Pyrene-conjugated-hyaluronan (Py-HA) stabilises reduced graphene oxide (Py-HA-RGO) in water, with the composite material providing a substrate for building up nanostructures of Au, Ag, Pd and Pt, of varying sizes, shape, and surface properties. Formation of the metal is effective using in situ UV irradiation (Au and Ag) or hydrogen gas at ambient pressure (Pd and Pt). The Py-HA is multifunctional in stabilising Py-HA-RGO in water and controlling the nature of the resulting metal nanostructures. The hybrid Au nanomaterials have been tested as a sensor material for hydrogen peroxide, using electrocatalysis, and the Pd nanomaterials are readily incorporated into hydrogen gas sensors using a drop casting technique, with both systems having nanostructured- dependent detecting responses. This journal is © The Royal Society of Chemistry.