Cobalt Polypyridyl Complexes as Redox Mediators for Lipoamide Dehydrogenase

Abstract

A series of cobalt polypyridyl complexes were synthesized and characterized by cyclic voltammetry in aqueous and acetonitrile solutions. Their mediation ability toward FADH 2 oxidation in a monoenzyme (lipoamide dehydrogenase) and a bienzyme (lipoamide dehydrogenase coupled to lactate dehydrogenase) system was studied. Of all the complexes tested, only the [Co(tpy) 2 ](PF 6 ) 2 , [Co(NH 2 -phen) 3 ](PF 6 ) 2 and [Co(CH 3 -phen) 3 ](PF 6 ) 2 showed a current enhancement indicative of an EC cat mechanism in the presence of lipoamide dehydrogenase and NADH. No cross reactivity was observed for these complexes in the presence of lactate dehydrogenase/ NAD þ and lactate. The results also suggest that factors such as hydrophobic interactions, steric hindrance, H-bonding and driving force are important when designing a redox mediator for a biosensor. Protein and/or cofactor adsorption fouled the electrode surface lowering the current response. A self-contained bienzymatic biosensor exhibited a linear response (peak current versus log [lactate]) for lactate concentrations between 5 M to 5 mM with a lowest detectable lactate concentration of 4.76 M.

Direct Intercalation of Bis-2,2′,2″,6-terpyridylcobalt(III) into Zirconium Phosphate Layers for Biosensing Applications

“…Figure shows characteristic cyclic voltammograms of the CPEs modified with [Co(tpy) 2 ] 3+ :ZrP, which confirm that the complex remains electroactive within ZrP. We observe a formal potential of 40.8 mV versus Ag/AgCl, which is in agreement with literature values for this complex . Table shows the electrochemical parameters of these modified CPEs.…”

“…10-fold in the presence of diaphorase. It is known that FADH 2 is a better electron shuttle than NADH alone . Similar experiments were performed with CPEs modified with [Co(tpy) 2 ] 2+ by Guadalupe et al, where in the presence of diaphorase, the electrocatalytic current was also enhanced .…”

“…Guadalupe et al used [Co(tpy) 2 ] 2+ for lactate sensing and demonstrated that coupling it to lipoamide dehydrogenase (LADH) or diaphorase can increase the catalytic current for NADH oxidation. The construction of bienzymatic devices by coupling mediators allows for a decrease in the overpotential for NADH electrooxidation and avoidance of common interferences for electrode fouling. − LADH or diaphorase allows for the complete NADH oxidation to form NAD + that can be reused in the catalytic cycle, without forming any radicals on the electrode surface.…”

“…Guadalupe et al and Abruña et al have used [Co(tpy) 2 ] 2+ and its derivatives to detect the electrooxidation of NADH in solution. , Guadalupe et al also used [Co(tpy) 2 ] 2+ for lactate sensing using lactate dehydrogenase in a monoenzymatic setup and lipoamide dehydrogenase and lactate dehydrogenase in a bienzymatic setup …”

“…These materials have been prepared to construct a lactate sensor, in which the electron mediator can oxidize NADH but whose electrochemical behavior is not pH-dependent. Cobalt complexes have been used for NADH oxidation. ,, We present in this paper the electrode kinetics of a CPE modified with [Co(tpy) 2 ] 3+ :ZrP in the presence of NADH. A bienzymatic lactate sensor based on the [Co(tpy) 2 ] 3+ :ZrP-modified CPE is also described.…”