Harnessing Amplified Fluorescence Resonance Energy Transfer in Conjugated Polymer Nanoparticles

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In this project funded by the Chemical Structure, Dynamic & Mechanism B Program of the Chemistry Division, Professor Elizabeth J. Harbron of the Department of Chemistry at The College of William and Mary will develop highly fluorescent organic nanoparticles for use in applications that require a change in fluorescence in response to a specific stimulus. The nanoparticles are derived from fluorescent conjugated polymers and are doped with stimulus-responsive dyes specific to each application. The interaction between the polymer and the dyes yields an amplified response to the stimulus, which means that it can be detected with lower input light levels and/or with much greater sensitivity than with the dyes alone. The targeted applications include nanoparticles that switch their fluorescence on and off for super-resolution microscopy and nanoparticles that change their fluorescence color and/or intensity to control or detect pH and mercury ions in water. These projects are ideally suited to the training and education of undergraduate and masters students because they involve visually appealing work with highly colored, fluorescent materials as well as the opportunity to work at the interface of physical, organic, and analytical chemistry. This group will continue its efforts to increase representation of underrepresented groups in chemistry through mentoring projects targeted toward women as well as advising and mentoring targeted to other groups traditionally underrepresented in chemistry.Conjugated polymer nanoparticles (CPNs or Pdots) hold exceptional promise as fluorophores for sensing and imaging applications due to their intense fluorescence brightness, high photostability, and colloidal stability in water. Their unique strength is the ability to act as light harvesting units, transferring the excitation energy of numerous chromophores to a small number of low-energy sites by fluorescence resonance energy transfer (FRET). CPNs functionalized with FRET-acceptor dyes exhibit amplified dye emission intensities due to this light harvesting effect. In this work, new CPNs functionalized with stimulus-responsive dyes will be developed. The stimulus-responsive dyes have two molecular forms that interconvert in response to a specific stimulus, but only one form can act as a FRET acceptor for the CPNs. Thus, the stimulus induces modulation of fluorescence intensity or color by activating/deactivating FRET. The sensitivity of the stimulus response is substantially increased in the CPNs as compared to the dye alone due to amplified FRET. Optimization of the energy transfer processes in dye-functionalized CPNs will be explored in the following systems: 1) photoactivated CPNs that undergo off-on photoswitching in response to visible light, 2) CPNs that can simultaneously photomodulate pH and provide fluorescence readout, and 3) CPNs that provide ratiometric detection of pH and of mercury ions in completely aqueous environments.