Metal ions doped carbon quantum dots: Synthesis, physicochemical properties, and their applications

A ratiometric fluorescence and light scattering sensing platform based on Cu-doped carbon dots for tryptophan and Fe(III)

A new Cu-doped carbon dots (Cu-CDs) were synthesized rapidly and simply via one-step thermolysis of Na₂[Cu(EDTA)] and ascorbic acid (AA) at 250°C for 2h with a high quantum yield of 9.8%. The Cu-CDs exhibits two signals of fluorescence at 396nm and second-order scattering (SOS) at 617nm under a single excitation wavelength of 308nm, and can be obviously enhanced by tryptophan (Trp) or Fe(III) leading to the ratiometric fluorescence and SOS response with a good linear wider range of 0.5-250μM and 0.1-50μM, respectively. This sensing system exhibits good selectivity and sensitivity toward Trp and Fe(III) over other analytes with a low detection limit of 275nM and 46nM, respectively. Furthermore, the proposed sensing system displays a prospective application for quantitative assay of Trp and Fe(III) in practical sample.

Synthesis of Fluorescent Carbon Dots as Selective and Sensitive Probes for Cupric Ions and Cell Imaging

A novel sensing system has been designed for the detection of cupric ions. It is based on the quenched fluorescence signal of carbon dots (CDs), which were carbonized from poly(vinylpyrrolidone) (PVP) and L-Cysteine (CYS). Cupric ions interact with the nitrogen and sulfur atoms on surface of the CDs to form an absorbed complex; this results in strong quenching of the fluorescence of the CDs via a fast metal-to-ligand binding affinity. The synthesized water-soluble CDs also exhibited a quantum yield of 7.6%, with favorable photoluminescent properties and good photostability. The fluorescence intensity of the CDs was very stable in high ionic strength (up to 1.0 M NaCl) and over a wide range of pH levels (2.0-12.0). This facile method can therefore develop a sensor that offers reliable, fast, and selective detection of cupric ions with a detection limit down to 0.15 μM and a linear range from 0.5 to 7.0 μM (R2 = 0.980). The CDs were used for cell imaging, observed that they were low toxicity to Tramp C1 cells and exhibited blue and green and red fluorescence under a fluorescence microscope. In summary, the CDs exhibited excellent fluorescence properties, and could be applied to the selective and sensitive detection of cupric ion and multicolor cell imaging.

Recent Advancements in Doped/Co-Doped Carbon Quantum Dots for Multi-Potential Applications

Carbon quantum dots (CQDs)/carbon nanodots are a new class of fluorescent carbon nanomaterials having an approximate size in the range of 2–10 nm. The majority of the reported review articles have discussed about the development of the CQDs (via simple and cost-effective synthesis methods) for use in bio-imaging and chemical-/biological-sensing applications. However, there is a severe lack of consolidated studies on the recently developed CQDs (especially doped/co-doped) that are utilized in different areas of application. Hence, in this review, we have extensively discussed about the recent development in doped and co-doped CQDs (using elements/heteroatoms—e.g., boron (B), fluorine (F), nitrogen (N), sulphur (S), and phosphorous (P)), along with their synthesis method, reaction conditions, and/or quantum yield (QY), and their emerging multi-potential applications including electrical/electronics (such as light emitting diode (LED) and solar cells), fluorescent ink for anti-counterfeiting, optical sensors (for detection of metal ions, drugs, and pesticides/fungicides), gene delivery, and temperature probing.

A fluorometric clenbuterol immunoassay using sulfur and nitrogen doped carbon quantum dots

A fluorometric clenbuterol immunoassay is described that uses S- and N-co-doped carbon quantum dots as the fluorescent probe. Strongly fluorescent S/N-doped carbon quantum dots (S/N-CDs) were synthesized by hydrothermal method using fructose as the carbon precursor and L-cysteine as S/N sources. The S/N-CDs were characterized by transmission electron microscopy, energy dispersive spectroscopy and Fourier transform infrared spectroscopy (FTIR). Under 350 nm photoexcitation, they display strong purple fluorescence with an emission peak at 405 nm. In pH 4.0 solution, the amino groups (confirmed by FTIR) on the carbon quantum dots were coupled to clenbuterol antibody (Ab) by amine-amine coupling reaction to quench the fluorescence. If clenbuterol (Clen) is added, it binds to the Ab to generate a stable Ab-Clen immunocomplex and free S/N-CD. This causes the fluorescence of nanoprobe to be restored. The fluorescence of the system increases linearly in the 0.07-1.7 ng·mL^-1 Clen concentration range. The probe of type S/N₄-CD displays the best sensitivity. The detection limit is 23 pg·mL^-1. Graphical abstract Schematic presentation of clenbuterol fluorometric immunoassay using sulfur and nitrogen doped carbon quantum dots.

Fluorescent Sensors for the Detection of Heavy Metal Ions in Aqueous Media

Due to the risks that water contamination implies for human health and environmental protection, monitoring the quality of water is a major concern of the present era. Therefore, in recent years several efforts have been dedicated to the development of fast, sensitive, and selective sensors for the detection of heavy metal ions. In particular, fluorescent sensors have gained in popularity due to their interesting features, such as high specificity, sensitivity, and reversibility. Thus, this review is devoted to the recent advances in fluorescent sensors for the monitoring of these contaminants, and special focus is placed on those devices based on fluorescent aptasensors, quantum dots, and organic dyes.

Recent insights into near-infrared light-responsive carbon dots for bioimaging and cancer phototherapy

The current developments of NIR-responsive CDs and their applications in bioimaging and phototherapy are highlighted in this review.

Red-emissive nitrogen doped carbon quantum dots for highly selective and sensitive fluorescence detection of the alachlor herbicide in soil samples

We report the synthesis of red-emissive nitrogen-doped carbon quantum dots and their applications in the highly selective and sensitive detection of the alachlor herbicide in soil samples.

Recent advances in carbon quantum dot (CQD)-based two dimensional materials for photocatalytic applications

This review presents up-to-date research findings and critical insights on trending topics of pristine CQDs and CQDs-based 2D nanomaterial composites.

Performance of C2H4 Reductant in Activated-Carbon- Supported MnOx-based SCR Catalyst at Low Temperatures

Hydrocarbons as reductants show promising results for replacing NH3 in SCR technology. Therefore, considerable interest exists for developing low-temperature (<200 °C) and environmentally friendly HC-SCR catalysts. Hence, C2H4 was examined as a reductant using activated-carbon-supported MnOx-based catalyst in low-temperature SCR operation. Its sensitivity to Mn concentration and operating temperature was parametrically studied, the results of which showed that the catalyst activity followed the order of 130 °C > 150 °C > 180 °C with an optimized Mn concentration near 3.0 wt.%. However, rapid deactivation of catalytic activity also occurred when using C2H4 as the reductant. The mechanism of deactivation was explored and is discussed herein in which deactivation is attributed to two factors. The manganese oxide was reduced to Mn3O4 during reaction testing, which contained relatively low activity compared to Mn2O3. Also, increased crystallinity of the reduced manganese and the formation of carbon black occurred during SCR reaction testing, and these constituents on the catalyst’s surface blocked pores and active sites from participating in catalytic activity.