Supported carbon dots serve as high-performance adsorbent for the retention of trace cadmium

Layered Double Hydroxide/Graphene Quantum Dots as a New Sorbent for the Dispersive Solid-Phase Microextraction of Selected Benzophenones, Phenols, and Parabens

In this study, the synthesis of a layered double hydroxide (LDH) composite with graphene quantum dots (GQDs) and its utilization for the development of a dispersive solid-phase extraction procedure are described. To this end, a carbonate-free Mg-Al LDH was synthesized. The development of the composite material made feasible the use of GQDs in a sample preparation procedure, while the incorporation of the GQDs in the LDH structure resulted in an 80% increase in extraction efficiency, compared to the bare LDH. As a proof of concept, the composite material was used for the development of an analytical method for the extraction, and preconcentration, of benzophenones, phenols, and parabens in lake water using high-performance liquid chromatography, coupled to a diode array detector. The analytical method exhibits low limits of quantification (0.10-1.33 μg L^-1), good recoveries (92-100%), and satisfactory enrichment factors (169-186). Due to the abovementioned merits, the easy synthesis and simple extraction, the developed method can be used for the routine analysis of the target compounds.

Carbon Dots: An Excellent Fluorescent Probe for Contaminant Sensing and Remediation

Pollution-induced degradation of the environment is a serious problem for both developing and developed countries. Existing remediation methods are restricted, necessitating the development of novel remediation technologies. Nanomaterials with unique characteristics have recently been developed for remediation. Quantum dots (QDs) are semiconductor nanoparticles (1-10 nm) with optical and electrical characteristics that differ from bigger particles owing to quantum mechanics, making them intriguing for sensing and remediation applications. Carbon dots (CDs) offer better characteristics than typical QDs, such as, CdSe QDs in terms of contaminant sensing and remediation. Non-toxicity, chemical inertness, photo-induced electron transfer, good biocompatibility, and adjustable photoluminescence behavior are all characteristics of CDs. CDs are frequently made from sustainable raw materials as they are cost-effective, environmentally compactable, and excellent in reducing waste generation. The goal of this review article is to briefly describe CDs fabrication methods, to deeply investigate the criteria and properties of CDs that make them suitable for sensing and remediation of contaminants, and also to highlight recent advances in their use in sensing and remediation of contaminants.

Chiral carbon dots - a functional domain for tyrosinase Cu active site modulation via remote target interaction

The nano-hybrid enzyme is an ideal catalytic system that integrates various advantages from biocatalysis and nanocatalysis into homogeneous and heterogeneous catalysis. However, great efforts are still needed to fully understand the interactions between nanoparticles and enzymes. Here, we show chiral carbon dots (CDs) as a new functional domain for tyrosinase Cu active site modulation via remote target interaction. Three kinds of chiral CDs (LCDs-1/-2/-3; DCDs-1/-2/-3) were fabricated by thermal treatment of citric acid and L/D-aspartic acid. Then a series of CDs/tyrosinase composites (namely, nano-hybrid-enzymes) were prepared, demonstrating good regulation of enzyme catalytic kinetics. Especially, we find that LCDs-1 is an irreversible inhibitor with great inhibition effect while the others are all reversible inhibitors. Furthermore, it is suggested by both experiments and all-atom molecular dynamics simulations that the joint effect of LCDs-1 and tyrosinase makes LCDs-1 serve as a new functional domain, which has a distinguished ability to control the conformational changes of the key sites of the active center of the tyrosinase (e.g., H60) and thus the escaping behavior of copper ions and the catalytic activity. This work opens a new route for nano-hybrid-enzyme design and enzyme activity regulation with chiral carbon materials as functional domains via remote target interaction.

Carbon Dot-Decorated Graphite Carbon Nitride Composites for Enhanced Solid-Phase Microextraction of Chlorobenzenes from Water

In this work, carbon dot-decorated graphite carbon nitride composites (CDs/g-C₃N₄) were synthesized and innovatively used as a SPME coating for the sensitive determination of chlorobenzenes (CBs) from water samples, coupled with gas chromatography-mass spectrometry. The CDs/g-C₃N₄ coating presented superior extraction performance in comparison to pristine g-C₃N₄, owing to the enhancement of active groups by CDs. The extraction capacities of as-prepared SPME coatings are higher than those of commercial coatings due to the functions of nitrogen-containing and oxygen-containing group binding, π-π stacking, and hydrophobic interactions. Under optimized conditions, the proposed method exhibits a wide linearity range (0.25-2500 ng L^-1), extremely low detection of limits (0.002-0.086 ng L^-1), and excellent precision, with relative standard deviations of 5.3-9.7% for a single fiber and 7.5-12.6% for five fibers. Finally, the proposed method was successfully applied for the analysis of CBs from real river water samples, with spiked recoveries ranging from 73.4 to 109.1%. This study developed a novel and efficient SPME coating material for extracting organic pollutants from environmental samples.

Novel Metal-Free Fluorescent Sensor Based on Molecularly Imprinted Polymer N-CDs@MIP for Highly Selective Detection of TNP

In this article, we designed a fluorometric sensor based on nitrogen-passivated carbon dots infused with a molecularly imprinted polymer (N-CDs@MIP) via a reverse microemulsion technique using 3-aminopropyltriethoxysilane as a functional monomer, tetraethoxysilane as a cross-linker, and 2,4,6-trinitrophenol (TNP) as a template. The synthesized probe was used for selective and sensitive detection of trace amounts of TNP. The infusion of N-CDs (QY-21.6 percent) with a molecularly imprinted polymer can increase the fluorescent sensor sensitivity to detect TNP. Removal of template molecules leads to the formation of a molecularly imprinted layer, and N-CDs@MIP fluorescence response was quenched by TNP. The developed fluorescence probe shows a fine linear range from 0.5 to 2.5 nM with a detection limit of 0.15 nM. The synthesized fluorescent probe was used to analyze TNP in regular tap and lake water samples.

Amphipathic carbon quantum dots-functionalized silica stationary phase for reversed phase/hydrophilic interaction chromatography

Carbon quantum dots (CQDs) are considered as good chromatographic separation materials. However, due to the hydrophily of the synthesized CQDs, their applications in HPLC are limited to HILIC for separating strong polar compounds only. In this work, a novel amphipathic CQDs with both hydrophobicity and hydrophily is developed as mixed-mode stationary phase for RPLC/HILIC. To give CQDs certain hydrophobicity, 1,8-diaminooctane is chosen as one of the carbon sources for introducing alkyl chain into CQDs. The amphipathic CQDs modified silica (CQDs/SiO₂) stationary phase has typical characteristic of RPLC/HILIC. Both hydrophobic and hydrophilic compounds including alkylbenzenes, polycyclic aromatic hydrocarbons, nucleosides and bases, amino acids, β-adrenoceptor blockers and agonists, sulfonamides, antibiotics and alkaloids obtain satisfactory separation on this CQDs/SiO₂ column. 14 nucleosides and bases commonly existing in living organisms achieve good separation on this amphipathic CQDs/SiO₂ column within 25 min and the resolutions reach 1.33-13.83 with an average column efficiency of 18,800. The retention mechanism of this novel CQDs/SiO₂ column is investigated by linear solvation energy relationship model. It is found that hydrophobic interaction, π-π stacking, hydrogen-bonding and electrostatic interactions are main retention interactions under RPLC mode. This work provides a new approach for synthesis of amphipathic CQDs. Also, it indicates that amphipathic CQDs with versatile functional properties have great prospect in separation science.

Novel synthesis of a dual fluorimetric sensor for the simultaneous analysis of levodopa and pyridoxine

Herein, a fluorimetric sensor was fabricated based on molecularly imprinted polymers (MIPs) with two types of carbon dots as fluorophores. The MIPs produced had similar excitation wavelengths (400 nm) and different emission wavelengths (445 and 545 nm). They were used for the simultaneous analysis of levodopa and pyridoxine. First, two types of carbon dots, i.e. nitrogen-doped carbon dots (NCDs) with a quantum yield of 43%, and carbon dots from o-phenylenediamine (O-CDs) with a quantum yield of 17%, were prepared using the hydrothermal method. Their surfaces were then covered with MIPs through the reverse microemulsion method. Finally, a mixture of powdered NCD@MIP and O-CD@MIP nanocomposites was used for the simultaneous fluorescence measurement of levodopa and pyridoxine. Under optimal conditions using response surface methodology and Design-Expert software, a linear dynamic range of 38 to 369 nM and 53 to 457 nM, and detection limits of 13 nM and 25 nM were obtained for levodopa and pyridoxine, respectively. The capability of the proposed fluorimetric sensor was investigated in human blood serum and urine samples. Graphical Abstract Schematic representation of nitrogen-doped carbon dots (NCDs), carbon dots from o-phenylenediamine (O-CDs), NCDs coated with imprinted polymers (NCD@MIPs), and O-CDs coated with imprinted polymers (O-CD@MIPs) in the presence and absence of levodopa and pyridoxine.

Recent Advances in Nanomaterials for Analysis of Trace Heavy Metals

In an effort to achieve high sensitivity analysis methods for ultra-trace levels of heavy metals, numerous new nanomaterials are explored for the application in preconcentration processes and sensing systems. Nanomaterial-based methods have proven to be effective for selective analysis and speciation of heavy metals in combination with spectrometric techniques. This review outlined the different types of nanomaterials applied in the field of heavy metal analysis, and concentrated on the latest developments in various new materials. In particular, the functionalization of traditional materials and the exploitation of bio-functional materials could increase the specificity to target metals. The hybridization of multiple materials could improve material properties, to build novel sensor system or achieve detection-removal integration. Finally, we discussed the future perspectives of nanomaterials in the heavy metal preconcentration and sensor design, as well as their respective advantages and challenges. Despite impressive progress and widespread attention, the development of new nanomaterials and nanotechnology is still hampered by numerous challenges, particularly in the specificity to the target and the anti-interference performance in complex matrices.

Applications of carbon quantum dots to alleviate Cd2+ phytotoxicity in Citrus maxima seedlings

Heavy metal pollution may affect plant growth. The focus of this study was to explore remediation agents that alleviate cadmium toxicity in plants. The Citrus maxima (grapefruit) seedlings were cultivated for 10 days under hydroponic conditions amended with different concentrations of Cd²⁺ (50 and 200 mg/L) and CDs (600 and 900 mg/L). Our observations on roots and leaves showed that, the plant exposed to 200 mg/L Cd²⁺ alone was damaged, supported by the changes in anthocyanin contents, activity of antioxidant enzymes and cell membrane peroxidation damage (up to 35.8-45%). However, the physiological properties of the plant were improved upon exposed to 200 mg/L Cd²⁺ plus 900 mg/L CDs; it can be ascribed to Cd²⁺ sorption to the co-exposed CDs which reduced its freely dissolved concentration by more than 22.5%, thus significantly reducing the amount of Cd²⁺ entered the plant roots by 50.7-89.4%. Due to the oxidative stress induced by Cd²⁺ exposure at 200 mg/L, expression of glutathione-producing genes was up-regulated by 30-360% relative to the control, while the genes expression upon exposure to 200 mg/L Cd²⁺ and 900 mg/L CDs was reduced by 48.4-91.5% relative to that exposed to 200 mg/L Cd²⁺ alone. However, detoxification of CDs on plant leaves at 600 mg/L was insignificant, because a portion of Cd²⁺ taken up by roots can be transported to leaves associated with the internalized CDs. Therefore, CDs can be utilized as a repair agent to mitigate toxicity of Cd²⁺ to plant especially at a high amendment level (900 mg/L).

Functionalized magnetic composites based on the aptamer serve as novel bio-adsorbent for the separation and preconcentration of trace lead

A magnetic functionalized bio-sorbent based on aptamer was designed for the selective separation of ultra-trace Pb²⁺, shortly termed as Fe₃O₄@Au@DNA. Pb(II) specific aptamer attached to the magnetic solid substrate served as affinity probe to capture and separate trace lead. Oligonucleotides with a polyA block were employed for the immobilization on the surface of AuNPs, with adenine sequences (polyA) as the part of effective anchoring block. The prepared Fe₃O₄@Au@DNA composites were characterized by FT-IR, SEM and XPS. The binding of lead on Fe₃O₄@Au@DNA composites surface was pH-dependent, the adsorption follows Langmuir model, and the adsorption dynamic fits the pseudo-second-order kinetics model. Procedure for lead separation and preconcentration was explored and combined with detection of graphite furnace atomic absorption spectrometry (GFAAS). Under the optimum condition, an enrichment factor of 17.73 was obtained with a sample volume of 1.0 mL. The limit of detection (LOD) was 57 ng L^-1 along with a relative standard deviation (RSD) of 2.06 (n = 9). The procedure was further validated by a certified reference material GBW08608 and several environmental and blood samples.

Ratio fluorometric determination of ATP base on the reversion of fluorescence of calcein quenched by Eu(III) ion using carbon dots as reference

A kind of nitrogen doped carbon dots (NCDs) with excellent stable luminescence performance was prepared by pyrolysis using ethanolamine as precursor. By simply mixing solution of NCDs and calcein-Eu³⁺, a ratio fluorometric probe with carbon dots as "internal reference" and calcein-Eu³⁺ as recognition group was constructed for ATP detection. The fluorescence of the calcein can be selectively quenched by Eu³⁺, and can be restored when ATP was added because Eu³⁺ ions exhibit higher affinity to the oxygen-donor atoms originated from phosphates than that from carboxylate groups. Meanwhile, fluorescence of NCDs was not affected by Eu³⁺, calcein or ATP. By adding NCDs as "internal reference" in the above system, a new ratiometric strategy for detecting ATP was conducted. The dynamic linear range for ATP detection was 5.0 × 10^-8 mol L^-1~ 2.0 × 10^-6 mol L^-1, and the detection limit was 2.0 × 10^-8 mol L^-1.The method was successfully applied to detecting ATP in adenosine disodium triphosphate injection. Compared with calcein- Eu³⁺ probe without NCDs as reference, the ratio fluorometric probe effectively reduced interference and improved the accuracy and sensitivity.