A Ratiometric Fluorescence Probe Based on Silver Nanoclusters and CdSe/ZnS Quantum dots for the Detection of Hydrogen Peroxide by Aggregation and Etching.

In this study, a ratiometric fluorescence nanoprobe is developed for the analysis of hydrogen peroxide (H2O2). Silver nanoclusters (AgNCs) were synthesized by chemical reduction method using sodium borohydride (NaBH4) as reducing agent, and were coupled with CdSe/ZnS quantum dots (QDs) to form the ratiometric fluorescence nanoprobe silver nanoclusters-quantum dots (AgNCs-QDs). The effect of the volume ratio of CdSe/ZnS QDs to AgNCs on the fluorescence ratio of AgNCs-QDs was investigated. The fluorescence characterization results show that two emission peaks of AgNCs-QDs are located at 473 nm and 661 nm, respectively. Transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS) results show that H2O2 can cause the fluorescence probe to aggregate, while etching AgNCs to produce silver ions, which together cause the fluorescence of the QDs in the ratiometric fluorescent probe to be quenched. Based on this strategy, the fluorescence intensity ratio of the two emission peaks F473/F661 exhibits a strong linear correlation with the concentration of H2O2. The detection range is 3.32 µM ~ 2.65 mM with a detection limit of 3.32 µM. In addition, the ratiometric fluorescence probe can specifically recognize H2O2 and has excellent anti-interference performance and good fluorescence stability. Importantly, the probe was utilized for the detection of H2O2 in serum, showing the possibility of the probe in clinical detection applications.

The Impact of Ar or N2 Atmosphere on the Structure of Bi-Fe-Carbon Xerogel Based Composites as Electrode Material for Detection of Pb2+ and H2O2.

In this study, bismuth- and iron-embedded carbon xerogels (XG) were obtained using a modified resorcinol formaldehyde sol-gel synthesis method followed by additional enrichment with iron content. Pyrolysis treatment was performed at elevated temperatures under Ar or N2 atmosphere to obtain nanocomposites with different reduction yields (XGAr or XGN). The interest was focused on investigating the extent to which changes in the pyrolysis atmosphere of these nanocomposites impact the structure, morphology, and electrical properties of the material and consequently affect the electroanalytical performance. The structural and morphological particularities derived from X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) measurements revealed the formation of the nanocomposite phases, mostly metal/oxide components. The achieved performances for the two modified electrodes based on XG treated under Ar or N2 atmosphere clearly differ, as evidenced by the electroanalytical parameters determined from the detection of heavy metal cations (Pb2+) or the use of the square wave voltammetry (SWV) technique, biomarkers (H2O2), or amperometry. By correlating the differences obtained from electroanalytical measurements with those derived from morphological, structural, and surface data, a few utmost important aspects were identified. Pyrolysis under Ar atmosphere favors a significant increase in the α-Fe2O3 amount and H2O2 detection performance (sensitivity of 0.9 A/M and limit of detection of 0.17 µM) in comparison with pyrolysis under N2 (sensitivity of 0.5 A/M and limit of detection of 0.36 µM), while pyrolysis under N2 atmosphere leads to an increase in the metallic Bi amount and Pb2+ detection performance (sensitivity of 8.44 × 103 A/M and limit of detection of 33.05 pM) in comparison with pyrolysis under Ar (sensitivity of 6.47·103 A/M and limit of detection of 46.37 pM).

Hydrogen peroxide fluorescent probe-monitored butyric acid inhibition of the ferroptosis process.

Short-chain fatty acids, such as butyrate, play pivotal roles in various physiological processes within the human body. Recent advances in understanding cell death pathways, specifically ferroptosis, have unveiled unique opportunities for therapeutic development. Ferroptosis is linked to iron accumulation and oxidative stress, whereas butyrate has emerged as a cellular protector against oxidative stress, potentially inhibiting ferroptosis. Hydrogen peroxide (H2 O2 ) is a key player in oxidative stress, and its monitoring has gained significance in disease mechanisms. We present an innovative fluorescent probe, HOP, capable of dynamically tracking intracellular H2 O2 levels, enabling spatial and temporal visualization. The probe exhibits high accuracy (limit of detection = 0.14 µM) and sensitivity, paving the way for disease diagnosis and treatment innovations. Importantly, HOP displayed minimal toxicity, making it suitable for cellular applications. Cellular imaging experiments demonstrated its ability to penetrate cells and monitor intracellular H2 O2 levels accurately. The HOP probe confirmed H2 O2 as a critical marker in ferroptosis. Our innovative HOP provides a powerful tool for tracking intracellular H2 O2 levels and offers insights into the modulation of ferroptosis, potentially opening new avenues for disease research and therapeutic interventions.

Electrodeposition of CoFeS nanoflakes on Cu2O nanospheres as an ultrasensitive sensing platform for measurement of the hydrazine and hydrogen peroxide in seawater sample.

Nanoarchitectured design of the metal sulfides with highly available surface and abundant electroactive centers and using them as electrocatalyst for fabricate the electrochemical sensors for the detection of hydrazine (N2H4) and hydrogen peroxide (H2O2) is challenging and desirable. Herein, Cu2O nanospheres powder is firstly prepared using chemical reduction of copper chloride and then drop-casted on the glassy carbon electrode (GCE) surface. In the next step, CoFeS nanoflakes are electrodeposited on Cu2O nanospheres by cyclic voltammetry method to form CoFeS/Cu2O nanocomposite as a detection platform for measuring N2H4 and H2O2. Accordingly, Cu2O nanospheres are not only used as substrate, but also guided the CoFeS nanoflakes to adhere to the electrode surface without need to any binder or conductive additive, which enhances the electrical conductivity of the sensing active materials. As the hydrazine sensor, the CoFeS/Cu2O/GCE displayed wide linear ranges (0.0001-0.021 mM and 0.021-1.771 mM), low detection limit (0.12 µM), very high sensitivities (103.33 and 21.23 mA mM-1 cm-2), and excellent selectivity. The as-made nanocomposite also exhibited low detection limit of 1.26 µM for H2O2 sensing with very high sensitivities (12.31 and 3.96 mA mM-1 cm-2) for linear ranges of 0.001-0.03 mM and 0.03-2.03 mM, respectively, and negligible response against interfering substances. The superior analytical performance of the CoFeS/Cu2O for N2H4 electro-oxidation and H2O2 electro-reduction can be attributed to structure stability, high electroactive surface area, and good availability to analyte species and electrolyte diffusion. Moreover, to examine the potency of the prepared nanocomposite in real applications, the seawater sample was analyzed and results display that the CoFeS/Cu2O/GCE can be utilized as a reliable and applicable platform for measuring N2H4 and H2O2.

A selective fluorescent turn-on probe for imaging and sensing of hydrogen peroxide in living cells.

Fluorescent turn-on probes have been extensively used in disease diagnosis and research on pathological disease mechanisms because of their low background interference. Hydrogen peroxide (H2O2) plays a vital role in regulating various cellular functions. In the current study, a fluorescent probe, HCyB, based on hemicyanine and arylboronate structures, was designed to detect H2O2. HCyB reacted with H2O2 and exhibited a good linear relationship for H2O2 concentrations ranging from 15 to 50 µM and good selectivity over other species. The fluorescent detection limit was 76 nM. Moreover, HCyB exhibited less toxicity and mitochondrial-targeting abilities. HCyB was successfully used to monitor exogenous or endogenous H2O2 in mouse macrophage RAW 264.7, human skin fibroblast WS1, breast cancer cell MDA-MB-231, and human leukemia monocytic THP1 cells.

An intelligent smartphone-test strip detection platform for rapid and on-site sensing of benzoyl peroxide in flour samples.

Benzoyl peroxide (BPO) is a commonly used flour whitener, but its excessive usage can have adverse effects on human health, such as nutrient loss, vitamin deficiencies and certain diseases. In this study, a europium metal organic framework (Eu-MOF) fluorescence probe was prepared, which exhibited a strong fluorescence emission at 614 nm upon excitation at 320 nm, with a high quantum yield of 8.11%. The red fluorescence of the probe could be effectively quenched by BPO through the inner filter effect (IFE) and photoinduced electron transfer (PET) mechanism. The detection process offered several advantages, including a wide linear range of 0-0.95 mM, a low detection limit of 66 nM and a fast fluorescence response of 2 min. Furthermore, an intelligent detection platform was designed to enhance the practical application of the detection method. This platform combined the portability and visuality of a traditional test strip with the color recognition capability of a smartphone, allowing for the visualization and quantitative detection of BPO in a convenient and user-friendly manner. The detection platform was successfully applied to the analysis of BPO in real flour samples with satisfactory recoveries (99.79%-103.94%), suggesting a promising strategy for the rapid and on-site detection of BPO in food samples.

Investigating nanocatalyst-embedding laser-induced carbon nanofibers for non-enzymatic electrochemical sensing of hydrogen peroxide.

In this present study, we explored the catalytic behaviors of the in situ generated metal nanoparticles, i.e., Pt/Ni, embedded in laser-induced carbon nanofibers (LCNFs) and their potential for H2O2 detection under physiological conditions. Furthermore, we demonstrate current limitations of laser-generated nanocatalyst embedded within LCNFs as electrochemical detectors and possible strategies to overcome the issues. Cyclic voltammetry revealed the distinctive electrocatalytic behaviors of carbon nanofibers embedding Pt and Ni in various ratios. With chronoamperometry at +0.5 V, it was found that modulation of Pt and Ni content affected only current related to H2O2 but not other interfering electroactive substances, i.e., ascorbic acid (AA), uric acid (UA), dopamine (DA), and glucose. This implies that the interferences react to the carbon nanofibers regardless of the presence of metal nanocatalysts. Carbon nanofibers loaded only with Pt and without Ni performed best in H2O2 detection in phosphate-buffered solution with a limit of detection (LOD) of 1.4 µM, a limit of quantification (LOQ) of 5.7 µM, a linear range from 5 to 500 µM, and a sensitivity of 15 µA mM-1 cm-2. By increasing Pt loading, the interfering signals from UA and DA could be minimized. Furthermore, we found that modification of electrodes with nylon improves the recovery of H2O2 spiked in diluted and undiluted human serum. The study is paving the way for the efficient utilization of laser-generated nanocatalyst-embedding carbon nanomaterials for non-enzymatic sensors, which ultimately will lead to inexpensive point-of-need devices with favorable analytical performance.

Novel and highly stable strategy for the development of microfluidic enzymatic assays based on the immobilization of horseradish peroxidase (HRP) into cotton threads.

The use of biological components in the development of new methods of analysis and point-of-care (POC) devices is an ever-expanding theme in analytical chemistry research, due to the immense potential for early diagnosis of diseases and monitoring of biomarkers. In the present work, the evaluation of an electrochemical microfluidic device based on the immobilization of horseradish peroxidase (HRP) enzyme into chemically treated cotton threads is described. This bioreactor was used as a channel for the build of the microfluidic device, which has allowed to use of a non-modified screen-printed electrode (SPE) as an amperometric detector. Cotton threads were treated using citric acid, and the immobilization of HRP has been performed by EDC/NHS crosslinking, connecting amine groups of the enzymes to carboxylic acids in the cellulosic structure. For the analytical evaluation, an amperometric assay for hydrogen peroxide detection was performed after the injection of H2O2 and hydroquinone (HQN) concomitantly. The enzymatic reaction consumes H2O2 leading to the formation of O-quinone, which is readily reducible at non-modified SPE. Several experimental parameters related to enzyme immobilization have been investigated and under the best set of conditions, a good analytical performance was obtained. In addition, the threads were freezer-stored and, after 12 weeks, 84% of hydrogen peroxide sensitivity was maintained, which is very reasonable for enzyme-based systems and still offers good analytical precision. Therefore, a simple and inexpensive microfluidic system was reported by crosslinking carboxylic groups to amine-containing macromolecules, suggesting a new platform for many other protein-based assays.

Enzyme-free and wide-range portable colorimetric sensing system for uric acid and hydrogen peroxide based on copper nanoparticles.

Uric acid (UA) is the final product of purine metabolism. A high concentration of UA in body fluid may lead to kidney stones, gout, and some cardiovascular diseases. Therefore, the non-invasive daily monitoring of UA is of great significance for both hyperuricemia patients and fit people. However, most of the current detection methods for UA are enzyme-dependent which limits the application scenarios and lacks portable instruments for on-site detection, including optics and electrochemistry. In this work, an enzyme-free and wide-range colorimetric sensor for UA and H2O2 detection was developed based on a mercaptosuccinic acid (MSA)-modified Cu nanoparticles (CuNPs). Under the action of UA or H2O2, with the cleavage of MSAs on the CuNPs surface, small Cu particles are further aggregated into larger particles with a lightning violet color. With the employment of the multi-channel handheld automatic photometer (MHAP), the concentration of UA and H2O2 can be determined on-site according to the absorbance measurement by the photodiodes. The linear range of UA was 5 µM-4.5 mM with the limit of detection (LOD) of 3.7 µM, while the linear range of H2O2 was 5 mM-500 mM and 5 µM-5 mM with the LOD of 4.3 µM. This approach has been applied to the detection of UA in human urine, providing more possibilities for non-invasive home health monitoring, community medical diagnosis, and broader prospects of on-site disease detection.

In-situ construction of fluorescent probes for hydrogen peroxide detection in mitochondria and lysosomes with on-demand modular assembling and double turn-on features.

Due to the diverse H2O2 distribution in organelles, fluorescent probes were usually required to be prepared separately, which limited the convenience and practicability. Herein, we reported a flexible strategy to in-situ construct H2O2 fluorescent probes in different organelles. A tetrazine fused probe TP was developed with rapid click reaction capacity and sensitive H2O2 response. When treated with H2O2, the turn-on fluorescence was effectively quenched by the tetrazine part. Only after click reaction with dienophiles, the fluorescence resumed. In application, cells were firstly treated with triphenylphosphorus tagged norbornene (TPP-NB) to label mitochondria, which was followed by the introduction of probe TP to trigger click reaction. The in-situ constructed probe P1 served as a local H2O2 sensor. In a similar way, probe P2 was in-situ constructed in lysosomes via probe TP and morpholine tagged norbornene (MP-NB). With this on-demand modular assembling and double turn-on features, our strategy to construct fluorescent probes presented high flexibility and anti-interference performance, which was expected to inspired more applications in biological studies.

Colorimetric detection of H2O2 with Fe3O4@Chi nanozyme modified µPADs using artificial intelligence.

Peroxidase mimicking Fe3O4@Chitosan (Fe3O4@Chi) nanozyme was synthesized and used for high-sensitive enzyme-free colorimetric detection of H2O2. The nanozyme was characterized in comparison with  Fe3O4 nanoparticles (NPs) using X-ray diffraction, Fourier-transform infrared spectroscopy, dynamic light scattering, and thermogravimetric analysis. The catalytic performance of Fe3O4@Chi nanozyme was first evaluated by UV-Vis spectroscopy using 3,3',5,5'-tetramethylbenzidine. Unlike Fe3O4NPs, Fe3O4@Chi nanozyme exhibited an intrinsic peroxidase activity with a detection limit of 69 nM. Next, the nanozyme was applied to a microfluidic paper-based analytical device (µPAD) and colorimetric analysis was performed at varying concentrations of H2O2 using a machine learning-based smartphone app called "Hi-perox Sens++ ." The app with machine learning classifiers made the system user-friendly as well as more robust and adaptive against variation in illumination and camera optics. In order to train various machine learning classifiers, the images of the µPADs were taken at 30 s and 10 min by four smartphone brands under seven different illuminations. According to the results, linear discriminant analysis exhibited the highest classification accuracy (98.7%) with phone-independent repeatability at t = 30 s and the accuracy was preserved for 10 min. The proposed system also showed excellent selectivity in the presence of various interfering molecules and good detection performance in tap water.

Controllable bisubstrate multi-colorimetric assay based on peroxidase-like nanozyme and complementary colorharmonic principle for semi-quantitative detection of H2O2 with the naked eye.

Naked-eye semi-quantitative (NEQ) assays should exhibit vivid color variations and one-to-one correspondence between the analyte concentrations and the color display. Herein, we report a bisubstrate multi-colorimetric system, constituted by 3,3',5,5'-tetramethylbenzidine (TMB) and dopamine (DA), which carries out a controllable NEQ assay based on the complementary colorharmonic principle. This bisubstrate system is a universal threshold NEQ assay with tunable sensitivity and detection window depending on the H2O2 concentration. The peroxidase-like activity of PEG@Fe3O4 NPs was used to catalyze the oxidations of TMB and DA by H2O2 to the colored products. On the basis of UV-vis spectra data, it was speculated that the oxidation product of TMB (TMB·+) could oxidize DA in this system. The concentration of DA controls the consumption of oxidant (H2O2) and the oxidation of TMB. By controlling the molar ratio of TMB to DA, the bisubstrate system precisely showed multicolor displays (e.g., three-color display: orange, gray, and blue) at submillimolar and millimolar concentrations of H2O2. The detection limit and sensitivity for H2O2 were 0.4 mM and 0.1 mM, respectively. Next, the system was applied to the threshold detection of hypoglycemia (orange), normal (gray), and hyperglycemia (blue) in spiked samples on both gel- and paper-based test strips. Digitalized colorimetric results using the red-green-blue (RGB) analysis with smartphone application were achieved. This work provides a new strategy of multi-colorimetric assay that takes advantages of controllability, threshold detection, vivid color variations, and reproducibility (CVs were 1.1-2.1%), which could be potentially useful for in-field and point-of-care applications.

Colorimetric detection of hydrogen peroxide and cholesterol using Fe3O4-brominated graphene nanocomposite.

Fe3O4-brominated graphene (Fe3O4-GBR) nanocomposites were synthesized via an in situ method using the precursors FeSO4.7H2O and GBR in different (1:1, 1:2, 2:1, 1:5, 1:10, 1:20, and 5:1) weight ratios at pH 11.5. The Fe3O4-GBR (1:5) nanocomposite in combination with H2O2 and 3,3',5,5'-tetramethylbenzidine (TMB) showed swift and superior intrinsic peroxidase mimetic enzyme activity compared with the other Fe3O4-GBR composites, GBR and Fe3O4, as observed by colorimetry. It was characterized using high-resolution scanning electron microscopy (HRSEM), energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (PXRD), and thermogravimetric analysis (TGA). Its catalytic activity was optimized by varying different parameters, and the optimum conditions for peroxidase mimetic activity were observed using 100 µL Fe3O4-GBR (1 mg/mL), 50 µL TMB (1 mg/mL), and 200 µL H2O2(1 mM) in 400 µL of acetate buffer of pH 2.3 at 30 °C temperature. Kinetic analysis has revealed the Michaelis-Menten kinetic behavior of peroxidase activity with Michaelis-Menten constants (Km) and maximum initial velocities (Vmax) of 0.082 mM and 14.1 nMs-1 respectively, for H2O2 and 0.086 mM and 5.1 nMs-1, respectively for TMB. The limit of detection and linear range were found to be 49.6 µM and 100-880 µM, respectively, for H2O2 and 41.9 µM and 47.6-952.3 µM, respectively, for cholesterol. On this basis, a simple, swift, sensitive, selective, and reproducible colorimetric assay to detect cholesterol levels in blood serum samples using Fe3O4-GBR nanocomposite has been developed. Thus, Fe3O4-GBR composite as compared to Fe3O4 and GBR has shown better peroxidase mimicking activity for biosensing.

An ESIPT-Dependent AIE Fluorophore Based on HBT Derivative: Substituent Positional Impact on Aggregated Luminescence and its Application for Hydrogen Peroxide Detection.

Aiming to develop the facile organic fluorophore possessing excited state intramolecular proton transfer (ESIPT) and aggregation-induced emission (AIE), we designed and synthesized two isomers with different linkage site between hydroxyl of 2-(2-hydroxyphenyl) benzothiazole (HBT) and a benzothiazole substituent (para position refers to p-BHBT and ortho position refers to o-BHBT). Fluorescence emission properties of p-BHBT and o-BHBT in THF/water mixtures with different water volume fractions indicated an opposite luminescence in aggregates, in which p-BHBT showed an ESIPT-dependent AIE properties while o-BHBT displayed ESIPT effect and aggregation-caused quenching (ACQ) qualities. A possible mechanism for molecular actions to illustrate the aggregating luminescence alteration of these two isomers had been proposed and verified by theoretical and experimental studies. More importantly, Probe-1, generated from dual ESIPT-AIE fluorophore p-BHBT, was successfully used as a ratiometric fluorescent chemosensor for highly selective (above 15-fold over other ROS) and sensitive (69-fold fluorescence enhancement with 0.22 µM of detection limit) detection of hydrogen peroxide in aqueous solution and living cells, respectively.

Microfluidic paper device with on-site heating to produce reactive peroxide species for enhanced smartphone enabled chemiluminescence signal.

Chemiluminescence signal amplification (CLSA) is of huge interest because of its sensitive detection in various applications such as food analysis, biomedical diagnosis and environmental monitoring. Due to this, there is a manifold attention to develop rapidly prototyped and miniaturized devices for CLSA. In this context, herein, a novel CLSA approach is demonstrated on a 3D printed microfluidic paper-based analytical device (µPADs), fabricated using Fused deposition modeling (FDM) printing technology. Influence of working temperature, ranging 30 °C-110 °C, on CL signal generation from well-established Luminol/Co+2 - H2O2 reaction was analyzed using a screen-printed flexible heater onto the 3D printed reaction platform. A smartphone-based capturing/detection system provided the amenability for a point-of-care testing system. For the first time, strong and stable CLSA was found with about 255% ± 5% increase in its signal intensity without using any additional external enhancers. The on-site working temperature was directly in proportional to the intensity of CL signal generated from Luminol/Co+2 - H2O2 reaction under optimum conditions, wherein the device had a wide linear range from 50 nM to 1 µM with a detection limit of 35 nM for H2O2 detection. The reliability of the developed amplification method was tested for practicability to detect the concentration of H2O2 in milk as real sample analysis. Overall, such CLSA mechanism in miniaturized µPADs will have strong potential for multiple CL based detection and monitoring application.

Evaluation of borinic acids as new, fast hydrogen peroxide-responsive triggers.

Hydrogen peroxide (H2O2) is responsible for numerous damages when overproduced, and its detection is crucial for a better understanding of H2O2-mediated signaling in physiological and pathological processes. For this purpose, various "off-on" small fluorescent probes relying on a boronate trigger have been prepared, and this design has also been involved in the development of H2O2-activated prodrugs or theranostic tools. However, this design suffers from slow kinetics, preventing activation by H2O2 with a short response time. Therefore, faster H2O2-reactive groups are awaited. To address this issue, we have successfully developed and characterized a prototypic borinic-based fluorescent probe containing a coumarin scaffold. We determined its in vitro kinetic constants toward H2O2-promoted oxidation. We measured 1.9 × 104 m-1⋅s-1 as a second-order rate constant, which is 10,000-fold faster than its well-established boronic counterpart (1.8 m-1⋅s-1). This improved reactivity was also effective in a cellular context, rendering borinic acids an advantageous trigger for H2O2-mediated release of effectors such as fluorescent moieties.

Lectin-Triggered Aggregation of Glyco-Gold Nanoprobes for Activity-based Sensing of Hydrogen Peroxide by the Naked Eye.

The purpose of this study was to develop a colorimetric assay for detecting hydrogen peroxide (H2 O2 ) through a combination of using an aryl boronate (AB) derivative and gold nanoparticles (AuNPs). The unique optical property of AuNPs is applied to design a detection probe. The aggregation of AuNPs could be directly observed as a color change by the naked eye. A mannoside-boronate-sulfide (MBS) ligand was designed that contains an arylboronate (AB), a mannoside, and a thiol group. The thiol group bonds covalently with the surface of AuNPs to obtain MBS@AuNPs. The mannoside moiety recognizes concanavalin A (Con A), a lectin with four carbohydrate recognition sites that can specifically recognize the non-reducing end of an α-D-mannoside or α-D-glucoside structure. The AB structure on MBS first reacts with H2 O2 and then inserts an oxygen atom in the B-H bond, which triggers intramolecular electron rearrangement to cleave the covalent bond, resulting in a MBSt mixture. The MBS or MBSt is then modified to citrate-coated AuNPs (c-AuNPs) to have MBS@AuNPs or MBSt@AuNPs. When the MBS@AuNPs are incubated with Con A, the Con A recognizes multiple mannosides on the surface of the MBS@AuNPs. Subsequently, the MBS@AuNPs aggregate and the solution's color changes from red to purple, but this color change does not occur in the case of MBSt@AuNPs. The phenomenon can be observed by the naked eye.

Red fluorescent nanoprobe based on Ag@Au nanoparticles and graphene quantum dots for H2O2 determination and living cell imaging.

A sensitive and turn-on fluorescence nanoprobe based on core-shell Ag@Au nanoparticles (Ag@AuNPs) as a fluorescence receptor and red emissive graphene quantum dots (GQDs) as a donor was fabricated. They were conjugated together through π-π stacking between the GQDs and single-strand DNA modified at the Ag@AuNPs surface. The absorption spectrum of the receptor significantly overlapped with the donor emission spectrum, leading to a strong Förster resonance energy transfer (FRET) and thus a dramatic quenching. The sensing mechanism relies on fluorescence recovery following DNA cleavage by •OH produced from Fenton-like reaction between the peroxidase-like Ag nanocore and H2O2. The red emissive feature (Ex/Em, 520 nm/560 nm) provides low background in physiological samples. The •OH production, great spectrum overlapping, and red emission together contributes to good sensitivity and living cell imaging capability. The fluorescence assay (intensity at 560 nm) achieves a low detection limit of 0.49 µM H2O2 and a wide linear range from 5 to 200 µM, superior to most of the reported fluorescent probes. The RSD value for 100 µM H2O2 was 1.4%. The nanoprobe exhibits excellent anti-interferences and shows low cytotoxicity. The recovery of 100 µM standard H2O2 in a cancer cell lysate was 85.8%. Most satisfactorily, it can realize monitoring and imaging H2O2 in living cells. This study not only presents a sensitive H2O2 probe but also provides a platform for detecting other types of reactive oxygen species.

Quantification of photocatalytically-generated hydrogen peroxide in the presence of organic electron donors: Interference and reliability considerations.

Photocatalytic H2O2 production is an innovative on-site H2O2 synthesis method to treat organic pollutants through Fenton-like reactions, avoiding the need and potential liability of H2O2 storage and transportation. Accurate quantification of H2O2 is crucial to explore the mechanism of photocatalytic H2O2 production and optimize reaction parameters. In this work, three common H2O2 quantification methods (i.e., titration with potassium permanganate (KMnO4), and colorimetry with ammonium metavanadate (NH4VO3) or N,N-diethylp-phenylenediamine-horseradish peroxidase (DPD-POD)) were compared and their susceptibility to interference by seven types of representative organics were considered. Interference mechanisms were explored based on the electron-donating (Egap) and electron-accepting (ELUMO) ability of the present organics. The accuracy of the KMnO4 titration method is greatly compromised by aromatic compounds even at 0.1 mM due to the increased KMnO4 consumption by direct oxidation. The presence of p-benzoquinone that directly reacts with NH4VO3 and DPD compromises these colorimetric methods, especially DPD-POD colorimetry at concentrations as low as 0.1 mM. The DPD-POD method should also be scrutinized in the presence of phenols due to significant disturbance by oxidation byproducts (e.g. hydroquinone inducing immediate color disappearance). A flowchart was generated to provide guidelines for selecting an appropriate H2O2 quantification method for different water matrices treated by Fenton-like reactions.

Development of a surface-modified paper-based colorimetric sensor using synthesized Ag NPs-alginate composite.

There has been an increase in the discovery and usage of sensors for the detection of chemical compounds in the field of analytical chemistry since the last several years. This has led to progressive research in nanotechnology for developing efficient nanomaterials for bio-chemical sensing applications. Thereby, a deft synthesis of silver nanoparticles (Ag NPs) under microwave irradiation was achieved using sodium alginate as a reducing and capping agent in a fast and cost-effective approach. As per the X-ray diffraction analysis, the average particle size of Ag NPs was found to be 10 nm. X-ray photoelectron spectroscpopy analysis showed characteristic peaks at binding energies of 368.10 and 374.11 eV indicating the formation of Ag NPs. The synthesized Ag NPs-alginate composite was further used to develop a paper-based sensor for the detection of H2O2. Detection of H2O2 is based on the discolouration of the Ag NPs-alginate composite modified paper sensor as a function of H2O2 concentration. The analysis of the decoloured paper strips was done by a smartphone camera and an RGB Colour Reader application (app) to measure colour intensity. The sensing characteristics were found in the range of 0.1-10 mM. The colour analysis revealed piecewise linear relationship of intensity of RGB to H2O2 concentration in the range of 0.1-1.5 and 2-10 mM with R2 values of 0.97 and 0.9778, respectively. Owing to the high sensitivity, selectivity, and cost-effectiveness, the developed paper sensor can be a potential tool for real-time analysis of H2O2.