Study of Au-Ag alloy film based infrared surface plasmon resonance sensors

Au-Ag alloy films deposited on the glass substrates are used, for the first time, as a wavelength-interrogated near infrared surface plasmon resonance (SPR) sensor. The values of resonance wavelength (lambda(R)) of the sensor at different angles of incidence are determined by absorptiometry and its refractive-index (RI) sensitivity is investigated using aqueous glucose solutions as the standard RI samples. As the incident angle increases from 7.5 degrees to 9.5 degrees, the SPR absorption peak shifts from lambda(R) = 1215 nm to 767.7 nm, the full width at half magnitude (FWHM) of the peak reduces from 292.8 nm to 131.4 nm, and the RI sensitivity decreases from 35648.3 nm/RIU down to 9363.6 nm/RIU. At the same initial lambda(R), the SPR sensor with the Au-Ag alloy film shows a higher sensitivity than that with the pure Au film (S = 29793.9 nm/RIU at lambda(R) = 1215 nm with a pure Au film). Adsorption of bovine serum album molecules from the aqueous solution of 1 mu mol/L protein results in a redshift of Delta lambda(R) = 12.1 nm with the Au-Ag alloy film and Delta lambda(R) = 9.5 nm with the pure Au film. The experimental data also indicate that the FWHM of the SPR absorption peak with the Au-Ag alloy film is larger than that at the same lambda(R) with the pure Au film, leading to a lower spectral resolution than that of the latter.