Hydrophobic carbon quantum dots with red fluorescence: An optical dual-mode and smartphone imaging sensor for identifying Chinese Baijiu quality.

Chinese Baijiu (Liquor) is a popular alcoholic beverage, and the ethanol content in Baijiu is closely related to its quality; therefore, it is of great significance to explore a facile, sensitive, and rapid method to detect ethanol content in Baijiu. Hydrophobic carbon quantum dots (H-CQDs) with bright red fluorescence (24.14 %) were fabricated by hydrothermal method using o-phenylenediamine, p-aminobenzoic acid, manganese chloride, and hydrochloric acid as reaction precursors. After the introduction of ultrapure water into the ethanol solution dissolved with H-CQDs, the aggregated H-CQDs resulted in significant changes in fluorescence intensity and absorbance. On this basis, a sensor for detecting ethanol by optical dual-mode and smartphone imaging was constructed. More importantly, the sensor can be used for detecting ethanol content in Chinese Baijiu with satisfactory results. This sensing platform has great potential for quality identification in Chinese Baijiu, broadening the application scope of CQDs in food safety detection.

A novel carbon-nanodots-based theranostic nano-drug delivery system for mitochondria-targeted imaging and glutathione-activated delivering camptothecin.

Chemotherapy is severely limited by continuously decreased therapeutic efficacy and uncontrolled side effects on normal tissue, which can be improved by constructing a nanoparticle-based drug delivery system (DDS). Nevertheless, no studies have reported on DDS-based on carbon-nanodots (CNDs), combining subcellular organelle-targeted imaging/drug delivery, high drug loading content, and glutathione (GSH)-sensitive drug release into one system. Herein, the as-fabricated CNDs can be covalently conjugated with a mitochondria-targeting ligand (triphenylphosphine, TPP), a smart GSH-responsive disulfide linker (S-S), and the anticancer drug (camptothecin, CPT) to initially prepare a theranostic nano-DDS (TPP-CNDs-S-CPT) with the drug loading efficiency of 64.6 wt%. Owing to excellent water dispersibility, superior fluorescence properties, satisfactory cell permeability, and favorable biocompatibility, TPP-CNDs-S-CPT was successfully used for intracellular mitochondrial-targeted imaging in vitro. High intracellular GSH concentrations in tumor cells caused the cleavage of S-S, resulting in concomitant activation and release of CPT, as well as significant fluorescence enhancement. In vivo, TPP-CNDs-S-CPT exhibited lower biological toxicity and even higher tumor-activatable performance than free CPT, as well as specific cancer therapy with few side effects. The mitochondria-targeted ability and the precise drug-release in tumor make TPP-CNDs-S-CPT a hopeful chemotherapy prodrug, providing significant theoretical basis and data support for in-depth understanding and exploration of chemotherapeutic DDS-based on CNDs.

A facile fluorescence platform for chromium and ascorbic acid detection based on "on-off-on" strategy.

In this paper, a facile and rapid fluorescence "on-off-on" strategy for the detection of chromium (Cr(VI)) and ascorbic acid (AA) was developed, which was based on the water-soluble carbon dots (CDs). The CDs was synthesized by a microwave-assisted treatment of L-tartaric acid, citric acid, and urea. The CDs have many advantages, such as high fluorescence quantum yield (20.5%) and good fluorescence stability. Based on inner filter effect (IFE) and static quenching, the fluorescence of the CDs can be quenched by Cr(VI) quickly; while the reduction of IFE and reducing action can make the fluorescence of the CDs recover by AA efficiently. Moreover, under the optimal experimental conditions, the CDs had a good detection performance for Cr(VI) in the range of 0.8 âˆ¼ 189 µM with the limit of detection (LOD) of 0.16 µM. The linear detection for AA was ranged from 0.43 to 25.7 µM with a LOD of 0.1 µM. More importantly, the as-constructed fluorescence detecting platform was successfully applied for Cr(VI) and AA detection in the environmental samples and fruit samples, respectively. In addition, the application potential of the CDs in fluorescent films and anti-counterfeiting materials was further discussed in detail. This work will provide a novel idea for designing a portable sensor based on the CDs to quickly and sensitively detect Cr(VI) and AA.

Piperazine-Based Mitochondria-Immobilized pH Fluorescent Probe for Imaging Endogenous ONOO- and Real-Time Tracking of Mitophagy.

ONOO- is mainly produced in mitochondria, and dysfunctional and damaged mitochondria are degraded in lysosomes through autophagy, so it is important to synthesize a single probe for dual detection of ONOO- and mitophagy. Unfortunately, mitochondria-immobilized fluorescent probes for dual detection of ONOO- and mitophagy have not yet been developed. Hence, we first reported a piperazine-based mitochondria-immobilized red-emitting fluorescent probe (PMR), which not only can detect ONOO- but also could be used to image cellular mitophagy by the pH variations because of the protonation of the piperazine moiety. PMR was designed and prepared by introducing a piperazine ring as the pH response group, a lipophilic cation as the targeting mitochondria moiety, and benzyl chloride for immobilizing mitochondrial proteins through thiol groups. PMR displayed an enhanced fluorescence response at 640 nm through mitochondrial acidification. Using these advantages of PMR, which was successfully used for visualizing the mitophagy process induced by rapamycin or starvation, and chloroquine can inhibit rapamycin-induced mitophagy and prevent the fusion of autophagosomes and lysosomes. PMR also showed good sensitivity with a detection limit of 23 nM to ONOO-, which was successfully applied in imaging exogenous/endogenous ONOO-. Combining the above design, PMR may be used to study the detailed function of the mitophagy and ONOO--associated physiological and pathological processes.

Intelligently design primary aromatic amines derived carbon dots for optical dual-mode and smartphone imaging detection of nitrite based on specific diazo coupling.

Primary aromatic amines derived carbon dots (PAA-CDs) with the protonated amino groups and high quantum yield of 46% were favorably obtained by one-step solvothermal treatment of m-phenylenediamine (m-PDA) in acidic environment. The interaction between the PAA-CDs and nitrite (NO2-) was inherited the characteristic reaction of m-PDA (a primary aromatic amine) and NO2-, resulting in strong fluorescence quenching and obvious absorption variation of the PAA-CDs. Meanwhile, a chromogenic reaction of diazo coupling can cause significant color changes. Hence, the PAA-CDs were developed for an optical dual-mode and smartphone imaging sensor for NO2- detection in the range of 3.0 ~ 40.0 µM with high selectivity, good sensitivity, and excellent anti-interference capability. A limit of detection (LOD) of 0.024 µM and 0.16 µM was implemented by fluorometry and colorimetry, respectively. For smartphone imaging colorimetry, the LODs of 0.46 µM (visible color) and 0.99 µM (fluorescence color) were acquired. More importantly, the established sensor has been successfully applied for the dynamic detection of NO2- in various food samples with the satisfying results. A smartphone imaging colorimetry method based on the CDs was firstly proposed to visually and quantitatively detect NO2-, which will broaden the application range of the CDs in food safety inspection.

A bifunctional fluorescence probe for dual-channel detecting of mitochondrial viscosity and endogenous/exogenous peroxynitrite.

The irregular viscosity in the mitochondrial can induce mitochondrial dysfunction. The content of peroxynitrite (ONOO-) is related to various physiological and pathological processes. However, many mitochondrial probes only realized the detection of viscosity or ONOO- in single channel, thus it is necessary to explore single fluorescence probe for dual-detecting mitochondrial viscosity and ONOO-. In this work, we designed and synthesized a novel fluorescence probe (PV) for dual-detecting viscosity and ONOO-, which was composed by intergrating a ONOO-- responsive arlyboronate with a twisting intramolecular charge transfer (TICT) mechanism and possessed the mitochondria-targeting ability due to its pyridinium cation. PV exhibited a significant increase in viscosity with red emission at 582 nm and high sensitivity to ONOO- levels with yellow emission at 507 nm. PV was also applied to living systems (including living cells and zebrafish) for viscosity and ONOO- detection using two different channels. Moreover, the ability of PV to track mitophagy may make ONOO- a powerful tool for its role in mitophagy.

N-Doped carbon dots for the fluorescence and colorimetry dual-mode detection of curcumin.

Nitrogen doped carbon dots (N-CDs) were synthesized by a one-step hydrothermal method with dopamine and ethylenediamine. The as-prepared N-CDs were characterized via transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), fluorescence spectrophotometer, UV-Vis spectrophotometry and Fourier transform infrared spectroscopy (FTIR). The average particle dimension of the as-prepared N-CDs was 2.68 nm, and the best excitation and emission wavelengths were 405 nm and 535 nm, separately. N-CDs exhibits excellent selectivity and sensitivity to detect the curcumin (Cur), attaining a wider linear range of 97.5 nM-67.9 µM and a limit of detection (LOD) of as low as 94 nM. Interestingly, N-CDs can also give responsive signals of a visible colour change (yellow to red). Moreover, a novel fluorescent/colorimetric dual-mode method has been successfully employed for the determination of Cur in real samples with good recoveries (94%-110%) and precision (RSD = 0.3-2.9%).

A butterfly-shaped ESIPT molecule with solid-state fluorescence for the detection of latent fingerprints and exogenous and endogenous ONOO- by caging of the phenol donor.

The latent fingerprints (LFPs) at the crime scene are unique and stable, which are considered as an important clue in criminal justice and forensic identification. Herein, a butterfly-shaped molecule DPTS with solid fluorescence plus excited-state intramolecular proton transfer (ESIPT) properties was used to develop for enhancing the visualization of the LFPs. Considering the solid fluorescence of DPTS, the color and efficiency of DPTS with a large Stokes shift (216 nm) can be tuned by changing the morphology of its aggregates, and gradually red-shifted (green-yellow-red) with increasing water content. Furthermore, its effectiveness for the detection of LFPs was demonstrated on various different substrates including paper box, tinfoil and weighting paper. The emissive fingerprint of DPTS obtained gave good fluorescence images with high contrast and resolution such as the core, delta, bifurcation, ridge termination, independent ridge and pores. Caging of the phenol donor of DPTS with a sensitive biomarker group provided DPTS-ONOO-, which had high sensitive with detection limit of 5 nM and the quantification limit of 21 nM toward ONOO-. Modularly derived DPTS-ONOO- was synthesized and demonstrated specific fluorescence imaging of exogenous and endogenous peroxynitrite (ONOO-) in living macrophage cells.

AIE-based fluorescent boronate probe and its application in peroxynitrite imaging.

Fluorescent probes have contributed greatly to our understanding of the biological role of peroxynitrite (ONOO-). The ONOO- fluorescence probe characterized by the arlyboronate received a moderate opening fluorescence response, and the borate-masked probe significantly increased the sensitivity of ONOO-. Thus, two simple fluorescent probes (ADB and ANB) with the recognition receptor of phenyl boronate moiety were constructed for the detection of ONOO-. The change of emission spectrum was affected differently by the electron donating (or withdrawing) of the substituents. ANB was shown to have a low sensitivity and quantum yield towards ONOO- in aqueous solution, whereas ADB with aggregation-induced emission (AIE) process exhibited not only good sensitivity for ONOO- with a detection limit of 75 nM, but also ADB could be used to quantitative detecting ONOO- in response to concentrations of ONOO- within 20 s. Importantly, ADB had good performance for the detection of exogenous ONOO- in the RAW 264.7 cells.

Carbon dots for ratiometric fluorescence detection of morin.

The B,N dual-doped carbon dots (B,N-CDs) for ratiometric fluorescence detection the morin were prepared from sodium tetraborate and polyethyleneimine through the single-step hydrothermal method. The B,N-CDs exhibited the optimum excitation and emission wavelength at 340 nm and 467 nm, respectively. Interestingly, the intensities of emission peak at 467 nm of B,N-CDs reduced meanwhile a new peak emerged at 560 nm with the continuous addition of morin, which revealed the ratio fluorescence characteristic between F560nm/F467nm and morin concentration with the linearity range and detection limit of 14.5-32.5 µmol/L and 0.3 µmol/L (S/N = 3), respectively. The interference of common antibiotics and remedies could be ignored when the concentration of morin was detected by the B,N-CDs, which demonstrating the outstanding selectivity. Furthermore, the proposed fluorescence method is used to detect morin in urine with recoveries are 99.8-104.5%. The results of this research indicate the feasibility and practicality of B,N-CDs as an effective fluorescent probe for the determination of morin.

Ratiometric fluorescent sensors for sequential on-off-on determination of riboflavin, Ag+ and l-cysteine based on NPCl-doped carbon quantum dots.

The fluorescent sensor, especially ratiometric fluorescent sensor, is one of the most important applications for CQDs, which is becoming a research hotspot. Herein, carbon quantum dots co-doped with nitrogen, phosphorus and chlorine (NPCl-CQDs) were synthesized by acid-base neutralization reaction exothermic carbonization method. The as-fabricated NPCl-CQDs could emit blue fluorescence and possess excellent fluorescence properties. Based on the FRET, multifunctional and ratiometric fluorescent sensors for "on-off-on" sequential determination of riboflavin, Ag+, and Cys with good selectivity and high sensitivity were established. The linear range of riboflavin, Ag+, and Cys are 0.50-10.18 µM and 15.89-27.76 µM, 0.66-1.46 mM and 1.50-4.20 mM, and 0.01-0.15 µM and 0.15-0.36 µM with the limit of detection of 3.50 nM, 26.38 µM, and 0.96 nM, respectively. Furthermore, the sensors were successfully used to determine riboflavin, Ag+, and Cys in tablets, river water, and human urine with the recoveries of 95.2-104.0%, 95.6-102.0%, and 94.8-106.4%, respectively. More importantly, the as-constructed "on-off-on" NPCl-CQDs-based ratiometric fluorescent sensors were applied for detecting riboflavin, Ag+, and Cys in HeLa cells with satisfying results. The finding of this study shows the feasibility and effectiveness of the NPCl-CQDs as the available ratiometric fluorescent sensors for the determination of riboflavin, Ag+, and Cys in real samples and living cells.

Fe3+ and intracellular pH determination based on orange fluorescence carbon dots co-doped with boron, nitrogen and sulfur.

The fluorescent boron, nitrogen and sulfur co-doped carbon dots (BNSCDs) were prepared by simple hydrothermal reaction of 4-carboxyphenylboronic acid and 2,5-diaminobenzenesulfonic acid at 200 °C for 8 h. The fluorescence of the BNSCDs could be quenched by Fe3+ based on the electron transfer between Fe3+ and BNSCDs, so a label-free, good selectivity and high sensitivity method for Fe3+determination was established with linear range and LOD of 1.5-692 µmol/L and 87 nmol/L, respectively. And then the fluorescent probe was employed for detection of Fe3+ in tap water, coal gangue, fly ash and food samples successfully. Moreover, the as-prepared BNSCDs could serve as a novel pH fluorescent probe in the range of pH 1.60-7.00, which could be attributed to the proton transfer of carboxyl groups on the surface of BNSCDs. More importantly, the pH fluorescent probe possesses fast, real-time and low toxicity, applying for intracellular pH fluorescence imaging in HIC, HIEC, LO2 and SMMC7721 cells. In view of its simplicity, timely response and outstanding compatibility, the as-fabricated BNSCDs show the potential applications in water quality and solid waste monitoring, food detection, real-time measuring of intracellular pH change in vitro.

Alizarin-based molecular probes for the detection of hydrogen peroxide and peroxynitrite.

Phenol fluorophores are a large family of fluorophores, which have attracted more and more attention in the design of probes. Using the self-assembly of aromatic boronic acid with Alizarin Red S (ARS) and Gallein (GAL), the novel chemosensors ARS-CBA and GAL-CBA were provided for hydrogen peroxide (H2O2), which demonstrated their ability to detect H2O2 with indicator displacement assay (IDA) by colorimetric and electrochemical measurements. After ARS-CBA and GAL-CBA reacted with H2O2, the systems displayed a red-shifted visible color change in aqueous media and off-on electrochemical signals showing generation of phenol. The chemosensor ARS-CBA also had good performance in fluorometric measurements and turn-off fluorescent response indicated removal of aromatic boronic acid. In addition, a designed near-infrared (NIR) dual-modal fluorescent probe alizarin blue S (ABS) was used for peroxynitrite (ONOO-) with a visible colorimetric change in dimethyl sulfoxide (DMSO) and "on-off" fluorescent response indicating the oxidation of hydroxyl. The flexible Phenol fluorophores are allowed to prepare multiple fluorescent probes towards H2O2 or ONOO- for environmental and physiological applications.

Boronate based sensitive fluorescent probe for the detection of endogenous peroxynitrite in living cells.

In this work, a novel boronate-based fluorescent probe (FAM) for the endogenous detection of peroxynitrite (ONOO-) has been developed by using anthracycline as the fluorophore, arlyboronate as the recognition moiety, lipophilic cation as the mitochondrial targeting moiety. Upon reaction of the probe with ONOO-, the oxidation and subsequent hydrolysis of ONOO- to arlyboronate triggers quite rapid fluorescence off-on response, providing a sensitive and highly selective method for the detection of ONOO-. In addition, probe holds high sensitivity with the detection limit of 3.2 nM and excellent specificity including a series of biologically relevant reactive oxygen species. Importantly, FAM with good water solubility displays excellent performances for imaging endogenous peroxynitrite produced by RAW264.7 cells.

A ratiometric and far-red fluorescence "off-on" sensor for sequential determination of copper(II) and L-histidine based on FRET system between N-acetyl-L-cysteine-capped AuNCs and N,S,P co-doped carbon dots.

A far-red fluorescence "off-on" sensing strategy is described for sequential ratiometric determination of Cu2+ and L-histidine (L-His) based on fluorescence resonance energy transfer (FRET) system. N,S,P co-doped carbon dots (N,S,P-CDs) and N-acetyl-L-cysteine functionalized gold nanoclusters (NAC-AuNCs) are used in the FRET system, which serve as energy donor and acceptor, respectively. After adding NAC-AuNCs into the solution of N,S,P-CDs, the fluorescence of N,S,P-CDs is effectively quenched, while the far-red fluorescence of NAC-AuNCs appears. Cu2+ can decrease fluorescence of NAC-AuNCs, and then L-His can effectively recover the fluorescence of NAC-AuNCs. The possible reason is that the stronger affinity between Cu2+ and L-His can pull Cu2+ away from the surface of NAC-AuNCs. Through it all, the emission intensity of N,S,P-CDs remains nearly constant, so the ratio of fluorescence intensities at 485 and 625 nm exhibits a linear correlation to the Cu2+ and L-His concentration, respectively. The sensing platform shows good selectivity towards Cu2+ and L-His with a linear range of 0.65-26.58 µM and 3.13-56.25 µM and determination limits of 0.50 µM and 0.374 µM, respectively. The proposed method has been successfully used for Cu2+ and L-His determination in real samples with satisfying results. Graphical abstract.

A fast detection of peroxynitrite in living cells.

Peroxynitrite (ONOO-) plays a crucial role in the regulation of diverse pathophysiological processes, and high level of ONOO- is profound association with numerous diseases. Herein, we developed an anthraquinone-based fluorescent probe L for ONOO- determination by a new recognition mechanism: amido oxidized nitroso-group by ONOO-. Probe L with amine-based recognition receptor is more selective to ONOO- than other reactive oxygen species, including H2O2 and ClO-. Furthermore, ONOO- could be rapidly detected by probe L with a Limit of Detection of 13 nM. More importantly, L could be used to monitor intracellular ONOO- in SMMC-7721 cells.

A label-free nano-probe for sequential and quantitative determination of Cr(VI) and ascorbic acid in real samples based on S and N dual-doped carbon dots.

A fluorescent sulfur and nitrogen dual-doped carbon dots (S,N-CDs) was prepared by a simple and one-step acid-base neutralization and exothermic carbonization method. Hexavalent chromium (Cr(VI)) could effectively quench the fluorescence of S,N-CDs based on inner filter effect (IFE) and dynamic quenching, whereas ascorbic acid (AA) could recover the fluorescence of S,N-CDs/Cr(VI) because of IFE weakening. So an "on-off-on" and label-free nano-probe consecutive determination of Cr(VI) and AA was constructed. This nano-probe system demonstrated excellent selectivity and sensitivity to Cr(VI) and AA with linear range of 0.065-198 µmol/L (3.38-10,296 µg/L) and 6.6-892 µmol/L (1.16-157 mg/L), respectively. Meanwhile, the as-prepared S,N-CDs possess low toxicity and could be used for multi-color cell imaging in SMMC 7721 cells. More importantly, this nano-probe was successfully employed for detection of Cr(VI) in tap water and AA in food samples. In view of its simple detection condition, rapid response, wide linear range, low detection limit and inexpensive instrument, the as-constructed nano-probe system could have a wide range of potential application, including water quality monitoring and evaluation, food inspection and testing and biomedical analysis.

Controllable Fabrication, Photoluminescence Mechanism, and Novel Application of Green-Yellow-Orange Fluorescent Carbon-Based Nanodots.

Carbon-based nanodots (CBNs), as spick-and-span carbon nanomaterials, have been widely studied and applied in numerous fields. However, the controlled fabrication and photoluminescence (PL) mechanism remains an incompletely understood and widely debated topic. Herein, green, yellow, and orange light-emitting CBNs were fabricated by a one-step hydrothermal process with 4-aminobenzoic acid and 1,3-diaminobenzene, 1,2-diaminobenzene, and 1,4-diaminobenzene as precursors, respectively; the resulting CBNs were named gCBNs, yCBNs, and oCBNs, respectively. By adjusting the reaction conditions, including precursor, solvent, atmosphere, and dissolved solvent, the controllable fabrication of CBNs can be realized. We speculate that the PL of CBNs is dominated by the degrees of oxidation and amidation, which, together, cause the differences in the density of N-states and quantum size, ultimately manifesting as changes in three CBNs' fluorescence behaviors. Finally, the CBNs were used as agents to image four model cells, demonstrating that CBNs are potentially useful in biological labeling and multicolor bioimaging. More importantly, CBNs can be conjugated to the targeted micromolecule, DNA, RNA, and/or anticarcinogen groups to construct nanocomposite materials, which could be applied to identify target materials and/or execute the sustained release of drugs. We want to offer a guide for controllable fabrication of CBNs and further expanding the application depth and breadth in the biomedical field.

Synthesis and spectral characteristics of two novel intramolecular charge transfer fluorescent dyes.

The synthesis and absorption/fluorescence properties of two novel intramolecular charge transfer (ICT) compounds of (fluorene-2-yl)-(9-ethylcarbazole-3-yl) ketene and 1-phenyl-3-(fluorenone-2-yl)-5-(9-ethylcarbazole-3-yl)-2-pyrazoline were reported. The primary structure of the target compounds was characterized by IR and (1)H NMR. The systems contained a fluorenone or a propenon group as an electron acceptor (A) and an N-ethylcarbazole and a pyrazoline group as electron donors (D). From the emissive properties it was concluded that the electronic coupling between D and A was sufficient to allow charge transfer in these molecules. The ICT maximal emission displayed a large wavelength shift and Stokes shifts increased in response to the increase of the solvent polarity. The highly solvatochromic properties made the two compounds of great interest as new classes of fluorescent probes, electroluminescent and electrofax materials.