Alkaline Phosphatase Based Amperometric Biosensor Immobilized by Cysteamine-Glutaraldehyde Modified Self-Assembled Monolayer

Abstract

Alkaline phosphatase (ALP) was immobilized with cross-linking agents glutaraldehyde and cysteamine by forming a self-assembled monolayer on a screen printed gold electrode. ALP converts p-nitrophenyl phosphate to p-nitrophenol and phosphate. p-Nitrophenol loses H⁺ ion and turns into the negatively charged compound p-nitrophenolate at medium pH. As a result, the unstable product formed is measured chronoamperometrically at an application potential of + 0.95 V. The biosensor response depends linearly on p-nitrophenyl phosphate concentration between 0.05 – 0.6 mM with a response time of 40 seconds. Detection limit of the biosensor is 0.033 mM.