Highly selective and sensitive turn-on fluorescent sensor for detection of Al3+ based on quinoline-base Schiff base

Chemically modified graphitic carbon nitride nanosheets for the selective turn-off fluorescence detection of Al(III) ions in crabs (Brachyura)

The selective and sensitive detection of Al(III) is critically important for human health since the level of Al(III) is an indicator of many diseases in humans. Herein, we developed a simple and sensitive fluorescent sensor for the detection of Al(III) in an aqueous solution based on the fluorescence of hydroxyl-functionalized graphitic carbon nitride nanosheets (HO/g-CN). OH/g-CN nanosheets were synthesized via the thermal pyrolysis of 1,3,5-triazine-2,4,6-triamine (as raw material) at 550 °C for 2 hours, followed by thermal alkali treatment at 730 °C for 2 min. The fluorescence of HO/g-CN at 377 nm (at 290 nm excitation) can be quenched by Al(III) effectively and selectively, and the linear relationship between the concentration of Al(III) and fluorescence intensity is in the range of 1.85-14.82 μM with a detection limit of 0.272 μM. The fluorescence turn-off effect of the Al(III) ion on the prepared HO/g-CN nanosheets could be attributed to the presence of oxygen- and nitrogen-containing functional groups on the surface of HO/g-CN that have chelating interactions with Al(III), leading to quenching. The surface functional groups of OH/g-CN were confirmed using different characterization techniques (FTIR, EDX, and XPS). Moreover, the prepared HO/g-CN exhibited remarkable long-term fluorescence stability in water (>30 days) and minimal toxicity. Importantly, a prepared novel fluorescent sensor (HO/g-CN) was successfully applied for the detection and determination of Al(III) in commercially available crab (Brachyura) samples.

Turn-on detection of Al3+ ions using quinoline-based tripodal probe: mechanistic investigation and live cell imaging applications

In this study, an easily synthesizable Schiff base probe TQSB having a quinoline fluorophore is demonstrated as a fluorescent and colorimetric turn-on sensor for Al3+ ions in a semi-aqueous medium (CH3CN/water; 4 : 1; v/v). Absorption, emission and colorimetric studies clearly indicated that TQSB exhibited a high selectivity toward Al3+, as observed from its excellent binding constant (Kb = 3.8 × 106 M-1) and detection limit (7.0 nM) values. TQSB alone was almost non-fluorescent in nature; however, addition of Al3+ induced intense fluorescence at 414 nm most probably due to combined CHEF (chelation-enhanced fluorescence) and restricted PET effects. The sensing mechanism was established via Job's plot, NMR spectroscopy, ESI-mass spectrometry, and density functional theory (DFT) analyses. Furthermore, to evaluate the applied potential of probe TQSB, its sensing ability was studied in real samples such as soil samples and Al3+-containing Digene gastric tablets as well as on low-cost filter paper strips. Fluorescence microscopy imaging experiments further revealed that TQSB can be used as an effective probe to detect intracellular Al3+ in live cells with no cytotoxicity.

An ultra-sensitive fluorescent probe for recognition of aluminum ions and its application in environment, food, and living organisms

The concentration of aluminum ions (Al3+) is closely related to the ecological environment, food safety, and human health, with excessive accumulation of Al3+ causing irreversible damage to both the ecological balance and human health. Therefore, a fluorescent probe ABHS, based on aminobenzoylhydrazide Schiff-base, was designed and synthesized in one step with a high yield. ABHS can form a 1:1 coordination complex with Al3+ in a pure water system. It exhibits ultra-sensitive and accurate detection of Al3+ even at low concentration of Al3+, with the detection limit of 6.7 nM. Furthermore, ABHS demonstrated significant enhancement of specific fluorescence for Al3+, with rapid response speed, good stability, and robust resistance to interference. Importantly, ABHS has shown excellent detection and imaging capabilities even in complex real environmental samples, food samples, and living organisms.

A quinoline derived Schiff base as highly selective 'turn-on' probe for fluorogenic recognition of Al3+ ion

A quinoline-derived Schiff base QnSb has been synthesized for fluorescent and colorimetric recognition of Al3+ ions in a semi-aqueous medium. The compound QnSb has been characterized by elemental analysis, FT-IR, 1H/13C NMR, UV-Vis and fluorescence spectral techniques. The crystal structure of the QnSb was confirmed by single crystal X-ray diffraction (SC-XRD) analysis. Notably, almost non-fluorescent QnSb served as a 'turn on' responsive probe for Al3+ by inducing a remarkable fluorescence enhancement at 422 nm when excited at 310 nm. The probe QnSb exhibited high selectivity for Al3+ in CH3CN/H2O (4:1, v/v) solution over several competing metal ions (e.g., Mg2+, Pb2+, Zn2+, Cd2+, Co2+, Cu2+, Ca2+, Ni2+, Fe3+/2+, Cr3+, Mn2+, Sn2+, and Hg2+). The limit of detection (LoD) was computed as low as 15.8 nM which is significantly lower than the permissible limit set by WHO for Al3+ ions in drinking water. A 1:1 binding stoichiometry of complex QnSb-Al3+ was established with the help of Job's plot, ESI-MS, NMR and DFT analyses. Based on its remarkable sensing ability, the probe QnSb was utilized to establish molecular logic gates, and the fluorescence detection of Al3+ could clearly be demonstrated on the filter paper test strips.

A Novel Multi-Functional Fluorescence Probe for the Detection of Al3+/Zn2+/Cd2+ and its Practical Applications

A novel multi-functional fluorescence probe HMIC based on hydrazide Schiff base has been successfully synthesized and characterized. It can distinguish Al3+/Zn2+/Cd2+ in ethanol, in which fluorescence emission with different colors (blue for Al3+, orange for Zn2+, and green for Cd2+) were presented. The limits of detection of HMIC towards three ions were calculated from the titration curve as 7.70 × 10- 9 M, 4.64 × 10- 9 M, and 1.35 × 10- 8 M, respectively. The structures of HMIC and its complexes were investigated using UV-Vis spectra, Job's plot, infrared spectra, mass spectrometry, 1H-NMR and DFT calculations. Practical application studies have also demonstrated that HMIC can be applied to real samples with a low impact of potential interferents. Cytotoxicity and cellular imaging assays have shown that HMIC has good cellular permeability and potential antitumor effects. Interestingly, HMIC can image Al3+, Zn2+ and Cd2+ in the cells with different fluorescence signals.

Computational Insights into Sensing Mechanism for Al3+ in a New Acylhydrazone Fluorescent Probe Based on Excited-State Intramolecular Proton Transfer (ESIPT) and Twisted Intramolecular Charge Transfer (TICT)

The work explored the fluorescent properties of probe N'-(2, 4-dihydroxy-benzylidene)pyridine-3-carbohydrazide (HL) and its sensing mechanism for the Al³⁺ ion in detail. HL has two competing deactivation processes: ESIPT and TICT. Upon light-excitation, only one proton can transfer, and the SPT1 structure is generated. The SPT1 form is highly emissive, which is inconsistent with the colorless emission observed in the experiment. Then a nonemissive TICT state was obtained by rotating the C-N single bond. The energy barrier of the TICT process is lower than that of the ESIPT process, which indicates that probe HL will decay to the TICT state and quench the fluorescence. When Al³⁺ is recognized by probe HL, strong coordinate bonds are formed between HL and Al³⁺, and then the TICT state is prohibited, and the fluorescence of HL is turned on. Al³⁺ as a coordinated ion can effectively remove the TICT state but cannot influence the photoinduced electron transfer (PET) process of HL.

A Bifunctional Fluorescence Probe Based on AIE-ICT Strategy for Visual Detection of Cu2+/Co2+ in Complex Matrix

A novel fluorescence chemical sensor-based probe 1-{[(E)-(2-aminophenyl)azanylidene]methyl}naphthalen-2-ol (AMN) was designed and synthesized, which performed a "naked eye" detection ability toward Cu²⁺ and Co²⁺ based on aggregation-induced emission (AIE) fluorescence strategy. It has sensitive detection ability for Cu²⁺ and Co²⁺. In addition, the color changed from yellow-green to orange under the sunlight, realizing the rapid identification of Cu²⁺/Co²⁺, which has the potential of on-site visual detection under the "naked eye". Moreover, different "on" and "off" fluorescence expressions were exhibited under excessive glutathione (GSH) in AMN-Cu²⁺ and AMN-Co²⁺ systems, which could be employed to distinguish Cu²⁺ from Co²⁺. The detection limits for Cu²⁺ and Co²⁺ were measured to be 8.29 × 10^-8 M and 9.13 × 10^-8 M, respectively. The binding mode of AMN was calculated to be 2:1 by Jobs' plot method analysis. Ultimately, the new fluorescence sensor was applied to detect Cu²⁺ and Co²⁺ in real samples (tap water, river water, and yellow croaker), and the results were satisfying. Therefore, this high-efficiency bifunctional chemical sensor platform based on "on-off" fluorescence detection will provide significant guidance for the advance development of single-molecule sensors for multi-ion detection.

A novel pyrene-based fluorescent probe for Al3+ detection

Based on the classical Schiff base reaction, fluorescent probe dimethyl 5-((pyren-1-ylmethylene)amino)isophthalate (PAI) is designed and synthesized through introducing Schiff base structure to pyrene unit for structural modification. The structure of the synthesized probe PAI is determined and characterized by FT-IR, ¹H NMR, ¹³C NMR and HRMS. PAI is a type of "turn-on" probe which can specifically recognize Al³⁺ ion with high selectivity. The limit of detection is calculated to be 3.07 × 10^-8 M, which proves the probe's high sensitivity and is lower than that of many efficient reported probes. The probe PAI is intrinsically non-fluorescent due to the photoinduced electron transfer (PET) process. However, the addition of Al³⁺ ion leads to the breakage of the carbon-nitrogen double bond of Schiff base in PAI resulting in the product without PET property, which shows a typical localized state with enhanced fluorescence and blue color. In addition, PAI can recognize Al³⁺ ion through test papers, which is in favor of the future research regarding to Al³⁺ ion sensing.

Insights into the photophysical properties of 2-(2'-hydroxyphenyl) benzazoles derivatives: Application of ESIPT mechanism on UV absorbers

In this present work, four novel molecules (BPN, BPNS, BPS, and BPSN), possessing excited-state intramolecular proton transfer (ESIPT) characteristics, were designed to quantify the impacts of substituent effects on their photophysical properties. By exploring the primary geometrical parameters concerning hydrogen bonds, it should be noticed that the intramolecular hydrogen bonds (IHBs) of the studied molecules have been strengthened at S₁ state. Infrared vibrational spectra analysis illustrates that adding electron-donating group thiophene to the proton donor side can weaken the IHBs in comparison to the electron-withdrawing group pyridine. Through investigating the absorption and fluorescence spectra, it can be clearly found that the maximum absorption peaks of the studied molecules are all located in the UVA region, and their regions of fluorescence peaks are harmless to human skin. Furthermore, considering the light intensity factor, it can be concluded that BPNS is the most potential to be used as UV absorbers in the studied molecules. This work investigates the effects of the positions and types of substituent groups on photophysical properties of 2-(2'-hydroxyphenyl) benzazoles derivatives, which can help design and exploit novel UV absorbers.

A novel water-soluble flavonol-based fluorescent probe for highly specific and sensitive detection of Al3+ and its application in onion and zebrafish

A novel and simple turn-on fluorescence probe (HD) for Al³⁺ detection was successfully developed based on flavonol derivatives. This probe exhibited a significantly enhanced fluorescence response toward Al³⁺ in aqueous solution which could be observed by naked-eye from poor fluorescence to strong light green emission. The probe HD displays highly specific detection for Al³⁺ over other competitive metal ions, and the detection limit of probe HD for Al³⁺ was determined to be 2.57 × 10^-8 M, which are much lower than the World Health Organization (WHO) guideline value for drinking food/water. The binding stoichiometry of probe HD with Al³⁺ was determined to be 1:1 according to Job's plot and ESI-HRMS analysis, and the binding constant was calculated to be 2.01 × 10⁴ M^-1. The probe HD exhibited high selectivity, high sensitivity, good anti-interface ability, and wide pH application range as well as the quantitative determination in the detection of Al³⁺. The coordination mechanism of probe HD with Al³⁺ was supported by density functional theory (DFT) calculations and HRMS analysis. In addition, the probe HD was found to have good cell permeability and could be applied for live-cell imaging to detect Al³⁺ in onions and zebrafish.

Fluorescent turn-on sensing of albumin proteins (BSA and ovalbumin) using vitamin B6 cofactor derived Schiff base

The detection of albumin proteins with high accuracy by facile analytical approaches is important for the diagnosis of various diseases. This manuscript introduced an easy-to-prepare Schiff base L by condensing vitamin B₆ cofactor pyridoxal 5'-phosphate (PLP) with 2-aminothiophenol for the fluorescence turn-on sensing of bovine serum albumin (BSA) and ovalbumin (OVA). The weakly emissive L showed a significant fluorescence enhancement at 485 and 490 nm in the presence of OVA and BSA with an estimated sensitivity limit of 1.7 µM and 0.3 µM, respectively. The formation of protein-ligand complex restricted the free intramolecular rotation of L is expected to show the selective fluorescence enhancement. The molecular docking and molecular dynamics simulations were performed to examine the binding affinity and modes between BSA/OVA and L. The practical utility of L as a fluorescent turn-on sensor was validated by quantifying BSA and OVA in various real biological samples of milk, serum, egg white and urine with good recovery percentages.

A simple "turn-on" fluorescent sensor for reversible recognition of aluminum ion in living cell

A simple and reliable "turn-on" fluorescent sensor (E)-1-[((2-hydroxyethyl)imino) methyl] naphthalen-2-ol (HNP) has been designed, synthesized, and characterized by ¹H-NMR, ¹³C-NMR, FT-IR, and EI-MS analysis. The binding property of HNP was examined employing UV-Vis and fluorescence spectroscopy. HNP exhibited high selectivity towards Al³⁺ among other cations and anions. The fluorescence titration experiment has established binding stoichiometry of HNP with Al³⁺ is 2:1, which can be further verified by HR-MS. The detection limit of HNP is 2.9 μM, and it can be reversible five-to-seven times to detect Al³⁺ without losing much efficiency which indicates that it can be a reliable probe for Al³⁺. Additionally, HNP was successfully applied for the detection of Al³⁺ in living cells. To achieve the detection of aluminum ion across a simple, reliable, and precise method, we have investigated the reversible detection (which can reversible response to Al³⁺ for five-to-seven times) of Al³⁺ through an extremely simple (requires only one-step reaction) "turn-on" fluorescent probe which enables us to visualize and analyze Al³⁺ with low detection limit (2.9 μM) and high selectivity in living cell without interference from the high abundant small biological molecules.

Theoretical study on the optical properties of an ESIPT-based fluorescent probe for phosgene

A fluorescent probe Pi with the excited-state intramolecular proton transfer (ESIPT) properties was synthesized and used to detect the phosgene in solution and gas phases. However, the detection mechanism of the fluorescent probe needs to be further studied. Herein, the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods were adopted to explore the molecular structures and electronic spectra properties of probe and its product Pio after reacting with phosgene. Through analysis for molecular structure parameters and infrared vibrations accompanied with the hydrogen bond of Pi, it is confirmed that the intramolecular hydrogen bond of Pi is enhanced under light excitation, which illustrates the occurrence of ESIPT reaction combined with the scanned potential energy curves. It can be seen from the simulated spectra that Pi shows double fluorescence through ESIPT process, while the fluorescent product Pio exhibits the single fluorescence due to the disappearance of intramolecular hydrogen bond. Through the study on the structure and optical properties of Pi and Pio, it can be helpful to deeply understand the intrinsic mechanism of the detection of phosgene by the Pi molecule probe, which also supplies a reference to the further study about the fluorescence probe.

The Application of Modified SBA-15 as a Chemosensor

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The Santa Barbara Amorphous (SBA-15), with a large surface area covered with abundant Si-OH active groups on the walls of its pores, can be modified with various organic compounds to build organic-inorganic hybrid materials, which can be used as a catalyst in organic reactions, drug delivery systems, nano sorbent due to its high capacity for removing heavy metals in waste water and as chemosensors for ions. Tunable and straight channels of SBA-15 facilitate the entrance and diffusion of ions through the channels. This paper presents a review of the past five years of literature covering the application of SBA-15 as an ions chemosensor in the liquid and gaseous media.

Naphthalimide appended isoquinoline fluorescent probe for specific detection of Al3+ ions and its application in living cell imaging

Herein, a novel Schiff base fluorescent probe NIQ based on naphthalimide and iso-quinoline units has been readily prepared for the selective detection of Al³⁺ ions. The obviously visible color changes and prominent fluorescence enhancement were observed upon the addition of Al³⁺ to NIQ, which could be attributed to the complexation of NIQ with Al³⁺ and thus leading to the inhibition of photo-induced electron transfer (PET) and the chelation-enhanced fluorescence (CHEF) progress. The limit of detection (LOD) was 52 nM that was far below the standard recommended by the WHO. Binding ratio (1:1) of NIQ with Al³⁺ ions was supported by Job's plot. The binding constant of NIQ for Al³⁺ were calculated to be 3.27 × 10⁵ M^-1 on the basis of benesi-Hildebrand plot. The plausible binding mechanism for NIQ towards Al³⁺ ions was evidenced by the density functional theory (DFT) and ¹H NMR titration experiment. Furthermore, this "turn-on" probe NIQ has been successfully applied as a biomarker for imaging the Al³⁺ ions in living cells.

Chromone functionalized pyridine chemosensor for cupric ions detection

A new Schiff base 2-ethoxy-3-{[(6-{[(2-ethoxy-4-hydroxy-2H-chromen-3-yl)methylidene]amino}pyridine-2-yl)imino]methyl}-2H-chromen-4-ol (CD) was synthesized as a result of the condensation of 2,6-diaminopyridine and 3-formyl chromone in 1:2 M ratio and used for cupric ions detection and characterized through FTIR, HRMS and ¹H NMR spectral techniques. The sensing capability of Schiff base for cupric ions as compared to other transition metal ions was examined by absorbance and emission studies. A considerable decrease in emission intensity appeared in Schiff base in the case of cupric ions while irrelevant changes were examined for the rest of the ions. The binding stoichiometry was obtained as 1:2 for CD: Cu²⁺ complex intended from the job's plot which was confirmed through HRMS spectral technique. DFT calculations were carried for the confirmation of structural relationships and absorption-emission data. The Regression coefficient, Limit of detection, and Association constant were obtained as 98.7%, 1.2 × 10^-6 M, and 3.26 × 10⁴ M^-1 respectively using Benesi-Hildebrand (B-H) equation. The sensing power of Schiff base CD to recognize cupric ions was unaltered by the addition of the rest of metal ions, which was authenticated through interference studies. Schiff base CD and its complex with cupric ions were found stable over an extensive time period as revealed by time-reliant studies. The data collected by pH studies revealed that the preferred pH range for detecting cupric ions by Schiff base CD was 6 to 11. The Schiff base was finally utilized for sensing cupric ions in a variety of spiked samples of water like canal water, tap water, groundwater, distilled water.

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.

A novel hydrazide Schiff base self-assembled nanoprobe for selective detection of human serum albumin and its applications in renal disease surveillance

Human serum albumin (HSA) is considered as a biomarker for the early diagnosis of renal disease, therefore identifying and detecting HSA in biological fluids (especially urine) with an easy method is of great importance. Herein, we report a novel hydrazide Schiff base fluorescent probe N'-((7-(diethylamino)-2-oxo-2H-chromen-3-yl)methylene)pyrazine-2-carbohydrazide (NPC), which self-assembled into nanoparticles in aqueous solution. Based on disassembly-induced emission and the site-specific recognition mechanism, the binding of NPC with HSA resulted in a fluorescence "turn-on" response. Probe NPC exhibited superior selectivity and sensitivity toward HSA with a detection limit of 0.59 mg L-1 in PBS and 0.56 mg L-1 in the urine sample. The site-binding mechanism of NPC with HSA was explored by fluorescence quenching study, Job's plot analysis, HSA destruction, site marker displacement and molecular docking. Fluorescence imaging of HSA in MCF-7 cells was achieved by using a non-toxic NPC probe, suggesting that NPC could be applied to visualize the level of HSA in vivo. More importantly, further practical applications of probe NPC in human urine samples were achieved with satisfactory results by using a fluorometer or test paper, which could provide extensive application in clinical diagnosis.

Solvothermal preparation of luminescent zinc(II) and cadmium(II) coordination complexes based on the new bi-functional building block and photo-luminescent sensing for Cu2+, Al3+ and L-lysine

In industry, over usage of Cu²⁺ and Al³⁺ will lead to toxic wastewater, which further to give serious pollution for the environment. On the other hand, L-lysine can enhance serotonin release in the amygdala, with subsequent changes in psychobehavioral responses to stress. Therefore it is the urgent problem to design a method for detecting the amount of Cu²⁺, Al³⁺, and L-lysine. In this work, through the solvothermal synthesis method, two new coordination complexes based on the new bifunctional building block 4'-(1H-1,2,4-triazole-1-yl)- [1,1'-biphenyl]-4-carboxylic acid (HL) have been synthesized, namely, [Zn(L)₂·4H₂O] (complex 1) and [Cd(L)₂·4H₂O] (complex 2). X-ray single-crystal diffractometer was used to analyze its structure, powder X-ray diffraction (PXRD) patterns confirmed that 1 and 2 powder's purity and 1 can keep stable during the detection process of Cu²⁺, Al³⁺, and L-lysine, respectively. Elemental analysis, thermogravimetric analysis, infrared analysis, ultraviolet analysis and fluorescent spectrum have been used to characterize these complexes. The photo-luminescent test showed that 1 can accurately recognize Al³⁺ and Cu²⁺ among various cations. On the other hand, 1 can distinguish L-lysine among amino acid molecules. Therefore, 1 can be utilized as a multifunctional fluorescent probe for Al³⁺(K_sv = 1.5570 × 10⁴ [M]^-1), Cu²⁺(K_sv = 1.4948 × 10⁴ [M]^-1) and L-lysine (K_sv = 4.9118 × 10⁴ [M]^-1) with low detection limits (17.5 μM, 18.2 μM, 5.6 μM) respectively.

A purine based fluorescent chemosensor for the selective and sole detection of Al3+ and its practical applications in test strips and bio-imaging

A novel purine Schiff base fluorescent probe (WYW), (E)-4-methyl-2-((2-(9-(naphthalen-1-yl)-8-(thiophen-2-yl)-9H-purin-6-yl)hydrazono)methyl)phenol, was designed and prepared as an excellent reversible fluorescent chemosensor for monitoring Al³⁺. The fluorogenic "turn-on" sensor WYW exhibited high selectivity towards Al³⁺ over other coexistent metal ions, accompanying with an obvious visual color change in DMSO/H₂O (9/1, v/v, pH = 7.4) media. The enhancement fluorescence of WYW could be attributed to the inhibition of PET and ESIPT process induced by Al³⁺. Notably, the WYW-Al³⁺ complex exhibited a fluorescence "turn-off" response towards F^- with exceptional selectivity via the displacement approach. The detection limit of WYW for Al³⁺ was calculated to be as low as 82 nM. The formation of complex WYW-Al³⁺ (1:1 stoichiometry) was confirmed by Job's methods and further verified by density functional theory (DFT) calculations. Furthermore, the probe WYW with low cytotoxicity and excellent membrane-permeable property has also been successfully applied for detecting low concertation Al³⁺ in living HeLa cells.

A multi-functional picolinohydrazide-based chemosensor for colorimetric detection of iron and dual responsive detection of hypochlorite

A novel effective chemosensor HPHN, (E)-6-hydroxy-N'-((2-hydroxynaphthalen-1-yl)methylene) picolinohydrazide, was synthesized. HPHN sensed Fe^3+/2+ with the changes of color from yellow to orange without obvious inhibition from other cations. In addition, HPHN could detect ClO^- by both the color change from yellow to colorless and the fluorescence quenching. The binding modes of HPHN with Fe^3+/2+ and ClO^- were determined to be 1:1 with Job plot and ESI-mass analysis. HPHN displayed low detection limits of 0.29 μM for Fe³⁺ and 0.77 μM for Fe²⁺. For ClO^-, the detection limit was 6.20 μM by colorimetric method and 3.99 μM by fluorescent one, respectively. Moreover, HPHN can be employed to quantify Fe³⁺ and ClO^- in environmental samples and apply to cell imaging for ClO^-.

Turn-on fluorescent probe towards glyphosate and Cr3+ based on Cd(ii)-metal organic framework with Lewis basic sites

Lewis basic site-functionalized porous Cd(ii)-MOF as a bi-functional fluorescent sensor of glyphosate and Cr³⁺ with exceptional LODs.

Highly selective and sensitive chemosensor for Al(III) based on isoquinoline Schiff base

As a colorimetric and fluorescent turn-on sensor to Al³⁺, N'-(2-hydroxybenzylidene)isoquinoline-3-carbohydrazide (HL) has been easily synthesized. The fluorescence intensity increases by 273 times in the presence of Al³⁺ at 458 nm. Meanwhile, the experiment data indicate that the limit of detection for Al³⁺ is 1.11 × 10^-9 M. Remarkably, the blue fluorescence signal of HL-Al³⁺ could be specially observed by the naked eye under UV light and is significantly different from those of other metal ions. Fluorescence switch based on the control of Al³⁺ and EDTA proved HL could act as a reversible chemosensor. According to ESI-MS result and the Job's plots, the 2:1 coordination complex formed by HL and Al³⁺ could be produced. Density functional theory calculations were performed to illustrate the structures of HL and complex. The cell imaging experiment indicates that HL can be applied for monitoring intracellular Al³⁺ levels in cells.

A dual-functional fluorescent probe for sequential determination of Cu2+/S2- and its applications in biological systems

A new acylhydrazine-derived Schiff base fluorescence probe DMI based on "ON-OFF-ON" fluorescence strategy was presented in this paper. Probe DMI could detect Cu²⁺ selectively and sensitively with dramatic fluorescence quenching in CH₃OH-PBS (v/v = 3:7) mixed solution. Once the complex DMI-Cu²⁺ interacted with S^2-, 10.67-folds fluorescence increase was induced via a displacement mechanism under the same experimental conditions. The corresponding detection limits for Cu²⁺ and S^2- were calculated to be 1.52 × 10^-8 M and 1.79 × 10^-8 M, respectively. The structures of DMI and DMI-Cu²⁺ were systematically characterized by Job's plot analysis, ESI-MS, IR, X-ray diffraction and density functional theory calculations. Furthermore, fluorescence imaging in MCF-7 cells and zebrafish demonstrated the probe DMI could act as a useful tool to monitor and track intracellular Cu²⁺ and S^2-, which was encouraged by remarkable fluorescence performance and low cytotoxicity. Importantly, the complex DMI-Cu²⁺ could be applied to detect corrupt blood samples, which could estimate the time of death.

Dual-Emission Zr-MOF-Based Composite Material as a Fluorescence Turn-On Sensor for the Ultrasensitive Detection of Al3

In this work, a novel zirconium-based metal-organic framework (MOF) composite material, UiO-(OH)₂@RhB, has been solvothermally prepared with zirconyl chloride octahydrate, 2,5-dihydroxyterephthalic acid, and rhodamine B (RhB) for ratiometric fluorescence sensing of Al³⁺ ions in an aqueous medium. The luminescence measurement results showed that, at the single excitation wavelength of 420 nm, the fluorescence intensity of the ligand at 500 nm increased significantly in the case of Al³⁺, while that of RhB at 583 nm changed slightly, together with an apparent color change. Under optimal conditions, UiO-(OH)₂@RhB exhibited an extraordinary sensitivity (10 nM), good selectivity, and a fast response (2 min) for Al³⁺. As far as we know, the limit of detection is superior to that of the current reported MOF-based Al³⁺ fluorescence sensors. The response mechanism suggested that -OH could capture Al³⁺ in water through coordination and high electrostatic affinity and achieved turn-on ratiometric fluorescence through the excited-state intramolecular proton transfer process and stable fluorescence of RhB. In addition, this sensor was also applied to actual food samples (grain beans), with the recoveries ranging from 89.08% to 113.61%. Such a turn-on ratiometric fluorescence sensor will provide a constructive strategy for the ultrasensitive detection of Al³⁺ in practical applications.

A Fluorescent Chemosensor Based on Schiff Base for the Determination of Zn2+, Cd2+and Hg2

Metal complexes were obtained by the reaction of zinc, cadmium and mercury(II) salts with Schiff base HL (N(salicylidene)benzylamine). HL was synthesized by the condensation reaction of benzylamine and 2-hydroxybenzaldehyde. The fluorescence properties of the Schiff base and its metal complexes were studied in ethanol-water solutions. HL was examined for its utility as a fuorescent chemosensor for the determination of Zn²⁺, Cd²⁺ and Hg²⁺ in aqueous samples. The HL chemosensor was found to be sensitive to Zn²⁺, Cd²⁺ and Hg²⁺ than some metal ions and its complexes emitted strong fluorescence at 452 nm for Zn²⁺ at 474 nm for Cd²⁺ and at 491 nm for Hg²⁺, respectively. It was determined that HL forms complexes with a ratio of 2:1 for Zn²⁺ and Hg²⁺ and with a ratio of 1:1 for Cd²⁺ by Job plots. For the detection of Zn²⁺, Cd²⁺ and Hg²⁺ in aqueous samples, pH, solvent type and ligand concentration were optimized for an analytical method based on HL chemosensor. HL gave a wide range of linearity with Zn²⁺, Hg²⁺ and Cd²⁺, the limit of detection was found to be 2.7 × 10^-7 M, 7.5 × 10^-7 M and 6.0 × 10^-7 M, respectively.

A highly selective colorimetric and fluorescent probe for quantitative detection of Cu2+/Co2+: The unique ON-OFF-ON fluorimetric detection strategy and applications in living cells/zebrafish

Identifying and detecting similar target cations through combining "turn on" and "turn off" fluorescence mechanism is effective and challenging. Now a new colorimetric and ON-OFF-ON fluorescent probe N'-((7-(diethylamino)-2-oxo-2H-chromen-3-yl)methylene)-3-hydroxy-2-naphthohydrazide (L) was reported, which could detect Cu²⁺ and Co²⁺ in phosphate buffered CH₃CH₂OH-H₂O solvent system. With the assistance of glutathione and pH adjustment, a unique ON-OFF-ON fluorescence detection strategy could be achieved for distinguishing Cu²⁺ and Co²⁺. The emission of probe could recover from the L-Cu²⁺ and L-Co²⁺ system by addition of GSH or adjusting pH value to 4, respectively, which is due to the abolishment of paramagnetic Cu²⁺/Co²⁺. Based on fluorescence titration experiments, the limit of detection was determined as 3.84 × 10^-9 M and 4.55 × 10^-9 M for Cu²⁺ and Co²⁺, respectively. Meanwhile, the detection limit reached 6.21 × 10^-8 M for Cu²⁺ and 6.96 × 10^-8 M for Co²⁺ according to absorbance signal output. Fast recognition of Cu²⁺/Co²⁺ can be achieved by obvious color changes from green to colorless under UV light, as well as from yellow to orange-red in room light. The binding mode of L toward Cu²⁺ and Co²⁺ have been systematically studied by Job's plot analysis, ESI-MS, IR and density functional theory calculations. Most strikingly, further practical applications of the probe L in fluorescence imaging were investigated in MCF-7 cells and zebrafish due to its low cytotoxicity and good optical properties, suggesting that L could serve as a fluorescent sensor for tracking Cu²⁺ and Co²⁺in vivo.

A novel chromone based colorimetric sensor for highly selective detection of copper ions: Synthesis, optical properties and DFT calculations

In this work, a new chromone based colorimetric sensor (ChrCS) was developed for highly selective detection of copper ions in semi-aqueous media. Evaluation of color and spectral changes displayed by the developed sensor shows that the sensor can be applied to detect copper ions in the presence of other competing metal ions and anions. The developed sensor, which contains biologically active chromone ring, shows excellent selectivity at microlevel for Cu²⁺ with a color change from colorless to yellow. Job's plot based on spectroscopic data showed the complex formation between ChrCS and Cu²⁺ ions has the stoichiometric ratio of 1:1 (ChrCS-Cu²⁺ complex). In addition, the binding constant of the ChrCS to Cu²⁺ was determined using the Benesi-Hildebrand equation. Furthermore, the test papers of the developed ChrCS were successfully prepared and employed to detect different concentration Cu²⁺ (10^-3 M to 10^-7 M) in aqueous solution. Importantly, sensor ChrCS was applied to detect Cu²⁺ ions in real water samples. To better understand the optical character of ChrCS and the effect of metal ion titration, density functional theory (DFT) calculations at the B3LYP/6-31 + G(d,p) level were performed for ChrCS and its complex ChrCS-Cu²⁺. Furthermore, on the basis of the Job's plot analysis DFT calculations, and reversible nature of the developed sensor, the sensing mechanism was demonstrated.