Integrated multienzyme electrochemical biosensors for the determination of glycerol in wines

The construction and performance of integrated amperometric biosensors for the determination of glycerol are reported. Two different biosensor configurations have been evaluated: one based on the glycerol dehydrogenase/diaphorase (GDH/DP) bienzyme system, and another using glycerol kinase/glycerol-3-phosphate oxidase/peroxidase (GK/GPOx/HRP). Both enzyme systems were immobilized together with the mediator tetrathiafulvalene (TTF) on a 3-mercaptopropionic acid (MPA) self-assembled monolayer (SAM)-modified gold electrode by using a dialysis membrane. The electrochemical oxidation of TTF at +150 mV (vs. Ag/AgCl), and the reduction of TTF+ at 0 mV were used for the monitoring of the enzyme reactions for the bienzyme and trienzyme configurations, respectively. Experimental variables concerning both the biosensors composition and the working conditions were optimized for each configuration. A good repeatability of the measurements with no need of cleaning or pretreatment of the biosensors was obtained in both cases. After 51 days of use, the GDH/DP biosensor still exhibited 87% of the original sensitivity, while the GK/GPOx/HRP biosensor yielded a 46% of the original response after 8 days. Calibration graphs for glycerol with linear ranges of 1.0 × 10−6 to 2.0 × 10−5 or 1.0 × 10−6 to 1.0 × 10−5 M glycerol and sensitivities of 1214 ± 21 or 1460 ± 34 μA M−1 were obtained with GDH/DP and GK/GPOx/HRP biosensors, respectively. The calculated detection limits were 4.0 × 10−7 and 3.1 × 10−7 M, respectively. The biosensors exhibited a great sensitivity with no significant interferences in the analysis of wines. The biosensors were applied to the determination of glycerol in 12 different wines and the results advantageously compared with those provided by a commercial enzyme kit.