The construction of ratiometric fluorescence assay has displayed fantastic advantages in improving semi-quantitative visualization capability by presenting successive color changes. Herein, long-wavelength emission nitrogen-doped carbon dots (N-CDs) were developed for intrinsic ratiometric detection of silver ions (Ag+) and glutathione (GSH), accompanied by visualization fluorescence variation of orange and green. The label-free N-CDs were favorably obtained through one-step hydrothermal synthesis and displayed single long-wavelength emission at 618 nm under the excitation wavelength of 478 nm. Interestingly, a ratio rising peak emerges at 532 nm and the emission at 618 nm decreases with the introduction of Ag+, which exhibits ratiometric fluorescence emission characteristics (I 618nm/I 532nm) in the range of 0–140 μM with significant fluorescence varying from orange to green. Furthermore, the fluorescence of CDs@Ag­(I) can be effectively ratiometric recovered by virtue of a specific reaction of GSH with Ag+, which is accompanied by the fluorescence of the solution returning from green to orange. In addition, the N-CDs hold excellent biocompatibility which can be implemented as the visualization biosensing platform for intracellular determination of Ag+ and GSH, demonstrating that proposed N-CDs have tremendous potential in biological systems.

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The novel strategy for color-tunable carbon dots (CDs) with superior dispersibility in an aqueous solution is originally proposed in a one-pot hydrothermal method. The optimized emission of resulted CDs progressively shifts from green to red with the adjustment of precursor solution from alkali to acid. The proposed three representative CDs entire green, yellow, and red fluorescences prepared separately on alkaline, neutral, and acidic aqueous solutions possess similar graphite structures in their carbon cores, while the diversification of PL emissions in these CDs are convinced to derive from the difference in their particle size and the content of nitrogen doping. Moreover, the regular variation of calculated band gaps for the three types of CDs are perfectly consistent with their PL emission characteristics. Further investigation of their radical scavenging activities based on the difference in surface states demonstrates that the CDs synthesized under alkaline conditions have stronger oxidation resistance. Thus, we can speculate that the amino groups on P-phenylenediamine precursors are more easily activated under acidic conditions, which results in an in-depth cross-linking that facilitates a long wavelength emission. In addition, the exceptional biocompatibility of these multicolored CDs enables tremendous potential applications in biological systems.

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We engineered a tumor microenvironment-triggered MSN-based anti-cancer nanocarrier for simultaneous delivery of DOX and chemodynamic agent.