Amino acid residues on the outside of proteins are discussed as potential sites for chemical coupling of proteins to sensor surfaces. This strategy is compared with the use of peptide tags, added to proteins, with an affinity for a particular surface material or chemical structure. Using molecular biology to extend the amino acid protein sequence, in order to include an immobilisation component, is also shown to be suitable for fusion to binding proteins, that can act as the immobilisation partner, so that a compendium of immobilisation strategies is seen to emerge from this common approach of protein engineering.