Theoretical investigation of plasmonic properties of gold-silver alloys for SPR biosensing applications

• Gold-to-silver ratios influence Surface Plasmon Resonance behaviour • Increasing silver portions in alloy enhances plasmon propagation and sensing depth • A new alloy-based biosensor demonstrates high sensitivity and improved performance • The proposed biosensor is feasible for real-world applications Surface Plasmon Resonance (SPR) arises from the light-induced excitation of free electrons near a metal surface, making it a key mechanism in biosensing applications. While gold and silver are the commonly used metals, gold-silver (Au-Ag) alloys have gained interest in SPR. However, the impact of different gold-to-silver composition ratios on SPR performance remains underexplored, complicating alloy selection for applications such as SPR biosensors. This study theoretically investigates the influence of Au-Ag alloy compositions on the Surface Plasmon Polariton (SPP) wave characteristics and SPR biosensor performance using the Transfer Matrix Method (TMM) and the Kretschmann configuration. Our findings suggest that specific alloy compositions can enhance sensitivity and propagation length, making them promising for high-performance biosensing applications. A proposed biosensor design incorporating an Au-Ag alloy, a CaF 2 glass prism, Black Phosphorus (BP) layers, and water as the sensing medium is discussed. Additionally, we outline the procedures and potential challenges associated with its practical implementation. This work contributes to advancing high-performance biosensing technologies and aligns with the Sustainable Development Goals (SDGs) 3 and 9 of the United Nations (UN).