  Fluorescent carbon nanoparticle (CNP) having 2-6 nm in size with quantum
yield of about ~3% were synthesized via nitric acid oxidation of carbon soot
and this approach can be used for milligram scale synthesis of these water
soluble particles. These CNPs are nano-crystalline with predominantly graphitic
structure and shows green fluorescence under UV exposure. While nitric acid
oxidation induces nitrogen and oxygen incorporation into soot particle that
afforded water solubility and light emitting property; the isolation of small
particles from a mixture of different size particles improved the fluorescence
quantum yield. These CNP shows encouraging cell imaging application. They enter
into cell without any further functionalization and fluorescence property of
these particles can be used for fluorescence based cell imaging application.
