Attachment of proteins to interfaces for use in nonlinear optical detection

A method comprising:

• a) forming a supported lipid bilayer on a surface of a substrate, wherein the supported lipid bilayer comprises an anchor molecule that comprises or bears a first affinity tag that is present in the lipid bilayer at a concentration greater than or equal to 10 mole percent;
• b) contacting the supported lipid bilayer with a protein at a concentration of less than 2 μM, wherein the protein comprises a second harmonic-active label, a second affinity tag capable of binding to the first affinity tag, and optionally a linker molecule positioned between the protein and the second affinity tag, thereby tethering the protein to the supported lipid bilayer in an oriented fashion while using less than 500 ng of the protein, wherein the tethered protein is tethered at a surface density of about 1×1012 molecules per cm2;
• and
• c) detecting an optical signal arising from the tethered protein before and after contacting the tethered protein with a ligand, wherein the optical signal is second harmonic light, and wherein a change in the optical signal detected before and after contacting the tethered protein with the ligand indicates that the protein has undergone a conformational change.