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This paper presents the development of a photoelectrochemical sensor for hypochlorous acid (HOCl) detection, employing a phenothiazine-based organic photosensitizer (Dye-PZ). The designed probe, Dye-PZ, follows a D-π-A structure with phenothiazine as the electron-donating group and a cyano-substituted pyridine unit as the electron-accepting group. A specific reaction of the phenothiazine sulfur atom with HOCl enables selective recognition. The covalent immobilization of Dye-PZ onto a titanium dioxide nanorod-coated fluorine-doped tin oxide electrode (FTO/TiO 2 ) using bromo-silane coupling agent (BrPTMS) resulted in the fabrication of the photoanode FTO/TiO 2 /BrPTMS/Dye-PZ. The photoanode exhibited a significant photoresponse under visible-light irradiation, with a subsequent reduction in photocurrent upon reaction with HOCl. The oxidation of the phenothiazine sulfur atom to a sulfoxide diminished the internal charge transfer (ICT) effect. Leveraging this principle, the successful photoelectrochemical sensing of HOCl was achieved. The sensor showed high stability, excellent reproducibility, and selective sensitivity for HOCl detection. Our study provides a novel approach for the development of efficient photoelectrochemical sensors based on organic photosensitizers, with promising applications in water quality monitoring and biosensing.

This study developed a new photoelectrochemical (PEC) sensor for the detection of the hydrazine (N 2 H 4 , HZ) based on a donor-π-bridge-acceptor (D-π-A) configuration organic photoactive dye (Dye-HZ). The dye was covalently immobilized on an FTO/TiO 2 (FTO: fluorine-doped tin oxide) substrate, resulting in a photoanode FTO/TiO 2 /Dye-HZ that exhibits a specific PEC response to N 2 H 4 . Hydrazine reacts with the acetyl group in the Dye-HZ molecule, leading to its removal and the formation of a hydroxy group. The hydroxy group dissociates a hydrogen ion, forming a phenoxide anion with strong electron-donating characteristics. As a result, the dye molecule exhibits a strong intramolecular charge transfer effect, significantly enhancing absorbance and photoelectric response under visible light irradiation, leading to a remarkable increase in photocurrent and enabling highly sensitive detection of hydrazine. Furthermore, the PEC sensor demonstrates excellent selectivity and can be applied for the detection of hydrazine in real water samples. This study presents an innovative PEC sensing approach for hydrazine based on responsive photoactive molecules, providing new insights for PEC detection of other environmental pollutants., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Hydrazine (N 2 H 4 ) is a widely used raw material in the chemical industry, but at the same time hydrazine has extremely high toxicity. Therefore, the development of efficient detection methods is crucial for monitoring hydrazine in the environment and evaluating the biological toxicity of hydrazine. This study reports a near-infrared ratiometric fluorescent probe (DCPBCl 2 -Hz) for the detection of hydrazine by coupling a chlorine-substituted D-π-A fluorophore (DCPBCl 2 ) to the recognition group acetyl. Due to the halogen effect of chlorine substitution, the fluorophore has an elevated fluorescence efficiency and a lowered pKa value and is suitable for physiological pH conditions. Hydrazine can specifically react with the acetyl group of the fluorescent probe to release the fluorophore DCPBCl 2 , so the fluorescence emission of the probe system significantly shifted from 490 nm to 660 nm. The fluorescent probe has many advantages, such as good selectivity, high sensitivity, large Stokes shift, and wide applicable pH range. The probe-loaded silica plates can realize convenient sensing gaseous hydrazine with content down to 1 ppm (mg/m 3 ). Subsequently, DCPBCl 2 -Hz was successfully applied to detect hydrazine in soils. In addition, the probe can also penetrate living cells and allow the visualization of intracellular hydrazine. It can be anticipated that probe DCPBCl 2 -Hz will be a useful tool for sensing hydrazine in biological and environmental applications., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Dissolved oxygen (O 2 ) and hydrogen sulfide (H 2 S) are two important indicators of water quality, their levels are of intimate dependence and varying over time. It is of great significance to monitoring of dissolved O 2 and H 2 S simultaneously in natural water, yet has not been reported because of lack of effective approaches. In this work, a portable electrochemical microsensor was developed for simultaneously quantifying dissolved O 2 and H 2 S. Here, Pd@Ni nanoparticles (NPs) were self-assembled onto the microelectrode by MXene titanium carbide (Ti 3 C 2 T x ), which were of responsibility towards O 2 and H 2 S detection within single electrochemical reduction process. On this regard, Pd NPs facilitated catalyzing the electrochemical reduction of O 2 , while Ni NPs were employed as recognition element for H 2 S detection. With the electrochemical reduction sweep, the initial application of a positive voltage rendered the Ni to be oxidized to be Ni ions, contributing to their following capture of surrounding S 2- to form nickel sulfide. Nickel sulfide with highly electrochemical activity were capable of generating detecting reduction current. In consequence, the as-designed microsensor can simultaneously determine O 2 concentrations ranging from 36 to 318 μM and H 2 S levels ranging from 0.1 to 2.5 μM with high selectivity. Finally, the portable microsensor was successfully applied to simultaneous detection dissolved O 2 and H 2 S in natural water in-site, the results of which were comparable to the classical methods., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

It is highly desirable to develop high-performance ratiometric fluorescent probes for SO 2 derivative detection and realize their application in biological imaging. In this study, we report the rational design of a novel negative photochromic spiropyran derivative, spiro[azahomoadamantane-pyran] (MAHD-SP), with notable orange fluorescence in its stable ring-opened state without UV regulation. The unsaturated double bond of MAHD-SP underwent the Michael addition reaction of the SO 2 derivative, making the fluorescence quenching of MAHD-SP obvious. Then, MAHD-SP, a fluorescent conjugated polymer PFO and a polymeric surfactant PEO 113 -b-PS 49 were used to construct a ratiometric fluorescent polymeric nanoprobe (RFPN) via a coprecipitation method. The probe exhibited high sensitivity and selectivity for the ratiometric detection of SO 2 derivatives in pure aqueous solutions. Moreover, the good biocompatibility of RFPN can be used to visualize exogenous and endogenous SO 2 derivative generation in living cells., (© 2022. Springer-Verlag GmbH Germany, part of Springer Nature.)

Photoswitchable fluorescent materials are desirable for many applications because their emission signals can be easily modulated on demand. In this study, novel photoswitchable multistate fluorescent supramolecular polymers (PMFSPs) were prepared via host-guest interactions under a facile ultrasonication strategy. In the system, photochromic fluorescent diarylethylene monomer (SDTE, donor) and adamantane-containing monomer (BAC) were covalently combined into the backbone of the guest polymer (P1) via radical copolymerization. Meanwhile, the host moiety (CDSP, acceptor) was synthesized by covalent incorporation of photochromic spiropyran dye (SPCOOH) with β-cyclodextrin. By adjusting the stimulation wavelength and utilizing photoinduced fluorescence resonance energy transfer (FRET), the supramolecular polymers can undergo reversible tristate fluorescence switching among none, red, and green. In addition, due to the high contrast, rapid photoresponsiveness and prominent photoreversibility of the prepared PMFSPs, we demonstrated that they have great potential in advanced anti-counterfeiting and multilevel information encryption.

Rationally developing an intelligent tool for high-contrast fluorescence imaging of latent fingerprints (LFPs) is gaining much concern in many applications such as medical diagnostics and forensic investigations. Herein, the off-on fluorescent polymer micelles (PMs) have been rationally designed and synthesized for high-contrast fluorescence imaging of LFPs through the cross-linking reaction of hydrazine (N 2 H 4 ) and aldehyde group of polymer. Excitingly, the cross-linking (N 2 H 4 ) induced emission of PMs has the property of aggregation-induced emission (AIE) and excited state intramolecular proton transfer (ESIPT), which could effectively address the notorious aggregation-caused quenching (ACQ) effects of conventional organic dyes. In addition, the cross-linking strategy can not only improve structural stability of PMs but also enhance its fluorescence brightness. The experiment results demonstrated that PMs showed high water dispersibility (100% aqueous solution), high selectivity, large Stokes shift (∼150 nm), good photostability, and excellent long-term stability. Because of the hydrophobic interaction between the PMs and fingerprint components, the PMs preferentially adhered onto the ridges of fingerprint, and then cross-linking (N 2 H 4 ) induced emission properties endowed the PMs for high-contrast imaging of LFPs in different substrates, especially the levels 1-3 details of LFPs. We expect that this strategy will provide vital support for LFPs technology.

Small-molecule photosensitizers have great application prospects in photoelectrochemical (PEC) sensing due to their defined composition, diversified structure, and adjustable photophysical properties. Herein, we propose a new strategy for PEC analysis based on the target-induced in situ formation of the organic photosensitizer. Taking thiophenol (PhSH) as a model analyte, we designed and synthesized a 2,4-dinitrophenyl (DNP)-caged coumarin precursor (Dye-PhSH), which was then covalently coupled onto the TiO 2 nanoarray substrate to obtain the working photoanode. Due to the intramolecular photoinduced electron transfer process, Dye-PhSH has only a very weak photoelectric response. Upon reacting with the target, Dye-PhSH undergoes a tandem reaction of the detachment of the DNP moiety and the intramolecular cyclization process, which leads to a coumarin dye with a pronounced photoelectric effect, thus achieving a highly selective turn-on PEC response to PhSH. For the first time, this study was to construct a PEC sensor by exploiting specific organic reactions for the in situ generation of small molecule-based photoactive material. It can be anticipated that the proposed strategy will expand the paradigm of PEC sensing and holds great potential for detecting various other analytes.

Ascorbic acid (AA), a major antioxidant in the central nervous system (CNS), is involved in withstanding oxidative stress that plays a significant role in the pathogenesis of Parkinson's disease (PD). Exploring the AA disturbance in the process of PD is of great value in understanding the molecular mechanism of PD. Herein, by virtue of a carbon fiber electrode (CFE) as a matric electrode, a three-step electrochemical process for tailoring oxygen-containing groups on graphene was well designed: potentiostatic deposition was carried out to fabricate graphene oxide on CFE, electrochemical reduction that assisted in removing the epoxy groups accelerated the electron transfer kinetics of AA oxidation, and electrochemical oxidation that increased the content of the carbonyl group (C═O) generated an inner-reference signal. The mechanism was solidified by ab initio calculations by comparing AA absorption on defected models of graphene functionalized with different oxygen groups including carboxyl, hydroxyl, epoxy, and carbonyl. It was found that epoxy groups would hinder the physical absorption of AA onto graphene, while other functional groups would be beneficial to it. Biocompatible polyethylenedioxythiophene (PEDOT) was further rationally assembled to improve the antifouling property of graphene. As a result, a new platform for ratiometric electrochemical measurements of AA with high sensitivity, excellent selectivity, and reproducibility was established. In vivo determination of AA levels in different regions of living mouse brains by the proposed method demonstrated that AA decreased remarkably in the hippocampus and cortex of a subacute PD mouse than those of a normal mouse.

Aggregation induced emission (AIE) dots have gained broad attention in fluorescence bioimaging and biosensors in virtue of their distinctive optical properties of splendid biocompatibility, high brightness and good photostability. However, the application of AIE dots in sensing and imaging of enzymes in cells remains at an early stage and needs to be further explored. In this report, we proposed a novel AIE-dot-based nanoprobe for hyaluronidase (HAase) detection using a simple electrostatic self-assembly of AIE dots with gold nanoparticles functionalized using hyaluronic acid (HA-AuNPs), named HA-AuNPs@AIEDs. The fluorescence of AIE dots can be obviously quenched by HA-AuNPs via fluorescence resonance energy transfer (FRET). HAase could degrade HA into small pieces and thus induce disassembly of AuNPs and AIEDs, accompanied by fluorescence recovery of AIEDs. The as-prepared nanoprobe exhibited high sensitivity, excellent selectivity, wide response range and desirable anti-interference for quantitative sensing of HAase in vitro. The detection limit was down to 0.0072 U mL -1 . Moreover, the nanoprobe displayed good biocompatibility and excellent photostability, and thus offered a practicable "turn-on" strategy for specific, high-contrast fluorescence imaging of HAase in live tumor cells. The AIE-based nanoprobe may provide a novel universal platform for recognition and imaging of HAase in tumors, and may be beneficial for related biological research.

Emulating the function of natural carboxylases to convert CO 2 under atmospheric condition is a great challenge. Herein we report a class of CO 2 -folded single-chain nanoparticles (SCNPs) that can function as recyclable, function-intensified carboxylase mimics. Lewis pair polymers containing bulky Lewis acidic and basic groups as the precursor, can bind CO 2 to drive an intramolecular folding into SCNPs, in which CO 2 as the folded nodes can form gas-bridged bonds. Such bridging linkages highly activate CO 2 , which endows the SCNPs with extraordinary catalytic ability that can not only catalyze CO 2 -insertion of C(sp 3 )-H for imitating the natural enzyme's function, it can also act on non-natural carboxylation pathways for C(sp 2 and sp)-H substrates. The nanocatalysts are of highly catalytic efficiency and recyclability, and can work at room temperature and near ambient CO 2 condition, inspiring a new approach to sustainable C 1 utilization., (© 2020 Wiley-VCH GmbH.)

g-C₃N₄ nanosheets (NSs) were prepared via H₂SO₄ exfoliation from the bulky g-C₃N₄ and the photocatalytic (PC) activities were investigated comprehensively using Rodamine B (RhB) and Chromotrope 2R (Ch2R) as candidate pollutants. The results showed that the pH value have important functions in the improvement of photodegradation performance of C₃N₄ NSs. RhB as cationic dye could be photodegraded more efficiently under acidic conditions while Ch2R as anionic dye was degraded easily in pH ≥ 11 solution. In particular, the Ch2R could be degraded completely within only 30 min in pH = 11 solution. It might be because the amphoteric C₃N₄ NSs surface with carboxyl and amino groups possessed negative and positive charges in alkaline and acidic conditions, respectively. These results presumably provided a new idea to enhance the pH-dependent photodegradation activity and degrade different types of pollutants selectively by adjusting the pH of amphoteric nanocatalyts.

Chalcogen bonding is regarded as a form of noncovalent interaction; however, harnessing chalcogen bonds to drive macromolecular self-assembly remains unexplored. Here we report two classes of chalcogen-bonding partner polymers and their unique self-assembly behaviors in THF/H 2 O solution. Using simple poly(4-vinylphenyl chalcogenide) (P4VCh, Ch = Te or Se) as the donor polymer and poly(ethylene oxide)- block -poly(4-vinylpyridine N -oxide) (PEO- b -P4VO) as the acceptor polymer, they can form donor-acceptor noncovalent complexes and further aggregate into tubular and spherical assemblies through interchain Te···O and Se···O chalcogen-chalcogen interactions. The small distinction in binding affinity of chalcogen bonds can dictate the assembly of different geometries. Moreover, mixing the strong and weak chalcogen-bonding pairs in various ratios can allow us to obtain ergodic phase evolution with tunable dimensionality and morphology.

Exploring unknown supramolecular interacting forces to create novel supramolecular materials is an eternal theme of supramolecular science. Here, we first report a new family of supramolecular polymers formed by unconventional chalcogen-bonding interactions. A class of chalcogen-containing macrocyclic receptors, termed as chalcogena[4]arene (ChA[4], Ch = Te and Se), are designed as chalcogen-bonding donors. Using homoditopic ChA[4]s as monomers, they can linearly polymerize with a twin-headed N -oxide dianion surfactant to organize into noncovalent polymer arrays via end-to-end Ch···O - chalcogen-chalcogen complexation in aqueous media and further self-assemble into supramolecular hydrogel fibers. The binding chemistries of different chalcogen bonds play a decisive role in tuning the parameters of noncovalent polymerizations and the mechanical properties of hydrogel networks. Moreover, such chalcogen-bonding-mediated polymer arrays can be reversibly disconnected by competing anions. This study would inspire a new direction inquiry of unorthodox supramolecular interactions and their related supramolecular materials.

Dynamically shaping protein assemblies into desired nanostructures is a grand challenge. Here we present a new strategy that exploits protein allosteric effect to flexibly manipulate protein amphiphilic self-assembly. This allosteric regulation emphasizes that a huge deformation of protein assemblies is stemmed from a tiny protein conformational switch. Using adenylate kinase as an allosteric protein, adenylate kinase (AKe)-based protein amphiphiles can transform their assembling architectures between 1D nanofilament and 2D crystalline nanosheet due to AKe conformation folding and unfolding. Control over the allosteric degree by tuning the allosteric signal level allows us to mold protein nanostructures in various morphologies and dimensionalities. This method is universal and would open a new avenue to construct dynamic protein structural materials.

The development of simple and effective tools for selective ratiometric detection of hypochlorite (ClO - ) is one of the most important goals for elucidating the biofunction of ClO - in associated diseases. However, most developmental probes suffer from the notorious aggregation-caused quenching (ACQ) effect that greatly limits their applications. Herein, we report on novel aggregation-induced emission dots (AIED) for ratiometric detection of ClO - via a co-precipitation strategy. The AIED nanoprobe displayed a ratiometric signal output, which was more promising to minimize the bad environmental factors and simultaneously avoided the ACQ effect. Notably, amphiphilic block copolymer endowed the nanoprobe with stable water dispersibility and easy modification. The as-prepared AIED probe exhibited high sensitivity (~ 89 nM), high selectivity, outstanding photostability, and prominent long-term fluorescence stability. Furthermore, the as-prepared AIED was applied for the visualized fluorescence detection of ClO - and further utilized to detect ClO - in real samples. We expect the nanoprobe to be an outstanding tool to understand ClO - -associated diseases. Graphical abstract Illustration of the probe for the detection of ClO - .

A simple and readily available fluorescent probe is needed for the real-time monitoring of endogenous cysteine (Cys) levels in living cells, as such a probe could be used to study the role of Cys in related diseases. Herein, we report the first fluorescent probe based on carbon dots (CDs-FITA) for the selective and ratiometric imaging of endogenous Cys in live cells. In this ratiometric fluorescent probe, a fluorescein derivative (FITA) that recognizes Cys is covalently linked to the surfaces of carbon dots (CDs); employing CDs greatly improves the water solubility of the probe. Acrylate on FITA is selectively cleaved by Cys in aqueous solution under mild conditions, leading to a dramatic increase in the fluorescence from fluorescein. The probe therefore allows the highly selective ratiometric fluorescent detection of Cys even in the presence of various interferents. The as-prepared CDs-FITA showed excellent performance when applied to detect Cys in blood serum. In addition, due to its negligible cytotoxicity, the CDs-FITA can also be utilized for the real-time monitoring of endogenous cysteine (Cys) levels in living cells. Graphical abstract Illustration of the CD-based probe for Cys imaging in living cells.

Imaging of hepatocellular nitric oxide (NO) in vivo is of great importance for understanding its roles in liver diseases, but such an imaging approach is still lacking. Herein, a hepatocyte-targeting fluorescent NO sensor has been fabricated. This sensor exhibits good water solubility, excellent selectivity, and high sensitivity (∼1.62 nM). The cells and in vivo imaging experiments reveal that Gal-RhB facilitates the visualization of hepatocellular NO in both HepG2 cells and zebrafish. These results demonstrate that Gal-RhB may be a promising tool for studying the function of NO in NO-associated liver diseases.

The development of simple methods with high sensitivity and selectivity to differentiate toxic aromatic thiols (thiophenols) from aliphatic thiols (cysteine, homocysteine, and glutathione) and hydrogen sulfide (H 2 S) is of great significance. Herein, we report on the fabrication of a novel near-infrared (NIR) fluorescent sensor for rapid and highly selective detection of thiophenols through the photoinduced electron transfer (PET) mechanism. In the presence of the thiophenols, an obvious enhancement of NIR fluorescence at 658 nm could be visualized with the aid of nucleophilic aromatic substitution (S N Ar) reaction. The sensor displays large Stokes shift (~ 227 nm), fast response time (< 30 s), high sensitivity (~ 8.3 nM), and good biocompatibility. Moreover, the as-prepared sensor possesses an excellent anti-interference feature even when other possible interferents exist (aliphatic thiols and H 2 S) and has been successfully utilized for thiophenol detection in both water samples and living cells. Graphical abstract Illustration of the sensor for thiophenol imaging in living cells.

The development of effective method for monitoring of endogenous hypochlorous acid (HClO) in vivo is of great significance for early diagnosis of lipopolysaccharide (LPS) induced acute liver injury. Herein, we report a polymer micelles-based ratiometric fluorescent probe (PM) based on the combination of intramolecular charge transfer (ICT) mechanism and fluorescence resonance energy transfer (FRET) principle for selective visualization of endogenous HClO in vivo. Upon the reaction of PM with HClO, the electron-donating thiourea moiety is oxidized and transformed into imidazoline moiety (electron-withdrawing group), resulting in a dramatic blue shift (˃100nm) in the fluorescence emission. The as-prepared PM shows good water dispersibility (100% aqueous media), fast response (<40s), high sensitivity (a detection limit of 1.75nM), and outstanding selectivity toward HClO over other ROS/RNS (50 equiv.). In addition, the vivo imaging experiments demonstrate that PM facilitates the visualization of endogenous HClO generation with LPS induced acute liver injury in zebrafish model., (Copyright © 2017 Elsevier B.V. All rights reserved.)

In this study, fluorescent silver nanoclusters (Ag NCs) were synthesized using denatured fish sperm DNA as the template. In contrast to other methods, this method did not use artificial DNA as the template. After their reaction with denatured fish sperm DNA, Ag + ions were reduced by NaBH 4 to form Ag NCs. The Ag NCs showed a strong fluorescence emission at 650 nm when excited at 585 nm. The fluorescence intensity increased fourfold at pH 3.78, controlled with Britton-Robinson buffer solution. The fluorescence of the Ag NCs was quenched in the presence of trace mercury ions (Hg 2 + ) in a weakly acidic medium and nitrogen atmosphere. The extent of the fluorescence quenching of Ag NCs strongly depends on the Hg 2 + ion concentration over a linear range from 2.0 nmol L -1 to 3.0 μmol L -1 . The detection limit (3σ/k) for Hg 2 + was 0.7 nmol L -1 . Thus, a sensitive and rapid method was developed for the detection of Hg 2 + ions., (Copyright © 2016 John Wiley & Sons, Ltd.)

Novel fluorescent silver nanoclusters (AgNCs) were synthesized using amido black 10B (AB) as a stabilizing agent and then employed for the detection of copper ions (Cu(2+)). The AB-stabilized AgNCs (AB-AgNCs) were well dispersed in aqueous solution with an average diameter of around 1.3 nm and exhibited illustrious blue fluorescence emission. Moreover, the fluorescence of AB-AgNCs could be quenched efficiently by Cu(2+), which might be a result of the coordination between Cu(2+) and the free recognition group of AB on surfaces of AB-AgNCs, inducing the aggregation of AB-AgNCs. Based on the linear decrease of fluorescence intensity, the Cu(2+) concentration was determined in the range of 0.01-1.1 μmol L(-1) and the limit of detection (LOD) was 4.0 nΜ. In addition, the detection of Cu(2+) could be performed with AB-AgNCs in the presence of other ions, including 13 kinds of conventional metal ions and 11 kinds of anions. Based on the above experiment, the developed AB-AgNC probe was successfully further applied to detect Cu(2+) in three electroplating effluents, which showed high accuracy.

In this work, we demonstrated a new ratiometric method for the quantitative analysis of pH inside living cells. The structure of the nanosensor comprises a biofriendly fluorescent bovine serum albumin (BSA) matrix, acting as a pH probe, and pH-insensitive reference dye Alexa 594 enabling ratiometric quantitative pH measurement. The fluorescent BSA matrix was synthesized by cross-linking of the denatured BSA proteins in ethanol with glutaraldehyde. The size of the as-synthesized BSA nanoparticles can be readily manipulated from 30 to 90 nm, which exhibit decent fluorescence at the peak wavelength of 535 nm with a pH response range of 6-8. The potential of this pH sensor for intracellular pH monitoring was demonstrated inside living HeLa cells, whereby a significant change in fluorescence ratio was observed when the pH of the cell was switched from normal to acidic with anticancer drug treatment. The fast response of the nanosensor makes it a very powerful tool in monitoring the processes occurring within the cytosol.