A biosensor based on the iridium nanoparticles dispersed in ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate (Ir-BMI.PF6) and a celery (Apium graveolens) extract as a source of polyphenol oxidase (PPO) was constructed. A modified support based on beta-cyclodextrin (beta-CDEP) was used for enzyme immobilization. The behavior of phenolic compounds was investigated by square-wave voltammetry and rutin was selected by presenting the greatest signal. The best performance was obtained with a composition of 70:10:10:10% (w/w/w/w) of the graphite powder:beta-CDEP:Nujol:Ir-BMI.PF6 composition, a PPO concentration of 500 units mL(-1), in 0.1 M phosphate buffer solution (pH 6.0) with frequency, pulse amplitude and scan increment at 100 Hz, 60 mV, and 3.0 mV, respectively. Under optimized conditions, the cathodic currents increased linearly for the rutin concentration range of 1.3 x 10(-7)-2.0 x 10(-6) M with a detection limit of 7.9 x 10(-8) M. This sensor demonstrated acceptable repeatability and reproducibility and the results for the rutin recovery ranged from 92.8 to 103.4%. A relative error of 0.7% was obtained in the rutin determination in simulated samples. (C) 2013 Elsevier Inc. All rights reserved.