Cross-linkage induced fluorescence: Fabrication of fluorescent organic particles via reaction between polyethyleneimine and dopamine-containing copolymers

Dopamine is the most abundant catecholamine neurotransmitter in the brain and has extensive applications in biomedicine and materials science. Here, novel metal-free fluorescent organic particles (FOPs) with excellent biocompatibility and high photostability, namely DA-PEG-PEI, were successfully synthesized through combination of ring-opening reaction and crosslinking reaction between polyethyleneimine (PEI) and dopaminecontaining copolymers (DA-PEGDGE). Because of the crosslink-enhanced emission (CEE) effect of PEI and a quantity of functional groups such as catechol and amines on the surface of the particles, DA-PEG-PEI FOPs possessed high water dispersibility and superior optical properties, making them highly potential for biological imaging applications. Moreover, owing to the existence of functional components/groups, such as amines, catechol groups, the resultant DA-PEG-PEI FOPs can be potentially applied for loading or carrying different bioactive molecules, such as anticancer agent bortezomib, siRNA and CPG oligodeoxynucleotide through formation of dynamic bonds or electrostatic interaction. Furthermore, this reaction can occur under ambient environment, room temperature, in the present of oxygen and without catalysts. Therefore, we believe that this work could not only provide a simple and elegant route for preparation of FOPs, but also have great potential for construction of multifunctional theranostic platforms.