Surface plasmon resonance (SPR) bio-sensors comprise an attenuated total reflection (ATR) system known as the Kretschmann geometry. The sensing surface comprises flat Au thin films deposited on a high index flat glass substrate (LAL-10, n = 1.72). This paper describes the effects of the 3D nano-textured Au thin films on the sensing properties are discussed. The nano-textured Au thin films were fabricated by the deposition of the uniform Au thin films on the (0001) vicinal sapphire substrates. The vicinal substrates comprise periodic atomic step lines and terraces. The step height is chiefly half lattice spacing of the sapphire (0.22 nm). The terrace width is governed by the off-cut angles. The stepped surface structure were reconstructed by the annealing at 900 to 1400oC (1 to 3 h) in air. The annealed stepped surfaces comprised stepped heights of 5 to 12 nm with the terrace width of 2.7 to 140 nm for the off-cut angles at 5 degrees. The laser diodes (635 nm) were used for the optical light source. It is found that the detection limit of the SPR bio-sensors using the flat Au thin films on the (0001) sapphire substrates is 1.6 ng/ml for the tumor marker (AFP, α-fetoprotein) by antibody/antigen reaction, which is almost the same to the performance of the flat Au thin films on the conventional high index glass substrates as expected by the simulation Winspal 2. The SPR sensitivities using the nano-textured Au thin films with the step height of 12 nm and the terrace width of 140 nm were one order of magnitude smaller than those of Au thin films on the flat (0001) sapphire, 20 ng/ml, probably due to the scattering of the surface plasmon and/or evanescent wave. However, well-designed nano-textured Au thin films will enhance the SPR sensitivity. The sapphire substrates could integrate optical devices and will provide novel optical-bio MEMS.
