodes was used at a vena cava site in swine. Several sensor designs were tested in vivo, with sensitivities of 1-5 x 10(-4) CNCR units (mg/dl).

Electrocatalytic glucose sensor.

High surface area platinum subjected to the appropriate electrical potential cycling regimes exhibits considerable electrocatalytic activity towards glucose oxidation. We have developed a special data processing method, the compensated net charge (CNC) method, to take advantage of the electrocatalytic activity of platinum. This method involves the determination of the net oxidation charge during one complete cycle of a cyclic voltammogram applied to the platinum electrode in a potentiodynamic mode. Under these conditions, the electrode response is very sensitive to glucose, completely insensitive to urea, and only moderately sensitive to amino acid concentration changes. Earlier work with other endogenous and exogenous potential co-reactants shows little interference. Data obtained in vitro and in vivo will be presented and discussed.