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A novel Nitrogen-Doped Water-Soluble carbon dot for highly selective Recognition of Mg2+ by chelation conjugation enhancement effect (CCE) and its application in Synergistically enhanced photodynamic antibacterial
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The development of novel materials for highly efficient and selective photocatalysis is crucial for their practical applications. Herein, we employ the host‐guest chemistry of porphyrin‐based metallacages to regulate the generation of reactive oxygen species and further use them for the selective photocatalytic oxidation of benzyl alcohols. Upon irradiation, the sole metallacage (6) can generate singlet oxygen (¹O2) effectively via excited energy transfer, while its complex with C70 (6⊃C70) opens a pathway for electron transfer to promote the formation of superoxide anion (O2⋅⁻), producing both ¹O2 and O2⋅⁻. The addition of 4,4′‐bipyridine (BPY) to complex 6⊃C70 forms a more stable complex (6⊃BPY) via the coordination of the Zn‐porphyrin faces of 6 and BPY, which drives fullerenes out of the cavities and restores the ability of ¹O2 generation. Therefore, benzyl alcohols are oxidized into benzyl aldehydes upon irradiation in the presence of 6 or 6⊃BPY, while they are oxidized into benzoic acids when 6⊃C70 is employed as the photosensitizing agent. This study demonstrates a highly efficient strategy that utilizes the host‐guest chemistry of metallacages to regulate the generation of reactive oxygen species for selective photooxidation reactions, which could promote the utilization of metallacages and their related host‐guest complexes for photocatalytic applications.
Maintaining proper mechanical strength and tissue volume is important for bone growth at the site of a bone defect. In this study, potassium magnesium phosphate hexahydrate (KMgPO4·6H2O, MPC) was applied to gelma-methacrylate hydrogel (GelMA) to prepare GelMA/MPC composites (GMPCs). Among these, 5 GMPC showed the best performance in vivo and in vitro. These combinations significantly enhanced the mechanical strength of GelMA and regulated the degradation and absorption rate of MPC. Considerably better mechanical properties were noted in 5 GMPC compared with other concentrations. Better bioactivity and osteogenic ability were also found in 5 GMPC. Magnesium ions (Mg2+) are bioactive and proven to promote bone tissue regeneration, in which the enhancement efficiency is closely related to Mg2+ concentrations. These findings indicated that GMPCs that can release Mg2+ are effective in the treatment of bone defects and hold promise for future in vivo applications.
Diabetes mellitus, an epidemic with a rapidly increasing number of patients, always leads to delayed wound healing associated with consistent pro-inflammatory M1 polarization, decreased angiogenesis and increased reactive oxygen species (ROS) in the microenvironment. Herein, a poly (lactic-co-glycolic acid) (PLGA)-based microneedle patch loaded with magnesium hydride (MgH2) (MN-MgH2) is manufactured for defeating diabetic wounds. The application of microneedle patch contributes to the transdermal delivery and the prolonged release of MgH2 that can generate hydrogen (H2) and magnesium ions (Mg²⁺) after reaction with body fluids. The released H2 reduces the production of ROS, transforming the pathological microenvironment induced by diabetes mellitus. Meanwhile, the released Mg²⁺ promotes the polarization of pro-healing M2 macrophages. Consequently, cell proliferation and migration are improved, and angiogenesis and tissue regeneration are enhanced. Such intelligent microneedle patch provides a novel way for accelerating wound healing through steadily preserving and releasing of H2 and Mg²⁺ locally and sustainably.
Detection of trace magnesium ion (Mg²⁺) is important in environmental and health monitoring. In this work, high‐performance Mg²⁺ sensor was developed from label‐free carbon dots. The novel carbon dots were prepared for the first time from natural rubber through the two‐step pyrolysis and hydrothermal method. They showed selectivity towards Mg²⁺ against a range of metal ions in solution and yielded a detection limit of 4.3 μM. The Mg²⁺ detection in real water samples showed an excellent recovery of 97.21 to 99.21 %. A paper‐based sensor was also fabricated as a portable device, showing a detection limit of 8.0 μM. UV‐vis and X‐ray absorption studies provided some evidences of the unique dynamic interactions between carbon dots and Mg²⁺ ions. In summary, the novelty of this work lies upon (i) developing a methodology of converting abundant, low‐cost natural rubber into carbon dots and (ii) fabricating sensitive and selective sensors from the label‐free carbon dots for the detection of Mg²⁺ both in solution and as paper‐based devices. The findings in this work will therefore have potential for environmental and health monitoring applications.
A Schiff base fluorescent probe compound H2L (N′‐(4‐bromo‐2‐hydroxy‐benzylidene)‐3‐hydroxy‐2naphthohydrazide) was synthesized using 3‐hydroxy‐2‐naphthoic acid hydrazide as raw material. The structure of H2L was characterized by NMR, IR, MS, and XRD methods. The fluorescence performance of H2L was studied by UV and FS. The results show that in 1 : 4 water system /DMSO solution (water system: 20 % triethanolamine:0.1 mol/L L‐cysteamine acid=1 : 1), H2L can be used to quickly identify Mg²⁺ with an obvious fluorescence enhancement and redshift. A color change “light green→bright yellow” can be clearly observed with the naked eye. The Mg²⁺ concentration shows a good linear relationship in the range of 0–1.0×10⁻⁵ mol/L, with a detection limit of 1.77×10⁻⁷ mol/L with good stability and reversibility. The response mechanism was explored through Job's curve, NMR titration and MS, which showed that Mg²⁺ can form a 1 : 1 complex with H2L. A gel (SAL) was prepared by doping H2L into sodium alginate (SA). SAL was found to show good adsorption properties for Mg²⁺ and can be easily distinguished by the naked eye under ultraviolet light. The microscopic morphology and composition of SAL before and after Mg²⁺ adsorption were analyzed by SEM‐EDS. H2L can be used for the qualitative detection of Mg²⁺ in actual water samples without being affected by other common metal ions, and has potential application value in the field of environmental detection.
Herein, we represent cation‐responsive fluorescent probes for the divalent cations Zn²⁺, Mg²⁺ and Ca²⁺, which show cation‐induced fluorescence enhancements (FE) in water. The Zn²⁺‐responsive probes Zn1, Zn2, Zn3 and Zn4 are based on o‐aminoanisole‐N,N‐diacetic acid (AADA) derivatives and show in the presence of Zn²⁺ FE factors of 11.4, 13.9, 6.1 and 8.2, respectively. Most of all, Zn1 and Zn2 show higher Zn²⁺ induced FE than the regioisomeric triazole linked fluorescent probes Zn3 and Zn4, respectively. In this set, ZN2 is the most suitable probe to detect extracellular Zn²⁺ levels. For the Mg²⁺‐responsive fluorescent probes Mg1, Mg2 and Mg3 based on o‐aminophenol‐N,N,O‐triacetic acid (APTRA) derivatives, we also found that the regioisomeric linkage influences the fluorescence responds towards Mg²⁺ (Mg1+100 mM Mg²⁺ (FEF=13.2) and Mg3+100 mM Mg²⁺ (FEF=2.1)). Mg2 shows the highest Mg²⁺‐induced FE by a factor of 25.7 and an appropriate Kd value of 3 mM to measure intracellular Mg²⁺ levels. Further, the Ca²⁺‐responsive fluorescent probes Ca1 and Ca2 equipped with a 1,2‐bis(o‐aminophenoxy)ethane‐N,N,N’,N’‐tetraacetic acid (BAPTA) derivative show high Ca²⁺‐induced FEs (Ca1 (FEF=22.1) and Ca2 (FEF=23.0)). Herein, only Ca1 (Kd=313 nM) is a suitable Ca²⁺ fluorescent indicator to determine intracellular Ca²⁺ levels.
An BODIPY probe for detection and imaging of Mg ²⁺ without interference from Ca ²⁺ is described.
The present paper reports on a chelation enhanced fluorescence (CHEF) effect that is observed on addition of certain metal ions to phosphorus doped carbon nanodots (P-CNDs). The effect is accompanied by a large shortwave shift of the emission peak. Highly passivated P-CNDs with sizes of around 3 nm were prepared from lactose and phosphoric acid, using a one-pot low temperature solvothermal method. The nanoparticles were purified according to polarity and size. The extent of blue shift and strength of enhancement depend on metal ions and actual pH value. For instance, the P-CND complex with Al(III) has a fluorescence that is shifted to shorter wavelengths, and the fluorescence quantum yield is enhanced from 12% (for the free P-CNDs) to almost 62% at 490 nm. The fluorescence is also enhanced and shifted by the ions Zn(II) and Cd(II). It is quenched by the ions Fe(II), Fe(III), Hg(II), Cu(II) and Sn(II), among others. The enhancement is attributed to the chelation of metal ions with the passivated surface functional groups of P-CNDs, mainly those of phosphorus. Phosphorous free CNDs (prepared via HCl instead of H3PO4) and low-passivated P-CNDs (prepared for longer period of time; typically 8 h) show no enhancement. The metal ion induced enhancement led to the design of a fluorometric assay for the detection of these ions. The detection limits are 4 nM for Al(III) and 100 nM for Zn(II). The two ions were quantified in spiked pharmaceutical formulations. Recoveries typically are 102% (for n = 7).
Graphical abstractThe fluorescence emission of phosphorous doped carbon nanodots is significantly enhanced and tuned after binding to Al³⁺, Zn²⁺ and Cd²⁺. The enhancement mechanism is attributed to chelation enhanced fluorescence (CHEF).
Magnesium (Mg2+) is an essential ion to the human body, playing an instrumental role in supporting and sustaining health and life. As the second most abundant intracellular cation after potassium, it is involved in over 600 enzymatic reactions including energy metabolism and protein synthesis. Although Mg2+ availability has been proven to be disturbed during several clinical situations, serum Mg2+ values are not generally determined in patients. This review aims to provide an overview of the function of Mg2+ in human health and disease. In short, Mg2+ plays an important physiological role particularly in the brain, heart, and skeletal muscles. Moreover, Mg2+ supplementation has been shown to be beneficial in treatment of, among others, preeclampsia, migraine, depression, coronary artery disease, and asthma. Over the last decade, several hereditary forms of hypomagnesemia have been deciphered, including mutations in transient receptor potential melastatin type 6 (TRPM6), claudin 16, and cyclin M2 (CNNM2). Recently, mutations in Mg2+ transporter 1 (MagT1) were linked to T-cell deficiency underlining the important role of Mg2+ in cell viability. Moreover, hypomagnesemia can be the consequence of the use of certain types of drugs, such as diuretics, epidermal growth factor receptor inhibitors, calcineurin inhibitors, and proton pump inhibitors. This review provides an extensive and comprehensive overview of Mg2+ research over the last few decades, focusing on the regulation of Mg2+ homeostasis in the intestine, kidney, and bone and disturbances which may result in hypomagnesemia.
A general quantitative pH sensor for environmental and intracellular applications was developed by the facile hydrothermal preparation of dicyandiamide (DCD) N-doped high quantum yield (QY) graphene quantum dots (GQDs) using citric acid (CA) as the carbon source. The obtained N-doped GQDs have excellent photoluminesence (PL) properties with a relatively high QY of 36.5%, suggesting that N-doped chemistry could promote the QY of carbon nanomaterials. The possible mechanism for the formation of the GQDs involves the CA self-assembling into a nanosheet structure through intermolecular H-bonding at the initial stage of the reaction, and then the pure graphene core with many function groups formed through the dehydration between the carboxyl and hydroxyl of the intermolecules under hydrothermal conditions. These N-doped GQDs have low toxicity, and are photostable and pH-sensitive between 1.81 to 8.96, giving a general pH sensor with a wide range of applications from real water to intracellular contents.
The development of novel materials for highly efficient and selective photocatalysis is crucial for their practical applications. Herein, we employ the host‐guest chemistry of porphyrin‐based metallacages to regulate the generation of reactive oxygen species and further use them for the selective photocatalytic oxidation of benzyl alcohols. Upon irradiation, the sole metallacage (6) can generate singlet oxygen (1O2) effectively via excited energy transfer, while its complex with C70 (6⊃C70) opens a pathway for electron transfer to promote the formation of superoxide anion (O2·−), producing both 1O2 and O2·−. The addition of 4,4'‐bipyridine (BPY) to complex 6⊃C70 forms a more stable complex (6⊃BPY) via the coordination of the Zn‐porphyrin faces of 6 and BPY, which drives fullerenes out of the cavities and restores the ability of 1O2 generation. Therefore, benzyl alcohols are oxidized into benzyl aldehydes upon irradiation in the presence of 6 or 6⊃BPY, while they are oxidized into benzoic acids when 6⊃C70 is employed as the photosensitizing agent. This study demonstrates a highly efficient strategy that utilizes the host‐guest chemistry of metallacages to regulate the generation of reactive oxygen species for selective photooxidation reactions, which will promote the utilization of metallacages and their related host‐guest complexes for photocatalytic applications.
In this study, we synthesized nitrogen-doped carbon dots (N-CDs) with remarkable photodynamic antibacterial properties by a hydrothermal method. The composite film was prepared by solvent casting method, compounding N-CDs with chitosan (CS). The morphology and structure of the films were analyzed by Fourier-transformed infrared spectroscopy (FTIR), scanning electron microscope (SEM), atomic force microscope (AFM), and transmission electron microscope (TEM) techniques. The films' mechanical, barrier, thermal stability, and antibacterial properties were analyzed. A preservation test of the films was studied on the samples of pork, volatile base nitrogen (TVB-N), total viable count (TVC), and pH were determined. Besides, the effect of film on the preservation of blueberries was observed. The study found that, compared with the CS film, the CS/N-CDs composite film is strong and flexible, with good UV light barrier performance. The prepared CS/7 % N-CDs composites showed high photodynamic antibacterial rates of 91.2 % and 99.9 % for E. coli and S. aureus, respectively. In the preservation of pork, it was found that its pH, TVB-N, and TVC indicators were significantly lower. The extent of mold contamination and anthocyanin loss was less in the CS/3 % N-CDs composite film-coated group, which could greatly extend the shelf life of food.
In view of the fluorescent switching properties and anti-fatigue properties of diarylethene, a diarylethene fluorescent chemosensor for the immediate detection of Zn2+ and Mg2+ in acetonitrile was synthesized in this paper. The structure of 1o was determined by performing spectroscopy and elemental analysis. The presence of Zn2+ or Mg2+ made the chemosensor 1o showed an obvious "turn-on" fluorescent signal (bright yellow-green for Zn2+ and bright cyan for Mg2+ ). The fluorescent change caused by the 1:1 binding of 1o and Zn2+ or Mg2+ might be due to hindering the ESIPT process, which were bolstered by Benesi-Hildebrand analysis, Job's plot curves, 1 H NMR titration and mass spectrometry. The detection limits were acquired from the standard curve plots for Mg2+ ions at 44.6 nM and for Zn2+ ions at 14 nM. Based on the fluorescent behaviors, a logic gate was constructed with the emission intensity at 528/518 nm as output signal, the UV/vis lights, Mg2+ /Zn2+ and EDTA as input signals. Exogenous Zn2+ and Mg2+ fluorescent bioimaging were performed on Hela cells with 1o, indicating its potential application in biodiagnostic analysis. In particular, 1o was manufactured into test paper, and Zn2+ or Mg2+ can be conveniently, efficiently and qualitatively identified by the fluorescent color variation of the test strips.
The magnesium (Mg²⁺) ion is the second most abundant intracellular cation after potassium, and it is involved in a variety of biological processes and physiological functions. Because of the different effects which are dependent on Mg²⁺ ion concentration, it is critical to monitor Mg²⁺ ion levels in biological systems. Here, we report the hydrothermal synthesis of photoluminescent N-doped carbon dots (NCDs) using 4-Hydroxybenzaldehyde and 1, 2, 4, 5-benzenetetramine tetrahydrochloride as carbon and nitrogen sources, respectively. The as-synthesized NCDs demonstrated excitation dependent photoluminescence (PL) with a quantum yield of 16.2%. Because of water dispersibility and chelating functional groups, NCDs were used for highly selective detection of Mg²⁺ ions using ratiometric PL enhancement with a detection limit of 60 μM. Following that, based on highly biocompatibility and sensing of Mg²⁺ ions in aqueous solutions, NCDs were employed as photoluminescent probe to detect the Mg²⁺ ions of mammalian cell lines such as J774, HeLa, and Hek293T, which is most likely due to effective complex formation between NCDs and the intracellular Mg²⁺ ions. As far as we could possibly know, this is the first report of aqueous solution dispersed carbon dots for intracellular sensing and imaging of Mg²⁺ ions based solely on an increase in NCDs PL intensity.
Zinc oxide nanoparticles (ZnO NPs) are important semiconductor materials with interesting photo-responsive properties. During the past, ZnO-based NPs have received considerable attention for photodynamic therapy (PDT) due to their biocompatibility and excellent potential of generating tumor-killing reactive oxygen species (ROS) through gentle photodynamic activation. This article provides a comprehensive review of the recent developments and improvements in optical properties of ZnO NPs as photosensitizers for PDT. The optical properties of ZnO-based photosensitizers are significantly dependent on their charge separation, absorption potential, band gap engineering, and surface area, which can be adjusted/tuned by doping, compositing, and morphology control. Here, we first summarize the recent progress in the charge separation capability, absorption potential, band gap engineering, and surface area of nanosized ZnO-based photosensitizers. Then, morphology control that is closely related to their synthesis method is discussed. Following on, the state-of-art for the ZnO-based NPs in the treatment of hypoxic tumors is comprehensively reviewed. Finally, we provide some outlooks on common targeted therapy methods for more effective tumor killing, including the attachment of small molecules, antibodies, ligands molecules, and receptors to NPs which further improve their selective distribution and targeting, hence improving the therapeutic effectiveness. The current review may provide useful guidance for the researchers who are interested in this promising dynamic cancer treatment technology.
Herein we report on the degradation performance of three phthalocyanine-photosensitized TiO2 nanocomposites on waste dyes such as Ponceau 4 R, Sella Fast Black, Congo Red, Select Brown, Indigo Carmine, Brilliant Blue, Fuchsin, Fluorescein and Naphthol Yellow S. All experiments were carried on at neutral pH, in ambient conditions, requiring only visible light and no additional oxidants. Chlorinated copper (II) α-phthalocyanine (αClCuPc), copper (II) β-phthalocyanine (βCuPc), and tetra-sulfonated copper (II) β-phthalocyanine (βSCuPc) increased the decolourization efficiency of TiO2 from moderate to high degrees, i.e., 30-100%, even for recalcitrant azo-dyes such as Ponceau 4 R, Sella Fast Black, Congo Red and Select Brown. Moreover, the photosensitized catalysts display good thermal, operational stability, and reusability, providing total organic carbon (TOC) removal above 50% within 180 minutes in batch conditions. The reactive oxygen species were generated in the presence of dissolved oxygen, through the activation of phthalocyanine/TiO2 and it can be combined further with enzymatic/microbial treatment to achieve total mineralization.
Herein we report the successful synthesis of stable silver nanoparticles (AgNPs) using 1,1′-(quinoxaline-2,3-diylbis(azanediyl))diethanol (QX) as the only stabilizer. The QX-AgNPs system was then employed as chromogenic probe for the selective detection of L-cysteine (Cys), Mg²⁺, and Sn²⁺ in the presence of interfering species. We discuss the role of pH for differentiation between Mg²⁺ and Sn²⁺ in terms of analyte-induced aggregation mechanisms. Limits of detection reached 2.7 nmol L⁻¹, 15 nmol L⁻¹ and 18 nmol L⁻¹ for Cys, and Mg²⁺ and Sn²⁺, respectively, which are levels comparable to other reported probes. Concerning Mg²⁺, the LOD found in this study was the lowest ever reported. The QX-AgNPs were also successfully employed in the quantification of Cys in urine and Mg²⁺ in tap water.
Recently, the development of green methods for carbon dots (CDs) synthesis using natural precursors has received considerable attention. In this regard, fluorescent CDs with high quantum yield have been synthesized from Red Beetroot as a natural precursor via a low-cost, simple, and green one-step hydrothermal treatment. The prepared CDs with a size range of 5-7 nm exhibited significant advantages, including great water solubility, low cytotoxicity, high quantum yield (27.6%), incredible resistance to pH alteration, high salty environments, and photobleaching. The fluorescence emission wavelength with maximum intensity for CDs was 525 nm at the excitation wavelength of 450 nm. These green-emitting CDs were employed for selective and sensitive measurement of Pd²⁺ in an aqueous solution. The addition of Pd²⁺ resulted in fluorescence quenching of CDs through a static quenching mechanism with an acceptable limit of detection of 33 nM in a linear range from 3μM to 43 μM. Also, the proposed fluorescent probe can be applied as a suitable sensor for measuring Pd²⁺ ions in Mineral and Well water samples with satisfactory recovery rates from 96.6 to 105.0%. Generated fluorescent CDs have been used as an attractive biocompatible label for cellular imaging and showed an excellent quenching response by the addition of Pd²⁺ ions. As a result, the proposed CDs-based probe could be utilized in various environmental applications.
In this work, nitrogen-doped carbon dots (N-CDs) based fluorescent probes were synthesized using m-phenylenediamine and citric acid as both nitrogen and carbon source through the hydrothermal method. The structural and optical properties of synthesized N-CDs were investigated by transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), UV–vis spectroscopy, Zeta potential, and photoluminescence (PL). The water-soluble N-CDs showed a narrow size distribution within 6–8 nm. The emission peak with maximum intensity for N-CDs was 535 nm at the excitation wavelength of 470 nm, and the quantum yield of N-CDs was 30.2%. The as-prepared N-CDs could be selectively quenched by Fe³⁺ ions with a limit of detection (LOD) of 13.8 nM in a linear range from 0.002 μM to 8 μM. Furthermore, examining the validity of the present fluorescence N-CDs probe showed that the proposed method has enough reliability and sensitivity for detecting Fe³⁺ ions in an acceptable recovery range from 97 to 106.4% in the real samples. The probe indicated high stability and selectivity to be a suitable candidate for environmental applications.
Herein, spirulina algae were used for synthesizing green fluorescent-carbon dots (G-CDs) due to their featured properties and compatibility in the environment. New G-CDs-based fluorescent probes have been synthesized through a facile hydrothermal method, and various techniques were employed to characterize chemical compositions, physical and optical operations of G-CDs. The G-CDs exhibited an optimal emission wavelength at 520 nm with an exaction wavelength at 450 nm, and quantum yield was found to be 32%. Remarkably, the intensity of fluorescence G-CDs could be selectivity and rapidly quenched by copper (II) ion (Cu²⁺), with the limit of detection of (LOD) 11.9 nM and a linear range of 0.01-0.1 μM. Meanwhile, upon adding oxalate (C2O4²⁻) into the solution, the fluorescence intensity of G-CDs was restored. The LOD for C2O4²⁻ detection was estimated to be 3.5 μM with the concentration in the range of 0-45 μM. Furthermore, the designed fluorescent probe has been successfully utilized for the detection of Cu²⁺ in tap and mineral water as well as for biosensing of Cu²⁺ in living cells without surface modification.
Zwitterionic carbon dots (CDs) have obtained great attention due to good photostability, high biocompatibility, and quantum yield. Herein, novel zwitterionic CDs were synthesized via a simple hydrothermal method of citric acid (CA) and l‐histidine as a carbon and nitrogen precursor, respectively. Prepared zwitterionic CDs have an average particle size of 4 nm in diameter and showed green fluorescence with a peak at 530 nm when excited at 470 nm, and quantum efficiency (QY) was found to be 39.34% using Rhodamine 6G as a baseline. The fluorescence intensity of zwitterionic CDs was quenched by rituximab in the range of 0‐400 μmol L‐1, with a limit of detection of 27 μmol L‐1. Besides, the synthesized zwitterionic CDs were represented low toxicity, good stability, high selectivity, and sensitivity sensing of rituximab, so that the zwitterionic CDs are a promising candidate for practical applications.
As magnesium ions have been considered as one of the most important cations for many physiological and pathological functions since the past century, selective and specific detection of magnesium ions with chemosensors has drawn great interest and became essential in biomedical and biological studies. Herein, we report on highly fluorescent boron doped carbon dots (BCDs) that are synthesized from catechol as carbon source and naphthalene boronic acid as the boron source by a simple solvothermal method. The obtained BCDs exhibited violet luminescence with quantum yield of 39.4 %, which is higher than any previous report. For the first time, the as-prepared BCDs were explored for highly selective and sensitive detection of Mg2+ ion over Ca2+ ion. This method is based on a fluorescence property resulting from the strong complex formed between Mg2+ and BCDs, with limit of detection (LOD) of about 39 µM, which is much less than the concentration range of intracellular Mg2+ ion in mammalian cells (0.5-0.7 mM). Remarkably, the BCDs can be effectively reusable upon gradual addition of EDTA to the BCDs-Mg2+ complex. The oxygen moieties on the BCDs surfaces are probable active binding sites towards Mg2+ ions for enhancing the fluorescence. Therefore, BCDs could be useful for the detection of Mg2+ ions without using expensive instruments and materials. To the best of our knowledge, this is the first report on detection of magnesium ion using carbon dots.
A new fluorescent schiff base chemosensor (H2L) was prepared for the sensitive and selective sensing of Mg²⁺ ions based on multiple mechanisms. H2L is a weak fluorescent (f = 0.031) due to PET process and CN isomerization. Upon addition of Mg²⁺, the complex [MgL] was formed and a remarkable fluorescence enhancement (f = 0.182) was produced. H2L had no such significant effect on the fluorescence in the presence of metal ions, such as Na⁺, Ag⁺, K⁺, Ca²⁺, Mg²⁺, Hg²⁺, Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺, Cr³⁺, Fe³⁺, and In³⁺. The satisfactory linear relationship was observed between the added concentrations of Mg²⁺ and the fluorescence intensity of H2L. The detection limit was 3.04 × 10⁻⁹ M with a rapid response time. Chemical inputs of Mg²⁺ and Fe³⁺ ions satisfy the conditions of INHIBIT molecular logic gate.
A fluorescent probe was rational designed and prepared to distinguish Mg²⁺ ion from Ca²⁺ ion, in which 8-hydroxyquinoline acted as not only a fluorophore but also a recognition group. Notably, this probe QB (8-hydroxyquinoline-5-benzothiazole) shows two fluorescence response modes for highly selective detection of Mg²⁺ ion, namely fluorescence ratiometric mode and turn-on mode, which can be realized by controlling the excitation wavelength at 356 nm or 425 nm. After the addition of Mg²⁺ ion, the color of the QB solution changed from colorless to yellow, which can be easily found by naked eye. All experimental results suggested that probe QB has a high selectivity toward Mg²⁺ ion in the presence of other cations. Its detection limit for Mg²⁺ ion was estimated as low as 0.142 μM, and this value was far lower than the intracellular concentration (0.5–1.2 mM). The detection mechanism was proposed further by the experiment of ¹H NMR titration and theoretical calculation. More significantly, this probe was successfully used to detect Mg²⁺ ion in brine samples as a quantitative method, and was also applied to detecting and imaging Mg²⁺ ion in living cells, indicating its great application value in practical use for the detection of Mg²⁺ ion.
Carbon quantum dot/carbon dot (CD) exhibiting sustained photoluminescence at longer wavelengths in aqueous solution is difficult to prepare, but has enormous potential in biomedical applications. For the first time, we report the magnesium(II) selective fluorescence enhancement of a red-light emitting anthrarufin and boric acid-derived CD in aqueous solution for direct evaluation of creatine kinase (CK) enzyme activity. The CD displayed visually detectable, intense red fluorescence only in the presence of magnesium ion (Mg2+) at physiological pH value when irradiated with an ultraviolet (UV) source. Concurrently, a significant increase in steady-state fluorescence intensity and fluorescence lifetime was documented. A time-dependent density functional theory (TD-DFT) analysis displayed a bathochromic shift in UV-visible (vis) absorption, and increased oscillator strength of transition resulting from the selective chelation of Mg2+ with β-hydroxy keto functionality on the surface of the CD. The CD-Mg2+ assembly was subsequently used to conceptualize the detection of CK directly through the exploration of the differential binding affinity of Mg2+ with adenosine triphosphate (ATP), adenosine diphophate (ADP), and CD that is otherwise not possible with commercially available kits as of today. Thus, the report delineated here usher grandeur potential of CD for biological explorations related to Mg2+ or ATP sensing and monitoring of Mg2+-dependent enzymatic activity through a clear understanding of the chemistry.
The fibrocartilaginous enthesis regeneration after rotator repair is still a major challenge. Although magnesium-based alloy orthopedic implant is effective to promote fibrocartilage formation at the tendon-bone interface in the anterior cruciate ligament reconstruction model, it was limited in the rotator cuff repair for its special anatomical structure. Herein, we developed a multifunctional self-healing magnesium ions-quaternized chitosan/Pluronic® F127(Mg-QCS/PF) hydrogels to achieve in-situ and customized release of Mg²⁺, and demonstrated the sustained release of Mg²⁺ from the hydrogel to significantly promote the rotator cuff repair in the rabbit rotator cuff tear model. The obtained hydrogels showed excellent self-healing and anti-compressive performance. Additionally, the good injectability and adhesive properties of the hydrogels make it easier and stable to deliver Mg²⁺ at the tendon-bone interface with irregular shapes. The release of Mg²⁺ from Mg-QCS/PF hydrogels improved the adhesion, proliferation and migration of bone mesenchymal stem cells (BMSCs) and MC3T3 cells in vitro compared with QCS/PF without Mg²⁺. Furthermore, the composite hydrogels significantly enhanced the fibrocartilaginous interface regeneration in the rabbit rotator cuff tear model in terms of repaired tendon mature scores, fibrocartilage regeneration, collagen remodeling and biomechanical properties. This is the first study to demonstrate the positive effects of Mg²⁺ for the rotator cuff healing in the rabbit preclinical model, and the results indicate that the acellular injectable self-healing Mg-doped hydrogels are candidates to effectively promote in situ regeneration of rotator cuff.
Photosensitization is a promising avenue of oxygen activation, which can overcome the spin selection rule to transform the ground state oxygen (3O2) into the highly reactive singlet oxygen (1O2). Carbon dots (CDs) are a promising type of carbon-based photosensitizers, and nitrogen doping can further improve the oxygen photosensitization performance. Although the roles of nitrogen doping in turning the optical properties (mainly absorption and fluorescence) of CDs have been well-studied, their association with the oxygen photosensitization was not reported. Herein, using the well-developed synthetic protocol of hydrothermal treatment of citric acid and ethylenediamine, we prepared nitrogen-doped CDs (N-CDs) of varied nitrogen contents. The oxygen photosensitization performances of the N-CDs were first confirmed with ROS investigation with TMB oxidation as the ROS probe and EPR. After XPS analysis of the surface nitrogen doping speciation, it was found that the changes of graphitic N and pyrrolic N correlated well with the oxygen photosensitization performances of N-CDs. Further theoretical calculations indicated that the two key factors for oxygen photosensitization, namely triplet activation and oxygen adsorption, are mainly associated with graphitic N and pyrrolic N, respectively. The results in this work help further understanding of the oxygen photosensitization mechanism of N-CDs, and are expected to be useful in future designing of carbon-based photosensitizers.
Carbon dots (CDs) are prepared through a simple one-step hydrothermal treatment of o-phenylendiamine (OPD) and show yellow photoluminescent (PL) emission under the ultraviolet excitation, which can be further enhanced by Cu ²⁺ ions owing to Cu ²⁺ ions induced aggregation of OPD-CDs through the coordination of Cu ²⁺ with amino groups on the surface of OPD-CDs. The aggregation induced emission enhancement (AIEE) property enables it feasible to develop a simple, sensitive and selective method to detect environmental and intracellular copper (II) ions. The limit of detection as low as 0.28 μmol/L (3σ/k) and a dynamic range from 0.5 μmol/L to 40 μmol/L make it very easy to detect the copper content in water samples, such as river closure reservoir. Furthermore, fluorescence imaging of intracellular Cu ²⁺ suggests that the AIEE features of OPD-CDs specific to Cu ²⁺ ions can be also applied in biological systems.
Materials for photosensitized oxygen activation is extremely important for a suite of photodynamic applications in biomedical, analytical and energy sectors. Carbon-based photosensitizers are attractive for their low cost and high stability, but most of them such as fullerene and graphene quantum dots suffer from low efficiency, and rational design of carbon-based photosensitizers remains a challenge. Given the similar chemical origin of phosphorescence and photosensitization, we herein synthesized a series of nitrogen-doped carbon dots (C-dots) and confirmed that their photooxidation activity correlated with their phosphorescence quantum yields, providing a direction for rational designing of such materials. Compared to other carbon nanomaterials and molecular photosensitizers, these C-dots have the highest activity, and they can finish oxidation reactions in a few seconds. The excellent photosensitized oxygen activation makes these water-soluble C-dots a promising oxidase-mimicking nanozyme for photodynamic antimicrobial chemotherapy and other applications.
A novel “off-on” fluorescent probe based on 1, 8-naphthalimide derivative for the detection of Mg²⁺ in ethanol solution was designed and synthesized. The probe displayed responses to Mg²⁺ with a fluorescence enhancement at 523 nm, accompanying with a distinct fluorescence change from nearly colorless to bright yellow-green. Besides, the probe showed a rapid detection process (45 s), high fluorescence enhancement (up to 15-fold), a good binding constant (6.17 × 10⁵ M⁻¹) and a low detection limit of Mg²⁺ (5.01 × 10⁻⁸ M). Moreover, density functional theory (DFT) calculations were also performed to support the responding mechanism between the probe and the coordination complex. In addition, the cell cytotoxicity experiments suggested that the probe is nearly non-toxic and the fluorescence scanning microscopic experiments demonstrated that the probe was capable of monitoring at the intracellular Mg²⁺ level successfully.
A new fluorescent sensor, 5-methyl-1H-pyrazole-3-carboxylic acid (6-methoxy-naphthalen-2-ylmethylene)-hydrazide (PYN), composed of a naphthalene group as the fluorogenic unit and a pyrazole carbohydrazide as the binding unit for metal ions has been designed and synthesized. The sensor shows excellent selectivity and sensitivity with a fluorescence enhancement towards Zn²⁺ and Mg²⁺ over other cations in aqueous acetonitrile solution. Turn-on fluorescent enhancements (FE) as high as ∼49 fold and ∼41 fold in mixed media for Zn²⁺ and, Mg²⁺ respectively were noticed. The signal enhancement of the sensor is based on chelation-enhanced fluorescence (CHEF) effect of PYN-Zn²⁺/Mg²⁺ with the inhibition of the photoinduced electron transfer (PET) effect. Moreover, the Job's plot established 1 : 1 stoichiometry of the complex formation between PYN and Zn²⁺ or Mg²⁺ ions. The limit of detection for Zn²⁺ and Mg²⁺ is as low as 2.2 × 10⁻⁷ M and 3.9 × 10⁻⁷ M respectively. PYN exhibited a second mode of selectivity for Zn²⁺ as it displaces Mg²⁺ from the PYN-Mg²⁺ complex. Density Functional Theory (DFT) calculations have been performed in order to show the structure and electronic properties of PYN and its complexes [PYN-Zn²⁺/Mg²⁺]. Cell imaging experiments confirmed that PYN can be used for monitoring intracellular Zn²⁺ and Mg²⁺ levels in living cells in vitro.
Thymol (2-isopropyl-5-methylphenol), the major constituent of ajwain, is a naturally occurring monoterpene phenol having antioxidant, anti-inflammatory and antimicrobial activities. Herein, we report 4-hydroxy-5-isopropyl-2 methylisophthalaldehyde (DFT) derived from thymol and its derivatives as selective fluorescent chemosensors for Mg2+ in aqueous medium. These probes can selectively detect Mg2+ ion and efficiently images intracellular free Mg2+ in living RAW 264.7 and HeLa cells under fluorescence microscope without any interference from common metal ions. Density Function Theory studies strongly support the experimental facts.
Two novel water-soluble coumarin-based compounds (OC7, NC7) were designed and synthesized as two-photon fluorescent probes for biological Mg2+ detection. The compounds feature a beta-keto acid as a high selective binding site for Mg2+ and the coumarin framework as the two-photon fluorophore. OC7 and NC7 show significant "off-on" detecting signals (9.1-fold and 23.8-fold fluorescence enhancement) and lower detection limits compared with previous reported two-photon fluorescent probes for Mg2+. Moreover, OC7-Mg2+ and NC7-Mg2+ exhibit large two-photon absorption cross sections (340 GM and 615 GM) at the near infrared wavelengths(740 nm and 860 nm), which indicates that the probes are very suitable for detection of Mg2+ in vivo. Both OC7 and NC7 are pH-insensitive and of low cytotoxicity and can be applied to image intracellular Mg2+ under two-photon microscopy (TPM). Our results provide a strategy to modify the coumarin fluorophore to get better two-photon fluorescent properties. And the results also suggest that electronic density of beta-keto acid plays a very important role in the recognition of Mg2+.
Carbon dots (Cdots) are an important probe for imaging and sensing applications because of their fluorescence property, good biocompatibility, and low toxicity. However, complex procedures and strong acid treatment are often required and Cdots suffer from low photoluminescence (PL) emission. Herein, a facile and general strategy using carbonization of precursors and then extraction with solvents is proposed for the preparation of nitrogen-doped Cdots (N-Cdots) with 3-(3,4-dihydroxyphenyl)-L-alanine (L-DOPA), L-histidine, and L-arginine as precursor models. After they are heated, the precursors become carbonized. Nitrogen-doped Cdots are subsequently extracted into N,N'-dimethylformamide (DMF) from the carbogenic solid. A core-shell structure of Cdots with a carbon core and the oxygen-containing shell was observed. Nitrogen has different forms in N-Cdots and oxidized N-Cdots. The doped nitrogen and low oxidation level in N-Cdots improve their emission significantly. The N-Cdots show an emission with a nitrogen-content-dependent intensity and Cdot-size-dependent emission-peak wavelength. Imaging of HeLa cells, a human cervical cancer cell line, and HepG2 cells, a human hepatocellular liver carcinoma line, was observed with high resolution using N-Cdots as a probe and validates their use in imaging applications and their multicolor property in the living cell system.