An apparatus for in-vivo measuring H2O2 oxidation within a living tissue. The apparatus includes an electrochemical probe and an electrochemical stimulator-analyzer. The electrochemical probe includes a sensing part and a handle. The sensing part includes a working electrode, a counter electrode, and a reference electrode. The working electrode includes a first biocompatible conductive needle coated with a layer of vertically aligned multi-walled carbon nanotubes. The counter electrode includes a second biocompatible conductive needle. The reference electrode includes a third biocompatible conductive needle. The electrochemical stimulator-analyzer is configured to generate a set of electrical currents in a portion of the living tissue.