Sensitive visual detection of intracellular zinc ions based on signal-on polydopamine carbon dots

Multi-applications of carbon dots and polydopamine-coated carbon dots for Fe3+ detection, bioimaging, dopamine assay and photothermal therapy

Carbon dots (CDs) or CDs/polymer composites have been applied in numerous fields. Here, novel CDs were synthesized by carbonization of egg yolk, and characterized by TEM, FTIR, XPS and photoluminescence spectra. The CDs were found to be approximate sphere in shape with an average size of 4.46 ± 1.17 nm, and emitted bright blue photoluminescence under UV irradiation. The photoluminescence of CDs was found selectively quenched by Fe³⁺ in a linear manner in the range of 0.05-0.45 mM, meaning they could be applied for Fe³⁺ detection in solution. Moreover, the CDs could be uptaken by HepG2 cells to exhibit bright blue photoluminescence. The intensity could reflect the level of intracellular Fe³⁺, indicating they could be further used for cell imaging and intracellular Fe³⁺ monitoring. Next, dopamine was polymerized on the surface of CDs to obtain the polydopamine (PDA)-coated CDs (CDs@PDA). We found PDA coating could quench the photoluminescence of CDs via inner filter effect, and the degree of quenching was linearly related to the logarithm of DA concentration (Log C_DA). Also, the selectivity experiment indicated the method had a high selectivity for DA over a number of possible interfering species. This indicated the CDs in combination with Tris buffer could be potentially applied as the assay kit of dopamine. At last, the CDs@PDA exhibited excellent photothermal conversion capability, and they could efficiently kill HepG2 cells under NIR laser irradiation. Overall, the CDs and CDs@PDA in this work exhibited many excellent advantages, and could be potentially used for multi-applications, such as Fe³⁺ sensor in solution and cellular, cell imaging, dopamine assay kit, as well as photothermal agents for cancer therapy.

Fabrication of manganese-coordinated polyphenol carbon dots for photothermal therapy and immune activation

Background

Nanoparticle-based photothermal therapy (PTT) is capable of inducing immunogenic cell death (ICD) and eradicating local tumor via hyperthermia. However, it can hardly prevent tumor recurrence and metastasis owing to inadequate immune activation.

Results

To this end, manganese-coordinated polyphenol carbon dots (MP-CDs) were synthesized by hydrothermal carbonization and metal–polyphenol coordination. This prepared MP-CDs had ultra-small particle size of 5 nm, excellent optical performance, good dispersibility in water and favorable biocompatibility. Under 808 nm near-infrared laser irradiation, the MP-CDs with high photothermal conversion efficiency could kill tumor cells and induce the release of damage-associated molecular patterns (DAMPs) from tumor cells. Notably, the MP-CDs can promote the maturation and antigen presentation ability of dendritic cells (DCs) via manganese-mediated immune activation.

Conclusion

The present work offers a versatile strategy to integrate functional metal into CDs via metal–polyphenol coordination for photothermal/immune therapy.

Wild jujube-based fluorescent carbon dots for highly sensitive determination of oxalic acid

Fluorescent carbon dots (CDs) were synthesized by a one-step hydrothermal treatment of wild jujube and dl-tryptophan. The structure and properties of the CDs were confirmed by transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet visible absorption spectroscopy, fluorescence spectroscopy and so on. The as-prepared CDs exhibit excellent excitation-independent but pH-dependent (4.0-12.0) fluorescent features and emit blue strong fluorescence under 365 nm light. Hg²⁺ can decrease the fluorescence intensity of the CDs through static quenching, while the addition of oxalic acid (OA) recovers it owing to the coordination binding between oxalic acid and Hg²⁺. Based on this, the as-prepared CDs were used as a new "off-on" fluorescent probe for highly sensitive determination of oxalic acid with a wide linear detection range of 0.1-20 mg L^-1 and a low detection limit of 0.057 mg L^-1. Moreover, the fluorescent probe was successfully applied to detect oxalic acid in tomato and cherry tomato samples with satisfactory results.