Facilely Prepared Carbon Dots as Effective Anode Modifier for Enhanced Performance of Microbial Fuel Cells

Microbial fuel cells (MFCs) are a promising technology for obtaining energy in wastewater. Effective extracellular electron transfer is one of the key factors for its practical application. In this work, carbon dots (CDs) enriched with oxygen-containing groups on the surface were synthesized as an efficient anode modifier using a simple hydrothermal method and common reactants. The experimental findings indicated that anodes modified with CDs exhibited increased electrical conductivity and greater hydrophilicity. These modifications facilitated increased microorganism loading and contributed to enhancing electrochemical processes within the anode biofilm. The CD-modified MFCs exhibited higher maximum power density (661.1 ± 42.6 mW·m-2) and open-circuit voltage (534.50 ± 6.4 mV), which were significantly better than those of the blank group MFCs (484.1 ± 14.1 mW·m-2 and 447.50 ± 12.1 mV). The use of simple carbon materials to improve the microbial loading on the MFCs anode and the electron transfer between the microbial-electrode may provide a new idea for the design of efficient MFCs.

Luminescence of carbon quantum dots and their application in biochemistry

Similar to fullerenes, carbon nanotubes and graphene, carbon dots (CDs) are causing a lot of research work in their own right. CDs are a type of surface-passivated quantum dot that contain carbon atoms. Their distinctive characteristics, such as luminescent emission that varies with size and wavelength, resistance to photobleaching, easy biological binding, lack of toxicity, and economical production without the need for intricate synthetic processes, have led to a noteworthy surge in attention within the research community. Different techniques can be utilized to create these CDs, spanning from basic candle burning to laser ablation. This review article delves into the principles of fluorescence technology, providing insights into how different synthesis methods of quantum dots impact their luminescent properties. Additionally, it highlights the latest applications of quantum dots in catalysis and biomedical fields, with special emphasis on the current status of luminescent properties in biology and chemistry. Towards the end, the article discusses the limitations of quantum dots in current practical applications, pointing out that CDs hold promising potential for future applications.

Dual targeting of Mg/N doped-carbon quantum dots with folic and hyaluronic acid for targeted drug delivery and cell imaging

Mg/N doped-carbon quantum dots (CQDs) with dual drug targeting and cell imaging properties was synthesized. Mg/N doped-CQDs synthesized by a hydrothermal method. Operating pyrolysis parameters such as temperature, time, and pH were optimized to achieve CQDs with high quantum yield (QY). This CQD applied in cellular imaging. For the first time, dual active targeting of Mg/N doped CQDs performed using folic acid and hyaluronic acid (CQD-FA-HA). Then, epirubicin (EPI) loaded on this nanocarrier as the final complex (CQD-FA-HA-EPI). Cytotoxicity analysis, cellular uptake, and cell photography performed for the complex on three cell lines, including 4T1, MCF-7, and CHO. In vivo studies were performed in BALB/c inbred female mice models bearing breast cancer. Characterization results showed the successful formation of Mg/N doped-CQDs with a high QY of 89.44%. In vitro drug release approved pH dependency of synthesized nanocarrier with a controlled release behavior. Cytotoxicity tests and cellular uptake results demonstrated increased toxicity and absorption into 4T1 and MCF-7 cell lines for targeted nanoparticles compared to free drug. In cell imaging, an increase in the entry of the complex into 4T1 and MCF-7 cells compared to free drug, confirmed the proper function of the synthesized complex. In vivo results indicated that the tumor volume of mice receiving CQD-FA-HA-EPI was the lowest among other studied groups, along with the lowest damage to the liver, spleen, and heart according to the histopathological analysis. Finally, CQD-FA-HA proposed as a novel platform with tumor targeting, drug carrier, and photoluminescence properties.

Deciphering photocatalytic degradation of methylene blue by surface-tailored nitrogen-doped carbon quantum dots derived from Kraft lignin

Lignin in black liquor can be used to manufacture carbon nanomaterials on a large scale. However, the effect of nitrogen doping on the physicochemical properties and photocatalytic performance of carbon quantum dots (NCQDs) remains to be explored. In this study, NCQDs with different properties were prepared hydrothermally by using kraft lignin as the raw material and EDA as a nitrogen dopant. The amount of EDA added affects the carbonization reaction and surface state of NCQDs. Raman spectroscopy showed that the surface defects increased from 0.74 to 0.84. Photoluminescence spectroscopy (PL) showed that NCQDs had different intensities of fluorescence emission at 300-420 nm and 600-900 nm. Meanwhile, NCQDs can photo-catalytically degrade 96 % of MB under simulated sunlight irradiation within 300 min. After three months of storage, the fluorescence intensity of NCQDs remained above 94 %, showing remarkable fluorescence stability. After four times of recycling, the photo-degradation rate of NCQDs was maintained above 90 %, confirming its outstanding stability. As a result, a clear understanding of the design of carbon-based photo-catalyst fabricated from the waste of the paper-making industry has been gained.

Nitrogen-doped cyan-emissive carbon quantum dots for fluorescence tetracycline detection and lysosome imaging

Tetracyclines (TCs) prevent the growth of peptide chains and the synthesis of proteins, and they are widely used to inhibit Gram-positive and -negative bacteria. For the detection of tetracyclines in cell and in vitro, a convenient and simple detection system based on nitrogen-doped cyan carbon quantum dots (C-CQDs) was developed. C-CQDs have excellent excitation-independent properties, the best optimal excitation peak is 360 nm and the best emission peak is 480 nm. Based on the inner filter effect (IFE), the fluorescence intensity of C-CQDs in solution decreases with the increase of tetracyclines. In the range of 0-100 μM, C-CQDs present a good linear relationship with three tetracyclines (CTC, TET, OCT), with R ² all greater than 0.999. C-CQDs can detect tetracycline in milk samples with recovery in the range of 98.2-103.6%, which demonstrates their potential and broad application in real samples. Furthermore, C-CQDs exhibit excellent lysosomal targeting, as indicated by a Pearson's coefficient of 0.914 and an overlap of 0.985. The internalisation of C-CQDs was mainly affected by lipid raft-mediated endocytosis in endocytic pathway experiments. These experiments indicate that C-CQDs can be effectively used to detect TC content and target lysosomes as an alternative to commercial dyes.

The highly sensitive “turn-on” detection of morin using fluorescent nitrogen-doped carbon dots

Graphic diagram of the synthesis of the N-CDs and the N-CDs based fluorescent sensor for the determination of morin.