Fluorescence behavior of non-functionalized carbon nanoparticles and their in vitro applications in imaging and cytotoxic analysis of cancer cells.

We report fluorescence behavior in non-functionalized carbon nanoparticles (NCNP) prepared from lamp soot and their application in imaging of normal and cancer cells. Structural characterization of these particles by Raman spectroscopy showed characteristic peaks located at 1350 and 1590 cm(-1) corresponding to the diamond-like (D) and graphite-like (G) bands of the carbon allotropes respectively with the characteristic ratio I(D)/I(G)=2.24. X-ray diffraction study confirmed the presence of amorphous as well as graphitized carbon in these nanostructures with minimum grain size ≈2 nm. A typical luminescence lifetime measured by time resolved fluorescence spectroscopy was obtained 3.54 ns. The photoluminescence behavior of these particles was excitation dependent and gave off blue, green and red fluorescence under UV, blue and green excitation, respectively. Cellular uptake of these NCNP yielded excellent results for cell imaging of human embryonic kidney, lung carcinoma and breast adenocarcinoma cells. Cell imaging was further correlated with cytotoxicity in the above mentioned cell lines and also in leukemia cell lines. Dose dependant cytotoxicity was observed after 24 h up to 48 h of incubation of nanoparticles. Fluorescence microscopy of nanoparticle-cell interaction clearly indicated aggregation of the particles.