It is well-known that plasmonic nanostructures can modify the fluorescence emission of nearby molecules. Although single particle measurements of plasmon-modified fluorescence provide rich data sets, acquisition is often time-consuming and requires specialized instrumentation. By contrast, when sufficiently homogeneous samples are available, performing ensemble measurements in bulk solution would appear to be a more convenient way to routinely characterize new nanomaterials. In addition to its convenience, bulk spectroscopy can also be readily compared to theoretical predictions because, unlike in single-particle measurements, many variables which determine the effect of plasmonic modificiation can be replaced by their reliable, ensemble-averaged values. Despite these apparent benfits, however, it has proven difficult to reliably measure plasmonic modification of fluorescence emission in bulk solution. Here, we identify key factors that commonly corrupt plasmon-modified fluorescence spectra and present an experimental framework to overcome them. Central to this framework is the use of dynamic DNA nanotechnology to control the association of a fluorophore with a nanostructure, permitting accurate plasmon-coupled and reference spectral measurements to be performed in the same solution with minimal perturbation. As a demonstration, we apply this framework to reproducibly measure the modification of fluorescence emission—encompassing both the magnitude of enhancement as well as spectral reshaping—of dye molecules associated with gold nanospheres and gold nanosphere dimers. We anticipate that routine and accurate bulk spectroscopic measurements such as these can guide the development of fluorescence-enhancing nanomaterials as well as deepen our fundamental understanding of plasmonic phenomena.

Plasmon-modified fluorescence spectroscopy of nanostructures in bulk solution

ACS Spring 2022

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