Nitrogen and chlorine co-doped carbon dots as probe for sensing and imaging in biological samples

A facile one-step hydrothermal synthesis approach was proposed to prepare nitrogen and chlorine co-doped carbon dots (CDs) using l-ornithine hydrochloride as the sole precursor. The configuration and component of CDs were characterized by transmission electron microscopy and X-ray photoelectron and Fourier transform infrared spectroscopies. The obtained CDs (Orn-CDs) with a mean diameter of 2.1 nm were well monodispersed in aqueous solutions. The as-prepared CDs exhibited a bright blue fluorescence with a high yield of 60%, good photostability and low cytotoxicity. The emission of Orn-CDs could be selectively and effectively suppressed by Fe(3+). Thus, a quantitative assay of Fe(3+) was realized by this nanoprobe with a detection limit of 95.6 nmol l(−1) in the range of 0.3–50 µmol l(−1). Furthermore, ascorbic acid could recover the fluorescence of Orn-CDs suppressed by Fe(3+), owing to the transformation of Fe(3+) to Fe(2+) by ascorbic acid. The limit of detection for ascorbic acid was 137 nmol l(−1) in the range of 0.5–10 µmol l(−1). In addition, the established method was successfully applied for Fe(3+) and ascorbic acid sensing in human serum and urine specimens and for imaging of Fe(3+) in living cells. Orn-CD-based sensing platform showed its potential to be used for biomedicine-related study because it is cost-effective, easily scalable and can be used without additional functionalization and sample pre-treatment.