Wavelength-Interrogated Surface Plasmon Resonance Sensor Based on Au-Ag Alloy Film

An Au-Ag alloy film surface plasmon resonance (SPR) sensor was studied experimentally and theoretically. SPR chips were prepared by sputtering a glass surface with a 50-nm-thick Au-Ag alloy film, and experiments were carried out with the wavelength-interrogated SPR sensor using the Kretschmann configuration. Aqueous sodium chloride and bovine serum albumin solutions were used to study the refractive index and adsorption sensitivities of the sensor. The results were compared with those obtained using Au film and Ag film SPR sensors. The refractive index sensitivity of the Au-Ag alloy film SPR sensor is higher than that of the Au film SPR sensor, but lower than that of the Ag film SPR sensor. The adsorption sensitivity of the Au-Ag alloy film SPR sensor is similar to that of the Ag film SPR, and three times of the Au film SPR sensor. Theoretical studies showed that that the sensitivity of the Au-Ag alloy film SPR is close to that of the Ag film SPR sensor, and 2.31 times of the Au film SPR sensor. The full width at half maximum of the Au-Ag film sensor is only 0.36 times of the Au or Ag film SPR sensors. The Au-Ag alloy film and Au film SPR sensors are chemically stable, but the Ag film SPR sensor is easily oxidized, so it is not often used. These results show that an Au-Ag alloy film can improve the sensitivity of the sensor, while retaining the accuracy. Au-Ag films could therefore be used as high-sensitivity, low cost, and stable SPR-sensitive materials.