Isolation and Characterization of Precise Dye/Dendrimer Ratios

Abstract

Fluorescent dyes are commonly conjugated to nanomaterials for imaging applications using stochastic synthesis conditions that result in a Poisson distribution of dye/particle ratios and therefore a broad range of photophysical and biodistribution properties. We report the isolation and characterization of generation 5 poly(amidoamine) (G5 PAMAM) dendrimer samples containing 1, 2, 3, and 4 fluorescein (FC) or 6‐carboxytetramethylrhodamine succinimidyl ester (TAMRA) dyes per polymer particle. For the fluorescein case, this was achieved by stochastically functionalizing dendrimer with a cyclooctyne “click” ligand, separation into sample containing precisely defined “click” ligand/particle ratios using reverse‐phase high performance liquid chromatography (RP‐HPLC), followed by reaction with excess azide‐functionalized fluorescein dye. For the TAMRA samples, stochastically functionalized dendrimer was directly separated into precise dye/particle ratios using RP‐HPLC. These materials were characterized using 1 H and 19 F NMR spectroscopy, RP‐HPLC, UV/Vis and fluorescence spectroscopy, lifetime measurements, and MALDI. High definition : Two approaches for the formation of generation 5 PAMAM samples containing precise dye/dendrimer ratios are presented. The first approach, using direct separation based on dye hydrophobicity, generated a set of TAMRA‐containing dendrimers, and the second, using click chemistry, generated a set of fluorescein‐containing dendrimer (see figure).