Researchers at Universidad Técnica Particular de Loja, Escuela Superior Politécnica de Chimborazo (ESPOCH), Università della Calabria, and Universidad Ecotec have computationally designed and optimized a surface plasmon resonance (SPR) sensor for detecting trace mercury, lead, and zinc ions in water, using a graphene oxide sensing layer atop an aluminum/aluminum oxide plasmonic stack on a borosilicate glass prism.
Schematic representation of the borosilicate-supported (B-sil)/Al/Al2O3/nanomaterial SPR sensor. Image from: Electron
The team compared four carbon nanomaterials as candidate sensing layers: graphene oxide, reduced graphene oxide, pristine graphene, and semiconducting single-walled carbon nanotubes, and evaluated each for angular sensitivity, resonance linewidth, and detection limit using transfer-matrix modeling. While single-walled carbon nanotubes and reduced graphene oxide produced larger angular shifts, both introduced severe resonance broadening. Graphene oxide offered the most balanced response: a measurable resonance shift combined with a comparatively narrow, well-defined resonance dip.
In the optimized configuration - a 60 nm aluminum film and 32 nm aluminum oxide layer beneath the graphene oxide coating - the simulated sensor reached angular sensitivities of up to 338°/RIU and limits of detection on the order of 10⁻⁵ refractive-index units (RIU) across individual mercury, lead, and zinc ion conditions, as well as binary mixtures of mercury with lead or zinc. Aluminum was chosen over the more conventional gold plasmonic layer as a lower-cost alternative, with the aluminum oxide layer serving to passivate the metal against oxidation while also tuning the optical response.
The work remains at the simulation stage and the sensor has not yet been fabricated or tested against real water samples, and the authors caution that the modeled limit of detection is an optical metric expressed in refractive-index units rather than a validated concentration threshold. They also note that real-world interference from other dissolved ions, pH, temperature, and organic matter was outside the scope of the current model. Next steps identified by the team include fabrication-tolerance analysis, selective surface functionalization to improve ion specificity, and experimental validation with real water samples.
