Gold-aluminum-based surface plasmon resonance sensor with a high quality factor and figure of merit for the detection of hemoglobin.

A gold (Au) and aluminum (Al)-based surface plasmon resonance (SPR) sensor, with a high-quality factor and figure of merit, for the detection of hemoglobin concentration in human blood is proposed. The sensing performance of a bimetallic Au grating over an Al film-based sensor depends on the thickness of the Al film. The sensor's performance is closely analyzed in terms of well-defined performance parameters: sensitivity, FWHM, and depth of SPR dips in order to optimize the thickness of Al film. With optimized thickness, we could achieve quality factor and figure of merit values of 286.2  RIU-1 and 0.97  deg-1, respectively. Al is chemically unstable, and, to address the oxidation problem, we analyzed the sensor with an ultrathin protective Au layer between the Au grating and Al film. We show that the introduction of an ultrathin Au layer gives stability to the sensor without much affecting the performance of the sensor. The obtained values of quality factor and figure of merit of the proposed sensor are 245.2  RIU-1 and 0.86  deg-1, respectively. We also discuss the potential of hemoglobin detection of the proposed sensor in the near-infrared region. Reported sensitivity of the sensor is 0.62°/dgL-1.