Direct intercalation of bis-2,2',2″,6-terpyridylcobalt(III) into zirconium phosphate layers for biosensing applications.

The direct intercalation reaction of Co(tpy)(2) with the highly hydrated θ phase of layered zirconium phosphate (θ-ZrP) resulted in the formation of the oxidized Co(tpy)(2) ion within the ZrP material. The X-ray powder diffraction patterns showed that the interlayer distance increases from 10.3 Å in θ-ZrP to 14.9 Å in the dry Co(tpy)(2)-intercalated ZrP {Co(tpy)(2):ZrP} phase. The complex remains electroactive within the layers of ZrP. The formal potential of a carbon paste electrode (CPE) modified with Co(tpy)(2):ZrP (E°' = 40.8 mV versus Ag/AgCl, 3.5 M NaCl) is non-pH-dependent. However, the sensitivity of the Co(tpy)(2):ZrP-modified CPE for the detection of reduced nicotinamide adenine dinucleotide (NADH) electrooxidation was lower than that of a previously reported CPE modified with Ru(phend)(2)bpy-intercalated ZrP. (1) To improve the characteristics of NADH electrooxidation of the Co(tpy)(2):ZrP-modified CPE, we included the enzyme diaphorase in solution, which increased the electrocatalytic current for NADH oxidation. A bienzymatic lactate biosensor was constructed and used for lactate sensing.