Rationalizing the Plasmonic Contributions to the Enhancement of Singlet Oxygen Production

The strong interaction between plasmonic metal nanoparticles and photosensitizers can significantly amplify their singlet oxygen (O-1(2)) production. However, improving the performance of these hybrid plasmonic nanostructures is hampered by the lack of understanding of how their plasmonic properties impact the enhancement of O-1(2) production. Here, we report that a Au core-based nanoparticle can outperform a Ag one. This result is striking as Ag is referred to as a better plasmonic metal than Au and forms the basis of our investigation. We use a novel approach based on a mini meta-analysis to elucidate and quantify the near- and far-field contributions to the plasmon-enhanced O-1(2) production by using a highly tunable model hybrid photosensitizer-metal core@shell nanoparticle. The correlation between time-resolved O-1(2) measurements and the experimental and simulated plasmonic optical properties was achieved by comparing the results of four new nanoparticles of different core composition (Au and Ag) and sizes (from 20 to 120 nm in diameter) with the data published in previous studies. Altogether, experiments and modeling in conjunction with statistical analysis revealed that, while the near and far fields work in synergy, it is the near field that dominates the photosensitizer-metal interactions and ultimately dictates the enhancement of O-1(2) production. This work improves our understanding of factors important in determining O-1(2) enhancement and paves the way to a quantitative description of plasmon-photosensitizer interactions for the rational design of complex nanostructures for boosting O-1(2) production.