Carbon dots with pH-responsive fluorescence: a review on synthesis and cell biological applications

This review summarizes state of the art synthesis and applications of carbon dots (CDs) with pH-responsive fluorescence. Following an introduction, the first section covers methods for the preparation of pH-responsive CDs, with subsections on general methods for preparing CDs (by hydrothermal, solvothermal, electrochemical, microwave, laser ablation, pyrolysis or chemical oxidation polymerization methods), and on precursors for synthesis. This is followed by a section on the mechanisms of pH-responsivity (by creating new functional groups, change of energy levels, protonation and deprotonation, aggregation, or by introduction shells). Several Tables are presented that give an overview of the wealth of methods and materials. A final section covers applications of carbon dots (CDs) with pH-responsive fluorescence for sensing, drug delivery, and imaging. The conclusion summarizes the current status, addresses challenges, and gives an outlook on potential future trends. Graphical abstract The synthesis and biological applications of carbon dots(CDs) with pH-responsive fluorescence are summarized. Precursors and methods for preparation of pH-responsive CDs, mechanisms of pH-responsivity, and biological applications of CDs with pH-responsive fluorescence for sensing, drug delivery, and imaging are discussed.