Phenothiazine appended thiophene derivative: a trilateral approach to copper ion detection in living cells and aqueous samples

This research paper unveils a fluorescent probe (PTZ-SCN) engineered for the specific detection of Cu2+, featuring a 10-ethyl-10H-phenothiazine-3-carbaldehyde and 2-(thiophen-2-yl) acetonitrile moiety. The fluorescence sensing behavior of PTZ-SCN towards various metal cations was scrutinized in CH3CN : HEPES (9 : 1) buffer aqueous solution. The UV absorbance of PTZ-SCN displayed a distinct red shift in the presence of Cu2+ cations, whereas other metal cations did not cause any interference. Similarly, the fluorescence emission of the probe was also only quenched by Cu2+ cations. The limit of detection (LOD) was calculated as 1.0461 × 10-8 M. PTZ-SCN showed the ability to identify Cu2+ using the colorimetric method, the fluorometric method and even through visual observation in a trilateral detection. We studied the recognition mechanism of PTZ-SCN for Cu2+ using 1H-NMR, HRMS analysis, and time-dependent density functional theory (TDDFT) calculations. Furthermore, our study encompassed the investigation of PTZ-SCN's practical applicability, bridging the gap from research to real-world implementation. This was achieved by employing test strips and water samples for the detection of Cu2+. Additionally, the PTZ-SCN probe's low cytotoxicity and effective imaging properties for Cu2+ in living cells were confirmed, indicating that PTZ-SCN shows the potential to serve as a promising probe for detecting Cu2+in vivo.

A very rare fluorescent chemosensor of zinc(II) exhibiting AIEE, ESIPT and TICT: Spectroscopic, crystallographic and theoretical exploration

The basic systems in this study are HL (1; 1:2 condensation product of 2,6-diformyl-4-ethylphenol and o-anisidine) and its ZnII and CdII complexes of composition [ZnII(LH)Cl2]·CH3OH (2) and [CdII(LH)Cl2] (3), all of which are synthesized and characterized by CHN elemental analyses, single crystal X-ray crystallography, powder X-ray diffraction (PXRD) and fourier transform infrared (FT-IR) spectrum. It has been established from the following experimental and theoretical studies that 1 is a fluorescent turn on sensor of ZnII ion and it exhibits all of excited state intramolecular proton transfer (ESIPT), photoinduced electron transfer (PET), twisted intramolecular charge transfer (TICT) and aggregation induced enhanced emission (AIEE): (i) Detailed absorption and emission (steady state / time resolved) studies in various single solvents, in solvent mixtures, with pH variation, with various single metal ions, with mixtures of metal ions, on varying temperature and on varying viscosity; (ii) dynamic light scattering (DLS) and scanning electron microscopy (SEM) in solvent mixtures; (iii) density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculations in ground and excites states of 1-3. It is shown that 1 can be efficaciously applied in inkless writing with the "write - erase - write" facility. The mechanisms/reasons of the observed properties have been addressed. The difference in fluorescence of ZnII and CdII complexes, unusual case of crystal structures of probe and complexes with ZnII and CdII, unusual features in the structures of 2 and 3 as well as a structure-property correlation have been discussed.

Facile one-step fabrication of Cu-doped carbon dots as a dual-selective biosensor for detection of pyrophosphate ions and measurement of pH

High-performance determination of pyrophosphate ions (PPi) and pH is an important goal in biological systems. In this work, Cu-doped carbon dots (Cu-CDs) were synthesized rapidly and simply via a one-pot hydrothermal method. The as-obtained Cu-CDs, with an average size of 2.55 nm, exhibit an excitation-independent fluorescence emission and possess desirable functional groups of carboxyl and amine, which can be served as fluorescence nanoprobes for detection of PPi based on surface passivation. Under the optimal condition, the linear range for detection of PPi was 0.05-20 µM, and the corresponding limit of detection (LOD) was 0.013 µM, indicative of a promising assay for the PPi. Moreover, the fluorescent intensity of the Cu-CDs is linear against pH value from 6 to 8.7 in buffer solution, suggesting the feasibility as a pH sensor. The synthesized Cu-CDs coated fluorescent paper indeed can monitor pH in urine with satisfaction by naked eyes through ultraviolet irradiation. The successful detection of PPi and the visual detection of pH value suggest a highly promising application of Cu-CDs in the field of biosensing.

Benzimidazole–acid hydrazide Schiff–Mannich combo ligands enable nano–molar detection of Zn2+ via fluorescence turn–on mode from semi–aqueous medium, HuH–7 cells, and plants

Herein, we have synthesized two unsymmetrical and dipodal Schiff–Mannich combo ligands, benzoic acid (3–benzoimidazol–1–ylmethyl–2–hydroxy–5–methyl–benzylidene)–hydrazide (H2BBH) and the hydroxyl analogue, 2–hydroxy–benzoic acid (3–benzoimidazol–1–ylmethyl–2–hydroxy–5–methyl–benzylidene)–hydrazide (H3BSH) for selective detection of Zn2+ in semi–aqueous...

Hydrazone-Based Small-Molecule Chemosensors

The hydrazone functional group is widely applied in several fields. The versatility and large use of this chemotype are attributed to its easy and straightforward synthesis and unique structural characteristics which is useful for different chemical and biological purposes. Recently hydrazone scaffold has been widely adopted in the design of small-molecule fluorescent and colorimetric chemosensors for detecting metals and anions because of its corresponding non-covalent interactions. This chapter provides an overview of hydrazone-based fluorescent and colorimetric chemosensors for anions and metals of biological interest, with their representative rational designs in the last 15 years. We hope this chapter inspires the development of novel and powerful fluorescent and colorimetric chemosensors for a broad range of applications.

A bisphenol based fluorescence chemosensor for the selective detection of Zn2+ and PPi ions and its bioluminescence imaging

A bisphenol based fluorescence "turn-on" chemosensor 4,4'-(propane-2,2-diyl)bis(2-((E)-(2-(benzo[d]thiazol-2-yl)hydrazineyldene)methyl)phenol) (BHMP) has been synthesized and its sensing behavior was tested towards various ionic species. The chemo-sensing behavior of BHMP has been established through absorption, fluorescence, NMR, and mass spectroscopic techniques. The probe BHMP selectively detects zinc ions over other metal ions and the resulting BHMP + Zn²⁺ ensemble serves as a secondary probe for the detection of pyrophosphate (PPi) anion specifically over other anions. The spectroscopic studies reveal the fluorescence enhancement of BHMP in association with Zn²⁺ ions was quenched in the presence of pyrophosphate (PPi) anions. A probable mechanism of this selective sensing behavior was described on the basis of "OFF-ON-OFF" strategy for detection of both cations and anions. Moreover, the biological applicability of the chemosensor BHMP was examined via cell imaging studies.

A Simple Isoniazid-Based N-Acylhydrazone Derivative as Potential Fluorogenic Probe for Zn2+ Ions

This study evaluated three isoniazid-based N-acylhydrazone derivatives (HL1, HL2, and HL3) varying their substituting groups (-H, -N(CH₃)₂, and -NO₂) as potential chemosensors for Zn²⁺ ions. To this end, the absorption and emission properties of these derivatives were investigated in the presence of Zn²⁺ ions. Results point to the derivative HL2 as the best chemosensor for Zn²⁺ ions because of its comparatively higher sensitivity. The color of this derivative changed from colorless to strong yellow with zinc addition, as indicated by the shift in UV-vis spectrum. Moreover, HL2 was the only derivative to emit fluorescence in the presence of Zn²⁺ ions, attributable to PET inhibition and bond isomerization promoted by coordination with this metal. LOD, LOQ, and binding constant values for HL2 + Zn²⁺ were 0.43 μmol.l^-1, 0.93 μmol.l^-1, and 5.04 × 10¹² l.mol^-1, respectively. The fluorescence of HL2 with other metal ions (Fe³⁺, Mg²⁺, Na⁺, Cd²⁺, Cu²⁺, Co²⁺, Ni²⁺, Ca²⁺, and K⁺) was also investigated. Zn²⁺ yielded the best result without Cd²⁺ interferences. Job's Plot showed that the stoichiometric ratio of the complex formed by HL2 and Zn²⁺ ions is 2:1 (ligand:metal). The strip test with adsorbed HL2 indicated fluorescence in the presence of zinc ions under 365 nm UV irradiation.

A dual functional turn-on non-toxic chemosensor for highly selective and sensitive visual detection of Mg2+ and Zn2+: the solvent-controlled recognition effect and bio-imaging application

A new dual functional turn-on chemosensor, 2,6-diformyl-4-methylphenol-di(isoquinolinyl-1-hydrazone) (HL), has been developed, which could highly selectively discriminate Mg²⁺ and Zn²⁺ in different solvent systems. The chemosensor HL exhibits rapid visual turn-on fluorescence enhancing recognition toward Mg²⁺/Zn²⁺, which is not interfered by other cations, especially for respective congeners Ca²⁺/Cd²⁺. The remarkable fluorescence enhancement (71-fold or 11-fold) was observed after adding Mg²⁺ in acetonitrile or Zn²⁺ in DMF-H₂O solvent systems. Additionally such a solvent medium-controlled platform could achieve the quantitative determination of Mg²⁺ and Zn²⁺ quantitation with low detection limits of 2.97 × 10^-8 M and 3.07 × 10^-7 M, respectively. Furthermore, the turn-on fluorescence sensing mechanism is also investigated by ¹H NMR, FT-IR and ESI-MS spectroscopy. Density functional theory (DFT) calculations derive optimized geometries of HL and its complexes. Notably, non-toxic HL also can be successfully applied as a visual probe for the practical determination of Mg²⁺/Zn²⁺ in MCF-7 cells, Zebrafish larvae, syrup and water samples, which might provide extensive application in biology and medicine fields.

"Turn-on" Pb2+ sensing and rapid detection of biothiols in aqueous medium and real samples

Detection of lead has continued to be of immense interest in the present industrial as well as environmental diaspora. To this end, we report a prudent Schiff base which enables the sensitive detection of Pb2+ ions in mixed aqueous medium. The probe is afforded by simple synthetic and purification processes. Further, the probe employs simple mechanistic detection of Pb2+ and also successively detects a host of biothiols. The sensor is also used to detect Pb2+ ions in real water samples and consecutive detection of a variety of biothiols, including functionalized thiouracils, in onion and garlic extract. The fact that the Pb2+-L ensemble is 'non-selective' towards any particular thiol substituted analyte in real samples could as well prove to be an interesting contribution for chemical and biological detoxification processes.

An azine-based carbothioamide chemosensor for selective and sensitive turn-on-off sequential detection of Zn(II) and H2PO4-, live cell imaging and INHIBIT logic gate

Hydrazino-carbothioamide, 1, serves as a turn-on fluorescent chemosensor to Zn²⁺ and the mixture shows green emission (λ_em 492) in presence of large number of ions with impressive limit of detection (LOD), 0.59 nM. Intense fluorescence of Zn-complex is selectively turn-off upon adding H₂PO₄^- only to the limit of detection, 26 μM, while other anions remain silent. The sensing mechanism of 1 is established by suppressing the ESIPT of 1 and complexation with Zn²⁺ (CHEF) is supported by Job's plot, ¹H NMR, and HR-MS data. Turn-on-off sequential detection of Zn²⁺ and H₂PO₄^- also have successfully been employed for the engineering of INHIBIT molecular logic gate. The sensor is non-toxic and has been used in identifying Zn²⁺ in the intracellular region of African green monkey kidney cells (Vero cells).

Intrinsically fluorescent and highly functionalized polymer nanoparticles as probes for the detection of zinc and pyrophosphate ions in rabbit serum samples

Intrinsically fluorescent polymer nanoparticles (F-PNPs) were synthetized from 2-hydroxy-5-methylisophthalaldehyde and melamine by solvothermal method. F-PNPs can emit strong yellow green fluorescence at 542 nm without the conjugation to any external fluorescent agent and surface modification. Owing to the abundant amino and hydroxyl groups on their surface, the F-PNPs possess multiple binding sites, good biocompatibility and excellent water-solubility. Addition of Zn²⁺ to the F-PNPs solution resulted in a blue shift (Δλ=40 nm) with obvious enhancement in the fluorescence intensity at 502 nm; while there was negligible change in the presence of other metal ions. The subsequent treatment with pyrophosphate (PPi) can cause fluorescence recovery of F-PNPs by pulling the Zn²⁺ out of the coordination cavity of F-PNPs-Zn²⁺ nanocomposites. No interference was observed from other anions and nucleotides, making the F-PNPs-Zn²⁺ ensembles highly sensitive and selective nanoprobes for PPi. The detection limit is 2.75 × 10^-8 M/L and 7.63 × 10^-8 M/L for Zn²⁺ and PPi, respectively. The proposed nanoprobes were then used for detecting the recovery of Zn²⁺ and PPi in rabbit serum samples, which were found to be 99.4-104.2% and 98.6-104.7%, respectively. The present strategy for the fabrication of nanoparticles may offer a new sight for the preparation of polymer nanostructures. The F-FNPs based probes can provide an accurate method for the detection of Zn²⁺ and PPi in serum samples.

Detection and discrimination of Zn2+ and Hg2+ using a single molecular fluorescent probe

A new fluorescent probe (SAPH) has been introduced which shows specific sensing towards Zn²⁺ and Hg²⁺ at two different wavelength maxima at physiological pH.

Tripodal cyanurates as selective transmembrane Cl− transporters

Tris-carboxyamide and tris-sulfonamide-based anion receptors with cyanuric acid core are developed for transmembrane chloride transport.

Combined experimental and theoretical studies on selective sensing of zinc and pyrophosphate ions by rational design of compartmental chemosensor probe: Dual sensing behaviour via secondary recognition approach and cell imaging studies

A compartmental chemosensor probe HL was designed and synthesized for dual sensing of zinc ions and PPi via secondary recognition approach.

Aggregation-Induced Emission (AIE) Fluorophore Exhibits a Highly Ratiometric Fluorescent Response to Zn2+ in vitro and in Human Liver Cancer Cells

Two novel organic fluorophores, containing bis-naphthylamide and quinoline motifs, have been designed and synthesized. One of the fluorophores contains an isobutylene unit and exhibits a significant aggregation-induced emission (AIE) and a remarkable highly selective ratiometric fluorescence response towards Zn²⁺ in solution as well as in human liver cancer cells. The AIE behavior of this fluorophore was fully verified by fluorescence and UV/Vis spectroscopy, quantum yield calculations, and single-crystal X-ray diffraction, which revealed an intricate crystal packing system. Conversely, a fluorophore that lacks the isobutylene moiety did not exhibit any significant fluorescent properties as a result of its more flexible molecular structure that presumably allows free intramolecular rotational processes to occur.

Low-Affinity Zinc Sensor Showing Fluorescence Responses with Minimal Artifacts

The study of the zinc biology requires molecular probes with proper zinc affinity. We developed a low-affinity zinc probe (HBO-ACR) based on an azacrown ether (ACR) and an 2-(2-hydroxyphenyl)benzoxazole (HBO) fluorophore. This probe design imposed positive charge in the vicinity of a zinc coordination center, which enabled fluorescence turn-on responses to high levels of zinc without being affected by the pH and the presence of other transition-metal ions. Steady-state and transient photophysical investigations suggested that such a high tolerance benefits from orchestrated actions of proton-induced nonradiative and zinc-induced radiative control. The zinc bioimaging utility of HBO-ACR has been fully demonstrated with the use of human pancreas epidermoid carcinoma, PANC-1 cells, and rodent hippocampal neurons from cultures and acute brain slices. The results obtained through our studies established the validity of incorporating positively charged ionophores for the creation of low-affinity probes for the visualization of biometals.

A NIR fluorescent probe for the detection of fluoride ions and its application in in vivo bioimaging

A near-infrared fluorescent probe has been developed, which is available for visualizing exogenous fluoride ions in vitro and in vivo.

Where is it and how much? Mapping and quantifying elements in single cells

The biological function of a chemical element in cells not only requires the determination of its intracellular quantity, but also the spatial distribution of its concentration. Different strategies can be employed to quantify and map the intracellular concentration of elements in single cells. The assessment of the intracellular elemental concentration, which is the relevant information, requires the measurement of cell volume. This challenging and demanding task requires combining different techniques allowing gathering of both morphological and compositional information on the same cell. Moreover, the need to analyse samples more similar to their natural state requires complex hardware equipment, and supplementary efforts in preparation protocols. Nevertheless, the response to the question: "where is it and how much?" is worth all these efforts. This review aims at providing an insight into the recent and most advanced techniques and strategies for quantifying and mapping chemical elements in single cells. We describe and discuss indirect detection techniques (label based) which make use of fluorescent dyes, and direct ones (label free), such as particle induced X-ray emission, proton backscattering spectrometry, scanning transmission ion spectrometry, nano-secondary ion mass spectrometry, X-ray fluorescence microscopy, complemented by X-ray imaging.

Highly photostable zinc selective molecular marker bearing flexible pivotal unit: opto-fluorescence enhancement effect and imaging applications in living systems

Novel molecular probes for imaging zinc in biological systems are gaining interest as they help in understanding the role of zinc in regulating various bio-events. In this regard, a new C2-symmetric molecular system has been developed and successfully applied as light-up material for signaling divalent zinc with green emission. The fluorescence enhancement was highly zinc specific and this newly developed probe bears a submicromolar detection capability. While probe and the ensemble -Zn(2+) exhibited remarkably high photostability, light-triggered fluorescence enhancement was observed in the case of -Zn(2+). The nature of the -Zn(2+) complex and the associated spectral shift are further supported by theoretical calculations. As the present probe absorbs in the visible region and emits in the green, it was preferred as a potential material for imaging zinc in biological systems including animal and plant cells such as pollen grains and fish egg cells. Such fluorescence imaging of zinc revealed the efficacy of the probe in detection and localization of zinc in various biological systems.

A thiosemicarbazone based chemo and fluorogenic sensor for Zn2+with CHEF and ESIPT behaviour: computational studies and cell imaging application

A novel diformyl-p-cresol (DFC)–thiosemicarbazide (TS) – based turn-on dual sensor that enables to determine, for the first time, the stepwise formation constants.

A multi-responsive turn-on flurogenic probe to sense Zn2+, Cd2+and Pb2+: left-right-center emission signal swing

A rationally designed multi-target probe can sense Zn²⁺, Cd²⁺and Pb²⁺through individual TURN-ON emission signals in physiological pH with signal swing.

A highly selective chemosensor for naked-eye sensing of nanomolar Cu(ii) in an aqueous medium

A colorimetric chemosensor was developed for the sensitive detection and quantification of Cu²⁺with a short response time in an aqueous medium.

Nanomolar Zn(ii) sensing and subsequent PPi detection in physiological medium and live cells with a benzothiazole functionalized chemosensor

Nanomolar zinc detection and subsequent pyrophosphate sensing in physiological media using a benzothiazole modified conjugated ligand and their application in paper strip and live cell imaging is demonstrated.

1,8-Naphthyridine-based molecular clips for off–on fluorescence sensing of Zn2+ in living cells

New 1,8-naphthyridine-based clip-like receptor as “off–on” fluorescent probe was designed and synthesised for selectively sensing Zn²⁺ in living cells.

A sole multi-analyte receptor responds with three distinct fluorescence signals: traffic signal like sensing of Al3+, Zn2+and F−

A dialdehyde-based ligand rendered discriminatory sensing of Al³⁺, Zn²⁺and F⁻ions. The non-toxic receptor could also facilitate target metal sensing in live HeLa cells through imaging studies.

A new ICT and CHEF based visible light excitable fluorescent probe easily detects in vivo Zn2+

A new chelator and ICT donor based visible light excitable Zn²⁺ sensor was designed and developed by integrating quinoline and 2-hydroxy-3-(hydroxymethyl)-5-methylbenzaldehyde.

An aggregation-induced emission (AIE) active probe renders Al(iii) sensing and tracking of subsequent interaction with DNA

A rationally designed aggregation-induced emission active ligand enables selective Al(iii) sensing and subsequent probing of the ensemble interaction with DNA.