Abstract
Intrinsic, non-traditional fluorescence of polyamidoamine (PAMAM) dendrimers that do not possess classical fluorophores has been attracting considerable interest for the last decade. Many hypotheses regarding the source of the fluorescence have appeared, but some of them are still disputable. In order to shed new light on the nature of the phenomenon, we applied quenchers that are normally used to study intrinsic fluorescence of proteins (i.e., KI, CsCl, and acrylamide). KI and acrylamide efficiently quenched steady state fluorescence of PAMAM G2, PAMAM G3, and PAMAM G4 dendrimers. Stern-Volmer plots exhibited a downward curvature that has been elucidated by heterogenous emission. We assume that there are two distinct fluorescent moieties in the dendrimer structure that are characterized by different accessibility to the quenchers.
Highlights
Polyamidoamine (PAMAM) dendrimers belong to dendritic polymers that have been the most intensively studied
The fluorophore has remained a subject of a debate, because PAMAM dendrimers do not possess conventional chromophores
Polyamidoamine (PAMAM) dendrimers generations 2, 3, and 4 (G2, G3, and G4), acrylamide, cesium chloride, and potassium iodide were obtained from Sigma-Aldrich
Summary
Polyamidoamine (PAMAM) dendrimers belong to dendritic polymers that have been the most intensively studied. These regular, monodisperse, hyperbranched macromolecules—possessing a core molecule, layers of branched monomers, and plenty of terminal groups—attract interest due to their many potential applications, especially in a biomedical field [1,2]. Researchers frequently used different fluorescent probes to investigate properties of dendrimers They observed a weak fluorescent background in the blue region that was firstly believed to be due to contamination, but when the observations were continuously repeated, the effect was attributed to PAMAM dendrimers, and believed to be their intrinsic fluorescence [3,4,5]. In 2001, Larson and Tucker published the first article fully devoted to the intrinsic fluorescence of carboxylate-terminated PAMAM dendrimers, where they attributed the fluorescence to an n→π*
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