Bioconjugation of luminescent silicon quantum dots to gadolinium ions for bioimaging applications

Luminescent imaging agents and MRI contrast agents are desirable components in the rational design of multifunctional nanoconstructs for biological imaging applications. Luminescent biocompatible silicon quantum dots (SiQDs) and gadolinium chelates can be applied for fluorescence microscopy and MRI, respectively. Here, we report the first synthesis of a nanocomplex incorporating SiQDs and gadolinium ions (Gd(3+)) for biological applications. The nanoconstruct is composed of a PEGylated micelle, with hydrophobic SiQDs in its core, covalently bound to DOTA-chelated Gd(3+). Dynamic light scattering reveals a radius of 85 nm for these nanoconstructs, which is consistent with the electron microscopy results depicting radii ranging from 25 to 60 nm. Cellular uptake of the probes verified that they maintain their optical properties within the intracellular environment. The magnetic resonance relaxivity of the nanoconstruct was 2.4 mM(-1) s(-1) (in terms of Gd(3+) concentration), calculated to be around 6000 mM(-1) s(-1) per nanoconstruct. These desirable optical and relaxivity properties of the newly developed probe open the door for use of SiQDs in future multimodal applications such as tumour imaging.     

Preparation of functionalized water-soluble photoluminescent carbon quantum dots from petroleum coke

Here we report a new strategy for preparation of water-soluble photoluminescent carbon quantum dots (CQDs) from petroleum coke. Petroleum coke was oxidized first in mixed concentrated H₂SO₄ and HNO₃, and then functionalized by hydrothermal ammonia treatment. The as-made CQDs and nitrogen-doped CQDs (N-CQDs) were characterized by UV–Vis absorption spectroscope, fluorescence spectroscope, transmission electron microscope, atomic force microscope, Raman spectrometer, X-ray powder diffractometer, X-ray photoelectron spectroscope and Fourier transform infrared spectrometer. The results show that the quantum yield of CQDs increases greatly from 8.7 to 15.8%, and the fluorescent lifetime increases from 3.86 to 6.11 ns after the hydrothermal treatment in ammonia. Moreover, the fluorescent color of N-CQDs can be tuned through the amount of doped nitrogen. Both CQDs and N-CQDs are water-soluble, and have uniform particle distribution, strong luminescence, and highly fluorescent sensitivity to pH in a range of 2.0–12.0. The uniform size distribution and nitrogen-doping of N-CQDs help to lead to high yield of radiative recombination, resulting in improved fluorescence properties. This work offers a simple pathway to produce high quality and enhanced photoluminescent CQDs from petroleum coke.     

Green and facile microwave assisted synthesis of (metal-free) N-doped carbon quantum dots for catalytic applications

Industrialization today leads to a significant increase in the environmental pollution, with number of phenols, pesticides, paints, solvents and other organic pollutants with potentially carcinogenic effect in natural resources. Investigation of some new semiconductor materials and their photocatalytic properties for removal of pollutants is a challenging work. However, limited usage of photoactive materials still requires the testing of new materials with photoactive properties. The current work introduces the swift and easy approach for synthesis of (metal–free) N–doped carbon quantum dots in water using microwave reactor. Synthesis was performed from glucose water solution by heating in microwave reactor for only 1 min, at low temperature and applied microwave power. The synthesized N–doped carbon quantum dots show remarkable photocatalytic activity for removal of toxic organic dye (Rose Bengal) under visible light irradiation. Almost 93% of the dye degradation is achieved after only 30 min of radiation. The uninspected result, that the pH of the medium has a significant effect on the performance of the synthesized material in the presence of organic dye, indicates that dots show dual behavior. In the neutral and basic conditions, they have the ability to degrade organic dye, whereas, by shifting the medium pH into acidic medium, they form a stable conjugate with Rose Bengal.     

Characterization and magnetic behavior of cobalt(II) and gadolinium(III) polyacrylates

The characterization and magnetic behavior of Co(II) and Gd(III) polyacrylates prepared by organic gelation synthesis have been studied. Gd(III)-polyacrylate shows a higher thermal stability due to stronger ionic interactions. IR spectra of both compounds reveal that carboxylate groups and water molecules exist in the coordination sphere with various forms of complexation. The samples are x-ray amorphous and have complex structures with the randomly distributing metal atoms along the PAA chain. The a.c. susceptibility measurements between 4.2 K and 250 K indicated a low temperature magnetic ordering. Annealing the samples at 160°C for 48 h result in the appearance of a spin-glass behavior in the in-phase and out-of-phase susceptibility curves. The presence of different sizes and shapes of clusters, however, precludes the determination of effective magnetic moments and Curie temperatures. © 1995 John Wiley & Sons, Inc.     

Green and continuous microflow synthesis of fluorescent carbon quantum dots for bio-imaging application

In this work, a simple, continuous and completely green method based on microflow technique is demonstrated for the synthesis of carbon quantum dots (CQDs) from diverse bio-based precursors. CQDs prepared from milk is illustrated as a case study to show the process feasibility. Crystalline fluorescent CQDs of 12.53% quantum yield and good stability are synthesized by the approach, even at 120°C. Systematic experiments further suggest their optical properties, bandgap energy, and fluorescence lifetime are closely related to the synthesis temperature. The maximum production rate of the CQDs was 51.1 mg/h at 180°C. Cytotoxicity and cellular imaging tests against 3T3 cells reveal the CQDs possess high biocompatibility, and can penetrate cell membranes and display bright fluorescence. The process versatility is investigated by expanding the precursor to watermelon juice, orange juice, and soy milk, indicating successful synthesis of small-sized CQDs of low cytotoxicity and strong photoluminescence by the technique.     

Fabrication of carboxyl functionalized CdSe quantum dots via ligands self-assembly and CdSe/epoxy fluorescence nanocomposites

A facile approach to introduce carboxyl groups onto the surface of CdSe quantum dots (QD) was achieved via oleic acid ligands self-assembly, and then CdSe quantum dots/epoxy fluorescence nanocomposites were successfully fabricated. The surface constitution of QD, the better dispersibility of QD in epoxy matrix, and the reactivity with epoxy of carboxyl groups functionalized QD were characterized by Fourier transform infrared (FT-IR), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC), respectively. As the result of surface modification, the carboxyl groups functionalized QD could be stably and homogenously dispersed in chloroform and acid anhydride cured epoxy matrix. The fresh fluorescence as well as the toughening behavior of the QD/epoxy nanocomposites was presented.     

Fabrication of amido group functionalized carbon quantum dots and its transparent luminescent epoxy matrix composites

Functional amido groups are modified onto the surface of carbon quantum dots (CQDs) in order to provide reactive groups. The modified CQDs are subsequently added into amine cured epoxy resin system. After curing reaction, transparent and luminescent composites are obtained. The modified CQDs are denoted as CQDs@NH₂, and composites studied in this article are denoted as CQDs@NH₂/epoxy. It is found that the dispersion of CQDs@NH₂ in epoxy matrix is effectively improved with the bridge of covalent bonding interface. As a result, the homogenously dispersed CQDs@NH₂ reduce light scattering. And more than double increased transparency and eightfold enhanced luminescence of CQDs@NH₂/epoxy are obtained compared with original CQDs@COONa/epoxy composites. This composite has potential for encapsulating materials in white light‐emitting diodes. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42667.     

Preparation of molecularly imprinted fluorescence sensor based on carbon quantum dots via precipitation polymerization for fluorescence detection of tetracycline

A facile and effective method was proposed to prepare the molecularly imprinted fluorescence sensor with carbon quantum dots, which were modified vinyl groups by acrylic acid on the surface. The obtained fluorescence composite material was investigated by transmission electron microscope and Fourier transform infrared spectra. After the experimental conditions were optimized, a linear range of 1.0–60 μmol L⁻¹ was obtained and the detection limit was 0.17 μmol L⁻¹. The novel fluorescence sensor can be successfully used to detect tetracycline in real samples. This study provides a convenient strategy for selective recognition and rapid detection of tetracycline in the complex environment.     

新型量子点的合成及荧光法测定痕量Cu(Ⅱ)

以巯基乙醇为修饰剂,合成了具有特殊光学性质的水溶性CdSe/CdS量子点。基于铜离子在pH 7.40的磷酸盐缓冲溶液中对该量子点的荧光具有较强的猝灭作用,建立了一种测定铜离子的新方法。在最佳实验条件下,体系的相对荧光强度与铜离子的浓度呈线性关系,线性范围为41.5~248.8μg/L,其线性回归方程为:ΔI=19.78 1.27c(μg/L),相关系数r=0.9921,检出限为8.5μg/L。     

Facile preparation of EDTA‐functionalized chitosan magnetic adsorbent for removal of Pb(II)

A novel magnetic adsorbent (EDTA /chitosan/ PMMS) was facilely prepared by reacting chitosan with EDTA anhydride in presence of PEI ‐ coated magnetic microspheres. The as‐synthesized EDTA/ chitosan /PMMS was characterized by XRD, SEM, TGA, FT‐IR , and VSM, and then employed in removal of heavy metals of Pb(II) from aqueous solution. The results of the batch adsorption experiments revealed that the adsorbents had extremely high uptake capacities for Pb(II) in the pH range of 2 to 5.5, and the adsorption kinetics for EDTA/ chitosan /PMMS was consistent with the pseudo – second ‐ order kinetic model. Moreover, its equilibrium data were fitted with the Langmuir isothermal model well, which indicated that the adsorption mechanism was a homogeneous monolayer chemisorptions process. The maximum adsorption capacity of EDTA/ chitosan /PMMS for Pb(II) was found to be 210 mg g ^{? 1} at pH 4 (30 ° C), and further reuse experiments results suggested that EDTA /chitosan/ PMMS could be a potential recyclable magnetic adsorbent in the practical wastewater treatment. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42384.     

Facile synthesis of functionalized porous carbon with three-dimensional interconnected pore structure for high volumetric performance supercapacitors

Functionalized porous carbon with three-dimensional (3D) interconnected pore structure has been successfully synthesized through direct heat-treatment of KOH-soaked soybeans. Benefiting from heteroatoms (N, O) doping, interconnected porous carbon framework with high surface area as well as high packing density (up to 1.1 g cm⁻³), the as-obtained porous carbon material exhibits high volumetric capacitance of 468 F cm⁻³, good rate capability and excellent cycling stability (91% of capacitance retention after 10,000 cycles) in 6 M KOH electolyte. More importantly, the as-assembled symmetric supercapacitor delivers high volumetric energy density of 28.6 Wh L⁻¹ in 1 M Na₂SO₄ aqueous solution.     

Facile and efficient synthesis of magnetic fluorescent nanocomposites based on carbon nanotubes

Multifunctional nanomaterials composed of magnetic and fluorescent nanoparticles have been one of the most extensive pursuits because of the potential application in bio-research. In this paper, we demonstrated an efficient method by coupling CdSe/CdS/ZnS quantum dots (QDs) with Fe₃O₄ magnetic nanoparticles(MNPs) while functionalized multiwall carbon nanotubes (f-MWCNTs) were used as matrix to synthesize a kind of magnetic fluorescent nanocomposite. Compared with other matrix materials, carbon nanotubes have the advantages of high surface areas and good biocompatibility. The incorporation of f-MWCNTs supplies plenty of nucleation sites for the preferential growth of Fe₃O₄ nanoparticles, avoiding the agglomeration phenomenon of Fe₃O₄ MNPs in traditional co-precipitation method. Moreover, the un-reacted functional groups of f-MCNTs can further adsorb biological species and drugs, averting the decline of fluorescent intensity caused by the modification of biological species and drugs. The synthetic product maintains the unique properties of rapid magnetic response and efficient fluorescence, which shows a broad application prospect in fluorescent labeling, biological imaging, cell tracking and drug delivery.     

Nanoreactor-confined synthesis and separation of yellow-luminescent graphene quantum dots with a recyclable SBA-15 template and their application for Fe(III) sensing

Graphene quantum dots (GQDs) have inspired growing research efforts. Although continuous progresses have been achieved in the syntheses of diverse GQDs, it is still a challenge in size-controllable and high-yield preparation of well dispersed GQDs via simple routes. Herein, we present a top-down synthesis of GQDs by using a SBA-15 template as a nanoreactor via a HNO₃ vapor cutting strategy. With the recyclable ordered mesoporous SBA-15 template and a silica grid, a high-yield (48%) preparation as well as a facile separation of yellow-luminescent GQDs have been achieved. The obtained GQDs containing abundant oxygen-containing groups (ca. 30% for oxygen content) showed a narrow size distribution (2.5–5.2 nm), good water solubility, good photostability and high selectivity for Fe(III) sensing in tap water with satisfying recovery. Further experiments indicated that Cu(II), Co(II), Mn(II), Ni(II) could also quench the fluorescence of the as-prepared GQD after its surface states being adjusted, which might presage more possible applications of this material.     

Facile one-step synthesis of cerium oxide-carbon quantum dots/RGO nanohybrid catalyst and its enhanced photocatalytic activity

Improvement in the catalytic activity of nanostructured cerium oxides (CeOx) was attained by incorporating in-situ generated heteroatom-(N and S)-doped carbon quantum dots/reduced graphene oxide (HDCQD@RGO) nanohybrid catalyst for the degradation of organic pollutants. The CeOx-HDCQD@RGO nanohybrid catalyst was synthesized by a facile, one-pot hydrothermal eco-friendly process. The HDCQD plays a vital role to improve the interaction between CeOx and RGO and function as a sensitizer for the electron-transfer process with CeOx. The size of CeOx and HDCQD are 10 nm and 5 nm, respectively. The nanostructured CeOx possesses multiple oxygen vacancies; this helps to generate the active oxygen and hydroxyl radicals. The active hydroxyl radical generation by the photocatalytic process with the help of nanostructured CeOx results in the improved photodegradation of organic pollutants. In addition, the prepared CeOx-HDCQD@RGO nanohybrid catalyst exhibits an improved water oxidation reaction. The CeOx-HDCQD@RGO nanohybrid performs as an excellent bifunctional catalyst for energy and environmental applications. The method presented here is a facile and environmentally friendly, scalable synthesis of the highly efficient catalyst.     

Facile synthesis of tubular magnetic carbon nanofibers by hypercrosslinked polymer design for microwave adsorption

In this study, a simple and efficient method for fabrication of tubular magnetic carbon nanofibers (TMCF) has been developed. Firstly, tubular polymer nanofiber precursors are synthesized by confined self-condensation method. After carbonization of polymer and in situ transformation of FeCl₃ at high temperature, TMCF loaded with Fe nanoparticles is obtained. It has been found that carbonization temperature has significant effects on conductivity, specific surface area, pore volume, defects number in carbon component, and magnetic content of TMCF. The influence of composition, structure, and filler content on microwave absorption properties is revealed. Meanwhile, the microwave absorption mechanism has been analyzed in depth, which benefits from the designed unique structure. The TMCF obtained at 700°C exhibited best performance with the filler content of 15%. The minimum reflection loss is −47.33 dB@2.2 mm, the effective absorption bandwidth is 6.5 GHz (RL < 10 dB), and the matching frequency is 14.1 GHz. The obtained TMCF is lightweight and possess excellent microwave absorption ability, which can be widely used as highly efficient microwave absorber.     

Fabrication of polymer‐gadolinium (III) complex nanomicelle from poly(ethylene glycol)‐polysuccinimide conjugate and diethylenetriaminetetraacetic acid‐gadolinium as magnetic resonance imaging contrast agents

Methoxy poly (ethylene glycol)‐graft‐α, β‐poly (aspartic acid) derivatives (mPEG‐g‐PAA‐N₃) were synthesized by sequential ring‐opening reaction of polysuccinimide (PSI) with mPEG‐NH₂ (MW: 2000 Da), and 1‐azido‐3‐aminopropane, respectively. Then N²‐(hex‐5‐yne)‐diethylenetriamine‐tetra‐t‐butylacetate (DTTA‐der) was conjugated to mPEG‐g‐PAA‐N₃ by click cycloaddition. After deprotection of carboxylic groups, mPEG‐g‐PAA‐DTTA macromolecular ligands were obtained. MPEG‐g‐PAA‐(DTTA‐Gd) complex nanomicelles were fabricated from mPEG‐g‐PAA‐DTTA and Gadolinium chloride. The formation of nanomicelles was confirmed by fluorescence spectrophotoscopy and particle size measurements. It was found that all the nanomicelles showed spherical shapes with core‐shell structures and narrow size distributions. Their sizes ranged from 50 to 80 nm, suggesting their passive targeting potential to tumor tissue. With the increase of graft degree (GD) of mPEG, the sizes of mPEG‐g‐PAA‐(DTTA‐Gd) nanomicelles showed a tendency to decrease. Compared with gadopentetate dimeglumine (Gd‐DTPA), mPEG‐g‐PAA‐(DTTA‐Gd) nanomicelles showed essential decreased cytotoxicity to KB cell line and enhanced T₁‐weighted signal intensity, especially at low concentration of gadolinium (III), suggesting their great potentials as magnetic resonance imaging contrast agents. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

水溶性碳量子点的制备及防伪应用

以壳聚糖为原料,采用水热法一步制备水溶性的荧光碳量子点（CQDs）,考察反应条件（壳聚糖质量浓度、温度和时间）对CQDs产物表面官能团和产率的影响,采用TEM、FTIR、XRD、UV-Vis和PL等技术对其形貌、结构和性能进行了表征,并探究其在防伪领域的应用。结果表明,当壳聚糖质量浓度为10 g/L,温度为180 ℃,时间为12 h时,制得的CQDs结构完整且产率较高;微观表现为球状纳米颗粒,直径约为36.2 nm,表面伴有羟基和氨基官能团;制得的CQDs在293和330 nm处均有吸收峰,表现为蓝色荧光,荧光量子产率约为39.8%。将其配制成墨水后,结合喷墨印刷,在自然光和紫外光下可有效实现加密信息的“显”和“隐”,具有较好的防伪效果。     

Synthesis of carbon quantum dots to fabricate ultraviolet-shielding poly(vinylidene fluoride) films

The paper presents a simple and effective approach to fabricating a poly(vinylidene fluoride) (PVDF) film with excellent ultraviolet (UV) shielding performance. Carbon quantum dots (CQDs) with a highly UV absorbing property were made via a hydrothermal reaction and were then added to a poly(vinyl alcohol) (PVA) solution. The PVDF membrane pretreated with an alkaline solution was immersed in the prepared CQD/PVA solution to coat a UV-shielding layer on the film surface. Fourier transform infrared spectroscopy, X-ray photoelectron spectrometry, X-ray diffraction, transmission electron microscopy, and UV–visible spectrophotometry were applied to study the structure, morphology, and optical performance of the CQD particles. The stability and UV-shielding performance of the obtained PVDF-OH@CQDs/PVA composite film were further investigated. The results showed that the CQD particles with diameter of 18 nm could be well dispersed in solution. Additionally, the CQDs had fairly high UV absorbance, and the PVDF-OH@CQDs/PVA composite film could shield the UV light completely. The method described in this paper is a promising one for fabricating UV-shielding composite films. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47555.     

Self-healing interfaces of poly(methyl methacrylate) reinforced with carbon fibers decorated with carbon quantum dots

Fiber-polymer matrix interfacial debonding is often observed when mechanical loads are applied to fiber reinforced polymer composites. These defects usually end-up leading to a catastrophic fracture of the composites. In this work, carbon quantum dots (CDs) were incorporated on the surface of carbon fibers (CF), and poly(methyl methacrylate) (PMMA) composites with these modified fibers were able to restore their original properties after been previously damaged. To this end, CDs were synthesized and used to decorate the surface of CF. These decorated CF were then incorporated into PMMA by using a high intensity mixer. The prepared composites were submitted to dynamic mechanical, three-point bending and self-healing tests. Fluorescent CDs with diameters of 10 nm and functional groups, such as amine and carboxylic groups were successfully synthesized by the microwave pyrolysis method. The deposition of CDs on the surface of CF was evaluated and quantified by UV–vis spectroscopy and 1.2 wt.% of CDs on CF was determined. Composites with different surface treatments (including the presence of CD) did not show significant differences in strength, stiffness and damping, suggesting that the surface treatments on CF did not lead to major changes in the degree of interfacial interaction. Self-healing tests showed that damaged composites with CD decorated CF were able to restore their original properties, while no self-healing effect was noted in composites with no CD on CF. The observed self-healing behavior between PMMA and CF decorated with CD is due to the interactions between chemical groups on the surface of the CD and PMMA. Thus, damages related to fiber-matrix interfacial detachments can be repaired through reversible interactions based on CD.     

Easy synthesis of highly fluorescent carbon quantum dots from gelatin and their luminescent properties and applications

A simple approach for the synthesis of fluorescent carbon dots (CQDs) has been developed by the hydrothermal treatment of gelatin in the presence only pure water. The as-synthesized CQDs were found to emit blue photoluminescence (PL) with a maximum quantum yield of 31.6%. Meanwhile, the CQDs exhibit excitation-dependent, pH-sensitive and up-converted PL properties. Importantly, these CQDs are demonstrated to be excellent bioimaging agents and fluorescent ink due to their stable emission, well dispersibility, low toxicity, long emission life time, and good compatibility with cells and macromolecules.