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The reactive nitrogen species (RNS) in lysosomes play a major role during the regulation of lysosomal microenvironment. Nitroxyl (HNO) belongs to active nitrogen species (RNS) and is becoming a potential diagnostic and therapeutic biomarker. However, the complex synthesis routes of HNO in biosystem always hinder the exact determination of HNO in living cells. Here, a rhodamine-based fluorescent probe used to determine nitroxyl (HNO) in lysosomes was constructed and synthesized. 2-(Diphenylphosphino)benzoate was utilized as the sensing unit for HNO and morpholine was chose as the targeting group for lysosome. Before the addition of HNO, the probe displayed a spirolactone structure and almost no fluorescence was found. After the addition of HNO, the probe existed as a conjugated xanthene form and an intense green fluorescence was observed. The fluorescent probe possessed fast response (3 min) and high selectivity for HNO. Furthermore, fluorescence intensity of the probe linearly related with the HNO concentration in the range of 6.0 × 10 -8 to 6.0 × 10 -5  mol L -1 . The detection limit was found to be 1.87 × 10 -8  mol L -1 for HNO. Moreover, the probe could selectively targeted lysosome with excellent biocompatibility and had been effectually utilized to recognize exogenous HNO in A549 cells., 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 © 2024 Elsevier Inc. All rights reserved.)

Nitroxyl (HNO) is an important reactive nitrogen that is associated with various states in physiology and pathology and plays a unique function in living systems. So, it is important to exploit fluorescent probes with high sensitivity and selectivity for sensing HNO. In this paper, a novel ratiometric fluorescent probe for HNO was developed utilizing intramolecular charge transfer (ICT) and fluorescence resonance energy transfer (FRET) mechanisms. The probe selected coumarin as energy donor, naphthalimide as energy receptor and 2-(diphenylphosphino)benzoate as the sensing site for detecting HNO. When HNO was not present, the 2-(diphenylphosphino)benzoate unit of the probe restricted electron transfer and the ICT process could not occur, leading to the inhibition of FRET process as well. Thus, in the absence of HNO the probe displayed the intrinsic blue fluorescence of coumarin. When HNO was added, the HNO reacted with the 2-(diphenylphosphino)benzoate unit of the probe to yield a hydroxyl group which resulting in the opening of ICT process and the occurring of FRET process. Thus, after providing HNO the probe displayed yellow fluorescence. In addition, the probe showed good linearity in the ratio of fluorescence intensity at 545 nm and 472 nm (I 545 nm /I 472 nm ) with a concentration of HNO (0.1-20 μM). The probe processed a detection limit of 0.014 μM and a response time of 4 min. The probe also specifically identified HNO over a wide pH scope (pH = 4.00-10.00), including physiological conditions. Cellular experiments had shown that this fluorescent probe was virtually non-cytotoxic and could be applied for ratiometric sensing of HNO in A549 cells., 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 © 2024 Elsevier B.V. All rights reserved.)

Au@MnO 2 nanoparticles (NPs), as core-shell nanostructures, have been widely used in ions, molecules and enzyme activities detection due to their stable properties and easy preparation, but their application in bacterial pathogens detection is rarely reported. In this work, Au@MnO 2 NPs is employed for Escherichia coli (E. coli) detection through monitoring and measuring β-galactosidase (β-gal) activity based enzyme-induced color-code single particle enumeration (SPE) method. In the existence of E. coli, p-aminophenylβ-D-galactopyranoside (PAPG) can be hydrolyzed to generate p-aminophenol (AP) by the endogenous β-gal of E. coli. MnO 2 shell reacts with AP and produces Mn 2+ , causing the blue shift of the localized surface plasmon resonance (LSPR) peak and color change of the probe from bright yellow to green. With the SPE method, the amount of E. coli can be quantified readily. The detection limit reaches 15 CFU/mL with dynamic range from 100 to 2900 CFU/mL. Besides, this assay is effectively employed to monitor E. coli in river water sample. The designed sensing strategy provides an ultrasensitive and low cost way for E. coli detection and has the possibility to detect other bacteria in environmental monitoring and food quality analysis., 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.)

Hydrogen sulfide (H 2 S) plays a cytoprotective role during mitophagy by detoxifying superfluous reactive oxygen species (ROS), and its concentration fluctuates in this process. However, no work has been reported to reveal the variation in H 2 S levels during autophagic fusion of lysosomes and mitochondria. Herein, we present a lysosome-targeted fluorogenic probe, named NA-HS, for real-time monitoring of H 2 S fluctuation for the first time. The newly synthesized probe exhibits good selectivity and high sensitivity (detection limit of 23.6 nM). Fluorescence imaging results demonstrated that NA-HS could image exogenous and endogenous H 2 S in living cells. Interestingly, the colocalization results revealed that the level of H 2 S was upregulated after autophagy began because of the cytoprotective effect, and was finally gradually reduced during subsequent autophagic fusion. This work not only affords a powerful fluorescence tool to monitor the variations in H 2 S levels during mitophagy, but also offers new insights into targeting small molecules for elaborating the complex cellular signal pathways., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests., (Copyright © 2023. Published by Elsevier B.V.)

A microdots array-based fluoremetric method with superwettability profile has been developed for the simultaneous and separate detection of Fe 3+ and Cu 2+ ions in red wine samples. A wettable micropores array was initially designed with high density by using polyacrylic acid (PAA) and hexadecyltrimethoxysilane (HDS), followed by the NaOH etching route. Zinc metal organic frameworks (Zn-MOFs) were fabricated as the fluorescent probes to be immobilized into the micropores array to obtain the fluoremetric microdots array platform. It was found that the fluorescence of Zn-MOFs probes could decrease significantly in the presence of Fe 3+ and/or Cu 2+ ions towards their simultaneous analysis. Yet, the specific responses to Fe 3+ ions could be expected if using histidine to chelate Cu 2+ ions. Moreover, the developed Zn-MOFs-based microdots array with superwettability profile can enable the accumulation of targeting ions from the complicated samples without any tedious pre-processing. Also, the cross-contamination of different samples droplets can be largely avoided so as to facilitate the analysis of multiple samples. Subsequently, the feasibility of simultaneous and separate detection of Fe 3+ and Cu 2+ ions in red wine samples was demonstrated. Such a design of microdots array-based detection platform may promise the wide applications in analyzing Fe 3+ and/or Cu 2+ ions in the fields of food safety, environmental monitoring, and medical diseases diagnostics., 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.)

Ferritin plays an important role in regulating the homeostasis of iron in cells by storing/releasing iron. Current methods usually explored the determination of iron content, but in-situ imaging of the iron storage/release from ferritin in cells cannot be achieved. Hence, an engineered self-assembled biomimetic-compartmented nanoprobe (APO@CDs) has been constructed. The protein shell of APO (apoferritin) acted as ion channel module to control iron ions entering/exiting ferritin cavity; the inner core of CDs (carbon dots) acted as signal module for iron ions response. Compared with CDs, the response sensitivity and specificity to iron ions (Fe3 + ) have been improved by using APO@CDs, and the cytotoxicity was significantly reduced. Additionally, compared with cells containing APO@CDs alone, the normalized fluorescence gray value of Fe 3+ -treated cells was significantly decreased (0.275), indicating that Fe 3+ has effectively entered the ferritin. Furtherly, that of Fe 3+ -treated cells incubated with deferoxamine (DFO) was significantly enhanced (0.712), showing that Fe 3+ was released from ferritin under the mediation of DFO. The results demonstrate that APO@CDs can be successfully applied to in-situ imaging of iron storage/release from ferritin in cells, providing a potential platform for the in-situ dynamic study of the iron storage/release in biomedical field., 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 © 2022 Elsevier B.V. All rights reserved.)

A nanozyme with 2D/1D heterostructure has been fabricated by the in-situ growth of molybdenum disulfide nanosheets (MoS 2 NSs) onto single-walled carbon nanotubes (SWCNTs). It was discovered that the so-obtained SWCNTs@MoS 2 nanozyme could exhibit greatly improved peroxidase-like catalysis, due to that the formed 2D/1D interfacial coupling in the heterostructure might provide more active sites and exhibit enhanced charge transferring during the catalytic reactions, as confirmed by the X-ray photoelectron spectroscopy, photoluminescence, electrochemical impedance spectra and radical capturing experiments. Furthermore, the catalysis of the developed nanozyme could be selectively inhibited by glutathione (GSH) through the competitive consumption of hydroxyl radicals with enzyme substrate in the catalytic reaction system. A SWCNTs@MoS 2 catalysis-based colorimetric strategy was further proposed for the quantitative analysis of GSH with the concentrations linearly ranging from 0.01 to 1000.0 μM. Besides, the feasibility of the developed colorimetric method was evaluated by monitoring GSH separately in the extractions from hela cells and human serum, promising the extensive applications for monitoring various biological species like GSH in the clinical laboratory. Importantly, such a fabrication route for nanozyme with 2D/1D heterostructure may pave the way towards the wide applications for designing various nanzymes with improved catalysis., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Recently, using nanomaterials to enhance the endocytosis capability and sensitivity of probes for RNA imaging in living cells has gotten the attention of many researchers. Nanomaterials, as a reliable alternative to transfection reagents, could prevent nucleic acid probes from being degraded by DNase, and bring them into sub-cellular locations for efficient internalization. Therefore, nanomaterial-based fluorescent probes (NFPs) provide a promising sensing platform to realize in situ RNA detection and imaging, which can reveal the expression of RNA at single cell level and provide large amount of information about RNA spatial localization. Meanwhile, many RNAs are in low abundance in living cells, resulting in difficulty in sensitive detection. Thus, the incorporation of NFPs and signal amplification strategy offers a broader prospect for the detection of RNAs, that have been proven as predominant therapeutic targets or diagnostic biomarkers. Herein, the purpose of our review is to first introduce the general procedure of NFPs used for in situ RNA imaging and how nanomaterials deliver these probes into living cells. Further, we focused on different kinds of nanomaterials that are mainly used for sensitive detection of RNAs and those in low abundance, through different signal read-out modes., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Water-soluble non-conjugated polymer dots (PDs) have been synthesized using hyperbranched polyethyleneimine (PEI) and dihydroxybenzaldehyde (DHB) for the first time via the Schiff base reaction at room temperature. The yielded non-conjugated PDs of PEI-DHB could display the well-defined spheric structure and good water solubility. In contrast to the common PDs otherwise showing blue emission, the PEI-DHB PDs could give out strong green fluorescence in aqueous media. Especially, the fluorescence of the PEI-DHB PDs could be specifically quenched by MnO 2 nanosheets through the inner filter effects and further restored by the thiocholine that could reduce MnO 2 nanosheets into Mn 2+ . Herein, thiocholine could be produced in hydrolysis reaction of acetylthiocholine catalyzed by the acetylcholinesterase (AChE), of which the catalytic activity could be irreversibly inhibitted by the introduction of organophosphates. A highly selective fluorimetric method was thereby been developed for the detection of organophosphorus pesticides using dimethyl-dichloro-vinyl phosphate as a model. The linear concentrations ranges from 0.050 to 2.5 μM. Importantly, the non-conjugated PDs probes with strong green fluorescence and high water solubility may promise the extensive applications in the environmental, food, and clinical analysis fields., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that can have appeared to influence this work., (Copyright © 2022 Elsevier B.V. All rights reserved.)

A magnet-renewable electroanalytical strategy has been initially developed for monitoring hydrogen sulfide (H 2 S) in aquaculture freshwater systems using magnetic Fe 3 O 4 -loaded silver metal-organic framework (Fe 3 O 4 @Ag-MOF). The magnetic composites were synthesized by a hydrothermal route and further attached onto the magnetic electrodes. It was discovered that the Fe 3 O 4 @Ag-MOF-based electrochemical sensors could exhibit the extremely sharp and steady signals of solid-state Ag/AgCl electrochemistry at a lower potential. Furthermore, the highly specific and irreversible S-Cl replacement reactions could occur in the presence of H 2 S, so as to induce the conversion of AgCl into non-electroactive Ag 2 S with the rational decline of Ag/AgCl signals. Importantly, the Fe 3 O 4 @Ag-MOF-modified electrodes could be renewed simply by the removal of the magnet after each of the detection cycles for the next immobilization of Fe 3 O 4 @Ag-MOF probes. The developed electroanalytical method could facilitate the detection of H 2 S in the linear range from 4.0 to 1400 nM, with a limit of detection down to 2.0 nM. Besides, it was employed to detect H 2 S in aquaculture freshwater samples of fish, crab, and shrimp, showing the satisfactory results., 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 © 2022 Elsevier B.V. All rights reserved.)

Rapid emergence of new strains of drug-resistant H1N1 influenza viruses calls for effective drugs for the controls prior to their outbreaks. In the present work, electrochemical H1N1 RNA beacons have been newly designed for exploring the potentiality of an anticancer agent of Bleomycin (BLM) with Fe (ΙΙ) ions (BLM-Fe(ΙΙ)) alternatively the treatment of drug-resistant H1N1 strains with H274Y gene mutation. Herein, biotinylated (-) ssRNA of H1N1 virus and its complementary (+) ssRNA were labeled with electrochemical signal probes of ferrocene and anthraquinone, respectively. The resultants were hybridized and conjugated with avidin-modified magnetic beads to create electrochemical RNA beacons. The electrochemical signal variation of the H1N1 RNA beacon treated with the RNA degradation agent of BLM-Fe(ΙΙ) were monitored. Results indicate that the BLM-Fe(ΙΙ) agent could effectively cleave both H1N1 dsRNAs and ssRNAs at selective cutting sites, as evidenced by the mass spectrometry analysis. This indicates that the BLM-Fe(II) agent could be utilized to block the viral-host infection process by curbing the host-cell viral RNA-mRNA transcription or inactivate the viruses through the cleavage of viral genomes. The efficiency of the BLM-Fe(ΙΙ) agent was verified with clinical seasonal H1N1 samples using real-time polymerase chain reaction. The therapeutic gene drug of BLM-Fe(ΙΙ) holds great potential for controlling new strains of H1N1 virus resistant to clinical antiviral drugs. More importantly, the so designed RNA beacons may provide a rapid, sensitive and cost-effective platform of drug screening by monitoring the drug-DNA/RNA interactions., 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 © 2021 Elsevier B.V. All rights reserved.)

Nanozymes' activities could be regulated by a simple and effective pH change in an in situ manner. In this work, for the first time, the peroxidase-like activity of Ni/Co layered double hydroxides (LDHs) was regulated via the alkaline-promoted reaction of fluorogenic substrate homovanillic acid and H 2 O 2 , and a promising tool for pH sensing was developed over the pH range of 8.3-9.6. As peroxidase nanozyme model, Ni/Co LDHs showed ease of preparation, low-cost, and water-solubility, which played an important role in this luminescence system. Based on the pH-dependent regulation of the Ni/Co LDHs activity, we constructed the bioassay platform for the determination urea, urease, penicillin G, and penicillinase with a wide linear range of 17-1000 µM, 3.3-270 mU mL -1 , 3.3-1300 µM and 3.3-100 mU mL -1 , respectively. This study not only demonstrated the alkaline-promoted modulation the nanozymes' activities, but also established a facile approach to develop novel bioassays., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Nanomaterial-based peroxidase-mimetics are an emerging research field that promises to produce alternatives to horseradish peroxidase for a variety of applications. Generally, some peroxidase-mimetics substrates are used in acidic condition (pH ≤ 7). Then, it is necessary to screen some peroxidase-mimetics substrates suitable for basic condition because that some peroxidase-mimetics leached ions in acidic solution. In this paper, using Ni/Co layered double hydroxides (LDHs) as a nano-peroxidase mimic model, we evaluated three fluorogenic substrates suitable for basic condition though experimental conditions, reaction kinetic and glucose detection assay. And the detection of glucose method based on homovanillic acid (HVA) as fluorescent substrate gave wide linear range (0.02-20 μM) and low detection limit (0.01 μM). We also developed a novel platform that could study the inhibitory effects of ascorbic acid and glutathione based on the system of Ni/Co LDHs-HVA-H 2 O 2 ., (Copyright © 2017 Elsevier B.V. All rights reserved.)

The synthesized NiCo 2 O 4 mesoporous spheres (MS) displayed intrinsic peroxidase and oxidase-like activity were firstly reported. The catalytic mechanism of the oxidase-like activity of NiCo 2 O 4 MS was analyzed in detail using the electron spin resonance (ESR) method. It is found that NiCo 2 O 4 MS could directly oxidize 3,3',5,5'-tetramethylbenzidine (TMB) but did not produce 1 O 2 and ·OH. And the mechanism of the peroxidase-like activity of NiCo 2 O 4 MS was also verified that the oxidation of TMB stemmed from not only ·OH but also 1 O 2 . Based on the NiCo 2 O 4 MS showed excellent peroxidase-like activity over a broad temperature range, especially at normal body temperature, a detection tool was designed for glucose determination in diabetics' serum samples. And this detection method based on NiCo 2 O 4 MS gave a lower limit of detection than the method using Co 3 O 4 NPs and NiO NPs, as the single-component oxides of NiCo 2 O 4 . Our study may open up the possibility to make a great influence on the next generation of enzyme mimetics system., (Copyright © 2016 Elsevier B.V. All rights reserved.)