Biosensors for enzymes can be tailored in two ways: enzyme anchored to the electrode and the substrate is the analyte or substrate is anchored to the electrode and the enzyme is the analyte. Previous work showed that both binding of substrate and catalytic reaction of a can be monitored by the surface immobilized enzyme.[i] Electrochemical biosensors that are targeting enzymes as analytes are based on substrate that is linked to the electrode surface. The sensing mechanism relies on the response induced by their catalytic activity. We study key enzymatic reactions on peptides and glycans by electrochemistry and surface analyses. Using kinases as model system, we were able to show electrochemical biosensing can be used for monitoring biocatalytic activity on peptides.[ii] The same methodology was also utilized to monitor kinase binding to both the catalytic site[iii] and the allosteric one.[iv] Sialylated glycans are of major importance and the related enzymatic processes can be used as biomarkers for cancer, viral infection and many more. A label free approach was recently reported by us, for sensing neuraminidase and sialyltransferase catalytic activities.[v]^,[vi] Here we’ll describe our ability to distinguish between binding and catalysis and demonstrate the advantages of this methodology for glycan substrate discrimination and enzyme selectivity. These tools are essential for evaluating pathogenic and pathological states and enable screening for inhibitors potency.