Refractive Index Sensor for Chemical Compound Detection Using the SPR Technique and Optimized MIM Nanostructures

In recent years, chemical and biological sensing using plasmonic nanostructures has gained significant attention due to their ability to detect a wide range of small chemical molecules, from biomarkers to narcotics. The primary appeal of the surface plasmon resonance (SPR) technique lies in the induction of a polariton at the metal–insulator interface under coupled conditions, which manifests as a distinct intensity minimum in reflectance spectra. In this study, a Cu/Ta₂O₅/Cu MIM-based nanostructure is proposed as a means to produce well-defined (narrow and deep) plasmonic responses that experience pronounced angular shifts when the surrounding dielectric environment changes. In other words, this enables the development of a precise thin-film-based chemical compound detection system. The approach relies on amplifying the near-field interaction between adjacent metal films by incorporating a high-optical-density dielectric layer only a few nanometers thick. Finite-element numerical simulations were used to guide the geometric optimization of the nanostructures, yielding optimal MIM dimensions of 20/5/20 nm, and the resulting systems were deposited at room temperature via non-reactive RF magnetron sputtering using an Intercovamex S16 system. Experimental validation was performed using angular interrogation in the Kretschmann configuration with a 633 nm light source.