Dielectric barrier discharge-assisted one-pot synthesis of carbon quantum dots as fluorescent probes for selective and sensitive detection of hydrogen peroxide and glucose

Ultrafine V2O5-anchored 3D N-doped carbon nanocomposite with augmented dual-enzyme mimetic activity for evaluating total antioxidant capacity

Total antioxidant capacity (TAC) can be evaluated by detecting the content of antioxidants, such as ascorbic acid, based on the enzyme-mimetic activity of nanomaterials. Herein, we fabricated a 3D-V₂O₅/NC nanocomposite using a self-templating strategy, which achieved ultrafine particles (∼2.5 nm), a porous carbon layer, large specific surface area (152.4 m²/g), N-doping and heterogeneous structure. The strong catalytic activity of 3D-V₂O₅/NC resulted from the integrated effect between the ultrafine structure of V₂O₅ nanoparticles and the 3D porous nitrogen-doped carbon framework, effectively increasing the number of active sites. This nanozyme presented a higher catalytic activity than its components or precursors in the nanocomposite (e.g., VN/NC, NC, V₂O₅, and VO₂/g-C₃N₄). ROS scavenging experiments confirmed that the dual enzyme-like activity of 3D-V₂O₅/NC (catalase-like and oxidase-like) resulted from their co-participation of ‧O₂^-, h⁺ and ‧OH, among which ‧O₂^- played a crucial role in the catalytic color reaction. By virtue of the 3D-V₂O₅/NC nanoenzyme activity and TMB as a chromogenic substrate, the mixed system of 3D-V₂O₅/NC + TMB + H₂O₂ provided a low detection limit (0.03 μM) and suitable recovery (93.0-109.5%) for AA. Additionally, a smartphone-based colorimetric application was developed employing "Thing Identify" software to evaluate TAC in beverages. The colorimetric sensor and smartphone-detection platform provide a better or comparable analytical performance for TAC assessment in comparison to commercial ABTS test kits. The newly developed smartphone-based colorimetric platform presents several prominent advantageous, such as low cost, simple/rapid operation, and feasibility for outdoor use.

Dielectric barrier discharge-accelerated one-pot synthesis of sulfur quantum dots for fluorescent sensing of lead ions and L-cysteine

Here, we report a novel method for the one-pot facile synthesis of sulfur quantum dots (SQDs) based on a dielectric barrier discharge (DBD)-accelerated H₂O₂ etching strategy within merely 20 min. The formation mechanism of SQDs was investigated, with which an "ON-OFF-ON" fluorescence sensor was developed for the detection of Pb²⁺ ions and L-cysteine.

Facile preparation of Cu-doped carbon dots for naked-eye discrimination of phenylenediamine isomers and highly sensitive ratiometric fluorescent detection of H2O2

Changing a detection analyte into a colored material is a key challenge for visual discrimination of isomers. In this work, a novel fluorescent probe incorporating Cu-doped carbon dots (Cu-CDs), for the first time, was developed for naked-eye discrimination of phenylenediamine isomers and highly sensitive ratiometric fluorescence detection of H₂O₂. In this strategy, Cu-CDs were synthesized by a facile hydrothermal approach using citric acid, formamide, and CuCl₂ as reactants. The prepared Cu-CDs exhibited outstanding peroxidase-like activity and stability. Consequently, a chemosensor platform based on Cu-CDs was constructed to enable naked-eye discrimination of phenylenediamine isomers through the H₂O₂-mediated oxidation reaction. Moreover, a Cu-CDs-based ratiometric fluorescence sensor was proposed as a means to sensitively detect H₂O₂ with a detection limit of 5.0 nM. The sensor was further employed for monitoring H₂O₂ in human serum, indicating its potential applications in other biologically related study.

Green Route for the Synthesis of Fluorescent Carbon Nanoparticles from Circassian Seeds for Fe(III) Ion Detection

A facile and green strategy was carried out for the preparation of fluorescent carbon nanoparticles (CNp) using non-toxic circassian seeds as carbon precursor (CNp, named ACNp). The surface of amorphous ACNp is latched with different surface moieties such as hydroxyl, carbonyl, ether and amino groups and it is confirmed by FTIR and XPS. These functionalities provide high solubility and stability to ACNp in aqueous medium. The surface of ACNp is highly negatively charged due to the presence of oxygen rich functional groups and it is confirmed by zeta potential. A reasonably good quantum yield (QY) of 5.1% is obtained for ACNp compared to other CNp derived from bioprecursors without any surface passivation. Circassian seeds are self sufficient for the synthesis of N doped CNp. The excitation dependent fluorescence property of ACNp is invariant under ionic and thermal environments. They exhibit good selectivity towards Fe³⁺ ions via static quenching mechanism with detection limit of 32.7 µM.

On-off-on nanosensors of carbon quantum dots derived from coal tar pitch for the detection of Cu2+, Fe3+, and L-ascorbic acid

Novel nitrogen-doped carbon quantum dots (N-CQDs) were synthesized by a chemical oxidation method using medium-low temperature coal tar pitch as the raw material. Such quantum dots were developed as a highly sensitive fluorescent "on-off-on" switch sensor for the selective and simultaneous sensing of Cu²⁺ and Fe³⁺. The as-prepared N-CQDs, which emit blue light, were characterized by TEM images, FT-IR spectra, Raman spectroscopy, XPS analysis, fluorescence spectra, and UV-vis absorption spectra. The results showed that the N-CQDs exhibit outstanding optical properties and high optical stability within the pH range of 4-10, with a quantum yield of approximately 7%. Additionally, the material performed as an "on-off" sensor which can be dramatically extinguished by Cu²⁺ and Fe³⁺. A linear relationship between Cu²⁺ and Fe³⁺ ion concentration and fluorescence intensity was observed in the range from 0 to 50 μM. The limits of detection of the fluorescent sensor toward Cu²⁺ and Fe³⁺ were 0.16 μM and 0.173 μM, respectively. The Fe³⁺-quenched N-CQDs were restored after adding L-ascorbic acid, due to the redox reaction between Fe³⁺ and L-ascorbic acid, which resulted in the detachment of Fe³⁺ from the surface of the N-CQDs. The linear range for the detection of L-ascorbic acid was 0-28 μM. Therefore, the amount of L-ascorbic acid can be measured by using the sensing system consisting of Fe³⁺ and N-CQDs. In consequence, N-CQDs are considered an important material for the detection of Cu²⁺ and Fe³⁺ in water samples or L-ascorbic acid in drugs.

Point discharge microplasma reactor for high efficiency conversion of H2S to SO2 for speciation analysis of sulfide and sulfite using molecular fluorescence spectrometry

A low temperature plasma integrating the merits of small size, simple operation and rich active particles has good performance in analytical chemistry. In this work, a point discharge microplasma was used as a reactor to facilitate the gaseous conversion reaction from H₂S to SO₂ with an excellent efficiency as high as 95%. By coupling this reactor with a fluorescence spectrometer, the speciation analysis of sulfide and sulfite was achieved in a simple, chromatographic separation-free, time-saving and practical way. Specifically, with the discharge off, only sulfite was quantified; with discharge on, both sulfide and sulfite were quantified; and with a simple subtraction, the speciation analysis could be easily attained. By the acidification process, a limit of detection of 7.7 μM by the proposed method was obtained for both sulfide and sulfite in aqueous medium, and this method was successfully utilized to analysis of real samples.

Green synthesis of fluorescent carbon quantum dots for the detection of mercury(ii) and glutathione

On–off–on detection of Hg²⁺ and GSH using green-synthesized CQDs from T. indica leaves for the first time.

Green synthesis of fluorescent carbon dots from Borassus flabellifer flowers for label-free highly selective and sensitive detection of Fe3+ ions

Fluorescent carbon dots were derived from Borassus flabellifer flowers by thermal pyrolysis method and used for label-free highly selective and sensitive detection of Fe³⁺ ions.

Gram-Scale Synthesis of Hydrophilic PEI-Coated AgInS2 Quantum Dots and Its Application in Hydrogen Peroxide/Glucose Detection and Cell Imaging

Assisted with polyethylenimine, 4.0 L of water-soluble AgInS₂ quantum dots (AIS QDs) were successfully synthesized in an electric pressure cooker. As-prepared QDs exhibit yellow emission with a photoluminescence (PL) quantum yield up to 32%. The QDs also show excellent water/buffer stability. The highly luminescent AIS QDs are used to explore their dual-functional behavior: detection of hydrogen peroxide (H₂O₂)/glucose and cell imaging. The amino-functionalized AIS QDs show high sensitivity and specificity for H₂O₂ and glucose with detection limits of 0.42 and 0.90 μM, respectively. A linear correlation was established between PL intensity and concentration of H₂O₂ in the ranges of 0.5-10 μM and 10-300 μM, while the linear ranges were 1-10 μM and 10-1000 μM for detection of glucose. The AIS QDs reveal negligible cytotoxicity on HeLa cells. Furthermore, the luminescence of AIS QDs gives the function of optical imaging.

New development in carbon quantum dots technical applications

As a newly emerged member in carbon nanomaterials family, carbon quantum dots (CQDs) attracted everincreasing attention owing to their ultracompact size, excellent photoluminescence, favorable biocompatibility, versatile surface and superior electron transfer ability. The past decade has witnessed continuous advancements in the production of CQDs with high photoluminescence quantum yields for various applications. Herein, we track the newest development of CQDs with advanced physicochemical properties and their applications in sensing, bioimaging, nanomedicine and catalysis, and propose the challenges and perspectives in this exciting and promising field.

Bio-nanoplatforms based on carbon dots conjugating with F-substituted nano-hydroxyapatite for cellular imaging

Carbon dots (CDs) have shown great promise in a wide range of bioapplications due to their tunable optical properties and noncytotoxicity. For the first time, a rational strategy was designed to construct new bio-nanoplatforms based on carboxylic acid terminated CDs (CDs-COOH) conjugating with amino terminated F-substituted nano-hydroxyapatite (NFAp) via EDC/NHS coupling chemistry. The monodisperse NFAp nanorods were functionalized with o-phosphoethanolamine (PEA) to provide them with amino groups and render them hydrophilic with respect to the ligand exchange process. The CDs-COOH@PEA-NFAp conjugates exhibits bright blue fluorescence under UV illumination, excellent photostability and colloidal stability. Due to their low cytotoxicity and good biocompatibility as determined by methyl thiazolyl tetrazolium (MTT) assay, the CDs-COOH@PEA-NFAp conjugates were successfully applied as bio-nanoplatforms to MCF-7 breast cancer cells for cellular imaging in vitro. More importantly, the functional CDs conjugated to NFAp provide an extended and general approach to construct different water-soluble NFAp bio-nanoplatforms for other easily functionalised luminescent materials. Therefore, these green nanoplatforms may be a prospective candidate for applications in bioimaging or targeted biological therapy and drug delivery.

H2O2-mediated fluorescence quenching of double-stranded DNA templated copper nanoparticles for label-free and sensitive detection of glucose

A label-free fluorescent sensor has been developed for glucose detection based on H₂O₂-mediated fluorescence quenching of ds-DNA templated Cu NPs.