Tricolor emissive carbon dots for ultra-wide range pH test papers and bioimaging

Recently, fluorescent pH test paper has been extensively explored for visual assays due to its easy preparation, low-cost, and portable feature. In addition, intracellular pH also plays important roles in different pathological and physiological processes for understanding cellular functions and providing critical assistance for early disease diagnosis. Herein, the tricolor emission multiple-cores@shell carbon dots (CDs) were synthesized via one-pot hydrothermal method using 5-amino-1,10-phenanthroline (Aphen) and citric acid (CA) as the carbon sources. The fluorescence emission of CDs showed an interesting pH dependence due to the special structure and properties, which can make the CDs to be used as the pH test paper to qualitatively and quantitatively detect pH value in a wide pH range. At the same time, because of good cell compatibility and low toxicity, CDs can be used as a new type of cell imaging marker to detect intracellular pH. The unique tricolor emission property of CDs can well avoid the fluorescent dyes and protein fluorescence interference.