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 bisalicylhydrazone based fluorescent probe for detecting Al3+ with high sensitivity and selectivity and imaging in living cells

A bisalicylhydrazone based fluorescence probe, bisalicyladehyde benzoylhydrazone (BS-BH), has been designed to detect Al3+. It exhibited high sensitivity and selectivity towards Al3+ in methanol-water media in physiological condition. Large stokes shifts (∼122 nm) and over ∼1000-fold enhanced fluorescence intensity were observed, which was ascribed to the formation of the two relatively independent rigid extended π conjugated systems bridged by biphenyl group when binding with Al3+. A 1:2 binding ratio between BS-BH and Al3+ was shown by Job's plot. Based on the fluorescence titration data, the detection limit was down to 3.50 nM and the association constant was evaluated to be 1.12 × 109 M-2. The plausible fluorescence sensing mechanism of suppressed ESIPT, inhibited PET, activated CHEF and restricted C = N isomerization was confirmed by a variety of spectral experiments and DFT / TD-DFT calculations. The reversibility of recognition of Al3+ for probe BS-BH was validated by adding Na2-EDTA. In addition, the MTT assay showed the good biocompatibility of BS-BH and BS-BH could be used for imaging Al3+ in living cells.

Fabrication of a New Coumarin Based Fluorescent "turn-on" Probe for Distinct and Sequential Recognition of Al3+ and F- Along With Its Application in Live Cell Imaging

A new coumarin based fluorescent switch PCEH is fabricated which displays high selective sensing towards Al3+ among other metal cations at physiological pH. On gradual addition of Al3+, PCEH shows a brilliant "turn-on" emission enhancement in MeOH/H2O (4/1, v/v) solution. This new fluorescent switch is proven to be a reversible probe by gradual addition of F- into the PCEH-Al3+ solution. Detection limit as well as binding constant values are calculated to be in the order of 10-9 M and 104 M-1 respectively. We have also explored its potential as a biomarker in the application of live cell imaging using breast cancer cells (MDA-MB-231 cell).

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 mitochondria-targeted fluorescent probe based on biocompatible RBH-U for the enhanced response of Fe3+ in living cells and quenching of Cu2+ in vitro

A rhodamine hydrazide conjugating uridine moiety (RBH-U) is firstly synthesized by screening different synthetic routes, and then developed as a fluorescence probe for selective detection of Fe³⁺ ions in an aqueous solution, accompanied by visual color change with naked eyes. Upon the addition of Fe³⁺ in a 1:1 stoichiometry, a 9-fold enhancement in the fluorescence intensity of the RBH-U was observed with an emission wavelength of 580 nm. In the presence of other metal ions, the "turn-on" fluorescent probe with pH-independent (value 5.0 to 8.0) is remarkably specific for Fe³⁺ with a detection limit as low as 0.34 μM. Further, the enhanced fluorescence intensity of RBH-U- Fe³⁺ can be quenched as a switch-off sensor to assist in the recognition of Cu²⁺ ions. Additionally, the colocalization assay demonstrated that RBH-U containing uridine residue can be used as a novel mitochondria-targeted fluorescent probe with rapid reaction time. Cytotoxicity and cell imaging of RBH-U probe in live NIH-3T3 cells suggest that it can be a potential candidate for clinical diagnosis and Fe³⁺ tracking toll for the biological system due to its biocompatibility and nontoxicity in NIH-3T3 cells even up to 100 μM.

A pyridyl functionalized rhodamine chemodosimeter for selective fluorescent detection of mercury ions and cell imaging

Rhodamines gain sustained attention owing to their great potential for probe design applications. Herein, the facile preparation of a new pyridyl functionalized rhodamine dye PR is reported, which has stable fluorescence signal in water with maximum emission peak at 594 nm and Stokes shift of 81 nm. Based on dye PR, a new fluorescent probe PRHg has been developed by modifying the spirolactone of PR with hydrazine hydrate so as to produce spirolactam recognizing group for sensing of Hg²⁺. PRHg exhibits high selectivity and sensitivity towards Hg²⁺ in water/ethanol (v/v = 4/1, pH = 7.0) by a specific Hg²⁺-binding promoted spirolactam ring opening and hydrolyzing process. And, the detection limit for Hg²⁺ is evaluated to be 8.5 nM. Besides, the probe can respond to Hg²⁺ within 40 min and over a wide pH range from 4.0 to 10.0. Moreover, PRHg (40 µM) performs low cytotoxicity to HeLa cells (over 91.0 % cell survival rate), which allows the probe to be employed for tracing intracellular Hg²⁺ by fluorescence imaging.

A chemosensing approach for the colorimetric and spectroscopic detection of Cr3+, Cu2+, Fe3+, and Gd3+ metal ions

Metal cations are present in domestic and industrial wastewater and have adverse effects on human and aqueous life. The present study describes the development of the molecular probe 9-anthracen-9-ylmethylene)hydrazineylidene)methyl)-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-8-ol (AMHMPQ) to detect Cr³⁺, Cu²⁺, Fe³⁺, and Gd³⁺ ions by using UV-visible, fluorescence, colorimetric and excitation-emission matrix (EEM) spectroscopy techniques. The interaction of Cr³⁺, Cu²⁺, Fe³⁺, and Gd³⁺ can be observed by the absorption maxima shift, turn-off, colour changes, and EEM shifts. In addition, fluorescence limits of detection 17.66 × 10^-6 M, 6.44 × 10^-9 M, 28.87 × 10^-8 M, and 12.49 × 10^-6 M in wide linear ranges, low limits of quantifications, high values of Stern-Volmer constant, Job's plot and Benesi-Hildebrand plot justify the 1:1 association affinity with association constants of 1.46 × 10⁴ M^-1, 1.86 × 10⁷ M^-1, 2.69 × 10⁵ M^-1, 2.13 × 10⁴ M^-1 for AMHMPQ-metal ions (Cr³⁺, Cu²⁺, Fe³⁺, and Gd³⁺ ions), respectively. Paper- and mask-based kits are developed to explore the utility of the designed chemosensor. Additionally, AMHMPQ acts as a reusable sensor for two, seven, two, and zero cycles for Cr³⁺, Cu²⁺, Fe³⁺, and Gd³⁺ ions, respectively, when checked with EDTA.

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.