Multicolor Photoluminescent Carbon Dots à La Carte for Biomedical Applications

Fluorescent carbon-based nanoparticles with dual-emission for sensing metal ions under various pH environments

Reactive dye alizarin red and ortho-phenylenediamine as raw materials, a novel carbon-based nanoparticle with dual-emission at 419 nm and 550 nm (DE-CNPs) was successfully synthesized through a hydrothermal process. The DE-CNPs exhibited distinct anti-quenching against extreme pH environments, and the integrated fluorescence color performed obvious pH dependence due to the alternating dominating of duel emissions. Besides qualified as a pH probe, the DE-CNPs were found further with high sensitivity and certain specificity for detecting metal ions in acid, base, or salt solutions. Typically, in a neutral aqueous solution, the initial yellow fluorescence transferred to blue for Cu2+/Pb2+/Cr3+, to white for Ag+/Fe3+, and to red for Al3+. Furthermore, gelatin was used as a restrictive matrix, and the DE-CNPs were embedded into the hydrogel network through physical cross-linking technology. Compared with nanoparticles, the hydrogel assembly (DE-CNPs@Gel) not only reserved original responding characteristics for detecting pH and metal ions, but also possessed better dispersity and processability as a practical candidate for the quality monitoring of water and soil.

Hydrothermal formation mechanism of lignocellulose-derived carbon dots: From sawdust to carbon nanomaterials with blue fluorescence

The conversion of lignocellulose into fluorescent lignocellulose-derived carbon dots (LCDs) via hydrothermal carbonization (HTC) has attracted significant attention. However, the degradation pathways of lignocellulose components, their contributions to LCDs formation, and the temporal evolution of LCDs' formation remain unclear. Given that HTC conditions influence LCDs' structure and fluorescence properties, an orthogonal design was applied to investigate these effects. Results show that HTC temperature and feedstock type are two key factors due to the diverse hydrolysis behaviors of components. A temperature of 190 °C effectively balances fluorescence clusters' generation and consumption, and the softwood, Pinus sylvestris var. mongolic, with its high hemicellulose and G-type lignin content, is an ideal feedstock. During HTC, LCDs are formed with a carbon core of conjugated cyclic structures from cross-linked, polymerized, and carbonized carbocyclic compounds, and a shell of polymer clusters from aliphatic hydrolysates. Here, hemicellulose and amorphous cellulose contribute to aliphatic and carbocyclic compounds, imparting hydrophilicity and fluorescence, while lignin supplies carbocyclic compounds essential for fluorescent carbon cores. As conjugation increased, the maximum fluorescence quantum yield (FQY) of LCDs reached 3.4 %. This work offers a theoretical basis for feedstock selection and explains the temporal formation process of LCDs, which is of great significance for the high-value utilization of lignocellulosic biomass and the regulation of LCDs' structures and optical properties.

A novel and high-performance tumor inhibitor of La, N co-doped carbon dots for U251 and LN229 cells

To address the medical challenges posed by glioblastoma, a novel and high-performance tumor inhibitor (La@FA-CDs) composed of folic acid and lanthanum nitrate hexahydrate, was successfully synthesized and demonstrated effectiveness in inhibiting the growth of U251 and LN299 cells. The microstructure of La@FA-CDs was extensively analyzed by FTIR, UV-Vis, XPS, TEM, AFM NMR, and nanoparticle size analyzer. The optical and electrical properties of La@FA-CDs were characterized using a fluorescence spectrometer and a zeta potential analyzer. Biological assays, including the CCK8 proliferation assay, scratch assay, flow cytometry, cytoskeleton staining, and live/dead staining were conducted to assess antitumor properties and cytotoxicity. The result revealed that the La50 %@FA-CDs demonstrated significantly enhanced antitumor activity relative to the undoped sample. Furthermore, the La50 %@FA-CDs demonstrated a dose-dependent cytotoxic effect on two glioblastoma cell lines U251 and LN299. The findings of this study suggested that treatment with La50 %@FA-CDs effectively inhibited migration and proliferation while promoting apoptosis in glioblastoma cells. Meanwhile, the La50 %@FA-CDs showed minimal cytotoxic effects on HEK 293 and HUVEC cells under standard conditions, with only slight toxicity observed in HUVEC cells at high (500 µM) concentrations. These results suggest that La50 %@FA-CDs could be a promising therapeutic agent for glioblastoma treatment, demonstrating both effective inhibition and favorable safety profiles.

Thioether-bridged carbon dots-dopamine quinone conjugate probe for glutathione sensing and discrimination between glioblastoma and normal cells

Sensitive and specific recognition and imaging of glioblastoma (GBM) cells are crucial for early diagnosis in GBM. Herein, a novel thioether-bridged fluorescence carbon dots (CDs@S for short)-dopamine quinone (DAQ) conjugate (termed as CDs@S-DAQ) probe with red emission was fabricated for sensitive sensing of glutathione (GSH) and selective fluorescence imaging of GBM cells. Due to the strong photo-induced electron transfer (PET) effect between DAQ (the acceptor) and CDs@S (the donor), the red fluorescence of CDs@S is significantly quenched. In the presence of GSH, on the one hand, GSH reduces the quinone structure to a hydroquinone structure via Michael addition reaction, which eliminates the PET effect between DAQ and CDs@S, resulting in the fluorescence restoring of CDs@S; on the other hand, it simultaneously induces the cleavage of the thioether bond linking DAQ and CDs, causing DAQ to detach from the CDs surface and reducing the PET effect, which leads to the fluorescence recovery of CDs. It has been demonstrated that the response of CDs@S-DAQ probe to GSH has a good linear relationship in the range from 0.5 to 10 mM, with an R2 value of 0.9978. Meanwhile, the as-fabricated CDs@S-DAQ probe has excellent stability, superior optical properties and low cytotoxicity. Based on these findings, the probe can be applied in live-cell fluorescence imaging, enabling discrimination between GBM cells and normal tissue cells according to their distinct GSH expression levels.

A Review of Dual-Emission Carbon Dots and Their Applications

Carbon dots (CDs), as a rising star among fluorescent nanomaterials with excellent optical properties and fascinating dual-emission characteristics, have attracted increasing attention in sensing, bio-imaging, drug delivery, and so on. The synthesis of dual-emission CDs (DE-CDs) and the establishment of ratiometric fluorescence sensors can effectively diminish background interference and provide more accurate results than single-emission CDs. Although DE-CDs have generated increased attention in many fields, the review articles about DE-CDs are still insufficient. Therefore, we summarized the latest results and prepared this review. This review first provides an overview of the primary synthesis route and commonly used precursors in DE-CDs synthesis. Then, the photoluminescence mechanism behind the dual-emission phenomenon was discussed. Thirdly, the application of DE-CDs in metal cation detection, food safety analysis, biosensing, cell imaging, and optoelectronic devices has been extensively discussed. Finally, the main challenges and prospects for further development are presented. This review presents the latest research progress of DE-CDs synthesis and its application in ratiometric sensing; hopefully, it can help and encourage researchers to overcome existing challenges and broaden the area of DE-CDs research.