A Schiff base fluorescence probe for highly selective turn-on recognition of Zn2+

Highly selective Zn2+ near-infrared fluorescent probe and its application in biological imaging

Zn2+ plays a vital role in regulating various life processes, such as gene expression, cell signaling, and brain function. In this study, a near-infrared fluorescent probe AXS was synthesized to detect Zn2+ with good fluorescence specificity, high selectivity, and high sensitivity; the detection limit of Zn2+ was 6.924 × 10-11 M. The mechanism of Zn2+ recognition by the AXS probe was investigated by 1H nuclear magnetic resonance titrations, UV-visible spectroscopy, fluorescence spectroscopy, Fourier-transform infrared spectroscopy, and high-resolution mass spectrometry. Test paper experiments showed that the AXS probe could detect Zn2+ in real samples. In addition, quantitative and qualitative detection of Zn2+ in common foodstuffs was achieved. For portable Zn2+ detection, a smartphone detection platform was also developed based on the AXS probe. Importantly, the AXS probe showed good bioimaging capabilities in Caenorhabditis elegans and mice.

Schiff Base Compounds as Fluorescent Probes for the Highly Sensitive and Selective Detection of Al3+ Ions

Two new Schiff base fluorescent probes (L and S) were designed for selectively detecting Al3+ ions in aqueous medium. Structural characterization of the purely synthesized compounds was acquired by IR, 1H NMR and 13C NMR. Moreover, their photochromic and fluorescent behaviors have been investigated systematically by UV–Vis absorption and fluorescence spectra. The two probes have both high selectivity and sensitivity toward Al3+ ions in aqueous medium. The 2:1 stoichiometry between the Al3+ and probes was verified by Job’s plot. Moreover, the limits of detection (LOD) for Al3+ by L and S were 1.98 × 10−8 and 4.79 × 10−8 mol/L, respectively, which was much lower than most previously reported probes. The possible recognition mechanism was that the metal ions would complex with Schiff base probes because of the prevalence of the species optimal for complex formation, inhibiting the structural isomerization of conjugated double bonds (-C=N-), inhibiting the proton transfer process in the excited state of the molecules and resulting in changes of its color and fluorescence behavior. Furthermore, the probes will have potential applications for selectively, detecting Al3+ ions in the environmental system with high accuracy and providing a new strategy for the design and synthesis of multi-functional sensors.

Highly fluorescent N doped C-dots as sensor for selective detection of Hg2+ in beverages

In this work, nitrogen doped carbon dots (NCDs) were synthesized through one step hydrothermal reaction using citric acid and ethylenediamine as precursors. The prepared NCDs exhibit high quantum yield of 67.4%, good stability, excellent selectivity and sensitivity. It was found that the NCDs have potential as a fluorescence sensor for the detection of Hg²⁺. Under optimal conditions, good linearity between the change in NCDs fluorescence intensity and Hg²⁺ concentration was obtained in the range of 0.3 to 2.0 μM with a detection limit at 0.24 μM. The possible detection mechanism was static quenching of NCDs by Hg²⁺. The established method was successfully applied to the determination of Hg²⁺ in beverage samples. The results indicated that the NCDs-based sensor has potential for detection of Hg²⁺ in real beverage sample.

Biphenyl Containing Amido Schiff base Derivative as a Turn-on Fluorescent Chemosensor for Al3+ and Zn2+ ions

A hydrazine derived Bis(2-hydroxybenzylidene)-[1,1'-biphenyl]-2,2'-dicarbohydrazide (sensor 1) has been synthesized and its sensing properties towards metal ions has been demonstrated using simple UV-visble spectroscopic, fluorometric technique and visible colour change. The...

A novel double target fluorescence probe for Al3+/Mg2+ detection with distinctively different responses and its applications in cell imaging

The metal cations, Al³⁺ and Mg²⁺, could affect human health and cell biological processes. Their fast and selective detection using one probe remains a challenge. A novel fluorescence probe, N'-((1-hydroxynaphthalen-2-yl)methylene)isoquinoline-3-carbohydrazide (NHMI), was developed for selectively monitoring Al³⁺ and Mg²⁺. The probe NHMI showed a distinctive "turn-on" fluorescence signal towards Al³⁺ and Mg²⁺ (cyan for Al³⁺ with 2556-folds enhancement and yellow for Mg²⁺ with 88-folds enhancement), which is quite distinct from other metal cations and allows for naked-eye detection. This interesting response was attributed to the influence of PET, ESIPT process and CHEF effect, when Al³⁺ or Mg²⁺ chelated with NHMI. Furthermore, the fluorescence titration experiments manifested that the detection limit of probe NHMI for Al³⁺/Mg²⁺ was as low as 1.20 × 10^-8 M and 7.69 × 10^-8 M, respectively. The formed complexes NHMI-Al³⁺ and NHMI-Mg²⁺ were analyzed by Job's plot, ESI-MS, ¹H NMR and FT-IR. The coordination pockets and fluorescence mechanisms of two metal complexes were explored by density functional theory calculation. Moreover, NHMI showed low cytotoxicity and good cell permeability. Fluorescence bioimaging of Al³⁺/Mg²⁺ in MCF-7 cells with NHMI indicated its potential application in biological diagnostic analysis.

Nanosensors Based on Structural Memory Carbon Nanodots for Ag+ Fluorescence Determination

Ag⁺ pollution is of great harm to the human body and environmental biology. Therefore, there is an urgent need to develop inexpensive and accurate detection methods. Herein, lignin-derived structural memory carbon nanodots (C_SM-dots) with outstanding fluorescence properties were fabricated via a green method. The mild preparation process allowed the C_SM-dots to remain plentiful phenol, hydroxyl, and methoxy groups, which have a specific interaction with Ag⁺ through the reduction of silver ions. Further, the sulfur atoms doped on C_SM-dots provided more active sites on their surface and the strong interaction with Ag nanoparticles. The C_SM-dots can specifically bind Ag⁺, accompanied by a remarkable fluorescence quenching response. This “turn-off” fluorescence behavior was used for Ag⁺ determination in a linear range of 5–290 μM with the detection limit as low as 500 nM. Furthermore, findings showed that this sensing nano-platform was successfully used for Ag⁺ determination in real samples and intracellular imaging, showing great potential in biological and environmental monitoring applications.

A Highly Selective Turn-On Fluorescent Probe for the Detection of Zinc

A novel turn-on fluorescence probe L has been designed that exhibits high selectivity and sensitivity with a detection limit of 9.53 × 10⁻⁸ mol/L for the quantification of Zn²⁺. ¹H-NMR spectroscopy and single crystal X-ray diffraction analysis revealed the unsymmetrical nature of the structure of the Schiff base probe L. An emission titration experiment in the presence of different molar fractions of Zn²⁺ was used to perform a Job’s plot analysis. The results showed that the stoichiometric ratio of the complex formed by L and Zn²⁺ was 1:1. Moreover, the molecular structure of the mononuclear Cu complex reveals one ligand L coordinates with one Cu atom in the asymmetric unit. On adding CuCl₂ to the ZnCl₂/L system, a Cu-Zn complex was formed and a strong quenching behavior was observed, which inferred that the Cu²⁺ displaced Zn²⁺ to coordinate with the imine nitrogen atoms and hydroxyl oxygen atoms of probe L.

A Simple Turn-off Schiff Base Fluorescent Sensor for Copper (II) Ion and Its Application in Water Analysis

An aniline-functionalized naphthalene dialdehyde Schiff base fluorescent probe L with aggregation-induced enhanced emission (AIEE) characteristics was synthesized via a simple one-step condensation reaction and exhibited excellent sensitivity and selectivity towards copper(II) ions in aqueous media with a fluorescence " turn-off " phenomenon. The detection limit of the probe is 1.64 × 10^-8 mol·L^-1. Furthermore, according to the results of the UV-vis/fluorescence titrations, Job's plot method and ¹H-NMR titrations, a 1:2 stoichiometry was identified. The binding constant between L and Cu²⁺ was calculated to be K_a = 1.222 × 10³. In addition, the AIEE fluorescent probe L could be applied to detection in real water samples with satisfactory recoveries in the range 99.10-102.90% in lake water and 98.49-102.37% in tap water.

An aniline trimer-based multifunctional sensor for colorimetric Fe3+, Cu2+ and Ag+ detection, and its complex for fluorescent sensing of L-tryptophan

The detection of metal ions and amino acids by the aniline oligomer-based receptor has not been reported yet, to the best of our knowledge. In this study, an efficient multifunctional cation-amino acid sensor (CAS) with aniline moiety and chiral thiourea binding site was synthesized by the reaction of aniline trimer and (S)-(+)-1-phenyl ethyl isothiocyanate. CAS can sense Fe³⁺, Cu²⁺, Ag⁺ ions, and L-tryptophan. These results can be recognized by the naked eye. The appropriate pH range for the quantitative analysis of Fe³⁺, Cu^2+, and Ag⁺ by CAS in DMSO/water (30 vol% water) was evaluated. The interaction between CCS and metal ions was analyzed by ¹H NMR titration. The detection limits of CAS for the Cu²⁺, Ag^+, and Fe³⁺ were 0.214, 0.099, and 0.147 μM, respectively. Moreover, the CASCu²⁺ complex can act as a turn-on fluorescence sensor for L-tryptophan. On the contrary, there is no response upon the addition of other amino acids, such as L-histidine, L-proline, L-phenylalanine, L-threonine, L-methionine, L-tyrosine, and L-cystine to CASCu²⁺ complex.

Polyoxometalate based ionic crystal: dual applications in selective colorimetric sensor for hydrated ZnCl2 and antimicrobial activity

One-pot synthesis of POM-salt ([Himi]₄[SiMo₁₂O₄₀] (1)) was achieved by mixing silicomolybdic acid and imidazole in acidic conditions and characterized by FTIR, TGA, SEM, EDX, ICP-OES and XPS.

Facile Microwave-Assisted Synthesis of Functionalized Carbon Nitride Quantum Dots as Fluorescence Probe for Fast and Highly Selective Detection of 2,4,6-Trinitrophenol

Functionalized carbon nitride quantum dots (CNQDs) are fabricated by moderate carbonization of L-tartaric acid and urea in oil acid media by a facile microwave-assisted solvothermal method. The obtained CNQDs are monodispersed with a narrow size distribution (average size of 3.5 nm), and exhibit excellent selectivity and sensitivity of fluorescence quenching for 2,4,6-trinitrophenol (TNP) with a quenching efficiency coefficient Ksv of 4.75 × 104 M-1. This sensing system exhibits a fast response time within 1 min and a wide linear response range from 0.1 to 15 μM. The limit of detection is as low as 87 nM, which is comparable or lower than the other probes. The application of the developed probe to the detection of TNP in spiked water samples yields satisfactory results. The mechanism of fluorescence quenching is also discussed. Graphical Abstract An optical sensor based on functionalized carbon nitride quantum dots (CNQDs) were fabricated from L-tartaric acid and urea by a facile one-pot microwave-assisted solvothermal method, and were effectively utilized to the detection of 2,4,6-trinitrophenol (TNP) based on fluorescence (FL) quenching.

A Schiff base-based fluorescent probe for the quick detection of ClO− ions

A new Schiff base 2-hydroxy-5-[(2,7-dihydroxy-1-naphthyl)methylideneamino]benzoic acid (HNMB) has been designed and synthesized. HNMB was characterized by Fourier-transform infrared spectroscopy (FTIR), electrospray ionization mass spectrometry (ESI–MS), nuclear magnetic resonance spectrometry (NMR), and single crystal X-ray diffraction. Fluorescence spectra show that HNMB could be used as a “turn-on” probe to detect ClO− ions from other anions in DMSO/H2O (v/v = 1:1) with a fast response time of 10 s and a low detection limit of 3.6 × 10−7 mol/L. Moreover, the probe could work in a wide pH range of 4–10. The detection mechanism was studied by ESI–MS.

A novel switch on and reversible optical sensor as an efficient, selective receptor for Zn(II) ion and its biological application

In the present study, a promising optical sensor (TR) was designed, synthesized, characterized and its chemosensing mechanism has been explored through ¹H NMR, ESI-MS, UV-Vis absorption and emission spectral studies. This compound exhibits a drastic change in its optical properties when treated with Zn²⁺, whereas other metal ions do not respond. This provides a naked eye detection for Zn²⁺ ion. In methanolic medium, Zn²⁺ ion induces strong fluorescence in TR with large Stokes shifts up to ∼132 nm. A 5-fold increase in fluorescence intensity of TR in presence Zn²⁺ ion is due to inhibition of ESIPT (Excited State Intramolecular Proton Transfer) and -C=N isomerization with large increase in the ICT (Intramolecular Charge Transfer) character of TR in the excited state. The Job's plot and BH plots reveal the formation of 1: 1 stoichiometry with an estimated binding constant of 3.9 × 10⁷ M^-1. The detection limit of TR was found to be 3.85 nM. The TR could be regenerated by adding EDTA solution to the complex formed during interaction. The pH studies indicate that TR could render pH dependent fluorescence measurements in a live physiological environment. Computational technique was used to optimize the structures and the theoretical results are correlated with the experimental results. The possible utilization of TR as bio-imaging fluorescent sensor with 98.57% cell viability to detect Zn²⁺ in HeLa cells was also explored by fluorescent cell imager.

A selective “turn-on” sensor for recognizing In3+ and Zn2+ in respective systems based on imidazo[2,1-b]thiazole

An imidazo[2,1-b]thiazole-based compound (X) was designed and synthesized as an “off–on–off” sensor for the multiple recognition of In³⁺ and Zn²⁺ in different systems.

An AIE and PET fluorescent probe for effective Zn(ii) detection and imaging in living cells

A sensitive fluorescent probe L for Zn²⁺ with aggregation-induced emission (AIE) properties has been synthesized.

A new fluorescent-colorimetric chemosensor based on a Schiff base for detecting Cr3+, Cu2+, Fe3+ and Al3+ ions

A new Schiff base derivative fluorescence-colorimetric chemosensor 2-hydroxy-5-[(2-hydroxy-1-naphthyl)methylideneamino]benzoic acid (H₃L), has been designed and synthesized. H₃L displayed high selectivity and sensitivity for detecting Cr³⁺, Cu²⁺, Fe³⁺ and Al³⁺ ions in DMF/H₂O (v/v = 1/1) solution. When Cr³⁺, Cu²⁺ or Fe³⁺ ions were added, the solution of H₃L in DMF/H₂O exhibited different color changes. While with the addition of Fe³⁺ or Al³⁺ ions, the solution of H₃L in DMF/H₂O displayed different fluorescence responses. The bonding modes and bonding ratios of H₃L and metal ions were explored by the Job's plot, ¹H NMR titration, and electrospray ionization mass spectrometry (ESI-MS). The detection limits of H₃L with Cr³⁺, Cu²⁺, Fe³⁺and Al³⁺ ions were 3.37 × 10^-7 M, 4.65 × 10^-7 M, 3.58 × 10^-7 M and 4.89 × 10^-7 M, respectively.

A selective diaminomaleonitrile-based dual channel emissive probe for Al3+ and its application in living cell imaging

A selective diaminomaleonitrile-based fluorescent probe for Al³⁺(L) has been synthesized and characterized. The sensing behavior of L towards different metal ions was investigated by fluorescent spectra and competition experiment. The results showed that L exhibited a dual channel emission (λ_em 522 & 558 nm) with yellow fluorescence in the presence of Al³⁺ over other metal ions in EtOH solution. The probe L was bound to Al³⁺ in a 1:2 stoichiometric manner as supported by Job's plot analysis. The binding constant was 9.55 × 10⁸ M^-2 with the detection limit of 10.3 nM. The turn-on response was attributed to the inhibition of PET and CN isomerization after binding with Al³⁺ while the dual emissions were due to ESIPT and ICT processes. In addition, the application of L for imaging Al³⁺ in living Hela cells was achieved.

A novel coumarin-based fluorescence chemosensor for Al3+ and its application in cell imaging

As an efficient turn-on fluorescent chemosensor for Al³⁺, a new coumarin derivative (CND) has been designed and synthesized by the condensation of 8-formyl-7-hydroxycoumarin with niacin hydrazide. The spectroscopic studies revealed that the sensor CND exhibited a remarkable fluorescence enhancement towards Al³⁺ with high selectivity and sensitivity in EtOH-HEPES (95:5, v/v, pH = 7.40), which was attributed to the photoinduced electron transfer (PET) and CN isomerization mechanism. Fluorescence titration calculations data showed that the detection limit and the association constants of CND for Al³⁺ were found to be 2.51 × 10^-7 M and 9.64 × 10⁴ M^-1, respectively. The results of experiments, including Job's plot, ¹H NMR titration and ESI-MS, revealed that the stoichiometric binding between CND and Al³⁺ was 1:1. The investigations of the pH dependency of CND for Al³⁺ detection, and the cell imaging suggested the sensor CND could be promisingly applied for the recognition of Al³⁺ in biological cells.

A multiple target chemosensor for the sequential fluorescence detection of Zn2+ and S2− and the colorimetric detection of Fe3+/2+ in aqueous media and living cells

A novel multiple target sensor DHIC was developed for the fluorescence detection of Zn²⁺ and S²⁻ and colorimetric detection of Fe^3+/2+. Moreover, DHIC could image sequentially Zn²⁺ and S²⁻ in living cells.

A dual functional fluorescent sensor for the detection of Al3+ and Zn2+ in different solvents

A new fluorescent sensor, X, was designed and synthesized based on imidazo[2,1-b]thiazole and 2-hydroxy-1-naphthaldehyde, which could be used to detect Al³⁺ in methanol buffer solution and detect Zn²⁺ in ethanol buffer solution, respectively.

Novel thiophene-based colorimetric and fluorescent turn-on sensor for highly sensitive and selective simultaneous detection of Al3+ and Zn2+ in water and food samples and its application in bioimaging

A novel bifunctional thiophene-based Schiff base TS as a colorimetric and fluorescent turn-on sensor for rapid and simultaneous detection of Al³⁺ and Zn²⁺ ions with high selectivity and sensitivity has been developed. The sensor shows remarkable fluorescence enhancement response for Al³⁺ and Zn²⁺ over a broad pH range with good anti-interference capability, which accompanied with an obvious color change easily detected by naked eyes. Sensor TS can detect as low as 3.7 × 10^-9 M for Al³⁺ and 3.0 × 10^-8 M for Zn²⁺, whereas respective association constants are 1.16 × 10⁴ M^-1 and 2.08 × 10⁴ M^-1. With the help of fluorescence titration and Job's plot, the stoichiometric ratio of TS with Al³⁺/Zn²⁺ was determined to be 1:1. The sensing mechanism of sensor TS with Al³⁺/Zn²⁺ based on the chelation-enhanced fluorescence (CHEF) was analyzed in detail through ¹H NMR titration, FTIR, HRMS and DFT studies. Moreover, sensor TS has been applied to the detection of Al³⁺ and Zn²⁺ in real environmental water and food samples as well as the filter paper-based test strips. Furthermore, sensor TS has good cell-permeability and can be used to selectively sense intracellular Al³⁺ and Zn²⁺ by bioimaging.

A ‘turn-on’ fluorescent chemosensor for the detection of Zn2+ ion based on 2-(quinolin-2-yl)quinazolin-4(3H)-one

2-(Quinolin-2-yl)quinazolin-4(3H)-one (Q) was synthesized via the Brønsted acid-promoted tandem cyclization/dehydrogenation reaction with a good yield. Compound Q is a selective ‘turn-on’ fluorescent sensor for Zn2+ ion without interference by Cd2+. The 1:1 binding model of Q to Zn2+ was confirmed by the Benesi-Hildebrand analysis, Job’s plot analysis and a ultraviolet-visible (UV-Vis) titration experiment. Furthermore, the light-on fluorescent response can be observed by the naked eye under UV-lamp irradiation (365 nm).

A Highly Selective Fluorescent Probe for Zn2+ Based on a Rhodamine-6G dye Derivative Modified by a Furan Unit

A fluorescent probe for Zn2+ based on rhodamine-6G has been synthesised. It showed excellent fluorescent specific selectivity and high sensitivity for Zn2+ compared with other metal ions, such as Fe3+, Cr3+, Hg2+, Ag+, Ca2+, Cu2+, Pb2+, Cd2+, Ni2+, Co2+ and Mg2+, in CH3CN–phosphate buffer saline solution. The distinct colour change and the rapid emergence of fluorescence emission provided ‘naked-eye’ detection of Zn2+. The detection limit of the fluorescent probe towards Zn2+ was 1.78 μM. In addition, the fluorescence lifetime and fluorescence quantum yield were measured.

A biomimetic fluorescent chemosensor for highly sensitive zinc(ii) detection and its application for cell imaging

To fabricate a novel biomimetic fluorescent chemosensor, PSaAEMA-co-PMPC was synthesized via atom transfer radical polymerization, and this copolymer could be used for the detection of zinc(ii) and cell imaging. A series tests with various metal ions verified the specific fluorescence response behavior. This novel biomimetic fluorescent chemosensor exhibits excellent selectivity for Zn²⁺ ions over a wide range of tested metal ions in an aqueous solution. Moreover, cytotoxicity and bio-imaging tests were conducted to study the potential bio-application of the chemosensor. Owing to the biomimetic portion (phosphorylcholine), this copolymer possesses outstanding biocompatibility and could clearly image cells. The results indicated that PSaAEMA-co-PMPC has great potential for application in zinc(ii) detection and cell imaging.

To fabricate a novel biomimetic fluorescent chemosensor, PSaAEMA-co-PMPC was synthesized via atom transfer radical polymerization, and this copolymer could be used for the detection of zinc(ii) and cell imaging.