A new fluorescent probe for sensing Al3+ ions in the solution phase and CH3COO- in the solid state with aggregation induced emission (AIE) activity

An AIE (aggregation induced emission) active probe DFP-AMQ was designed and synthesized as a hexa-coordinated N₂O donor chelator for the selective sensing of Al³⁺ colorimetrically as well as fluorimetrically with a 27-fold fluorescence enhancement for CH₃CN-H₂O (9 : 1, v/v, pH 7.2, HEPES buffer). The fluorescence enhancement occurred through the blocking of ESIPT, chelation enhanced fluorescence effect (CHEF) arose, and as a result fluorescence enhancement was observed through 1 : 1 complexation with Al³⁺ ions. Detailed spectroscopic studies including UV-Vis, FTIR, ¹H NMR, and HRMS studies were carried out to characterize the probable structure of DFP-AMQ including the complexation of DFP-AMQ with Al³⁺ ions. The spectrophotometric and spectrofluorimetric titrations revealed strong binding towards Al³⁺ and the K _d values were obtained from UV-Vis (3.26 × 10^-5 M^-1) and fluorescence titration (2.02 × 10^-5 M^-1). The limit of detection of Al³⁺ by DFP-AMQ was 1.11 μM. The quantum yields of DFP-AMQ and [DFP-AMQ-Al]⁺ were calculated to be 0.008 and 0.211, respectively. Dynamic light scattering (DLS) studies showed that the sizes of the particles increased with increasing water percentage due to aggregation. SEM (scanning electron microscopy) studies revealed interesting morphological changes in microstructures in which DFP-AMQ demonstrated a rod-like shape, which was converted to a spherical-like shape in the presence of Al³⁺ and when DFP-AMQ aggregated in H₂O it showed aggregated block-like shape. In the solid phase, DFP-AMQ with nitrate has no particular shape, but in the presence of acetate, it converts to stone-like shape. This probe (DFP-AMQ) could be employed for on-site Al³⁺ ion detection in the solid state.

Lowest aqueous picomolar fluoride ions and in vivo aluminum toxicity detection by an aluminum(iii) binding chemosensor

Aluminum toxicity in biological systems is a well-known issue yet remains as a prevalent and unsolvable problem due to the lack of proper molecular tools that can detect free aluminum(iii) or Al(iii) ions in vivo. Herein, we report a water-soluble photo-induced electron transfer (PET)-based turn-ON/OFF fluorometric chemosensor for the dual detection of Al(iii) and fluoride ions in aqueous media with a nanomolar (∼1.7 × 10^-9 M) and picomolar (∼2 × 10^-12 M, lowest ever detection so far) detection limit, respectively. Fluoride ions in sea water could be detected as well as the recognition of non-contamination in drinking water. In addition, using live-cell microscopy, Al(iii) ions were detected in live biological samples in vivo to aid establishing the aluminum-toxicity effect.

Quinoline based reversible fluorescent probe for Pb2+; applications in milk, bioimaging and INHIBIT molecular logic gate

We report the modular design and synthesis of an amine dangled Schiff base quinoline-morpholine conjugate (QMC) for highly selective detection of Pb²⁺ ions via fluorimetry. The sensing strategy of QMC towards Pb²⁺ ion exhibits a large blue shift with fluorescent enhancement via the intramolecular charge transfer (ICT) process. At the same time, QMC coordination with Pb²⁺, the CN single bond rotation between quinoline and morpholine rings and the CN isomerization process were blocked. Best of our knowledge, this is the first blue shifted turn-on fluorescent chemosensor for Pb²⁺ ion via the ICT process. Furthermore, QMC selectively detects Pb²⁺ ion without any interference with alkali, alkaline earth, and transition metal ions, and limit of detection (LOD) downs to 13 μM, which is a permissible level of Pb²⁺ ion in drinking water reported by WHO. The 1:2 binding stoichiometry between QMC and Pb²⁺ was confirmed by fluorimetric, ¹H NMR titration, mass spectrometry, and theoretical studies. Finally, QMC was potentially applied for the sensing of Pb²⁺ ions in milk, red wine, live cells and an INHIBIT molecular logic function was constructed by using Pb²⁺ and EDTA as chemical inputs.

Development of chalcone-based derivatives for sensing applications

The sensing of various analytes including metal ions and anions is at an incredible speed due to their widespread use in biological processes. Various small molecular species have been reported for the detection of various analytes, with the advantage of low cost and high sensitivity. Among various classes of organic molecules, chalcones are suitable candidates for the design of new chemosensors for targeted ions. In this review, using extensive examples of chalcone-based chemosensors, we explore the design, mechanism, and performance of various chemosensors for the detection of different ions. We believe that this review will provide new insight for researchers in related areas to develop chemosensors for various targeted ions.

A squaraine-based fluorescence turn on chemosensor with ICT character for highly selective and sensitive detection of Al3+ in aqueous media and its application in living cell imaging

A novel and simple squaraine-based fluorescent chemosensor SQ-BH bearing the benzoylhydrazine moiety was developed for the highly sensitive and selective detection of Al³⁺ in methanol-water mixture. The chemosensing behaviors of SQ-BH and its binding interaction with Al³⁺ were explored by various spectroscopic analyses. The reversibility of Al³⁺ recognition process was investigated using EDTA. The results of experiments and DFT/TDDFT calculations revealed that the chemosensor SQ-BH obeyed a turn on mechanism which was associated with the inhibited photoinduced electron transfer (PET), the enhanced intramolecular charge transfer (ICT) and the activated chelation enhanced fluorescence (CHEF). Furthermore, the fluorescent chemosensor SQ-BH whose excellent biocompatibility was confirmed by a standard MTT assay could be used to detect Al³⁺ in living cells, indicating its potential application value in biological fields.

Fluorescent schiff base probes for sequential detection of Al3+ and F- and cell imaging applications

Two novel Schiff-base fluorescent probers SQ and NQ based on 8-hydroxyquinoline moiety were designed and synthesized. The both probes were capable of binding with Al³⁺ by naked eye detection to produce a significant fluorescence enhancement response with a detection limit of 1.48 × 10^-8 and 4.23 × 10^-8 M, respectively. At the same time, the formed complexes SQ-Al³⁺ and NQ-Al³⁺ could sequentially detect F^-, and the detection limits of F^- were determined to be 1.64 × 10^-7 and 3.58 × 10^-8 M, respectively. The "off-on-off" fluorescence response process demonstrated that the binding were reversible. The probes were further successfully utilized to detect Al³⁺ and F^- in vitro PC12 cells.

Rhodamine-based fluorescent probe for sequential detection of Al3+ ions and adenosine monophosphate in water

Organic nanoparticles (N1) were prepared by dispersing thiophene-conjugated rhodamine derivative 1 in a buffer solution (10 mM TRIS, pH 7.4, containing 1% DMSO, v/v). N1 selectively recognized Al³⁺ ions through the "OFF-ON" switching mechanism of the spirolactam ring in rhodamine. The resulting N1·Al³⁺ complex recognized the biologically important molecule adenosine monophosphate (AMP) through a cation displacement process with a detection limit of 2 nM. N1 was capable of determining the concentration of Al³⁺ ions in environmental and biological samples. Portable test strips of N1 were prepared for the recognition of Al³⁺ ions and AMP for practical uses. Furthermore, it was demonstrated that the N1·Al³⁺ complex facilitated real-time monitoring of AMP concentration in the hydrolysis of ATP and ADP.

Pyrene-phenylglycinol linked reversible ratiometric fluorescent chemosensor for the detection of aluminium in nanomolar range and its bio-imaging

Pyrene-phenylglycinol tangled ratiometric sensor (R)-1 was developed for the detection of Al³⁺ ion over other metal ions. Ratiometric behaviour of (R)-1 for Al³⁺ ion explained through monomer emission and excimer quenching leads to avoiding the π-π interactions of bis-pyrene rings. Pull-push to push-pull binding mechanism is successfully explained by DFT and sensing of Al³⁺-ions demonstrated in living cells. The LOD of (R)-1 for Al³⁺ downs to nanomolar concentrations which is lower than the allowed concentration of drinking water set by the (World Health Organization) WHO.

Dual recognition of Al3+ and Zn2+ ions by a novel probe based on diarylethene and its application

We synthesized a new fluorescent probe 1O by attaching a diarylethene molecule to a functional group. The probe can be used to detect Al3+ and Zn2+ at the same time with high selectivity, and its detection limit is very low. When Al3+ was added, the fluorescence intensity was increased 310 folds, and was accompanied by a fluorescent color change from black to grass-green. Similarly, after the addition of Zn2+, the fluorescence intensity was enhanced 110 folds, with a concomitant color change from black to yellow-green. Moreover, based on the properties of 1O, we designed a logic circuit, and that also can be used for water sample testing.

Turn-On Fluorescent Sensors for the Selective Detection of Al3+ (and Ga3+) and PPi Ions

Rationally designed multiple hydroxyl-group-based chemosensors L1-L4 containing arene-based fluorophores are presented for the selective detection of Al³⁺ and Ga³⁺ ions. Changes in the absorption and emission spectra of L1-L4 in ethanol were easily observable upon the addition of Al³⁺ and Ga³⁺ ions. Competitive binding studies, detection limits, and binding constants illustrate significant sensing abilities of these chemosensors with L4, showing the best results. The interaction of Al³⁺/Ga³⁺ ions with chemosensor L4 was investigated by fluorescence lifetime measurements, whereas Job's plot, high-resolution mass spectrometry, and ¹H NMR spectral titrations substantiated the stoichiometry between L4 and Al³⁺/Ga³⁺ ions. The solution-generated [L-M³⁺] species further detected pyrophosphate ion (PPi) by exhibiting emission enhancement and a visible color change. The binding of Al³⁺/Ga³⁺ ions with chemosensor L4 was further supported by density functional theory studies. Reversibility for the detection of Al³⁺/Ga³⁺ ions was achieved by utilizing a suitable proton source. The multiionic response, reversibility, and optical visualization of the present chemosensors make them ideal for practical applications for real samples, which have been illustrated by paper-strip as well as polystyrene film-based detection.

A new multi-analyte fluorogenic sensor for efficient detection of Al3+and Zn2+ions based on ESIPT and CHEF features

The synthesized ESIPT based fluorogenic chemosensor, H₂L, selectively detects Zn²⁺and Al³⁺in a MeOH–H₂O (4/1, v/v, pH = 7.2) medium.

A two-pocket Schiff-base molecule as a chemosensor for Al3+

A new Schiff-base molecule with two binding pockets acts as a selective fluorescent chemosensor for Al³⁺.

Unveiling a versatile heterocycle: pyrazoline – a review

The design and synthesis of novel fluorescent heterocyclic dyes is a “hotspot” research area, due to their favourable photophysical and electronic properties, which could allow huge advances in the fields of physics, chemistry and biology.

Development of a cell permeable red-shifted CHEF-based chemosensor for Al(3+) ion by controlling PET

A structurally modified quinazoline derivative (L) acts as highly selective chemosensor for Al(3+) ions in DMSO-H2O (1:9, v/v) over the other competitive metal ions. L shows a red shifted fluorescence after the addition of Al(3+) ions and later the further fluorescence enhancement is due to chelation enhanced fluorescence (CHEF) through inhibition of photoinduced electron transfer (PET). This probe (L) detects Al(3+) ions as low as 9nM in DMSO-H2O (1:9, v/v) at biological pH. The non-cytotoxic probe (L) can efficiently detect the intercellular distribution of Al(3+) ions in living cells under a fluorescence microscope to exhibit its sensible applications in the biological systems.

A highly selective and sensitive fluorescent turn-on Al3+ chemosensor in aqueous media and living cells: experimental and theoretical studies

A highly selective and sensitive fluorescent chemosensor exhibited enhanced fluorescence in the presence of Al³⁺ and in living cells.

Two Different Emission-Wavelength Fluorescent Probes for Aluminum Ion based on Tunable Fluorophores in Aqueous Media

Two simply and highly selective aluminium ion fluorescent probes based on 4-aminoantipyrine derivate have been successfully synthesized and systemically characterized, The investigation of absorption and emission spectra revealed that the compounds exhibited highly selective fluorescence behaviours toward Al(3+) in aqueous media and showed differential fluorescent emission peaks corresponding to blue and green. which resulted from different fluorophores, and the fluorescence process is attributed to the Photoinduced Electron Transfer (PET) mechanism, In addition, the association constants between sensors L1 and L2 with aluminum ion are 1.58 × 10(6) M(-1) and 8.72 × 10(6) M(-1), respectively, which were obtained by fluorescent titration experiments. Moreover, the binding site of sensors with Al(3+) were determined by (1)HNMR titration experiments.

Effect of metal oxidation state on FRET: a Cu(i) silent but selectively Cu(ii) responsive fluorescent reporter and its bioimaging applications

A new structurally characterized cell permeable rhodamine-cinnamaldehyde hybrid (HL) behaves as a Cu(ii) ions selective chemosensor through FRET process which depends on +2 state of copper ion exclusively.

Aminomethylpyrene-based imino-phenols as primary fluorescence switch-on sensors for Al3+ in solution and in Vero cells and their complexes as secondary recognition ensembles toward pyrophosphate

Three aminomethylpyrene-based salicyl-imines, viz.L1, L2 and L3 were designed and synthesized for Al³⁺ ion sensing.

Selective and sensitive turn-on chemosensor for Al(iii) ions applicable in living organisms: nanomolar detection in aqueous medium

A new crystallographically characterized non-cytotoxic CHEF based highly sensitive Al(iii) ion selective chemosensor (L) is useful to detect the Al(iii) ions' distribution in A549 cell lines and also able to sense Al(iii) ions in tea extract.

An easy and accessible water-soluble sensor for the distinctive fluorescence detection of Zn2+ and Al3+ ions

A water-soluble fluorescence sensor was facilely synthesized and it can be used for the distinctive fluorescence detection of Zn²⁺ and Al³⁺ ions.

A rhodamine-based ‘turn-on’ Al3+ ion-selective reporter and the resultant complex as a secondary sensor for F− ion are applicable to living cell staining

A new cell permeable rhodamine based Schiff base (L) senses nanomolar level of Al³⁺ ions through CHEF process and its Al(iii) complex (2) behaves as a highly F⁻ ions selective biomarker through fluorescence quenching in HEPES buffer.