Controlled Amplification of Photochemical Reactions 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 prepares and studies nanoparticles which act as amplifiers for photochemical (light-induced) reactions. As one example, chemotherapy drugs can be attached to light-reactive (photoreactive) molecules which release their drug only at the site of the tumor instead of throughout the body. Photoreactive molecules must react efficiently so that the dose of light is minimized, but not so efficiently that they react when exposed to normal room light. In order to optimize this process, Professor Harbron's research group synthesizes photoreactive nanoparticles by combining fluorescent polymers with photoreactive molecules. In these new nanoparticles, the polymer gathers light energy and delivers it to the attached photoreactive molecules. The current project develops applications in the photorelease of small molecules and in the production and detection of reactive oxygen species. Applications are envisioned in photodynamic therapy and sensor development. This project also serves as training for undergraduate and master's level research students, who learn organic, physical, and analytical chemistry techniques while receiving academic and career planning advise. Outside of the lab, Professor Harbron continues to work as a mentor with the Chemistry Women Mentorship Network and with the William and Mary Scholars Undergraduate Research Program, which seeks to develop research skills in students from underrepresented groups. Professor Harbron founded and chairs a new Diversity, Outreach, and Publicity committee in her department that is working to broaden participation in science and promote scientific dialogue on campus. Light is an appealing stimulus for molecular transformations because it can be delivered to a sample with high spatiotemporal resolution and control of exposure energy and intensity. In conjunction with light stimulation, photoresponsive molecules are being used in an increasing number of exciting applications, from imaging to catalysis. The ideal photoresponsive substance reacts efficiently with light and yet not so efficiently that it responds to ambient light in an uncontrolled fashion. Achieving this balance in reactivity is one of the major challenges in the field. Other challenges include water solubility and tuning light responsiveness into the visible to near-infrared region. To address these challenges, the current project pairs photoresponsive dyes with conjugated polymer nanoparticles (CPNs). These are exceptionally bright fluorophores that absorb and emit in the visible to near-infrared. They can be suspended in water. When doped with dyes, CPNs act as powerful light harvesters, funneling the energy of hundreds of chromophores to a single dye molecule via fluorescence resonance energy transfer (FRET). Pairing the CPNs' efficient excitation and energy transfer processes with a dye's less efficient photochemical reaction amplifies the reactivity of the dye in a controlled fashion. This project optimizes the "controlled amplification" approach and extends it to address photoreactivity challenges. The specific aims are: to develop CPNs doped with photoremovable protecting groups to enhance and control photorelease, and to use CPNs doped with photochromic dyes to quantify the CPN properties that maximize photoreactivity. The research also seeks to develop CPNs that both generate superoxide and report on its relative concentration via ratiometric fluorescence.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.