A highly specific and sensitive turn-on fluorescence probe for hypochlorite detection and its bioimaging applications

Development of high performance fluorescent chemosensors for the detection of ClO⁻in vitro and in vivo is very desirable, because many human diseases are caused by ClO⁻. In this paper, a highly selectivity and sensitive fluorescent probe, EDPC, based on 3-acetylcoumarin, was synthesized, which could respond to ClO⁻ and exhibit an “off–on” mode in Tris–HCl buffer (pH = 7.2, 10 mM, 50% C₂H₅OH) solutions. The detection limit of the EDPC probe for ClO⁻ was as low as 1.2 × 10⁻⁸ M. Moreover, the high selectivity and high sensitivity of EDPC towards ClO⁻ are attributed to the oxidation reaction between the C–O of the coumarin lactone and the C C formed by aldol condensation and the mechanism was further verified using ESI-MS and DFT. Additionally, the concentrations of ClO⁻ in real water were also calculated using the EDPC probe and showed good recovery. Finally, the distribution of intracellular endogenous ClO⁻ was gained by confocal fluorescence microscopy in living HEK293T cells.

A new probe, EDPC, was designed and synthesized for highly specific and sensitive detection of ClO⁻ with a fast response time in living cells.     

A simple colorimetric and ratiometric fluoride ion probe with large color change

Two colorimetric and ratiometric fluoride ion probes SHJ-1 and SHJ-2 based on the acylhydrazone skeleton have been developed. Among the eight anions (F⁻, Cl⁻, Br⁻, I⁻, ClO₄⁻, H₂PO₄⁻, HSO₄⁻, CH₃COO⁻), the present probes showed high selectivity and sensitivity toward fluoride ion detection with obvious color change. Notably, the probe SHJ-1 exhibited a red shift of 145 nm upon fluoride sensing, which is the largest value among fluoride ion probes based on acylhydrazone derivates to date. ¹HNMR titration study and theoretical calculations suggested that the strong binding of the probe SHJ-1 to fluoride as well as the further deprotonation may facilitate the intramolecular charge transfer transition. These two probes are 1 : 1 complexed with fluoride ions, and the detection limits were calculated to be 1.24 μM for SHJ-1 and 15.73 μM for SHJ-2.

Two colorimetric and ratiometric fluoride ion probes SHJ-1 and SHJ-2 based on the acylhydrazone skeleton have been developed.     

Green synthesis of surface-passivated carbon dots from the prickly pear cactus as a fluorescent probe for the dual detection of arsenic(iii) and hypochlorite ions from drinking water

Efforts were made to develop a simple new approach for the green synthesis of surface-passivated carbon dots from edible prickly pear cactus fruit as the carbon source by a one-pot hydrothermal route. Glutathione (GSH) was passivated on the surface of the CDs to form a sensor probe, which exhibited excellent optical properties and water solubility. The prepared sensor was successfully characterized by UV-visible spectrophotometry, fluorescence spectrophotometry, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The simple sensing platform developed by the GSH-CDs was highly sensitive and selective with a “turn-off” fluorescence response for the dual detection of As³⁺ and ClO⁻ ions in drinking water. This sensing system exhibited effective quenching in the presence of As³⁺ and ClO⁻ ions to display the formation of metal complexes and surface interaction with an oxygen functional group. The oxygen-rich GSH-CDs afforded a better selectivity for As³⁺/ClO⁻ ions over other competitive ions. The fluorescence quenching measurement quantified the concentration range as 2–12 nM and 10–90 μM with the lower detection limit of 2.3 nM and 0.016 μM for the detection of As³⁺ and ClO⁻ ions, respectively. Further, we explored the potential applications of this simple, reliable, and cost-effective sensor for the detection of As³⁺/ClO⁻ ions in environmental samples for practical analysis.

Efforts were made to develop a simple new approach for the green synthesis of surface-passivated carbon dots from edible prickly pear cactus fruit as the carbon source by a one-pot hydrothermal route.     

Novel fluorescent probes for the fluoride anion based on hydroxy-substituted perylene tetra-(alkoxycarbonyl) derivatives

The fluoride anion (F⁻) sensing abilities of 1-hydroxyl-3,4,9,10-tetra (n-butoxyloxycarbonyl) perylene (probe 1) and 1-hydroxyl-mono-five-membered S-heterocyclic annulated tetra (n-butoxyloxycarbonyl) perylene (probe 2) were studied through visual detection experiments, UV-Vis, fluorescence, and ¹H NMR titrations. The probes were sensitive and selective for distinguishing F⁻ from other anions (Cl⁻, Br⁻, I⁻, SO₄⁻, PF₆⁻, H₂PO₄⁻, BF₄⁻, ClO₄⁻, OH⁻, CH₃COO⁻, and HPO₄²⁻) through a change of UV-Vis and fluorescence spectra. The absorption and fluorescence emission properties of the probes arise from the intermolecular proton transfer (IPT) process between a hydrogen atom on the phenolic O position of probe and the F⁻ anion. The sensing mechanism was supported by theoretical investigation. Moreover, probe-based test strips can conveniently detect F⁻ without any additional equipment, and they can be used as fluorescent probes for monitoring F⁻ in living cells.

The fluoride anion (F⁻) sensing abilities of two fluorescent probes based on hydroxy-substituted perylene tetra-(alkoxycarbonyl) derivatives were studied through visual detection experiment, UV-Vis, fluorescence, and ¹H NMR titrations.     

A methylene blue-based near-infrared fluorescent probe for rapid detection of hypochlorite in tap water and living cells

A methylene blue-based near-infrared fluorescent probe was designed for the selective determination of hypochlorite (ClO⁻), over other reactive oxygen species or interfering agents. Acetylated methylene blue was synthesized by introducing the acetyl group into the methylene blue framework, which can specifically recognize exogenous and endogenous ClO⁻. The acetylated methylene blue fluorescent probe was characterized by ¹H NMR, ¹³C NMR and HRMS. The response process and possible mechanism were studied using products of the probe. The emission response of the probe to ClO⁻ presented good linear relationship in the 0–60 μM concentration range, with the detection limit of 0.1 μM (measured at 660 nm and 690 nm). The absorption and emission wavelengths of acetylated methylene blue are both in the near-infrared region; in addition, the probe itself and the degradation products were well-dissolved in water and have almost no toxicity. The probe was used for intracellular ClO⁻ imaging and showed a large fluorescence enhancement (about 200-fold increase).

We developed a MB-based probe to detect OCl⁻, whose product is almost non-toxic. The fluorescence enhancement times are large.     

Design and controllable synthesis of ethylenediamine-grafted ion imprinted magnetic polymers for highly selective adsorption to perchlorate

A series of ethylenediamine-grafted ion imprinted magnetic polymers (Fe₃O₄@IIPs) were synthesized via ultrasonic assisted suspension polymerization with perchlorate (ClO₄⁻) as an ion imprinting template. They were characterized by XRD, EA, VSM, FTIR and XPS and applied as adsorbents for ClO₄⁻ removal from aqueous solutions. The effects of the usage amount of crosslinking agent divinylbenzene (DVB) used for preparation on the structure and the adsorptive performance of Fe₃O₄@IIPs were investigated. The results show that the Fe₃O₄@IIPs have an average size of 200–800 nm, which increases with the increase of the amount of DVB from 0 to 2 g during the preparation process. The saturation magnetization intensities are at 35.6–42.8 emu g⁻¹, which decrease with the increase of the usage amount of DVB. The addition of DVB is beneficial to the formation and stability of the ion imprinted cavity of Fe₃O₄@IIPs. The effects of the solution pH value, initial concentration of ClO₄⁻, and adsorption time on the adsorption properties of ClO₄⁻ in aqueous solutions were investigated. The results show that the adsorption capability is affected significantly by solution pH value and reaches the maximum adsorption capacity at pH 3.0. The best adsorption capacity and selectivity of Fe₃O₄@IIPs to ClO₄⁻ can be obtained when the usage amount of DVB is at 0.5 g for synthesis. The adsorption mechanisms might include both ion exchange and electrostatic interaction. The isothermal adsorption curves mainly obey the Langmuir model with the theoretical maximum adsorption capacities (q_m,c) at 76.92–111.1 mg g⁻¹ and the experimental maximum adsorption capacities (q_m,e) at 75.7–108.9 mg g⁻¹, respectively, which are much higher than those of the non-ion imprinted material (Fe₃O₄@NIP, q_m,NIP: q_m,c at 60.61 mg g⁻¹ and q_m,e at 59.0 mg g⁻¹). The adsorption kinetic studies show that the adsorption processes reach equilibrium within 10 min and the kinetic data are well fitted to the pseudo-second-order model. There is almost no interference by the coexisting anions for the selective adsorption of ClO₄⁻, with a imprinting factor (α) at 1.8, and selectivity factor (β) larger than 5.9 for several kinds of common co-existing anions, respectively. The Fe₃O₄@IIPs are ideal candidates for removal of ClO₄⁻ from aqueous solution.

A series of ethylenediamine-grafted ion imprinted magnetic polymers (Fe₃O₄@IIPs) were synthesized via ultrasonic assisted suspension polymerization with perchlorate (ClO₄⁻) as an ion imprinting template.     

Gum acacia-based silver nanoparticles as a highly selective and sensitive dual nanosensor for Hg(ii) and fluorescence turn-off sensor for S2− and malachite green detection

A facile and green method was adopted to synthesize highly selective gum acacia-mediated silver nanoparticles as dual sensor (fluorescence turn-on and colorimetric) for Hg(ii) and fluorescence turn-off sensor for S²⁻ and malachite green. The mechanism proposed for a dual response towards Hg(ii) is the redox reaction between Ag(0) and Hg(ii), resulting in the formation of Ag(i) and Hg(0) and electron transfer from gum acacia to Ag(i), which further leads to the formation of an Ag@Hg nanoalloy. The enhanced fluorescence signal was quenched selectively by S²⁻ owing to the formation of Ag₂S and HgS. The reported nanosensor was found to be useful for sensing malachite green via the inner filter effect. The linear ranges were 3 nmol L⁻¹ to 13 μmol L⁻¹ for Hg(ii), 3–170 μmol L⁻¹ for S²⁻ and 7–80 μmol L⁻¹ for malachite green, and the corresponding detection limits were 2.1 nmol L⁻¹ for Hg(ii), 1.3 μmol L⁻¹ for S²⁻ and 1.6 μmol L⁻¹ for malachite green.

Gum acacia-stabilized silver nanoparticles for the detection of Hg(ii), S²⁻ and malachite green.     

A coumarin Schiff's base two-photon fluorescent probe for hypochlorite in living cells and zebrafish

Selective and sensitive fluorescent probes for ClO⁻ are desirable due to the importance of ClO⁻ in biological processes. Here, a coumarin Schiff''s base, compound 1, has been developed and successfully used as a one- and two-photon fluorescent probe for ClO⁻ with high selectivity. This probe can recognize ClO⁻ with obvious color change from yellow-green to colorless and green to blue fluorescence emission, which can be observed by the naked eye. The properties of low cytotoxicity and good cell permeability allow it to be used for ClO⁻ detection in living cells and zebrafish by both one- and two-photon microscopy imaging. All these results indicate that the compound is a sensitive probe with potential for analysis of ClO⁻ in biological samples. The mechanism by which probe 1 recognizes ClO⁻ is possibly nucleophilic addition followed by hydrolysis.

A coumarin Schiff''s base compound can selectively recognize ClO⁻ and can be successfully applied to the detection of ClO⁻ in living cells and zebrafish by one- and two-photon fluorescence modes.     

Chemosensors based on N-heterocyclic dyes: advances in sensing highly toxic ions such as CN− and Hg2+

CN⁻ and Hg²⁺ ions are harmful to both the environment and human health, even at trace levels. Thus, alternative methods for their detection and quantification are highly desirable given that the traditional monitoring systems are expensive and require qualified personnel. Optical chemosensors (probes) have revolutionized the sensing of different species due to their high specificity and sensitivity, corresponding with their modular design. They have also been used in aqueous media and different pH ranges, facilitating their applications in various samples. The design of molecular probes is based on organic dyes, where the key species are N-heterocyclic compounds (NHCs) due to their proven photophysical properties, biocompatibility, and synthetic versatility, which favor diverse applications. Accordingly, this review aims to provide an overview of the reports from 2016 to 2021, in which fluorescent probes based on five- and six-membered N-heterocycles are used for the detection of CN⁻ and Hg²⁺ ions.

This review considers the most recent advances in sensing highly toxic ions such as CN⁻ and Hg²⁺. Specifically, probes bearing N-heterocyclic compounds for their proven versatility for applications in the development of chemosensors are analyzed.     

Efficient one-pot green synthesis of tetrakis(acetonitrile)copper(i) complex in aqueous media

New simple, fast, effective and environmentally friendly one-pot method for the synthesis of extensively used tetrakis(acetonitrile)copper(i) complexes with BF₄⁻, PF₆⁻ and ClO₄⁻ counterions is invented and optimized. The approach suggested allows using water as solvent and minimizes amounts of toxic organic reagents in the synthetic protocol.

New simple, fast, effective and environmentally friendly one-pot method for the synthesis of extensively used tetrakis(acetonitrile)copper(i) complexes with BF₄⁻, PF₆⁻ and ClO₄⁻ counterions is invented and optimized.     

Zinc(ii)-based coordination polymer encapsulated Tb3+ as a multi-responsive luminescent sensor for Ru3+, Fe3+, CrO42−, Cr2O72− and MnO4−

A zinc(ii)-based coordination polymer (CP), namely [Zn(modbc)₂]_n (Zn-CP) (modbc = 2-methyl-6-oxygen-1,6-dihydro-3,4′-bipyridine-5-carbonitrile), has been synthesized and characterized. Single-crystal structural determination reveals that Zn-CP is a two-dimensional framework structure with tetranuclear homometallic Zn₄(modbc)₄ units cross-linked by modbc. The excellent luminescence as well as good stability of Zn-CP do not enable it to have selective sensing capability for different ions. After encapsulation of Tb³⁺ in Zn-CP, the as-obtained fluorescent functionalized Tb³⁺@Zn-CP maintained excellent luminescence as well as stability, which made it a highly selective and sensitive multiresponsive luminescent sensor for Ru³⁺, Fe³⁺, CrO₄²⁻, Cr₂O₇²⁻, and MnO₄⁻ with high sensitivity, good anti-interference performance, and quick response time (∼10 s). The detection limits are 0.27 μM, 0.57 μM, 0.10 μM, 0.43 μM and 0.15 μM, respectively. A possible sensing mechanism was discussed in detail.

A composite, Tb³⁺@Zn-CP, for sensing Ru³⁺, Fe³⁺, CrO₄²⁻, Cr₂O₇²⁻ and MnO₄⁻ with fast response times was reported.     

Photoluminescent sea urchin-shaped carbon-nanobranched polymers as nanoprobes for the selective and sensitive assay of hypochlorite

This work reports donor–acceptor type sea urchin-like carbon nanobranched polymers (SUCNPs). As a novel carbon-based nanomaterial, SUCNPs were effectively synthesized for the first time through a facile and economical solvothermal approach employing uric acid and l-cysteine as nitrogen/sulfur sources. The nitrogen-rich structure of the heterocylic aromatic polymer led to a blue fluorescence at the excitation/emission maxima of 350/436 nm with robust photostability. SUNCPs showed highly selective ability towards hypochlorite (ClO⁻) against other relevant interfering substances. Upon exposure to a growing concentration of ClO⁻, SUCNPs fluorescence presented a gradual rise with a remarkable blue shift by virtue of the inhibition of photoinduced charge transfer (PCT) process. A linear relationship was established between the fluorescence intensity ratio (I_{401 nm}/I_{436 nm}) and the ClO⁻ concentration in the range of 0.1–200 μM. The detection limit was as low as 30 nM (3σ/k). The “turn-on” type nanoprobe was further used in real samples and paper-based analytical chips efficiently, implying its application in a sophisticated and convenient platform.

A photoluminescent sea urchin-like carbon nanobranched polymer has been prepared and applied for sensitive fluorescence recognition of hypochlorite.     

Comparative study on synchronous adsorption of arsenate and fluoride in aqueous solution onto MgAlFe-LDHs with different intercalating anions

In this study, a series of MgAlFe-LDHs (Cl⁻, NO₃⁻, intercalation, and calcined products of a CO₃²⁻ interlayer) was synthesized and used for adsorption of arsenate and fluoride in individual contaminants and coexisting pollutant systems. Effects of various factors such as initial pH of solution, dosage of materials, coexisting ions, contact time, and initial pollutant concentrations were evaluated. Experimental results showed that different intercalating anions had a significant effect on adsorption performance of arsenate and fluoride in water. The adsorption of arsenate and fluoride on MgAlFe-CLDH, MgAlFe–Cl-LDH or MgAlFe–NO₃-LDH can be described by different adsorption isotherm equations. During the simultaneous removal process, arsenate and fluoride competed for adsorption sites of the adsorbent materials, and the fluoride ions had advantages in the competitive adsorption on MgAlFe–Cl-LDH and MgAlFe–NO₃-LDH. MgAlFe–NO₃-LDH was used to adsorb arsenate and fluoride in coexisting pollution systems (the concentration of each pollutant was 2 mg L⁻¹, the adsorbent dosage was 1.5 g L⁻¹). The remaining arsenic concentration was reduced to less than 10 μg L⁻¹ and the remaining fluoride ion concentration to below 20 μg L⁻¹ which meets the World Health Organization''s, EPA''s and China''s drinking water standards for arsenic and fluoride limits. A possible mechanism is discussed with support from further XRD, SEM, and XPS analysis of the materials after their adsorption.

During the simultaneous removal process, arsenate and fluoride competed for the adsorption sites of the adsorbent materials.     

The sensing mechanism of a flavone-based ESIPT fluorescent chemodosimeter for selective recognition towards fluoride: a theoretical

The sensing mechanism of 3-hydroxyflavone-based (3-HF) fluorescent chemodosimeter 3-triisopropylsilylflavone (3-TPSF) for detecting fluoride (F⁻) has been theoretically investigated. The calculated Laplacian bond order confirms that the Si–O bond of 3-TPSF is the reaction site of F⁻. The free energy barrier of 18.33 kcal mol⁻¹ indicates that F-triggered desilylation reaction can occur and then form the anionic state of 3-HF (3-HF⁻) with a fluorescence peak at 545 nm. 3-HF⁻ captures H⁺ of the mixed aqueous medium to be transformed into 3-HF with an intramolecular hydrogen bond (O₁–H⋯O₂). The energy barrier of 1.86 kcal mol⁻¹ in the S₁ state obtained from the constructed potential energy curves confirms that the excited state intramolecular proton transfer (ESIPT) in 3-HF occurs to form a tautomer structure, which produces a long-wavelength emission of 549 nm. The fluorescence emitted from both 3-HF⁻ and 3-HF agrees with the experimental value of 530 nm appearing after adding F⁻. Charge transfer analyses indicate that the extent of intramolecular charge transfer in 3-HF⁻ is more intense than that of 3-TPSF, which induces a large Stokes shift of 180 nm. Therefore, the sensing mechanism is attributed to the combination of a large charge transfer feature and ESIPT that are caused by desilylation reaction. The significant fluorescence change makes 3-TPSF a chemodosimeter for detecting F⁻.

The sensing mechanism of 3-hydroxyflavone-based (3-HF) fluorescent chemodosimeter 3-triisopropylsilylflavone (3-TPSF) for detecting fluoride (F⁻) has been theoretically investigated.     

A highly selective fluorescent probe for detection of Cd2+ and HSO3− based on photochromic diarylethene with a triazole-bridged coumarin-quinoline group

A novel photochromic diarylethene containing a quinoline-linked 3-aminocoumarin Schiff base unit (1O) was synthesized and used for the selective detection of Cd²⁺ and HSO₃⁻. The synthesized probe exhibited a straightforward response for the selective detection of Cd²⁺. Its fluorescence emission red-shifted ∼126 nm and was enhanced 24.9 fold in the presence of Cd²⁺. Meanwhile, the fluorescence color of 1O changed from dark cyan to golden yellow. The binding stoichiometry between 1O and Cd²⁺ was determined to be 1 : 1. A molecular logic circuit with three inputs and one output was successfully constructed with its light and metal-responsive behaviors. In addition, 1O was able to selectively recognize HSO₃⁻ with a 135-fold enhanced fluorescence emission and a notable fluorescence color change from dark cyan to bright cyan. The ¹H NMR and mass spectrometry analyses suggest that the HSO₃⁻ sensing of 1O is based on the hydrolysis of the Schiff base group of 1O.

A novel photochromic diarylethene containing a quinoline-linked 3-aminocoumarin Schiff base unit (1O) was synthesized and used for the selective detection of Cd²⁺ and HSO₃⁻.     

A real-time ratiometric fluorescent probe for imaging of SO2 derivatives in mitochondria of living cells

A real-time ratiometric fluorescent probe (IN-CZ) for highly selective detection of sulfite was designed and synthesized, which is based on modulating the intramolecular charge transfer (ICT) of the hemicyanine dye platform. The mechanism of using the probe is mainly through the Michael addition that occurs between IN-CZ and sulfite with a detection limit of 2.99 × 10⁻⁵ M. IN-CZ displays a fast response (within 1 minute) and is highly selective for SO₃²⁻/HSO₃⁻ over ROS, biologically relevant ions, biological mercaptans and other reactive species. More importantly, IN-CZ was suitable for ratiometric fluorescence imaging in living cells, by real-time monitoring of SO₃²⁻/HSO₃⁻ changes in mitochondria targeted in living cells.

A real-time ratiometric fluorescent probe (IN-CZ) for highly selective detection of sulfite was designed and synthesized, which is based on modulating the intramolecular charge transfer of the hemicyanine dye platform.     

Application of pyrite and chalcopyrite as sensor electrode for amperometric detection and measurement of hydrogen peroxide

The sensing performance of solid-state amperometric sensors based on natural sulfide minerals, i.e., pyrite and chalcopyrite, has been characterized for the detection and measurement of hydrogen peroxide (H₂O₂) in aqueous medium. The sensors showed a wide linear relationship range between response current and the concentration of H₂O₂ from 1.0 × 10⁻⁵ mol L⁻¹ to 1.0 × 10⁻² mol L⁻¹ and 1.0 × 10⁻⁴ mol L⁻¹ to 3.0 × 10⁻² mol L⁻¹ for pyrite and chalcopyrite, respectively. The limit of detection (LOD) was as low as 8.6 × 10⁻⁶ mol L⁻¹ and 5.2 × 10⁻⁵ mol L⁻¹ (S/N = 3), respectively. The electrodes exhibited great sensitivity, repeatability and short response time (less than 5 s). The results show that pyrite and chalcopyrite can be used as a natural, low cost, reliable and sensitive sensor for hydrogen peroxide detection, creating a new and high value application for the sulfide minerals.

The sensing performance of solid-state amperometric sensors based on natural sulfide minerals, i.e., pyrite and chalcopyrite, has been characterized for the detection and measurement of hydrogen peroxide (H₂O₂) in aqueous medium.     

Electrochemical detection of 2-nitrophenol using a heterostructure ZnO/RuO2 nanoparticle modified glassy carbon electrode

A highly selective chemisensor for 2-nitrophenol detection was fabricated using ZnO/RuO₂ nanoparticles (NPs) synthesized by impregnation method. The as-synthesized NPs were characterized through UV-vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), Energy dispersive X-ray spectroscopy (EDS), FTIR and X-ray diffraction (XRD). A glassy carbon electrode was modified with as-synthesized ZnO/RuO₂ nanoparticles and utilized as a chemical sensor for the detection of 2-nitrophenol. The fabricated sensor exhibited excellent sensitivity (18.20 μA μM⁻¹ cm⁻²), good reproducibility, short response time (8.0 s.), the lowest detection limit (52.20 ± 2.60 pM) and long-term stability in aqueous phase without interference effects. Finally, the fabricated sensor was validated as a 2-NP probe in various environmental water samples at room conditions.

A highly selective chemisensor for 2-nitrophenol detection was fabricated using ZnO/RuO₂ nanoparticles (NPs) synthesized by impregnation method.     

Design and synthesis of stable indigo polymer semiconductors for organic field-effect transistors with high fluoride sensitivity and selectivity

We report the design and synthesis of two novel indigo donor–acceptor (D–A) polymers, PIDG-T-C20 and PIDG-BT-C20, comprising an indigo moiety that has intramolecular hydrogen-bonds as the acceptor building block and thiophene (T) and bithiophene (BT) as the donor building block, respectively. PIDG-T-C20 and PIDG-BT-C20 exhibited characteristic p-type semiconductor performance, achieving hole mobilities of up to 0.016 and 0.028 cm² V⁻¹ s⁻¹, respectively, which are highest values reported for indigo-based polymers. The better performing PIDG-BT-C20 was used for the fabrication of water-gated organic field-effect transistors (WGOFETs), which showed excellent stability at ambient conditions. The PIDG-BT-C20-based WGOFETs exhibited rapid response when fluoride ions were introduced to the water gate dielectric, achieving a limit of detection (LOD) of 0.40 mM. On the other hand, the devices showed much lower sensitivities towards other halide ions with the order of relative response: F⁻ ≫ Cl⁻ > Br⁻ > I⁻. The high sensitivity and selectivity of PIDG-BT-C20 to fluoride over other halides is considered to be realized through the strong interaction of the hydrogen atoms of the N–H groups in the indigo unit with fluoride ions, which alters the intramolecular hydrogen-bonding arrangement, the electronic structures, and thus the charge transport properties of the polymer.

A p-type indigo polymer semiconductor is developed for water-gated organic field-effect transistors (WGOFET) for sensing fluoride ions.     

A coumarin–dihydroperimidine dye as a fluorescent chemosensor for hypochlorite in 99% water

The hypochlorite anion (OCl⁻), a reactive oxygen species (ROS), is an important microbicidal agent in the immune system. Accurate and selective detection of OCl⁻ in environmental and biological samples by a fluorescent molecular sensor is an important subject. All previously reported sensors, however, have suffered from tedious multi-step synthesis for the sensors and the use of large amounts of organic solvents for the analysis. Herein, we report that a coumarin–dihydroperimidine dye prepared by facile condensation behaves as a fluorescent sensor for OCl⁻ in 99% water. The sensor exhibits weak fluorescence, but OCl⁻-selective dehydrogenation of its dihydroperimidine unit creates a strong blue fluorescence. This turn-on fluorescence response facilitates selective and sensitive detection of OCl⁻ in the physiological pH range. Ab initio calculation revealed that the fluorescence enhancement by OCl⁻ is triggered by intramolecular proton transfer from the coumarin –OH to the imine nitrogen of the formed perimidine moiety.

A coumarin–dihydroperimidine dye exhibits strong blue fluorescence by OCl⁻-selective dehydrogenation of the dihydroperimidine unit, and facilitates selective and sensitive fluorometric detection of OCl⁻ in 99% water.