A benzothiazole-based fluorescent probe for distinguishing and bioimaging of Hg 2+ and Cu 2+

Fast tracking of Hg2+ ions in living cells, food, and environmental samples using a new mitochondria-targeted red emitting probe and its portable applications

Mercury is one of the most hazardous heavy metals and is capable of biomagnification, thereby posing severe risks to ecosystems and human health. Therefore, selective, sensitive, and rapid detection of Hg2+ in a wide range of samples is essential. Herein, we report the synthesis of a new 2-(benzo[d]thiazol-2-yl) phenol-based fluorescent probe (PyS) and its potential as a fluorescent probe for detecting Hg2+ ions in various real samples such as rice, garlic, shrimp, and root samples. When interacting with Hg2⁺, the non-fluorescent probe solution emitted strong red fluorescence at 638 nm in a solution of DMSO/H2O (1/9, v/v). The other ions showed no significant interference during Hg2+ detection. In addition, PyS displayed a rapid response time among the reaction-based systems (3-4 min), low detection limit (72.5 nM), linear response trend in the range of 0-22.00 μM, and large Stokes shift (243 nm). Additionally, PyS can serve as a paper, cotton swab, and polysulfone capsule kit for qualitative detection of Hg2⁺, enabling on-site quantitative detection of Hg2⁺ in beach soil and water samples using a smartphone app. It also can effectively detect Hg2⁺ in living cells in a concentration-dependent manner, thereby highlighting its potential for bioimaging in living organisms.

Bright green cellulose-based fluorescent probe toward Au3+ smartphone technology recognition and its visualization application

In this study, a novel fluorescent probe, MAC-2, for the detection of Au3+ was designed and synthesised using cellulose as a carrier combined with benzothiazole derivatives. The structure of the probe was confirmed by SEM, XRD, FTIR, and 1H NMR, also the optical properties of the product were investigated. MAC-2 showed bright green fluorescence under a 365 nm UV lamp and exhibited significant quenching behaviour toward Au3+. MAC-2 utilises more sustainable biomass resources, featuring green and biodegradable characteristics that meet environmental requirements. Compared with most reported probes, it exhibits notable fluorescence properties. The limit of detection (LOD) is as low as 0.057 μM, and the response time is 1 min. It also demonstrates good specific recognition and anti-interference abilities. In addition, a smartphone was used as a portable signal processing device to achieve rapid detection of Au3+ concentration. Meanwhile, MAC-2 was successfully prepared as a fluorescent test strip, providing a potential application for the convenient detection of Au3+. The high sensitivity and selectivity exhibited by cellulose-based fluorescent probes in detecting Au3+ offer valuable insights and new ideas for the detection of other metal ions and biomolecules. These inspirations will help promote the continuous development of research and applications in related fields.

Bifunctional materials based on poly(3-aminocarbazole) for efficient and highly selective detection and adsorption of Hg2+ in water

Herein, two poly(3-aminocarbazole) derivatives containing imidazole N-type acceptor were synthesized and reported, which are named PCPI and PCBI respectively. The fluorescence spectrum shows that PCPI (Em = 498 nm) and PCBI (Em = 398 nm) both have a strong fluorescence emission. It is worth noting that PCPI has a larger stokes shift of 153 nm, which is beneficial for improving the sensitivity of the sensor and enhancing its anti-interference ability. As expected, our experimental results indicate that both PCPI and PCBI can cause a specific response of "fluorescence OFF" to Hg2+ compared with other ions. And PCPI and PCBI both have excellent detection capabilities for Hg2+, with detection limits of 69.8 nM and 11.4 nM respectively. Moreover, PCBI exhibits excellent absorption of Hg2+ with a maximum absorption capacity of 477.8 mg/g at 20 °C. It indicates that PCBI can be used as a functional material for the detection and removal of Hg2+ in water.

A Novel AIE-Active Salicylaldehyde-Schiff Base Probe with Carbazole Group for Al3+ Detection in Aqueous Solution

A donor-acceptor Schiff-base fluorescent probe BKS with chelation enhanced fluorescence (CHEF) mechanism was designed and synthesized via benzophenone(Acceptor), salicylaldehyde and carbazole(Donor) for Al3+ detection, which exhibited typical aggregation-induced emission (AIE) characteristic. BKS probe could provide outstanding selectivity to Al3+ with a prominent fluorescence "turn-on" at 545 nm in a wide pH range from 2 to 11. By the Job's plot, the binding stoichiometry ratio of probe BKS to Al3+ was determined 1:1. The proposed strategy offered a very low limit of detection at 1.486 µM in THF/H2O(V/V = 1:4, HEPBS = 10 mM, pH = 7.40), which was significantly lower than the standard of WHO (Huang et al., Microchem J 151:104195, 2019)-(Yongjie Ding et al., Spectrochim Acta Mol Biomol Spectrosc 167:59-65, 2021) guidelines for drinking water. BKS probe could provide a wider linear detection range of 50 to 500 µM. Furthermore, the probe could hardly be interfered by other examined metal ions. The analysis of Al3+ in real water samples with appropriate recovery (100.72 to 102.85) with a relative standard deviation less than 2.82% indicated the accuracy and precision of BKS probe and the great potential in the environmental monitoring of Al3+.

Review on Synthesis of 2-(2-Hydroxyaryl) Benzothiazoles (HBT) for Excited-State Intra-molecular Proton Transfer (ESIPT)-Based Detection of Ions and Biomolecules

In this review, we present a systematic and comprehensive summary of the recent developments in the synthetic strategies of 2-(2-hydroxyarylsubstituted)-benzothiazole (HBT) framework along with incorporation of various substituents on phenolic and benzothiazole rings which affect the emission process. The literature, spanning the years 2015-2024, on excited-state intramolecular proton transfer (ESIPT)-based studies of HBT derivatives comprising the effects of solvent polarity, substituents, and extended conjugation on fluorophores has been searched. ESIPT, intramolecular charge transfer, and aggregation-induced emissions enable these fluorescent probes to specifically interact with analytes, thereby altering their luminescence characteristics to achieve analyte detection. These fluorescent probes exhibit large Stokes shifts, high quantum yields, and excellent color transitions. Finally, the applications of HBTs as ESIPT-based fluorescent probes for the detection of cations, anions, and biomolecules have been summarized. We anticipate that this review will provide a comprehensive overview of the current state of research in this field and encourage researchers to develop novel ESIPT-based fluorophores with new applications.

Ratio-fluorescent and naked-eye visualized dual-channel sensing strategy for Cu2+ and alkaline phosphatase activity assay

The levels of Cu2+ and alkaline phosphatase (ALP) are the important indicators of the developed stage of the relative diseases. Herein, a binary ratio-fluorescent and smartphone-assisted visual strategy basing on 4'-aminomethyl-4, 5', 8-trimethylpsoralen (AMT) and the oxidation of o-phenylenediamine was developed. Under the action of Cu2+, the fluorescent molecule, 3-diaminophenazine (DAP) formed which can act as a fluorescent acceptor of the ratio-fluorescent sensor. The emission spectrum of AMT overlapped with the excitation spectrum of DAP and, thus, it can act as the fluorescent donor of the ratio-fluorescent sensor. With the increasing concentration of Cu2+ and ALP, the fluorescent intensity of AMT decreased and the fluorescent intensity of DAP increased. The dual-emission reverse change ratio-fluorescent sensor realized the sensitive detection Cu2+ and ALP with the detection limits of 2 nM and 0.03 U/mL, respectively. In addition, the acceptable recoveries were obtained when the Cu2+ and ALP in spiked samples were detected. Furthermore, the relative activity of ALP was assessed by increasing the concentrations of the inhibitor Na3VO4 and IC50 of 25 μM was obtained. Importantly, the target concentration-dependent color change of DAP allowed us to utilize R/B ratio values to design the smartphone-assisting visual detection model of Cu2+ and ALP activity with the detection limits of 0.1 μM and 0.18 U/mL. This simple, flexible, dual-mode sensor strategy has a potential for disease diagnosis and drug screening.

Pyrene-Based "Turn-On" Fluorescent Polymeric Probe with Thioacetal Units in the Main Chain for Mercury(II) Detection in Aqueous Solutions and Living Cells

A water-soluble polymeric pyrene-based polythioacetal (PTA-Py) with thioacetal units in the main chain is simply synthesized by direct polycondensation of 3, 6-dioxa-1, 8-octanedithiol, 1-pyrene formaldehyde, and mPEG2k-SH. The probe PTA-Py shows a good fluorescence response to Hg2+ ions due to the Hg2+-promoted deprotection reaction of thioacetal groups to regenerate the original 1-pyrene formaldehyde compound. After adding Hg2+ to the PTA-Py solution, the fluorescence intensity (FI) gradually increases with increasing concentrations of Hg2+. Compared with other metal ions, the probe exhibits high sensitivity, good selectivity, and rapid response to Hg2+. The low detection limits are 12.3 nm in ethanol-PBS buffer and 13.3 nm in water, respectively. The results imply that the simply synthesized water-soluble polymeric probe had potential applications in the rapid detection of Hg2+ ions in aqueous solutions. Moreover, the polymeric PTA-Py shows high sensitivity for CH3Hg+ with detection limits of 26.5 nm in ethanol/PBS buffer. In addition, PTA-Py can efficiently detect Hg2+ ions in HeLa cells. The results demonstrate that a valuable method is developed for biocompatible polymeric sensors for Hg2+ ions in biological and environmental samples.

Triphenylamine-Based Polythioacetal for Selective Sensing of Mercury(II) with High Specificity and Sensitivity

Utilizing the mercury (Hg2+)-triggered deprotection of thioacetals to aldehyde groups, we constructed a water-soluble triphenylamine (TPA)-based polythioacetal PTA-TPA with thioacetal groups in the backbones for efficient sensing of Hg2+ in aqueous solutions. PTA-TPA is conveniently prepared by polycondensation of 3, 6-dioxa-1,8-octanedithiol (DODT) with 4-(N,N-diphenylamino) benzaldehyde (TPA-CHO) using thiol-terminated mPEG2k-SH as a capping agent. The interaction of Hg2+ with PTA-TPA activates the aggregation-induced emission (AIE) process of TPA-CHO molecules, which makes the emission enhanced, and the emission color changes to sky blue, while other metal ions do not interfere with the sensing process. PTA-TPA can be used as a highly selective and ultrafast detection system for Hg2+ with a low detection limit (LOD) of 9.88 nM and a fast response of less than 1 min. In addition, the prepared test strips report the presence of Hg2+ with an LOD as low as 1 × 10-5 M. Intracellular imaging applications have demonstrated that PTA-TPA acts as a biocompatible fluorescent probe for efficient Hg2+ sensing in HeLa cells. Overall, the PTA-TPA fluorescence probes have the characteristics of easy synthesis, cost-effective, ultrafast detection speed, high selectivity, and high sensitivity, which can be used in practical applications.

A terpyridyl-rhodamine hybrid fluorescent probe for discriminative sensing of Hg (II) and Cu (II) in water and applications for molecular logic gate and cell imaging

Sensitive and discriminative sensing of more than one analyte with a single fluorescent probe is significant and challenging. Herein a new terpyridyl-rhodamine hybrid, namely TRH, has been rationally designed and prepared with two responsive groups in the molecular structure, which facilitate the discriminative detection of Hg2+ and Cu2+ ions in water with detection limits of 4.9 and 53.3 nM by ratiometric fluorescence change (F595/F485) and fluorescence quenching, respectively. Investigations show that the selectivity to Hg2+ ions can be attributed to Hg2+-promoted spirolactam ring opening and further hydrolysis, followed by a through-bond energy transfer (TBET) process. The selective fluorescence quenching to Cu2+ ions probably can be ascribed to the binding Cu2+ to terpyridyl that triggers a ligand-to-metal charge transfer (LMCT) process, which can also efficiently inhibit the TBET process induced by Hg2+ ions and promotes the discriminative sensing of Cu (II) and Hg (II). In addition, the fluorescent responses to Hg2+ and Cu2+ ions cover a wide pH range. Moreover, a combinatorial logic gate with the functions of NOR and INHIBIT has been fabricated by using Hg2+ and Cu2+ ions as chemical input signals, and fluorescence at 485 and 595 nm as output signals. Besides, TRH also exhibits sensitive and discriminative sensing ability to Hg2+ and Cu2+ ions by the fluorescence of rhodamine fluorophore. Significantly, based on the fluorescence signal output of rhodamine moiety, TRH can be used as a tracer for the discriminative sensing of Hg2+ and Cu2+ ions by using living cells.

A highly selective and sensitive ICT-based Cu2+ fluorescent probe and its application in bioimaging

Cu²⁺ is an essential trace element for the organism, but its excess can also cause irreversible damage to the organism. As such, a "Turn-Off" fluorescent probe DPAP for the specific detection of Cu²⁺ was successfully constructed. DPAP exhibits large Stokes shift (120 nm), fast reaction speed (1 min), low detection limit (15.2 nM), low toxicity, and good cell permeability. Cu²⁺ quenches the fluorescence of DPAP by blocking its intramolecular charge transfer process to achieve the detection of Cu²⁺ and has been confirmed by HRMS, ¹H NMR and DFT calculations. Excitingly, the five-cycle detection of Cu²⁺ and the successful recovery of trace Cu²⁺ in environmental water samples fully demonstrate the potential of DPAP for practical applications. In particular, DPAP can observe the distribution and translocation patterns of exogenous Cu²⁺ in HeLa cells and zebrafish in real-time. This research concept has offered important theoretical support for the study of the environmental behavior of heavy metal ions.

Heterocyclic Organic Compounds as a Fluorescent Chemosensor for Cell Imaging Applications: A Review

Fluorometric determination of different biologically, industrially, and environmentally important analytes is a powerful technique because this technique has excellent selectivity, high sensitivity, rapid photoluminescence response, low cost, applicability to bioimaging, and low detection limit. Fluorescence imaging is a powerful technique for screening different analytes in the living system. Heterocyclic organic compounds have been extensively used as a fluorescence chemosensor for the determination of different biologically important cations like Co2+, Zn2+, Cu2+, Hg2+, Ag+, Ni2+, Cr3+, Al3+, Pd2+, Fe3+ Pt2+, Mn2+, Sn2+, Pd2+, Au3+, Pd2+, Cd2+, Pb2+ and other ions in biological and environmental systems. These compounds also showed significant biological applications such as anti-cancer, anti-ulcerogenic, antifungal, anti-inflammatory, anti neuropathic, antihistaminic, antihypertensive, analgesic, antitubercular, antioxidant, antimalarial, antiparasitic, antiglycation, antiviral anti-obesity, and antibacterial potency. In this review, we summarize the heterocyclic organic compounds based on fluorescent chemosensors and their applications in bioimaging studies for the recognition of different biologically important metal ions.

A FRET-based ratiometric fluorescent probe for Hg2+ detection in aqueous solution and bioimaging in multiple samples

Mercury ion, as a metal cation with great toxic effect, is widely present in various production and living environments. It seriously threatens human health and environmental safety. It is of great significance to develop convenient and effective methods for mercury ion detection. Here, we designed and synthesized a new ratiometric fluorescent probe (namely APS-NA) for the detection of mercury ions in the environment and multiple biological samples. The probe is constructed by covalently connecting two fluorophores with lipolic acid to achieve fluorescence resonance energy transfer (FRET). In the molecular structure of APS-NA, acridone is used as an energy donor, 1,8-naphthalimide is used as an energy acceptor, and a dithioacetal group is used as the reaction site for Hg²⁺. The intact APS-NA mainly shows the green fluorescence from the acceptor moiety 1,8-naphthalimide; the presence of Hg²⁺ ions would break the dithioacetal linkage between acridone and 1,8-naphthalimide; the defunctionalization of FRET would lead to bright blue fluorescence emission of acridone; thus ratiometric fluorescent detection of Hg²⁺ can be achieved by this recognition process. The probe not only has a large Stokes shift (Δλ = 110 nm), but also has high selectivity, high sensitivity (low detection limit 30 nM) and naked eye visualization. In addition, we have successfully used this probe for the detection Hg²⁺ of actual samples and imaging of a variety of organisms. These results indicate that the probe has broad application prospects.

An ESIPT-based reversible ratiometric fluorescent sensor for detecting HClO/H2S redox cycle in living cells

HClO and H₂S, as two kinds of crucial small biomolecules, are endowed various roles in biological organisms. The redox balance between HClO and H₂S is closely related to the physiological and pathological processes. Thus, it is significant to monitor the redox process between HClO and H₂S. Inspired by the advantages of ratiometric fluorescent probes, we firstly developed a reversible ratiometric fluorescent probe (BT-Se) for HClO and H₂S via combination of phenyl selenide as the response group and 2-(2'-hydroxyphenyl)benzothiazole dye as the fluorophore. The proposed probe BT-Se could detect HClO with well-separated dual emission (110 nm), fast response, good selectivity and sensitivity owing to the oxidation reaction of the Se atom induced by HClO. Moreover, only H₂S could effectively recover the fluorescence of the detection system to the original state via H₂S induced-reduction of selenoxide. Cell imaging studies demonstrated that the probe BT-Se was capable of ratiometric monitoring the changes of intracellular HClO/H₂S, which suggested that it has great potential for researching the biological functions of HClO and H₂S.

Vinyl substituted triphenylamine based turn-off fluorescent probe for selective and sensitive detection of mercury (II) in water and live cells

Here, we report vinyl substituted triphenylamine (TPA-alk) fluorescent probe for the rapid and efficient detection of mercury ion (Hg²⁺) in water and biological environment. TPA-alk detects Hg²⁺ selectively over a wide range of competitive metal ions with a blue shift of 43 nm in the UV absorbance spectrum. The detection limit is found to be 0.146 µM (29.2 ppb) with high selectivity over a wide range of competitive metal ions. DFT study explains the blue shift in the UV-vis absorption band of the optical probe upon the addition of Hg²⁺. Cell viability assay illustrates that the probe is biocompatible and it has low cytotoxicity even at its higher concentration. Cell imaging studies demonstrate the efficiency of the TPA-alk probe for the micromolar detection of mercury (II) in live BMG1 cells.

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

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

A novel ESIPT-based fluorescent probe with dual recognition sites for the detection of hydrazine in the environmental water samples and in-vivo bioimaging

Hydrazine (N₂H₄), an important chemical intermediate, has been widely used in industrial production and agricultural life, but it has also caused environmental pollution. A novel ESIPT-based fluorescent probe with dual recognition sites, 2-(benzothiazole-2-yl)-1,4-imphenyl bis 4-bromobutyric acid (BRBA), was developed to selectively detect N₂H₄ under complex conditions. BRBA exhibits accurate detection for N₂H₄ with a good linear relationship ranging from 0 to 150 μM, and the LOD can reach 0.1 μM. Importantly, taking advantage of low cytotoxicity and a large Stokes shift, BRBA can be utilized to monitor environmental water samples and successfully applied to imaging HeLa cells and zebrafish.

Mitochondria-targetable colorimetric and far-red fluorescent sensor for rapid detection of SO2 derivatives in food samples and living cells

Sulfur dioxide (SO₂) derivatives are intertwined with many physiological and pathological processes in living systems, and excess intake of them are associated with various diseases. Herein, we have rationally constructed a novel colorimetric and far-red fluorescent probe for HSO₃^- based on a rhodamine analogue skeleton bearing a 3-quinolinium carboxaldehyde moiety. The novel probe exhibited a significant far-red fluorescence "Turn-on" response to HSO₃^-, along with obvious color change from reddish to purple via the specific 1,4-nucleophilic addition reaction of HSO₃^- with the quinolinium moiety in 3-(4-(2-carboxyphenyl)-7-(diethylamino)chromenylium-2-yl)-1-methylquinolin-1-ium hypochlorite trifluoromethanesulfonate (AQCB). The AQCB had excellent water-solubility, and presented rapid response (<15 s),highsensibility(LOD = 49 nM) and selectivity toward HSO₃^-. In addition, the probe was able to detect the content of HSO₃^- in food samples with satisfactory results. Furthermore, the probe possessed good cell membrane and could be successfully applied for imaging HSO₃^- in the mitochondria of living cells.

An AIE based fluorescent chemosensor for ratiometric detection of hypochlorous acid and its application

Detecting and imaging intracellular hypochlorous acid (HClO) is of great importance owning to its prominent role in numerous pathological and physiological processes. In this contribution, a novel AIE-based fluorescent chemosensor has been developed by employing a benzothiazole derivative. The synthesized probe displayed remarkable ratiometric fluorescent response to HClO with a large emission shift (139 nm), resulting in naked-eye fluorescence changes from red to blue. Under the optimal conditions, this probe was capable of quantitatively detecting HClO within 10 s, and possessed good sensitivity and high selectivity toward HClO over other biologically relevant species. Moreover, it has been successfully utilized to image the exogenous and endogenous HClO in living cells through dual channels, and conveniently detect hypochlorous acid solution on test strips with better accuracy, demonstrating its potential for monitoring HClO in biological and environment fields.

A dual-function luminescent probe for copper(II) ions and pH detection based on ruthenium(II) complex

A new ruthenium complex-based luminescent probe Ru-impa for Cu²⁺ and pH detection has been synthesized and characterized. Ru-impa could rapidly and selectively detect Cu²⁺ in aqueous solutions and the working pH ranges from weakly acidic to alkaline. The detection limit calculated using the S/N and S/B ratio was 24.7 nM and 3.4 μM, respectively. The test strips for practical detecting application were also prepared and the actual detection limit in drinking water was found to be 3 μM, which is lower than the WHO-guided drinking water limit (30 µM) and the upper limit of human serum free copper content (1.7-3.9 μM). Luminescence imaging study showed that Ru-impa could monitor Cu²⁺ level fluctuation in the cells. In addition, Ru-impa also shows a sensitive on-off luminescence response when pH > 10, indicating that it can also be used as a pH sensor under extremely alkaline conditions.

Dicyanoisophorone-based fluorescent probe with large Stokes shift for ratiometric detection and imaging of exogenous/endogenous hypochlorite in cell and zebrafish

A novel dicyanoisophorone-based red-emissive fluorescence probe (YT) with large Stokes shift (230 nm) was synthesized for rapid (<20 s) and selective detection of hypochlorite ions in nearly 100% aqueous medium. YT responded to hypochlorite ions via the ClO^--promoted oxidative deprotection of thioacetal, leading to a red shift in its fluorescence maximum from 590 nm to 640 nm accompanied by naked-eye color change from orange to red. The emission response of the probe toward ClO^- presented a good linear relationship in the 5-160 μM concentration range, with the LOD of 4.64 μM. Further, the probe YT was successfully employed in exogenous and LPS-induced endogenous imaging of ClO^- in live cells and zebrafish, demonstrating its potential applications in biological science.

A novel hydrazone-based fluorescent "off-on-off" probe for relay sensing of Ga3+ and PPi ions

A novel hydrazone-based fluorescent probe (E)-3-((2-(benzo[d]thiazol-2-yl)hydrazono)methyl)-4H-chromen-4-one (BTC) has been rationally designed and synthesized. BTC can subsequently detect Ga³⁺ and PPi ions through the absorption and emission off-on-off response with high specificity. Importantly, fluorescent probe BTC can well discriminate Ga³⁺ from Al³⁺ and In³⁺. The association constant (K) was calculated as 2.06 × 10⁴M^-1, and the limit of detection (LOD) was calculated as 4.88 × 10^-2μM. Competitive binding studies also illustrated good results of the probe BTC towards Ga³⁺. Job's plot and HRMS results substantiated the 1:1 stoichiometry between BTC and Ga³⁺ ion. The interaction binding mode of BTC with Ga³⁺ was proposed by HRMS, ¹H NMR spectral titration, UV-vis absorption and fluorescence spectral measurements. The combination of the restraint of the photo-induced electron transfer (PET) process and the chelation enhanced fluorescence (CHEF) process is responsible for the fluorescence enhancement of this probe. The in situ chelated BTC-Ga³⁺ could further monitor pyrophosphate ion (PPi) by demetallization process with quenching fluorescence emission. Additionally, the BTC and BTC-Ga³⁺ showed good cell permeability and could detect Ga³⁺ and PPi ions in onioninner epidermal cells, respectively.

A novel 1,8-naphthalimide-based Cu2+ ion fluorescent probe and its bioimaging application

A new 1,8-naphthalimide-based Schiff base compound, named as (Z)-2-butyl-6-(((2-hydroxyphenyl)imino)methyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (BHBD), has been simply synthesized with high yields. BHBD can be employed as a "turn-on" fluorescent probe for Cu²⁺ ion with high sensitivity, high selectivity and relatively low detection limit (0.48 × 10^-6 M). The fluorescence emission of BHBD is very weak in H₂O/THF (v/v: 7/3) mixture, which is significantly enhanced after addition of Cu²⁺ ion. The proposed mechanism is verified by ¹H NMR, Job's plot and TOF-MS experiments. Anti-interference experiment, cytotoxicity assay and pH influence results indicated that BHBD meets the requirements of bioimaging. Therefore, BHBD has been successfully applied in detecting Cu²⁺ ion in HeLa cells.

New Fluorescent Probes for the Sensitive Determination of Glyphosate in Food and Environmental Samples

In this paper, a dual-functional probe, 2-(benzothiazol)-4-(3-hydroxy-4-methylphenyl) imino phenol (BHMH), was synthesized and characterized for the simultaneous detection of Cu2+ and Fe3+ in dimethyl sulfoxide/4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (DMSO/HEPES) (1:4, v/v, pH = 6.0). The limits of detections (LODs) for Cu2+ and Fe3+ were 9.05 and 48 nM, respectively. Based on the competitive coordination, the complex BHMH-Cu2+/Fe3+ exhibited good sensitivity and selectivity for glyphosate. The LODs of BHMH-Cu2+ and BHMH-Fe3+ for glyphosate were 0.41 and 0.63 μM, respectively. The probe quantitatively detected glyphosate in tap water, Songhua River water, local water and soil, and food samples. The colorimetric on-site glyphosate sensing through the probe BHMH-Cu2+ was also studied based on smartphones. BHMH and BHMH-Cu2+/Fe3+ exhibited outstanding imaging capabilities for Cu2+, Fe3+, and glyphosate in living cells with low cytotoxicity, especially the first time for glyphosate.

A bifunctional fluorescent probe for sensing of Al3+ and H2S

Al3+ and H2S play essential roles in various physiological processes. However, excess Al3+ and H2S are harmful to health. Therefore, it is necessary to design a sensitive method for the detection of Al3+ and H2S. In this work, compound L was developed based on salicylaldoxime and 4-aminobenzamide. L displayed aggregation-induced emission (AIE) characteristics in the solid state due to a unique dimer formation via intermolecular hydrogen bonds. In addition, L could serve as a multi-responsive fluorescence probe for Al3+ based on the coordination reaction in a MeOH/H2O (9/1, v/v, pH = 7.4) medium and for H2S based on the addition reaction in EtOH/H2O (7/3, v/v, pH = 7.4) solution. In addition, L showed a fluorescence colorimetric response to Al3+ in the solid state. Furthermore, L was applied to detect Al3+ and H2S in actual water samples.

White light employing luminescent engineered large (mega) Stokes shift molecules: a review

Large (mega) Stokes shift molecules have shown great potential in white light emission for optoelectronic applications, such as flat panel display technology, light-emitting diodes, photosensitizers, molecular probes, cellular and bioimaging, and other applications. This review aims to summarize recent developments of white light generation that incorporate a large Stokes shift component, key approaches to designing large Stokes shift molecules, perspectives on future opportunities, and remaining challenges confronting this emerging research field. After a brief introduction of feasible pathways in generating white light, exemplifications of large Stokes shift molecules as white light candidates from organic and inorganic-based materials are illustrated. Various possible ways to design such molecules have been revealed by integrating the photophysical mechanisms that are essential to produce red-shifted emission upon photoexcitation, such as excited state intramolecular proton transfer (ESIPT), intramolecular charge transfer (ICT), excited state geometrical relaxation or structural deformation, aggregation-induced emission (AIE) alongside the different formations of aggregates, interplay between monomer and excimer emission, host-guest interaction, and lastly metal to ligand charge transfer (MLCT) via harvesting triplet state. Furthermore, previously reported fluorescent materials are described and categorized based on luminescence behaviors on account of the Stokes shifts value. This review will serve as a rationalized introduction and reference for researchers who are interested in exploring large or mega Stokes shift molecules, and will motivate new strategies along with instigation of persistent efforts in this prominent subject area with great avenues.

A turn-on red-emitting fluorescent probe for determination of copper(II) ions in food samples and living zebrafish

Herein, we developed a turn-on red-emitting fluorescent probe for the sensitive and selective detection of copper ions (Cu²⁺) in food samples and living zebrafish. The probe employs a hemicyanine scaffold as the fluorophore and a 2-pyridinecarbonyl group as the recognition receptor and quenching moiety. The 2-pyridinecarbonyl moiety can be specifically cleaved by Cu²⁺ and results in an approximately 18-fold fluorescence enhancement of the probe, thereby providing a fluorescence turn-on assay for Cu²⁺. Additionally, the probe exhibited excellent selectivity, high sensitivity, a broad linear relationship (0.020 to 8.0 μM), and a low limit of detection (4.0 nM, S/N = 3) for Cu²⁺. Concomitantly, the probe exhibited satisfactory analytical performance when used with actual food samples. Moreover, the probe could be used for in situ determination of Cu²⁺ in both living plant tissues and in living zebrafish.

Highly selective detection of Cu2+ in aqueous media based on Tb3+-functionalized metal-organic framework

In this work, a metal-organic framework UiO-66-(COOH)₂ has been synthesized and is further functionalized with Tb³⁺ through coordination interactions. The functionalized MOF, denoted as Tb³⁺@UiO-66-(COOH)₂, is fully characterized and further developed as an excellent fluorescent probe to monitor Cu²⁺ ions in aqueous media by fluorescence quenching effect. Tb³⁺@UiO-66-(COOH)₂ exhibits high selectivity and sensitivity, broad linear concentration range (0-200 μM), low detection limits (0.23 μM), fast response speed (within 1 min), as well as in situ naked eye observation under UV light for sensing Cu²⁺ ion. Furthermore, this probe was successfully employed to detect Cu²⁺ ion in real water with good recovery. Hence, this work developed a very excellent fluorescent sensor with high potential practical applications for detection of Cu²⁺ ion in environmental water samples.

Colorimetric detection of Hg2+ with an azulene-containing chemodosimeter via dithioacetal hydrolysis

Azulene is a bicyclic aromatic chromophore that absorbs in the visible region. Its absorption maximum undergoes a hypsochromic shift if a conjugated electron-withdrawing group is introduced at the C1 position. This fact can be exploited in the design of a colorimetric chemodosimeter that functions by the transformation of a dithioacetal to the corresponding aldehyde upon exposure to Hg2+ ions. This chemodosimeter exhibits good chemoselectivity over other metal cations, and responds with an unambiguous colour change clearly visible to the naked eye. Its synthesis is concise and its ease of use makes it appropriate in resource-constrained environments, for example in determing mercury content of drinking water sources in the developing world.

Recent Progress in Small-Molecule Fluorescent Probes for Detecting Mercury Ions

Mercury is a highly toxic and non-essential element that is found in every corner of the globe. The small amount of mercury produced by various pathways eventually enters freshwater and marine ecosystems, circulating through the food chain (especially fish) and causing various environmental problems in aspects including plants, animals, and human. There are several traditional quantitative methods developed for mercury ions (II) analysis in water samples. However, due to the complexity of the detection process, high cost and strong technical expertise, it is difficult to detect mercury ions in real-time. Therefore, in recent years, a large number of researchers have developed small-molecule fluorescent probes for Hg ions detection. Fluorimetry has the advantages of convenient detection, short response time, high sensitivity and good selectivity. This review summarized the small-molecule fluorescent probes for mercuric ion detection developed in recent years according to the chemical structural classification, compared their performances and elaborated the mechanism. We hope that the review will help the researches for the designs of metal ions fluorescent probes and their applications with certain reference value.

A review on nanostructure-based mercury (II) detection and monitoring focusing on aptamer and oligonucleotide biosensors

Heavy metal ion pollution is a severe problem in environmental protection and especially in human health due to their bioaccumulation in organisms. Mercury (II) (Hg²⁺), even at low concentrations, can lead to DNA damage and give permanent harm to the central nervous system by easily passing through biological membranes. Therefore, sensitive detection and monitoring of Hg²⁺ is of particular interest with significant specificity. In this review, aptamer-based strategies in combination with nanostructures as well as several other strategies to solve addressed problems in sensor development for Hg²⁺ are discussed in detail. In particular, the analytical performance of different aptamer and oligonucleotide-based strategies using different signal improvement approaches based on nanoparticles were compared within each strategy and in between. Although quite a number of the suggested methodologies analyzed in this review fulfills the standard requirements, further development is still needed on real sample analysis and analytical performance parameters.

A dual-functional probe for sensing pH change and ratiometric detection of Cu2

A series of benzothiazole-based compounds were synthesized and characterized. Among them, probe Z showed significant dual-functional performance which was capable of sensing pH change and Cu²⁺. Probe Z displayed fluorescent turn-on under alkaline conditions due to deprotonation of the hydroxyl group along with the obviously color change from colorless to mint green. Interestingly, it further achieved in ratiometric detection of Cu²⁺ through absorbance or fluorescence signals in strong alkaline condition. The limit of detection was calculated correspondingly as 0.37 μM and 1.35 μM, respectively. Especially, the combination of the XNOR and INHIBIT logic gates could be used to confirm that one medium was in neutrality or alkalinity condition. Moreover, Z was successfully used in real water samples and test paper for fast identification of Cu²⁺, respectively.