Abstract: Methods and devices to continuously measure electrochemical activity of one or more biochemical or molecular markers (FIG. 9). A substrate having electronics for measuring electrochemical activity and a plurality of electrodes such that the electrodes are in contact with the subcutaneous layer are attached to subject's skin or intravenously. The devices measure a biochemical process associated with one or more biochemical or molecular markers in vivo by detecting an electrochemical signal in subcutaneous layer (or intravenously) using the plurality of electrodes.