Electrochemical studies on horseradish peroxidase covalently coupled with redox dyes

The present study aims at investigating the use of redox dyes as non-diffusional electron mediators in hydrogen peroxide biosensors using horseradish peroxidase (HRP). We observe that the two redox dyes Safranine O and Neutral Red covalently bound to HRP, efficiently mediate electron transfer from the active site of the enzyme to the electrode surface. Dyes bound to the enzyme using a spacer arm diaminohexane further enhance the electron transfer. The enzyme electrodes show a linear response to the concentration of H2O2 up to 500 μM concentration and with a detection limit of around 50 μM. The dyes can be used as coupled mediators to develop a successful electro-optical biosensor.