Highly chemoselective turn-on fluorescent probe for ferrous (Fe2+) ion detection in cosmetics and live cells

A Carbamoyl Oxime-Based Highly Specific Fluorescent Chemodosimeter for Monitoring Labile Fe2+ in Food and Living Organisms

Iron is an essential element in the composition of living organisms and plays a crucial role in a wide range of biological activities. The human body primarily obtains essential iron through the consumption of food. Therefore, it is vital for the health of human body to maintain iron homeostasis. The reducing character of the cellular microenvironment enables Fe2+ to occupy a dominant position within the cell. Hence, there is an urgent need for a simple and sensitive tool that can detect a large amount of Fe2+ in organisms. In this work, a highly specific fluorescent chemodosimeter NPCO ("NP" represents the naphthalimide fluorophore, and "CO" represents the carbamoyl oxime structure) for the detection of Fe2+ with excellent sensitivity (LOD = 82 nM) was constructed by incorporating a novel carbamoyl oxime structure as the recognition group. NPCO can be effectively employed for the detection of Fe2+ in food samples, living cells, and zebrafish. Furthermore, by using soybean sprouts as a model plant, the application of NPCO was expanded to detect Fe2+ in plants. Therefore, NPCO could be used as an excellent assay tool for detecting Fe2+ in organisms and is expected to be an important aid in exploring the mechanism of iron regulation.

Detecting labile heme and ferroptosis through 'turn-on' fluorescence and lipid droplet localization post Fe2+ sensing

Iron, a crucial biologically active ion essential for metabolic processes in living organisms, plays a vital role in biological functions, and imbalances in iron levels can lead to various diseases. In this study, we have developed two simple "turn-on" fluorescent probes, NOPy and NOCN, for the quick and selective detection of Fe2+ at nanomolar levels (LOD of 35 nM), accompanied by significant absorption and emission shifts, along with colorimetric demarcation. Both fluorophores exhibit an excellent "turn-on" emission response upon encountering Fe2+ in the cells. Flow cytometry and confocal fluorescence imaging studies demonstrate enhanced fluorescence signals in response to labile iron, efficiently detecting heme during erastin-induced ferroptosis. Interestingly, we also observed that the product formed after Fe2+ sensing localizes within the lipid droplets. These water-soluble and highly sensitive reactive probes, NOPy and NOCN, enable investigations of iron-dependent physiological and pathological conditions. The development of these probes represents an advancement in the field, offering a rapid and selective means for detecting Fe2+ with minimal cytotoxicity.

Small-Molecule Fluorescent Probes for Binding- and Activity-Based Sensing of Redox-Active Biological Metals

Although transition metals constitute less than 0.1% of the total mass within a human body, they have a substantial impact on fundamental biological processes across all kingdoms of life. Indeed, these nutrients play crucial roles in the physiological functions of enzymes, with the redox properties of many of these metals being essential to their activity. At the same time, imbalances in transition metal pools can be detrimental to health. Modern analytical techniques are helping to illuminate the workings of metal homeostasis at a molecular and atomic level, their spatial localization in real time, and the implications of metal dysregulation in disease pathogenesis. Fluorescence microscopy has proven to be one of the most promising non-invasive methods for studying metal pools in biological samples. The accuracy and sensitivity of bioimaging experiments are predominantly determined by the fluorescent metal-responsive sensor, highlighting the importance of rational probe design for such measurements. This review covers activity- and binding-based fluorescent metal sensors that have been applied to cellular studies. We focus on the essential redox-active metals: iron, copper, manganese, cobalt, chromium, and nickel. We aim to encourage further targeted efforts in developing innovative approaches to understanding the biological chemistry of redox-active metals.

Synthesis, Crystal Structure and Fluorimetric Study of 2-phenylphthalazin-1(2H)-one: a Highly Selective Florescent Chemosensor for Detection of Fe3+ and Fe2+ Metal Ions

A ligand, 2-phenylphthalazin-1(2H)-one (K), was synthesized by refluxing 2-formylbenzoic acid with phenyl hydrazine in presence of ethanol. FTIR, elemental analysis and single crystal XRD techniques were used to elucidate the structure. Fluorimetric turn-off response was recorded when solution of ligand (K) in DMF was treated with aqueous solution of Fe3+ and Fe2+ metal ions. No specific changes were observed on addition of other metal ions (Pb2+, Cd2+, Mn2+, Zn2+, Ba2+, Ni2+, Al3+, Ag1+, Co2+, Ca2+, Cu2+, Mg2+, Cr3+). Limit of Detection (LOD) was calculated for Fe2 and Fe3+as 2.4 µM and 2.5µM respectively, which is quite below to the recommended value 5.4 µM of the Environment Protection Agency of USA. Association constants for Fe3+ and Fe2+ metal ions were determined as 6 × 10-4 M-1 and 3.6 × 10-4 M-1 respectively. Benesi-Hildebrand plot confirmed 1:1 binding ratio between metal ions and ligand.

Development of a Golgi-targeted fluorescent chemosensor for detecting ferrous ions overload under Golgi stress

Ferrous ion (Fe²⁺) is a crucial metal ion in the body and participates in the diseases related to oxidation and reduction. Golgi apparatus is the main subcellular organelle of Fe²⁺ transport in cells, and the stability of its structure is related to the Fe²⁺ at an appropriate concentration. In this work, a turn-on type Golgi-targeting fluorescent chemosensor Gol-Cou-Fe²⁺ was rationally designed for sensitive and selective detection of Fe²⁺. Gol-Cou-Fe²⁺ showed excellent capacity of detecting exogenous and endogenous Fe²⁺ in HUVEC and HepG2 cells. It was used to capture the up-regulated Fe²⁺ level during the hypoxia. Moreover, the fluorescence of sensor was enhanced over time under Golgi stress combining with the reduce of Golgi matrix protein GM130. However, elimination of Fe²⁺ or addition of nitric oxide (NO) would restore the fluorescence intensity of Gol-Cou-Fe²⁺ and the expression of GM130 in HUVEC. Thus, development of chemosensor Gol-Cou-Fe²⁺ provides a new window for tracking Golgi Fe²⁺ and elucidating Golgi stress-related diseases.

Preparation of temperature-responsive nanomicelles with AIE property as fluorescence probe for detection of Fe3+ and Fe2

Temperature-responsive nanomicelles with aggregation induced emission (AIE) property were prepared by the host-guest complexation of ferrocene functionalized tetraphenyl (TPE-Fc) and β-cyclodextrin-poly (N-isopropylacrylamide) (β-CD-(PNIPAM)₇). The AIE chromophore TPE-Fc bound to the hydrophobic cavity of cyclodextrin serves as the core of micelles, and temperature sensitive PNIPAM serves as the shell to give the micelles good solubility. The size of the nanomicelles is about 100 nm. At the excitation wavelength of 340 nm, the strongest fluorescent emission peak was 421 nm. The introduction of cyclodextrin star polymer increased the fluorescence intensity of nanomicelles, thus improving the recognition of probe to Fe³⁺ and Fe²⁺. The fluorescent probe can quickly detect Fe³⁺ and Fe²⁺ in water within 5 min even in the presence of various interfering ions. The detection limits of Fe³⁺ and Fe²⁺ were 1.04 μM and 0.78 μM, respectively in the range of 10-90 μM. The formation of complex between the probe and Fe³⁺/Fe²⁺ was supported by Job's plot. The probe was successfully applied to the detection of Fe³⁺and Fe²⁺ in actual water sample with a good recovery. In addition, a possible sensing mechanism for the interaction of iron ions with amide bond groups of nanomicelles was proposed.

Synthesis and characterization of phenothiazine sensor for spectrophotometric and fluorescence detection of cyanide

A sensitive and selective phenothiazine-based sensor (PTZ) has been successfully synthesized. The sensor PTZ displayed specific identification of CN^- 'turn-off' fluorescence responses with a quick reaction and strong reversibility in an acetonitrile:water (90:10, V/V) solution. The sensor PTZ for detecting CN^- exhibits the marked advantages of quenching the fluorescence intensity, fast response time (60 s), and low value of the detection limit. The concentration that is authorized for drinking water by the WHO (1.9 μM) is far higher than the detection limit, which was found to be 9.11 × 10^-9 . The sensor displays distinct colorimetric and spectrofluorometric detection for CN^- anion due to the addition of CN^- anion to the electron-deficient vinyl group of PTZ, which reduces intramolecular charge transfer efficiencies. The 1:2 binding mechanism of PTZ with CN^- was validated by fluorescence titration, Job's plot, HRMS, ¹ H NMR, FTIR analysis, and density functional theory (DFT) investigations, among other methods. Additionally, the PTZ sensor was successfully used to precisely and accurately detect cyanide anions in actual water samples.

Recent development of small-molecule fluorescent probes based on phenothiazine and its derivates

Fluorescence probes, as analytical tools with the ability to perform rapid and sensitive detection of target analytes, have made outstanding contributions to environmental analysis and bioassays. Considering the expanding developments in these areas, fluorophores play a key role in the de-sign of fluorescence probes. Compared to classical fluorophores, phenothiazines with elec-tron-rich characteristics have been widely applied to construct electron donor-acceptor dyes, which exhibit outstanding performance in both fluorimetric and colorimetric analysis. In addition, these probes also exhibit the pronounced ability in both solution and solid-state, achieving portable detection for environmental analysis. In this review, we summarize recent advances in the performance of phenothiazine-based fluorescent probes for detecting various analytes, especially in cations, anions, ROS/RSS, enzyme and other small molecules. The general design rules, response mechanisms and practical applications of the probes are analyzed, followed by a discussion of exiting challenges and future research perspectives. It is hoped that this review will provide a few strategies for the development of phenothiazine-based fluorescent probes.

Luminescent Metal Complexes as Emerging Tools for Lipid Imaging

Fluorescence microscopy is a key tool in the biological sciences, which finds use as a routine laboratory technique (e.g., epifluorescence microscope) or more advanced confocal, two-photon, and super-resolution applications. Through continued developments in microscopy, and other analytical methods, the importance of lipids as constituents of subcellular organelles, signalling or regulating molecules continues to emerge. The increasing recognition of the importance of lipids to fundamental cell biology (in health and disease) has prompted the development of protocols and techniques to image the distribution of lipids in cells and tissues. A diverse suite of spectroscopic and microscopy tools are continuously being developed and explored to add to the "toolbox" to study lipid biology. A relatively recent breakthrough in this field has been the development and subsequent application of metal-based luminescent complexes for imaging lipids in biological systems. These metal-based compounds appear to offer advantages with respect to their tunability of the photophysical properties, in addition to capabilities centred around selectively targeting specific lipid structures or classes of lipids. The presence of the metal centre also opens the path to alternative imaging modalities that might not be applicable to traditional organic fluorophores. This review examines the current progress and developments in metal-based luminescent complexes to study lipids, in addition to exploring potential new avenues and challenges for the field to take.

Ratiometric fluorescence nanoprobe based on carbon dots and terephthalic acid for determining Fe2+ in environmental samples

A ratiometric fluorescent nanoprobe using carbon dots (CDs) and involving oxidation of terephthalic acid (TPA) induced by hydroxyl radicals (·OH) was developed for sensitively and selectively determining Fe²⁺ ions. When Fe²⁺ ions are added to the TPA@CDs/H₂O₂ system, ·OH produced through the Fenton reaction oxidizes the non-fluorescent TPA to give 2-hydroxyl terephthalic acid, which fluoresces at 423 nm when excited at 286 nm. The ·OH and Fe³⁺ produced quench CD fluorescence at 326 nm. The 2-hydroxyl terephthalic acid to CD fluorescence intensity ratio linearly increased as the Fe²⁺ concentration increased in the range 0.5-50 μM, and the detection limit was 0.25 μM. The new assay is very selective because it involves dual-emission reverse change ratio fluorescence sensing, which can exclude matrix effects. The new nanoprobe was used to determine Fe²⁺ concentrations in real water samples, and the recoveries were found to be acceptable. Schematic of the ratiometric fluorometric method for determining Fe²⁺ based on CDs and TPA.

Selective Fe(ii)-fluorescence sensor with validated two-consecutive working range using N,S,I-GQDs associated with garlic extract as an auxiliary green chelating agent

The goal of this work was to use the pyrolysis process to synthesize graphene quantum dots doped with garlic extract (as N,S-GQDs) and simultaneously co-doped with iodine (as I-GQDs). XPS, HR-TEM, FE-SEM/EDX, FT-IR, fluorescence, and UV-visible absorption spectroscopy were used to characterize the N,S,I-GQDs and analyze their morphological images. The quantum yield of N,S,I-GQDs was found to be 45%, greater than that of undoped GQDs (31%). When stimulated at 363 nm, the N,S,I-GQDs display a strong fluorescence intensity at a maximum wavelength of 454 nm. Using N,S,I-GQDs as a fluorescence quenching sensor for screening tests with various metal ions, it was discovered that they are extremely selective towards Fe2+ over Fe3+ and other ions. Thus, solution pH, concentration of N,S,I-GQDs, quantity of garlic extract, EDTA and AgNO3 concentration as masking agents, reaction duration under ultrasonic aid, and tolerable limit of Fe3+ presence in the target analyte were all optimized for Fe2+ detection. A highly sensitive detection of Fe2+ was obtained using a linear curve with y = 141.34x + 5.5855, R 2 = 0.9961, LOD = 0.11 mg L-1, and LOQ = 0.35 mg L-1. The method precision, given as RSDs, was determined to be satisfactory at 1.04% for intra-day analysis and 3.22% for inter-day analysis, respectively. As a result, the selective determination of trace amounts of Fe2+ in real water samples using such labile multi-element doped GQDs in conjunction with garlic extract as a green chelating agent to maintain its enhanced sensitivity was successfully applied with good recoveries ranging from 89.16 to 121.45%.

Recent Progress in Fluorescent Probes For Metal Ion Detection

All forms of life have absolute request for metal elements, because metal elements are instrumental in various fundamental processes. Fluorescent probes have been widely used due to their ease of operation, good selectivity, high spatial and temporal resolution, and high sensitivity. In this paper, the research progress of various metal ion (Fe³⁺,Fe²⁺,Cu²⁺,Zn²⁺,Hg²⁺,Pb²⁺,Cd²⁺) fluorescent probes in recent years has been reviewed, and the fluorescence probes prepared with different structures and materials in different environments are introduced. It is of great significance to improve the sensing performance on metal ions. This research has a wide prospect in the application fields of fluorescence sensing, quantitative analysis, biomedicine and so on. This paper discusses about the development and applications of metal fluorescent probes in future.

Aggregation-induced emission (AIE) from poly(1,4-dihydropyridine)s synthesized by Hantzsch polymerization and their specific detection of Fe2+ ions

As an important metal element widely existing in nature and the human body, the simple and specific detection of Fe2+ ions has always been of interest.

A highly effective "turn-on" camphor-based fluorescent probe for rapid and sensitive detection and its biological imaging of Fe2

In this work, a novel fluorescent probe CBO was synthesized for detecting Fe²⁺ using the natural monoterpenketone camphor as the starting material. The probe CBO displayed turn-on fluorescence to Fe²⁺ accompanied by the solution change from colorless to green. As expected, there was an excellent linear relationship between the fluorescence intensity of probe CBO and the concentration of Fe²⁺ (0-20 μM), and the detection limit was as low as 1.56×10^-8 M. In particular, CBO could selectively sense Fe²⁺ more than other analytes (Fe³⁺ included) through the N-oxide strategy, and quickly responded to Fe²⁺ (60 s) over a wide pH (4-14) range. Additionally, based on the rapid fluorescence response of CBO to Fe²⁺, a simple test strip-based detector was designed for boosting practical applicability. The probe CBO had been successfully applied to the fluorescence imaging of Fe²⁺ in onion cells and living zebrafish. The probe CBO was a powerful tool of detecting Fe²⁺ level in organisms, which was of significance to understand the role of Fe²⁺ in Fe²⁺-related physical processes and diseases.

Monitoring of Fe (II) ions in living cells using a novel quinoline-derived fluorescent probe

Physiologically, Fe(III) and Fe(II) is the most important redox pairs in a variety of biological and environmental procedures with its capability of transition. The detection of physiological iron, especially Fe(II), has become the recent research focus of investigations on revealing the mechanism of iron-related metabolism. In this work, we exploited a novel quinoline-derived fluorescent probe, YTP, for the detection of Fe(II). It could monitor the level of Fe(II) with a linear range of 0-2.0 equivalent and the detection limit of 0.16 µM. High selectivity from other analytes including Fe(III) and steadiness for over 24 h confirmed the practicability of YTP. YTP was further applied in real buffer systems and in cellular imaging. The probe could achieve the semi-quantitative monitoring of Fe(II) in living cells. This work provided a potential implement for the detection of Fe(II), and raised important information for further researches on the redox pairs of iron, in mechanism and in practice.

Two birds with one stone: A highly sensitive near-infrared BODIPY-based fluorescent probe for the simultaneous detection of Fe2+ and H+ in vivo

Ferrous ion (Fe²⁺) plays an essential role in many physiological and pathological processes, and its cellular metabolism is closely related to acidic pH. However, the lack of multifunctional Fe²⁺ probes has hindered the further study of Fe²⁺ in vivo. Herein, we report a dual-responsive near-infrared (NIR) fluorescent probe BODIPY-Fe for the simultaneous of Fe²⁺ and H⁺ in vivo by harnessing the N-oxide strategy and photoinduced electron transfer (PeT) mechanism. BODIPY-Fe exhibited NIR fluorescence at 671 nm, rapid response to Fe²⁺ within 90 s, and high sensitivity of low LOD of 292 nM towards Fe²⁺. Moreover, BODIPY-Fe could sensitively and selectively detect Fe²⁺ and H⁺ in the lysosomes of living cells simultaneously. Notably, BODIPY-Fe was able to noninvasively visualize Fe²⁺ and H⁺ in vivo, showing "ON-OFF-ON" NIR fluorescence signal changes. This work demonstrates that BODIPY-Fe has great potential to promote the simultaneous imaging of Fe²⁺ and H⁺ in biological systems.

A New Spiropyran-Based Fluorescent Probe for Dual Sensing of Ferrous Ion and pH

A new spiropyran-based fluorescent probe was developed for dual detection of Fe²⁺ ion and pH. Addition of Fe²⁺ and Ag⁺ to the probe solution enhanced the fluorescence intensity by 6 and 5 fold, respectively. Addition of Fe³⁺, Hg²⁺ and Ni²⁺ caused slight increase in the fluorescence intensity of the probe. While addition of other common metal ions did not bring about substantial change of the fluorescence. Thus the probe can be used for fluorescence turn-on detection of Fe²⁺ ion in ethanol/water (9:1) medium. The detection limit of the probe for Fe²⁺ is 0.77 µM. The suitable pH range for the probe to detect Fe²⁺ was pH 3 - 9. Other metal ions including Li⁺, Na⁺, K⁺, Ag⁺, Cu²⁺, Zn²⁺, Co²⁺, Ni²⁺, Mn²⁺, Sr²⁺, Hg²⁺, Ca²⁺, Mg²⁺, Al³⁺, Cr³⁺, and Fe³⁺ did not cause marked interference with Fe²⁺ recognition. The color of the probe solution was yellow at pH 1 - 2 and colorless at other pH values. The fluorescence intensity of the probe was low at pH 1 - 12 and increased significantly when the pH was 13 and 14, indicating that the probe can be used as a colorimetric and fluorescent probe for sensing extremely acidic or extremely alkaline conditions through different channels.