Mediator-modified electrodes for catalytic NADH oxidation: high rate constants at interesting overpotentials.

Carbon paste electrodes were modified with a nitrofluorenone derivative, 2,4,7-trinitro-9-fluorenone, adsorbed on zirconium phosphate (ZP). After electrochemical reduction of the fluorenone derivative, it turns into a very efficient mediator for electrocatalytic NADH oxidation, with a formal potential of about +250 mV vs. Ag/AgCl. The electrochemistry and the electrocatalytic properties of the mediator were investigated with cyclic voltammetry and rotating disk electrode methodology. The second order rate constant with NADH was evaluated and found to be higher than 10(6) M(-1) s(-1), thus approaching true diffusion controlled currents for NADH oxidation.

Bioelectrochemical monitoring of phenols and aromatic amines in flow injection using novel plant peroxidases.

An amperometric flow system combined with a glucose oxidase-mutarotase reactor was optimized and used to determine aromatic amines and phenols using peroxidase-modified graphite electrodes. An increase in currents upon injection of the analyzed substrate was shown to be approximated by a Michaelis-Menten type dependence. The detection limit was calculated as 3 times the noise, and the sensitivity was calculated as Imax/K(m)app. Commercially available horseradish peroxidase was compared with tobacco anionic and peanut cationic peroxidases for determination of aromatic amines and phenols. Detection limits of 10 nM for determination of o-aminophenol and o- and p-phenylenediamine achieved with a tobacco peroxidase-modified electrode give a promise for further improvements in sensitivities and detection limits of biosensors.

Nonanastomotic aneurysms in venous homologous grafts and bovine heterografts in femoropopliteal bypasses.

In the absence of a suitable autologous vein for a long distal femoropopliteal bypass, the homologous vein appears to be a good substitute. However, the patency rate after one year is less than 50 per cent and nonanastomotic aneurysms occurred in one third of our patients followed for more than one year. These two complications may be related to an immune response which may be lessened by preservation of the graft in the frozen state. Bovine heterografts function well when placed subfascially for femoropopliteal bypasses ending above the knee. Failure rate is high when the distal end of the graft extends across the knee joint. In our experience nonanastomotic aneurysms have developed in 50 per cent of patent grafts followed for more than one year, although other surgeons have reported an incidence of only 3 to 20 per cent. In the follow-up of twenty-three venous homografts and twenty bovine heterografts placed as femoropopliteal bypasses, eight nonanastomotic aneurysms appeared and required replacement. This occurrence was noted in more than 33 per cent of grafts patent beyond one year. When an adequate autologous vein is not available, the composite Dacron-vein graft is the best substitute.