Excitation-independent hollow orange-fluorescent carbon nanoparticles for pH sensing in aqueous solution and living cells

We report an ingenious strategy for fabrication of hollow orange fluorescent carbon nanoparticles (HFCNs) and demonstrate their applications for pH biosensing and fingerprint detection. HFCNs have been synthesized using 5-amino salicylic acid as carbon source via one-step hydrothermal treatment without further surface passivation or modification. The as-prepared HFCNs possess excellent hollow structure and bright orange fluorescence. The HFCNs display a remarkable emission enhancement in the orange fluorescence region when the pH is increased from 3.0 to 10.0. The pKa value of HFCNs is found to be 5.97 and a good linearity is shown in the pH range of 5.25-6.75, which makes HFCNs an effective intracellular pH imaging agent for acidic microenvironments. The confocal fluorescent microscopic images of HFCNs-stained latent fingerprint are achieved successfully, suggesting that they have great promise for practical criminal investigations as a simple, fast, and accurate tool.