Immobilization of the Glucose-Galactose Receptor Protein onto a Au Electrode Through a Genetically Engineered Cysteine Residue

Studies by electrochemical impedance spectroscopy demonstrate that the wild-type glucose-galactose receptor (GGR) protein does not interact significantly with a Au surface, even through nonspecific interactions. Only the GGR A1C mutant, where alanine is replaced by a cysteine residue at the N-terminus, can form a protein film on Au suitable for creating an impedance biosensor. Impedance measurements of glucose binding at equilibrium allow estimation of the dissociation constant as approximately 6.6 , about 32 times higher than that for the native protein in solution. This change likely arises from surface immobilization rather than from cysteine introduction.