Development of Fluorescent Temperature-responsive Nanogels

1. Development of Fluorescent Temperature-responsive Nanogels Steven Manning, Lisa Kelly, Lisa George and Eli Zukowski Department of Chemistry and Biochemistry, University of Maryland, Baltimore County Experimental: Results: Abstract:N-isopropylacrylamide(NIPAM) nanogels have shown unique temperature-dependent phase change behavior at a lower critical solution temperature (LCST) of 32°C, ideal for the development of ‘smart’ packaging, optical sensing, and drug delivery vehicles. In this work, we demonstrate the ability to copolymerize strongly absorbing and fluorescent benzo[ghi]perylene “swallow tail” derivatives with NIPAM, producing a dynamic self-reporting polymer system. These “swallow tail” fluorophores exhibit highly solvachromatic emission spectra with maximums ranging from 468nm (hexane) to 613nm (water) resulting from solvent polarity. Free radical polymerization of NIPAM, N,N’-methylenebisacrylamide, and compound 3 in THF yielded nanogels with temperature-dependent fluorescence emission maxima. Below LCST, yellow emission is observed (600nm) which broadens and blue-shifts (505nm) upon heating above LCST due to polymer phase change. • Preserved stimuli-responsive properties: Synthesis of Benzo[ghi]perylene ‘swallow tail’ derivatives and polymer size modulation: Figure 5: Particle size measurements of undoped and dye doped pNIPAMnanogel dispersions in water(.02% w/v) as a function of temperature determined by DLS. Introduction: • Successful fluorescent dye doping of polymers: Figure 6: Fluorescence spectra (337nm excitation) of undoped and dye doped pNIPAMnanogels at 15°C. All dye doped dispersions (.08, .04, and .02)%w/v show >1500% emission increase at 600nm. A 400nm filter was employed to block excitation scatter. • Temperature-responsive emission changes: Figure 2: (top) Synthesized benzo[ghi]perylene derivative fluorophores. (bottom) Copolymerization scheme employed for dye doping of pNIPAMnanogels Figure 7: Fluorescence emission of pNIPAMnanogel dispersions (.04%w/v) above and below LCST. Conclusions: We have developed a novel, fluorescent temperature-responsive nanogel system through copolymerization of crosslinked N-isopropylacrylamide with benzo[ghi]perylene derivatives. Future work includes the modulation of phase change temperature for utilization in drug delivery, medical imaging, and smart packaging applications. Figure 3: Fluorescence of 1 (337nm excitation) in solvents of varying polarity. The dye is highly solvachromatic and emission maximums range from 469nm(hexane) to 613nm (water) Figure 4:The effect of surfactant concentration on nanogel particle sizes as determined by dynamic light scattering. Particle diameters ranged from 70nm to 550nm (lines to guide the eye) while maintaining temperature-responsive properties. Figure 1: The effect of temperature on average pNIPAMnanogel particle diameter taken by dynamic light scattering. At 32°C, particles collapse from 280nm to 140nm