Highly selective fluorescent probe for sequential recognition of copper(II) and iodide ions

Dual-channel fluorescence dye: Fluorescent color-dependent visual detection of microplastics and selective polyurethane

In this study, we developed a dual-channel fluorescent dye ((E)-N'-(4-(diphenylamino)benzylidene)pyrazine-2-carbohydrazide) DPC for visual detection of 8 types of microplastics (MPs; HDPE, MDPE, LDPE, PET, PU, PVC, PS, and PP) and selective PU. The intramolecular charge transfer (ICT) and aggregation-induced emission (AIE) properties of DPC were demonstrated by the spectroscopic analysis, DFT calculations, and Tyndall effect. MPs and nonplastics (cellulose, chitin, sand, shell, and wood) were stained with DPC in water and their respective fluorescence signals in the blue and green channels were analyzed. The staining procedure using DPC was optimized with the concentration of DPC and staining time as parameters. DPC was able to effectively stain 8 types of MPs and only PU in blue and green fluorescence signals, respectively. Furthermore, false positive detections of DPC were minimized through additional ethanol treatment after staining. Moreover, the effects of temperature, pH, and salinity on the staining ability of DPC were investigated. Surprisingly, DPC was able to selectively detect PU through the green fluorescence signal even in a single environment where various MPs existed. Most importantly, DPC is the first fluorescent dye capable of selectively monitoring PU in the green channel as well as staining 8 types of MPs in the blue channel. DPC showed promising potential to be used for MP monitoring on real environmental samples.

A Benzothiazole-Based Fluorescence Turn-on Sensor for Copper(II)

A new benzothiazole-based chemosensor BTN (1-((Z)-(((E)-3-methylbenzo[d]thiazol-2(3H)-ylidene)hydrazono)methyl)naphthalen-2-ol) was synthesized for the detection of Cu²⁺. BTN could detect Cu²⁺ with "off-on" fluorescent response from colorless to yellow irrespective of presence of other cations. Limit of detection for Cu²⁺ was determined to be 3.3 μM. Binding ratio of BTN and Cu²⁺ turned out to be a 1:1 with the analysis of Job plot and ESI-MS. Sensing feature of Cu²⁺ by BTN was explained with theoretical calculations, which might be owing to internal charge transfer and chelation-enhanced fluorescence processes.

Simple and sensitive colorimetric sensors for the selective detection of Cu(ii)

A simple, sensitive colorimetric probe for detecting Cu(ii) ions with fast response has been established with a detection limit of 2.82 μM. UV-Vis spectroscopy along with metal ion response, selectivity, stoichiometry, competition was investigated. In the presence of copper(ii), the UV-Vis spectrum data showed significant changes and the colorimetric detection showed a color change from colorless to yellow. After the selective binding of receptor L with Cu(ii), the UV-visible absorption at 355 nm decreased dramatically, a new absorbance band appeared at 398 nm and its intensity enhanced with the increase in the amount of Cu(ii). Moreover, it exhibited highly selective and sensitive recognition towards Cu(ii) ions in the presence of other cations over the pH range of 7-11. The complex structure was verified by FT-IR spectroscopy, elemental analysis and quantum mechanical calculations using B3LYP/6-31G(d) to illustrate the complex formation between L and Cu(ii). According to the Job plot and the quantum mechanical calculations, the stoichiometric ratio for the complex formation was proposed to be 1 : 1.

A Selective Ratiometric Receptor 2-((E)-(3-(prop-1-en-2-yl)phenylimino)methyl)-4-nitrophenol for the Detection of Cu2+ ions Supported By DFT Studies

A Schiff-base 2-((E)-(3-(prop-1-en-2-yl)phenylimino)methyl)-4-nitrophenol (Receptor 1) colorimetric probe was synthesized and its UV-visible and fluorescence spectral properties for the sensing of Cu^+ 2 ions in CH₃OH/H₂O (60:40,v/v) solvent system was explored. The Receptor 1 showed the discriminating spectral behavior with the addition of Cu²⁺ ions solution. The other metal ions showed no significant effect towards Receptor 1. Moreover, the addition of Cu²⁺ ions to the Receptor 1 demonstrated the shift in the peak towards longer wavelength of 405 nm due to the ligand to metal charge transfer (LMCT) effect. The red-shift and new peak at 405 nm are due to the deprotonation of the -OH group and formation of complex and O-Cu covalent bond, respectively. A slight increase in the Cu²⁺ ion concentration exhibited strong absorption and fluorescence properties, leading to the spontaneous change in color from pale yellow to orange. Additionally, Density Functional Theory (DFT) studies were performed to investigate the interaction of Cu²⁺ ions with Receptor 1. The decrease in the energies (3.59062 kcal/mol to 0.36028 kcal/mol) of Cu²⁺-Receptor-1 complex compared to Receptor 1 confirms the strong interaction with high stability. The association constant (Ka) of Cu²⁺-Receptor-1 complex was found as 175000 M^- 1. The limit of detection (LOD) was calculated and noted as 179 nM.

A new highly selective colorimetric Schiff base chemosensor for determining the copper content in artisanal cachaças

This work demonstrated the feasibility of applying the Schiff base 5-bromo-2-salicyl-beta-alanine as a colorimetric chemosensor for the spectrophotometric quantification of the copper content in artisanal cachaças. For this, the experimental conditions were optimized to obtain an efficient, sensitive, reversible, and highly selective chemosensor to Cu²⁺ ions. The complex stoichiometry was 1:1, with a formation constant of 5.82 × 10² L mol^-1 and molar absorptivity of 5.82 × 10³ mol L^-1 cm^-1. Then, a spectrophotometric analytical method was developed and validated according to the Brazilian legislation. The linearity of the analytical curve was demonstrated by ANOVA, at a confidence level of 95%. The limits of detection and quantification were 0.0659 and 0.200 mg L^-1, respectively. The coefficients of variation for both the intra- and inter-day precisions were lower than 3.83%, and the accuracy presented a mean recovery of 100.55 ± 2.87%. The absence of a matrix effect was confirmed by the standard addition method, and the copper content in three artisanal cachaças from different geographical origins was estimated as lower than 2.93 mg L^-1. This result was in accordance with the Brazilian legislation but reinforces the need to carry out stricter quality control to achieve exportation standards. Therefore, the proposed method can be considered a simple, selective, linear, precise, and accurate tool that involves only a simple complexation reaction through the addition of the chemosensor solution in a buffered medium. As a consequence, the simplicity, practicality, rapidity, and low cost of synthesis of the proposed Schiff base chemosensor are highlighted.

A novel dual functional pyrene-based turn-on fluorescent probe for hypochlorite and copper (II) ion detection and bioimaging applications

A novel dual-function fluorescent probe PPH was conveniently synthesized by linking pyrazinehydrazide unit and pyrenyl fluorophore. The present probe PPH could be used for simultaneous detection of ClO^- and Cu²⁺ through a fluorescence turn-on response. The probe PPH displayed excellent selectivity and sensitivity towards ClO^- and Cu²⁺ over other anions and metal ions. The detection limits of PPH for ClO^- and Cu²⁺ were calculated to be as low as 4.02 nM and 157 nM, respectively. The probe PPH had good pH stability and was highly responsive to ClO^- and Cu²⁺ in a wide pH range. Furthermore, this probe could be readily applied to visualize ClO^- and Cu²⁺ on the test paper. Additionally, this probe was successfully utilized to the fluorescence imaging of ClO^- and Cu²⁺ in HeLa cells.

Theoretical investigation on the ESIPT mechanism and fluorescent sensing mechanism of 2-(2'-hydroxyphenyl) thiazole-4-carboxaldeyde in methanol

2-(2'-Hydroxyphenyl) thiazole-4-carboxaldeyde (aldehyde 1) and hemiacetal 2 were selected to study the mechanism of excited-state intramolecular proton transfer and the detecting of Al³⁺ ion in methanol by using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. Our theoretical results are in good agreement with the experimental values. The intramolecular H-bond is enhanced in the first excited-state based on the analyses of structural parameters, frontier molecular orbitals and electronic spectra. The stronger intramolecular H-bond is more favorable for ESIPT process. In order to further demonstrate the proton transfer process, we constructed the potential energy curves of probe 1 and 2 in both ground- and excited-states, and concluded that proton transfer processes in probe 1 and 2 are apt to happen in the S₁ state. In addition, the Mayer bond order, energy gap and absorption and fluorescence spectra were applied to interpret the process of detection of Al³⁺ ion.

A Pentapeptide with Tyrosine Moiety as Fluorescent Chemosensor for Selective Nanomolar-Level Detection of Copper(II) Ions

Herein, we have investigated principally with the use of UV and fluorescence (steady-state and time-resolved) spectroscopy the interactions between selected pentapeptides with tyrosine residue (EYHHQ, EHYHQ, EHHQY, and KYHHE) and various metal ions (Cu²⁺, Mn²⁺, Co²⁺, Ni²⁺, Zn²⁺, Cr³⁺, Cd²⁺, Ag⁺, Pb²⁺, Sr²⁺, Ba²⁺, Ca²⁺, Mg²⁺, Al³⁺, Fe²⁺, and Ga³⁺) in order to establish the relationship between the position of a tyrosine residue in the peptide sequence and the metal ion-binding properties. Among the peptides studied, EHYHQ was evaluated as an efficient and selective ligand for developing a chemosensor for the detection of copper(II) ions. While significant fluorescence emission quenching was observed for that peptide in the presence of Cu²⁺ cations, other metal cations used at the same and at considerably higher concentrations caused a negligible change of the fluorescence emission spectrum, indicating a high selectivity of EHYHQ for Cu²⁺ ions. Under optimum conditions, fluorescence intensity was inversely proportional to the concentration of Cu²⁺ ions. The limit of detection of Cu²⁺ ions with the use of EHYHQ was determined at the level of 26.6 nM. The binding stoichiometry of the complexes of the studied peptides with Cu²⁺ ions was evaluated spectrophotometrically and fluorimetrically (as in the case of EHYHQ confirmed by mass spectrometry) and found to be 1:2 (Cu²⁺-peptide) for all the investigated systems. Furthermore, the stability constant (K) values of these complexes were determined. The reversibility of the proposed Cu²⁺ ions sensor was confirmed, the pH range where the sensor acts was determined, while its analytical performance was compared with some other reported recently fluorescent sensors. The mechanism of the interactions between EHYHQ and Cu²⁺ was proposed on the basis of NMR spectroscopy investigations.

Two donor–acceptor (D–A) type Zn(ii) complexes as fluorescent probes for highly selective detection of iodide

Two noval donor-acceptor (D–A) type Zn(ii) complexes ([Zn₂(L¹)₂(MeCN)(MeOH)]·(MeCN) (1) and [ZnL²(H₂O)] (2)) were obtained and selectively detected iodide as fluorescent probes.

Multifunctional Magnetic-Fluorescent Nanoparticle: Fabrication, Bioimaging, and Potential Antibacterial Applications

Magnetic-fluorescent nanoparticles integrating imaging and therapeutic capabilities have unparalleled advantages in the biomedical applications. Apart from the dual ability of unique biomolecular fluorescent recognition and magnetic modes, the nanoparticle also endows combined effective therapies with high physiological stability, long-term imaging, rapid response time, and excellent circulation ability. Herein, we developed a carboxyl-functionalized magnetic nanoparticle that was further functionalized by polydopamine (PDA) and Schiff base ligand (3-aminopyridine-2-carboxaldehyde N(4)-methylthiosemicarbazone, HL) to form multilayered coating single nanoparticles (Fe₃O₄@PDA@HL). Our work showed that the aggregation-induced emission (AIE) effect could be produced by embedding In³⁺ into the Fe₃O₄@PDA@HL nanostructure, which offered a new opportunity for utilization as a fluorescent detection and therapeutic platform. Cellular fluorescent imaging experiments provided bacterial cell biodistribution, demonstrating their excellent luminescent performance, magnetic aggregation, and separation capability. We simultaneously confirmed that the synergistic antibacterial effect was closely related to both Fe₃O₄@PDA@HL and In³⁺, leading to the disruption of membrane integrity and the leakage of intracellular components, thus inducing bacterial death. This approach presented in our work could promote the development of future bioimaging and clinical therapy applications.

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.

A fast, highly selective and sensitive colorimetric and fluorescent sensor for Cu2+ and its application in real water and food samples

A new oligothiophene functionalized Schiff base sensor 3TDC has been successfully designed and synthesized. Sensor 3TDC exhibited "naked-eye" colorimetric and selective "on-off" fluorescence response toward Cu²⁺ with high selectivity and sensitivity within a wide pH range. The binding ratio of the sensor 3TDC and Cu²⁺ was determined to be 1:1 through fluorescence titration, Job's plot, ¹H NMR titration, FTIR and DFT studies. The detection limit is calculated to be as low as 2.81 × 10^-8 M, which is much lower than the allowable level of Cu²⁺ in drinking water set by U.S. Environmental Protection Agency (~20 μM) and the World Health Organization (~30 μM). The binding constant (K_a) of Cu²⁺ to sensor 3TDC was found to be 2.52 × 10⁴ M^-1. Sensor 3TDC for Cu²⁺ detection exhibited fast fluorescence response within 30 s and high anti-interference performance. Moreover, sensor 3TDC could be used as an effective fluorescent sensor for detecting Cu²⁺ ions in various real water and food samples with good accuracy and high precision.

Selectively detecting toluene and benzaldehyde by two stable lanthanide–organic frameworks as luminescent probes

Two stable lanthanide–organic frameworks as luminescent probes to sensitively detect for toluene and benzaldehyde through luminescent quenching.

A dual-response sensor based on NBD for the highly selective determination of sulfide in living cells and zebrafish

A dual chemosensor, 1-NO₂, showing fluorogenic and colorimetric responses was developed for the detection of sulfide in vitro and in vivo.

Novel Cu2+-specific “Turn-ON” fluorescent probe based on [5]helicene with very large Stokes shift and its potential application in living cells

The sensor provides Cu²⁺-sensitive with low detection limit and very large Stokes shift, and can induce the emission in the HepG2 cellular system.

A one-step synthesized acridine-based fluorescent chemosensor for selective detection of copper(ii) ions and living cell imaging

A highly selective and sensitive fluorescence quenching chemosensor (ACC) for Cu²⁺ detection in HEPES buffer and living cell imaging was developed.

Colorimetric detection of iron and fluorescence detection of zinc and cadmium by a chemosensor containing a bio-friendly octopamine

A chemosensor containing a bio-friendly octopamine was developed for the colorimetric detection of iron and fluorescence detection of zinc and cadmium.

A novel supramolecular organogel based on acylhydrazone functionalized pillar[5]arene acts as an I- responsive smart material

A novel organic gelator (PZ) has been synthesized by rationally connecting a pillar[5]arene moiety and a bis(hexadecyloxy)phenyl functionalized acylhydrazone moiety. PZ could self-assemble into a supramolecular polymer and form a stable organogel (OPZ) in cyclohexanol by multi-self-assembly driving forces such as C-Hπ, ππ, vdW and hydrogen bonding interactions. The organogel (OPZ) shows blue aggregation-induced emission (AIE). Interestingly, the organogel OPZ could sense iodide ions (I^-) in the gel-gel state with high selectivity and sensitivity. The detection limit of OPZ for I^- is 9.4 × 10^-8 M, indicating high sensitivity to I^-. Furthermore, a thin film based on OPZ was prepared, which could be used as a smart material for the detection of I^- as well as a fluorescent security display material.