In the reaction, catalase converts hydrogen peroxide to hydrogen
dioxide and carbon dioxide in the presence of oxygen. There
is an intermediate surface between the bioactive layer and the teflon
membrane of the DO probe and during the enzymatic reaction
dissolved oxygen concentration in the intermediate surface decreased
relative to the substrate concentration added into the reaction
medium. The measurements with the developed biosensor
were carried out at steady-state conditions. DDO is the differences
of the dissolved oxygen concentration when the substrate is not in
the reaction medium and after addition of substrate into the reaction
medium to obtain a new steady-state DO concentration. It is
well known that calcium is a cofactor for catalase and it plays an
activator role for the catalase so when the calcium was injected
into the reaction medium it increased the activity of the enzyme
and in this case the dissolved oxygen concentration changed relative
to the calcium concentration added into the reaction medium.