A fluorescent chemosensor for selective detection of chromium (III) ions in environmentally and biologically relevant samples

A simple single step one pot multicomponent reaction was performed to synthesize N-(tert-butyl)-2-(furan-2-yl)imidazo[1,2-a]pyridine-3-amine (TBFIPA). The synthesized TBFIPA was subjected to library of cations to study its ability for selective and sensitive detection of specific metal ions. Selective detection of chromium ions by TBFIPA were found from the significant hypsochromic shift (335 nm → 285 nm) in the UV-Visible spectra. The fluorescent TBFIPA displays complete quenching of fluorescence under UV lamp (365 nm) only in the presence of chromium without the interference of common metal ions. Binding constant (ka) obtained from Benesi-Hildebrand plot is 0.21 × 105 M-1, limit of detection (LOD) and limit of quantification (LOQ) of TBFIPA toward Cr3+ ions are 4.70 × 10-7 M and 1.56 × 10-7 M, respectively. The mechanism proposed during complex formation were supported by stoichiometric Job continuous variation plot, 1H NMR titration and ESI-MS spectroscopic data. All the experimental confirmation for complex formation were corroborated with theoretical DFT studies optimized using RB3LYP/6-31G(d) basis set. The selectivity and sensitivity of TBFIPA toward Cr3+ ions are found suitable to design a user-friendly silica based portable test kit. Alongside, TBFIPA was successfully utilized for imaging onion epidermal cells. Furthermore, the results obtained for biological, environmental, and industrial samples provided solid evidence to estimate chromium ions using TBFIPA in these real samples.

Hydrazide Schiff base Compound Containing Triphenylphosphonium Units for Fluorescence Sensing of Al3+ and its real Sample Applications

Al3+ excess in the body can cause many diseases. The development of chemosensors for the detection of Al3+ is therefore highly desirable. A hydrazide Schiff base compound containing triphenylphosphonium units (ER) was prepared and used as fluorescence turn-on sensor for the sensing of Al3+. Detection of Al3+ among various metals has been achieved successfully through the formation of Al3+-ligand coordination complexes. To detect Al3+, the "turn on" property of the fluorogenic chemosensor was investigated. Fluorescence sensing studies were carried out in CH3OH-Water (v/v, 9/1, pH 7.0) at λem = 528 nm. The LOD for sensing of Al3+ was found to be 0.129 µM. Using Job's graph, the stoichiometric ratio of ER- Al3+ was determined to be 1:1. The binding constant was determined to be 1.7 × 107 M-1 between Al3 + and the chemosensor ER. Finally, the determination of Al3+ in real herbal teas was carried out by using the sensing function of the chemosensor ER.

A rhodamine based fluorescent and colorimetric chemosensor for the detection of Cr3+ ions and its utility in a molecular logic gate

A new rhodamine based fluorescent and colorimetric chemosensor S1 was synthesized for the selective recognition of Cr3+, a trivalent metal ion. The interaction of S1 toward different metal ions has been studied via fluorescence and UV-visible spectroscopy. The studies revealed that the fluorescence and colorimetric changes of chemosensor S1 are prominent for Cr3+ over other competitive metal ions. Moreover, the chemosensor S1 exhibits 1 : 1 complex formation with Cr3+ as apparent from the Job's plot and the Benesi-Hildebrand (B-H) plot. Density functional theory (DFT) studies also revealed that the Cr3+ ion is coordinated to three atoms of S1, which validates the formation of a complex between S1 and Cr3+. The limit of detection (LOD) of chemosensor S1 for Cr3+ was 0.21 μM. Furthermore, to explore the recyclability of S1, ethylenediaminetetraacetic acid (EDTA) was added to the S1-Cr3+ solution. On the addition of EDTA to the solution of S1-Cr3+, the reversibility of the complex was observed, and a colorimetric variation was also observed on the addition of Cr3+ and EDTA to S1 which mimics the "INHIBIT "molecular logic gate. Chemosensor S1 also demonstrated practical utility through detection of Cr3+ in the solid state.

Recent developments in the creation of a single molecular sensing tool for ternary iron (III), chromium (III), aluminium (III) ionic species: A review

Rational design of a molecular sensing tool is an important topic in molecular recognition, signalling, and optoelectronics that has piqued the interest of chemists, biologists, and environmental scientists. Approximately 150 years have passed since the beginning of the fluorescent chemosensor sector. Due to the paramagnetic properties of Cr3+ and Al3+ , it is tough to prepare a photoluminescence plug-in detector. Most dye-based Al3+ sensors must be utilized in organic or mixed solvents for robust hydration of Al3+ in water. The sophisticated molecular design of sensors, conversely, allows for the detection of these metal ions in aqueous medium. The design of chemosensors using various fluorophores and their mechanisms of action have been thoroughly discussed. A literature survey covering the design of chemosensors and their mechanisms of action have been thoroughly discussed covering the period 2010-2022 and that was carried out including innovative and exemplary activities from numerous groups throughout the world that have significantly contributed to this sector. The most important advantages of these probes are their aqueous solubility and quick response with outstanding selectivity and sensitivity for temporal distribution with high fidelity of metals in living cells.

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.

A rhodamine based chemodosimeter for the detection of Group 13 metal ions

A new rhodamine derivative, HL-CIN, derived from a reaction between N-(rhodamine-6G)lactam-ethylenediamine (L1) and trans-cinnamaldehyde, is reported here for the colorimetric and fluorogenic sensing of Group 13 trivalent cations, namely Al³⁺, Ga³⁺, In³⁺ and Tl³⁺. The absorption intensity of the probe increases significantly at 530 nm whereas the fluorescence intensity enhances massively at 558 nm upon interaction with these metal ions. Other relevant metal ions could not impart any noticeable color change or fluorescence enhancement. The quantum yield or fluorescence life time of HL-CIN increases considerably in the presence of these Group 13 metal ions. Different spectral studies such as ESI-mass, FT-IR, ¹H and ¹³C NMR spectra, establish that HL-CIN undergoes hydrolysis in the presence of the trivalent cations and a rhodamine species in its ring opened form (i.e. N-(2-aminoethyl)-2-((6Z)-3-(ethylamino)-6-(ethylimino)-2,7-dimethyl-6H-xanthen-9-yl)benzamide, (L2)) along with cinnamaldehyde are produced. The rhodamine species in its ring opened form (L2) is responsible for the color change and strong increment in the absorbance and fluorescence of HL-CIN with Group 13 cations. Interaction between L1 and these metal ions could not produce the same outcome. It has been used in test paper strips and to detect these cations in real samples.

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.

Chain length effect of spiro-ring N-alkylation on photophysical signalling parameters in Fe(III) selective rhodamine probes

Manifestation of photophysical signalling parameters in rhodamine derivatives exhibiting complexation induced spiro-ring opening is crucial for the realization of selective metal ion detection at trace levels. Substitution of various functional groups, such as alkylation to the core architecture, modulates the physico-chemical properties of such molecular probes. Despite a few studies, relationships between the extent of photophysical signal modulations and the chain lengths of n-alkyl substituents are still elusive. In this investigation, a few molecular probes based on the rhodamine B (1-5) and rhodamine 6G (6-10) platform were synthesized by their derivatization with n-alkyl substituents of varying chain lengths at the amino-donor of their spiro-ring end, which exhibited Fe(III)-selective absorption and fluorescence 'off-on' signal transduction along with colorization of solution. The Fe(III)-selectivity in these probes remained the same despite their structural distinctions through varied n-alkyl chain lengths of the substituents; however, the quantifiable signalling parameters such as spectroscopic enhancement factors, sensitivity, the kinetics of spiro-ring opening and effectiveness of probe-Fe(III) interactions were analyzed. These parameters were also correlated in terms of the influence of different chain lengths of n-alkyl substituents that efficiently contributed to their inter-componential interactive stereo-electronic environment.

Rhodamine 6G-based efficient chemosensor for trivalent metal ions (Al3+, Cr3+ and Fe3+) upon single excitation with applications in combinational logic circuits and memory devices

A new rhodamine 6G-based chemosensor (L3) was synthesized and characterized by ¹H, ¹³C, IR and mass spectroscopy studies. It exhibited an excellent selective and sensitive CHEF-based recognition of trivalent metal ions M³⁺ (M = Fe, Al and Cr) over mono and di-valent and other trivalent metal ions with prominent enhancement in the absorption and fluorescence intensity for Fe³⁺ (669-fold), Al³⁺ (653-fold) and Cr³⁺ (667-fold) upon the addition of 2.6 equivalent of these metal ions in the probe in H₂O/CH₃CN (7 : 3, v/v, pH 7.2). The corresponding K_d values were evaluated to be 1.94 × 10^-5 (Fe³⁺), 3.15 × 10^-5 (Al³⁺) and 2.26 × 10^-5 M (Cr³⁺). The quantum yields of L3, [L3-Fe³⁺], [L3-Al³⁺] and [L3-Cr³⁺] complexes in H₂O/CH₃CN (7 : 3, v/v, pH 7.2) were found to be 0.0005, 0.335, 0.327 and 0.333, respectively, using rhodamine-6G as the standard. The LODs for Fe³⁺, Al³⁺ and Cr³⁺ were determined by 3σ methods and found to be 2.57, 0.78 and 0.47 μM, respectively. The cyanide ion snatched Fe³⁺ from the [Fe³⁺-L3] complex and quenched its fluorescence via its ring-closed spirolactam form. Advanced level molecular logic devices using different inputs (2 and 4 input) and a memory device were constructed.

Chelate-free “turn-on”-type fluorescence detection of trivalent metal ions

For the detection of trivalent ions, the chelate-free pH-responsive “Turn-ON”-type fluorescence probes based on INAs were constructed. Based on the X-ray analysis, cationic INAs formed unique outer-sphere complexes for AlIII ions.

Stereochemical Geometries and Photoluminescence in Pseudo-Halido-Zinc(II) Complexes. Structural Comparison between the Corresponding Cadmium(II) Analogs

Six pseudohalide zinc(II) containing a variety of N-donor auxiliary amines were structurally characterized. These include two mononuclear trigonal bipyramidal [Zn(NTB)(N3)]ClO4·½H2O (3) and [Zn(TPA)(NCS)]ClO4 (4), two distorted octahedral [Zn(1,8-damnph)2(dca)2] (5) and [Zn(8-amq)2(dca)2] (6a) as well as two 1D polymeric chains catena-[Zn(isq)2(μ1,5-dca)2] (7) and catena-[Zn(N,N-Me2en)2(μ1,5-dca)]dca (8), where NTB = tris(2-benzimidazolylmethyl)amine, TPA = tris(2-pyridylmethyl)amine, 1,8-damnph = 1,8-diaminonaphthalene, 8-amq = 8-amino-quinoline, isq = isoquinoline (isq) and N,N-Me2en = N,N-dimethylethylenediamine. In general, with the exception of 6 and 8, the complexes exhibited luminescence emission in MeOH associated with red shift of the emission maxima, and the strongest visible fluorescence peak was detected at 421 nm (λex = 330 nm) in the case of Complex 5.

BODIPY-Pyridylhydrazone Probe for Fluorescence Turn-On Detection of Fe3+ and Its Bioimaging Application

A novel pyridylhydrazone-tethered BODIPY (BODIPY-PH) was synthesized, fully characterized via nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopic (FTIR), and single-crystal X-ray diffraction (SC-XRD) techniques, and developed for the selective detection of Fe3+ through fluorescent enhancement process. This derivative showed 1:1 binding with Fe3+ in an acetonitrile-water mixture (1:9 v/v) with the binding constant (K) of 5.4 × 104 M−1 and the limit of detection of 0.58 µM. The Fe3+ complexation reaction has been proved to be a reversible process and could be effectively repeated up to three cycles. The electronic properties of BODIPY-PH and its Fe3+ complex modeled by the density functional theory (DFT) method suggested the presence of chelation-enhanced fluorescence (CHEF) effect in the Fe3+ binding reaction. The X-ray absorption spectroscopy (XAS) probed at Fe K-edge confirmed the complex formation between BODIPY-PH and the Fe3+ in an octahedral geometry. Finally, bioimaging against human embryonic kidney (Hek293) cell, through confocal fluorescence microscopic technique indicated that the BODIPY-PH displayed good permeability and low toxicity toward the tested cell lines and showed enhanced fluorescent signal in the cells incubated with Fe3+ proving its capability for Fe3+ analysis in cellular matrix.

Sensitive and rapid detection of Cr3+ in live cells by a red turn-on fluorescent probe

A new probe RB-CR for the detection of Cr³⁺ was constructed based on the conjugation between rhodamine B and phenylthiourea. The Cr³⁺ could trigger opening of the rhodamine spirolactam of RB-CR upon complexation selectively, sensitively and rapidly, resulting in a pronounced enhancement of absorption and fluorescence signal. Further fluorescence imaging study has suggested that RB-CR could be applied as a probe for Cr³⁺ surveillance in living HepG2 cells with low cytotoxicity, which provide us the feasibility of exploring the Cr³⁺ recognition process by the turn-on fluorescence response.

Rational design and bioimaging application of water-soluble Fe3+ fluorescent probes

The carboxyl group improves the water-solubility of Fe³⁺ fluorescent probes, while resulting in different performances based on its position.

An anthracene–quinoline based dual-mode fluorometric–colorimetric sensor for the detection of Fe3+ and its application in live cell imaging

A highly sensitive anthracene–quinoline based dual-mode sensor has been synthesized and used for the fluorometric and colorimetric detection of Fe³⁺ and in live cell imaging.

X-ray structure of two Schiff bases: TURN-ON sensing of Fe3+ and Al3+ in the HepG2 cell line

The efficiency of the fluorescence sensitivity of a sensor may be tuned by the modulation of the steric and electronic parameters in the structure. In this study, the thiophenyl Schiff base (E)-N¹-(phenyl(pyridin-2-yl)methyl)-N²-(thiophen-2-ylmethylene)benzene-1,2-diamine (HL') exhibited very high selectivity and a sensitive fluorescence enhancement towards Fe³⁺ with violet emission (λ_em, 385 nm; LOD, 3.8 nM). On the other hand, the naphthyl Schiff base (E)-1-(((2-((phenyl(pyridin-2-yl)methyl)amino)phenyl)imino)methyl)naphthalen-2-ol (H₂L'') exhibited fluorescence sensitivity towards Al³⁺, showing blue emission (λ_em, 502 nm; LOD, 3.3 nM) in H₂O (HEPES buffer, pH 7.4) medium. The emission enhancement of HL' upon binding to Fe³⁺ may be considered to be due to the restriction of intramolecular rotation, while the selectivity of H₂L'' towards Al³⁺ may be due to the turn on emission through the restriction of excited state intramolecular proton transfer (ESIPT) and the introduction of chelation enhanced fluorescence (CHEF). Furthermore, DFT computation supported the sensing strategy and the probes were applied for intracellular detection of Fe³⁺ and Al³⁺ in HepG2 cell lines.

Application of real sample analysis and biosensing: Synthesis of new naphthyl derived chemosensor for detection of Al3+ ions

A new chemosensor (NANH) based on naphthyl moiety was synthesized with good selectivity and sensitivity towards Al³⁺ ions via the inhibition by operating through dual mechanisms like photo-induced electron transfer (PET) and excited-state intramolecular proton transfer (ESIPT). The synthesized NANH was validated by various techniques such as ¹H, ¹³C NMR and mass spectrum. While prominent fluorescent enhancement was observed from the NANH upon binding with Al³⁺ ions, however, other metal ions have not responded in the emission spectrum. Detection limit and association constant of NANH for Al³⁺ were calculated as 1.2 × 10^-7 M and 4.09 × 10⁴ M^-1 by using fluorescence titration method. Binding ratio (1:1) of NANH with Al³⁺ ions were proved by Job's plot and DFT studies. Furthermore, aluminium in variety of water samples was determined, and NANH could be used for biosensing of Al³⁺ in living cells.

The Role of Zinc(II) Ion in Fluorescence Tuning of Tridentate Pincers: A Review

Tridentate ligands are simple low-cost pincers, easy to synthetize, and able to guarantee stability to the derived complexes. On the other hand, due to its unique mix of structural and optical properties, zinc(II) ion is an excellent candidate to modulate the emission pattern as desired. The present work is an overview of selected articles about zinc(II) complexes showing a tuned fluorescence response with respect to their tridentate ligands. A classification of the tridentate pincers was carried out according to the binding donor atom groups, specifically nitrogen, oxygen, and sulfur donor atoms, and depending on the structure obtained upon coordination. Fluorescence properties of the ligands and the related complexes were compared and discussed both in solution and in the solid state, keeping an eye on possible applications.

A flexible tripod fluorescent probe for multiple cations detection and its application in living cells

To the flexible tripod platform tren (tris(2-aminoethyl)amine), a Rhodamine and two naphthalene fluorophores were introduced. The resulting fluorescence probe named TRN was fully characterized and employed in cell imaging. Probe TRN exhibited high selectivity and excellent sensitivity for the simultaneous fluorescence detection of Zn²⁺/Hg²⁺/Al³⁺/Cu²⁺. The significant changes in the fluorescence color make naked-eye detection possible. Furthermore, fluorescence imaging experiments of Zn²⁺/Hg²⁺/Al³⁺/Cu²⁺ in living PC3 cells demonstrated its value for practical applications in biological systems.

Malonyl-based Chemosensors: Selective Detection of Fe3+ Ion in Aqueous Medium

Two novel malonyl-based chemosensors, N,N'-bis(ethyl-4'-benzoate)-1,3-propanediamide (1) and N,N'-bis(ethyl-3'-benzoate)-1,3-propanediamide (2), have been synthesized and screened towards various biologically important metal ions such as Na⁺, Mg²⁺, K⁺, Ca²⁺, Al³⁺, Cr³⁺, Mn²⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Ag⁺, Cd²⁺, Hg²⁺, Ti³⁺, and Pb²⁺. The emission spectral studies of both 1 and 2 displayed 84 - 91% turn-off emission responses selectively with Fe³⁺ ion in aqueous buffer (MeCN/H₂O, 1:4, v/v, pH = 7.4) solution. Chemosensors 1 and 2 exhibited remarkable sensing ability towards Fe³⁺ ion over other metal ions with limit of detection (LOD) of 4.28 and 4.33 μM, respectively. The binding stoichiometry of 1 and 2 with Fe³⁺ ion was studied by Benesi-Hildebrand fitting, Stern-Volmer plot and Job's plots, revealing that both chemosensors (1 - 2) bind with Fe³⁺ metal ion in 1:1 stoichiometric ratio with the apparent association constant (K_a) 8.90 × 10³ and 11.16 × 10³ M^-1, respectively. Furthermore, the interactions of chemosensors (1 - 2) with metal ion were also investigated by using density functional theory (DFT) at B3LYP hybrid functional using 6-31G and LanL2DZ basis sets.

Recent progress in chemosensors based on pyrazole derivatives

Colorimetric and fluorescent probes based on small organic molecules have become important tools in modern biology because they provide dynamic information concerning the localization and quantity of the molecules and ions of interest without the need for genetic engineering of the sample. In the past five years, these probes for ions and molecules have attracted great attention because of their biological, environmental and industrial significance combined with the simplicity and high sensitivity of absorption and fluorescence techniques. Moreover, pyrazole derivatives display a number of remarkable photophysical properties and wide synthetic versatility superior to those of other broadly used scaffolds. This review provides an overview of the recent (2016-2020) findings on chemosensors containing pyrazole derivatives (pyrazoles, pyrazolines and fused pyrazoles). The discussion focuses on the design and physicochemical properties of chemosensors in order to realize their full potential for practical applications in environmental and biological monitoring (sensing of metal ions, anions, explosives, and biomolecules). We also present our conclusions and outlook for the future.

Switching of Fluorescent Zn/Cd Selectivity in N,N,N',N'-Tetrakis(6-methoxy-2-quinolylmethyl)-1,2-diphenylethylenediamine by One Asymmetric Carbon Atom Inversion

A quinoline-based hexadentate ligand, (S,S)-N,N,N',N'-tetrakis(6-methoxy-2-quinolylmethyl)-1,2-diphenylethylenediamine ((S,S)-6-MeOTQPh₂EN), exhibits fluorescence enhancement at 498 nm upon addition of 1 equiv of Zn²⁺ (I_Zn/I₀ = 12, φ_Zn = 0.047) in aqueous DMF solution (DMF/H₂O = 2:1). Addition of 1 equiv of Cd²⁺ affords a much smaller fluorescence increase at the same wavelength (I_Cd/I₀ = 2.5, I_Cd/I_Zn = 21%). The trivalent metal ions such as Al³⁺, Cr³⁺, and Fe³⁺ also exhibit fluorescence enhancement at 395 nm (I_Al/I₀ = 22, I_Cr/I₀ = 6 and I_Fe3+/I₀ = 13). In contrast, meso-6-MeOTQPh₂EN exhibits a Cd²⁺-selective fluorescence increase at 405 nm in the presence of 1 equiv of metal ion (I_Cd/I₀ = 11.5, φ_Cd = 0.022), while Zn²⁺ induces a smaller fluorescent response under the same experimental conditions (I_Zn/I₀ = 3.3, I_Zn/I_Cd = 29%). In this case, the fluorescence intensities of meso-6-MeOTQPh₂EN in the presence of a large amount of Zn²⁺ and Cd²⁺ become similar. This diastereomer-dependent, fluorescent metal ion specificity is derived from the Zn²⁺-specific intramolecular excimer formation in (S,S)-6-MeOTQPh₂EN-Zn²⁺ complex and higher binding affinity of meso-6-MeOTQPh₂EN with Cd²⁺ in comparison to Zn²⁺. The more conformationally restricted diastereomeric pair, namely, cis- and trans-TQDACHs (cis- and trans-N,N,N',N'-tetrakis(2-quinolylmethyl)-1,2-diaminocyclohexanes), both exhibit Zn²⁺-specific fluorescence enhancement because of the high metal binding affinity and intramolecular excimer forming property derived from the rigid DACH backbone.

Development of Rhodamine 6G-Based Fluorescent Chemosensors for Al3+-Ion Detection: Effect of Ring Strain and Substituent in Enhancing Its Sensing Performance

Four rhodamine 6G-based chemosensors (H 3 L1-H 3 L4) are designed for selective detection of Al3+ ion. They are characterized using various spectroscopic techniques and X-ray crystallography. All absorption and emission spectral studies have been performed in 10 mM N-(2-hydroxyethyl)piperazine-N'-ethanesulfonic acid (HEPES) buffer solution at pH 7.4 in H2O/MeOH (9:1, v/v) at 25 °C. In absorption spectra, chemosensors exhibit an intense band around 530 nm in the presence of Al3+ ion. Chemosensors (H 3 L1-H 3 L4) are nonfluorescent when excited around 490 nm. The presence of Al3+ ion enhances the emission intensity (555 nm) many times. The formation of complexes 1-4 is established with the aid of different spectroscopic techniques. The limit of detection value obtained in the nanomolar range confirms the high sensitivity of the probes toward Al3+ ion. It has been observed that the presence of aliphatic spacers in the diamine part and different halogen substituents in the salicylaldehyde part strongly influences the selectivity of the chemosensors toward Al3+ ion. The propensity of the chemosensors to identify intracellular Al3+ ions in triple-negative human breast cancer cell line MDA-MB-468 by fluorescence imaging is also examined in this study.

Supramolecular assembly of a 4-(1-naphthylvinyl)pyridine-appended Zn(ii) coordination compound for the turn-on fluorescence sensing of trivalent metal ions (Fe3+, Al3+, and Cr3+) and cell imaging application

The as-synthesized Zn(ii) coordination compound exhibited turn-on fluorescence sensing of analytical group-IIIA metal ions (Fe³⁺, Al³⁺, and Cr³⁺) and applications in cell imaging.

A rhodamine based biocompatible chemosensor for Al3+, Cr3+ and Fe3+ ions: extraordinary fluorescence enhancement and a precursor for future chemosensors

A rhodamine based chemosensor, 3-(((2-(3',6'-bis(ethylamino)-2',7'-dimethyl-3-oxospiro[isoindoline-1,9'-xanthen]-2-yl)ethyl)imino)methyl)-2-hydroxy-5-methylbenzaldehyde (HL-CHO), has been developed for the detection of Al3+, Cr3+ and Fe3+ ions. The absorbance of HL-CHO at 528 nm increases significantly in HEPES buffer in methanol : water (9 : 1, v/v) (pH 7.4) in the presence of Al3+, Cr3+ and Fe3+ ions with the alteration of solution color from colorless to pink. The fluorescence intensity of the probe at 550 nm enhances by 1465, 588 and 800 fold in the presence of Al3+, Cr3+ and Fe3+ ions, respectively. To the best of our knowledge, this huge increase in fluorescence intensity with Al3+ and Cr3+ has not been observed for other rhodamine based chemosensing systems. The weak fluorescence and no coloration of the probe are due to the existence of a spirolactam ring. The trivalent cations induce the opening of the spirolactam ring and consequently change the color and the fluorescence intensity followed by the 1 : 1 complex formation with HL-CHO which are evident from Job's analysis, ESI mass spectral analysis and elemental analysis. The quantum yield and lifetime of HL-CHO have increased considerably in the presence of the trivalent cations. The high sensitivity of the probe towards all the cations is evident from the nM order of LOD values. This has been used in living cell imaging studies with the human neuroblastoma SH-SY5Y cell line. Having appended -CHO groups for Schiff-base condensation with other amines, HL-CHO could be a potential precursor for future chemosensors.

A smart chemosensor: Discriminative multidetection and various logic operations in aqueous solution at biological pH

A novel rhodamine-pyrazole based molecular probe was designed and easily synthesized. The probe could to detect several analytes in aqueous solution at biological pH (HEPES, pH = 7.2). Several heavy metal cations, including Cu²⁺, Fe³⁺, Al³⁺, Hg²⁺ and Ni²⁺ were detected discriminately by the probe. Also, the novel compound exhibited a good sensory selectivity towards S₂O₅^2- by both absorption and emission spectra. Moreover, probe/Cu²⁺ complex could to detect several anions, including F^-, CN^-, S^2-, CH₃COO^-, CO₃^2- and NO₂^-. Furthermore, the probe exhibited a high potential to work as a molecular system able to perform a number of logical operations such as AND, NAND, NOR and INHIBIT logic gates.

A chemosensoring molecular lab for various analytes and its ability to execute a molecular logical digital comparator

We reported here the unique ability of a Rhodamine 6G-based probe (3) to detect discriminately several targets, including H⁺, HO^-, Cu²⁺, Hg²⁺, Fe³⁺, Co²⁺, Cd²⁺, Zn²⁺, Sn²⁺, Ni²⁺, Al³⁺, Pb²⁺, Ce³⁺and Ag⁺, by unambiguously colorimetric and fluorimetric outcomes. In aqueous solutions, the presence of proton induced the ring-opening of rhodamine moiety but the presence of hydroxide induced the conversion of 2-hydroxyphenyl hydrazone moiety from the non-fluorescent benzenoid form into the fluorescent quinoid form. The probe could to distinguish between different cations in DMF and to work like an artificial tongue at molecular level. Several logic gates including OR, INHIBIT and TRANSFER, were performed by the probe. Moreover, the probe is able to execute three INHIBIT logic gates by two inputs, which was exploited to execute a digital molecular comparator.

Chelation of specific metal ions imparts coplanarity and fluorescence in two imidazo[1,2-a]pyridine derivatives: Potential chemosensors for detection of metal ions in aqueous and biosamples

Synthesis and chelation induced fluorescence emission from two imidazo[1,2-a]pyridine derivatives are described. The nonfluorescent molecule 1 containing N and O donor atoms, achieves coplanarity upon interactions with trivalent cations Al³⁺, Fe³⁺ and Cr³⁺, that favors fluorescence emission. Molecule 2 containing two N donor atoms attains coplanarity upon interaction with the only Zn²⁺ and becomes fluorescent. Both molecules 1 and 2 form a 1:1 complex with interacting metal ions. Other trivalent metal ions (including Bi³⁺ and In³⁺) and common divalent metal ions (including Hg²⁺ and Cd²⁺) fail to form any complex with 1 or 2, and they do not interfere in the detection of Zn²⁺, Al³⁺, Fe³⁺ or Cr³⁺ ions. Noninterference of other metal ions renders 1 and 2 suitable for the detection of fungal cells contaminated with Zn²⁺, Al³⁺, Fe³⁺ or Cr³⁺ ions.

Recent Advances on Iron(III) Selective Fluorescent Probes with Possible Applications in Bioimaging

Iron(III) is well-known to play a vital role in a variety of metabolic processes in almost all living systems, including the human body. However, the excess or deficiency of Fe3+ from the normal permissible limit can cause serious health problems. Therefore, novel analytical methods are developed for the simple, direct, and cost-effective monitoring of Fe3+ concentration in various environmental and biological samples. Because of the high selectivity and sensitivity, fast response time, and simplicity, the fluorescent-based molecular probes have been developed extensively in the past few decades to detect Fe3+. This review was narrated to summarize the Fe3+-selective fluorescent probes that show fluorescence enhancement (turn-on) and ratiometric response. The Fe3+ sensing ability, mechanisms along with the analytical novelties of recently reported 77 fluorescent probes are discussed.

New rhodamine B-based chromo-fluorogenic probes for highly selective detection of aluminium(iii) ions and their application in living cell imaging

Two rhodamine B-based fluorescent probes, BOS1 and BOS2, were designed and synthesized with good yields via the condensation reactions between the o-diaminobenzene modified rhodamine core structure (RBO) and salicylaldehyde derivatives. Both the probes exhibited remarkable absorbance-on and fluorescence-on responses to Al³⁺ over other metal ions in ethanol–water (1 : 9, v/v) medium via the rhodamine ring-opening approach, which can be used for “naked-eye” Al³⁺ detection over a broad pH range (5–9). The fluorescence intensities of the probes were linear with the Al³⁺ ion concentration, resulting in a low limit of detection of 1.839 μM (BOS1) and 1.374 μM (BOS2) for Al³⁺. In addition, the MTT assays and cell imaging experiments of Al³⁺ in SGC-7901 living cells demonstrated that the probes had negligible cytotoxicity, and were cell permeable and suitable for sensing Al³⁺ in biological systems.

Two rhodamine B-based fluorescent probes exhibited remarkable absorbance-on and fluorescence-on responses to Al³⁺, which can be used for biological imaging.

A differentially selective probe for trivalent chemosensor upon single excitation with cell imaging application: potential applications in combinatorial logic circuit and memory devices

A new rhodamine 6G-benzylamine-based sensor (L1) shows selective recognition of trivalent metal ions with advanced level molecular logic gate and bio-imaging applications.

Rhodamine scaffolds as real time chemosensors for selective detection of bisulfite in aqueous medium

Rhodamine and its derivatives have been widely used in designing fluorescent ‘turn on’ cation sensors, while very few rhodamine based fluorescent probes have been reported to date for the detection of anions in water.

GB, Latiyan S, Jain S. Remarkably selective biocompatible turn-on fluorescent probe for detection of Fe3+ in human blood samples and cells

The robust nature of a biocompatible fluorescent probe is demonstrated, by its detection of Fe³⁺ even after repeated rounds of quenching (reversibility) by acetate in real human blood samples and cells in vitro.