Wavelength-Dependent Angular Sensitivity Signatures in SPR Sensors: Is the 633 nm Wavelength Still Optimal for the Latest Designs?

Abstract

Research focused on improving the sensitivity of surface plasmon resonance (SPR) analytical technology has led to the investigation of different electric field enhancement elements for incorporation with classic sensor structures. Over the past ten years, considerable attention has been given to ceramic, metal oxide, and 2-D materials that not only improve the magnitude of the field but are also used as affinity layers for improved adsorption of molecules. However, focusing on the improvements these materials deliver can lead designers to explore only some of the multiple dependencies associated with sensitivity. When using the angular interrogation mode (AIM), the impacts of working with different wavelengths are generally disregarded, as a fixed value of $\lambda =633$ nm is commonly adopted. Choosing 633 nm is often justified for achieving near-zero reflectivity and good sensitivity. However, newer SPR designs lack the determination of optimal wavelength-dependent sensitivity points. This article numerically investigates sensitivity as a function of wavelength for SPR sensors. We systematically study the effects of operating outside $\lambda =633$ nm and show that the signature produced by bare metal sensors does not always resemble the signatures produced by field-enhanced designs. Examinations are based on Graphene and BaTiO3. Furthermore, we demonstrate how imposing thresholds on optimization targets can be leveraged to sustain high-sensitivity results, and we elaborate on the pertinent trade-offs. Our approach shows further performance improvements in designs for which highly efficient benchmarks have already been demonstrated.