Improvement of carbon paste-based enzyme electrode using a new ionic liquid [Pmim][PF6] as the binder

A new carbon ionic liquid electrode (CILE) has been constructed using a low melting point (39 A degrees C) hydrophobic ionic liquid (IL) 1-propyl-3-methylimidazolium hexafluorophosphate ([Pmim][PF6]) as the binder. Both cyclic voltammetry and electrochemical impedance spectroscopy demonstrate that, in addition to the composition optimization of the IL/graphite composite, heating the composite at a temperature a little higher than the melting point of [Pmim][PF6] can also lower the background current and enhance the mechanical strength of the CILE. The heated CILE is more sensitive than the traditional carbon paste electrode for the detection of H2O2. Glucose oxidase (GOx) can be easily entrapped in the bulk IL/graphite composite. Heating the GOx-modified CILE (GOx-CILE) at the melting point of [Pmim][PF6] does not lower the catalytic activity of GOx. As compared with n-octylpyridinium hexafluorophosphate (melting point 65 A degrees C) as the binder, [Pmim][PF6]-based CILE is much better in signal-to-noise ratio. Under the optimum conditions, the [Pmim][PF6]-based GOx-CILE has a linear amperometric response to glucose over a concentration range of 2.0-26 mM with the detection limit as low as 0.39 mM. It follows that choosing an IL with a melting point of ca. 40 A degrees C as a binder to fabricate enzyme-entrapped CILEs is a good strategy for the enhancement of the performance of the electrode.