Excitation-dependent Fluorescence Research Articles

Green synthesis of fluorescent carbon dots from canon ball fruit for sensitive detection of Fe3+ and catalytic reduction of textile dyes

In this work, a simple, sustainable and economically feasible approach has been reported to synthesis Carbon Dots (CDs) by taking Canon Ball (CB) fruit as a bio-mass precursor. The properties of the synthesized CDs were analysed using various characterization techniques such as TEM, FTIR, PSA, Raman, UV–Visible and Fluorescence spectroscopy. The CDs have particle size of 11.2 nm, showed blue emission when exposing to UV light at wavelength of 365 nm and excitation dependent fluorescence behaviour with appreciable quantum yield of 7.01%. The synthesized CDs have excellent stability on exposure to different environments like pH, ionic concentrations and storage time. Further, it served as a probe for sensing Fe3+ ions selectively among different metal ions investigated. The Limit of Detection (LOD) was found to be 0.071 μM in the dynamic range of 0.6–3.3 μM of ferric ion concentration. Additionally, the CDs showed excellent catalytic activity in the treatment of two harmful textile dyes Azure B (AB) and Toluidine Blue (TB) via catalytic reduction with the assistance of NaBH4.

Cost-effective route to nanodiamonds from low-rank coal and their fluorescent & dielectric characteristics

The synthesis of nanodiamonds from abundant and inexpensive precursors has recently piqued the curiosity of researchers. It has the potential to significantly reduce the cost of nanodiamonds and open up a plethora of new applications. In this work, fluorescent nanodiamonds with smaller particle sizes with rich surface functionality are synthesized from low-grade coal lignite by employing a facile acidic oxidation and ultrasonication approach. The extracted nanodiamond particles are hydrophilic and display high excitation-dependent fluorescence in the aqueous medium. The excitation-dependent fluorescence can be ascribed to the collaboration and competition of the OH and COOH functional groups. The as-synthesized nanodiamonds also show good dielectric permittivity and ac conductivity over a wide frequency range at room temperature. The present research opens up the possibility of mass production of nanodiamonds on the industrial scale from a low-cost precursor.

Tunable fluorescent carbon dots from biowaste as fluorescence ink and imaging human normal and cancer cells

Growing global biowaste and its environmental issues challenge the need for converting biowastes into a beneficial product. Among the biowaste, here kiwi fruit (Actinidia Deliciosa) peels are considered for the preparation of carbon dots (CDs). Using a green one-pot hydrothermal-carbonization method, kiwi fruit peels were effectively converted into valuable kiwi fruit peel carbon dots (KFP-CDs). The morphology, physio-chemical and optical properties of as-synthesized KFP-CDs were analyzed using various analytical techniques such as X-ray powder diffraction, Raman spectroscopy, attenuated total reflection-Fourier transform infrared spectroscopy, field emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, Ultraviolet–visible, and fluorescence spectroscopy. The KFP-CDs revealed a homogeneous spherical shape, monodispersed with an average size of 5 nm. The characterization confirms that KFP-CDs have functional groups such as –CN, –COOH, and –OH which are responsible for the easy dispersion of KFP-CDs in aqueous media. Without any preprocessing, KFP-CDs exhibit strong fluorescence upon exposure to UV light. Further, KFP-CDs displayed excitation-dependent fluorescence emission with a good quantum yield of about 18%. Thus by considering the excellent properties of KFP-CDs, KFP-CDs were used as fluorescent ink for drawing and writing without any capping/passivation agent. The pictures and words were instantaneously viewed when exposed to UV light. In addition, KFP-CDs tested for cell imaging in four human cell lines (normal and cancer cells) bestowed excellent biocompatibility and low cytotoxicity, which is important for the safe and long-term development of cellular imaging. The findings imply that KFP-CDs can be utilized as a cell labeling agent for mesenchymal stem cells, breast cancer, and thyroid cancer cells in vitro imaging. Thus, these observations revealed that investigating sustainable resource-based CDs can open up new avenues for tackling environmental issues.

Carbon dots derived from Beta vulgaris: evaluation of its potential as antioxidant and anticancer agent

Carbon dots (CDs) endowed with outstanding physico-chemical characteristics expeditiously garnered tremendous popularity in the scientific community. CDs can be synthesized from a variety of natural resources and can replace metal semiconductor quantum dots in the range of applications such as bio-imaging, sensing and catalysis. Herein, CDs are green synthesized from Beta vulgaris via a single step hydrothermal approach (b-CDs). The synthesized carbon dots are characterized using UV–visible spectrophotometry, Fluorescence spectroscopy, High resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FT-IR), x-ray diffraction technique (XRD) and Raman spectroscopy. The b-CDs hence developed exhibited the signature ‘excitation-dependent fluorescence emission’ with its most intense emission in the green region. The quantum yield for the b-CDs obtained by this synthetic approach evinced an appreciable value of 11.6%. The antioxidant property of b-CDs are evaluated using 2, 2-diphenyl-1-picrylhydrazyl (DPPH) assay to obtain a maximum scavenging activity of 94.5% at a concentration of 1000 μg ml−1 and its underlying mechanisms are illustrated. The blood compatibility of b-CDs are assessed using haemolysis assay and the cytotoxicity evaluated using MTT assay shows significant cell growth-inhibition against the human breast cancer (MCF-7) and hepatocellular carcinoma (HepG2) cell lines. This succinct study demonstrates the inherent therapeutic potential of biocompatible carbon dots.

Carbon nanodot\u2013based electrogenerated chemiluminescence biosensor for miRNA-21 detection

A simple carbon nanodot–based electrogenerated chemiluminescence biosensor is described for sensitive and selective detection of microRNA-21 (miRNA-21), a biomarker of several pathologies including cardiovascular diseases (CVDs). The photoluminescent carbon nanodots (CNDs) were obtained using a new synthesis method, simply by treating tiger nut milk in a microwave reactor. The synthesis is environmentally friendly, simple, and efficient. The optical properties and morphological characteristics of the CNDs were exhaustively investigated, confirming that they have oxygen and nitrogen functional groups on their surfaces and exhibit excitation-dependent fluorescence emission, as well as photostability. They act as co-reactant agents in the anodic electrochemiluminescence (ECL) of [Ru(bpy)3]2+, producing different signals for the probe (single-stranded DNA) and the hybridized target (double-stranded DNA). These results paved the way for the development of a sensitive ECL biosensor for the detection of miRNA-21. This was developed by immobilization of a thiolated oligonucleotide, fully complementary to the miRNA-21 sequence, on the disposable gold electrode. The target miRNA-21 was hybridized with the probe on the electrode surface, and the hybridization was detected by the enhancement of the [Ru(bpy)3]2+/DNA ECL signal using CNDs. The biosensor shows a linear response to miRNA-21 concentration up to 100.0 pM with a detection limit of 0.721 fM. The method does not require complex labeling steps, and has a rapid response. It was successfully used to detect miRNA-21 directly in serum samples from heart failure patients without previous RNA extraction neither amplification process.Graphical abstract

Synthesis, solution and solid-state fluorescence of nitrogen self-doped carbon dots derived from Chlorella pyrenoidosa

In this work, we report a simple and green approach for the synthesis of nitrogen-doped carbon dots from Chlorella pyrenoidosa, hereafter referred to as CP-CDs, via microwave-assisted hydrothermal carbonization without any additives. The effects of temperature (170–210 °C) and time (1–3 h) on the structure, functional groups, optical properties and formation route of the CP-CDs were assessed in detail. FTIR, XPS, and XRD results showed that high temperatures promoted the nitrogen doping level, resulting in good fluorescence intensity and high quantum yields (QYs). As the reaction temperature increased from 170 °C to 210 °C, the amount of nitrogen doped into the CP-CDs increased significantly from 4.1% to 11.9% and the absolute QY improved from 1.79% to 2.31%. The CP-CDs solutions exhibited excitation-dependent blue fluorescence from 360 to 527 nm with the excitation from 280 to 460 nm. The optimal preparation temperature and time for CP-CDs aqueous solution were 210 °C and 2 h, respectively. The solid-state CP-CDs without any further processing exhibited self-quenching resistant performance. The obtained CP-CDs as fluorescence inks could be used in security printing.

Green synthesis of a novel carbon dots from red Korean ginseng and its application for Fe2+ sensing and preparation of nanocatalyst

In the current study, we have synthesized a novel spherically shaped, water-soluble and green carbon dots (CDs, 2 nm) from a renewable source, aqueous root extract of red Korean ginseng (RKG) via highly efficient microwave irradiation method. The as-synthesized CDs showed excitation-dependent fluorescence emission behavior and therefore, applied for the selective detection of Fe2+ ions via fluorescent quenching method with the detection limit of 0.27 μM. We also investigated the effect of pH and high salt concentration on the fluorescent intensity of CDs. After that, silver nanoparticles (AgNPs, 15 nm) were synthesized using those CDs without adding additional reducing and stabilizing agents. The as-synthesized AgNPs showed high catalytic efficiency in reducing/degrading organic dyes, such as rhodamine B (RhB), methyl orange (MO) and congo red (CR) in presence of NaBH4. The pseudo first order rate constants for the reduction of RhB, MO and CR at room temperature were 0.27, 0.26 and 0.18 min−1 respectively. The synthesized AgNPs were also tested for the catalytic reduction of carcinogenic Cr (VI) to non-toxic Cr (III) in presence of formic acid, and ∼85% reduction was obtained within 15 min. All these results clearly demonstrated that the novel green CDs and the CD-derived AgNPs have multiple applications in the field of sensing and catalysis.

One-pot alkali cutting-assisted synthesis of fluorescence tunable amino-functionalized graphene quantum dots as a multifunctional nanosensor for sensing of pH and tannic acid

Herein, a one-pot alkali cutting-assisted synthesis approach has been developed to gain fluorescence (FL) tunable amino functionalized GQDs (NH2-GQDs), which exhibit concentration- and excitation-dependent FL behaviors, due to the self-assembled J-type aggregation effect and different electronic transitions governed by graphene basal plane and functional groups. While NH2-GQDs possess brighter FL emission than pristine GQDs, owning to the functionalization of amino groups with strong electron withdrawing ability. Particularly, the pH-dependent FL behavior of NH2-GQDs further reflects the FL emission mechanism originated from the intrinsic zigzag sites and introduced amino and carboxylic groups, which is available for pH sensing. Moreover, the NH2-GQDs also show a FL quenching upon reaction with tannic acid (TA), resulting in the construction of a FL turn-off TA sensing platform. A good linear relationship is obtained between logarithm of FL intensity (log F) and TA concentration in a linear dynamic range of 1–40 μM and a limit of detection of 43.3 nM (3σ/s, n = 9) is achieved, with a precision of 0.08% RSD at a concentration level of 5 μM (n = 9). This work features a simple and direct approach to acquire multifunctional nanosensor, providing great potential for further applications in chem/biosensing.

Curauá-derived carbon dots: Fluorescent probes for effective Fe(III) ion detection, cellular labeling and bioimaging

This study reports the generation of curauá-derived carbon dots (C-dots) and their suitability for Fe(III) detection, bioimaging and FACS analysis. C-dots were generated from curauá (Ananas erectifolius) fibers by a facile one-step hydrothermal approach. They exhibited graphite-like structure with a mean diameter of 2.4 nm, high water solubility, high levels of carboxyl and hydroxyl functional groups, excitation-dependent multicolor fluorescence emission (in the range 450 nm - 560 nm) and superior photostability. C-dots were highly selective and effective for the detection of ferric Fe(III) ion in an aqueous medium with a detection limit of 0.77 μM in the linear range of 0–30 μM, a value much lower than the guideline limits proposed by the World Health Organization (WHO). In biological cell systems, C-dots were very well tolerated by B16F1 mouse melanoma and J774.A1 mouse macrophages cell lines, both of which effectively internalized C-dots in their cytoplasmic compartment. Finally, C-dots were effective probes for long-term live cell imaging experiments and multi-channel flow cytometry analysis. Collectively, our findings demonstrate that curauá-derived C-dots serve as versatile and effective natural products for Fe(III) ion sensing, labeling and bioimaging of various cell types. This study adds novel C-dots to the library of carbon-based probes and paves the way towards a sustainable conversion of a most abundant biomass waste into value-added products.

Three distinct concentration-dependent chromophores of non-traditional intrinsic luminescence: The mechanism and special properties

Non-traditional intrinsic luminescence (NTIL) have presented many unique properties, which are quite different from traditional fluorescent materials. In this work, using non-aromatic amines, we found three distinct fluorescent peaks at 400 nm, 440 nm and 500 nm, respectively, in a concentration increasing process. The direct proofs obtained from NMR and other techniques suggested that these peaks might originate from different concentration-dependent aggregates. On the other hand, our results well explained the weird phenomena that NTIL systems presented the excitation-dependent fluorescence (EDF) or excitation-independent fluorescence (EIF) in various cases. We proposed a strategy to prepare fluorescent systems with unique property of tunable emission and controllable EDF or EIF, which would be useful in multi-color imaging applications.

Metal Cation-Responsive and Excitation-Dependent Nontraditional Multicolor Fluorescent Hydrogels for Multidimensional Information Encryption.

Fluorescent polymeric hydrogels especially multicolor fluorescent polymeric hydrogels (MFPHs) have important applications in information storage, encryption, and encoding. MFPHs are generally prepared by incorporating multiple traditional fluorescent materials into hydrogels. In recent years, nontraditional luminescent polymers without any traditional π-conjugated chromophores have received increasing attention. Here, we report a novel type of nontraditional MFPHs prepared by in situ polymerization of acrylamide (AAm) in the presence of poly(itaconic acid) (PITAc). The hydrogen-bonded mechanically strong PAAm/PITAc hydrogels show strong intrinsic fluorescence, and the fluorescence emission is excitation-dependent and metal cation-responsive. More impressively, the hydrogels treated with metal cations also possess excitation-dependent fluorescence. We developed a multi-ion inkjet printing (MIIP) technique to print texts or designed patterns onto the hydrogel surface using different metal cation solutions as inks, and then variable texts or patterns appear under the irradiation of UV, violet, and blue lights. Patterns can be further changed by selective printing, erasing, or reprinting on some regions. Therefore, multidimensional information encryption is achieved. This work provides a new strategy for preparing MFPHs for wide applications.

Dramatically Enhanced and Red-shifted Photoluminescence Achieved by Introducing an Electron-withdrawing Group into a Non-traditional Luminescent Small Organic Compound.

Small organic compounds without any traditional fluorescent chromophores are generally non-emissive, and only very few are reported to emit weak blue fluorescence. Here we synthesized a non-traditional luminescent small organic compound N-(2,2,2-trifluoroethyl)acrylamide (TFAM) with dramatically enhanced and red-shifted photoluminescence by introducing a strong electron-withdrawing group into acrylamide (AM). Very impressively, TFAM emits cyan (472 nm) and yellow-green (560 nm) fluorescence in solutions and solid state, respectively. TFAM also shows aggregation-induced emission enhancement (AIEE) and excitation-dependent fluorescence (EDF) characteristics, as well as temperature and metal cations-responsive fluorescence. Theoretical calculations show that the introduction of electron-withdrawing group leads to a lower energy gap between the HOMO-LUMO energy levels in TFAM than in AM. And strong cooperative hydrogen bonds are formed in TFAM molecules, resulting in rigidification of molecular conformations. The study provides a strategy for preparing non-traditional luminescent compounds with enhanced and red-shifted photoluminescence.

Microwave-Assisted Synthesis of Carbon Dot - Iron Oxide Nanoparticles for Fluorescence Imaging and Therapy.

Fluorescence microscopy is commonly used to image specific parts of a biological system, and is applicable for early diagnosis of cancer. Current fluorescent probes, such as organic dyes and quantum dots, suffer from poor solubility and high toxicity, respectively, demonstrating a need for a colloidal stable and non-toxic fluorescent probe. Here we present an iron oxide and carbon dot (CD) based nanoparticle (CNPCP) that displays optical properties similar to those of conventional fluorescent probe and also exhibits good biocompatibility. Fluorescent CDs were synthesized from glucosamine onto chitosan – polyethylene glycol (PEG) graft copolymer using microwave irradiation. These NPs were monodispersed in aqueous environments and displayed excitation-dependent fluorescence; they demonstrated good size stability and fluorescence intensity in biological media. In vitro evaluation of CNP as fluorescent probes in cancer cell lines showed that these NPs caused little toxicity, and allowed fast and quantitative imaging. Model therapeutic doxorubicin (DOX) was conjugated onto the NPs (CNPCP-DOX) to demonstrate the multifunctionality of the NPs, and in vitro studies showed that CNPCP-DOX was able to kill cancer cells in a dose dependent manner. These results indicate the potential of using CNPCPs as fluorescent probes capable of delivering chemotherapeutics.

A Highly Sensitive and Selective Probe for the Colorimetric Detection of Mn(II) Based on the Antioxidative Selenium and Nitrogen Co-Doped Carbon Quantum Dots and ABTS•.

Herein, selenium and nitrogen co-doped carbon quantum dots (Se/N-CQDs) were hydrothermally synthesized by using citric acid, histidine, and sodium selenite, which had sp3 and sp2 hybridized carbon atoms and showed excitation-dependent fluorescence behavior. Furthermore, due to the redox reaction of ABTS•+ and Se/N-CQDs, Se/N-CQDs had the excellent antioxidant capacity that it was demonstrated by scavenging ABTS•+ with the fading of blue. Based on the synergistic effect of Se/N-CQDs and Mn(II) on ABTS•+, Se/N-CQDs and ABTS•+, as a stable, sensitive, selective, and reproducible colorimetric sensor, was applied to the detection of Mn(II) with a detection limit of 1.69 μM and a linear range of 0 to 142.90 μM. More importantly, the probe was successfully applied to detecting Mn(II) in tap water, illustrating that it could be a promising tool for Mn(II) detection in water environments.

Facile synthesis of nitrogen doped carbon dots from waste biomass: Potential optical and biomedical applications

Abstract We report a facile, one-pot hydrothermal synthesis of surface passivated, nitrogen doped carbon dots (N-CDs) from jackfruit peel and tamarind peel precursors. The synthesized N-CDs emit strong excitation dependent fluorescence in the blue region. The samples illustrate exciting quantum confined optical properties. Graphitization of N-CDs is identified by X-ray diffraction. Surface functionalization is confirmed by FT-IR studies whereas nitrogen doping by X-ray photoelectron spectroscopy. The average size of synthesized N-CDs estimated from transmission electron images is 6.4 nm and 5.3 nm for jackfruit peel and tamarind peel precursors respectively. Quantum yield of N-CDs from jackfruit peel (13.04%) is higher than that from tamarind peel (6.13%). Appreciable anti-cancerous activity of the as-prepared carbon dots could be detected with DLA tumour cells extracted from mice. The work proposes an innovative design to yield blue luminescent carbon dots with high quantum yield from biowaste, providing a green and sustainable alternative to traditional carbon sources.

A facile green synthesis of functionalized carbon quantum dots as fluorescent probes for a highly selective and sensitive detection of Fe3+ ions

In this study, we have reported an economical, easy, greener and non-toxic synthesis route of water soluble carbon quantum dots (CQDs) through hydrothermal treatment using gelatin as precursor. Under the UV lamp of wavelength 365 nm, the as-prepared CQDs exhibit strong blue fluorescence along with CIE coordinate index of (0.17, 0.14) and possess a quantum yield of 22.7% with rhodamine B as standard. The morphology of as-synthesized CQDs as investigated by TEM measurement confirmed their spherical shape and also revealed that their sizes varied in the scale of 0.5–5 nm. Furthermore, the CQDs showed excitation dependent fluorescence emission behaviour in range of 280 nm to 420 nm as a result of quantum confinement effect. Apart from this, in CQDs solution, the addition of Fe3+ ion lead to fluorescence quenching effect. These results revealed that the as-synthesized CQDs have a sensitive response towards the Fe3+ ion. The calculated limit of detection (LOD) is 0.2 μM with correlation coefficient R2 = 0.996 in the concentration range 0 to 50 μM. More remarkably, the application of CQDs for monitoring the trace level of Fe3+ ion in tap water yielded acceptable recoveries (103.33%-105%). Therefore, this work provides a novel additional fluorescent probe for the detection of Fe3+ ion in real world.

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 32.7µM.

Photoluminescent chiral carbon dots derived from glutamine

The integration of luminescence and chirality in carbon dots (CDs) encourages candidates to explore novel functions and applications of CDs, however, the preparation of chiral CDs is very limited. Herein, we report a hydrothermal method to fabricate chiral CDs by utilizing amino acid enantiomers as the precursors. LGln-CDs or DGln-CDs with uniform size of 3–4 nm show excitation-dependent blue fluorescence in solutions. Circular dichroism measurement confirms the opposite optical rotation of chiral CDs in the region from 200 nm to 300 nm, and the signals can be regulated by concentrations of CDs solution. Time-dependent density functional calculation reveals that polypeptides may exist on the surface of CDs due to the polycondensation of L/DGln at high temperature, and the optical activity of CDs originates from the stacking of neighboring carbonyl groups. The facile synthetic methodology proposed will provide potential opportunities for the preparation and application of chiral and chiroptical CDs-based materials.

Significantly Red-Shifted Emissions of Nonconventional AIE Polymers Containing Zwitterionic Components.

Nonconventional luminescence polymers without any aromatic structures have attracted great interest from researchers due to their special structure and excellent biocompatibility. However, these materials mostly emit in the blue or green region, in which preparation of materials with long-wavelength (especially near-infrared) emission is still a great challenge. In this work, it is found that 2-(dimethyl amino) ethyl methacrylate (DMA) and itaconic anhydride (ITA) undergo a ring-opening reaction at room temperature, and subsequently generate zwitterionic compound (IDMA). Based on the clustering-triggered emission (CTE) mechanism, ionic bond can effectively promote the isolated electron-rich chromophores to form new emissive clusters with extended electron delocalization. Herein, two oligomers (P1 and P2) with different fluorescence emissions by controlling the concentration of zwitterionic monomers before polymerization are synthesized. It is worth noting that the maximum emission wavelength of P2 at high concentration is up to 712 nm, which is very rare in previous reports. In addition, the resulting oligomer (P2) shows typical aggregation-enhanced emission (AEE), excitation-dependent fluorescence, temperature-sensitive emission, and solvatochromism. The cytotoxicity assay demonstrates that P2 was low toxic to Huh7 and LM3 cells, and suitable for cell imaging. This research provides the possibility for rational molecular design and the feasibility of luminescence regulation.

Blue-emitting carbon quantum dots: Ultrafast microwave synthesis, purification and strong fluorescence in organic solvents

The impurity of unpurified carbon quantum dots (CQDs) severely limits their application. In this paper, CQDs synthesized by ultrafast microwave hydrothermal method from L-cystine were purified by both dialysis and direct phase-transfer. The as-obtained CQDs in basic aqueous reaction mixture show excitation-independent fluorescence around 505 nm with a maximum excitation at 421 nm and pH-responsive emission intensity. However, after purification by dialysis the CQDs display excitation-dependent blue fluorescence from 410 to 500 nm with respect to the excitation from 310 to 430 nm. Particularly, the CQDs purified by direct phase-transfer into various organic solvents show two strong blue fluorescence peaks respectively focusing on 422–434 nm and 400–410 nm with a maximum excitation at 370–372 nm. The quantum yield of the CQDs decreases to 45.1% after a purification by dialysis from the original 82.7%, while it decreases to 57.5% after a purification of phase-transfer. The CQDs extracted in organic solvents are demonstrated to be pure small crystalline-carbon nanoparticles with chemically surface-grafted groups, while the dialyzed CQDs will physically adsorb additional L-cystine, sodium and by-product nitrate ions. The difference of surface state and solvent environment of these CQDs shall contribute to the different fluorescence property. Such strong luminescent, pure CQDs in organic solvents should have obvious advantages in further applications.