Key Findings
The proposed SPR sensor achieves a sensitivity of 269.397 degrees per RIU and a figure of merit (FOM) of 180.6 per RIU. When compared to a conventional BK7/Ag/analyte structure, which has a sensitivity of 185.620 degrees per RIU, the multilayer design represents an improvement of approximately 45.1 percent. It also outperformed versions utilizing only AlSb, TeO2, or CdGa2S4, which showed sensitivities between 200 and 203.68 degrees per RIU. Additionally, the sensor posted a quality factor of 181.04 per RIU and a combined sensitivity factor of 179.679 per RIU.
Technical Details
The sensor employs a six-layer architecture modeled via the transfer matrix method at a wavelength of 633 nanometers. The stack consists of:
- A BK7 prism (refractive index 1.515).
- A 55-nanometer silver (Ag) film (complex refractive index 0.056266 + 4.27761i), selected as the optimum thickness to minimize reflectance to 0.002464.
- A 1-nanometer tellurium dioxide (TeO2) layer (refractive index 2.2596) to confine the electromagnetic field and prevent silver oxidation.
- A 1-nanometer cadmium gallium sulfide (CdGa2S4) layer (refractive index 2.4482) to enhance plasmonic coupling.
- A 0.53-nanometer aluminium antimonide (AlSb) layer (complex refractive index 3.8638 + 0.0035982i) to increase the effective sensing area for biomolecular adsorption.
Background & Context
Traditional bacteria detection methods, such as PCR, microbial culture, and enzyme-linked immunosorbent assays, often require complex instrumentation and lengthy preparation. SPR sensing offers a label-free, real-time alternative by measuring shifts in the resonance angle caused by changes in the refractive index when bacteria are present at the metal-dielectric interface.
Significance & Outlook
By engineering the material stack, the researchers have increased the sensitivity and stability of the evanescent electromagnetic field. This theoretical design addresses the inherent weakness of silver-based sensors—namely air degradation—while maintaining the resonance sharpness necessary for high detection accuracy in rapid, on-site testing environments.
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