A novel on-off-on fluorescent chemosensor for relay detection of Fe3+ and PPi in aqueous solution and living cells

Highly Selective Turn-on Fluorescence Sensor for Cd2+ Ions by Tripodal Organic Ligand

Organic fluorescence sensor for selectively detecting and quantifying toxic heavy metal ions has received significant interest due to their environmental hazards. Herein, we have designed and synthesized a simple tripodal Schiff base ligand (1) based on hydroxy-naphthaldehyde and tris(2-aminoethyl)amine (TREN) and demonstrated highly selective turn-on fluorescence sensing of Cd2+ ions. The free ligand did not show any fluorescence in DMF. In contrast, Cd2+ (10- 4 M) addition exhibited a strong enhancement of fluorescence at 450 nm. Interestingly, other metal ions including Zn2+, which exhibit similar chemistry, did not show any turn-on fluorescence. The concentration-dependent studies of 1 with Cd2+ showed the detection limit of 6.78 × 10- 8 M. NMR spectra of 1 with Cd2+ and computational studies were performed to understand the mechanism of sense.

A fluorescent Salamo-Salen-Salamo-Zn(II) sensor for bioimaging and biosensing H2PO4- in Zebrafish and plants

A newly designed and synthesized Salamo-Salen-Salamo-Zn(II) complex sensor (sensor ZT) was extensively explored for anion sensing studies. The selectivity and sensitivity of the sensor ZT towards H2PO4- ions were based on ICT and CHEF effects, and via displacement pathways in DMSO/H2O (9:1, v/v) medium in the presence of other anions like, PO43-, HPO42- and P2O74- in a short time, separately. The prepared ZT sensor has excellent association constant and low detection lines. The sensing mechanism and binding mode of the sensor were studied by UV-Vis spectroscopy, HR-MS, 1H NMR titration and theory calculations (DFT & TD-DFT) for analytes. The time response and stability of the sensor are also given. Meanwhile, the sensor ZT can be widely used as a simple and effective solid-state optical sensor to detect H2PO4- by intuitive fluorescence changes. In addition, besides the environment can be used as a powerful instrument for detecting H2PO4-, based on the good biocompatibility and tissue permeability of ZT, effectively monitoring H2PO4- in cellular distribution by confocal microscopy using Zebrafish and bean sprout.

A pyridine dicarboxylate based hydrazone Schiff base for reversible colorimetric recognition of Ni2+ and PPi

A pyridine dicarboxylate Schiff-base DAS was synthesized for cascade colorimetric recognition of Ni²⁺ and PPi. The selectivity and sensitivity of chemosensor DAS was investigated through colorimetric and UV-vis studies in MeOH-PBS (5 : 1, v/v, pH = 7.4). The chemosensor formed a 2 : 1 complex with Ni²⁺ metal ions with a binding constant of K_a = 3.07 × 10³ M^-2. Besides, a plausible sensing mechanism is confirmed by single crystal X-ray diffraction (SC-XRD), Job's plot and Benesi-Hildebrand plot (B-H plot) experiments. Furthermore, the DAS-Ni²⁺ ensemble formed 'in situ' was used to selectively recognise PPi. The limit of detection (LOD) of DAS for Ni²⁺ was found to be 0.14 μM and that of the DAS-Ni²⁺ ensemble for PPi was found to be 0.33 μM. Also, the potential of the chemosensor has been applied for solid state detection of Ni²⁺ as well as to mimic the 'INHIBIT' logic gate on the addition of Ni²⁺ ions and PPi.

A naphthol hydrazone Schiff base bearing benzothiadiazole unit for fluorescent detection of Fe3+ in PC3 cells

Naphthol hydrazone derivatives are recognized as efficient chelating agents for both qualitative and quantitative detection of metal ions. Here we design a naphthol hydrazine-based chemosensor with covalently linking a strong electron-withdrawing benzothiadiazole group to modulate the molecular electronic structure, nominated as NtHzBtd. The fluorescent probe performs excellent selectivity and sensitivity towards Fe³⁺ with 1:1 binding stoichiometry, while exhibiting a quick response at 55 s with a relatively low limit of detection of 0.036 µM. A series of spectroscopic measurements in tandem with theoretical calculations suggest that the probe undergoes both intramolecular charge transfer (ICT) and chelation enhanced quenching (CHEQ) processes. Successful color rendering of paper strips and bioimaging in PC3 cells demonstrate the promising applicability of NtHzBtd for portable Fe³⁺ detection in real samples and biosystems.

Sensing and Imaging of PPi in vivo using Lanthanide-based Second Near-infrared Luminescent Probes

pathological changes. Here, we reported a luminescent nanoprobe for the detection and imaging of PPi in vivo based on a lanthanide nanoparticle with luminescence at the second near-infrared window modified...

Selective sensing of PPi by fluorogenic Al(III)-probe complex in aqueous medium

A newly designed Schiff base probe JN has been synthesized. It is highly selective and sensitive towards Al³⁺ in nearly 100% aqueous medium by exhibiting a dramatic "turn-on" fluorescence response at 495 nm (λ_ex = 450 nm). The sensing mechanism of JN towards Al³⁺ ions was proposed as the combination of PET, ICT, ESIPT, and CHEF processes according to spectra studies and theory calculations. The in situ generated mononuclear Al(III) complex JN-Al³⁺ could sequentially detect PPi ions by turn-off fluorescence response. The selectivity and sensitivity of the JN-Al³⁺ complex towards PPi ions are based on demetalization process. Interestingly, the fact that Al³⁺ can bind with 1, 2, or 3 PPi has been revealed by HRMS study. The probes JN and JN-Al³⁺ complexes were able to capture Al³⁺ and PPi ions, respectively, as demonstrated by fluorescence imaging of the adult zebrafish and onion inner epidermal cells samples.

Novel Fluorescent Probe toward Fe3+ Based on Rhodamine 6G Derivatives and Its Bioimaging in Adult Mice, Caenorhabditis elegans, and Plant Tissues

A new fluorescent probe LXY based on the rhodamine 6G platforms has been designed, synthesized, and characterized, which could recognize Fe³⁺ effectively in HEPES buffer (10 mM, pH = 7.4)/CH₃CN (2:3, v/v). And the distinct color change and the rapid emergence of fluorescence emission at 550 nm achieved "naked eye" detection of Fe³⁺. The interaction mode between them was achieved by Job's plot, MS, SEM, and X-ray single-crystal diffraction. Importantly, the crystal structures proved that Fe³⁺ could induce the rhodamine moiety transform the closed-cycle form to the open-cycle form. But it is interesting that Fe³⁺ did not appear in the crystal structures. Meanwhile, the limit of detection (LOD) of LXY to Fe³⁺ was calculated to be 3.47 × 10^-9. In addition, the RGB experiment, test papers, and silica gel plates all indicated that the probe LXY could be used to distinguish Fe³⁺ quantitatively and qualitatively on-site. Moreover, the probe LXY has also been successfully applied to Fe³⁺ image in Caenorhabditis elegans, adult mice, and plant tissues. Thus, LXY was considered to have some potential for application in bioimaging.

Highly Selective Recognition of Pyrophosphate by a Novel Coumarin-Iron (III) Complex and the Application in Living Cells

In this paper, a novel NL-Fe3+ ensemble was designed as a fluorescent chemosensor for highly selective detection of pyrophosphate (PPi) in DMSO/H2O (2:8/v:v, pH = 7.2) solution and living cells. NL showed a strong affinity for Fe3+ and was accompanied by obvious fluorescence quenching. Upon the addition of PPi to the generated NL-Fe3+ ensemble, the fluorescence and absorption spectra were recovered completely. Spectroscopic investigation showed that the interference provoked by common anions such as adenosine-triphosphate (ATP), adenosine diphosphate (ADP), and phosphates (Pi) can be ignored. The detection limit of NL-Fe3+ to PPi was calculated to be 1.45 × 10−8 M. Intracellular imaging showed that NL-Fe3+ has good membrane permeability and could be used for the detection of PPi in living cells. A B3LYP/6-31G(d,p) basis set was used to optimize NL and NL-Fe3+ complex.

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.

A novel fluorescent chemosensor based on coumarin and quinolinyl-benzothiazole for sequential recognition of Cu2+ and PPi and its applicability in live cell imaging

In this study, a highly selective fluorescent sensor (E)-2-((2-(benzo[d]thiazol-2-yl)quinolin-8-yl)oxy)-N'-((7-(diethylamino)-2-oxo-2H-chromen-3-yl)methylene)acetohydrazide (TQC) was synthesized from 2-methylquinolin-8-ol and 4-(diethylamino)-2-hydroxybenzaldehyde and its structure was characterized by ¹H NMR, ¹³C NMR, ESI-HR-MS and density functional theory (DFT) calculation. Sensor TQC showed an obvious "on-off-on" fluorescence response to Cu²⁺ and PPi in a DMSO/HEPES (3:2 v/v, pH = 7.4) buffer system. The detection limits of sensor TQC were 0.06 μM to Cu²⁺ and 0.01 μM to PPi. In addition, sensor TQC showed a 1:1 binding stoichiometry to Cu²⁺ and TQC-Cu²⁺ complex showed a 2:1 binding stoichiometry to PPi. The optimum pH range of sensor TQC and TQC-Cu²⁺ was 3-8. Further studies demonstrated that sensor TQC could be made into test paper strips for the qualitative of Cu²⁺ and PPi and showed sequentially "on-off-on" fluorescent bio-imaging of Cu²⁺ and PPi in HeLa cells.

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.