A Photoelectrochemical Sensor for the Detection of Hypochlorous Acid with a Phenothiazine-Based Photosensitizer.

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/TiO2) using bromo-silane coupling agent (BrPTMS) resulted in the fabrication of the photoanode FTO/TiO2/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.

Rational design of a negative photochromic spiropyran-containing fluorescent polymeric nanoprobe for sulfur dioxide derivative ratiometric detection and cell imaging.

It is highly desirable to develop high-performance ratiometric fluorescent probes for SO2 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 SO2 derivative, making the fluorescence quenching of MAHD-SP obvious. Then, MAHD-SP, a fluorescent conjugated polymer PFO and a polymeric surfactant PEO113-b-PS49 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 SO2 derivatives in pure aqueous solutions. Moreover, the good biocompatibility of RFPN can be used to visualize exogenous and endogenous SO2 derivative generation in living cells.

Tailoring Oxygen-Containing Groups on Graphene for Ratiometric Electrochemical Measurements of Ascorbic Acid in Living Subacute Parkinson's Disease Mouse Brains.

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.

Chalcogen-Bonding Supramolecular Polymers.

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.

CO2 -Folded Single-Chain Nanoparticles as Recyclable, Improved Carboxylase Mimics.

Emulating the function of natural carboxylases to convert CO2 under atmospheric condition is a great challenge. Herein we report a class of CO2 -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 CO2 to drive an intramolecular folding into SCNPs, in which CO2 as the folded nodes can form gas-bridged bonds. Such bridging linkages highly activate CO2 , which endows the SCNPs with extraordinary catalytic ability that can not only catalyze CO2 -insertion of C(sp3 )-H for imitating the natural enzyme's function, it can also act on non-natural carboxylation pathways for C(sp2 and sp)-H substrates. The nanocatalysts are of highly catalytic efficiency and recyclability, and can work at room temperature and near ambient CO2 condition, inspiring a new approach to sustainable C1 utilization.

Shaping Protein Amphiphilic Assemblies via Allosteric Effect: From 1D Nanofilament to 2D Rectangular Nanosheet.

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.

Selective ratiometric fluorescence detection of hypochlorite by using aggregation-induced emission dots.

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 near-infrared fluorescent sensor with large Stokes shift for rapid and highly selective detection of thiophenols in water samples and living cells.

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 (H2S) 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 (SNAr) 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 H2S) 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.

Real-time monitoring of endogenous cysteine levels in living cells using a CD-based ratiometric fluorescent nanoprobe.

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.

Silver nanoclusters stabilized with denatured fish sperm DNA and the application on trace mercury ions detection.

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 NaBH4 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 (Hg2+ ) in a weakly acidic medium and nitrogen atmosphere. The extent of the fluorescence quenching of Ag NCs strongly depends on the Hg2+ ion concentration over a linear range from 2.0 nmol L-1 to 3.0 µmol L-1 . The detection limit (3σ/k) for Hg2+ was 0.7 nmol L-1 . Thus, a sensitive and rapid method was developed for the detection of Hg2+ ions.

Copper ion detection using novel silver nanoclusters stabilized with amido black 10B.

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.

A portable electrochemical microsensor for in-site measurement of dissolved oxygen and hydrogen sulfide in natural water.

Dissolved oxygen (O2) and hydrogen sulfide (H2S) 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 O2 and H2S 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 O2 and H2S. Here, Pd@Ni nanoparticles (NPs) were self-assembled onto the microelectrode by MXene titanium carbide (Ti3C2Tx), which were of responsibility towards O2 and H2S detection within single electrochemical reduction process. On this regard, Pd NPs facilitated catalyzing the electrochemical reduction of O2, while Ni NPs were employed as recognition element for H2S 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 S2- 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 O2 concentrations ranging from 36 to 318 µM and H2S levels ranging from 0.1 to 2.5 µM with high selectivity. Finally, the portable microsensor was successfully applied to simultaneous detection dissolved O2 and H2S in natural water in-site, the results of which were comparable to the classical methods.

Supramolecular Polymers with Photoswitchable Multistate Fluorescence for Anti-Counterfeiting and Encryption.

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 ß-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.

A near-infrared ratiometric fluorescent probe for hydrazine and its application for gaseous sensing and cell imaging.

Hydrazine (N2H4) 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 (DCPBCl2-Hz) for the detection of hydrazine by coupling a chlorine-substituted D-π-A fluorophore (DCPBCl2) 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 DCPBCl2, 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/m3). Subsequently, DCPBCl2-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 DCPBCl2-Hz will be a useful tool for sensing hydrazine in biological and environmental applications.

Target-Induced In Situ Formation of Organic Photosensitizer: A New Strategy for Photoelectrochemical Sensing.

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 TiO2 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.

Cross-Linking Induced Emission of Polymer Micelles for High-Contrast Visualization Level 3 Details of Latent Fingerprints.

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 (N2H4) and aldehyde group of polymer. Excitingly, the cross-linking (N2H4) 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 (N2H4) 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.

Rational design of a HA-AuNPs@AIED nanoassembly for activatable fluorescence detection of HAase and imaging in tumor cells.

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.

Solution Self-Assembly of Chalcogen-Bonding Polymer Partners.

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/H2O 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.

Photodegradation of Cationic and Anioic Dyes by pH-Dependent Dispersion of Amphoteric g-C3N4 Nanosheets.

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.