Application of room temperature ionic liquids to the development of electrochemical lipase biosensing systems for water-insoluble analytes

Biosensors have been prepared by modification of glassy carbon electrodes with functionalised multiwalled carbon nanotubes (MWCNT) dispersed in the room temperature ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethane)sulfonimide (BmimNTF2) 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)/BmimNO3 mixture is a better electrolyte than aqueous buffer alone. The response signal in the buffer–BmimNO3 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 μg 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–BmimNTF2/Lip biosensor is proposed.

Research highlights
► Lipase enzyme biosensors with multi-walled carbon nano-tubes prepared in ionic liquid Lipase biosensor.
► For olive oil triglycerides dissolved in ionic liquid Analytical response due to phenols.
► It released in presence of lipase No interferences from cholesterol or glycerol Biosensor mechanism - hydrolysis of triglycerides by lipase.