A novel fluorescein-based fluorescent probe for detection Hg2+ and bioimaging applications

Colorimetric fluorescence of the 1,10-phenantholineyl-imidazole sensor probe for the selective detection of Zn2+ and Cd2+ ions

A colorimetric fluorescent probe, 4-(1H-imidazolo[4,5-f][1,10]phenanthroline-2-yl)-N, N-diphenylaniline (PIN), was designed, synthesized and characterized for the sensitive and selective detection of Zn2+ and Cd2+. The color of the solution changed from blue to yellow visible to the naked eye with the addition of Zn2+ and Cd2+. The probe PIN showed good anti-interference to Zn2+ and Cd2+ in the presence of a variety of metal ions, and the fluorescence intensity showed a good linear relationship with the concentrations of Zn2+ and Cd2+, with detection limits of 34.84 nM and 35.76 nM, respectively. The probe PIN complexed 2:1 with Zn2+ and Cd2+, and the complexation constants were 1.03 × 104 M-1 (PIN - Zn2+, R2 = 0.9971) and 1.50 × 104 M-1 (PIN - Cd2+, R2 = 0.9981), respectively. In addition, the PIN could be recovered by EDTA and could be effectively monitored for Zn2+ and Cd2+ at pH 4-11, with good results in actual water samples. The HepG-2 cells maintained over 95 % of viability after 24 h exposure to PIN, which identified the extremely low toxic of PIN and could be used for in vivo cell imaging.

Bioinspired peptide sensors with tailorable structure for specific and in-situ tracking of Hg2+ biodistribution in living cells upon acute exposure

Metal-biomolecule interactions that are ubiquitous in nature provide fundamental knowledge and rich structural motifs for the development of functional molecules and smart sensors. In this work, inspired by the active sites in metalloproteins, a biomimetic peptide sensor was designed for the selective recognition and activatable sensing of Hg2+ in living biosystems. Tetraphenylethylene (TPE) with typical aggregation-induced emission (AIE) behavior, was introduced as the activatable signal transducer to enable high signal-to-background signaling. The tailorable side chains and flexible peptide linkage were exploited to tune the coordination affinity, selectivity, and fluorescence response toward Hg2+. Benefiting from the rapid response (1 min), high specificity and nanomolar sensitivity, the peptide sensor allows investigating the mechanism of acute toxicity of Hg2+. Capable of penetrating plasma membrane, the peptide sensor revealed the dosage-dependent and dynamic subcellular biodistribution behavior of Hg2+. The finding that Hg2+ preferentially accumulates and rapidly enriches in nucleoli of cells upon short exposure, evidences the adverse effect toward ribosome biogenesis and the resultant genetic deficiencies. These results highlight the peptide sensors as promising tools for not only on-site detection, but also studying the cell biology and toxicology of this metal ion in living biosystems.

Terbium Vanadate Nanowires-Based Electrochemical Sensors for Mercury Ions

Terbium vanadate nanowires were synthesized via a facile chemical approach using sodium vanadate and terbium chloride. Morphology, structure, composition, and electrochemical characteristics of the terbium vanadate nanowires were investigated by different techniques. Terbium vanadate nanowires with single crystalline tetragonal TbVO4 phase possess smooth surface and flat tips. The length of the nanowires is longer than 5 μm, and diameter is 40-100 nm. Terbium vanadate nanowires modified electrode was used for trace-level mercury ions (Hg2+) detection. One well-defined stripping peak exists at - 0.34 V at the terbium vanadate nanowires modified electrode in 0.1 mM Hg2+ solution. Buffer solution pH value, deposition time, deposition potential, and standing time are pH = 1, 150 s, - 1.5 V, and 60 s, respectively. Detection limit for Hg2+ detection is 0.18 nM, and linear range is 0.01-100 μM. The proposed terbium vanadate nanowires modified electrode exhibits significant selectivity, stability, and reproducibility toward Hg2+. The usefulness of the developed sensor based on the terbium vanadate nanowires modified electrode was verified by Hg2+ detection in real samples.

Antimicrobial, antioxidant, cell imaging and sensing applications of fluorescein derivatives: A review

Fluorescein itself is a synthetic organic compound and a prominent member of the xanthene dye family. It exhibits strong fluorescence under ultraviolet (UV) or blue light excitation, making it widely used in various applications, including fluorescence microscopy, flow cytometry, immunoassays, and molecular biology techniques. One of the reasons fluorescein derivatives are highly valuable is their tunable fluorescence properties. Through chemical modifications of the fluorescein structure, different functional groups or substituents can be introduce, altering the compound's fluorescence characteristics such as emission wavelength, intensity, and photo stability. This flexibility allows for tailoring of fluorescent probes to specific experimental requirements, enhancing their utility in a range of scientific disciplines. Fluorescein derivatives also possess excellent antimicrobial and antioxidant activity. This review sheds light on the significant impact of fluorescein derivatives as biological active compounds, highlighting their potential in designing new therapeutic agents with antimicrobial properties. Additionally, their role as antioxidants is discussed. A major aspect covered in the review is the application of fluorescein derivatives as powerful cell imaging probes. Their unique fluorescent properties make them valuable tools for visualizing cellular structures and processes, opening up new possibilities for studying cellular dynamics and interactions.

Shedding Light on Heavy Metal Contamination: Fluorescein-Based Chemosensor for Selective Detection of Hg2+ in Water

This article discusses the design and analysis of a new chemical chemosensor for detecting mercury(II) ions. The chemosensor is a hydrazone made from 4-methylthiazole-5-carbaldehyde and fluorescein hydrazide. The structure of the chemosensor was confirmed using various methods, including nuclear magnetic resonance spectroscopy, infrared spectroscopy with Fourier transformation, mass spectroscopy, and quantum chemical calculations. The sensor's ability in the highly selective and sensitive discovery of Hg2+ ions in water was demonstrated. The detection limit for mercury(II) ions was determined to be 0.23 µM. The new chemosensor was also used to detect Hg2+ ions in real samples and living cells using fluorescence spectroscopy. Chemosensor 1 and its complex with Hg2+ demonstrate a significant tendency to enter and accumulate in cells even at very low concentrations.

Benzoate-based thermally activated delayed fluorescence materials

Compounds PTZ-MBZ (methyl 3-(10H-phenothiazin-10-yl)benzoate) and DMAC-MBZ (methyl 3-(9,9-dimethylacridin-10(9H)-yl)benzoate) were conveniently synthesized, and they exhibited TADF properties with lifetimes of 0.80 and 2.17 μs, respectively. The spatially separated highest occupied molecular orbital and lowest unoccupied molecular orbital resulted in a very small singlet-triplet energy gap of 0.0152 eV and 0.0640 eV, respectively. Thermally activated delayed fluorescence materials with short lifetime could be used as promising luminescent materials for organic light-emitting diodes.

A Recent Update on Rhodamine Dye Based Sensor Molecules: A Review

Herein we have discussed such important modified rhodamine compounds which have been used as chemosensors for the last 7-8 years. This review covered some chemosensors for the detection of metal ions like Al(III), Cu(II), Hg(II), Co(II), Fe(III), Au(III), Cr(III), and some anion like CN-. The selectivity, sensitivity, photophysical properties (i.e., UV-Vis spectral studies, fluorescence studies giving special emphasis to absorption wavelength in UV-Vis spectra and excitation and emission wavelength in fluorescence spectra), binding affinity, the limit of detection, and the application of those chemosensors are described clearly. Here we have also discussed some functionalized rhodamine-based chemosensors that emit in the near-infrared region (NIR) and can target lysosomes and detect lysosomal pH. Their versatile applicability in the medicinal ground is also delineated. We have focused on the photophysical properties of spirolactam rhodamine photoswitches and applications in single-molecule localization microscopy and volumetric 3D light photoactivable dye displays. The real-time detection of radical intermediates has also been exemplified.

An “AIE + ESIPT” mechanism-based benzothiazole-derived fluorescent probe for the detection of Hg2+ and its applications

A simple “AIE + ESIPT” mechanism-based fluorescent probe for Hg2+ detection has been developed. The probe is applicable to detect Hg2+ in living cells, natural water, and seafood samples.

Fabrication of Orange Fluorescent Boron-Doped Graphene Quantum Dots for Al3+ Ion Detection

Aluminum is a kind of metal that we often encounter. It can also be absorbed by the human body invisibly and will affect our bodies to a certain extent, e.g., by causing symptoms associated with Alzheimer’s disease. Therefore, the detection of aluminum is particularly important. The methods to detect metal ions include precipitation methods and electrochemical methods, which are cumbersome and costly. Fluorescence detection is a fast and sensitive method with a low cost and non-toxicity. Traditional fluorescent nanomaterials have a high cost, high toxicity, and cause harm to the human body. Graphene quantum dots are a new type of fluorescent nanomaterials with a low cost and non-toxicity that can compensate for the defects of traditional fluorescent nanomaterials. In this paper, c-GQDs and o-GQDs with good performance were prepared by a bottom-up hydrothermal method using o-phenylenediamine as a precursor and citric acid or boric acid as modulators. They have very good optical properties: o-GQDs exhibit orange fluorescence under UV irradiation, while c-GQDs exhibits cyan fluorescence. Then, different metal ions were used for ion detection, and it was found that Al³⁺ had a good quenching effect on the fluorescence of the o-GQDs. The reason for this phenomenon may be related to the strong binding of Al³⁺ ions to the N and O functional groups of the o-GQDs and the rapid chelation kinetics. During the chelation process, the separation of o-GQDs’ photoexcited electron hole pairs leads to their rapid electron transfer to Al³⁺, in turn leading to the occurrence of a fluorescence-quenching phenomenon. In addition, there was a good linear relationship between the concentration of the Al³⁺ ions and the fluorescence intensity, and the correlation coefficient of the linear regression equation was 0.9937. This illustrates the potential for the wide application of GQDs in sensing systems, while also demonstrating that Al³⁺ sensors can be used to detect Al³⁺ ions.

Organic Molecules Containing N, S and O Heteroatoms as Sensors for the Detection of Hg(II) Ion; Coordination and Efficiency toward Detection

Rapid detection of potentially toxic heavy metals like Hg(II) has attracted great attention in the last few decades due to the importance to maintain a safe and sustainable environment for human beings. Coordination chemistry and concepts therein, play an important role in the detection of Hg(II). Size, charge, and nature of the donor atom and the respective cation (metal ion), are crucial in selective interactions between the sensor and metal ions. The sensors designed for the purpose, coordinate to Hg(II) ion through various donor sites, coordination causes a change in the electron density in organic molecules and results in either visible color change or enhancing/quenching fluorescence intensity. Since Hg(II) is soft metal, with d10 electron system, so majority of the sensors have soft donor sites which prefer to coordinate with Hg(II). Oxygen is also present in some chelating ligands which is least preferred coordination site, due to its hard nature. There are several reports of replacing other ligating sites by sulfur for enhanced mercury sensing. In some cases, desulfurization is being detected as clear change in spectral behavior during the sensing process. Efforts are still in progress to design and introduce a sensor with utmost sensitivity and selectivity. In this review, we made an attempt to explain the coordination aspects of Hg(II) detectors, reasons for poor efficiency and possible suggestions to improve the selection criterion of various compounds. It will help researchers to know about important concepts in designing more sensitive and selective sensors for detection of Hg(II) in environmental and biological samples.

Investigation on fluorescein derivatives with thermally activated delayed fluorescence and their applications in imaging

Fluorescein derivatives with thermally activated delayed fluorescence (TADF) show much stronger competition ability and vaster prospects than traditional fluorescein dyes due to their prominent long lifetime. It will be of great significance to synthesize more fluorescein derivatives with TADF. In this work, compounds DCF-MPYA and FL with TADF properties were obtained by fine tuning the substituents' structure on the basis of fluorescein derivative DCF-MPYM. Their long-lived triplet excited states (21.78 μs, 32.0 μs) were proved by nanosecond time-resolved transient difference absorption spectra. The steady-state and time-resolved fluorescence spectra showed that DCF-MPYA and FL exhibited red fluorescence around 645 nm and 651 nm, respectively. The results of sensitivity to oxygen and heavy atoms further demonstrated that the time-resolved fluorescence spectra originate from the delayed fluorescence. The time correlated single-photon counting (TCSPC) data indicated that DCF-MPYA and FL showed long-lived lifetimes of 13.16 μs and 23.72 μs, respectively. The energy gap (ΔE_ST) between the singlet (S₁) and triplet (T₁) states of DCF-MPYA and FL was calculated to be 3.32 meV and 9.98 meV from the decay rate of DF as a function of temperature. The small energy gap is conducive to the occurrence of efficient TADF at room temperature. Meanwhile, Gaussian calculation was employed to observe the electron density of DCF-MPYA and FL in the ground and excited states. The calculation results indicate that the shapes and energy levels of the highest occupied molecular orbitals (HOMOs), lowest unoccupied molecular orbitals (LUMOs), and LUMOs+1 for the monoanion and dianion forms are similar and thus DCF-MPYA and FL exhibit almost the same luminescence properties. Finally, DCF-MPYA and FL with low toxicity were used in confocal and time-resolved fluorescence imaging. Our construction strategy will be beneficial for developing more fluorescein derivatives with TADF in the future.

Compounds DCF-MPYA and FL with microsecond scale lifetimes were obtained by fine tuning the substituents' structure on the basis of a fluorescein derivative with thermally activated delayed fluorescence (TADF) properties.