Simple Fluorescence Sensing Approach for Selective Detection of Fe3+ Ions: Live-Cell Imaging and Logic Gate Functioning

Nano fluorescent probe based on acyclic cucurbituril for Fe3+ detection in cells

Fe3+ is an essential element for the human body, and its regulation in cells is associated with serious diseases. Therefore, the ability to detect Fe3+ in living cells is highly valuable. In this study, we successfully developed a novel supramolecular fluorescent probe (ACB-TPE), based on an acyclic cucurbituril and tetraphenylethylene derivatives. The ACB-TPE probe retains the aggregation-induced emission property of TPE, and it can achieve highly specific recognition of Fe3+ ions without interference from other metal ions, anions, or amino acids. The binding constant between ACB-TPE and Fe3+ is 1.42 × 105, and the detection limit is 8.36 × 10-8 M. Additionally, the probe displayed a high response speed to Fe3+. Importantly, the ACB-TPE probe exhibited strong fluorescence emission in living cells, enabling the detection of Fe3+ through bioimaging. These make it a valuable tool for studying the role of Fe3+ regulation in cellular processes and disease pathogenesis. A significant contribution to the field of cellular metal ion detection and regulation is made by the probe's unique properties and applications.

A comprehensive review on colorimetric and fluorometric investigations of dual sensing chemosensors for Cu2+ and Fe3+ ions from the year 2017 to 2023

Dual sensing chemosensors for copper(II) and iron(III) ions are molecules or compounds designed to selectively detect and differentiate between these specific metal ions. Because metal ions like copper(II) and iron(III) are essential to so many industrial, biological, and environmental processes, their detection and measurement have become increasingly important. In this work, a novel dual-sensing chemosensor that combines high selectivity and sensitivity is presented. It is intended to detect copper(II) (Cu2+) and iron (III)(Fe3+) ions concurrently. The chemosensor combines two different recognition components into one platform and achieves dual-mode detection by combining optical and electrochemical sensing approaches. Using a dual sensing chemosensors for two cations can save money and time compared to preparing two separate chemosensors to sense each of those cations separately. We often use various techniques, including spectroscopy, fluorescence, and electrochemistry, to monitor and measure the changes induced by the interaction between the chemosensors and the metal ions. Discussions have been held on the excitation and emission wavelengths, media used in the spectroscopic measurements, binding constant with coordination binding mode, detection mechanism, and detection limit (LOD). This extensive review paper investigates colorimetric and fluorometric dual sensing analysis for Cu2+ and Fe3+ ions which includes more than sixty papers from the year of 2017 to 2023.

Synthesis of Di(thiophen-2-yl) Substituted Pyrene-Pyridine Conjugated Scaffold and DFT Insights: A Selective and Sensitive Colorimetric, and Ratiometric Fluorescent Sensor for Fe(III) Ions

In this context, we used the multicomponent Chichibabin pyridine synthesis reaction to synthesize a novel di(thiophen-2-yl) substituted and pyrene-pyridine fluorescent molecular hybrid. The computational (DFT and TD-DFT) and experimental investigations were performed to understand the photophysical properties of the synthesized new structural scaffold. The synthesized ligand displays highly selective fluorescent sensing properties towards Fe3+ ions when compared to other competitive metal ions (Al3+, Ba2+, Ca2+, Cd2+, Co2+, Cr3+, Cu2+, Fe2+, Hg2+, Na+, Ni2+, Pb2+, Sr2+, Sn2+ and Zn2+). The photophysical properties studies reveal that the synthesized hybrid molecule has a binding constant of 2.30 × 103 M-1 with limit of detection (LOD) of 4.56 × 10-5 M (absorbance mode) and 5.84 × 10-5 M (emission mode) for Fe3+ ions. We believe that the synthesized pyrene-conjugated hybrid ligand can serve as a potential fluorescent chemosensor for the selective and specific detection of Fe3+ ions.

A novel one-stepped synthesized Schiff-base fluorescence probe for specific recognition of zinc ions with highly sensitive and its application in living cells

Fluorescent turn-on receptors are extensively employed for the detection of Zn ions contamination in the environment due to its simplicity, convenience and portability. However, developing highly sensitive and cell-imageable fluorescent turn-on probe for the recognition of Zn ions in living organisms remains a significant challenge. Herein, we have successfully synthesized a novel Schiff base probe (H2L) with a significant fluorescence turn-on response (Zn ions) by one-step synthetic method. In this work, H2L exhibited high sensitivity to Zn2+ ions upon interaction with various common metal ions in HEPES buffer solution. Its detection limit is 1.87 × 10-7 M, which is lower than the requirement of Environmental Protection Agency (EPA) and World Health Organization (WHO) guidelines. The fluorescence titration and Job's plot analysis suggested a 1:1 binding ratio between the probe and Zn ion, and the single-crystal structures obtained further confirmed this inference. In addition, the fluorescent sensor demonstrated recyclability, maintaining its fluorescence intensity for up to 6 cycles without significant decrease, which holds promise for future investigations on reversible fluorescent chemosensors. Notably, fluorescence imaging experiments demonstrated that H2L could be successfully used for the detection of Zn2+ in live cells.

Real-time optical detection of mercury contamination in drinking water using an amphiphilic recognition probe at liquid crystal/aqueous interfaces

Mercury contamination is a global environmental issue due to its toxicity and persistence in ecosystems. It poses a particular risk in aquatic systems, where it bioaccumulates and biomagnifies, leading to serious health impacts on humans. Therefore, effective detection technologies for mercuric ions in natural water resources are highly desirable. However, most existing detection methods are time-consuming, require complicated sample pre-treatment, and rely on expensive equipment, which hinders their widespread use in real-time detection. Here, we present a convenient, rapid, portable, user-friendly, and cost-effective sensing system for detecting Hg2+ ion contamination in water. This system utilizes a highly selective, amphiphilic, and structurally simple molecular probe, N-dodecylamine-di-thiocarbamate (DDC). DDC molecules align at the interface between the liquid crystal (LC) and water, inducing a homeotropic LC orientation. In water samples contaminated with Hg2+, a bright optical texture is observed, indicating the alignment of the 5CB LC in a planar manner at the LC/aqueous boundary. The minimum detectable concentration (LOD) for Hg2+ ions is 5.0 μM in distilled water, with a broad detection range from 5.0 μM to 2 mM. The sensor selectively detects Hg2+ ions over other common interfering metal ions, including Pb2+, Co2+, Ni2+, Cu2+, Cd2+, Zn2+, Cr2+, Mg2+, Na+, K+, and Ca2+. Boolean logic gates, bar graphs, and truth tables are employed to explain the selectivity of this liquid crystal-based sensor. This work demonstrates the significant potential of the sensor for monitoring mercuric ions in natural water resources, offering a promising strategy for controlling mercury pollution.

Fluorescence chemosensing and bioimaging of metal ions using schiff base probes working through photo-induced electron transfer (PET)

Though metal ions like copper, iron, zinc, etc. are essential, but their dyshomeostasis is associated with several disorders. Therefore, fast, sensitive, and cost-effective monitoring of these cations will have a significant impact. Many recently reported small organic molecules were able to detect a specific metal ion because of certain variations in the electron/charge transfer processes occurring in those molecules after binding with metal ions. In this context, Schiff base molecules were widely used as fluorescence turn-on/turn-off probes for the detection of metal ions like Al3+, Cu2+, Zn2+, Fe3+, Ag+, heavy metal ions, etc. In this article, we have reviewed the recent developments in fluorimetric chemosensing of metal ions by Schiff bases based on the photo-induced electron transfer (PET) process. A variety of examples have been discussed in which PET was used as a cation recognition mechanism. Particular focus is placed on the molecular probes used for sensing, including their design, selectivity, sensitivity, and in some cases their potential bioimaging applications.

A Novel Rhodamine B Derivative as a "Turn-on" Fluorescent Sensor for Cu2+ with High Selectivity and Sensitivity

The number of "turn-on" fluorescent probes for Cu2+ is relatively limited, and interference from other metal cations presents a significant challenge for these sensors. In this study, we synthesized and characterized a rhodamine B-based sensor, designated as RBHP, using 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (PMBP) and rhodamine B hydrazide. Selectivity, sensitivity, solvent effects, water content, and pH of RBHP in relation to Cu²⁺ were conducted. RBHP exhibited an exceptionally low fluorescence background signal in acetonitrile and demonstrated a "turn-on" fluorescent response to Cu²⁺. The PMBP-based acylhydrazone moiety and acetonitrile as the detection solvent are crucial for the selective detection. RBHP shows potential as a highly selective and sensitive fluorescent sensor for Cu2+.

l-cysteine capped MoS2 QDs for dual-channel imaging and superior Fe3+ ion sensing in biological systems

MoS2 quantum dots (MQDs) with an average size of 1.9 ± 0.7 nm were synthesized using a microwave-assisted method. Absorbance studies confirmed characteristic transitions of MoS2, with absorption humps at 260-280 nm and 300-330 nm, and a band gap of 3.6 ± 0.1 eV. Fluorescence emission studies showed dominant blue and some green emissions under 315 nm excitation, with an absolute quantum yield of ∼9%. The MQDs exhibited fluorescence stability over time after repeated quenching cycles across various pH and media systems. In vitro toxicity tests indicated cytocompatibility, with around 80% cell survival at 1000 mg L-1. Confocal imaging demonstrated significant uptake and vibrant fluorescence in cancerous and non-cancerous cell lines. The MQDs showed strong selectivity towards Fe3+ ions, with a detection limit of 27.61 ± 0.25 nM. Recovery rates for Fe3+ in phosphate buffer saline (PBS) and simulated body fluid (SBF) systems were >97% and >98%, respectively, with a relative standard deviation (RSD) within 3%, indicating precision. These findings suggest that MQDs have high potential for diagnostic applications involving Fe3+ detection due to their fluorescence stability, robustness, enhanced cell viability, and dual-channel imaging properties.

Biomolecular Interactions and Anticancer Mechanisms of Ru(II)-Arene Complexes of Cinnamaldehyde-Derived Thiosemicarbazone Ligands: Analysis Combining In Silico and In Vitro Approaches

Our study focuses on synthesizing and exploring the potential of three N-(4) substituted thiosemicarbazones derived from cinnamic aldehyde, alongside their Ru(II)-(η6 -p-cymene)/(η6-benzene) complexes. The synthesized compounds were comprehensively characterized using a range of analytical techniques, including FT-IR, UV-visible spectroscopy, NMR (1H, 13C), and HRMS. We investigated their electronic and physicochemical properties via density functional theory (DFT). X-ray crystal structures validated structural differences identified by DFT. Molecular docking predicted promising bioactivities, supported by experimental observations. Notably, docking with EGFR suggested an inhibitory potential against this cancer-related protein. Spectroscopic titrations revealed significant DNA/BSA binding affinities, particularly with DNA intercalation and BSA hydrophobic interactions. RuPCAM displayed the strongest binding affinity with DNA (Kb = 6.23 × 107 M-1) and BSA (Kb = 9.75 × 105 M-1). Assessed the cytotoxicity of the complexes on cervical cancer cells (HeLa), and breast cancer cells (MCF-7 and MDA-MB 231), revealing remarkable potency. Additionally, selectivity was assessed by examining MCF-10a normal cell lines. The active complexes were found to trigger apoptosis, a vital cellular process crucial for evaluating their potential as anticancer agents utilizing staining assays and flow cytometry analysis. Intriguingly, complexation with Ru(II)-arene precursors significantly amplified the bioactivity of thiosemicarbazones, unveiling promising avenues toward the creation of powerful anticancer agents.

Fluorescent MnO2@DEHP Nanoprobe for Rapid and Selective Detection of Fe(III) ions

Particle extraction via the liquid-liquid interface (PELLI) method has been utilized to produce Di-(2-ethylhexyl) phosphate (DEHP) coated MnO2 fluorescent nanoprobe denoted as MnO2@DEHP for the selective detection of Fe3+ ions. The synthesized MnO2@DEHP nanoprobe was characterized by various instrumental techniques such as FT-IR, PXRD, TEM, EDAX, HRTEM, DLS, and XPS. Since the high concentration of Fe3+ in waste water leads to water pollution, which in turn affects the ecosystem, and causes severe health hazards. Therefore, accurate detection of Fe3+ ions in the aqueous systems is essential as they are involved in various chemical and biological processes in living things. Here, the synthesized MnO2@DEHP nanoprobe selectively detects Fe3+ ions in the presence of various metal ions in an aqueous media by fluorescence quenching (turn-off) mechanism. The limit of detection (LOD) of MnO2@DEHP nanoprobe for Fe3+ was found to be 0.49 µM. The test-strip method and real water sample analysis were also used to demonstrate the viability of MnO2@DEHP as a fluorescent nanoprobe to detect Fe3+ ions visually and in environment monitoring applications.

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.

Host-guest interactions of coumarin-based 1,2-pyrazole using analytical and computational methods: Paper strip-based detection, live cell imaging, logic gates and keypad lock applications

A novel Coumarin-based 1,2-pyrazole, HCPyTSC is synthesised and characterized. The chemosensor has been shown to have efficient colourimetric and fluorescence sensing capabilities for the quick and selective detection of fluoride and copper ions. At 376 and 430 nm, the HCPyTSC exhibits selective sensing for Cu2+ and F- ions. By examining the natural bond orbital (NBO) analysis and the potential energy curve (PES) of the ground state for the function of the C-H bond, it has been determined from the theoretical study at hand that the deprotonation was taken from the 'CH' proton of the pyrazole ring. For F- and Cu2+, the HCPyTSC detection limits were 4.62 nM and 15.36 nM, respectively. Similarly, the binding constants (Kb) for F- and Cu2+ ions in acetonitrile medium were found to be 2.06 × 105 M-1 and 1.88 × 105 M-1. Chemosensor HCPyTSC with and without F- and Cu2+ ions have an emission and absorption response that can imitate a variety of logic gates, including the AND, XOR, and OR gates. Additionally, a paper-based sensor strip with the HCPyTSC was created for use in practical, flexible F- sensing applications. The paper-based sensor was more effective in detecting F- than other anions. The effectiveness of HCPyTSC for the selective detection of F- in living cells as well as its cell permeability were examined using live-cell imaging in T24 cells.

Synthesis of a novel hydrazone-based compound applied as a fluorescence turn-on chemosensor for iron(iii) and a colorimetric sensor for copper(ii) with antimicrobial, DFT and molecular docking studies

Hydrazone-hydrazide-based linkers perform a crucial role in environmental as well as biological fields. Such linkers are employed to detect exact metal ions at a minute level; hence, numerous probes are available. Even though thiophene-based molecules have a unique position in the medicinal arena, only very few chemosensors are reported based on such a moiety. In this current work, a novel hydrazide-hydrazone-based fluorogenic molecule 5-bromo-2-hydroxy-N'-[(1E)-1-(thiophen-2-yl)ethylidene]benzohydrazide (L) has been successfully designed and synthesized. The sensing studies of L demonstrated a ratio metric as well as turn-on-enhanced fluorescence and colorimetric response toward Fe3+ and Cu2+ ions, respectively and it was observed to be insensitive toward various metal ions. The Job plots revealed that the binding stoichiometry of L and metal ions is 2 : 1. In addition, density functional theory (DFT) results strongly suggested that L can be used as a powerful colorimetric sensor for the detection of Cu2+ ions. In vitro antimicrobial activities of L were evaluated by disk diffusion and results revealed good antibacterial activities against E. coli. Further, molecular docking was executed with DNA gyrase (PDB ID: 1KZN) of E. coli and the calculated interaction energy value was found to be -7.7 kcal mol-1. Finally, molecular docking, fluorescence, colorimetry and the HOMO-LUMO energy gap of the compound can provide new insights into developing drugs and detecting metals in biomolecules.

Pyrene Functionalized Luminescent Phenylalanine for Selective Detection of Copper (II) Ions in Aqueous Media

A novel pyrene-based fluorescent chemosensor 1 (pyren-1-ylmethyl)-L-phenylalanine was designed and synthesized by combining 1-pyrenecarboxyaldehyde and L-phenylalanine. 1 was characterized by several analytical methods and used as a fluorescent chemosensor for the selective and sensitive detection of Cu²⁺ ions through "turn-off" mechanism with a detection limit of 2 × 10^-8 M. 1 can also be used to detect Cu²⁺ ions in a natural water sample and exhibits gelation properties with high thermal stability.