Fluorescent detection of Zn(II) and In(III) and colorimetric detection of Cu(II) and Co(II) by a versatile chemosensor

Colorimetric and Fluorometric N-Acylhydrazone-based Chemosensors for Detection of Single to Multiple Metal Ions: Design Strategies and Analytical Applications

The development of optical sensors for metal ions has gained significant attention due to their broad applications in biology, the environment, and medicine. Colorimetric and fluorometric detection methods are particularly valued for their simplicity, cost-effectiveness, high detection limits, and analytical power. Among various chemical probes, the hydrazone functional group stands out for its extensive study and utility, owing to its ease of synthesis and adaptability. This review provides a comprehensive overview of N-acylhydrazone-based probes, serving as highly effective colorimetric and fluorometric chemosensors for a diverse range of metal ions. Probes are categorized into single-ion, dual-ion, and multi-ion chemosensors, each further classified based on the detected metal(s). Additionally, the review discusses detection modes, detection limits, association constants, and spectroscopic measurements.

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.

AIEE activated Pyrene-Dansyl coupled FRET probe for discriminating detection of lethal Cu2+ and CN-: Bio-Imaging, DNA binding studies and prompt prognosis of Menke's disease

In present work a pyrene-dansyl dyad functionalized chemoreceptor, DPNS is unveiled towards ultrasensitive chromo-fluorogenic detection of heavy and transition metal ions (HTMs) like Cu2+ and pernicious CN-. It demonstrated distinct chromogenic responses; colorless to faint yellow (Cu2+), intense yellow (CN-) from contaminant aqueous sources. Cu2+ instigated alteration in DPNS fluorescence from feeble emission to sparkling green with LOD: 37.75 × 10-9 M, cyan emission for CN- having LOD 61.51 × 10-8M. In particular, chemical scaffold of DPNS consists of -C = N, O = S = O donor entitities that escalates overall polarity thereby providing an excellent binding pocket for simultaneous Cu2+ and CN- recognition with distinct photophysical signaling. Impressively, presence of two fluorophoric moieties triggers FRET, CHEF phenomenon. The conceivable host:guest interactive pathway is manifested by LMCT- FRET-PET-CHEF, C = N isomerization for Cu2+ and ICT-H-bonding for CN-. An exquisite experimental and theoretical corroboration further strengthened the recognition phenomenon. In addition owing to pyrene excimer formation, DPNS exhibits AIEE with increasing water fraction. Notably, DPNS could successfully undergo intracellular tracking of Cu2+ in Tecoma Stans, Peperomia Pellucida. DPNS•••Cu2+ adduct displayed significant intercalative DNA binding activity rationalized by spectral investigation, competitive EB binding, viscosity study. The overall findings, excellent properties endows DPNS a potential contender towards discriminative detection of Cu2+ and CN- like toxic industrial contaminants.

A Fluorescent and Colorimetric Chemosensor Detecting Pd2+ Based on Chalcone Structure with Triphenylamine

A fluorometric and colorimetric chemosensor DiPP ((E)-3-(4-(diphenylamino)phenyl)-1-(pyridin-2-yl)prop-2-en-1-one) based on chalcone structure with a triphenylamine group was synthesized. Sensor DiPP detected Pd2+ with fluorescence turn-off and via colorimetry variation of yellow to purple. The binding ratio of DiPP to Pd2+ turned out to be 1 : 1. Detection limits for Pd2+ by DiPP were analyzed to be 0.67 µM and 0.80 µM through the fluorescent and colorimetric methods. Additionally, the fluorescent and colorimetric test strips were applied for probing Pd2+ and displayed that DiPP could obviously discriminate Pd2+ from other metals. The binding feature of DiPP to Pd2+ was presented by ESI-mass, Job plot, NMR titration, ESI-mass, and DFT calculations.

Kinetics and Mechanism of In(III) Ions Electroreduction on Cyclically Renewable Liquid Silver Amalgam Film Electrode: Significance of the Active Complexes of In(III)—Acetazolamide

The results of kinetic measurements revealed an accelerating effect of acetazolamide (ACT) on the multistep In(III) ions electroreduction in chlorates(VII) on a novel, cyclically renewable liquid silver amalgam film electrode (R–AgLAFE). The kinetic and thermodynamic parameters were determined by applying the DC polarography, square-wave (SWV) and cyclic voltammetry (CV), as well as electrochemical impedance spectroscopy (EIS). It was shown that ACT catalyzed the electrode reaction (“cap-pair” effect) by adsorbing on the surface of the R–AgLAFE electrode. The catalytic activity of ACT was explained as related to its ability to form active In(III)- acetazolamide complexes on the electrode surface, facilitating the electron transfer process. The active complexes constitute a substrate in the electroreduction process and their different structures and properties are responsible for differences in the catalytic activity. The determined values of the activation energy ΔH≠ point to the catalytic activity of ACT in the In(III) ions electroreduction process in chlorates(VII). Analysis of the standard entropy values ΔS0 confirm changes in the dynamics of the electrode process.

Coordination of Distal Carboxylate Anion Alters Metal Ion Specific Binding in Imidazo[1,2-a]pyridine Congeners

Imidazo[1,2-a]pyridine derivatives have excellent potential for chelation with transition metal ions. Two new imidazo[1,2-a]pyridine-8-carboxylates were synthesized and characterized by ¹H NMR, ¹³C NMR, HRMS, and single crystal-XRD techniques. Methyl carboxylate (probe 1) turns on fluorescence upon coordination with Zn²⁺, while sodium carboxylate (probe 2) turns off its fluorescence upon coordination with Co²⁺ or Cu²⁺ ions present in aqueous acetonitrile medium. ¹³C NMR study revealed that the change in metal ion specific binding was due to the involvement of carboxylate anion in complex formation with Co²⁺ or Cu²⁺ ions. The carboxylate anion at 8-position also enhanced the sensitivity of detection of probe 2 by an order of magnitude (detection limits: 3.804 × 10^-7 M, probe 1/Zn²⁺; 0.420 × 10^-7 M, probe 2/Co²⁺ and 0.304 × 10^-7 M, probe 2/Cu²⁺). The detection limits of probes 1 and 2 comply well with the World Health Organization (WHO) and US Environmental Protection Agency (US-EPA) guidelines for detection of heavy metal ions present in drinking water and ground water. Both the probes form a 1:1 complex with Zn²⁺, Co²⁺ or Cu²⁺, and the stoichiometry was verified by Job plot and ESI-mass analysis. The sensing mechanism is explained using ¹³C NMR experiments, ESI-mass analytical data and theoretical DFT calculations. The suitability of probes 1 and 2 for on-site detection and quantitative determination of Zn²⁺, Co²⁺ and Cu²⁺ ions present in biological, environmental and industrial samples is demonstrated. In addition, both 1 and 2 are used for detection of intracellular contamination of Zn²⁺, Co²⁺ or Cu²⁺ ions in onion epidermal cells.

a Versatile Schiff Base Chemosensor for the Determination of Trace Co2+, Ni2+, Cu2+, and Zn2+ in the Water and Its Bioimaging Applications

In this work, a simple and versatile Schiff base chemosensor (L) was developed for the detection of four adjacent row 4 metal ions (Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺) through colorimetric or fluorescent analyses. L could recognize the target ions in solutions containing a wide range of other cations and anions. The recognition mechanisms were verified with a Job's plot, HR-MS assays, and ¹H NMR titration experiments. Then, L was employed to develop colorimetric test strips and TLC plates for Co²⁺. Meanwhile, L was capable of quantitatively measuring the amount of target ions in tap water and river water samples. Notably, L was used for imaging Zn²⁺ in HepG2 cells, zebrafish, and tumor-bearing mice, which demonstrated its potential biological applications. Therefore, L can probably serve as a versatile tool for the detection of the target metal ions in environmental and biological applications.

A quinoline-benzothiazole-based chemosensor coupled with a smartphone for the rapid detection of In3+ ions

A newly designed quinoline-benzothiazole probe 2-((Z)-((E)-benzo[d]thiazol-2(3H)-ylidenehydrazono)methyl)quinolin-8-ol (L) was synthesized by reacting 8-hydroxyquinoline-2-carbaldehyde with 2-hydrazinobenzothiazole and structurally characterized by various spectroscopic techniques. The sensing ability of probe L was studied with various cations using colorimetry, test paper strips, a red-green-blue (RGB) model and UV-visible spectrophotometry in DMSO : H₂O (3 : 7, v/v). The pale yellow colour of L turns into orange on contact with In³⁺ ions, whereas other tested metal ions did not show any change in colour. The probe L exhibits an absorbance band at 360 nm due to ligand-to-ligand charge transfer (LLCT); upon interaction with In³⁺ ions, it exhibits a band at 445 nm due to ligand-to-metal charge transfer (LMCT). The probe L binds In³⁺ in a 2 : 1 ratio with an association constant of 8.1 × 10⁵ M^-1 and this is established using the Job's and Benesi-Hildebrand (B-H) methods. The probe L can work in the pH range of 4-8 without interfering with other competing ions. It can be used to detect quantities as low as 2.3 ppb and 85 ppb by spectrophotometry and RGB, respectively. The binding mechanism was studied by ¹H NMR titration, ESI mass and FT-IR spectral analysis and well supported by theoretical studies. Overall, probe L demonstrates promising potential for the detection of In³⁺ ions in the semi-aqueous phase and this is its first report as a colorimetric chromogenic probe.

A Fluorescent Probe for the Fast Detection of Hypochlorite and its Applications in Water, Test Strip and Living Cells

Hypochlorite (ClO^-) mediated by oxidative stress play an important role in the body's defense system due to their physiological and pathological significance. In this work, a new and simple probe was designed and synthesized to detect hypochlorite. This probe could rapidly respond to hypochlorite in a short time (20 s) in aqueous media, and showed excellent selectivity and sensitivity, and a wide pH range of 3 ̶ 12, as well as the low detection limit of 1.44 nM. In addition, it was successfully applied to the detection of ClO^- in water sample, test paper experiment, and cell imaging.

Developing a new chemosensor targeting zinc ion based on two types of quinoline platform

A chemosensor DQ (2-(2-(quinolin-2-yl)hydrazinyl)-N-(quinolin-8-yl)acetamide), based on two quinoline moieties, has been synthesized. DQ could detect zinc ion through fluorescence turn-on in aqueous media. Limit of detection was calculated as 0.07 μM, far lower than the standard of WHO for zinc ion. The practicality of DQ was demonstrated via the successful results of reusability with EDTA, easy detection on the test strip, and precise quantification in real water samples. Additionally, sensor DQ could be applied to bioimaging of zinc ion in zebrafish. Sensing process of zinc ion by DQ was studied through fluorescence and UV-Vis spectroscopy, ¹H NMR titration, and ESI-mass spectrometry.

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.

Sensing of zinc ions and sulfide using a highly practical and water-soluble fluorescent sensor: applications in test kits and zebrafish

A practical fluorescent sensor was synthesized for recognition of Zn²⁺ and S²⁻ and applied in various applications such as in live zebrafish.

A novel turn on fluorescent probe for the determination of Al3+ and Zn2+ ions and its cells applications

Early detection of probes is very important for limiting toxic effects of various transition metal ions for example aluminum and zinc. Monitoring of these metal ions can be challenging via conventional methods since they are high cost instrumentations, time consuming and so on. We report facile preparation of a fluorescence probe containing biphenyl groups that effectively selective and superb sensitivity towards aluminum (III) and zinc (II) in neutral solutions without interference from each other and other ions. In neutral pH value, the probe FOB displayed the OFF-ON fluorescence enhancement at 464 nm and 512 nm toward aluminum (III) and zinc (II), respectively. The detection limit values of FOB for Al³⁺ and Zn²⁺ in neutral solutions were 1.27 and 1.02 nM, respectively and these values were significantly lower than permitted Al³⁺ and Zn²⁺ concentrations in drinking water determined by the World Health Organization (WHO) and European Water Quality. Also, fabricated cyano-biphenyl based probe is effective for sensing for aluminum (III) and zinc (II) in living human colon cancer cells even when employed at low concentrations (1.0 μM). Overall, this work allows us to obtain a great potential to be applied to detect Al³⁺ and Zn²⁺.

A new colorimetric and fluorescent probe based on Rhodamine B hydrazone derivatives for cyanide and Cu2+ in aqueous media and its application in real life

A simple selective colorimetric and fluorimetric chemosensor RD based on Rhodamine B hydrazone derivatives was designed and synthesized, which showed both colorimetric and fluorescence responses for cyanide and Cu²⁺ in aqueous solution with specific selectivity and high sensitivity. In the presence of cyanide, the sensor exhibited a visible color change from colorless to pale yellow by naked-eyes and rapidly produced a strong yellow fluorescence in aqueous solution. The detection limit on fluorescence response of RD sensor to CN^- is down to 3.54×10^-7M. In addition, compared to other metal ions such as Fe³⁺, Hg²⁺, Ag⁺, Ca²⁺, Cu²⁺, Co²⁺, Ni²⁺, Cd²⁺, Pb²⁺, Cr³⁺, Zn²⁺ and Mg²⁺ in aqueous solutions, RD could show both colorimetric and fluorescence responses rapidly for Cu²⁺. Notably, this sensor can be used as a molecular switch controlled by CN^- and H⁺ cyclically. Test strips based on RD were fabricated that could be used as a convenient and efficient CN^- and Cu²⁺ test kits. RD could detect cyanide in germinated potato, bitter almond and tap water. This chemosensor enabled detection of two ions, which do not need to rely on two different sensors.

Dual-response detection of Ni2+ and Cu2+ ions by a pyrazolopyrimidine-based fluorescent sensor and the application of this sensor in bioimaging

Herein, a dual-response fluorescent sensor, L, based on pyrazolopyrimidine was designed and developed for the simultaneous detection of Ni²⁺ and Cu²⁺ ions in the presence of other metal ions; the structural characterization of L was carried out by FTIR spectroscopy, NMR spectroscopy, HRMS and X-ray diffraction analysis. The sensor L effectively displayed fluorescence quenching towards the Ni²⁺ and Cu²⁺ ions with high sensitivity without interference from other metal ions. The results reveal that L binds to Ni²⁺ and Cu²⁺ in a 2 : 1 pattern, which matches well with the result of the Job's plot. The association constants of L with Ni²⁺ and Cu²⁺ were 3.2 × 10⁴ M⁻¹ and 7.57 × 10⁴ M⁻¹, respectively. The detection limits (DLs) are down to 8.9 nM for Ni²⁺ and 8.7 nM for Cu²⁺. The fluorescence imaging of L in T-24 cells was investigated because of the low cytotoxicity of L, indicating that L could be used to detect Ni²⁺ and Cu²⁺ in living cells.

A pyrazolopyrimidine-based fluorescent sensor L was developed and applied for detection of Cu²⁺ and Ni²⁺ in ethanol solution by photoluminescence quenching. It shows low cytotoxicity and good imaging characteristics for Cu²⁺ and Ni²⁺ in living cells.

A hydrazono-quinoline-based chemosensor sensing In3+ and Zn2+via fluorescence turn-on and ClO−via color change in aqueous solution

A multi-target sensor, based on hydrazono-quinoline, was developed for fluorescence turn-on detection of In³⁺ and Zn²⁺ and colorimetric detection of ClO⁻.