A DCM-based NIR sensor for selective and sensitive detection of Zn2+ in living cells

Fluorescent Probes as a Tool in Diagnostic and Drug Delivery Systems

Over the last few years, the development of fluorescent probes has received considerable attention. Fluorescence signaling allows noninvasive and harmless real-time imaging with great spectral resolution in living objects, which is extremely useful for modern biomedical applications. This review presents the basic photophysical principles and strategies for the rational design of fluorescent probes as visualization agents in medical diagnosis and drug delivery systems. Common photophysical phenomena, such as Intramolecular Charge Transfer (ICT), Twisted Intramolecular Charge Transfer (TICT), Photoinduced Electron Transfer (PET), Excited-State Intramolecular Proton Transfer (ESIPT), Fluorescent Resonance Energy Transfer (FRET), and Aggregation-Induced Emission (AIE), are described as platforms for fluorescence sensing and imaging in vivo and in vitro. The presented examples are focused on the visualization of pH, biologically important cations and anions, reactive oxygen species (ROS), viscosity, biomolecules, and enzymes that find application for diagnostic purposes. The general strategies regarding fluorescence probes as molecular logic devices and fluorescence–drug conjugates for theranostic and drug delivery systems are discussed. This work could be of help for researchers working in the field of fluorescence sensing compounds, molecular logic gates, and drug delivery.

Schiff Bases: A Versatile Fluorescence Probe in Sensing Cations

Metal cations such as Zn²⁺, Al³⁺, Hg²⁺, Cd²⁺, Sn²⁺, Fe²⁺, Fe³⁺ and Cu²⁺ play important roles in biology, medicine, and the environment. However, when these are not maintained in proper concentration, they can be lethal to life. Therefore, selective sensing of metal cations is of great importance in understanding various metabolic processes, disease diagnosis, checking the purity of environmental samples, and detecting toxic analytes. Schiff base probes have been largely used in designing fluorescent sensors for sensing metal ions because of their easy processing, availability, fast response time, and low detection limit. Herein, an in-depth report on metal ions recognition by some Schiff base fluorescent sensors, their sensing mechanism, their practical applicability in cell imaging, building logic gates, and analysis of real-life samples has been presented. The metal ions having biological, industrial, and environmental significance are targeted. The compiled information is expected to prove beneficial in designing and synthesis of the related Schiff base fluorescent sensors.

A near-infrared Fluorescent Probe Based on Dicyanisophorone for the Detection of Zinc Ions (Zn2+) in Water and Living Cells

As one of the important metal ions, zinc ions (Zn²⁺) are widely involved in various physiological and pathological processes, and play fundamental roles in neurotransmission, cell metabolism and apoptosis. However, the convenient monitor of Zn²⁺ in environmental and biological samples remains challenging. In this study, a small molecule dicyanoisophorone-based schiff base incorporating with o-phenylenediamine was synthesized. It can rapidly combine with Zn²⁺ to emit significant near-infrared fluorescence (maximum emission wavelength: 660 nm), so it can be used as a probe to quantitatively detect Zn²⁺ in the range of 0-10 μM, with a detection limit as low as 4.8 nM, showing the probe has high sensitivity for Zn²⁺. And the probe has a fast response time to Zn²⁺ (less than 30 s) and a large Stoke-shift (179 nm). In addition, the high recovery rates in practical water samples, and the clear fluorescent images in living A549 cells were obtained, which are of great significance for the detection of Zn²⁺ in the environment and biosystem. Due to its simple operation, good selectivity and anti-interference ability, short detection time and high sensitivity, this probe has great application potential as a fast detection tool for Zn²⁺ in environmental water and biological samples.

A comparison of the mineral element content of 70 different varieties of pear fruit (Pyrus ussuriensis) in China

Background

Pyrus ussuriensis (Maxim.) is a unique pear tree that grows in northern China. The tree has strong cold resistance and can withstand low temperatures from -30 °C to -35 °C. Due to its unique growth environment, its fruit is rich in minerals and has much higher levels of minerals such as K, Ca and Mg than the fruit of Pyrus pyrifolia (Nakai.) and Pyrus bretschneideri (Rehd.) on the market, and many say the ripe fruit tastes better than other varieties. A comprehensive analysis of the characteristics of mineral elements in the fruits of different varieties of P. ussuriensis will provide a valuable scientific basis for the selection, breeding and production of consumer varieties of P. ussuriensis, and provide a more complete understanding of nutritional differences between fruit varieties.

Methods

In this study, 70 varieties of wild, domesticated and cultivated species of P. ussuriensis from different geographical locations were compared. Targeting four main mineral elements and eight trace mineral elements contained in the fruit, the differences in mineral content in the peel and pulp of different varieties of P. ussuriensis were analyzed, compared and classified using modern microwave digestion ICP-MS.

Results

The mineral elements in the fruit of P. ussuriensis generally followed the following content pattern: K > P > Ca > Mg > Na > Al > Fe > Zn > Cu > Cr > Pb > Cd. The mineral element compositions in the peel and pulp of different fruits were also significantly different. The four main mineral elements in the peel were K > Ca > P > Mg, and K > P > Mg > Ca in the pulp. The mineral element content of wild fruit varieties was higher than that of cultivated and domesticated varieties. Correlation analysis results showed that there was a significant positive correlation between K, P and Cu in both the peel and pulp of P. ussuriensis fruit (P < 0. 01). Cluster analysis results showed that the 70 varieties of P. ussuriensis could be divided into three slightly different categories according to the content of the peel or pulp. According to the contents of the fruit peel, these varieties were divided into: (1) varieties with high Na, Mg, P, K, Fe and Zn content, (2) varieties with high Ca content and (3) varieties with medium levels of mineral elements. According to the fruit pulp content, these varieties were divided into: (1) varieties with high Mg, P and K content, (2) varieties with low mineral element content, and (3) varieties with high Na and Ca content. The comprehensive analysis of relevant mineral element content factors showed that 'SSHMSL,' 'QYL,' 'SWSL' and 'ZLTSL-3' were the best varieties, and could be used as the focus varieties of future breeding programs for large-scale pear production.

A "Turn-On" fluorescent probe for detection and removal of Zn2+ in aqueous and its application in living cells

Using 3-hydroxy-2-naphthoic acid hydrazine and 4-(diethylamino) salicylaldehyde. as raw materials, compound L with an acylhydrazones structure was synthesized. The structure of compound L was characterized by nuclear magnetic resonance spectroscopy, X-ray single crystal diffraction, Fourier transform infrared spectroscopy, and mass spectrometry. The results show that Compound L can quickly and selectively recognize zinc ions in the H₂O/DMSO (V:V = 3:7) solvent system. After that, the spectral performance of probe L was studied by fluorescence spectroscopy and UV-vis spectroscopy. The results show that the combination with Zn²⁺ can significantly enhance the fluorescence intensity of probe L while being almost unaffected by other coexisting ions. After that, Job's curve method, nuclear magnetic titration analysis, and mass spectrometry were used to study the binding mechanism of probe L and Zn²⁺. The results showed that probe L coordinated with Zn²⁺ is 1:1. The linear equations of different concentrations of Zn²⁺ and fluorescence intensity were obtained by fitting, and the detection limit of probe L for Zn²⁺ was determined to be 6.75 × 10^-9 mol/L. The experimental study of standard addition and recovery showed that probe L could be used for the quantitative detection of Zn²⁺ in natural water samples. After that, we prepared L-doped sodium alginate hydrogel (SAL). The research results show that SAL has obvious adsorption capacity for Zn²⁺ in solution, and the color change before and after adsorption can be easily distinguished by the naked eye under ultraviolet light. SEM-EDS study showed that the microscopic morphology and composition of SAL changed significantly before and after adsorption. This fluorescent probe can be used for detection and removal of Zn²⁺ in aqueous solution. Also, probe L is effective for sensing for zinc (II) in living tumor cells. Overall, this work allows us to obtain a great potential to be applied to detect and remove Zn²⁺.

Turn on Fluorescence Sensing of Zn2+ Based on Fused Isoindole-Imidazole Scaffold

Optical chemosensors caused a revolution in the field of sensing due to their high specificity, sensitivity, and fast detection features. Imidazole derivatives have offered promising features in the literature as they bear suitable donor/acceptor groups for the selective analytes in the skeleton. In this work, an isoindole-imidazole containing a Schiff base chemosensor (1-{3-[(2-Diethylamino-ethylimino)-methyl]-2-hydroxy-5-methyl-phenyl}-2H-imidazo[5,1-a]isoindole-3,5-dione) was designed and synthesized. The complete sensing phenomena have been investigated by means of UV-Vis, fluorescence, lifetime measurement, FT-IR, NMR and ESI-MS spectroscopic techniques. The optical properties of the synthesized ligand were investigated in 3:7 HEPES buffer:DMSO medium and found to be highly selective and sensitive toward Zn²⁺ ion through a fluorescence turn-on response with detection limit of 0.073 μm. Furthermore, this response is effective in gel form also. The competition studies reveal that the response of the probe for Zn²⁺ ion is unaffected by other relevant metal ions. The stoichiometric binding study was performed utilizing Job’s method which indicated a 1:1 sensor–Zn²⁺ ensemble. Computational calculations were performed to pinpoint the mechanism of sensing.

A bifunctional peptide-based fluorescent probe for ratiometric and "turn-on" detection of Zn(II) ions and its application in living cells

In this work, a bifunctional peptide-based fluorescent probe L containing a tetrapeptide scaffold (Pro-Gly-His-Trp-NH₂) and a dansyl group was synthesized using solid phase peptide synthesis (SPPS) technology. As designed, L, based on a FRET mechanism, exhibited high selectivity, excellent ratiometric signals, and fast response to Zn²⁺ in aqueous solutions at an excitation wavelength of 280 nm. In addition, when excited at 320 nm, L exhibited a fluorescent "turn-on" response towards Zn²⁺ based on PET mechanism. More importantly, the stoichiometry of L and Zn²⁺ was determined to be 2:1 by fluorescent titration, Job's plot method, and ESI-MS spectrometry. The association constant for Zn²⁺ ions was determined to be 6.26 × 10⁸ M^-2, while the limit of detection (LOD) of L was estimated as 5.43 nM, which is a much lower value than WHO and EPA guidelines for drinking water. Moreover, L was successfully applied to detect both Zn²⁺ and Cu²⁺ in living cells due to good biocompatibility and excellent low toxicity.

Estrogen Receptor β-Targeted Near-Infrared Inherently Fluorescent Probe: A Potent Tool for Estrogen Receptor β Research

Estrogen receptor β (ERβ) is associated with many diseases, and ERβ probes can help to reveal the complex role of ERβ and promote the development of ERβ-targeted therapy. Herein, we designed and synthesized the first ERβ-targeted near-infrared (NIR) inherently fluorescent probe P5, which showed the advantages of high ERβ selectivity, good optical properties, and excellent ERβ imaging capability in living cells. The probe was successfully utilized to explore ERβ motion characteristic, and for the first time, the diffusion coefficient of ERβ was obtained. Moreover, P5 was also successfully applied to the in vivo imaging of ERβ in the prostate cancer mice model. Therefore, this ERβ-targeted NIR probe might be employed as a potential tool for the research of ERβ and related diseases.

A novel fluorescent probe based on a triphenylamine derivative for the detection of HSO3- with high sensitivity and selectivity

A novel highly active fluorescence chemical sensor (TBQN) for HSO₃^- was synthesized by the Knoevenagel reaction based on triphenylamine-benzothiazole as a new fluorophore. The probe possessed good selectivity toward HSO₃^- and anti-interference ability with common ions. The fluorescence and UV-vis spectra of the TBQN probe were significantly changed after the addition of HSO₃^-. At the same time, the probe solution released obvious green fluorescence. Moreover, the limit of detection for HSO₃^- was calculated to be 3.19 × 10^-8 M. The TBQN probe displayed a rapid response to HSO₃^- and it took about 3 min to complete the recognition. The detection mechanism is the nucleophilic addition reaction between HSO₃^- and -C[double bond, length as m-dash]C- in the probe molecule. The π-conjugation and ICT (intramolecular charge transfer) transition in the TBQN molecule were destroyed by this addition, which resulted in the change of the fluorescence before and after the addition of HSO₃^-. Then, the mechanism was verified by theoretical calculations, ¹H NMR measurements and mass spectroscopy. In addition, the probe showed low cytotoxicity and could be used for biological imaging in RAW264.7 cells.

Development of a novel NIR viscosity fluorescent probe for visualizing the kidneys in diabetic mice

Viscosity is an important parameter for evaluating cell health, and abnormal viscosity can cause a variety of intracellular organelle function disorders. The mitochondria are a key organelle in cells, and the viscosity of the mitochondria determines the state of the cell. In this work, we report a novel near-infrared fluorescent probe, referred to as NI-VD, that has a large Stokes-shift and a satisfactory response multiple. NI-VD can sensitively detect changes in cell viscosity in cells and tissues, and it can effectively avoid interference from the overlap of excitation and emission light. The fluorescence spectrum shows that NI-VD has maximum emission peaks at 730 nm, and the fluorescence intensity is amplified with an increase in the solution viscosity. The response from pure PBS solution to glycerol changes by 13-fold. After confirmation in a variety of cell and biological models, NI-VD can detect the changes in viscosity in mitochondria. Most importantly, this study is the first to visualize the differences between the kidneys of diabetic mice and normal mice. This approach is a new solution for the diagnosis and treatment of diabetic nephropathy.