Water soluble, red emitting, carbon nanoparticles stimulate 3D cell invasion via clathrin-mediated endocytic uptake

Bright, fluorescent nanoparticles with excitation and emission towards the red end of the spectrum are highly desirable in the field of bioimaging. We present here a new class of organic carbon-based nanoparticles (CNPs) with robust quantum yield and fluorescence towards the red region of the spectrum. Using organic substrates like para-phenylenediamine (PPDA) dispersed in diphenyl ether and reflux conditions, we achieved scalable amounts of CNPs of the average size of 25 nm. These CNPs were readily uptaken by different mammalian cells, and we show that they prefer clathrin-mediated endocytosis for their cellular entry route. Not only can these CNPs be specifically uptaken in cells, but they also stimulate cellular processes like cell invasion from 3D spheroid models. These new class of CNPs, which have sizes similar to proteinaceous ligands, hold immense potential for their surface functionalization, whereby they could be explored as promising bioimaging agents for biomedical imaging and intracellular drug delivery.