Fluorescence properties of carba nicotinamide adenine dinucleotide for glucose sensing.

Carba nicotinamide adenine dinucleotide (cNAD) may serve as a stable cofactor for the enzyme-based detection of glucose. Many characteristics of cNAD and its reduced form cNADH resemble those of NAD and NADH, respectively. The fluorescence lifetimes of cNADH are determined to be 0.32(2) ns and 0.66(3) ns compared to 0.28(2) ns and 0.60(3) ns for NADH, and the temperature dependence of these lifetimes hints towards identical processes for quenching. The maximum emission occurs at 464 nm for both cNADH and NADH and absorbance maxima are found at 360 nm and 340 nm, respectively. In contrast to previous suggestions the respective maximum extinction coefficient of cNADH equals that of NADH and amounts to 6.2(2) mM(-1) cm(-1). When changing from NADH to cNADH we observe a ~50% increase in quantum efficiency, which--together with the larger excitation wavelength and the higher stability--should make cNAD a well suited alternative as coenzyme for robust glucose detection.