Chemically diverse small molecule fluorescent chemosensors for copper ion

A fluorescence ionic probe utilizing Cu2+ assisted competition for detecting glyphosate abused in green tea

Food fraud caused by the violation of glyphosate use in tea is frequently exposed, posing a potential health risk to consumers and undermining trust in food safety. In the work, an ionic fluorescent probe "[P66614] [4HQCA]-Cu2+ (PHQCA-Cu2+)" was constructed using Cu2+ and ionic liquids coordination through a competitive coordination strategy to detect glyphosate. This probe exhibited a prominent "turn-on" fluorescence response in glyphosate detection. PHQCA-Cu2+was destroyed by glyphosate with its strong coordination capability, and a new complex re-formed simultaneously between glyphosate and the Cu2+ in it, where Cu2+ served as an "invisible indicator" influencing fluorescence changes. Remarkably, PHQCA-Cu2+formed rapidly within 5 s, demonstrated exceptional sensitivity and selectivity, and satisfactory detection performance on paper strips impregnated withPHQCA-Cu2+.Importantly,PHQCA-Cu2+showed excellent recoveries in various green tea, which offered a viable method for identifying contaminated products from the supply chain quickly to enhance overall food safety surveillance.

Colorimetric and Fluorometric N-Acylhydrazone-based Chemosensors for Detection of Single to Multiple Metal Ions: Design Strategies and Analytical Applications

The development of optical sensors for metal ions has gained significant attention due to their broad applications in biology, the environment, and medicine. Colorimetric and fluorometric detection methods are particularly valued for their simplicity, cost-effectiveness, high detection limits, and analytical power. Among various chemical probes, the hydrazone functional group stands out for its extensive study and utility, owing to its ease of synthesis and adaptability. This review provides a comprehensive overview of N-acylhydrazone-based probes, serving as highly effective colorimetric and fluorometric chemosensors for a diverse range of metal ions. Probes are categorized into single-ion, dual-ion, and multi-ion chemosensors, each further classified based on the detected metal(s). Additionally, the review discusses detection modes, detection limits, association constants, and spectroscopic measurements.

A Review on Pyrazolines as Colorimetric Fluorescent Chemosensors for Cu2

The Pyrazoline derivatives display promising potential as sensitive and selective chemosensors for detecting Cu2+ ions. It has undergone screening for its sensing behavior with various metals using absorption, emission spectroscopic techniques. Their unique structure incorporates both donating and accepting sites, characterized by delocalized orbitals. These derivatives exhibit notable chromogenic and fluorogenic capabilities facilitated by intramolecular charge transfer. The sensors based on pyrazoline demonstrate exceptional selectivity, low detection limits, and precise detection of metal ions, particularly Cu2+. This review offers a comprehensive summary of recent discoveries concerning as pyrazoline-based "On-Off" chemosensors. The discussion places emphasis on exploring the design and photophysical properties of these chemosensors, with the primary objective of detecting Cu2+ metal ions. The unique features of pyrazoline derivatives make them promising candidates for practical applications in environmental and biological monitoring, showcasing their potential significance in advancing sensing technologies.

Excited-state dynamics of 4-hydroxyisoindoline-1,3-dione and its derivative as fluorescent probes

Fluorescent probes have become promising tools for monitoring the concentration of peroxynitrite, which is linked to many diseases. However, despite focusing on developing numerous peroxynitrite based fluorescent probes, limited emphasis is placed on their sensing mechanism. Here, we investigated the sensing mechanism of a peroxynitrite fluorescent probe, named BHID-Bpin, with a focus on the relevant excited state dynamics. The photoexcited BHID-Bpin relaxes to its ground state via an efficient nonradiative process (∼300 ps) due to the presence of a minimum energy conical intersection between its first excited state and ground state. However, upon reacting with peroxynitrite, the Bpin moiety is cleaved from BHID-Bpin and BHID is formed. The formed BHID exhibits strong dual band fluorescence which is caused by an ultrafast excited-state intramolecular proton transfer process (∼1 ps).

A highly sensitive and selective rhodamine-semicarbazide based fluorescent sensor for Cu2+ detection in real water samples and fluorescence bioimaging in HepG2 cells

A colorimetric and fluorescent sensor, selective for Cu2+ ions, was synthesized in two steps using a rhodamine-based compound attached to the semicarbazide-picolylamine moiety (RBP). Spectroscopic measurements, including UV-Vis absorption and fluorescence emission, were conducted in the semi-aqueous medium containing acetonitrile/4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid, denoted as MeCN/HEPES buffer (2:8, v/v, pH 7.0). The sensor exhibited high selectivity towards Cu2+ ions compared to other cations and demonstrated remarkable sensitivity towards Cu2+ ions, with a limit of detection at the nanomolar level. The calculated transitions indicated a 1:1 stoichiometric binding of RBP to Cu2+ ions based on a 4-coordination mode involving additional chelation in the semi-aqueous medium. The sensing mechanism for the detection of Cu2+ ions was investigated using high-resolution mass spectroscopy. The sensor could be employed as a real-time chemosensor for monitoring Cu2+ ions. Furthermore, the sensor has the potential for utilization in the detection of Cu2+ ions in actual water samples with the high precision and accuracy, as indicated by the small relative standard derivation values. The 50th percentile cytotoxicity concentration of RBP was found to be 22.92 μM. Additionally, the fluorescence bioimaging capability of RBP was demonstrated for the detection of Cu2+ ions in human hepatocellular carcinoma (HepG2) cells.

A Small-Molecule Ratiometric Photoacoustic Probe for the High-Spatiotemporal-Resolution Imaging of Copper(II) Dynamics in the Mouse Brain

Copper dysmetabolism is associated with various neurodegenerative disorders, making high-spatiotemporal-resolution imaging of Cu2+ in the brain essential for understanding the underlying pathophysiological processes. Nevertheless, the current probes encounter obstacles in crossing the blood-brain barrier (BBB) and providing high-spatial-resolution in deep tissues. Herein, we present a photoacoustic probe capable of imaging Cu2+ dynamics in the mouse brain with high-spatiotemporal-resolution. The probe demonstrates selective ratiometric and reversible responses to Cu2+ , while also efficiently crossing the BBB. Using the probe as the imaging agent, we successfully visualized Cu2+ in the brain of Parkinson's disease (PD) model mouse with a remarkable micron-level resolution. The imaging results revealed a significant increase in Cu2+ levels in the cerebral cortex as PD progresses, highlighting the close association between Cu2+ alternations in the region and the disease. We also demonstrated that the probe can be used to monitor changes in Cu2+ distribution in the PD model mouse brain during L-dopa intervention. Mechanism studies suggest that the copper dyshomeostasis in the PD mouse brain was dominated by the expression levels of divalent metal transporter 1. The application of our probe in imaging Cu2+ dynamics in the mouse brain offers valuable insights into the copper-related molecular mechanisms underlying neurodegenerative diseases.

Ultrasensitive Visual Tracking of Toxic Cyanide Ions in Biological Samples Using Biocompatible Metal-Organic Frameworks Architectures

The extraordinary accumulation of cyanide ions within biological cells is a severe health risk. Detecting and tracking toxic cyanide ions within these cells by simple and ultrasensitive methodologies are of immense curiosity. Here, continuous tracking of ultimate levels of CN--ions in HeLa cells was reported employing biocompatible branching molecular architectures (BMAs). These BMAs were engineered by decorating colorant-laden dendritic branch within and around the molecular building hollows of the geode-shelled nanorods of organic-inorganic Al-frameworks. Batch-contact methods were utilized to assess the potential of hollow-nest architecture for inhibition/evaluation of toxicant CN--ions within HeLa cells. The nanorod BMAs revealed significant potential capabilities in monitoring and tracking of CN- ions (88 parts per trillion) in biological trials within seconds. These results demonstrated sufficient evidence for the compatibility of BMAs during HeLa cell exposure. Under specific conditions, the BMAs were utilized for in-vitro fluorescence tracking/sensing of CN- in HeLa cells. The cliff swallow nest with massive mouths may have the potential to reduce the health hazards associated with toxicant exposure in biological cells.

Label-free multimodal analysis of copper ions at below permissible exposure limit in the aqueous medium

An anthraimidazoledione based amphiphilic dye molecule was synthesized that shows formation of tuneable charge-transfer state in solution, susceptible to change in pH, polarity and hydrogen bonding ability of the medium. The compound also showed formation of nanoscopic self-assembled structure in water medium. The probe molecule can achieve multimodal detection (colorimetric, fluorimetric and electrochemical) of copper ions as low as 0.3 ppm in the aqueous medium. Addition of copper leads to dose-dependent ratiometric change in solution color from yellow to purple. The mechanistic investigation indicates that the coordination of copper ions was possible via simultaneous engagement of both imidazole nitrogen ends and neighbouring hydroxyl unit. Not only optical property, the changes in microenvironment also influence the selectivity as well as sensitivity of the probe molecule towards Cu2+ ions. Further, the optical probe is used for detection as well as quantification of copper ions in natural water samples without any sample pretreatment. Low-cost, reusable paper strips are developed for rapid, on-location detection of residual Cu2+ in real-life samples.

Bright photoactivatable probes based on triphenylethylene for Cu2+ detection in tap water and tea samples

Photoactivatable probes can switch fluorescence on from a weak or nonemission state to improve the sensitivity of the sensing system. In this work, we successfully constructed three highly emissive photoactivatable probes, 2-DP, 1-2-DP and 2-2-DP, for Cu2+ detection. Under UV irradiation, the photoluminescence quantum yields of 2-DP, 1-2-DP and 2-2-DP display approximately 52.4-, 11.5- and 49.2-fold enhancement, respectively. Cu2+ selectively quenches the bright photoactivated fluorescence, resulting in an approximately 38-fold fluorescence reduction. The highly selective fluorescence response to Cu2+ yields an excellent low detection limit of 5.8 nM. Moreover, the photoactivatable probes were successfully applied for Cu2+ determination in tap water and tea samples with recovery ranges of 95%-105% and 97%-106%, respectively. This work provides a more sensitive and efficient methodology for Cu2+ detection in heavy metal pollution and food safety.

An ultra-sensitive fluorescent probe for recognition of aluminum ions and its application in environment, food, and living organisms

The concentration of aluminum ions (Al3+) is closely related to the ecological environment, food safety, and human health, with excessive accumulation of Al3+ causing irreversible damage to both the ecological balance and human health. Therefore, a fluorescent probe ABHS, based on aminobenzoylhydrazide Schiff-base, was designed and synthesized in one step with a high yield. ABHS can form a 1:1 coordination complex with Al3+ in a pure water system. It exhibits ultra-sensitive and accurate detection of Al3+ even at low concentration of Al3+, with the detection limit of 6.7 nM. Furthermore, ABHS demonstrated significant enhancement of specific fluorescence for Al3+, with rapid response speed, good stability, and robust resistance to interference. Importantly, ABHS has shown excellent detection and imaging capabilities even in complex real environmental samples, food samples, and living organisms.

A Naphthoquinoline-Dione-Based Cu2+ Sensing Probe with Visible Color Change and Fluorescence Quenching in an Aqueous Organic Solution

Copper metal ions (Cu2+) are widely used in various industries, and their salts are used as supplementary components in agriculture and medicine. As this metal ion is associated with various health issues, it is necessary to detect and monitor it in environmental and biological samples. In the present report, we synthesized a naphthoquinoline-dione-based probe 1 containing three ester groups to investigate its ability to detect metal ions in an aqueous solution. Among various metal ions, probe 1 showed a vivid color change from yellow to colorless in the presence of Cu2+, as observed by the naked eye. The ratiometric method using the absorbance ratio (A413/A476) resulted in a limit of detection (LOD) of 1 µM for Cu2+. In addition, the intense yellow-green fluorescence was quenched upon the addition of Cu2+, resulting in a calculated LOD of 5 nM. Thus, probe 1 has the potential for dual response toward Cu2+ detection through color change and fluorescence quenching. 1H-NMR investigation and density functional theory (DFT) calculations indicate 1:1 binding of the metal ion to the small cavity of the probe comprising four functional groups: the carbonyl group of the amide (O), the amino group (N), and two t-butyl ester groups (O). When adsorbed onto various solid surfaces, such as cotton, silica, and filter paper, the probe showed effective detection of Cu2+ via fluorescence quenching. Probe 1 was also useful for Cu2+ sensing in environmental samples (sea and drain water) and biological samples (live HeLa cells).

A Sensitive Probe of Meso-Cyanophenyl Substituted BODIPY Derivative as Fluorescent Chemosensor for the Detection of Multiple Heavy Metal Ions

A fluorescent turn-on chemosensor (BA) was constructed by attaching bis(pyridin-2-ylmethyl)-amine (DPA) unit to the BODIPY scaffold. It can give a prominent green/yellow fluorescent response selectivity with each of Zn2+/Hg2+/Cd2+/Ca2+/Mn2+/Pb2+/Al3+. The 1:1 stoichiometry of BA and metal ions was drawn from the analysis of Job's plot. The limit detection of BA in recognition of Zn2+/Hg2+/Cd2+/Ca2+/Mn2+/Pb2+/Al3+ is ranged in 50.8-146.6 nM. There exists a linear relationship between the fluorescence intensity and concentration of metal ions (Zn2+: 4-15 µM). The mechanism of fluorescence signal "turn-on" is based on the photo induced transfer (PET) in the excited state of BA. The coordinated metal ions significantly weakened the electron-donating ability nitrogen atom in DPA, thus recovering the emission character of BODIPY. The substituted group at the phenyl ring in meso-position of BODIPY scaffold determines the recognizable list of metal ions.

Highly selective Cu2+ detection with a naphthalimide-functionalised pillar[5]arene fluorescent chemosensor

Ligand 1, a rim-differentiated pillar[5]arene macrocycle modified with five naphthalimide groups through click chemistry, serves as an effective ratiometric fluorescent chemosensor for Cu2+. In contrast to the monomeric naphthalimide control compound 2, which shows only monomer emission, ligand 1 demonstrates dual emission characteristics encompassing both the monomer and excimer of the naphthalimide moieties. The binding properties of ligand 1 toward 15 different metal ions were systematically investigated in CH2Cl2/CH3CN (v/v, 1 : 1) by UV-vis and fluorescence spectroscopy. Remarkably, ligand 1 exhibits exceptional selectivity for Cu2+ ions. Upon complexation with Cu2+, the excimer emission of ligand 1 diminishes, concomitant with an enhancement of its monomer emission. The binding ratio for 1·Cu2+ was determined to be 1 : 1, with an association constant of (3.39 ± 0.40) × 105 M-1 calculated using a nonlinear least-squares curve-fitting method. Furthermore, the limit of detection (LOD) was found to be 185 ± 7 nM. Our results from 1H NMR titration, high-resolution mass spectrometry analysis and density functional theory calculations of 1·Cu2+ suggest synergistic coordination between Cu2+ and the triazole groups on ligand 1.

Recent advances in the synthesis and utility of thiazoline and its derivatives

Thiazolines and their derivatives hold significant importance in the field of medicinal chemistry due to their promising potential as pharmaceutical agents. These molecular entities serve as critical scaffolds within numerous natural products, including curacin A, thiangazole, and mirabazole, and play a vital role in a wide array of physiological reactions. Their pharmacological versatility encompasses anti-HIV, neurological, anti-cancer, and antibiotic activities. Over the course of recent decades, researchers have extensively explored and developed analogs of these compounds, uncovering compelling therapeutic properties such as antioxidant, anti-tumor, anti-microbial, and anti-inflammatory effects. Consequently, thiazoline-based compounds have emerged as noteworthy targets for synthetic endeavors. In this review, we provide a comprehensive summary of recent advancements in the synthesis of thiazolines and thiazoline-based derivatives, along with an exploration of their diverse potential applications across various scientific domains.

Progress in appended calix[4]arene-based receptors for selective recognition of copper ions

In the past two decades, there has been significant progress in the design and development of synthetic receptors for molecular recognition as they find application in the field of chemical, biological, medical, and environmental sciences. Synthetic receptors based on calix systems appended with fluorogenic and chromogenic groups have gained considerable attention for sensing and recognition of ions and molecules. Copper (Cu2+) is an essential element required in trace amounts in all living organisms to carry out various biological processes. The aim of this review is to summarize advancement in π-conjugated fluorogenic and chromogenic groups appended to calix[4]arene motifs for detection and quantitation of Cu2+ ion. The focus is to present a comprehensive account of extended calix[4]arene systems with different linkers and highlight the unique design and binding characteristics for the recognition and sensing of Cu2+ ions.

Flourescence sensors for heavy metal detection: major contaminants in soil and water bodies

Due to the increasing consumption of heavy metals, there is a rising need for specific and useful methods that are employed for the detection of heavy metals. Fluorescence sensing is a highly selective, rapid and biosensing technique that is employed in the determination of some heavy metals in any sample of soil or water, any other living person, the food being consumed or any other substance which are being used daily. These fluorescent methods are a type of analytical technique and they are mainly based on detection. Many types of metal conjugated molecules have been used of the detection of these heavy metals with various mechanisms. We have taken into account some specific sensor molecules as they were more suitable and easily accessible. These techniques that were employed in the detection of various heavy metals such as copper, lead and mercury have been discussed in the following review article.

A Dipeptide-derived Dansyl Fluorescent Probe for the Detection of Cu2+ in Aqueous Solutions

A novel dansyl-based fluorescent probe (DG) was designed via the introduction of a dipeptide, glycyl-L-glutamine. DG showed good selectivity and sensitivity towards Cu2+ in aqueous solutions in the pH span of ~ 6-12. The coordination of Cu2+ with the dipeptide moiety led to the fluorescent quenching of the dansyl fluorophore. The association constant value for Cu2+ was 0.78 × 104 M- 1 in a 1 to 1 stoichiometric ratio. The detection limit in HEPES buffer solution (10 mM, pH 7.4) was 1.52 µM. DG also showed strong anti-interference capability in the presence of other metal ions. It was worth noting that DG maintained the detection ability towards Cu2+ in real water samples and cell imaging, implying the potential application opportunities in complicated environments.

A Rhodamine-coumarin Triazole Conjugate as a Fluorescent Chemodosimeter for Cu(II) Detection and its Application in Live Cell Bioimaging

A rhodamine-triazole fluorescent probe bearing a coumarin moiety RTC was synthesized using the Cu(I)-catalyzed click reaction. The rhodamine-triazole conjugate was highly selective to Cu2+ among other metal ions, including Ca2+, Co2+, Cu2+, Cd2+, Mg2+, Fe2+, Fe3+, Hg2+, Zn2+, Ni2+, Pd2+ and Pb2+ in physiological conditions. Upon the addition of Cu2+, the colorless RTC solution turned pink and exhibited a significant fluorescence emission centered at 578 nm. The binding of Cu2+ induced a hydrolysis reaction, leading to a release of the coumarin unit from the rhodamine probe, as confirmed by mass spectrometric data. From the fluorescence titration, the detection limit of RTC for Cu2+ was determined to be 21 nM (1.3 ppb). The sensor was responsive to Cu2+ in a wide pH range and successfully applied to monitor Cu2+ in HEK293T cells by confocal fluorescence imaging.

Diphenyl imidazole-based fluorescent chemosensor for Al3+ and its Al3+ complex toward water detection in food products

A sophisticated fluorescent chemosensor, 2-(4-nitrophenyl)-4,5-diphenyl-1H-imidazole (NPDI), was designed and synthesized through a one-step condensation reaction. NPDI exhibited a fluorescence enhancement response toward Al3+, accompanied by significant emission color change without interference from other tested metal ions. The binding stoichiometry and mechanism was corroborated using various techniques. The limit of detection (LOD) for Al3+ could reach 7.25 × 10-8 mol/L and the binding constant was found to be 1.47 × 105 L/mol. Furthermore, the in-situ formed NPDI·Al complex functioned a secondary chemosensor for water by quenching effect. The fluorescence quenching mechanism could be attributed to hydrogen bonding interaction of nitro substituent with water. The LOD was calculated to be 0.012 %, indicating NPDI·Al heightened sensitivity to water. Additionally, NPDI·Al complex was employed for the moisture detection in the surroundings. Finally, the practical application of NPDI·Al complex had been successfully used in the determination of water content in food products.

Current and Future of "Turn-On" Based Small-Molecule Copper Probes for Cuproptosis

Increasing evidence shows that abnormal copper (Cu) metabolism is highly related to many diseases, such as Alzheimer's disease, Wilson's disease, hematological malignancies and Menkes disease. Very recently, cuproptosis, a Cu-dependent, programmed cell death was firstly described by Tsvetkov et al. in 2022. Their findings may provide a new perspective for the treatment of related diseases. However, the concrete mechanisms of these diseases, especially cuproptosis, remain completely unclear, the reason of which may be a lack of reliable tools to conduct highly selective, sensitive and high-resolution imaging of Cu in complex life systems. So far, numerous small-molecular fluorescent probes have been designed and utilized to explore the Cu signal pathway. Among them, fluorescence turn-on probes greatly enhance the resolution and accuracy of imaging and may be a promising tool for research of investigation into cuproptosis. This review summarizes the probes developed in the past decade which have the potential to study cuproptosis, focusing on the design strategies, luminescence mechanism and biological-imaging applications. Besides, we put forward some ideas concerning the design of next-generation probes for cuproptosis, aiming to tackle the main problems in this new field. Furthermore, the prospect of cuproptosis in the treatment of corresponding diseases is also highlighted.

Cu2+-assisted sensing of fungicide Thiram in food, soil, and plant samples and the ratiometric detection of Hg2+ in living cells by a low cytotoxic and red emissive fluorescent sensor

Metal ions and pesticides are extensively used in many industries and agriculture. However, they cause significant environmental pollution and various adverse health effects. Therefore, the development of sensitive and selective techniques to detect them is necessary for human health and the ecosystem. In this paper, we report a novel red-emitting fluorescence probe with a large Stokes shift (∼220 nm) based on rhodamine and isophorone units. The probe shows a ratiometric fluorescence response toward Hg²⁺ ions; however, Cu²⁺ ions quench the red fluorescence signal. The decomposition of the probe-Cu²⁺ complex allows detection of Thiram followed by recovery of the red fluorescence signal of the probe. In addition, the probe shows a good linear response to Hg²⁺, Cu²⁺, and Thiram, with detection limits of 122.0 nM, 29.0 nM, and 72.0 nM, respectively. The practical applicability of the probe has been successfully tested in real samples. Moreover, smartphone detection and light-responsive capsule fabrication have been established, for easy and quick detection. The probe possesses very low cytotoxicity and allows visualization of Hg²⁺ and Cu²⁺ ions in HeLa cells. Therefore, the present probe is expected to be an effective tool assisting in easy, quick, and reliable detection of Thiram, Hg²⁺, and Cu²⁺ ions.

BODIPY as a Multifunctional Theranostic Reagent in Biomedicine: Self-Assembly, Properties, and Applications

The use of boron dipyrromethene (BODIPY) in biomedicine is reviewed. To open, its synthesis and regulatory strategies are summarized, and inspiring cutting-edge work in post-functionalization strategies is highlighted. A brief overview of assembly model of BODIPY is then provided: BODIPY is introduced as a promising building block for the formation of single- and multicomponent self-assembled systems, including nanostructures suitable for aqueous environments, thereby showing the great development potential of supramolecular assembly in biomedicine applications. The frontier progress of BODIPY in biomedical application is thereafter described, supported by examples of the frontiers of biomedical applications of BODIPY-containing smart materials: it mainly involves the application of materials based on BODIPY building blocks and their assemblies in fluorescence bioimaging, photoacoustic imaging, disease treatment including photodynamic therapy, photothermal therapy, and immunotherapy. Lastly, not only the current status of the BODIPY family in the biomedical field but also the challenges worth considering are summarized. At the same time, insights into the future development prospects of biomedically applicable BODIPY are provided.

Design, Synthesis, and Biomedical Application of Multifunctional Fluorescent Polymer Nanomaterials

Luminescent polymer nanomaterials not only have the characteristics of various types of luminescent functional materials and a wide range of applications, but also have the characteristics of good biocompatibility and easy functionalization of polymer nanomaterials. They are widely used in biomedical fields such as bioimaging, biosensing, and drug delivery. Designing and constructing new controllable synthesis methods for multifunctional fluorescent polymer nanomaterials with good water solubility and excellent biocompatibility is of great significance. Exploring efficient functionalization methods for luminescent materials is still one of the core issues in the design and development of new fluorescent materials. With this in mind, this review first introduces the structures, properties, and synthetic methods regarding fluorescent polymeric nanomaterials. Then, the functionalization strategies of fluorescent polymer nanomaterials are summarized. In addition, the research progress of multifunctional fluorescent polymer nanomaterials for bioimaging is also discussed. Finally, the synthesis, development, and application fields of fluorescent polymeric nanomaterials, as well as the challenges and opportunities of structure-property correlations, are comprehensively summarized and the corresponding perspectives are well illustrated.

"Turn-on" fluorescent sensor for oleanolic acid based on o-phenyl-bridged bis-tetraphenylimidazole

Fluorescent sensors had been extensively applied on sensing various biomolecules effectively, but no fluorescent sensor for oleanolic acid was presented up to now. In this work, the first fluorescent sensor for oleanolic acid was designed and synthesized based on o-phenyl-bridged bis-tetraphenylimidazole (PTPI). PTPI was prepared by bridging two tetraphenylimidazole units and o-phenylenediamine via Schiff-base condensation in yield of 86%. PTPI showed high sensing selectivity for oleanolic acid among 26 biomolecules and ions. The blue fluorescence at 482 nm was enhanced by 4.5 times after sensing oleanolic acid in aqueous media. The fluorescence sensing ability of PTPI for oleanolic acid maintained stable in pH = 5-9. The detecting limitation was as low as 0.032 μM. The detecting mechanism was clarified as 1:1 binding stoichiometry by fluorescence Job's plot, mass spectrometry, ¹H nuclear magnetic resonance and fourier transform infrared spectroscopy. The detecting ability of PTPI for oleanolic acid was successfully used for paper test and real samples of grapes and Kuding tea with recoveries in the range of 96.0%-106.0%, indicating the good application potential for on-site detecting oleanolic acid in real samples of fruits and food.

A Bifunctional Fluorescence Probe Based on AIE-ICT Strategy for Visual Detection of Cu2+/Co2+ in Complex Matrix

A novel fluorescence chemical sensor-based probe 1-{[(E)-(2-aminophenyl)azanylidene]methyl}naphthalen-2-ol (AMN) was designed and synthesized, which performed a "naked eye" detection ability toward Cu²⁺ and Co²⁺ based on aggregation-induced emission (AIE) fluorescence strategy. It has sensitive detection ability for Cu²⁺ and Co²⁺. In addition, the color changed from yellow-green to orange under the sunlight, realizing the rapid identification of Cu²⁺/Co²⁺, which has the potential of on-site visual detection under the "naked eye". Moreover, different "on" and "off" fluorescence expressions were exhibited under excessive glutathione (GSH) in AMN-Cu²⁺ and AMN-Co²⁺ systems, which could be employed to distinguish Cu²⁺ from Co²⁺. The detection limits for Cu²⁺ and Co²⁺ were measured to be 8.29 × 10^-8 M and 9.13 × 10^-8 M, respectively. The binding mode of AMN was calculated to be 2:1 by Jobs' plot method analysis. Ultimately, the new fluorescence sensor was applied to detect Cu²⁺ and Co²⁺ in real samples (tap water, river water, and yellow croaker), and the results were satisfying. Therefore, this high-efficiency bifunctional chemical sensor platform based on "on-off" fluorescence detection will provide significant guidance for the advance development of single-molecule sensors for multi-ion detection.

Development of a Fluorescein-Based Probe with an "Off-On" Mechanism for Selective Detection of Copper (II) Ions and Its Application in Imaging of Living Cells

Copper is a common metallic element that plays an extremely essential role in the physiological activities of living organisms. The slightest change in copper levels in the human body can trigger various diseases. Therefore, it is important to accurately and efficiently monitor copper ion levels in the human body. Recent studies have shown that fluorescent probes have obvious advantages in bioimaging and Cu²⁺ detection. Therefore, a novel Cu²⁺ probe (N2) was designed and synthesized from fluorescein, hydrazine hydrate and 5-p-nitrophenylfurfural that is sensitive to and can detect Cu²⁺ within 100 s. The response mechanism of the N2 probe to Cu²⁺ was studied by several methods such as Job's plots and MS analysis, which showed that the Cu²⁺ and the N2 probe were coordinated in a complexation ratio of 1:1. In addition, compared with other cations investigated in this study, the N2 probe showed excellent selectivity and sensitivity to Cu²⁺, exhibiting distinct fluorescence absorption at 525 nm. Furthermore, in the equivalent range of 0.1-1.5, there is a good linear relationship between Cu²⁺ concentration and fluorescence intensity, and the detection limit is 0.10 μM. It is worth mentioning that the reversible reaction between the N2 probe and Cu²⁺, as well as the good biocompatibility shown by the probe in bioimaging, make it a promising candidate for Cu²⁺ biosensor applications.

A color-change fluorescence sensor for oleanolic acid based on chiral camphanic decorated bis-cyanostilbene

Although various fluorescent sensors for biomolecules had been extensively reported, the effective fluorescent sensor was seldom reported for detecting oleanolic acid up to now. This work reports the first color-change fluorescence sensor for oleanolic acid based on a bridging bis-cyanostilbene derivative with chiral camphanic groups (C-BCS). C-BCS possessed the chartreuse fluorescence in aqueous media, which transferred to strong blue fluorescence in the presence of oleanolic acid. This sensing ability of C-BCS for oleanolic acid exhibited the high selectivity among all kinds of biomolecules and ions. The good linearity between the fluorescence intensity and concentration of oleanolic acid was acquired in the range of 0.2 × 10^-6 to 8.0 × 10^-6 M with the detecting limitation of 0.0582 μM. The 1:1 binding process was clarified as oleanolic acid located in the opening cavity composed of two bridging cyanostilbene units and two chiral camphanic groups based on multiple hydrogen bonds and hydrophobic interaction. The detecting ability of C-BCS was applied on sensing oleanolic acid in thin-layer chromatography analysis, imprinting experiment, tap water, and tea samples, suggesting the effective on-site sensing abilities of C-BCS for oleanolic acid in real samples and daily life.

Coumarin Xanthene Combined Probe for the Multi-Color Detection of Metal Ions and Electrospun Fibers Developed for Real-Time Monitoring

A coumarin-rhodamine (RhBC)-fused colorimetric/fluorescent probe was designed and synthesized. The probe is effective in Cu²⁺/Hg²⁺ ion sensing. With the added Cu²⁺ to RhBC in water: N, N-dimethyl formamide (8:2, v/v), the cyclic form of RhBC, is converted into the open ring form and shows a clear color change from yellow to red. In the presence of additional participating cations, this moiety shows effectiveness for Cu²⁺ and Hg²⁺ ions. The RhBC's detection limit by the UV-visible spectral method was 8.81 × 10^-6 M for Cu²⁺ ions and 2.26 × 10^-5 M for Hg²⁺ ions. The detection limit in the fluorescence titration spectra was 2.02 × 10^-7 M for Cu²⁺ ions and 6.11 × 10^-8 M for Hg²⁺ ions. A 1:1 stoichiometric ratio was validated between the probe and copper/mercury ions by the method of the job plot. Moreover, RhBC-combined polyurethane electrospun nanofibers were synthesized. These nanofibers could detect Cu²⁺ in real samples with no complications, with an instinctive color difference from yellow to red and a weak orange color for mercury ions.

A Near InfraRed Emissive Chemosensor for Zn2+ and Phosphate Derivatives Based on a Di-(2-picolyl)amine-styrylflavylium Push-Pull Fluorophore

A new Near InfraRed (NIR) fluorescent chemosensor for metal ions and anions is herein presented. The fluorophore is based on a styrylflavylium dye, a synthetic analogue of the natural anthocyanin family, with a di-(2-picolyl)amine (DPA) moiety as the metal chelating unit. The substitution pattern of the styrylflavylium core (with tertiary amines on positions 7 and 4') shifts the optical properties of the dye towards the NIR region of the electronic spectra, due to a strong push-pull character over the π-conjugated system. The NIR chemosensor is highly sensitive to the presence of Zn²⁺, which induces a strong CHelation Enhanced Fluorescence (CHEF) effect upon binding to the DPA unit (2.7 fold increase). The strongest competing ion is Cu²⁺, with a complete fluorescence quenching, while other metals induce lower responses on the optical properties of the chemosensor. Subsequent anion screening of the Zn²⁺-chemosensor coordination compound has demonstrated a distinct selectivity towards adenosine 5'-triphosphate (ATP) and adenosine 5'-diphosphate (ADP), with high association constants (K ~ 10⁶ M^-1) and a strong CHEF effect (2.4 and 2.9 fold fluorescence increase for ATP and ADP, respectively). Intracellular studies with the Zn²⁺-complexed sensor showed strong luminescence in the cellular membrane of Gram^- bacteria (E. coli) and mitochondrial membrane of mammalian cells (A659), which highlights its possible application for intracellular labelling.

Interplay of conformational relaxation and hydrogen bond dynamics in the excited states of fluorescent Schiff base anions

Time resolved fluorescence spectroscopic investigation of four Schiff base anions has established that their excited state dynamics is governed by several solvent properties: polarity, viscosity and hydrogen bond donating ability. With viscous protic solvents like glycerol, fluorescence lifetimes of anions have been found to be markedly longer than those in ethanol, implying that conformational relaxation of molecules plays a key role in their nonradiative relaxation. Surprisingly, the lifetimes in less viscous aprotic solvents, like acetonitrile, are found to be even longer. The only plausible rationalization of this observation is in the light of hydrogen bond-assisted nonradiative phenomena that are operative in protic solvents. This contention draws support from a time evolution of the emission in the red end of the spectrum in low to moderately hydrogen bond donating protic solvents, with regard to an absence of such a rise time in aprotic solvents and strongly hydrogen bond donating solvents, viz., 2,2,2-trifluoroethanol. Rudimentary quantum chemical calculations provide a preliminary idea about the nature of excited state hydrogen bond redistribution involved in the process.

Carbazole-thiophene based fluorescent probe for selective detection of Cu2+ and its live cell imaging

Highly sensitive and specific imaging of copper ion (Cu²⁺) in living cells is essential for better understanding the physiological and metabolic processes. We develop a novel fluorescent probe based on carbazole-thiophene for specific Cu²⁺ detection in living cells. Job's plot and density functional theory (DFT) confirmed a stoichiometric ratio of 2:1 between the probe molecules and Cu²⁺. This probe exhibits strong fluorescence in aqueous media, while its fluorescence intensity significantly decreased in the presence of Cu²⁺. An in vitro assay shows that the fluorescent probe has rapid response within 5 s and high sensitivity for the detection of Cu²⁺ in the range from 1 to 10 μM with a detection limit of 0.29 μM. Live cell studies reveal that the fluorescent probe has good cell-membrane permeability and can successfully visualize the fluctuation of the intracellular Cu²⁺ concentration. In addition, the fluorescent probe has low cytotoxicity, which may provide a new tool for monitoring other analytes in living cells.

Relay detection of Cu2+ and bovine serum albumin by a dansyl derivative-based fluorescent probe

A dansyl derivative-based fluorescent probe, namely, DGly, was developed for relay detection of Cu²⁺ and bovine serum albumin (BSA) with high selectivity and sensitivity. The fluorescence intensity of DGly at 540 nm displayed "on-off-on" phenomenonafter Cu²⁺ and BSA were added in sequence. Correspondingly, the solution color changed from yellow to dark and then to yellowish white under 365 nm UV light irradiation; thus, the solution could be detected by the naked eye. The association constant of DGly-Cu²⁺ was stronger than that of DGly-BSA and DGly-Cu²⁺-BSA. Hence, BSA was detected after a complex was formed between DGly and Cu²⁺. The relay detection of Cu²⁺ and BSA was not influenced by other competitive interferents, and the detection limits of Cu²⁺ and BSA were 1.32 and 0.26 μM, respectively. Analysis of Cu²⁺ in real water samples validated the detection performance of the method proposed herein; it achieved satisfactory recovery and relative standard deviation values. This work demonstrated that introducing metal ions can be an effective way to improve the sensitivity of BSA detection.

Development of lab-on-chip biosensor for the detection of toxic heavy metals: A review

Recently, a decrease in water availability and quality has been raised due to rapid industrialization, unsustainable agricultural activities and anthropogenic activities. Heavy metals are considered significant pollutants in the water environment, cause environmental hazards and health effects to humans. For monitoring water contaminants utilized different conventional techniques. Still, they have some drawbacks, such as cost expensive, ecological issues, and processing time, requiring technicians and researchers to operate them effectively. Biosensors have become reasonable devices for screening and identifying environmental contaminants because of their different benefits contrasted with other detecting techniques. This review summarizes the toxic effect of heavy metal and their source, occurrence. A detailed discussion is provided on the heavy metal recognition materials for detecting heavy metals in wastewater. Lab on chip (LOC) is an emerging micro-electrical mechanical system (MEMS) device that intakes liquid and makes it move through the micro-channels, to accomplish fast, cost-effective and profoundly sensitive analysis with significant yield. LOC also provided a discussion on numerous laboratory functions on a single platform. This article attempts to discuss the detection of heavy metals using lab on a chip by suitable recognition materials. Further, the design and fabrication mechanism and their recognition abilities of LOC were also reviewed. The review mainly focuses on the application of LOC biosensors, pros, and cons, and suggests a roadmap towards future development to enhance the practical use in pollutant monitoring.

Theoretical study on the optical properties of an ESIPT-based fluorescent probe for phosgene

A fluorescent probe Pi with the excited-state intramolecular proton transfer (ESIPT) properties was synthesized and used to detect the phosgene in solution and gas phases. However, the detection mechanism of the fluorescent probe needs to be further studied. Herein, the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods were adopted to explore the molecular structures and electronic spectra properties of probe and its product Pio after reacting with phosgene. Through analysis for molecular structure parameters and infrared vibrations accompanied with the hydrogen bond of Pi, it is confirmed that the intramolecular hydrogen bond of Pi is enhanced under light excitation, which illustrates the occurrence of ESIPT reaction combined with the scanned potential energy curves. It can be seen from the simulated spectra that Pi shows double fluorescence through ESIPT process, while the fluorescent product Pio exhibits the single fluorescence due to the disappearance of intramolecular hydrogen bond. Through the study on the structure and optical properties of Pi and Pio, it can be helpful to deeply understand the intrinsic mechanism of the detection of phosgene by the Pi molecule probe, which also supplies a reference to the further study about the fluorescence probe.