Oxidized carbon powder for enzyme immobilization on screen printed biosensors

Carbon powders were subjected to an oxidation treatment with hydrogen peroxide in order to create surface oxygen groups (mainly carboxylic and phenolic groups) on printed electrodes for further covalent immobilisation of biomolecules. The oxidizing treatment modifies the surface chemistry of the carbon by creating surface-oxygen complexes that make it more acidic. Furthermore, the pH value of the carbon slurry was found to be changed from 6.5 to 4.4 after oxidizing step which introduced acidic groups on the surface. The porous structure of the carbonaceous support was not affected by oxidation as resulted by scanning electron microscopy before and after the treatment. Printed electrode's were fabricated by depositing several ink layers on a PVC substrate. Different oxidized carbon powders (including rhodium, (10%), including dextran (25%) and lysine coupled graphite) were printed to obtain the working electrodes. Glucose oxidase was used as a model enzyme to test several immobilisation methods on the treated screen printed surfaces. Binding of the enzyme were performed on (1) EDC activated, (2) CDI activated surfaces and also, (3) Lysine coupled surfaces by using EDC activation, respectively. Moreover, storage stabilities at 4oC were investigated.