A Dual-emitting Two-dimensional Nickel-based Metal-organic Framework Nanosheets: Eu3+/Ag+ Functionalization Synthesis and Ratiometric Sensing in Aqueous Solution

Using two-dimensional (2D) nickel-based metal organic framework (Ni-MOF) nanosheets as a matrix, Eu³⁺ and Ag⁺ were incorporated to synthesize Ag/Eu@Ni-MOF with double luminescence centers of Eu³⁺ ion (615 nm) and organic ligand (524 nm). And a ratiometric luminescence sensor is constructed based on Ag/Eu@Ni-MOF for sensitive detection of biothiols in aqueous solutions. The dual-emissive fluorescence properties can be tuned by changing the amounts of Ag⁺ ions doping. The results of temperature and pH effects on the fluorescence of Ag/Eu@Ni-MOF indicates that the Ag/Eu@Ni-MOF is a temperature-sensitive material and the fluorescence of Ag/Eu@Ni-MOF can keep stable over a wide pH range. Due to the binding of -SH in cysteine (Cys) and glutathione (GSH) with Ag⁺, the ligand luminescence was significantly inhibited by weakening the Ag?+?influence on the energy transfer process in the MOFs. Therefore, ratiometric fluorescent sensing of biomolecular thiols was realized based on the dual-emission Ag/Eu@Ni-MOF. More importantly, the fluorescence color change can be observed with naked eyes to realize visual detection. The ratiometric fluorescent sensor exhibits high performance for Cys and GSH detection with a wide linear range of 5-250 µM and a relatively low detection limit of 0.20 µM and 0.17 µM, respectively. Furthermore, the biothiols content in human serum was determined with satisfactory results. It proves the Ni-MOF nanosheets can be used as a stable matrix for construction luminescent MOFs for the first time, and validate the great potential of Ag/Eu@Ni-MOF as a ratiometric fluorescent probe for point-of-care testing (POCT) in disease diagnosis.

     

Gold‐Cluster‐Based Dual‐Emission Nanocomposite Film as Ratiometric Fluorescent Sensing Paper for Specific Metal Ion

A dual‐emission ratiometric fluorescent sensing film for metal ion detection is designed. This dual‐emission film is successfully prepared from chitosan, graphitic carbon nitride (g‐C₃N₄), and gold nanoclusters (Au NCs). Here, it is shown that the g‐C₃N₄ not only serves as the fluorescence emission source, but also enhances the mechanical and thermal stability of the film. Meanwhile, the Au NCs are adsorbed on the surface of chitosan film by the electrostatic interaction. The as‐prepared dual‐emission film can selectively detect Cu²⁺, leading to the quench of red fluorescence of Au NCs, whereas the blue fluorescence from g‐C₃N₄ persists. The ratio of the two fluorescence intensities depends on the Cu²⁺ concentration and the fluorescence color changes from orange red to yellow, cyan, and finally to blue with increasing Cu²⁺ concentration. Thus, the as‐prepared dual‐emission film can be worked as ratiometric sensing paper for Cu²⁺ detection. Furthermore, the film shows high sensitivity and selectivity, with low limit of detection (LOD) (10 ppb). It is observed that this novel gold‐cluster‐based dual‐emission ratiometric fluorescent sensing paper is an easy and convenient way for detecting metal ions. It is believed that this research work have created another avenue for the detection of metal ions in the environment.     

A Significant Fluorescent Aptamer Sensor Based on Carbon Dots and Graphene Oxide for Highly Selective Detection of Progesterone

In this paper, a fluorescent aptamer sensor was constructed based on the carbon dots (CDs) and graphene oxide (GO). This sensor combines the excellent fluorescence performance of CDs with the high specificity of aptamer, which can detect progesterone (P₄) with high sensitivity and selectivity. In the absence of P₄, the CDs-aptamer system and GO form a fluorescence resonance energy transfer process (FRET), which quenches the fluorescence of the CDs. When P₄ is added, the aptamer specifically binds to it, resulting the fluorescence of the CDs is recovered. At optimal conditions, the fluorescence intensity recovered by the CDs has a linear relationship with the concentration of P₄ in the range of 0.1–120 nM and the detection limit is 3.3?×?10^–11 M. Besides, the sensor has satisfactory detection results of P₄ in milk, indicating that constructed method has enormous potential for application in food safety.

     

A Dansyl-Rhodamine Ratiometric Fluorescent Probe for Hg<Superscript>2+</Superscript> Based on FRET Mechanism

Based on resonance energy transfer (FRET) from dansyl to rhodamine 101, a new fluorescent probe (compound 1) containing rhodamine 101 and a dansyl unit was synthesized for detecting Hg²⁺ through ratiometric sensing in DMSO aqueous solutions. This probe shows a fast, reversible and selective response toward Hg²⁺ in a wide pH range. Hg²⁺ induced ring-opening reactions of the spirolactam rhodamine moiety of 1, leading to the formation of fluorescent derivatives that can serve as the FRET acceptors. Very large stokes shift (220 nm) was observed in this case. About 97-fold increase in fluorescence intensity ratio was observed upon its binding with Hg²⁺.     

Selective Ratiometric Fluorescence Detection of Acetate Based on a Novel Schiff Base Derivative

A ratiometric fluorescence and colorimetric probe based on 5,5′-methylene-bis-salicylaldehyde-p-nitrophenylhydrazone (1), which was characterized by ¹H NMR, mass spectrometer and elemental analysis, was prepared through Schiff base reaction. The probe exhibited visible color changes from yellow to purple upon interacting with acetate ion. Particularly, the compound showed ratiometric fluorescence response to acetate with significant blue shift about 150 nm from 410 nm to 560 nm. Thence, the probe 1 was a selective ratiometric fluorescence probe for acetate ion in DMSO solution.     

Magneto-optical properties of α-Fe2O3@ZnO nanocomposites prepared by the high energy ball-milling technique

Magnetic–fluorescent nanocomposites (NCs) with 10 wt% of α-Fe₂O₃ in ZnO have been prepared by the high energy ball-milling. The crystallite sizes of α-Fe₂O₃ and ZnO in the NCs are found to vary from 65 nm to 20 nm and 47 nm to 15 nm respectively as milling time is increased from 2 to 30 h. XRD analysis confirms presence of α-Fe₂O₃ and ZnO in pure form in all the NCs. UV–vis study of the NCs shows a continuous blue-shift of the absorption peak and a steady increase of band gap of ZnO with increasing milling duration that are assigned to decreasing particle size of ZnO in the NCs. Photoluminescence (PL) spectra of the NCs reveal three weak emission bands in the visible region at 421, 445 and 485 nm along with the strong near band edge emission at 391 nm. These weak emission bands are attributed to different defect – related energy levels e.g. Zn-vacancy, Zn interstitial and oxygen vacancy. Dc and ac magnetization measurements show presence of weakly interacting superparamagnetic (SPM) α-Fe₂O₃ particles in the NCs. ⁵⁷Fe-Mössbauer study confirms presence of SPM hematite in the sample milled for 30 h. Positron annihilation lifetime measurements indicate presence of cation vacancies in ZnO nanostructures confirming results of PL studies.     

Synthesis of Water Dispersible Fluorescent Carbon Nanocrystals from <Emphasis Type="Italic">Syzygium cumini</Emphasis> Fruits for the Detection of Fe<Superscript>3+</Superscript> Ion in Water and Biological Samples and Imaging of <Emphasis Type="Italic">Fusarium avenaceum</Emphasis> Cells

In this work, water dispersible fluorescent carbon nanocrystals (NCs) were synthesized by a simple, green and low cost hydrothermal method using Syzygium cumini (jamun) as a carbon source at 180 °C for 6 h. The average size of carbon NCs was found to be 2.1 ± 0.5 nm and shown bright blue fluorescence when excited at 365 nm under UV lamp. The carbon NCs were characterized by spectroscopic (UV-visible and fluorescence, Fourier transform infrared and dynamic light scattering) and high resolution transmission electron microscopic techniques. The quantum yield of carbon NCs was found to be ~5.9 % at 438 nm emission wavelength when excited at 360 nm. It was noticed that none of the metal ions quenched the fluorescence intensity of carbon NCs at 438 nm except for Fe³⁺, indicating the formation of Fe³⁺ ion-carbon NCs complexes. The linear range was observed in the concentration range of 0.01–100 μM with the corresponding detection limits of 0.001 μM, respectively. Furthermore, the carbon NCs were used as probes for imaging of fungal (Fusarium avenaceum) cells.     

A solvent-governed surface state strategy for rational synthesis of N and S co-doped carbon dots with multicolour fluorescence

ABSTRACT

Multicolour emissive carbon dots (CDs) are widely investigated by virtue of their merits on fluorescent properties. Method on heteroatom doping assisted with various solvents has been proved efficient in achieving multiple-colour-emissive CDs, especially long-wavelength emission. Herein, a synthesis of multicolour-emissive CDs by controlled surface function is reported. By tuning the thermal-pyrolysis temperature and molar ratio of reactants, optimal emission of the resulted CDs gradually shifts from blue to yellow light with the assistance of different solvents. According to the emissive relationship dependent on excitation, fluorescence lifetimes, and FT-IR of these CDs, the different surface states participated with S and N elements on the surface of carbogenic core govern fluorescent colours of the CDs. In terms of the applications, blue CDs (B-CDs) exhibits high sensitivity for ion detections of Ag⁺ and Fe³⁺, which is further illustrated to have different quenching mechanisms each other because that these ions have the affinity interaction with different surface groups of the CDs. Moreover, blue and yellow CDs solutions are mixed with PVP water solution to fabricate white-light CDs/PVP film, which exhibits stable fluorescence with a CIE coordinate of (0.32, 0.33) and endows these CDs as potentially fluorescent nanomaterial in the solid state lighting field.     

Temperature dependent luminescence of Dy3+ doped BaYF5 nanoparticles for optical thermometry

Dy³⁺ doped BaYF₅ nanoparticles with tetragonal structure were synthesized by hydrothermal method and solvothermal method. The structural and the luminescent properties of the samples were characterized by X-ray diffraction pattern, TEM and photoluminescence spectra. Emission of Dy³⁺ originated from ⁴I_15/2 located at 450 nm and ⁴F_9/2 located at 478 nm, 573 nm and 660 nm were observed under excitation of 355 nm laser. Behavior of fluorescence intensity ratio with temperature increasing from room temperature to approximately 800 K was investigated. And the optimum temperature range for thermometry is obtained to be 550–800 K according to its sensitivity-temperature relation, indicating the potential application of BaYF₅:Dy³⁺ as a luminescent temperature sensor.     

One-pot synthesis of carbon dots co-doped with N and S: high quantum yield governed by molecular state and fluorescence detection of Ag+

Fluorescent carbon-based nanoparticles, called chronically as carbon dots (CDs), were synthesised from citric acid (CA) and 2-Aminothiophenol (2AT) via an N and S co-doped hydrothermal method. After a series of micro-structural characterisation, N and S elements could be sufficiently doped by means of the heteroatom in the CDs solution. The as-prepared CDs solution showed blue colour fluorescence with the highest QY of 78.6%, and study on the UV–visible and PL spectra further revealed that the outstanding fluorescence of as-prepared CDs mainly originates from the generated molecular fluorophores instead of the surface state. Owing to the strong fluorescence, the as-prepared CDs can be used as a sensing probe for the detection of Ag⁺ with high sensitivity and selectivity. However, the changes of fluorescence intensity exhibited the complex nature of the quenching mechanism due to the –SH and –NH₂ groups on the fringes of carbonaceous cores or molecular fluorophores to aggregate into another fluorescent cores with the assistance of Ag⁺ ions, which promises a new approach for efficient detection of Ag⁺ for the application in industrial pollutants.

This figure shows citric acid (CA) and 2-Aminothiophenol (2AT) via an N and S co-doped hydrothermal method to prepare CDs with blue colour fluorescence and the highest QY of 78.6%. Owing to the excellent fluorescence, the as-prepared CDs can be used as a sensing probe for the detection of Ag⁺ with high sensitivity and selectivity, and the changes of fluorescence intensity exhibited the complex nature of the quenching mechanism due to the –SH and –NH₂ groups on the fringes of carbonaceous cores or molecular fluorophores to aggregate into another fluorescent cores with the assistance of Ag⁺ ions, which promises a new approach for efficient detection of Ag⁺ for the application in industrial pollutants.     

Versatile Fluorescent Carbon Dots from Citric Acid and Cysteine with Antimicrobial,Anti-biofilm,Antioxidant, and AChE Enzyme Inhibition Capabilities

Nanostructured fluorescent particles derived from natural molecules were prepared by a green synthesis technique employing a microwave method. The precursors citric acid (CA) and cysteine (Cys) were used in the preparation of S- and N-doped Cys carbon dots (Cys CDs). Synthesis was completed in 3 min. The graphitic structure revealed by XRD analysis of Cys CDs dots had good water dispersity, with diameters in the range of 2–20 nm determined by TEM analysis. The isoelectric point of the S, N-doped CDs was pH value for 5.2. The prepared Cys CDs displayed excellent fluorescence intensity with a high quantum yield of 75.6?±?2.1%. Strong antimicrobial capability of Cys CDs was observed with 12.5 mg/mL minimum bactericidal concentration (MBC) against gram-positive and gram-negative bacteria with the highest antimicrobial activity obtained against Staphylococcus aureus. Furthermore, Cys CDs provided total biofilm eradication and inhibition abilities against Pseudomonas aeruginosa at 25 mg/mL concentration. Cys CDs are promising antioxidant materials with 1.3?±?0.1 μmol Trolox equivalent/g antioxidant capacity. Finally, Cys CDs were also shown to inhibit the acetylcholinesterase (AChE) enzyme, which is used in the treatment of Alzheimer’s disease, even at the low concentration of 100 μg/mL.

     

A Colorimetric and Ratiometric Fluorescent Chemosensor for Fluoride Based on Proton Transfer

N-Phenyl-N’-(3-quinolinyl)urea (1) has been developed as a highly selective colorimetric and ratiometric fluorescent chemosensor for fluoride ion based on a proton transfer mechanism. Evidences for the mechanism were provided by UV-vis and fluorescence titration and especially ¹H and ¹⁹F NMR experiments. The sensor gave the largest ratiometric fluorescent response reported so far (R_max/R_min = 2620) to fluoride. Taking H⁺ as the “recovering reagent”, the sensor can be reversibly “used” and “recovered” for several cycles with only a slight decay of the response ability.     

A Fluorescence Turn-on Sensor for Hg<Superscript>2+</Superscript> with a Simple Receptor Available in Sulphide-Rich Environments

Detection of Hg²⁺ in complex natural environmental conditions is extremely challenging, and no entirely successful methods currently exist. Here we report an easy-to-prepare fluorescent sensor B3 with 2-aminophenol as Hg²⁺ receptor, which exhibits selective fluorescence enhancement toward Hg²⁺ over other metal ions. Especially, the fluorescence enhancement was unaffected by anions and cations existing in environment and organism. Moreover, B3 can detect Hg²⁺ in sulphide-rich environments without cysteine, S^2- or EDTA altering the fluorescence intensity. Consequently, B3 is capable of distinguishing between safe and toxic levels of Hg²⁺ in more complicated natural water systems with detection limit ≤2 ppb.     

比率型碳点荧光传感器检测机理与应用研究进展

比率型荧光传感器由于具有抗干扰能力强和灵敏度高等优点,在食品安全、金属离子检测、环境污染分析等许多领域显示出巨大的应用潜力。而碳点作为一种新型荧光材料,不仅具有优良的荧光性能,而且毒性低、易于表面功能化,非常适合构建比率型荧光传感器。本文就近年来比率型碳点荧光传感器在检测领域的研究进展进行综述,重点阐述了碳点的荧光检测机理,并根据碳点使用情况的不同,对不同类型的比率型碳点荧光传感器进行了分类总结。最后提出了该领域亟待解决的困难和问题,并对其在分析物检测方面的发展方向进行了展望。     

A highly selective fluorescent chemosensor for Cu2+ based on a diarylethene with a 2,1,3‐benzoxadiazole unit

A novel photochromic diarylethene containing a 2,1,3‐benzoxadiazole structure has been synthesized and its multicontrollable fluorescence properties have been systematically studied by the stimulation of light and metal ions. The compound exhibited favorable photochromism and fluorescent switching properties. Furthermore, it can serve as a fluorescent chemosensor for highly selective recognition of Cu²⁺ in aqueous acetonitrile. When triggered by Cu²⁺, it displayed a remarkable blue shift from 594 to 524 nm (70 nm) with a significant fluorescence color change from yellow to bright green. As a result, a logic circuit has also been constructed on the basis of light and chemical stimulation.     

Near-white emitting QD-LED based on hydrophilic CdS nanocrystals

In this work we report fabrication of a nanocrystal (NC)-based hybrid organic–inorganic LED with structure of ITO/PEDOT:PSS/PVK/CdS-NCs/(Al or Mg:Ag). The hydrophilic CdS NCs were synthesized using a novel aqueous thermochemical method at 80 °C and sizes (around 2 nm) were controlled by thioglycolic acid (TGA) as the capping agent. The favorite feature of these NCs is their relatively high emission intensity and broad, near-white emission. The hydrophilic CdS NCs were successfully spin coated using Triton X-100 as the wetting agent. The fabricated LEDs demonstrated a turn on voltage about 7 V for Al metallic contact. The electroluminescence was a broad spectrum at 540 and 170 nm width, which was about 50 nm red shifted compared to photoluminescence spectra. The CIE color coordinates of the LED at (0.33, 0.43) demonstrated a near white light LED with an emission on green–yellow boundary of white. Annealing of the device up to 190 °C had a positive effect on the performance, possibly due to better contacts between layers. Replacing Al contacts with Mg:Ag reduced the turn-on voltage to 6 V and changed CIE color coordinate to (0.32, 0.41). The EL peak was also shifted to 525 nm, with a brightness of 15 Cd/m² at working voltage of 15 V. The current efficiency and external quantum efficiency of device were 0.08 Cd/A and 0.03% at current densities higher than 10 mA/cm².     

One step synthesis of ultra-high quantum yield fluorescent carbon dots for “on-off-on” detection of Hg2+ and biothiols

In this paper, the carbon dots (CDs) with strong blue fluorescence were synthesized through hydrothermal method, which using folic acid, ammonium citrate and ethylenediamine as precursors. The prepared CDs with a high absolute quantum yield of 81.94% and showed excellent stability in high concentration salt solution and different pH conditions. With the addition of Hg²⁺, the signal of CDs was selectively quenched. At the same time, the CDs-Hg²⁺ system could be recovered after the introduction of biothiols. Moreover, the fluorescence of CDs showed a good linear relationship with Hg²⁺ (1–15 µM), and the detection limit as low as 0.08 µM. In addition, the prepared CDs with low toxicity could be used to detect Hg²⁺ in living cells and actual water samples.

     

Dual Fluorometric Detection of Fe3+ and Hg2+ Ions in an Aqueous Medium Using Carbon Quantum Dots as a “Turn-off” Fluorescence Sensor

The present study aimed to develop a carbon dots-based fluorescence (FL) sensor that can detect more than one pollutant simultaneously in the same aqueous solution. The carbon dots-based FL sensor has been prepared by employing a facile hydrothermal method using citric acid and ethylenediamine as precursors. The as-synthesized CDs displayed excellent hydrophilicity, good photostability and blue fluorescence under UV light. They have been used as an efficient “turn-off” FL sensor for dual sensing of Fe³⁺ and Hg²⁺ ions in an aqueous medium with high sensitivity and selectivity through a static quenching mechanism. The lowest limit of detection (LOD) for Fe³⁺ and Hg²⁺ ions was found to be 0.406 µM and 0.934 µM, respectively over the concentration range of 0-50 µM. Therefore, the present work provides an effective strategy to monitor the concentration of Fe³⁺ and Hg²⁺ ions simultaneously in an aqueous medium using environment-friendly CDs.

Graphical Abstract

     

The Contribution of Raman Scattering to the Fluorescence of the Polyene Antibiotic Amphotericin B

Fluorescence has recently been applied to the analysis of the molecular organization state of the polyene antibiotic amphotericin B (AmB) in solution or in lipid membranes. The polyene chain of AmB monomer gives rise to two fluorescence emissions; S₁(2¹A_g) → S₀(1¹A_g) between 500 and 700 nm, S₂(1¹B_u) → S₀(1¹A_g) between 400 and 500 nm. However, Raman scattering might interfere with the S₂ → S₀ emission fluorescence due to the weak fluorescence quantum yield and close proximity to the exciting lines. In fact, we show here that a change in the excitation wavelength results in a shift of three emission bands, an effect which excludes their assignment to fluorescence. These bands originate from the water Raman at 3382 cm^-1and AmB resonance Raman at 1556 and 1153 cm^-1. As a consequence, some former conclusions on the molecular organization state of AmB should be reconsidered.     

A Ratiometric and near-Infrared Fluorescent Probe for Imaging Cu<Superscript>2+</Superscript> in Living Cells and Animals

We have rationally constructed a novel ratiometric and near-infrared Cu²⁺ fluorescent probe based on a tricarbocyanine chromophore. The new probe NIR-Cu showed a ratiometric fluorescent response to Cu²⁺ with a large emission wavelength shift (up to 142 nm) in the far-red to near-infrared region. The probe also displayed a large variation in the fluorescence ratio (I₆₃₆/I₇₇₈) to Cu²⁺ species with high sensitivity and selectivity. Additionally, the developed probe NIR-Cu was suitable for fluorescence imaging of Cu²⁺ in living cells and mice.