Oxidization and aggregation of first generation poly(amidoamine) with an enhanced fluorescent performance

Organic amines are apt to be oxidized in natural environment. Therefore, preparation of fluorescent materials derived from organic amines should think of the role of oxidized amines. However, this is neglected according to some reports. Herein, first generation poly(amidoamine) (PAMAM 1.0G) dendrimers with inherent weak photoluminescence was oxidized by ambient oxygen under heating of 180 °C for 60 min which brought an obvious enhancement of fluorescent quantum yield (QY). The oxidation was proved by both infrared and ¹H nuclear magnetic resonance. Image of transmission electron microscope (TEM) also revealed the aggregation of PAMAM 1.0G after they were suffered from the lasting heating. The enhancement of QY was also observed when the mixture of aqueous solution of PAMAM 1.0G and citric acid were disposed under the same conditions. And the QY reached as high as 64.40%, which is much higher than that of the fluorescent materials derived from sole citric acid. TEM image also exhibited the aggregation of the product. The carboxyl of the aggregated particle could be activated by N-hydroxysuccinimide and could be bonded with bovine serum albumin realizing the fluorescent labeling of BSA finally, which was demonstrated by the image of gel electrophoresis.