A single molecular probe for multi-analyte (Cr³⁺, Al³⁺ and Fe³⁺) detection in aqueous medium and its biological application

Mechanistic Innovations in Fluorescent Chemosensors for Detecting Toxic Ions: PET, ICT, ESIPT, FRET and AIE Approaches

Fluorescent chemosensors have become vital tools for detecting toxic ions due to their exceptional sensitivity, selectivity, and rapid response times. These sensors function through various mechanisms, each providing unique advantages for specific applications. This review offers a comprehensive overview of the mechanistic innovations in fluorescent chemosensors, emphasizing five key approaches: Photoinduced Electron Transfer (PET), Fluorescence Resonance Energy Transfer (FRET), Intramolecular Charge Transfer (ICT), Aggregation-Induced Emission (AIE), and Excited-State Intramolecular Proton Transfer (ESIPT). We highlight the substantial progress made in developing these chemosensors, discussing their design principles, sensing mechanisms, and practical applications, with a particular focus on their use in detecting toxic ions relevant to environmental and biological contexts.

A Simple Schiff Base Probe for Quintuplicate-Metal Analytes with Four Emission-Wavelength Responses

A versatile mono-Schiff compound consisting of o-aminobenzene-hydroxyjulolidine (ABJ-MS) has been easily synthesized using a one-step reaction. ABJ-MS displays four diverse fluorescence responses to the addition of Zn2+/Al3+/Fe3+/Ag+, with the maximum fluorescence emission at 530 nm undergoing a hypsochromic shift to 502/490/440/430 nm, synchronously with the discriminating fluorescence enhancement being 10.6/22.8/2.6/7.1-fold, respectively. However, the addition of Cu2+ into ABJ-MS leads to an opposite behavior, namely, fluorescence quenching. Meanwhile, ABJ-MS also displays distinct absorption changes after adding these five metal ions due to different binding affinities between them and ABJ-MS, which gives ABJ-MS quite a versatile detecting nature for Cu2+/Zn2+/Al3+/Fe3+/Ag+. Moreover, ABJ-MS can mimic a series of versatile AND/OR/INH-consisting logic circuits on the basis of the Cu2+/Zn2+/Al3+/Fe3+/Ag+-mediated diverse optical responses. These will endow the smart ABJ-MS molecule and potential applications in the multi-analysis chemosensory and molecular logic material fields.

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.

Aza-phenol Based Macrocyclic Probes Design for "CHEF-on" Multi Analytes Sensor: Crystal Structure Elucidation and Application in Biological Cell Imaging

Metal bound macrocyclic compounds found in biological systems inspired us to design and synthesize two Robson-type macrocyclic Schiff-base chemosensors, H ₂ L1 (H ₂ L1=1,11-dimethyl-6,16-dithia-3,9,13,19-tetraaza-1,11(1,3)-dibenzenacycloicosaphane-2,9,12,19-tetraene-1,11-diol) and H ₂ L2 (H ₂ L2=1,11-dimethyl-6,16-dioxa-3,9,13,19-tetraaza-1,11(1,3)-dibenzenacycloicosaphane-2,9,12,19-tetraene-1,11-diol). Both the chemosensors have been characterized with different spectroscopic techniques. They act as multianalyte sensor and exhibit "turn-on" fluorescence toward different metal ions in 1X PBS (Phosphate Buffered Saline) solution. In presence of Zn²⁺, Al³⁺, Cr³⁺ and Fe³⁺ ions, H ₂ L1 exhibits ∼6-fold enhancement of emission intensity, while H ₂ L2 shows ∼6-fold enhancement of emission intensity in the presence of Zn²⁺, Al³⁺ and Cr³⁺ ions. The interaction between the different metal ion and chemosensor have been examined by absorption, emission, and ¹H NMR spectroscopy as well as by ESI-MS⁺ analysis. We have successfully isolated and solved the crystal structure of the complex [Zn(H ₂ L1)(NO₃)]NO₃ (1) by X-ray crystallography. The crystal structure of 1 shows 1:1 metal:ligand stoichiometry and helps to understand the observed PET-Off-CHEF-On sensing mechanism. LOD values of H ₂ L1 and H ₂ L2 toward metal ions are found to be ∼10^-8 and ∼10^-7 M, respectively. Large Stokes shifts of the probes against analytes (∼100 nm) make them a suitable candidate for biological cell imaging studies. Robson type phenol based macrocyclic fluorescence sensors are very scarce in the literature. Therefore, the tuning of structural parameters as the number and nature of donor atoms, their relative locations and presence of rigid aromatic groups can lead to the design of new chemosensors, which can accommodate different charged/neutral guest(s) inside its cavity. The study of the spectroscopic properties of this type of macrocyclic ligands and their complexes might open a new avenue of chemosensors.

Interplay of conformational relaxation and hydrogen bond dynamics in the excited states of fluorescent Schiff base anions

Time resolved fluorescence spectroscopic investigation of four Schiff base anions has established that their excited state dynamics is governed by several solvent properties: polarity, viscosity and hydrogen bond donating ability. With viscous protic solvents like glycerol, fluorescence lifetimes of anions have been found to be markedly longer than those in ethanol, implying that conformational relaxation of molecules plays a key role in their nonradiative relaxation. Surprisingly, the lifetimes in less viscous aprotic solvents, like acetonitrile, are found to be even longer. The only plausible rationalization of this observation is in the light of hydrogen bond-assisted nonradiative phenomena that are operative in protic solvents. This contention draws support from a time evolution of the emission in the red end of the spectrum in low to moderately hydrogen bond donating protic solvents, with regard to an absence of such a rise time in aprotic solvents and strongly hydrogen bond donating solvents, viz., 2,2,2-trifluoroethanol. Rudimentary quantum chemical calculations provide a preliminary idea about the nature of excited state hydrogen bond redistribution involved in the process.

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.

A novel water-soluble flavonol-based fluorescent probe for highly specific and sensitive detection of Al3+ and its application in onion and zebrafish

A novel and simple turn-on fluorescence probe (HD) for Al³⁺ detection was successfully developed based on flavonol derivatives. This probe exhibited a significantly enhanced fluorescence response toward Al³⁺ in aqueous solution which could be observed by naked-eye from poor fluorescence to strong light green emission. The probe HD displays highly specific detection for Al³⁺ over other competitive metal ions, and the detection limit of probe HD for Al³⁺ was determined to be 2.57 × 10^-8 M, which are much lower than the World Health Organization (WHO) guideline value for drinking food/water. The binding stoichiometry of probe HD with Al³⁺ was determined to be 1:1 according to Job's plot and ESI-HRMS analysis, and the binding constant was calculated to be 2.01 × 10⁴ M^-1. The probe HD exhibited high selectivity, high sensitivity, good anti-interface ability, and wide pH application range as well as the quantitative determination in the detection of Al³⁺. The coordination mechanism of probe HD with Al³⁺ was supported by density functional theory (DFT) calculations and HRMS analysis. In addition, the probe HD was found to have good cell permeability and could be applied for live-cell imaging to detect Al³⁺ in onions and zebrafish.

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.

Substitution Effect on 2-(Oxazolinyl)-phenols and 1,2,5-Chalcogenadiazole-Annulated Derivatives: Emission-Color-Tunable, Minimalistic Excited-State Intramolecular Proton Transfer (ESIPT)-Based Luminophores

Minimalistic 2-(oxazolinyl)-phenols substituted with different electron-donating and -withdrawing groups as well as 1,2,5-chalcogenadiazole-annulated derivatives thereof were synthesized and investigated in regard to their emission behavior in solution as well as in the solid state. Depending on the nature of the incorporated substituent and its position, emission efficiencies were increased or diminished, resulting in AIE or ACQ characteristics. Single-crystal analysis revealed J- and H-type packing motifs and a so-far undescribed isolation of ESIPT-based fluorophores in the keto form.

A highly stable Zn coordination polymer exhibiting pH-dependent fluorescence and as a visually ratiometric and on–off fluorescent sensor

A thermally and chemically stable Zn coordination polymer exhibiting pH-dependent fluorescence behaves as a multi-responsive fluorescent sensor for ratiometric and on–off detection of multiple analytes.

The influence of linker substitution on the fluorescence responsive sensing of isostructural coordination polymers: visual turn-on, ratiometric, and turn-off sensing in water

Linker substituents show great impacts on the luminescence properties and sensing performances of isostructural coordination polymers, causing turn-on or ratiometric sensing of Fe³⁺, Al³⁺, and Cr³⁺ and turn-off sensing of CrO₄²⁻ and Cr₂O₇²⁻.

Highly selective and sensitive chemosensor for Al(III) based on isoquinoline Schiff base

As a colorimetric and fluorescent turn-on sensor to Al³⁺, N'-(2-hydroxybenzylidene)isoquinoline-3-carbohydrazide (HL) has been easily synthesized. The fluorescence intensity increases by 273 times in the presence of Al³⁺ at 458 nm. Meanwhile, the experiment data indicate that the limit of detection for Al³⁺ is 1.11 × 10^-9 M. Remarkably, the blue fluorescence signal of HL-Al³⁺ could be specially observed by the naked eye under UV light and is significantly different from those of other metal ions. Fluorescence switch based on the control of Al³⁺ and EDTA proved HL could act as a reversible chemosensor. According to ESI-MS result and the Job's plots, the 2:1 coordination complex formed by HL and Al³⁺ could be produced. Density functional theory calculations were performed to illustrate the structures of HL and complex. The cell imaging experiment indicates that HL can be applied for monitoring intracellular Al³⁺ levels in cells.

Hyperbranched Poly(amido amine) Entrapped Tetraphenylethene as a Fluorescence Probe for Sequential Quadruple-Target Detection and Its Potential as a Chemical Logic Gate

Fluorescence sensors exhibit great potential as molecular logic gates to perform computation on a nanometer scale. For achieving the more complex artificial intelligence activities, developing complex logic gates using multitarget sensing systems with multi-input characteristics is highly desirable. Herein, a water-soluble quadruple-target fluorescence sensor that embeds a small amount (4.1 wt %) of tetraphenylethene (TPE) units into hyperbranched poly(amido amine) (TPE-HPA) has been designed. The nonfluorescent TPE-HPA could experience the fluorescence "off-on-off-on-off" by sequential addition of sodium hexametaphosphate (SHMP), Fe³⁺, ascorbic acid (AA), and H₂O₂. The as-prepared quadruple-target sensor showed good sensitivity and selectivity to SHMP, Fe³⁺, AA, and H₂O₂, and the limit of detection values were 29 nM, 20 nM, 0.66 μM, and 0.78 μM, respectively. On the basis of the multitarget sensing nature of TPE-HPA, chemical or electrochemical-induced logic gates were constructed, including YES, NOT, OR, NOR, NAND, INHIBIT, IMP, and higher logic systems.

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.

Triazatruxene-Rhodamine-Based Ratiometric Fluorescent Chemosensor for the Sensitive, Rapid Detection of Trivalent Metal Ions: Aluminium (III), Iron (III) and Chromium (III)

We investigated the ability of a novel triazatruxene-rhodamine-based (TAT-ROD) chemosensor to detect the trivalent metal ions aluminium (Al³⁺), iron (Fe³⁺) and chromium (Cr³⁺). Operating via the through-bond energy transfer (TBET) pathway, the chemosensor exhibited low detection limits of 23.0, 25.0 and 170.0 nM for Al³⁺, Fe³⁺ and Cr³⁺, respectively, along with high sensitivity and selectivity during a brief period (<15 s). The binding ratio of the chemosensor and trivalent metal ions achieved by Job's method was 3:1, and when we added ethylenediaminetetraacetic acid (EDTA), the sensing process reversed. Altogether, our TAT-ROD chemosensor marks the first triazatruxene-based colorimetric and fluorometric metal ion sensor reported in the literature.

HSA functionalized Gd2O3:Eu3+ nanoparticles as an MRI contrast agent and a potential luminescent probe for Fe3+, Cr3+, and Cu2+ detection in water

PVP capped Gd₂O₃:Eu³⁺ (PVP@Gd₂O₃:Eu³⁺) and HSA functionalised PVP@Gd₂O₃:Eu³⁺ (HSA@PVP@Gd₂O₃:Eu³⁺) NPs as fluorescent detection probe for metal ion detection and MRI contrast agent.

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 lysosome-targetable fluorescent probe for imaging trivalent cations Fe3+, Al3+ and Cr3+ in living cells

An effective morpholine-type naphthalimide chemsensor, N-p-chlorophenyl-4-(2-aminoethyl)morpholine-1,8-naphthalimide (CMN) has been developed as a lysosome-targeted fluorometric sensor for trivalent metal ions (Fe³⁺, Al³⁺ and Cr³⁺). Upon the addition of Fe³⁺, Al³⁺ or Cr³⁺ ions, the probe CMN showed an evident naked-eye color changes which pale yellow solution of CMN turned deepened and it displayed turn-on fluorescence response in methanol. CMN showed a significant selective and sensitive toward Fe³⁺, Al³⁺ or Cr³⁺ ions, while there was no obvious behavior to other monovalent or divalent metal ions from the UV-vis and fluorescence spectrum. Based on the Job's plot analyses the 1:1 coordination mode of CMN with Fe³⁺, Al³⁺ or Cr³⁺ was proposed. The limit of detection (LOD) observed were 0.65, 0.69 and 0.68 μM for Fe³⁺, Al³⁺ and Cr³⁺ ions, respectively. The N-atom of morpholine directly involved in complex formation, CMN emitted fluorescence through inhibition of photoinduced electron transfer (PET). This probe exhibited excellent imaging ability for Fe³⁺, Al³⁺and Cr³⁺ ions in living cells with low cytotoxicity. Significantly, the cellular confocal microscopic research indicated that the lysosome-targeted group of morpholine moiety was introduced which realized the capability of imaging lysosomal trivalent metal ions in living cells for the first time.

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.

Sequential and recyclable sensing of Fe3+ and ascorbic acid in water with a terbium(iii)-based metal-organic framework

A water-stable three-dimensional (3D) metal-organic framework (MOF) of {[Tb(Cmdcp)(H₂O)₃]₂(NO₃)₂·5H₂O}_n (1, H₃CmdcpBr = N-carboxymethyl-(3,5-dicarboxyl)pyridinium bromide) has been synthesized and characterized. MOF 1 is highly emissive, giving rise to green luminescence that can be quenched by Fe³⁺ due to the partial overlap of its excitation spectrum with the absorption spectrum of Fe³⁺. The subsequent introduction of ascorbic acid (AA) leads to the reduction of Fe³⁺ into Fe²⁺, accompanied by the near-entire recovery of MOF 1 emission. The density functional theory (DFT) calculation results support the proposed mechanism. Such a sensing cycle is further transferable to urine and serum samples with a satisfactory near-quantitative recovery, highlighting its good potential in biologically relevant applications.

Highly Selective and Sensitive Turn-Off-On Fluorescent Probes for Sensing Al3+ Ions Designed by Regulating the Excited-State Intramolecular Proton Transfer Process in Metal-Organic Frameworks

The concept of high-performance excited-state intramolecular proton transfer (ESIPT)-based fluorescent metal-organic framework (MOF) probes for Al³⁺ is proposed in this work. By regulating the hydroxyl groups on the organic linker step by step, new fluorescent magnesium-organic framework (Mg-MOF) probes for Al³⁺ ions were established based on the ESIPT fluorescence mechanism. It is observed for the first time that the number of intramolecular hydrogen bonds between adjacent hydroxyl and carboxyl groups can effectively adjust the ESIPT process and lead to tunable fluorescence sensing performance. Together with the well-designed porous and anionic framework, the Mg-TPP-DHBDC probe decorating with a pair of intramolecular hydrogen bonds exhibits extra-high quantitative fluorescence response to Al³⁺ through an unusual turn-off (0-1.2 μM) and turn-on (4.2-15 μM) luminescence sensing mechanism. Notably, the 28 nM limit of detection value represents the lowest record among all reported MOF-based Al³⁺ fluorescent sensors up to now. Benefited from the unique turn-off-on ESIPT fluorescence detection process, the Mg-TPP-DHBDC MOF sensor exhibits single Al³⁺ detection compared with other 16 common metal ions including Ga³⁺, In³⁺, Fe³⁺, Cr³⁺, Ca²⁺, and Mg²⁺. Impressively, such an Al³⁺ selective sensing process can even be fulfilled by the reusable MOF test paper detected by naked eyes. Overall, the quantitative Al³⁺ detection, together with the extraordinary sensitivity, selectivity, fast response, and good reusability, strongly supports our concept of ESIPT-based fluorescent MOF Al³⁺ probes and makes Mg-TPP-DHBDC one of the most powerful Al³⁺ fluorescent sensors.

An easy-to-synthesize multi-photoresponse smart sensor for rapidly detecting Zn2+ and quantifying Fe3+ based on the enol/keto binding mode

A readily available salicylaldazine-modified fluorene Schiff base (EASA-F) exhibits fast fluorescent OFF–ON response to Zn²⁺ and OFF–ON–OFF behavior to Fe³⁺ synchronously accompanied the diverse absorption-ratiometric and colorimetric changes.

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.

Ultrahigh luminescence quantum yield lanthanide coordination polymer as a multifunctional sensor

The investigation and development of advanced multifunctional and sensitive sensors with high luminescent quantum yield and the capability of detecting different analytes, such as metal ions, is imperative. Due to its inherent properties the lanthanide coordination complex is one candidate for sensing applications, particularly for multifunctional sensors. Herein, we present two series of alkali ion decorated lanthanide coordination polymers (Ln-CPs), which show ultrahigh luminescence quantum yields (QYs) of 77% (1a) and 92% (2a). To the best of our knowledge, 1a represents the first trifunctional lanthanide complex sensor that can simultaneous detect and discriminate three different analytes, namely H+/Cd2+/Cr3+ through a multimode optical response. Furthermore, the limit of detection (LOD) for Cr3+ is an ultralow value of 2.0 × 10-9 M with a sensing time of 2 h, which is comparable to the most sensitive Cr3+ chemosensor. More interestingly, 92% (2a) is an unprecedented luminescence QY among the reported lanthanide coordination complexes.

Self-Assembly of Amphiphilic Schiff Base and Selectively Turn on Circularly Polarized Luminescence by Al3

We designed glutamide-derived amphiphilic Schiff bases containing three different aldehyde moieties for the fabrication of circularly polarized luminescence (CPL) emitting materials. Upon self-assembly in acetonitrile, Schiff bases featuring 4-(dimethylamino)-2-hydroxylbenzaldehyde and 1-hydroxy-2-naphthaldehyde groups form supramolecular gels with twist and fiber structures, respectively, whereas Schiff bases featuring 2-hydroxy-1-naphthaldehyde groups form precipitation with flake structures. Although emission and circular dichroism signals can be detected from the supramolecular gels formed by amphiphilic Schiff bases, none of them exhibits a circularly polarized luminescence (CPL). Although Mg²⁺, Zn²⁺, and Al³⁺ can significantly enhance the fluorescence of the Schiff bases, interestingly, only Al³⁺ ion is able to turn on the CPL emission. This study on the one hand provides a simple method for the fabrication of CPL-emitting supramolecular materials and on the other hand offers a novel way for the sensing of aluminum ion with supramolecular materials.

Polydopamine Dots-Based Fluorescent Nanoswitch Assay for Reversible Recognition of Glutamic Acid and Al3+ in Human Serum and Living Cell

We developed a facile and feasible fluorescent nanoswitch assay for reversible recognition of glutamate (Glu) and Al³⁺ in human serum and living cell. The proposed nanoswitch assay is based on our recently developed method for controlled synthesis of fluorescent polydopamine dots (PDADs) at room temperature with dopamine as the sole precursor. The fluorescence of nanoswitch assay could be quickly and efficiently quenched by Glu (turn-Off), and the addition of Al³⁺ could recover the fluorescence of the PDADs-Glu system (turn-On). Meanwhile, the reversible recognition of Glu and Al³⁺ in this nanoswitch system was stable after three cycles. Additionally, the system displayed excellent performance for Glu and Al³⁺ determination with a low detection limit of 0.12 and 0.2 μM, respectively. Moreover, PDADs are successfully applied to determine Glu and monitor Al³⁺ in human serum. Noteworthy, the nanoswitch assay is transported into HepG2 cells and realized "Off" detection of Glu and "On" sensing Al³⁺ in the living cells. Therefore, this PDADs-based nanoswitch assay provides a strategy to develop reversible recognition biosensors for intracellular and external molecular analysis.

Application of a Novel "Turn-on" Fluorescent Material to the Detection of Aluminum Ion in Blood Serum

A novel "turn-on" fluorescent bioprobe, 1,2,3,4,5-penta(4-carboxyphenyl)pyrrole sodium salt (PPPNa), with aggregation-enhanced emission characteristics was synthesized for the in situ quantitative detection of Al³⁺ in serum. It exhibited a high selectivity to Al³⁺ in both simulated serum and fetal calf serum with no interferences from other metal ions or serum components observed and no isolation required. A weak interaction between PPPNa and serum albumin was found, which caused no interference, but enhanced fluorescence response of PPPNa to Al³⁺ and improved detection sensitivity. The limit of detection was determined to be 1.50 μmol/L Al³⁺ in phosphate-buffered saline solution containing 33 μg/mL bovine serum albumin (BSA) and decreased to 0.98 μmol/L as BSA concentration increased to 100 μg/mL. The fluorescence "turn-on" mechanism of the PPPNa probe to detect Al³⁺ was proposed. A bidentate complex is formed between the carboxy group of PPPNa and Al³⁺, causing the photoluminescence (PL) emission enhancement by aggregation. BSA chains further strengthen the stacking compactness of the aggregates of PPPNa and Al³⁺ and consequently enhance the PL emission of PPPNa by further promoting the restriction of intramolecular rotation of the phenyl ring. Its application to the in situ Al³⁺ was successfully demonstrated with HeLa cells and NIH 3T3 cells. The low cytotoxicity and highly selective response of PPPNa to Al³⁺ endow its great potentials to in vivo detecting and imaging of Al³⁺ as well as an absorbent of Al³⁺.