Enhanced Biosensing Activity of Bimetallic Surface Plasmon Resonance Sensor

Surface plasmon resonance (SPR) sensors present a challenge when high sensitivity and small FWHM (full width at half maximum) are required to be achieved simultaneously. FWHM is defined by the difference between the two extreme values of the independent variable at which the value of the dependent variable is equal to half of its maximum. A smaller value of FWHM indicates better accuracy of SPR measurements. Theoretically, many authors have claimed the possibility of simultaneously achieving high sensitivity and small FWHM, which in most of the cases has been limited by experimental validation. In this report, an experimental study on the improved surface plasmon resonance (SPR) characteristics of gold over silver bimetallic sensor chips of different film thicknesses is presented. A comparative study of antigen-antibody interaction of the bimetallic chip using a custom-made, low-cost, and portable SPR device based on an angular interrogation scheme of Kretschmann configuration is performed. Pulsed direct current (DC) magnetron-sputtered bimetallic films of gold over silver were used in the construction of the SPR chip. The FWHM and sensitivity of the bimetallic sensors were firstly characterized using standard solutions of known refractive index which were later immobilized with monoclonal anti-immunoglobulin G (IgG) in the construction of the SPR biochip. Spectroscopic measurements such as ultraviolet-visible light spectroscopy (UV-Vis) and Fourier-transform infrared spectroscopy (FTIR) were used for the confirmation of the immobilization of the antibody. The performance of the bimetallic SPR biochip was investigated by exposing the sensor to various concentrations of the target protein. The results indicated that the bimetallic sensors of silver/gold had a 3.5-fold reduced FWHM compared to pure gold-based sensors, indicating a higher detection accuracy. In addition, they exhibited a significant shift in resonance angle as high as 8.5 +/- 0.2 due to antigen-antibody interaction, which was similar to 1.42-fold higher than observed for pure silver-based sensors.