Se & N co-doped carbon dots for high-performance fluorescence imaging agent of angiography

Both long wavelength excitation and emission are highly desired for fluorescent carbon dots in biorelated applications. According to semiconductor theory, heteroatom doping is an effective way to tune the band gap of a semiconductor. In this work, we developed an exceedingly simple and mild one-pot method to synthesize selenium and nitrogen co-doped carbon dots (Se&N-CDs) by using low cost citric acid, ethane diamine and selenium powder as the starting materials. After doping the Se element into N-CDs, the absorption of Se&N-CDs was expanded from UV to the visible light region (similar to 497 nm). More important is that the Se&N-CDs show a strong green light emission with a high quantum yield of B52%, attributed to the new Se-state introduced in the Se&N-CDs due to the low electronegativity of Se. Furthermore, we successfully demonstrate that Se&N-CDs have an excellent performance as a dye for fluorescein fundus angiography (FFA). After injection, a clear vascular image in the retina and detailed images of the capillary bed were exhibited in the FFA image. This will provide a great advantage for bio-imaging and diagnosis.