Highly selective fluorescent probe for switch-on Al3+ detection and switch-off F− detection

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.

Synthesis of a super-low detection limit fluorescent probe for Al3+ and its application in fluorescence imaging of zebrafish and cells

A novel fluorescent probe N'-(2-hydroxybenzylidene)-indole-3-formylhydrazine (JHK) was designed and synthesized based on the condensation reaction of indole-3-formylhydrazine and salicylaldehyde. The probe JHK solution could highly selectively recognize Al3+ by the obvious fluorescence enhancement (288-fold) after adding Al3+. And the probe solution with Al3+ had a very high fluorescence quantum yield (89.29 %). The detection limit was calculated to be 1.135 nM, which was significantly lower than many reported detection limits, indicating that the probe JHK had pretty good sensitivity. The ratio of JHK to Al3+ (1:1) and the sensing mechanism were determined by Job's plot, 1H NMR spectra, FTIR spectra, ESI-MS and Gaussian calculation. The probe solution and medium-speed filter paper were successfully used to make test papers for more convenient detection of Al3+. Furthermore, the probe JHK had been successfully applied to the detection of Al3+ in real water, zebrafish and living cells.

Investigation on non-radioactive behavior of an acylhydrazone-based fluorescent probe: Coexistence of PET and TICT mechanisms

A fluorescent probe (E)-((2,4-dihydroxybenzyl)diazenyl)(pyridin-2-yl)methanone (HL) to effectively and selectively detect Al³⁺ was designed and synthesized in the experiment. Herein, we explained the excited state dynamics mechanism of HL by using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The potential energy surfaces (PESs) proved that the excited-state intramolecular proton transfer (ESIPT) process hardly occurs due to the high reaction barriers, so the fluorescence quenching behavior of HL was not based on ESIPT. The frontier molecular orbitals (FMOs) and spectral properties were analyzed to better understand the origination of fluorescence quenching. It was found that an electron on C = N in HL could be transferred to the fluorophore during excitation in the absence of Al³⁺, accompanied by the PET process. The excited state could undergo a twisted intramolecular charge transfer (TICT) process, releasing non-radiative decay. After binding to Al³⁺, the photo-induced electron transfer (PET) process has no longer occurred, and the TICT process is eliminated, resulting in a significant fluorescence enhancement. Therefore, the calculation results well explain the quenching and enhancement behaviors of fluorescence before and after the reaction with Al³⁺.

A portable and intelligent logic detector for simultaneous and in-situ detection of Al3+ and fluoride in groundwater

To develop a convenient and intelligent detector for simultaneous and in-situ detection of Al³⁺ and F^- in groundwater, a novel organic probe called RBP has been prepared. With the increase of Al³⁺, RBP showed a significant fluorescence enhancement at 588 nm, and the detection limit was 0.130 mg/L. After combining with fluorescent internal standard CDs, the fluorescence of RBP-Al-CDs at 588 nm was quenched due to the replace of F^- for Al³⁺, while the CDs at 460 nm remained unchanged, and the detection limit was 0.0186 mg/L. For convenient and intelligent detection, an RBP-based logic detector has been developed for simultaneous detection of Al³⁺ and F^-. Within the ultra-trace, low concentration, and high concentration range of Al³⁺ and F^-, the logic detector can achieve rapid feedback on their concentration levels ("U", "L" and "H") through different output modes of the signal lamps. The development of logical detector is of great significance for studying the in-situ chemical behavior of Al³⁺ and F^- and for daily household detection.

A New Reversible Colorimetric Chemosensor Based on Julolidine Moiety for Detecting F. J Fluoresc 2021;31:1675-1682. [PMID: 34387807 DOI: 10.1007/s10895-021-02801-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

We synthesized an original reversible colorimetric chemosensor PDJ ((E)-9-((2-(6-chloropyridazin-3-yl)hydrazono)methyl)-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-8-ol) for the detection of F^-. PDJ displayed a selective colorimetric detection to F^- with a variation of color from colorless to yellow. Limit of detection of PDJ for F^- was calculated as 12.1 µM. The binding mode of PDJ and F^- turned out to be a 1:1 ratio using Job plot. Sensing process of F^- by PDJ was demonstrated by ¹H NMR titration and DFT calculation studies that suggested hydrogen bond interactions followed by deprotonation. Moreover, the practicality of PDJ was demonstrated via a reversible test with TFA (trifluoroacetic acid).

Synthesis and characterization for a highly selective bis(salamo)-based chemical sensor and imaging in living cell

A new sensor H₅L for continuous identification of Cu²⁺, Al³⁺ and lysine was synthesized by Schiff base reactions. The sensor could specifically recognized Cu²⁺ in the EtOH/H₂O (1:1 v/v) solution by UV-vis spectra, and the binding constant with Cu²⁺ can reach 10¹¹ M^-1, meanwhile, it was found by the naked-eye that the color of the solution was changed from colorless to yellow. The copper complex L-Cu²⁺ formed by the sensor H₅L and Cu²⁺ could further recognize Al³⁺ and lysine in the fluorescence spectra. The LOD values of the three objects were 2.67 × 10^-8, 1.96 × 10^-8 and 5.59 × 10^-9 M, respectively. In addition, fluorescence intracellular images of Al³⁺ and lysine were performed and obtained satisfactory results.

Theoretical investigation on the ESIPT mechanism and fluorescent sensing mechanism of 2-(2'-hydroxyphenyl) thiazole-4-carboxaldeyde in methanol

2-(2'-Hydroxyphenyl) thiazole-4-carboxaldeyde (aldehyde 1) and hemiacetal 2 were selected to study the mechanism of excited-state intramolecular proton transfer and the detecting of Al³⁺ ion in methanol by using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. Our theoretical results are in good agreement with the experimental values. The intramolecular H-bond is enhanced in the first excited-state based on the analyses of structural parameters, frontier molecular orbitals and electronic spectra. The stronger intramolecular H-bond is more favorable for ESIPT process. In order to further demonstrate the proton transfer process, we constructed the potential energy curves of probe 1 and 2 in both ground- and excited-states, and concluded that proton transfer processes in probe 1 and 2 are apt to happen in the S₁ state. In addition, the Mayer bond order, energy gap and absorption and fluorescence spectra were applied to interpret the process of detection of Al³⁺ ion.

A Naphthalimide-Based Fluorescence "Off-on-Off" Chemosensor for Relay Detection of Al3+ and ClO. Front Chem 2019;7:549. [PMID: 31428604 PMCID: PMC6687763 DOI: 10.3389/fchem.2019.00549]

A novel Al³⁺ chemosensor NPA was designed and synthesized on basis of the mechanism of ICT and CHEF. Upon addition of Al³⁺, the probe NPA displayed a bright green fluorescence under UV radiation and visual color change from yellow to colorless. Spectrum titrations showed that NPA could be recognized as a fluorescent turn-on probe with 10^-8 M detection level. The probe was successfully applied in real water sample and test paper. More important, NPA-Al³⁺ complex were used as a fluorescent turn-off probe for the detection of ClO^- with the detection as low as 2.34 × 10^-8 M. The performance of NPA to Al³⁺ and NPA-Al³⁺ complex to ClO^- demonstrated that NPA could be served as a sensitive probe and exhibit INHIBIT logic gate behavior with Al³⁺ and ClO^- as inputs.

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⁺.

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.

A highly sensitive and selective fluorescent probe for quantitative detection of Al3+ in food, water, and living cells

Three novel β-pinene-based fluorescent probes 2a–2c were designed and synthesized for the selective detection of Al³⁺. Probe 2a showed higher fluorescence intensity toward Al³⁺ than the other two compounds. Probe 2a determined the concentration of Al³⁺ with a rapid response time (45 s), wide pH range (pH = 1–9), excellent sensitivity (LOD = 8.1 × 10⁻⁸ M) and good selectivity. The recognition mechanism of probe 2a toward Al³⁺ was confirmed by ¹H NMR, HRMS and DFT analysis. Probe 2a was successfully used as a signal tool to quantitatively detect Al³⁺ in food samples and environmental water samples. Furthermore, probe 2a was successfully utilized to label intracellular Al³⁺, indicating its promising applications in living cells.

Probe 2a exhibiting high sensitivity, good selectivity, wide pH range, lower detection limit, and rapid detection for Al³⁺, probe 2a was applied for the successful detection of Al³⁺ in water samples, food samples and HeLa cells.

Acylhydrazone as a novel “Off–On–Off” fluorescence probe for the sequential detection of Al3+and F−

An acylhydrazone,SPBH,acts as a sequential fluorescence “Off–On–Off” probe for Al³⁺/F⁻, and the phenomenon was detectable by the naked eye.