Design of a colorimetric and turn-on fluorescent probe for the detection of Al(III)

A simple fluorescent probe for selectively detecting Al3+ and F- in living cells and growing tea plants

Aluminum (Al3+) and fluorine (F-) ions can be easily enriched in tea plants. When they excessively accumulate in tea, they can affect the health of tea lovers. Herein, a simple, highly sensitive and selective fluorescent probe (named BHMP) for Al3+ and F- detection was developed through a one-step condensation reaction, in which benzothiazole acted as a fluorophore and acceptor and hydrazine-Schiff base as a recognition unit. The probe was characterized comprehensively using spectroscopic methods, and the structure-activity relationship was systematically researched through crystal structure and theoretical calculations. Its sensitivity was measured via the fluorescent titration experiment, and the limit of detection (LOD) towards Al3+ was up to 1.04 × 10-8 mol L-1. Furthermore, we successfully utilized BHMP to visually detect the presence of Al3+ in living cells and tea tree roots through fluorescence confocal imaging. The successful detection of Al3+ in tea tree roots indicated that BHMP could be used as a candidate fluorescent chemosensor to dynamically monitor the variation in enriched Al3+ under the influence of the environment during tea tree growth. Our study provides a reference for the control of Al3+ concentration during the growth of tea plants and provides new insights into improving tea quality control.

A naked-eye visible aluminium (III)-based complex fluorescence sensor for sensitive detection of mesotrione

Mesotrione, which is a kind of herbicide to control broad-leaved weeds, has been increasingly used due to its excellent selectivity, rapid process and low toxicity. However, the excessive application of mesotrione have led to widespread contamination. Herein, a turn-on competitive coordination-based fluorescent probe, 2-hydroxy-1-(9-purin)-methylidenehydrazinenaphthalene (HPM), has been successfully synthesized. HPM could effectively detect Al3+ in CH3OH/HEPES (1/9, v/v) with low limit of detection (LOD) being 0.2 µM via coordination. HPM also exhibited excellent imaging capabilities for Al3+ in living cells with low cytotoxicity. On the basis of the competitive coordination of HPM with Al3+, the [HPM-Al3+] complex could also serve as a potential fluorescence sensor for detecting mesotrione with the LOD of 0.2 µM. Furthermore, [HPM-Al3+] complex was applied for the detection of mesotrione in real samples and test paper. Finally, the mechanism of [HPM-Al3+] for sensing mesotrione was investigated deeply as well. This work designed a new convenient method for on-site detection of mesotrione without the large-scale equipment or complicated pre-treatment.

Diethylaminophenol appended pyrimidine bis hydrazone for the sequential detection of Al3+ and PPi ions

In this study, a novel easy-to-prepare diethylaminophenol appended pyrimidine bis hydrazone (HD) has been designed and developed. The probe exhibits excellent sequential sensing characteristics towards Al3+ and PPi ions. The emission studies, various spectroscopic techniques and lifetime results have been utilized to understand the binding mechanism of HD with Al3+ ions and, to discover the specificity as well as the efficacy of the probe in sensing Al3+ ions. The good association constant in addition to the lower detection limit values makes the probe effective for the detection of Al3+. The in-situ produced HD-Al3+ ensemble could consecutively detect PPi via a turn-off fluorescence response and the selectivity and sensitivity characteristics of the generated ensemble towards PPi were described based on the demetallation approach. The overall sensing property of HD was perfectly employed for constructing logic gates, real water, and tablet applications. Paper strips, as well as cotton-swab experiments, were also conducted inorder to check the practical utility of the synthesized probe.

Method for highly selective, ultrasensitive fluorimetric detection of Cu2+ and Al3+ by Schiff bases containing o-phenylenediamine and o-aminophenol

Schiff base probes (1 and 2) made from o-phenylenediamine and o-aminophenol were appeared as highly selective fluorimetric chemosensor of Cu²⁺ and Al³⁺ ions respectively. Strong fluorescence emission of probe 1 at 415 nm (excitation at 350 nm) was instantly turned off on addition of Cu²⁺. Very weak fluorescence of probe 2 at 506 nm (excitation at 400 nm) was immediately turned on specifically by Al³⁺. Job's plot and ESI-MS results suggested 1:1 molar stoichiometric ratio of metal ion and probe in their respective complexes. Probe 1 and 2 had demonstrated very low detection limit (9.9 and 2.5 nM respectively). Binding of Cu²⁺ with probe 1 was found chemically reversible on addition of EDTA, while complexation between Al³⁺ and probe 2 was not reversible. On the basis of density functional theory (DFT) and spectroscopic results, probable mode of sensing of the metal ions by the probes were proposed. Quenching of the fluorescence of probe 1 by Cu²⁺ was attributed to the extensive transfer of charge from the probe molecule to paramagnetic copper ion. Whereas, in the Al³⁺-complex of probe 2, photo-induced electron transfer (PET) process from the imine nitrogen to salicylaldehyde moiety was restricted and thereby the weak emission intensity of probe 2 was enhanced significantly. Effective pH range of sensing the metal ions by probe 1 and 2 were 4 to 8 and 6 to 10 respectively. Probe 1 was also applied in the design of a logic gate for Cu²⁺ detection. Moreover, probe 1 and 2 was also used in water sample analysis for quantitative estimation of Cu²⁺ and Al³⁺ respectively.

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.

A Novel Schiff Base-Modified Dialdehyde Cellulose-Based Fluorescent Probe for Al3+ and Its Application in Environmental Analysis

Cellulose is the most abundant natural polymer with good biodegradability and biocompatibility. In this paper, a novel fluorescent probe DAC-SD-NA for aluminum (Al³⁺ ) detection is successfully synthesized based on dialdehyde cellulose (DAC). DAC-SD-NA exhibited a remarkable "turn-on" fluorescence response to Al³⁺ in a wide pH range, and the fluorescence color of DAC-SD-NA solution turned from colorless to bright blue at the presence of Al³⁺ . The detection limit for Al³⁺ is computed to be 6.06×10^-7 m. The reaction mechanism of DAC-SD-NA towards Al³⁺ is confirmed by Job's plot, X-ray photoelectron spectroscopy, and density functional theory (DFT) calculations. In view of DAC-SD-NA exhibited good sensitivity and selectivity, it is applied to detect Al³⁺ in real water. What's more, DAC-SD-NA-loaded fluorescent hydrogel can serve as a convenient tool for the detection of Al³⁺ .

A novel AIE fluorescent probe based on myrtenal for Cu2+ detection in a near-perfect aqueous medium and bioimaging in vegetables and zebrafish

An AIE-active fluorescent probe MHTS with good sensitivity and selectivity for the detection of Cu2+ was synthesized from myrtenal.

A novel near-infrared turn-on fluorescent probe for the detection of Fe3+ and Al3+ and its applications in living cells imaging

In this study, a new hemicyanidine-based colorimetric-fluorescent probe L has been synthesized and characterized by X-ray single crystal diffraction, NMR, HRMS and other technologies. The probe L serves as a "turn-on" probe for the detection of Fe³⁺ and Al³⁺ ions in DMF-HEPES system with a high sensitivity and an excellent selectivity. The probe L manifesting the color of the solution containing L turns red on the addition of Fe³⁺, and turns pink on the addition of Al³⁺. The fluorescence turn-on detection of Fe³⁺ and Al³⁺ ions is attributed to the photo-induced electron transfer (PET) process and the exertion of the chelation-enhanced fluorescence effect (CHEF) mechanism. The results of thin layer silica gel plate coloration experiments also present the same characteristics. Additionally, we further demonstrate that the probe L exhibit good cell permeability and could be employed to monitor Fe³⁺ and Al³⁺ ions in the living cells.

Fluorescent schiff base probes for sequential detection of Al3+ and F- and cell imaging applications

Two novel Schiff-base fluorescent probers SQ and NQ based on 8-hydroxyquinoline moiety were designed and synthesized. The both probes were capable of binding with Al³⁺ by naked eye detection to produce a significant fluorescence enhancement response with a detection limit of 1.48 × 10^-8 and 4.23 × 10^-8 M, respectively. At the same time, the formed complexes SQ-Al³⁺ and NQ-Al³⁺ could sequentially detect F^-, and the detection limits of F^- were determined to be 1.64 × 10^-7 and 3.58 × 10^-8 M, respectively. The "off-on-off" fluorescence response process demonstrated that the binding were reversible. The probes were further successfully utilized to detect Al³⁺ and F^- in vitro PC12 cells.

An experimental and computational study on naphthylideneimine based pH sensitive fluorescence probe for zinc

Rational design chelating fluorescent sensors probing metal ions in biological system are continuously hot essays nowadays, especially for zinc detection. Herein, a naphthylideneimine based zinc fluorescence probe (3) was prepared and characterized in this work. Structural features and optical properties of 3 and its metallic complexes were characterized. Fluorescent experiment indicates 3 is extremely sensitive and selective for Zn²⁺ with a strong fluorescence enhancement (∼34 folds) in aqueous buffer solution with a limit of detection (LOD) of 3.78 × 10^-7 mol L^-1. Formation constant (logK_a) of the chelating complex of 3 and Zn²⁺ ion was determined to be 4.45. Theoretical studies were carried out to get deep insight into the response mechanism in the sensing process. Density functional theory (DFT) methods calculated formation Gibbs free energy (Δ_rG_m^ө) of the deprotonated complexes model (3^2- ⊃ Zn) is -2.9 kcal/mol, which is in good agreement with the experimental result. The calculation results show that the low excitation states can be ascribe to S0 → T2 and S0 → S1 at 390-430 nm and 310-330 nm, respectively, due to the π → π∗ transition. Finally, yeast cell imaging experiments indicate that 3 can monitor intracellular Zn²⁺ as well. These findings would enable this fluorescent probe to be used as a Zinc sensor.

Rhodamine-azobenzene based single molecular probe for multiple ions sensing: Cu2+, Al3+, Cr3+ and its imaging in human lymphocyte cells

A photoinduced electron transfer (PET) and chelation-enhanced fluorescence (CHEF) regulated rhodamine-azobenzene chemosensor (L) was synthesized for chemoselective detection of Al³⁺, Cr³⁺, and Cu²⁺ by UV-Visible absorption study whereas Al³⁺ and Cr³⁺ by fluorimetric study in EtOH-H₂O solvent. L showed a clear fluorescence emission enhancement of 21 and 16 fold upon addition of Al³⁺ and Cr³⁺ due to the 1:1 host-guest complexation, respectively. This is first report on rhodamine-azobenzene based Cr³⁺ chemosensor. The complex formation, restricted imine isomerization, inhibition of PET (photo-induced electron transfer) process with the concomitant opening of the spirolactam ring induced a turn-on fluorescence response. The higher binding constants 6.7 × 10³ M^-1 and 3.8 × 10³ M^-1 for Al³⁺ and Cr³⁺, respectively and lower detection limits 1 × 10^-6 M and 2 × 10^-6 M for Al³⁺ and Cr³⁺, respectively in a buffered solution with high reversible nature describes the potential of L as an effective tool for detecting Al³⁺ and Cr³⁺ in a biological system with higher intracellular resolution. Finally, L was used to map the intracellular concentration of Al³⁺ and Cr³⁺ in human lymphocyte cells (HLCs) at physiological pH very effectively. Altogether, our findings will pave the way for designing new chemosensors for multiple analytes and those chemosensors will be effective for cell imaging study.

A Highly Selective Fluorescence "Turn on" and Absorbance-Ratiometric Detection of Al3+ in Totally H2O and its Application in Test Paper

A novel naphthalene based fluorescence probe NBDH was designed and synthesized. Probe NBDH exhibited highly selective and sensitive responses towards Al³⁺ in HEPES-NaOH buffer solution (pH = 7.4). In addition, the detection of NBDH to Al³⁺ could be achieved through dual channels embodied in significant fluorescent turn-on signal and ratiometric absorbance response. The stoichiometry ratio of NBDH-Al³⁺ was 1:1 by fluorescence job' plot and binging mechanism was further varified by the FT-IR, NMR titration and HRMS. Furthermore, NBDH was achieved in real sample detection, and a series of color test paper were developed for visual detecting Al³⁺ ions.

A novel crown ether-acylhydrazone turn-on fluorescent chemosensor for Al3+ ion

A novel fluorescent chemosensor based on crown ether-acylhydrazone (L) was synthesized and characterized. The sensor L exhibited high selectivity and sensitive recognition towards Al³⁺ through a significant "turn-on" fluorescence response at 444 nm in methanol solution. While, other competitive ions had no such significant effects on the fluorescence emission. The associated spectra behavior might be attributed to the formation of 2:1 L-Al³⁺ complex and the proposed binding mode of L-Al³⁺ was demonstrated by the fluorescence titration profiles, Job's plot, ESI-MS spectrometry, ¹H NMR titration and the IR analysis. Besides the high reproducibility of the optical signals, very low detection limit of 0.24 μM was calculated. The association constant (K_s) for L-Al³⁺ complex was about 5.56 × 10⁹ ± 8.19 × 10⁷ M^-2. The results of various experiments showed the sensor L followed a turn-on mechanism via of the suppression of CN isomerization and excited state intramolecular proton transfer (ESIPT) process and the activation of chelation-enhanced fluorescence (CHEF). Theoretical calculations using DFT/B3LYP method was also used to get insight into the sensing mechanism and electronic structure of L. The sensor L could be conceived as an effective and practical fluorescent chemosensor for determination of Al³⁺.