Electrochemical biosensors have been made to detect the metabolic markers, pH, O2 and glucose, and nitric oxide (NO), the signalling molecule involved in angiogenesis. A novel three-dimensional (3-D) graphene/ionic liquid (IL) nanocomposite demonstrates highly sensitive detection of NO in phosphate buffered saline (PBS). An arginine-glycine-aspartic acid (RGD) peptide-functionalised biomimetic graphene film has been used as both a cell culture and sensing matrix to detect NO released by human umbilical vein endothelial cells (HUVECs) in real-time under acetylcholine (Ach) stimulation. The amount of NO released is dose-dependent and inhibited by NG-nitro-L-arginine methyl ester (L-NAME). A poly(ethyleneimine) (PEI)-coated anodically electrodeposited iridium oxide film (AEIROF) exhibiting super-Nernstian response to pH functions as miniature pH sensor for detecting acute changes in extracellular pH due to the interaction of porcine aortic ECs (PAECs) with fibronectin and thrombin. Thrombin causes dissolution of fibronectin, extracellular acidification of PAECs and a change in cell morphology from stretched to round cells. O2 and glucose biosensors based on a novel electropolymerised redox polymer are developed and prepared by one-step electropolymerisation of methylene blue (MB+) and pyrrole for the O2 biosensor, with the addition of glucose oxidase (GOD) for the glucose biosensor. The O2 biosensor demonstrates superior sensitivity towards dissolved O2 at atmospheric (atm) O2 concentrations and below and is insensitive to pH. The glucose biosensor exhibits direct electron transfer (DET) and is insensitive to pH from pH 6 to 8 in N2-purged PBS and from pH 4 to 8 in atm O2 PBS.