(a) Unit cell of the CMH-HMM simulated geometry. (b) Calculated TM-polarization reflectance spectra of an Au helix array on the HMM, with water as the surrounding medium, and angle of incidence θ_i = 50^∘. The spectrum for pure water is shown in black, while red and blue curves correspond to two different mole fractions of 1,2,3-propantriol in distilled water. (c) Sketches of the simulated geometry with different percentages of the helix surfaces covered by bound analytes, and the corresponding resonance wavelength shift for the BPP modes as a function of the surface coverage. (d) Sketch of the geometry and resonance wavelength shift for mode A, B and C with surface coverage of 20%, but with all analytes bound within a narrow disk at different distances D away from the HMM surface. D is normalized relative to the helix height h.