Biosensors have been prepared by modification of glassy carbon electrodes with functionalised multi-walled carbon nanotubes (MWCNT) dispersed in the room temperature ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethane)sulfonimide (BmimNTF(2)) and with lipase cross-linked with glutaraldehyde. The biosensor was applied to the determination of olive oil triglycerides by cyclic voltammetry. A phosphate buffer (pH 7.0)/BmimNO(3) mixture is a better electrolyte than aqueous buffer alone. The response signal in the buffer-BmimNO(3) mixture was found to increase with the number of cycles until a constant current was achieved. The calibration curve obtained exhibited a sigmoid shape and a four-parameter model was used to fit the data which gave a limit of detection of 0.11 mu g mL(-1). Close inspection of such calibration curves showed two distinct linear regions indicating changes in the mechanism of the electrochemical response. Overall, the oxidative analytical response was found to be due to phenolic compounds present in the olive oil, released in the presence of lipase, rather than due to triglycerides per se. It was also found that there were no interferences from either cholesterol or glycerol. A possible mechanism of olive oil determination at a MWCNT-BmimNTF(2)/LiP biosensor is proposed. (C) 2011 Elsevier B.V. All rights reserved.