the cavity q which remains in the 10 6 range the monolayer formation is further confirmed by estimating the surface density of br monomers u03c3 br in the adsorbed layer which can be extracted from the resonant shift where u03b4 u03bb u03bb is the fractional resonant wavelength shift at saturation r is the microsphere radius u03b1 br is the molecular polarizability in excess to that of the displaced water and n s and n m are the refractive indices of the sphere 1 47 and the pbs solution 1 33 respectively see s arnold m khoshsima i teraoka s holler f vollmer opt lett 28 272 2003 the total excess polarizability of one br monomer for a tm mode a br is the sum of the protein u03b1 p the lipids u03b1 l and the retinal u03b1 r contributions u03b1 br u03b1 p u03b1 l u03b1 r 1 05 u00d7 10 4 au 5 73 u00d7 10 3 au 160 au u2248 1 64 u00d7 10 4 au u02dc 2 4 u00d7 10 3 u00e5 3 see z salamon g tollin biophys j 80 1557 2001 h m lee j kim c j kim k s kim j chem phys 116 6549 2002 and m.