Flow injection analysis of L-lactate in milk and yoghurt by on-line microdialysis and amperometric detection at a disposable biosensor

Abstract

A disposable lactate biosensor able to operate in flow injection analysis is described and characterized. The biosensing layer, obtained by glutaraldehyde co-crosslinking of lactate oxidase with bovine serum albumin, was cast on an underlying electropolymerized layer of overoxidized polypyrrole. The resulting biosensor was interference-free and showed a K′_M value of 2.4 mmol l⁻¹ and a maximum current density of 440 µA cm⁻². When integrated in a flow injection analysis system, a sensitivity of 300 ± 10 nA mmol⁻¹ l, a linear response up to 1 mmol l⁻¹ and detection limits in the low micromolar range were obtained. The introduction of a microdialysis membrane-based sampler reduced the sensitivity to 7.9 ± 0.2 nA mmol⁻¹ l and extended the linear range up to 50 mmol l⁻¹ lactate. The anti-interference characteristics of the biosensor permitted lactate determination in untreated milk and diluted yoghurt samples.