Plasmonic-Based Sensing Using an Array of Au-Metal Oxide Thin Films

An optical plasmonic-based sensing array has been developed and tested for the selective and sensitive detection of H-2, CO, and NO2 at a temperature of 500 degrees C in an oxygen-containing background. The three-element sensing array used Au nanoparticles embedded in separate thin films of yttria-stabilized zirconia (YSZ), CeO2, and TiO2. A peak in the absorbance spectrum due to a localized surface plasmon resonance (ISPR) on the Au nanoparticles was monitored for each film during gas exposures and showed a blue shift in the peak positions for the reducing gases, H-2 and CO, and a red shift for the oxidizing gas, NO2. A more in-depth look at the sensing response was performed using the multivariate methods of principal component analysis (PCA) and linear discriminant analysis (LDA) on data from across the entire absorbance spectrum range. Qualitative results from both methods showed good separation between the three analytes for both the full array and the Au-TiO2 sample. Quantification of LDA cluster separation using the Mahalanobis distance showed better cluster separation for the array, but there were some instances with the lowest concentrations where the single Au-TiO2 film had separation better than that of the array. A second method to quantify cluster separation in LDA space was developed using multidimensional volume analysis of the individual cluster volume, overlapped cluster volume, and empty volume between clusters. Compared to the individual sensing elements, the array showed less cluster overlap, smaller cluster volumes, and more space between clusters, all of which were expected for improved separability between the analytes.