Reagentless enzyme electrode for malate based on modified polymeric membranes Original Research Article

A series of polymeric membranes have been employed as outer barriers in an amperometric malate dehydrogenase (MDH)/diaphorase (DI) or MDH/DI/NAD+/mediator enzyme electrode for the determination of malate in undiluted neutral or acidic media. MDH/DI were physically entrapped with NAD+ and mediator in a mixed ester cellulose membrane. Outer membranes such as non-anionic surfactant-modified cellulose acetate/Tween-80 and unplasticised spin coated PVC/polycarbonate (PC) resin in conjunction with an ascorbate oxidase (AOD) layer were utilised. Mechanical strength, thickness studies and diffusional properties of the membranes were investigated. Hexacyanoferrate(III), 2,4-dichlorophenolindophenol (DCPI) and naphthoquinone (NQ) were tested as mediators for enzymatically produced NADH using cyclic voltammetry. Analytical utility of the sensors is demonstrated.