Synthesis of fluorescent carbon dots via microwave carbonization of citric acid in presence of tetraoctylammonium ion,and their application to cellular bioimaging

A jelly-like form of carbon dots (C-dots) was prepared by microwave-assisted synthesis from citric acid in the presence of tetraoctylammonium bromide. The effect of the concentration of tetraoctylammonium bromide was examined. The synthesized carbon dots were characterized by UV–vis, XRD, FTIR, fluorescence and HR-TEM. Fluorescence extends from 350 to 600 nm, and the corresponding excitation wavelengths range from 300 to 460 nm. Quantum yields are at around 0.11. A cytotoxicity study showed carbon dots to be cell permeable and biocompatible which renders them appropriate for imaging applications. The dots were used to image HeLa cell lines via the blue fluorescence of the dots.

C-dots were synthesized from citric acid by microwave heating in presence of varying concentrations of tetraoctylammonium bromide (TOAB) as a micellar template. The excellent optical properties of the nanoparticles make them well suitable for bio-imaging of HeLa cells.

     

Fabrication of carbon quantum dots via ball milling and their application to bioimaging

Carbon quantum dots (CQDs) with an average diameter of 3 nm, exhibiting blue photoluminescence, have been obtained from commercial conductive carbon black by a cost-effective and straightforward exfoliation method using dry ball milling in the presence of sodium carbonate. As a secondary abrasive medium, sodium carbonate provides effective exfoliation of carbon black with a high degree of CQD graphitization and plays an essential role in the functionalization of CQDs with oxygen groups. Due to the low toxicity of CQDs against HeLa cancer cells (cell viability above 90% at a CQD concentration of 200 μg cm⁻³) and the ability to penetrate cells and emit blue light, CQDs are possibly suitable for biological imaging of cells.     

Synthesis and bioimaging application of red-emissive carbon dots

Fluorescent red-emissive carbon dots (RCDs) were synthesized using the solvothermal method with citric acid as a carbon source, N,N-dimethylformamide as a nitrogen source, and formamide as a solvent. The as-synthesized RCDs show red fluorescence in an aqueous solution and have an excellent stability towards photobleaching as well as extremely low cytotoxicity and are successfully used for cell and zebrafish imaging. The results indicate that RCDs have potential applications in both in vitro and in vivo bioimaging.     

Highly fluorescent carbon polymer dots prepared at room temperature,and their application as a fluorescent probe for determination and intracellular imaging of ferric ion

Carbon polymer dots (CPDs) were prepared by a one-pot aqueous synthetic route from ascorbic acid and diethylenetriamine at room-temperature. The CPDs under 350-nm excitation exhibit blue fluorescence peaking at 430 nm with a quantum yield of 47%. Other features include an average diameter of 5 nm, a fluorescence that is independent of the excitation wavelength, good water dispersibility and photostability, and excellent biocompatibility. The CPDs are shown to be viable fluorescent probes for ferric ion which acts as a strong quencher. The response to Fe(III) is linear in the 0.2 to 10 μM concentration range, and the detection limit is 0.1 μM. The probe was applied to the determination of Fe(III) in environmental waters and to intracellular imaging of ferric ions in HeLa cells.

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Graphical abstract Carbon polymer dots (CPDs) are prepared from ascorbic acid and diethylenetriamine (DETA) at room-temperature (RT). The RT-CPDs exhibit excellent optical performance, biocompatibility and selectivity of quenching by ferric ions. This can be applied for determination and intracellular imaging of ferric ion.

     

Tetraphenylethylene and N-isopropylacrylamide block polymer-grafted carbon dots with their application in cellular imaging

Carbon dots (CDs) grafted with block polymer of tetraphenylethylene (TPE) and N-isopropylacrylamide (CD-g-poly(TPE-block-NIPAM)) were synthesized, which are aggregation-induced emission (AIE) nanoparticles. The CD-g-poly(TPE-block-NIPAM) exhibited different fluorescence behaviors in tetrahydrofuran (THF) and water. In THF, the CD-g-poly(TPE-block-NIPAM) could fluoresce, but only from CDs, and the TPE block showed no fluorescence. The fluorescence of CDs was quenched ,and the TPE block showed AIE, when the CD-g-poly(TPE-block-NIPAM) were dispersed in water. The CD-g-poly(TPE-block-NIPAM) showed no cytotoxicity, which could be easily internalized by human breast cancer cells and human embryonic kidney cells with high fluorescence, and they can be used as fluorescent tracers for living cells.     

One-pot electrochemical synthesis of functionalized fluorescent carbon dots and their selective sensing for mercury ion

We propose a simple, economical, and one-pot method to synthesize water-soluble functionalized fluorescent carbon dots (C-Dots) through electrochemical carbonization of sodium citrate and urea. The as-prepared C-Dots have good photostability and exhibit a high quantum yield of 11.9%. The sizes of the C-Dots are mainly distributed in the range of 1.0–3.5 nm with an average size of 2.4 nm. It has been further used as a novel label-free sensing probe for selective detection of Hg²⁺ ions with detection limit as low as 3.3 nM. The detection linear range is 0.01–10 μM. The as-prepared C-Dots are also successfully applied for the determination of Hg²⁺ in real water samples.     

Synthesis of multicolor luminescent adjustable carbon dots and their application in anti-counterfeiting

A novel approach for fabricating color-adjustable carbon dots (CDs) is proposed via hydrothermal treatment of p-aminobenzenesulfonic acid and o-, m-, or p-phenylenediamines, respectively. The as-synthesized CDs can emit blue, green, and orange fluorescence and are named b-CDs, g-CDs, and o-CDs, respectively. All of them have strict excitation independence and excellent photostability. Variations of photoluminescence emitting them are attributed to the difference in their particle size, the degree of oxidation, and the content of N-related states on their surface. Furthermore, these multicolor CDs have been used as fluorescents inks, which perform well in anti-counterfeiting and information security.     

Synthesis of nitrogen- and iron-containing carbon dots,and their application to colorimetric and fluorometric determination of dopamine

Nitrogen- and iron-containing carbon dots (N,Fe-CDs) are synthesized by hydrothermal treatment of branched polyethylenimine (BPEI) and hemin at 180 °C. The N,Fe-CDs are mainly doped with nitrogen and trace amounts of iron(III). The N,Fe-CDs also display intrinsic fluorescence with excitation/emission maxima at 365/452 nm and a quantum yield of 27 %. The nanodots are shown to act as peroxidase mimics by catalyzing the oxidation of tetramethylbenzidine (TMB) by hydrogen peroxide to form a blue product whose quantity can be determined by photometry at 652 nm. This was exploited to design colorimetric and fluorometric assays for dopamine (DA). The colorimetric assay is based on the oxidation of DA by H₂O₂ in presence of the N,Fe-CDs and TMB. It has an instrumental detection limit of 40 nM (at an S/N ratio of 3), and a visual detection limit of 0.4 μM. The fluorometric assay is based on an inner filter effect that is caused by the formation of oxidized TMB which overlaps (and absorbs) the emission of the N,Fe-CDs located at 452 nm. The fluorometric detection limit is as low as 20 nM (at an S/N ratio of 3).

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Graphical abstract Carbon dots containing nitrogen and iron (N,Fe-CDs) were synthesized by hydrothermal treatment of branched polyethylenimine and hemin. The N,Fe-CDs display excellent fluorescent properties, peroxidase-like activity and potential application in colorimetric and fluorometric detection of dopamine.

     

Synthesis, characterisation and bioimaging of a fluorescent rhenium-containing PNA bioconjugate

A new rhenium tricarbonyl complex of a bis(quinoline)-derived ligand (2-azido-N,N-bis((quinolin-2-yl)methyl)ethanamine, L-N(3)), namely [Re(CO)(3)(L-N(3))]Br was synthesized and characterized in-depth, including by X-ray crystallography. [Re(CO)(3)(L-N(3))]Br exhibits a strong UV absorbance in the range 300-400 nm with a maximum at 322 nm, and upon photoexcitation, shows two distinct emission bands at about 430 and 560 nm in various solvents (water, ethylene glycol). [Re(CO)(3)(L-N(3))]Br could be conjugated, on a solid phase, to a peptide nucleic acid (PNA) oligomer using the copper(I)-catalyzed azide-alkyne cycloaddition reaction (Cu-AAC, "click" chemistry) and an alkyne-containing PNA building block to give Re-PNA. It was demonstrated that upon hybridisation with a complementary DNA strand (DNA), the position of the maxima and emission intensity for the hybrid Re-PNA·DNA remained mainly unchanged compared to those of the single strand Re-PNA. The rhenium-containing PNA oligomer Re-PNA could be then mediated in living cells where they have been shown to be non-toxic contrary to the general notion that organometallic compounds are usually unstable under physiological conditions and/or cytotoxic. Furthermore, Re-PNA could be detected in living cells using fluorescent microscopy.     

Kilogram-scale synthesis of carbon quantum dots for hydrogen evolution,sensing and bioimaging

A facile, low-cost, green, kilogram-scale synthesis of high quality CQDs were synthesized. The throughput of CQDs is 1.4975 kg in one pot and the as-prepared CQDs have a highly crystalline hexagonal structure with remarkable solubility, stability, and biocompatibility. It showed outstanding electrocatalytic activity, Fe³⁺ sensitivity and good biocompatibility.     

Kilogram-scale synthesis of carbon quantum dots for hydrogen evolution,sensing and bioimaging

The development of large-scale synthetic methods for high quality carbon quantum dots (CQDs) is fundamental to their applications. However, the macroscopic preparation and scale up synthetic of CQDs is still in its infancy. Here, we report a facile, green, kilogram-scale synthesis of high quality fluorescent CQDs derived from poplar leaves via a one-step hydrothermal method. Notably, the throughput of CQDs can reach a level up to as high as 1.4975 kg in one pot. The structure and properties of the as-prepared CQDs were assessed through TEM, XRD, XPS and various spectroscopic methods. The obtained high quality CQDs with a photoluminescent quantum yield of 10.64% showed remarkable stability in aqueous media, rich functional groups, high photostability, consistent photoluminescence within biological pH range and low cytotoxicity. On account of these good properties, we demonstrated the multifunctional application to electrocatalytic water splitting, Fe³⁺ sensing and bioimaging. It showed remarkable electrocatalytic activity, Fe³⁺ sensitivity and good biocompatibility. This study provides a green, facile, inexpensive and large-scale method for producing high quality CQDs, which provides application value for large-scale production of CQDs.     

Synthesis of water-dispersible fluorescent, radio-opaque, and paramagnetic CdS:Mn/ZnS quantum dots: a multifunctional probe for bioimaging

Ultra-small (3.1 nm) multifunctional CdS:Mn/ZnS core-shell semiconductor quantum dots (Qdots), which possess fluorescent, radio-opacity, and paramagnetic properties, have been shown here. To demonstrate in vivo bioimaging capability, a rat was administered endovascularly with Qdots conjugated with a TAT peptide. The labeling efficacy of these Qdots was demonstrated on the basis of the histological analysis of the microtome sliced brain tissue, clearly showing that TAT-conjugated Qdots stained brain blood vessels.     

Synthesis and application of fluorescent N,S co-doped carbon dots based on on-off-on quenching mode for the collaboration detection of iron ions and ascorbic acid

Nitrogen and sulfur co-doped carbon dots (NS-CDs) were synthesized by one-step solvothermal method using oleic acid as the medium, ʟ-cystine and citric acid monohydrate as precursors. Based on the “on-off-on” fluorescence quenching mode, a novel method was established for determination of both Fe³⁺ and ascorbic acid. The synthesized NS-CDs can be employed as fluorescence chemical sensors for the direct determination of free iron in the aqueous phase and indirect determination of the ascorbic acid contents of vitamin C tablets with linear ranges of 0–10 μM (n = 3) and 0–30 μM (n = 3), and detection limits of 36.6 and 102.5 nM, respectively. These results demonstrate that the proposed method exhibits good selectivity and linearity.     

Synthesis of carbon quantum dots for DNA labeling and its electrochemical,fluorescent and electrophoretic characterization

Nanoparticles as a progressively developing branch offer a tool for studying the interaction of carbon quantum dots (CQDs) with DNA. In this study, fluorescent CQDs were synthesized using citric acid covered with polyethylene glycol (PEG) as the source of carbon precursors. Furthermore, interactions between CQDs and DNA (double-stranded DNA and single-stranded DNA) were investigated by spectral methods, gel electrophoresis, and electrochemical analysis. Primarily, the fluorescent behavior of CQDs in the presence of DNA was monitored and major differences in the interaction of CQDs with tested single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA) were observed at different amounts of CQDs (µg mL^?1: 25, 50, 100, 250, 500). It was found that the interaction of ssDNA with CQDs had no significant influence on the CQDs fluorescence intensity measured at the excitation wavelengths of 280 nm, 350 nm, and 400 nm. However, in the presence of dsDNA, the fluorescence intensity of CQDs was significantly increased. Our results provide basic understanding of the interaction between CQDs and DNA. Such fabricated CQDs-DNA might be of great benefit for the emerging nanomaterials based biosensing methods.     

Sensing cyanide ion via fluorescent change and its application to the microfluidic system

We introduce a cyanide selective microfluidic platform, in which fluorescent chemodosimeter 1 displayed a selective green fluorescence upon the addition of cyanide. Our system was examined in aqueous solution, and the ‘OFF-ON’ type emission change can be monitored over 500 nm. In addition, colorimetric change was also observed upon the addition of cyanide. The practical use of the probe was demonstrated by its application to the detection of cyanide in the living cells.     

Perspectives of magnetic nature carbon dots in analytical chemistry: From separation to detection and bioimaging

Magnetic nature carbon dots (MNCDs) are fast growing materials with extremely unique physico-chemical properties and physiological ability to extend their applications from separation science to detection and bio-/magnetic resonance imaging applications. Recent studies have revealed that the MNCDs are significantly used as promising agents in analytical chemistry for the separation and identification of trace level target analytes. Further, the MNCDs have been used as probes for bioimaging of cells and magnetic resonance imaging (MRI) of tumors. Due to the lack of comprehensive reviews in this emerging field especially MNCDs applications in analytical chemistry, this review may provide quick guide and reference on the MNCDs-based analytical approaches for the separation and detection of trace level analytes, and bio- and MR- imaging of various cells. In this review article, we will summarize the synthetic approaches for the fabrication of MNCDs. The main part of this proposed review is devoted to the tremendous applications of MNCDs (Fe₃O₄@CDs, metal ion (Fe³⁺, Mn²⁺, Co²⁺ and Gd²⁺)-doped CDs, MnO₂@CDs) in analytical chemistry from separation science to detection and bio- and MR imaging. Finally, we will explore the challenges and future prospects of magneto fluorescent carbon dots in biomedical applications.     

P,N Codoped carbon dots as an efficient “off-on” fluorescent probe for lipoic acid detection and its cellular dual-color imaging

A facile single hydrothermal method was developed to synthetize P,N codoped carbon dots (P,N/CDs), which show strong and stable fluorescence, good water solubility, low toxicity and good biocompatibility. Hence, a novel and efficient “off-on” P,N/CDs fluorescent probe was developed for the highly sensitive detection of lipoic acid (LA) for the first time. The fluorescence of the P,N/CDs was quenched by Cu²⁺ forming a P,N/CDs-Cu²⁺ complex, which acted as the “off” process, but Cu²⁺ could be removed by LA, due to stronger chelating between LA and Cu²⁺, forming a more stable complex, which recovered the fluorescence of the P,N/CDs, in order to achieve the “on” process. Under optimal conditions, the concentration of LA and the increased fluorescence intensity of the P,N/CDs-Cu²⁺ complex displayed a good linear relationship within the range of 0.05–28 μM, with a detection limit (S/N = 3) of 0.02 μM. The established “off-on” fluorescent probe was successfully applied to the analysis of LA in urine samples. The average recoveries were in the range of 98.3–101.5%, with a relative standard deviations of less than 3.1%. In addition, the P,N/CDs were also successfully applied to cellular dual-color imaging of live T24 cells. The results show that the P,N/CDs have great application potential in clinical diagnosis, bioassay and bioimaging.

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双量子点纳米复合物NO比率荧光探针的合成与应用

通过静电吸附作用,合成了CdSe@SiO_2-CdTe双量子点的纳米复合物.一氧化氮(NO)与CdTe量子点表面Cd离子结合形成Cd-NO复合物,引起CdTe量子点荧光猝灭,而不影响CdSe量子点的荧光.当NO浓度在0.1~2.2μmol/L之间变化时,该探针荧光强度比值I_(603)/I_(532)符合线性关系(R=-0.995 4),从而实现对NO的定量检测.     

Synthesis and pore formation study of amorphous mesoporous aluminophosphates in the presence of citric acid

Amorphous mesoporous aluminophosphates (AlPO) with high thermal stability were synthesized from Al(NO3)3 and H3PO4 in the presence of citric acid (CA). The effects of different synthetic conditions, such as pH value, citric acid content, and calcined temperature, on the formation of the mesoporous structure of AlPO materials were investigated. The results of N2 adsorption/desorption and other characterization means demonstrate that the presence of a certain amount of citric acid in the synthetic mixture can result in the formation of uniform mesoporous AlPO materials in a wide pH range from 3.5 to 10. Thermal gravimetry and differential thermal analysis suggest that the existence of a moderate interaction between citric acid and the AlPO network might be a critical factor in obtaining uniform mesostructure. Therefore, as an organic additive, citric acid can be regarded as a template for the mesopore formation of AlPO materials.