Silver nanoclusters-catalyzed luminol chemiluminescence for hydrogen peroxide and uric acid detection

Surface-Defect-Involved Chemiluminescence Boosted by Gold-Silver Bimetallic Nanoclusters for Bioanalysis

Chemiluminescence (CL) as a powerful analytical tool has garnered increasing interest. However, traditional molecular-based CL luminophores suffer from low emission efficiency due to limited total CL photons emitted per luminophore, driving efforts to explore amplified strategies or novel probes to boost the emission. Although metal nanoclusters (NCs) as luminescent nanoprobes have been extensively studied for electrochemiluminescence and photoluminescence (PL) owing to their intriguing luminescent properties, the CL performance using metal NCs as emitters is often ignored. Herein, based on the synergistic effect within the bimetallic NCs, a series of glutathione-coated Au-Ag bimetallic NCs (GSH-AuAg NCs) were optimized by adjusting precursor ratios and achieved the maximum CL response at a Au:Ag molar ratio of 5:1. To our surprise, CL emission with GSH-AuAg NCs as emitters was triggered with oxidant reagents such as KMnO4, and bimetallic NCs display boosted CL emission (ca. 6.2-fold) compared to monometallic NCs owing to the synergistic effect on enhancing the emission efficiency. Surface-defect-involved CL was revealed by collecting the CL spectra with a maximum emission wavelength of around 750 nm and an obvious red shift of 140 nm compared to PL spectra. The mechanism reveals the KMnO4-injected hole into the valence band through redox reactions with GSH ligands, leading to CL emission by efficient radiative charge recombination with pre-existing electron. A sensing platform based on the GSH-AuAg NCs/oxidant system was constructed for sensing H2O2 and glucose, demonstrating the potential of GSH-AuAg NCs as CL emitters in analytical applications.

Z/Ce@hemin enzymes with enhanced peroxidase activity for monitoring and screening the oxidative stress models of Parkinson's disease

Inspired by natural enzymes, artificial enzymes have garnered significant interest due to their simplicity of production, robustness under harsh conditions, and enhanced stability. This study introduces, for the first time, a novel Z/Ce@hemin composite enzyme, constructed by anchoring hemin onto zeolitic imidazolate framework-8 (ZIF-8)-encapsulated ceria (CeO2) nanoparticles. This innovative design overcomes the challenges of hemin dimerization, enhances substrate affinity, and accelerates mass transport, leading to significantly improved peroxidase-like activity. The enzyme also demonstrates remarkable stability and resistance to environmental interference. Utilizing this Z/Ce@hemin composite, a sensitive and selective colorimetric detection system was developed for rapid and accurate quantification of hydrogen peroxide (H2O2), a key oxidative stress marker. This approach was successfully applied in cellular models and Caenorhabditis elegans models of Parkinson's disease, enabling precise monitoring of H2O2. The study provides a groundbreaking platform for oxidative stress modeling and expands possibilities in neurodegenerative disease research and therapeutic screening.

Boronic acid ester-based hydrogel as surface-enhanced Raman scattering substrates for separation, enrichment, hydrolysis and detection of hydrogen peroxide residue in dairy product all-in-one

Rapid and selective separation, enrichment and detection of trace residue all-in-one in complex samples is a major challenge. Hydrogels with molecular sieve properties can selectively separate and enrich target analytes, and the combination with high sensitivity detection of surface-enhanced Raman scattering (SERS) is expected to achieve the above all-in-one detection. Herein, the core-shell structured Au@poly(N-isopropylacrylamide)-phenylboronic acid hydrogel (Au@PNIP-VBA) with boronic acid ester groups was prepared by thermally initiated polymerization. The boronic acid ester groups in hydrogel are selectively hydrolyzed by hydrogen peroxide (H2O2) to hydroxyl structures, leading to a reduction in SERS signals. The Au@PNIP-VBA hydrogel has molecular sieve properties and high SERS activity, making it suitable for separation, enrichment, hydrolysis and detection of H2O2 all-in-one. A rapid SERS method was developed for analysis of H2O2 based on the Au@PNIP-VBA hydrogel with the linear range of 8.5 × 10-2-6.8 mg L-1 and the detection limit of 33 μg L-1. The method was successfully applied to the determination of H2O2 residue in fresh milk, pure milk, yogurt and camel milk, with the recoveries were in the range of 82.2%-109.3% and the relative standard deviations were 2.8%-8.3%. This efficient all-in-one strategy has the advantages of simple sample pre-treatment, rapid analysis (30 min) and high sensitivity, making it highly promising for food quality and safety analysis.

Gold-Mercury-Platinum Alloy for Light-Enhanced Electrochemical Detection of Hydrogen Peroxide

In this study, a simple and easy synthesis strategy to realize the modification of AuHgPt nanoalloy materials on the surface of ITO glass at room temperature is presented. Gold nanoparticles as templates were obtained by electrochemical deposition, mercury was introduced as an intermediate to form an amalgam, and then a galvanic replacement reaction was utilized to successfully prepare gold-mercury-platinum (AuHgPt) nanoalloys. The obtained alloys were characterized by scanning electron microscopy, UV-Vis spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction techniques. The electrochemical sensing performance of the AuHgPt-modified electrode for hydrogen peroxide was evaluated by cyclic voltammetry and chronoamperometry. Under light conditions, the AuHgPt-modified electrode exhibited a desirable current response in the detection of hydrogen peroxide due to the synergistic effect of the localized surface plasmon resonance effect inherent in gold nanoparticles, and this synergistic effect improved the sensitivity of hydrogen peroxide detection. Meanwhile, the AuHgPt-modified electrode also exhibited better stability and reproducibility, which makes the modified electrode have great potential for various applications in the field of electrochemical sensing.

Convenient in situ self-assembled formation of dual-functional Ag/MXene nanozymes for efficient chemiluminescence sensing

MXenes are attracting increasing interest as a low-cost carrier for the development of nanozymes with enhanced peroxidase or oxidase-like activity. In this work, silver nanoparticles (AgNPs) were synthesized and loaded on Ti3C2 MXene nanosheets (denoted as Ag/MXene) by a simple method, using MXene as a support and reducing agent. The synthesized Ag/MXene composites exhibited satisfactory stability and the peroxidase activity was higher than that of the single components. In the presence of luminol and hydrogen peroxide (H2O2), Ag/MXene could catalyze H2O2 to produce reactive oxygen species (ROS) and act on luminol to generate strong chemiluminescent (CL) signals. Free radical scavenging experiments and electron paramagnetic resonance spectroscopy confirmed the production of these radicals. In this regard, we fabricated a facile biosensor for glutathione (GSH) and uric acid (UA) detection and the results showed good linear relationship between GSH and UA. The linear ranges of GSH and UA were 50 nM to 20 μM and 1 μM to 35 μM, respectively, with low detection limits of 0.83 nM and 0.37 μM. The sensor platform established in this study provides the possibility for developing MXene biosensors with high sensitivity and performance, and lays the solid foundation for expanding the application of MXene in biosensors.

VS4 Nanodendrites with Narrow Bandgaps in Activating Dissolved Oxygen for Boosted Chemiluminescence and Hemin Detection by Unexpected Quenching

Chemiluminescence (CL)-based analytical methods utilize luminophores that need to be activated with an oxidizing agent to trigger CL emission. Despite its susceptibility to decomposition when exposed to external light or trace metals, hydrogen peroxide (H2O2) has been widely used to develop chemiluminescent methods due to the limited number of suitable alternatives for activating chemiluminescent luminophores. Also, analytical methods based on the well-known luminol/H2O2 CL system have low sensitivity. Dissolved oxygen (DO) is a naturally abundant and environmentally benign alternative oxidant for luminol and other CL luminophores. However, DO alone is inactive and needs an efficient catalyst or a coreaction accelerator for its activation. Because of the narrow bandgap of VS4 (ca. 1.12 eV), it can facilitate fast electron-transfer kinetics with an acceptor molecule such as DO. Here, we introduce vanadium tetrasulfide (VS4) to boost CL for the first time. Under the optimized conditions, VS4 nanodendrite catalyzes the generation of reactive oxygen species by activating DO which subsequently reacts with luminol to generate intense CL. It enhances the CL intensity of luminol/DO by about 10,000 times. Surprisingly, hemin remarkably quenches the generated CL of luminol/DO/VS4 nanodendrites, which is completely opposite to its typical enhancement of luminol CL. Based on the remarkable concentration-dependent quenching of the luminol/DO/VS4 nanodendrite CL by hemin, we have developed a sensitive CL method that can selectively detect hemin in the linear concentration range of 1-250 nM and achieved a limit of detection of 0.11 nM. The practical utility of the developed method was demonstrated by the determination of hemin in a pharmaceutical drug for the treatment of acute intermittent porphyria and in human serum. This study demonstrates that VS4 holds great promise in analytical method development.

A luminescent MOF-based nonenzymatic probe for colorimetric/photothermal/fluorescence triple-mode assay of uric acid in body fluids

Monitoring the levels of uric acid (UA) in body fluids is of great significance in the clinical diagnosis and therapy of related diseases. Herein, a novel nanocomposite R6G@Fe-MOF based nonenzymatic probe is presented to provide a ratiometric fluorescent, colorimetric, and photothermal triple read-out signal for the visual, sensitive, and convenient assay of UA. The framework structure of the in situ encapsulated R6G@Fe-MOF is found to decompose upon the addition of UA, resulting in the reduction of Fe3+ to Fe2+. This reduction will lead to a rapid increase in fluorescence emission (FL) at 430 nm. Simultaneously, the FL at 573 nm will decrease remarkably due to the inner filter effect (IFE) between UA and R6G@Fe-MOF. Furthermore, the reaction of the generated Fe2+ with potassium ferricyanide (K3 [Fe(CN)6]) can in situ generate Prussian blue (PBNPs) with outstanding color and photothermal properties, which allow for easy colorimetric and photothermal signal readout. The detection limits (LOD) for the colorimetric, fluorometric and photothermal detection are low at 1.68 μM, 0.236 μM, and 1.32 μM respectively. Ultimately, it is successfully employed to determine UA in urine, serum, and saliva, yielding satisfactory results. The constructed R6G@Fe-MOF sensor provides a simple, sensitive, and accurate determination of UA that can be tailored to meet the needs of various applications, and also provides new perspectives for the design and development of versatile sensors for diverse uses.

Boosting Photo-Electro-Fenton Process Via Atomically Dispersed Iron Sites on Graphdiyne for InVitro Hydrogen Peroxide Detection

Hydrogen peroxide (H2 O2 ) is essential in oxidative stress and signal regulation of organs of animal body. Realizing in vitro quantification of H2 O2 released from organs is significant, but faces challenges due to short lifetime of H2 O2 and complex bio-environment. Herein, rationally designed and constructed a photoelectrochemical (PEC) sensor for in vitro sensing of H2 O2 , in which atomically dispersed iron active sites (Hemin) modified graphdiyne (Fe-GDY) serves as photoelectrode and catalyzes photo-electro-Fenton process. Sensitivity of Fe-GDY electrode is enhanced 8 times under illumination compared with dark condition. The PEC H2 O2 sensor under illumination delivers a wide linear range from 0.1 to 48 160 µm and a low detection limit of 33 nm, while demonstrating excellent selectivity and stability. The high performance of Fe-GDY is attributed to, first, energy levels matching of GDY and Hemin that effectively promotes the injection of photo-generated electrons from GDY to Fe3+ for reduced Fe2+ , which facilitates the Fe3+ /Fe2+ cycle. Second, the Fe2+ actively catalyzes H2 O2 to OH- through the Fenton process, thereby improving the sensitivity. The PEC sensor demonstrates in vitro quantification of H2 O2 released from different organs, providing a promising approach for molecular sensing and disease diagnosis in organ levels.

Protein-Templated Metal Nanoclusters: Molecular-like Hybrids for Biosensing, Diagnostics and Pharmaceutics

The use of proteins as biomolecular templates to synthesize atomically precise metal nanoclusters has been gaining traction due to their appealing properties such as photoluminescence, good colloidal- and photostability and biocompatibility. The synergistic effect of using a protein scaffold and metal nanoclusters makes it especially attractive for biomedical applications. Unlike other reviews, we focus on proteins in general as the protective ligand for various metal nanoclusters and highlight their applications in the biomedical field. We first introduce the approaches and underlined principles in synthesizing protein-templated metal nanoclusters and summarize some of the typical proteins that have been used thus far. Afterwards, we highlight the key physicochemical properties and the characterization techniques commonly used for the size, structure and optical properties of protein-templated metal nanoclusters. We feature two case studies to illustrate the importance of combining these characterization techniques to elucidate the formation process of protein-templated metal nanoclusters. Lastly, we highlight the promising applications of protein-templated metal nanoclusters in three areas-biosensing, diagnostics and therapeutics.

Recent Advances in Nanomaterial-Based Chemiluminescence Probes for Biosensing and Imaging of Reactive Oxygen Species

Reactive oxygen species (ROS) play important roles in organisms and are closely related to various physiological and pathological processes. Due to the short lifetime and easy transformation of ROS, the determination of ROS content in biosystem has always been a challenging task. Chemiluminescence (CL) analysis has been widely used in the detection of ROS due to its advantages of high sensitivity, good selectivity and no background signal, among which nanomaterial-related CL probes are rapidly developing. In this review, the roles of nanomaterials in CL systems are summarized, mainly including their roles as catalysts, emitters, and carriers. The nanomaterial-based CL probes for biosensing and bioimaging of ROS developed in the past five years are reviewed. We expect that this review will provide guidance for the design and development of nanomaterial-based CL probes and facilitate the wider application of CL analysis in ROS sensing and imaging in biological systems.

BSA-stabilized silver nanoclusters for efficient photoresponsive colorimetric detection of chromium(VI)

Hexavalent chromium is a highly toxic substance, which will pose a serious threat to human life and health and the entire ecosystem. Therefore, it is crucial to establish a simple and rapid detection method for hexavalent chromium. In this work, we fabricated bovine serum albumin-stabilized silver nanocluster (BSA-Ag₁₃ NC) which exhibited photoresponsive oxidase-like activity, catalyzing the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to the blue oxidized state TMB (oxTMB) in a short time. Interestingly, 8-hydroxyquinoline (8-HQ) can significantly inhibit the color reaction of TMB oxidation while Cr(VI) can interact specifically with 8-HQ to restore this chromogenic reaction. Based on the above facts, a colorimetric sensing system for detecting Cr(VI) was developed. The sensing system shows a wide linear range, and good selectivity, with a low detection limit of 2.32 nM. Moreover, this sensing system could be successfully applied to the detection of Cr(VI) in lake water, tap water, and sewage with satisfactory results.

A simple spectrophotometric determination of hydrogen peroxide solution via spectral delta from redox reaction with sodium hypochlorite

Hydrogen peroxide (H₂O₂) is widely used in the synthesis of organic chemicals, bleaching of paper pulp, and the treatment of wastewater and as a food additive, important mediator of redox processes in natural water, and a disinfectant. However, H₂O₂ stock solution is unstable and slowly decomposes when exposed to, for example, light, elevated temperatures, or metal compounds. Therefore, the ability to measure the exact concentration of H₂O₂ stock solution is important for its proper use in diverse applications. This work proposes a simple method for the spectrophotometric determination of H₂O₂ solution via chemical reaction with sodium hypochlorite that is inexpensive and easy to acquire. The proposed method is based on the stoichiometric spectral change of hypochlorite ion at 292.5 nm following a redox reaction with a sample solution of H₂O₂. Due to high relationship between the spectral delta value and the applied H₂O₂ concentration (0.00188-0.03000%), H₂O₂ stock solution can be easily quantified.

Platinum nanoparticles confined in metal-organic frameworks as excellent peroxidase-like nanozymes for detection of uric acid

High levels of uric acid (UA) in humans can cause a range of diseases, and traditional assays that rely on uric acid enzymes to break down uric acid are limited by the inherent deficiencies of natural enzymes. Fortunately, the rapid development of nanozymes in recent years is expected to solve the above-mentioned problems. Hence, we used a host-guest strategy to synthesize a platinum nanoparticle confined in a metal-organic framework (Pt NPs@ZIF) that can sensitively detect UA levels in human serum. Unlike previously reported free radical-catalyzed oxidation systems, its unique electron transfer mechanism confers excellent peroxidase-like activity to Pt NPs@ZIF. In addition, UA can selectively inhibit the chromogenic reaction of TMB, thus reducing the absorbance of the system. Therefore, using the peroxidase-like activity of Pt NPs@ZIF and using TMB as a chromogenic substrate, UA can be detected directly without relying on natural enzymes. The results showed a relatively wide detection range (10-1000 μM) and a low detection limit (0.2 μM). Satisfactory results were also obtained for UA in human serum. This study with simple operation and rapid detection offers a promising method for efficiently detecting UA in serum.

Novel Electrochemical Sensors Based on L-Proline Assisted LDH for H2O2 Determination in Healthy and Diabetic Urine

In this paper, a novel non-enzymatic modified glassy carbon (GC) sensor, of the (GC-Ag_paste)-catalytic proline-assisted LDH type, for H₂O₂ determination was fabricated, studied, characterized and employed to determine the hydrogen peroxide content in healthy and diabetic human urine. LDH (whose composition can be schematized as [Zn^IIAl^III (OH)₂]⁺ NO₃^-·nH₂O) is glued to glassy carbon by means of silver paste, while proline, which increases the catalytic properties of LDH, is used free in solution in the phosphate buffer. A voltametric survey was first conducted to ascertain the positive effect induced by the presence of proline, i.e., the increase of sensor sensitivity. Then a deep study of the new three-electrode amperometric proline-assisted LDH sensor, whose working electrode was of the same type as the one used to perform the cyclic voltammetry, was carried out, working at first in static air, then in a nitrogen atmosphere. Possible interferences from various substances, both oxidants and antioxidants, were also investigated. Lastly, the new amperometric sensor was successfully used to determine the H₂O₂ level in human urine from both healthy and diabetic subjects. The effect of proline in enhancing the properties of the sensor system was also investigated. The limit of detection (LOD) of the new catalytic sensor was of the order of 0.15 mmol L^-1, working in air, and of 0.05 µmol L^-1, working in nitrogen atmosphere.

Enhancement effect of 2, 3-dimethyl maleic acid on luminol chemiluminescence reactions and its application in detection of sequence-specific DNA related to hepatitis B virus

2, 3-dimethyl maleic acid (DMMA) was found to enhance luminol-H₂O₂ chemiluminescent (CL) reactions, among which the strongest enhancement effect was observed by using polyethyleneimine-templated gold nanoclusters (PEI-Au NCs) as the catalyst. With the addition of DMMA, the CL signal of the PEI-Au NCs-catalyzed luminol-H₂O₂ reaction enhanced about 630-fold, and a flash-type CL profile was obtained. Mechanism studies showed that the luminophore was still 3-aminophthalate anions in the excited state (3-APA*), and superoxide radical (O₂^·-) played an important role during the CL process. Under the optimized experimental conditions, the lowest concentration of PEI-Au NCs can be detected was 0.168 nM which was 82-fold lower than that without an enhancer. Furthermore, the catalytic activity of biotinylated PEI-Au NCs in the DMMA-enhanced luminol system was similar to PEI-Au NCs, providing a good opportunity for the development of CL bioanalysis platforms using PEI-Au NCs as the label. Thus, the DMMA-enhanced luminol-H₂O₂ system was applied to the CL detection of sequence-specific DNA related to the hepatitis B virus (HBV) using PEI-Au NCs as the label. The CL platform exhibited linearly enhanced CL response with the increasing amount of target DNA ranging from 0.0025 to 0.5 pmol. As low as 0.002 pmol of HBV DNA could be sensitively detected, which was superior to the previously reported methods.

Chemiluminescence resonance energy transfer determination of uric acid with fluorescent covalent organic framework as energy acceptor

A simple and feasible strategy was developed for the preparation of fluorescent covalent organic frameworks (COFs) TpPa-1@FL. The TpPa-1-1@FL was prepared via a self-assembly strategy by soaking non-fluorescent COFs TpPa-1 into strong fluorescent fluorescein (FL) solution. A chemiluminescence resonance energy transfer (CRET) system was constructed by the combination strong fluorescent TpPa-1@FL with TCPO-hydrogen peroxide (H₂O₂) reaction. The chemiluminescence (CL) signal of the system was further improved by the addition of bovine serum albumin (BSA). The CRET system can determine H₂O₂ with a linear range response from 5.0 µmol/L to 20.0 mmol/L and a detection limit of 1.1 µmol/L. The CRET system was further exploited for indirect detection of uric acid with coupling of uricase. A good linear relationship was obtained for uric acid in the 10.0-400.0 µmol/L concentration range with a detection limit of 3.8 µmol/L. The practicability of this method was assessed by the determination of uric acid in real samples of human serum and urine.

Continual and accurate home monitoring of uric acid in urine samples with uricase-packaged nanoflowers assisted portable electrochemical uricometer

A convenient, fast and non-invasive portable electrochemical uricometer (PUM) assisted with the uricase-packaged nanoflowers (NFs) was constructed for continually and accurately monitoring of uric acid (UA) in urine samples at random intervals in just 20 s. Only a small amount of urine (50 μL) was needed for each test. Electrochemical deposition was adopted to modify gold nanoparticles (AuNPs) on screen-printed carbon electrodes (SPCE) and uricase-inorganic hybrid NFs (UOx-NFs) induced by calcium ions (Ca²⁺) were introduced for UA detection with expected specificity. Cyclic voltammetry (CV) (detection limit of 8.87 μM and liner range of 0-4 mM) and amperometry (detection limit of 0.82 μM and liner range of 0-5 mM) protocols were studied for UA detection, respectively. Finally, the uric acid in urine had be successfully continually monitored from volunteers with various dietary choosing, the results of which can be adopted as the effective evidence for uric acid control.

A nanostructured microfluidic device for plasmon-assisted electrochemical detection of hydrogen peroxide released from cancer cells

Non-invasive liquid biopsies offer hope for a rapid, risk-free, real-time glimpse into cancer diagnostics. Recently, hydrogen peroxide (H₂O₂) was identified as a cancer biomarker due to its continued release from cancer cells compared to normal cells. The precise monitoring and quantification of H₂O₂ are hindered by its low concentration and the limit of detection (LOD) in traditional sensing methods. Plasmon-assisted electrochemical sensors with their high sensitivity and low LOD make a suitable candidate for effective detection of H₂O₂, yet their electrical properties need to be improved. Here, we propose a new nanostructured microfluidic device for ultrasensitive, quantitative detection of H₂O₂ released from cancer cells in a portable fashion. The fluidic device features a series of self-organized gold nanocavities, enhanced with graphene nanosheets having optoelectrical properties, which facilitate the plasmon-assisted electrochemical detection of H₂O₂ released from human cells. Remarkably, the device can successfully measure the released H₂O₂ from breast cancer (MCF-7) and prostate cancer (PC3) cells in human plasma. Briefly, direct amperometric detection of H₂O₂ under simulated visible light illumination showed a superb LOD of 1 pM in a linear range of 1 pM-10 μM. We thoroughly studied the formation of self-organized plasmonic nanocavities on gold electrodes via surface and photo-electrochemical characterization techniques. In addition, the finite-difference time domain (FDTD) simulation of the electric field demonstrates the intensity of charge distribution at the nanocavity structure edges under visible light illumination. The superb LOD of the proposed electrode combining gold plasmonic nanocavities and graphene sheets paves the way for the development of non-invasive plasmon-assisted electrochemical sensors that can effectively detect low concentrations of H₂O₂ released from cancer cells.

A novel metal organic gel with superior oxidase-like activity for efficient and sensitive chemiluminescence detection of uric acid

It is found that MIL-100(Fe) gels, as a kind of metal-organic gels (MOGs), constitutting of iron (Fe³⁺) and trimesic acid (H₃BTC), has been regarded as the efficient catalyst of luminol chemiluminescence (CL) system without the presence of extra oxidants in the present work. MIL-100(Fe) gels that have possessed mimicking oxidase-like activity can excellently enhanced luminol CL intensity by accelerating the generation of reactive oxygen species. Furthermore, with the addition of uric acid (UA), the CL signal has been dramatically inhibited under alkaline condition. Hence, the CL intensity inhibiting ratio (I₀/I_S) was proportional to the increasing concentration of UA in the rang from 10 nM to 4000 nM with the detection limit of 5.9 nM. This method has been successfully applied for analysis of UA with acceptable recoveries ranging from 97.0% to 107.9% in urine sample. These results indicates that this study open up a novel, sensitive and convenient method to detect UA in biological samples.

AIEgens-based fluorescent covalent organic framework in construction of chemiluminescence resonance energy transfer system for serum uric acid detection

A covalent organic framework (COF) with aggregation-induced emission (AIE) property was successfully synthesized through in situ marriage of a commonly used AIE molecule tetraphenylethylene (TPE) with Schiff base network (SNW-1) through a simple one-pot method. The TPE@SNW-1 was characterized with different techniques of Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and nitrogen adsorption/desorption experiments. The fluorescence of the TPE@SNW-1 strongly depends on the composition of tetrahydrofuran-water binary system. The AIE property of TPE@SNW-1 was directly supported with particle size distribution by dynamic light scattering technique. With the TPE@SNW-1 as an energy acceptor, a chemiluminescence resonance energy transfer (CRET) system was constructed with bis(2,4,6-trichlorophenyl) oxalate (TCPO)-hydrogen peroxide (H₂O₂) reaction as an energy donor. The chemiluminescence (CL) signal displays a good linear relationship with concentration of H₂O₂ in the 5.0-1000.0 μmol·L^-1 range, and a detection limit of 2.34 μmol L^-1. The system was further exploited to determine uric acid based on the fact that equal stoichiometric amount of H₂O₂ can be concurrently generated under the catalysis of uricase. The procedure exhibits a linear response to uric acid concentration in the range 10.0-150.0 μmol·L^-1 and a detection limit of 4.94 μmol·L^-1. The practicability of the method was demonstrated  in the determination of uric acid in human serum samples.

Determination of dopamine based on its enhancement of gold-silver nanocluster fluorescence

Dopamine (DA) is one of the most important neurotransmitters in human bodies and its sensitive detection remains a challenge. Herein, protein stabilized gold-silver nanoclusters (Au-AgNCs) were synthesized at first. It was found that the introduction of dopamine lead to a significant enhancement of the fluorescence from the nanoclusters, together with a red-shift of the peak. Through related spectroscopic and electrochemical studies, the fluorescence enhancement was attributed to the reduction of the nanoclusters by dopamine. This enhancement was then adopted for quantitative measurements, and linear responses toward dopamine in the ranges 0.01-1.7 μM and 1.7-10 μM were constructed. A limit of detection was obtained at 6.9 nM. The present study provided a facile and efficient method for the determination of dopamine, and the method was successfully applied for related measurements in serum samples.

Spectrophotometric determination of hydrogen peroxide in water with peroxidase-catalyzed oxidation of potassium iodide and its applications to hydroxylamine-involved Fenton and Fenton-like systems

A spectrophotometric method for the rapid measurement of hydrogen peroxide (H₂O₂) in aqueous solutions was developed in this study. This method is based on a reaction catalyzed by peroxidase (POD) in which potassium iodide (KI) is oxidized to generate the stable yellow-colored I₃^- within 15 s. The absorbance of the generated I₃^- at both 350 nm and 400 nm had good linear relationships with H₂O₂ concentration in the range of 0-70 μM (R² > 0.999) with sensitivities of 2.34 × 10⁴ M^-1 cm^-1 and 5.30 × 10³ M^-1 cm^-1 respectively. Meanwhile, through calculation, the detection limits of the proposed POD-KI method at 350 nm and 400 nm were 0.09 μM and 0.33 μM, respectively. Even when the concentration of H₂O₂ was up to 350 μM, the absorbance of the generated I₃^- at 350 nm did not decrease observably. The generated I₃^- was found to be stable enough in ultrapure water, underground water, reservoir water and samples containing the strong reducing agent hydroxylamine. Moreover, the proposed POD-KI method was successfully used to analyze trace H₂O₂ in rainwater, and to monitor the change of H₂O₂ concentration in the Fenton, hydroxylamine/Fenton and hydroxylamine/Cu(II)/H₂O₂ systems. Overall, the POD-KI method could be adopted as a candidate method to determine H₂O₂ in Fenton and Fenton-like systems, and especially in those involving hydroxylamine.

Electrochemiluminescent biosensor for ultrasensitive detection of lymphoma at the early stage using CD20 markers as B cell-specific antigens

Herein, by taking advantage of the special binding of an aptamer to the membrane surface of a B cell and accumulation of the positive charges of a nanocomposite, including luminol-chitosan-platinum nanoparticles (L-Cs-Pt NPs), on the negatively charge of the aptamer phosphate backbone, a sensitive, simple, selective and rapid strategy for the detection of lymphoma cells by a new label-free electrogenerated chemiluminescence (ECL) aptasensor has been introduced. With increasing concentrations of B lymphoma cells, the nanocomposite detaches from the aptamer, leading to a decrease in the ECL of a luminol and H₂O₂ system. With high loading of luminol and Pt NPs on a chitosan, together with the electrocatalytic effect of Pt NPs, enhanced sensitive detection of cancer cells with a limit of detection of 31 cells/mL was achieved. Step-by-step modification and biosensor response to cancer cells was monitored by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and ECL. The aptasensor exhibited excellent specificity for lymphoma cells vs breast cancer (MCF-7) and human embryonic kidney (HEK293) cell lines as potential interferents. Finally, the performance of the aptasensor in blood samples was assessed against a commercial flow cytometric method. Satisfactory results confirmed the applicability of the proposed biosensing platform.

Highly dispersed silver imbedded into TiN submicrospheres for electrochemical detecting of hydrogen peroxide

We report the fabrication of silver nanoparticles evenly imbedded into TiN submicrospheres via one-pot solvothermal reaction and subsequent nitridation for electrochemical detecting of hydrogen peroxide. The precursor of TiO₂ submicrospheres and high dispersion of silver nanoparticles are regulated by the alcoholysis of tetrabutyl titanate and reducibility of enol in vitamin C. The ion nitriding promoted the conductivity and micro-nano porous structure on the surface of TiN submicrospheres, which increase the dispersity of silver nanoparticles and make contributions to avoid aggregations. More importantly, the electrochemical response of Ag-TiN submicrospheres to H₂O₂ was remarkably enhanced due to the co-effects of Ag and N-doping. It provides a superior sensing performance for electrochemical detection of hydrogen peroxide at − 0.3 V with a high sensitivity of 33.25 μA mmol L⁻¹ cm⁻², wide linear range of 0.05–2100 μM and low detection limit of 7.7 nM. The fabricated sensor also reliably applied in detection of H₂O₂ in milk samples with good reproducibility, repeatability and storage stability.

Nanomaterial-enhanced chemiluminescence reactions and their applications

Chemiluminescence (CL) analysis is a trace analytical method that possesses advantages including high sensitivity, wide linear range, easy operation, and simple instruments. With the development of nanotechnology, many nanomaterial (NM)-enhanced CL systems have been established in recent years and applied for the CL detection of metal ions, anions, small molecules, tumor markers, sequence-specific DNA, and RNA. This review summarizes the research progress of the nanomaterial-enhanced CL systems the past five years. These CL reactions include luminol, peroxyoxalate, lucigenin, ultraweak CL reactions, and so on. The CL mechanisms of the nanomaterial-enhanced CL systems are discussed in the first section. Nanomaterials take part in the CL reactions as the catalyst, CL emitter, energy acceptor, and reductant. Their applications are summarized in the second section. Finally, the challenges and opportunities are discussed.

Recent Advances in Electrochemiluminescence and Chemiluminescence of Metal Nanoclusters

Metal nanoclusters (NCs), including Au, Ag, Cu, Pt, Ni and alloy NCs, have become more and more popular sensor probes with good solubility, biocompatibility, size-dependent luminescence and catalysis. The development of electrochemiluminescent (ECL) and chemiluminescent (CL) analytical methods based on various metal NCs have become research hotspots. To improve ECL and CL performances, many strategies are proposed, from metal core to ligand, from intermolecular electron transfer to intramolecular electron transfer. Combined with a variety of amplification technology, i.e., nanostructure-based enhancement and biological signal amplification, highly sensitive ECL and CL analytical methods are developed. We have summarized the research progresses since 2016. Also, we discuss the current challenges and perspectives on the development of this area.

In Situ Formed Catalytic Interface for Boosting Chemiluminescence

Designing the catalytic interface that preferentially attracts reactants is highly desirable for amplifying chemiluminescence (CL) emission. Herein, to boost the generation of reactive oxygen species (ROS) from dissolved O₂ molecule, flower-like cobalt hydroxide (f-Co(OH)₂) based catalytic interface with hierarchical and porous architecture were in situ created in the coexistence of BSA and Co²⁺. Benefiting from the oxidase-like catalysis capability and the unique microstructure of f-Co(OH)₂, ROS was efficiently produced. Meanwhile, the capping ligands of BSA endowed the interface with the capability of enriching functionality through the interaction between BSA and luminol. 100-fold CL enhancement was achieved using the as-prepared catalytic interface compared with the classical luminol-Co²⁺ or luminol-BSA system. Moreover, the proposed catalytic amplification mechanism could be extended to the different proteins such as lysozyme, protamine, thrombin, papain. Based on the quenching effect on CL, a sensitive sensing platform was constructed for the determination of ascorbic acid with satisfied results. Our finding provided a novel "all-in-one" route to design the catalytic interface for amplifying CL emission.

Nano-fluorescent probes based on DNA-templated copper nanoclusters for fast sensing of thiocyanate

A fast and label-free fluorescent sensor was developed to determine SCN⁻via inhibiting the formation of DNA-templated copper nanoclusters (CuNCs).

Hydrogen Peroxide Sensors for Biomedical Applications

Hydrogen peroxide (H2O2) is an important molecule within the human body, but many of its roles in physiology and pathophysiology are not well understood. To better understand the importance of H2O2 in biological systems, it is essential that researchers are able to quantify this reactive species in various settings, including in vitro, ex vivo and in vivo systems. This review covers a broad range of H2O2 sensors that have been used in biological systems, highlighting advancements that have taken place since 2015.

A ratiometric fluorescent probe for detection of uric acid based on the gold nanoclusters-quantum dots nanohybrid

Herein, we developed a simple strategy for the preparation of dual-emission fluorescent nanohybrid constructed of gold nanoclusters (Au NCs) and quantum dots (QDs). The bovine serum albumin-capped Au NCs can be directly used as the stabilizers to prepare CdS QDs. The synthesized bovine serum albumin-capped Au NCs and CdS QDs nanohybrid (BSA-Au NCs/QDs) displayed dual emission bands respectively at 490 nm and 685 nm. An obvious fluorescence quenching around 685 nm was detected with the addition of hydrogen peroxide (H₂O₂) in the presence of Fe²⁺ ions, and the fluorescence emission peak at 490 nm was not affected. Uricase can break down uric acid to produce H₂O₂, and we further used the BSA-Au NCs/QDs as a ratiometric fluorescent probe for determination of uric acid with the linear range from 0.67 to 60 μmol·L^-1 and the detection limit of 0.21 μmol·L^-1.

Electrochemical Sensors Fabricated by Electrospinning Technology: An Overview

Nanofibers or nanofibrous membranes prepared by electrospinning possess many attractive properties, including excellent mechanical properties, high specific surface area and high porosity, making them attractive for sensor application, especially for the electrochemical sensors. Many nanomaterials are used as additives to improve the conductivity, sensitivity and selectivity of sensors. Based on the different modifiers of electrode materials, electrochemical sensors can be divided into enzyme sensors and non-enzyme sensors. In this review, we summarize the recent progress of the electrochemical sensors fabricated by electrospinning, including hydrogen peroxide (H2O2) sensors, glucose sensors and other sensors. In addition, the sensing mechanisms of various electrochemical sensors are introduced in detail. Finally, future research directions of electrochemical sensors based on electrospinning and the challenges faced by large-scale applications of electrospun electrochemical sensors are presented.

Water-soluble Hemin-mPEG-enhanced Luminol Chemiluminescence for Sensitive Detection of Hydrogen Peroxide and Glucose

In the present study, we synthesized a water-soluble substance (Hemin-mPEG) at room temperature by using hemin and poly(ethylene glycol) methyl ether (mPEG). It was found that the Hemin-mPEG maintained the excellent catalytic activity inherited from hemin, and was first used to catalyze a luminol-H₂O₂ chemiluminescence (CL) system to generate an intense and slow CL signal. The results of a mechanism research showed that the presence of Hemin-mPEG could promote the production of oxygen-relative radicals from H₂O₂ and dissolved oxygen in solution. Based on this mechanism, an ultra-sensitive, cheap and simply practical sensor for detecting glucose and H₂O₂ was developed. Under the most optimal experimental conditions, H₂O₂ and glucose detection results exhibited a good linear range from 0.002 to 3 μM and from 0.02 to 4 μM, respectively, and the detection limits were 1.8 and 10 nM, respectively. This approach has been successfully used to detect glucose in actual biological samples, and achieved good results.

Spectrophotometric determination of trace hydrogen peroxide via the oxidative coloration of DPD using a Fenton system

A low-cost and environmentally-friendly spectrophotometric method for hydrogen peroxide (H₂O₂) determination based on the oxidative coloration reaction of N,N'-diethyl-p-phenylenediamine (DPD) via the Fenton reactions in aqueous water was established. The generated pink radical cation (DPD⁺) showed maximum absorption at 551 nm. Importantly, under the optimal conditions (pH 3.0, 20 mM DPD, 1.5 mM Fe(II) and reaction time of 45 s), the increase in absorbance at 551 nm for DPD⁺ generation was linear with respect to the addition of H₂O₂ (0-12 μM). The sensitivity and the detection limit of the proposed Fenton-DPD method for H₂O₂ determination at 551 nm were (2.55 ± 0.01) × 10⁴ M^-1 cm^-1 and 0.05 μM, respectively. The stoichiometric factor for the reaction of H₂O₂ with DPD was 1:1.18. The absorbance of the generated DPD⁺ was found to be stable in different types of water within 20 min. Moreover, the proposed Fenton-DPD method could be used for the analysis of the trace H₂O₂ in rainwater and determine the rate constants that involved H₂O₂ with high accuracy.

Colorimetric detection of hydrogen peroxide and glucose by exploiting the peroxidase-like activity of papain

Papain, a natural plant protease that exists in the latex of Carica papaya, catalyzes the hydrolysis of peptide, ester and amide bonds. In this work, we found that papain displayed peroxidase-like activity and catalyzed the oxidation of 3,3',5',5'-tetramethylbenzidine (TMB) in the presence of H2O2. This results in the formation of a blue colored product with an absorption maximum at 652 nm. The effects of experimental parameters including pH and reaction temperature on catalytic activity of papain were investigated. The increase of absorbance induced by the catalytic effect of papain offers accurate detection of H2O2 in the range of 5.00-90.0 μM, along with a detection limit of 2.10 μM. A facile colorimetric method for glucose detection was also proposed by combining the glucose oxidase (GOx)-catalyzed glucose oxidation and papain-catalyzed TMB oxidation, which exhibited a linear response in the range of 0.05-0.50 mM with a detection limit of 0.025 mM. The method proposed here displayed excellent selectivity, indicating that common coexisting substances (urea, uric acid, ascorbic acid, maltose, lactose and fructose) in urine did not interfere with detection of glucose. More importantly, the suggested method was successfully used to precisely detect the glucose concentration in human urine samples with recoveries over 96.0%.