A comprehensive review on colorimetric and fluorometric investigations of dual sensing chemosensors for Cu2+ and Fe3+ ions from the year 2017 to 2023

Dual sensing chemosensors for copper(II) and iron(III) ions are molecules or compounds designed to selectively detect and differentiate between these specific metal ions. Because metal ions like copper(II) and iron(III) are essential to so many industrial, biological, and environmental processes, their detection and measurement have become increasingly important. In this work, a novel dual-sensing chemosensor that combines high selectivity and sensitivity is presented. It is intended to detect copper(II) (Cu2+) and iron (III)(Fe3+) ions concurrently. The chemosensor combines two different recognition components into one platform and achieves dual-mode detection by combining optical and electrochemical sensing approaches. Using a dual sensing chemosensors for two cations can save money and time compared to preparing two separate chemosensors to sense each of those cations separately. We often use various techniques, including spectroscopy, fluorescence, and electrochemistry, to monitor and measure the changes induced by the interaction between the chemosensors and the metal ions. Discussions have been held on the excitation and emission wavelengths, media used in the spectroscopic measurements, binding constant with coordination binding mode, detection mechanism, and detection limit (LOD). This extensive review paper investigates colorimetric and fluorometric dual sensing analysis for Cu2+ and Fe3+ ions which includes more than sixty papers from the year of 2017 to 2023.

Semi-quantitative and visual detection of Cu2+ and glyphosate in real samples and living cells using fluorescent and colorimetric dual-signals peptide-based probe

The excessive emission of copper ions (Cu2+) and the abuse of glyphosate (Glyp) have caused serious harm to the ecological environment and human health, so it is important to develop a fast and convenient method for the analysis of Cu2+ and glyphosate to ensure environmental and food safety. Herein, a dual-signals peptide-based probe (FASRH) with fluorescent and colorimetric was prepared using 5-carboxyl fluorescein modified tetrapeptide (Ala-Ser-Arg-His-NH2). FASRH was successfully used to recognize Cu2+ as a fluorescence "on-off" probe, forming the FASRH-Cu2+ complex with non-fluorescence. As a new promising cascade probe, FASRH-Cu2+ complex probe has high selectivity (only Glyp), good sensitivity (50.2 nM), good anti-interference ability and wide pH range (7.0-11.0) for the detection of glyphosate by ligand replacement method. In addition, the recognizable color changed markedly under 365 nm UV light and natural light. Notably, FASRH not only achieved accurate monitoring of Cu2+ and glyphosate in two real water samples, but also successfully applied to detect Cu2+ and glyphosate in live Hacat cells based on low cytotoxicity. Moreover, it is worth noting that FASRH-impregnated test strips exhibited significant fluorescence and colorimetric color changes for Cu2+ and glyphosate via naked eye. Furthermore, smartphone-assisted FASRH was used for the portable detection of Cu2+ and glyphosate based on the advantages of simplicity, low cost and fast response.

The crystal structure of (E)-3′,6′-bis(diethylamino)-2-((5-(diethylamino)-2-hydroxybenzylidene)amino)spiro[isoindoline-1,9′-xanthen]-3-one, C39H45N5O3

C33H31BrN4O3, monoclinic, P21/n (no. 14), a = 11.8558(12) Å, b = 12.1159(11) Å, c = 24.014(2) Å, β = 94.812(2)°, V = 3437.3(6) Å3, Z = 4, Rgt (F) = 0.0574, wRref (F 2) = 0.1725, T = 296(2) K.

Two rhodamine-azo based fluorescent probes for recognition of trivalent metal ions: crystal structure elucidation and biological applications

Two rhodamine and azo based chemosensors (HL1 = (3',6'-bis(ethylamino)-2-((2-hydroxy-3-methoxy-5-(phenyldiazenyl)benzylidene)amino)-2',7'-dimethylspiro[isoindoline-1,9'-xanthen]-3-one) and HL2 = (3',6'-bis(ethylamino)-2-(((2-hydroxy-3-methoxy-5-(p-tolyldiazenyl)benzylidene)amino)-2',7'-dimethylspiro[isoindoline-1,9'-xanthen]-3-one) have been synthesized for colorimetric and fluorometric detection of three trivalent metal ions, Al³⁺, Cr³⁺ and Fe³⁺. The chemosensors have been thoroughly characterized by different spectroscopic techniques and X-ray crystallography. They are non-fluorescent due to the presence of a spirolactam ring. The trivalent metal ions initiate an opening of the spirolactam ring when excited at 490 nm in Britton-Robinson buffer solution (H₂O/MeOH 1 : 9 v/v; pH 7.4). The opening of the spirolactam ring increases conjugation within the probe, which is supported by an intense fluorescent pinkish-yellow colouration and an enhancement of the fluorescence intensity of the chemosensors by ∼400 times in the presence of Al³⁺ and Cr³⁺ ions and by ∼100 times in the presence of Fe³⁺ ions. Such a type of enormous fluorescence enhancement is rarely observed in other chemosensors for the detection of trivalent metal ions. A 2 : 1 binding stoichiometry of the probes with the respective ions has been confirmed by Job's plot analysis. Elucidation of the crystal structures of the Al³⁺ bound chemosensors (1 and 4) also justifies the 2 : 1 binding stoichiometry and the presence of an open spirolactam ring within the chemosensor framework. The limit of detection (LOD) values for both the chemosensors towards the respective metal ions are in the order of ∼10^-9 M which supports their application in the biological field. The biocompatibility of the ligands has been studied with the help of the MTT assay. The results show that no significant toxicity was observed up to 100 μM of chemosensor concentration. The capability of our synthesized chemosensors to detect intracellular Al³⁺, Cr³⁺ and Fe³⁺ ions in the cervical cancer cell line HeLa was evaluated with the aid of fluorescence imaging.

A Conjugated Polymer Fluorescent Sensor for Continuous Identification of Copper(II) and Pyrophosphate in Blood Serum and Synovial Fluid

A novel "on-off-on" super-sensitive conjugated polymer fluorescence sensor (PPE-DPA) was developed and it was applied to realize the continuous recognition of Cu²⁺ and pyrophosphate (PPi). The fluorescence intensity decreased linearly with the change of Cu²⁺ from 0.05 to 5.0 μmol L^-1 and the limit of detection was 24 nmol L^-1. The fluorescence intensity was linearly enhanced with the increase of PPi from 0.5 to 12.0 μmol L^-1 and the limit of detection was 230 nmol L^-1. In addition, this method was applied to detect PPi in the blood serum and synovial fluid of patients with arthritis and satisfactory results were obtained. Thus, the PPE-DPA is not only an effective tool for detecting Cu²⁺ and PPi in samples, but also presents a potential way to diagnose arthritis.

Fluorescent probe for Cu2+ and the secondary application of the resultant complex to detect cysteine

A special fluorescent probe has been developed, one that demonstrated excellent "off-on-type" change in fluorescence with high selectivity toward Cu2+. Interestingly, the probe-Cu2+ complex could detect cysteine due to the ability of this amino acid to strongly coordinate Cu2+, and no obvious interference was observed from other amino acids and anions. According to the proposed mechanism, addition of cysteine induced decomplexation of the probe-Cu2+ form. Furthermore, the results of confocal microscopy experiments demonstrated the potential of using the probe to image Cu2+ in living cells and mice.

A novel terephthalaldehyde based turn-on fluorescent chemosensor for Cu2+ and its application in imaging of living cells

A new terephthaldehyde-based chemosensor 1 bearing an aminophenol recognition unit has been synthesized and applied to the fluorescent sensing of metal ions. Molecular system 1 acts as a highly selective and sensitive fluorescence turn-on sensor for Cu²⁺. The sensing mechanism has been explored. It is proposed that Cu²⁺ binds with the imine and hydroxyl moiety of 1 in 1 : 2 binding stoichiometry, thereby enhancing the fluorescence at 386 nm. The detection limit and association constant (K_a) of 1 with Cu²⁺ were found to be 0.62 μM and 6.67 × 10⁴ M^-1, respectively. Chemosensor 1 has shown excellent specificity towards Cu²⁺ and has been successfully applied to the determination of Cu²⁺ in live L929 cells.

Two sugar-rhodamine "turn-on" fluorescent probes for the selective detection of Fe3

Two new sugar-rhodamine fluorescent probes (RDG1 and RDG2) have been synthesized and characterized by ¹H NMR, ¹³C NMR and HRMS. Their UV-Vis, fluorescence spectra and fluorescence-response to Fe³⁺ are investigated and discussed. RDG1 had a very nice linear relationship between UV absorbance and Fe³⁺ concentration with the correlation coefficient as high as 0.997 and the detection limit is 3.46×10^-6M. Upon the addition of Fe³⁺, the spirolactam ring of RDG1 was opened and a 1:1 metal ligand complex was formed from Job's plot. The results showed that RDG1 can be used as an effective fluorescent probe for selective detection of Fe³⁺ in water. RDG2 was incorporated the well-known rhodamine group and a water-soluble d-glucose group within one molecule and can be used for detecting Fe³⁺ in natural water as a selective fluorescent sensor. The addition of Fe³⁺ into RDG2 resulted in a strongly enhanced fluorescence as well as color change of solution from colorless to pink. Job's plot of RDG2 indicated 1:1 stoichiometry of RDG2-Fe³⁺. RDG2 can serve as a probe for Fe³⁺ between pH=4.0 to 7.0 and it's detection limit is 2.09×10^-6M. The OFF-ON fluorescent mechanisms of RDG1-Fe³⁺ and RDG2-Fe³⁺ are proposed.

A new fluorene-based Schiff-base as fluorescent chemosensor for selective detection of Cr3+ and Al3

2-((9H-fluoren-2-ylimino) methyl)phenol (F3) was synthesized by condensation reaction of 9H-fluoren-2-amine and 2-hydroxybenzaldehyde in EtOH and characterized by its melting point, ¹H-,¹³C NMR and molecular mass. F3 exhibits a high selectivity for detection of Cr³⁺ and Al³⁺ ions as a fluorescent chemosensor and showed a single emission band at 536nm upon excitation at 333nm according to fluorescence emission studies. The addition of Cr³⁺ and Al³⁺ make a significant increase in fluorescent intensity at 536nm in CH₃CN, while other metal ions have almost no influence on the fluorescence. The fluorescence enhancement was attributed to the inhibited CN isomerization and the obstructed excited state intra-molecular proton transfer (ESIPT) of compound F3. Job's plot and DFT calculations data showed that the binding stoichiometries of F3 with Cr³⁺ and Al³⁺ are 2:1. The association constants (K_a) for Cr³⁺ and Al³⁺ were calculated and found to be 8.33×10⁴M^-1 and 5.44×10⁴M^-1, respectively. The detection limits were also calculated for Cr³⁺ and Al³⁺ and found to be 2.5×10^-7mol/L and 3.1×10^-7mol/L, respectively.

Facile rhodamine-based colorimetric sensors for sequential detections of Cu(ii) ions and pyrophosphate (P2O74−) anions

Two rhodamine hydrazine derivatives Rh1 and Rh2 with catechol and ether functionalities have been synthesized and utilized towards sequential colorimetric detections of Cu(ii) and pyrophosphate (PPi) ions in a semi-aqueous medium.

Single Chemosensor for Double Analytes: Spectrophotometric Sensing of Cu(2+) and Fluorogenic Sensing of Al(3+) Under Aqueous Conditions

(E)-N-((8-Hydroxy-1,2,3,5,6,7-hexahydropyrido-[3,2,1-ij]-quinolin-9-yl)methylene)-4-tert-butyl -benzhydrazide has been developed as a single, dual-functional chemosensor. The chemosensor showed a good selectivity and sensitivity toward to Al(3+) and Cu(2+) at a low detection limit, respectively. Theoretical calculations have also been carried out to understand the configuration of the complexes.

Highly sensitive SERS sensor for mercury ions based on the catalytic reaction of mercury ion decorated Ag nanoparticles

Schematic diagram of the SERS sensing mechanism for mercury ions by a catalytic oxidation reaction.

Chemodosimeter approach for nanomolar detection of Cu2+ ions and their bio-imaging in PC3 cell lines

A new rhodamine–azaindole based fluorescence probe for Cu²⁺ has been synthesized which shows fluorescence resonance energy transfer process in acetonitrile. Further, the probe undergoes Cu²⁺ promoted hydrolysis in mixed aqueous media as well as in the intracellular systems.