Integrated nanoparticle-fluorophore systems are an emerging class of hybrid materials with potential for a great variety of applications, including super-resolution bioimaging, single molecule tracking, and the fabrication of new optoelectronic devices. Within these systems, Metal-Enhanced Fluorescence (MEF) is a phenomenon that arises through the unique near-field interactions between organic fluorophores and metallic nanoparticles. These interactions can enhance the brightness of the fluorophores by operating under two mechanistic pathways: increased rate of fluorophore excitation, and increased rate of fluorophore emission. It is critical, however, to garner a comprehensive understanding of the balance between the two MEF mechanisms in order to optimize its use for customized applications.<br/>In this work, silver nanoplates (AgNP) were synergistically integrated with a photoactivatable system consisting of a fluorogenic boron dipyrromethene (BODIPY), which could be selectively activated by UVA or UVC light in the presence of a photoacid generator (PAG). Light irradiation of the PAGs promotes the release of <i>p</i>-toluenesulfonic acid, which encourages the formation of an analogous, fluorescent BODIPY species. The activation is performed in solution and in thin polymer films. The presence of AgNP enhances the output of steady-state emission via MEF. Furthermore, ground-breaking work entailing the use of single molecule fluorescence microscopy was ingeniously executed to distinguish the two MEF mechanisms between the quenched and non-quenched BODIPY fluorochromes and AgNP. The increased excitation mechanism was prominent amongst both dyes and occurred to approximately the same extent in each BODIPY. Interestingly, the dye exhibiting a higher quantum yield expressed the increased emission mechanism of MEF by approximately twice as much in comparison to its fluorogenic counterpart. This work illustrates how single molecule techniques can be used to understand nanoparticle-fluorophore interactions and represents a methodology towards the elucidation of MEF mechanisms in nano-molecular systems.

How silver nanostructures enhance the fluorescence of a model hybrid nanoparticle-fluorophore system

ACS Spring Meeting 2021

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