Carbon nanoforms have emerged as a versatile bioimaging tool. In this work, we have synthesized four different carbon nanoparticles of different dimensions (10–100 nm) and variable fluorescence quantum efficiency (0.007 to 0.37) from four different carbon sources by phosphorus pentoxide-mediated combustion. The fluorescence quantum efficiency of the resulting self-passivated nanoparticles has been empirically correlated to the molecular weight and viscosity of the respective carbon source used in the synthesis. The carbon nanoparticles have been found to be significantly biocompatible as observed in the MTS assay. We have applied these biocompatible luminescent carbon nanoparticles as high brightness fluorescent probes for staining human blood platelets with very high target specificity.