Sensors suitable for the sensing/detection of biological or chemical agents may be fabricated by immobilizing biological and/or chemical recognition components (selectors or probes) on a substrate by the polymerization of a suitable monomer in the presence of the selectors or probes, for example, by Polysiloxane Monolayer Immobilization (PMI). PMI may involve the polymerization of polysiloxane onto a substrate, onto which selector molecules are adsorbed or otherwise immobilized. The resulting immobilized selector molecule may then be used to interact with specific molecules (targets) within a mixture of molecules, thereby enabling those specific molecules to be detected and/or quantified.