This invention relates to a method for the fabrication of photonic biosensor arrays and applications of arrays produced by the method in the biomedical field. A method for the fabrication of a biosensor array for plasmon resonance-based sensing of a plurality of different biological targets simultaneously, the method comprising: (i) providing a transparent substrate; ii) providing seed metallic nanoparticles in the form of a colloid; (iii) depositing said colloid as discrete metallic islands on the transparent substrate, each of said metallic islands comprising a plurality of metallic nanoparticles; (iv) washing the substrate in order to remove unadhered material; (v) developing the substrate in a growth solution, which solution comprises a salt of the same metal which is present in the form of discrete metallic islands on the substrate, a reducing agent, a capping agent and optionally a surfactant; (vi) washing the developed substrate; and (vii) functionalising each of said metallic islands with a different functionalising molecule using a common chemical process to attach said different functionalising molecules to said metallic islands.