A Novel Class of Greenish-Yellow Emitting Carbon Dots Stimulate Collective Cell Migration and 3D Uptake In Vivo**

We present a new class of nitrogen-doped greenish-yellow fluorescent carbon dots (CDs) synthesized using a one-step hydrothermal method. These bright fluorescent nanoparticles have excitation and emission spectra near the red region of the visible light spectrum which is quite useful for bioimaging applications. Using organic molecules like ortho-phenylenediamine (OPDA), L-ascorbic acid and urea, yellow fluorescent carbon dots (CDs) were synthesized. We obtained a scalable number of greenish-yellow CDs having an average size of 3 nm. The CDs show significant emission spectra in the yellow fluorescence region (λ<inf>em</inf>=557 nm). The CDs show remarkable stability in their fluorescence in different pH conditions, ionic stability, photostability as well as thermal stability. These CDs are efficiently uptaken by mammalian cells through the clathrin-mediated pathway. Apart from in vitro studies, we have also used zebrafish larvae as a 3D in vivo model and showed that CDs were uptaken efficiently by larvae showing maximum accumulation and fluorescence in the yolk sac region and the notochord region. The CDs also offer enhancement in cell proliferation, hence showing the application in wound healing. The fluorescence of CDs is quite robust and is not affected by most external stimuli; therefore can be explored as a promising bioimaging tool for targeted bioimaging and biomedical applications.