Fluorescent carbazolyldithiane as a highly selective chemodosimeter via protection/deprotection functional groups: a ratiometric fluorescent probe for Cd(II)

A carbazole-based bis-dithiane (1) was rationally constructed in a straightforward manner for the selective and ratiometric fluorescent detection of Cd²⁺ with the concept of aldehyde group protection/deprotection. The probe showed a ratiometric fluorescent response to Cd²⁺ with a large emission wavelength shift (>50 nm) and displayed high selectivity for Cd²⁺ over other metal ions due to distinct deprotection conditions. In addition, a Cd²⁺-promoted dethioacetalization mechanism was proposed.     

A ratiometric fluorescent probe for iron(III) and its application for detection of iron(III) in human blood serum

A simple and versatile ratiometric fluorescent Fe³⁺ detecting system, probe 1, was rationally developed based on the Fe³⁺-mediated deprotection of acetal reaction. Notably, this reaction was firstly employed to design fluorescent Fe³⁺ probe. Upon treatment with Fe³⁺, probe 1 showed ratiometric response, with the fluorescence spectra displaying significant red shift (up to 132 nm) and the emission ratio value (I₅₂₂/I₃₉₀) exhibiting approximately 2362-fold enhancement. In addition, the probe is highly sensitive (with the detection limit of 0.12 μM) and highly selective to Fe³⁺ over other biologically relevant metal ions. The sensing reaction product of the probe with Fe³⁺ was confirmed by NMR spectra and mass spectrometry. TD-DFT calculation has demonstrated that the ratiometric response of probe 1 to Fe³⁺ is due to the regulation of intramolecular charge transfer (ICT) efficiency. Moreover, the practical utility in fluorescence detection of Fe³⁺ in human blood serum was also conducted, and probe 1 represents the first ratiometric fluorescent probe that can be used to monitor Fe³⁺ level in human blood serum. Finally, probe 1 was further employed in living cell imaging with pancreatic cancer cells, in which it displayed low cytotoxicity, satisfactory cell permeability, and selective ratiometric response to Fe³⁺.     

Influence of Donor on the Sensing Performance of a Series of Through‐Bond Energy Transfer‐Based Two‐photon Fluorescent Cu2+ Probes

Optical properties of a series of molecular two‐photon fluorescent Cu²⁺ probes containing the same acceptor (rhodamine group) are analyzed using time‐dependent density functional theory in combination with analytical response theory. Special emphasis is placed on evolution of the probes' optical properties in the presence of Cu²⁺. In this study, the compound with naphthalene as the donor is shown to be excellent ratiometric fluorescent chemosensor, whereas the compound with quinoline derivative as the donor shows off/on‐typed colorimetric fluorescent response. For the compound with naphthalimide derivative as the donor, changing the connection between the donor and acceptor can efficiently prevent the fluorescent quenching of the probe both in the absence and presence of Cu²⁺. The donor moiety and the connection between donor and acceptor are thus found to play dominant roles on sensing performance of these probes. Moreover, distributions of molecular orbitals involved in the excitation and emission of the probes are analyzed to explore responsive mechanism of the probes. The through‐bond energy transfer process is theoretically demonstrated. Our results are used to elucidate the available experimental measurements. This work is helpful to understand the relationships of structure with optical properties for the studied probes.     

Phenanthroline-fluorescein molecular hybrid as a ratiometric and selective fluorescent chemosensor for Cu2+ via FRET strategy: synthesis,computational studies and in vitro applications

A FRET-based chemosensor L containing donor phenanthroline and acceptor fluorescein moiety was designed, synthesised and characterised for the ratiometric fluorescent detection of Cu²⁺ in organo-aqueous solution. Probe L showed high selectivity and excellent sensitivity towards Cu²⁺ ions by exhibiting both colorimetric and fluorometric changes due to opening of the spirolactum ring of fluorescein upon complexation with Cu²⁺. In presence of Cu²⁺ ions, probe L formed L-Cu²⁺ complex in 1:1 stoichiometric fashion which is established on the basis of Job’s plot and mass spectroscopy. We also performed DFT computational studies to know the binding nature and coordination feature of the complex. Furthermore, fluorescence imaging studies revealed that probe L was cell permeable and could be used to detect intracellular Cu²⁺ in living cells.     

FRET‐based Fluorescent and Colorimetric Probe for Selective Detection of Hg(II) and Cu(II) with Dual‐mode

A dual‐function fluorescence resonance energy transfer (FRET)‐based fluorescent and colorimetric probe was rationally fabricated from an energy donor coumarin moiety and an energy acceptor rhodamine moiety linked by a thiohydrazide arm for selective detection of Hg²⁺ and Cu²⁺. Two distinct mechanisms were used for the selective detection. Results revealed that probe 1 showed high fluorescent selectivity towards Hg²⁺ and evident colorimetric selectivity for Cu²⁺, which was suitable for ‘naked‐eye’ detection.     

Integration of Metal-Organic Frameworks with Bi-Nanoprobes as Dual-Emissive Ratiometric Sensors for Fast and Highly Sensitive Determination of Food Hazards

Functional nanoprobes which detect specific food hazards quickly and simply are still in high demand in the field of food-safety inspection research. In the present work, a dual-emission metal-organic framework-based ratiometric fluorescence probe was integrated to detect Cu²⁺ and Pb²⁺ with rapidness and ease. Specifically, quantum dots (QDs) and carbon quantum dots (CQDs) were successfully embedded into zeolitic imidazolate framework-67 (ZIF-67) to function as a novel ratiometric fluorescent sensing composite. The ratiometric fluorescence signal of CQDs/QDs@ZIF-67 was significantly aligned with the concentration of metal ions to give an extremely low detection limit of 0.3324 nM. The highly sensitive and selective CQDs/QDs@ZIF-67 composite showed potential for the rapid and cost-effective detection of two metal ions.     

A Logic Fluorescent Chemosensor Based on Eu3+ Functionalized Cd-MOFs for Sensing Fe3+ and Cu2+ Synchronously

One of the most critical and yet unsolved issues is the effective monitoring of multiple heavy metal ions in complex systems through their specific function in fluorescence detection. In this work, luminescence-active cadmium base metal-organic frameworks (Cd-MOFs) based on the planar and rigid π-conjugated structure ligand benzo-(1,2;3,4;5,6)-tris (thiophene-2’-carboxylic acid) (H₃BTTC) was chosen. A series of sensing experiments demonstrated that the Cd-MOFs exhibits selective and sensitive response for Fe³⁺ and Eu³⁺ through fluorescence “turn off” and “antenna effect” respectively. In addition, the encapsulation of Eu³⁺ inside the Cd-MOFs (Eu³⁺@Cd-MOFs) led to an excellent probe with dual emission. To this end, a programmable fluorescence platform was developed to detect Fe³⁺ and Cu²⁺, in which the emission peaks of both the ligand and Eu³⁺ are completely quenched by Fe³⁺. The ratiometric detection of Cu²⁺ leads to a decrease in Eu³⁺ emission, while the ligand emission remains stable. To demonstrate the strategy, the fluorescence (Output) of Cd-MOFs, Eu³⁺@Cd-MOFs, and the analytes (Eu³⁺, Fe³⁺, and Cu²⁺, input) achieved elementary Boolean logic operations (OR, NOR, AND) and they constitute a logic fluorescent chemosensor to analyze Fe³⁺ and Cu²⁺ synchronously.     

A Novel Naked-Eye and Dual-Channel Responsive Fluorescent Probe for Cu2+ Based on 3,4-Disubstituted-1,8-naphthalimide

A new 3,4-disubstituted-1,8-naphthalimide derivative H1 was designed and synthesized as a selective fluorescent probe for Cu²⁺ over miscellaneous metal ions in aqueous media. Upon mixing with Cu²⁺ in CH₃OH:H₂O (1:1, volume ratio), the increase of fluorescence intensity and a bathochromic shift of absorbance of H1 could be observed with a notable color response (changing from yellow to pink). Furthermore, Cu²⁺ coordinates to the probe H1 and a 1:1 metal-ligand complex was formed.     

Phenoxazine‐based Near‐infrared Fluorescent Probes for the Specific Detection of Copper (II) Ions in Living Cells

Abstract : It is well known that copper ions play a critical role in various physiological processes. However, a variety of human diseases are tightly correlated with copper overload. Although there are numerous fluorescent probes capable of detecting copper ions, most of them are “turn‐off” probes owing to copper (II) ions fluorescence quenching effect, resulting in poor sensitivity. Herein, a novel “turn‐on” near‐infrared (NIR) fluorescent probe PZ‐N based on phenoxazine was designed and synthesized for the selective detection of copper (II) ions (Cu²⁺). Upon the addition of Cu²⁺, the probe could quickly react with Cu²⁺ and emit strong fluorescence, along with colour change from colourless to obvious blue. Moreover, the probe PZ‐N showed good water solubility, high selectivity, and excellent sensitivity with low limit of detection (1.93 nM) towards copper (II) ions. More importantly, PZ‐N was capable of effectively detecting Cu²⁺ in living cells.     

A Naphthalimide-Based Fluorescent Probe for the Detection and Imaging of Mercury Ions in Living Cells

The selective and efficient monitoring of mercury (Hg²⁺) contamination found in the environment and ecosystem has been carried out. Thus, a new 1,8-naphthalimide-based fluorescent probe NADP for the detection of Hg²⁺ based on a fluorescence enhancement strategy has been designed and synthesized. The NADP probe can detect Hg²⁺ with high selectivity and sensitivity and a low detection limit of 13 nm . The detection mechanism was based on a Hg²⁺-triggered deprotection reaction, resulting in a dramatic change in fluorescence from colorless to green at physiological pH. Most importantly, biological investigation has shown that the NADP probe can be successfully applied to the monitoring of Hg²⁺ in living cells and zebrafish with low cytotoxicity.     

5-氨基-1,10-菲咯啉：可异构化杂环螯合荧光载体作为比例计量型锌离子荧光探针的一种原型

5-amino-l,10-phenanthroline （5-AP）, as a tautomeric heterocyclic aromatic chelating fluorophore （THACF）, can sense Zn^2＋ selectively by shifting emission from 495 to 564 nm upon Zn^2＋ addition in ethanol. The ratiometric fluorescent sensing behavior has been correlated to the tautomerization of 5-AP affected by solvents and metal chelation. The strategy using THACF as ratiometric fluorescent sensor for Zn^2＋ not only simplifies the synthetic procedure but also gives a promising alternative for Zn^2＋ ratiometric fluorescent sensor design.     

Cu nanoclusters-based ratiometric fluorescence probe for ratiometric and visualization detection of copper ions

Copper is a highly toxic environmental pollutant with bioaccumulative properties. Therefore, sensitive detection of Cu²⁺ is very important to prevent over-ingestion, and visual detection is preferred for practical applications. In this work, we developed a simple and environmental friendly approach to synthesize hyperbranched polyethyleneimine-protected copper nanoclusters (hPEI-Cu NCs) with great stability against extreme pH, high ionic strength, thiols etching and light illumination, which were then conjugated to the surface of silica coated CdSe quantum dots (QDs) to design a ratiometric fluorescence probe. In the presence of different amounts of Cu²⁺ ions, the fluorescence of Cu NCs can be drastically quenched, while the emission from QDs stayed constant to serve as a reference signal and the color of the probe changed from yellow-green to red, resulting in ratiometric and visualization detection of Cu²⁺ ion with high accuracy. The detection limit for Cu²⁺ was estimated to be 8.9 nM, much lower than the allowable level of Cu²⁺ in drinking water (∼20 μM) set by U.S. Environmental Protection Agency. Additionally, this probe can be also applied for the determination of Cu²⁺ ion in complex real water samples.     

An efficient sensor for relay recognition of Zn and Cu through fluorescence ‘off–on–off’ functionality

A new bis(8-carboxamidoquinoline) dangled binaphthol derivatized fluorescent sensor (L) was designed and synthesized. L behaves ratiometric response to Zn²⁺ with high selectivity accompanied by remarkable emission enhancement and red shift. The resultant L–Zn²⁺ complex can act as a Cu²⁺ sensing probe with fluorescence quenching behavior through direct Zn²⁺ ion replacement. Furthermore, the binding modes of Zn²⁺ and Cu²⁺ with L are elucidated by X-ray crystallographic analysis, respectively.     

Ratiometric fluorescent and colorimetric sensors for Cu based on 4,5-disubstituted-1,8-naphthalimide and sensing cyanide via Cu displacement approach

Two 4,5-disubstituted-1,8-naphthalimide derivatives 1 and 2 were synthesized as ratiometric fluorescent and colorimetric sensors for Cu²⁺, respectively. In 100% aqueous solutions of 1, the presence of Cu²⁺ induces a strong and increasing fluorescent emission centered at 478 nm at the expense of the fluorescent emission of 1 centered at 534 nm. Compound 2 senses Cu²⁺ by means of a colorimetric (primrose yellow to pink) method with a thorough quench in emission attributed to the deprotonation of the secondary amine conjugated to the naphthalimide fluorophore. 1-Cu²⁺ and 2-Cu²⁺ sense cyanide in ratiometric way via colorimetric and fluorescent changes.     

Ratiometric fluorescent Zn chemosensor constructed by appending a pair of carboxamidoquinoline on 1,2-diaminocyclohexane scaffold

By appending a pair of carboxamidoquinoline pendants onto 1,2-diaminocyclohexane scaffold via N-alkylation, multifunctionalized ACAQ was designed and synthesized as a water soluble fluorescent ratiometric chemosensor for Zn²⁺. In 50% aqueous methanol buffer pH 7.4 solution, upon excitation at 316 nm, ACAQ (5 μM) displayed a selective ratiometric fluorescence changes with a shift from 410 to 490 nm in response to the interaction with Zn²⁺. After binding with 1 equiv of Zn²⁺, ACAQ exhibited a 12-fold enhancement in I₄₉₀/I₄₁₀ characterized by a clear isoemissive point at 440 nm. The metal sensor binding mode was established by Job’s plot and the combined fluorescence and ¹H NMR spectroscopic method. The selectivity of the probe toward biological relevant cations and transition metal ions was proven to be good. In addition, the interference caused by Cu²⁺ and Cd²⁺ in the quantitation of Zn²⁺ can be completely eliminated by the use of diethyldithiocarbamate as the screening agent. Exploitation of ACAQ as the sensing probe, ratiometric determination of Zn²⁺ with the limit of detection (LOD) at 28.3 nm can be realized. In addition, the unique responsive properties of the probe toward Fe³⁺ and Zn²⁺ were used to construct a fluorescent switch. The membrane permeability of ACAQ to living cells and bio-imaging of Zn²⁺ were demonstrated.     

A Highly Copper‐Selective Ratiometric Fluorescent Sensor Based on BODIPY

A new ratiometric fluorescent sensor ( 1 ) for Cu²⁺ based on 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) with di(2‐picolyl)amine (DPA) as ion recognition subunit has been synthesized and investigated in this work. The binding abilities of 1 towards different metal ions such as alkali and alkaline earth metal ions (Na⁺, K⁺, Mg²⁺, Ca²⁺) and other metal ions ( Ba²⁺, Zn²⁺, Cd²⁺, Fe²⁺, Fe³⁺, Pb²⁺, Ni²⁺, Co²⁺, Hg²⁺, Ag⁺) have been examined by UV‐vis and fluorescence spectroscopies. 1 displays high selectivity for Cu²⁺ among all test metal ions and a ～10‐fold fluorescence enhancement in I₅₈₂/I₅₅₈ upon excitation at visible excitation wavelength. The binding mode of 1 and Cu²⁺ is a 1:1 stoichiometry determined via studies of Job plot, the nonlinear fitting of the fluorometric titration and ESI mass.     

A compact fluorescence/circular dichroism dual-modality probe for detection,differentiation, and detoxification of multiple heavy metal ions via bond-cleavage cascade reactions

Selective detection of multiple analytes in a compact design with dual-modality and theranostic features presents great challenges. Herein, we wish to report a coumarin-thiazolidine masked d-penicillamine based dual-modality fluorescent probe COU-DPA-1 for selective detection, differentiation, and detoxification of multiple heavy metal ions (Ag⁺, Hg²⁺, Cu²⁺). The probe shows divergent fluorescence (FL) /circular dichroism (CD) responses via divergent bond-cleavage cascade reactions (metal ion promoted C-S cleavage and hydrolysis at two distinctive cleavage sites): FL “turn-off” and CD “turn-on” for Ag⁺ (no hydrolysis), FL “turn-on” and CD “turn-off” for Hg²⁺ (imine hydrolysis), and FL “self-threshold ratiometric” and CD “turn-off” for excess Cu²⁺ (lactone and imine hydrolysis), providing the first example of a fluorescence/CD dual-modality probe for multiple species with complimentary responses. Moreover, the bond-cleavage cascade reactions also lead to the formation of d-penicillamine heavy metal ion complexes for potential detoxification treatments.     

Ratiometric Fluorescent Paper-Based Sensor Based on CdTe Quantum Dots and Graphite Carbon Nitride Hybrid for Visual and Rapid Determination of Cu2+ in Drinks

A simple and effective ratiometric fluorescence sensor of CdTe QDs/GCNNs for on-site and rapid analysis of Cu²⁺ has been established by mixing physically CdTe QDs and graphite carbon nitride (GCNNs). Two emissions peaks of CdTe QDs at 572 nm and GCNNs at 436 nm are both excitated at 340 nm. Under a UV lamp, fluorescent of traffic yellow CdTe QDs is linearly quenched by Cu²⁺ (as the detection signal), while blue GCNNs remains unchanged (as the reference), resulting in a distinguishable color change gradually from pink yellow to blue. The limit of detection (LOD) of this new sensor for Cu²⁺ is as low as 0.47 ng mL⁻¹ with 1.4 % RSD. The established method has been successfully applied to detection of Cu²⁺ in various drinks with satisfactory results. Moreover, a paper-based sensor, which has been prepared by soaking cellulose acetate membrane in CdTe QDs/GCNNs sensor solution, has a wide semiquantitative detection range for Cu²⁺ (0.01 ~ 5.0 μg mL⁻¹). It has realized successfully on-site and rapid determination of Cu²⁺ in red wine without any pretreatment procedure and is of great promotion and application value in determination of Cu²⁺ in liquid samples.     

Benzimidazole-based ratiometric fluorescent receptor exhibiting molecular logic gate for Cu and Fe

We synthesized a novel fluorescent receptor based upon a benzimidazole moiety in a dipodal framework. The receptor exhibited a dual fluorescence emission which is quenched upon addition of Cu²⁺ or Fe³⁺. Interestingly, the receptor offers a ratiometric property and an ‘OR’ logic gate property to Cu²⁺ and Fe³⁺.     

Ratiometric Fluorescent Chemosensor for Selective Detection Cr3+ based on Carbazole and Benzimidazole

A novel Cr³⁺‐selective ratiometric fluorescent chemosensor 1‐substitued‐2‐carbazoleylbenzoimidazole ( L ) based on benzimidazole and carbazole was synthesized and characterized by nuclear magnetic resonance (¹H/¹³C NMR), Fourier transform infrared spectrometry (FTIR), and mass spectroscopy. L could selectively detect Cr³⁺ over other metal ions by UV–vis absorption and fluorescence emission spectroscopic methods in CH₃CN. L showed ratiometric fluorescent recognition of Cr³⁺; the fluorescent responses could be observed by naked eye under a UV lamp. The binding stoichiometry ratio of the L –Cr³⁺ complex was found to be 1:1 according to Job’s plot and MALDI‐TOF MS analysis. The results of DFT calculation supported this conclusion.