Biosensor based on laccase and an ionic liquid for determination of rosmarinic acid in plant extracts

Abstract

Novel biosensors based on laccase from Aspergillus oryzae and the ionic liquids (ILs) 1- n-butyl-3-methylimidazolium hexafluorophosphate (BMIPF 6) and 1- n-butyl-3-methylimidazolium tetrafluoroborate (BMIBF 4) were constructed for determination of rosmarinic acid by square-wave voltammetry. The laccase catalyzes the oxidation of rosmarinic acid to the corresponding o-quinone, which is electrochemically reduced back to rosmarinic acid at +0.2 V vs. Ag/AgCl. The biosensor based on BMIPF 6 showed a better performance than that based on BMIBF 4. The best performance was obtained with 50:20:15:15% (w/w/w/w) of the graphite powder:laccase:Nujol:BMIPF 6 composition in 0.1 mol L −1 acetate buffer solution (pH 5.0). The rosmarinic acid concentration was linear in the range of 9.99 × 10 −7 to 6.54 × 10 −5 mol L −1 ( r = 0.9996) with a detection limit of 1.88 × 10 −7 mol L −1. The recovery study for rosmarinic acid in plant extract samples gave values from 96.1 to 105.0% and the concentrations determined were in agreement with those obtained using capillary electrophoresis at the 95% confidence level. The BMIPF 6-biosensor demonstrated long-term stability (300 days; 920 determinations) and reproducibility, with a relative standard deviation of 0.56%.