Presence Of Horseradish Peroxidase Research Articles

Bioactive Hydrogels Based on Tyramine and Maleimide Functionalized Dextran for Tissue Engineering Applications

Hydrogels are widely used in tissue engineering due to their ability to form three-dimensional (3D) structures that support cellular functions and mimic the extracellular matrix (ECM). Despite their advantages, dextran-based hydrogels lack intrinsic biological activity, limiting their use in this field. Here, we present a strategy for developing bioactive hydrogels through sequential thiol–maleimide bio-functionalization and enzyme-catalyzed crosslinking. The hydrogel network is formed through the reaction of tyramine moieties in the presence of horseradish peroxidase (HRP) and hydrogen peroxide (H2O2), allowing for tunable gelation time and stiffness by adjusting H2O2 concentrations. Maleimide groups on the hydrogel backbone enable the coupling of thiol-containing bioactive molecules, such as arginylglycylaspartic acid (RGD) peptides, to enhance biological activity. We examined the effects of hydrogel stiffness and RGD concentration on human mesenchymal stem cells (hMSCs) during differentiation and found that hMSCs encapsulated within these hydrogels exhibited over 88% cell viability on day 1 across all conditions, with a slight reduction to 60–81% by day 14. Furthermore, the hydrogels facilitated adipogenic differentiation, as evidenced by positive Oil Red O staining. These findings demonstrate that DexTA–Mal hydrogels create a biocompatible environment that is conducive to cell viability and differentiation, offering a versatile platform for future tissue engineering applications.

Development of injectable microgel-based scaffolds via enzymatic cross-linking of hyaluronic acid-tyramine/gelatin-tyramine for potential bone tissue engineering

Currently, the healing of large bone defects relies on invasive surgeries and the transplantation of autologous bone. As a less invasive treatment option, the provision of microenvironments that promote the regeneration of defective bones holds great promise. Here, we developed hyaluronic acid (HA)/gelatin (Ge) microgel-based scaffolds to guide bone regeneration. To enable the formation of microgels by enzymatic cross-linking in the presence of horseradish peroxidase (HRP) and hydrogen peroxide (H2O2), we modified the polymers with tyramine (TA). Spectrophotometry and proton nuclear magnetic resonance (1H NMR) spectroscopy analysis confirmed successful tyramine substitution on polymer backbones. To enable the formation of microgels by a water-in-oil emulsion approach, the HRP and H2O2 concentrations were tuned to achieve the gelation in a few seconds. By varying the stirring speed from 600 to 1000 rpm, spherical microgels were produced with an average size of 116 ± 8.7 and 68 ± 4.7 μm, respectively. The results showed that microgels were injectable through needles and showed good biocompatibility with the cultured human osteosarcoma cell line (MG-63). HA/Ge-TA microgels served as a promising substrate for MG-63 cells since they improved the alkaline phosphatase activity and level of calcium deposition. In summary, the developed HA/Ge-TA microgels are promising injectable microgel-based scaffolds in bone tissue engineering.

A personal glucose meter-utilized strategy for portable and label-free detection of hydrogen peroxide

Rapid and precise detection of hydrogen peroxide (H2O2) holds great significance since it is linked to numerous physiological and inorganic catalytic processes. We herein developed a label-free and washing-free strategy to detect H2O2 by employing a hand-held personal glucose meter (PGM) as a signal readout device. By focusing on the fact that the reduced redox mediator ([Fe(CN)6]4-) itself is responsible for the final PGM signal, we developed a new PGM-based strategy to detect H2O2 by utilizing the target H2O2-mediated oxidation of [Fe(CN)6]4- to [Fe(CN)6]3- in the presence of horseradish peroxidase (HRP) and monitoring the reduced PGM signal in response to the target amount. Based on this straightforward and facile design principle, H2O2 was successfully determined down to 3.63 μM with high specificity against various non-target molecules. We further demonstrated that this strategy could be expanded to identify another model target choline by detecting H2O2 produced through its oxidation promoted by choline oxidase. Moreover, we verified its practical applicability by reliably determining extracellular H2O2 released from the breast cancer cell line, MDA-MB-231. This work could evolve into versatile PGM-based platform technology to identify various non-glucose target molecules by employing their corresponding oxidase enzymes, greatly advancing the portable biosensing technologies.

ZnO Precursor’s ability to catalyze formation of reactive oxygen species to degrade aqueous organic pollutants

Advanced oxidative processes (AOP) could mitigate emerging and persistent pollutants in drinking water. Yet there is a dearth of economical materials to generate the reactive oxygen species (ROS) that are responsible for pollutant degradation in AOPs. In this work, we design a zinc hydroxychloride monohydrate (ZHCM) silicon dioxide photocatalytic nanocomposite to generate ROS for non-selective degradation of drinking water contaminants. ZHCM is an intermediate phase in the sol–gel synthesis of ZnO-SiO2-Ag nanocomposites containing 63–100 % ZnO. Typically, ZHCM is calcinated around 500 °C to crystallize into ZnO, yet we find that this calcination step may decrease photocatalytic activity. ZHCM exhibited higher methylene blue degradation efficiency through both catalysis (31 % after 4 h) and photocatalysis (98 % after 4 h) compared to the ZnO composites (∼0% and 78 % after 4 h). ZHCM had the highest photodegradation efficiency for ciprofloxacin and caffeine. The increased catalytic and photocatalytic activity of these model pollutants is attributed to the generation of two ROS: superoxide anions in UV light and peroxide anions in the absence of light. These ROS were identified using a new modified biological assay measuring the chemiluminescence of luminol in the presence of horseradish peroxidase. Results are further verified via scavenger quenching tests. The ZHCM and ZnO-SiO2-Ag are characterized for their antimicrobial activity measured by E. coli growth inhibition zones, band gaps, crystalline domains, and surface areas. This work demonstrates the potential to synthesize, at lower temperatures, a photocatalyst with enhanced ROS generation and reduced UV dependency.

Dopamine as a polymerizable reagent for enzyme-linked immunosorbent assay using horseradish peroxidase

We demonstrate that dopamine can be used as a reagent for colorimetric enzyme-linked immunosorbent assay (ELISA) using horseradish peroxidase (HRP). Dopamine was able to be polymerized in the presence of HRP and H2O2, and black polydopamine was obtained after the enzymatic reaction. Because of the black color, the absorbance was significantly changed in the whole range of the visible light region. Here, an indirect competitive ELISA based on the polymerization of dopamine was performed to detect a fluoroquinolone antibiotic, enrofloxacin. The antibiotic is commonly used in livestock farming. The anti-antibiotics antibody was produced from egg yolk from chicken hens. In the visible range, sufficient absorbance changes of ∼0.4∼0.5 and a low background level for the ELISA response were obtained, and the 50 % inhibitory concentration value at 450 nm was determined to be 26 ppb. The performance of the indirect competitive ELISA based on the polymerization of dopamine was compared to that based on the oxidation of catechol because dopamine has a catechol skeleton. By the complex of HRP and H2O2, catechol can be oxidized to o-benzoquinone having a maximum absorption wavelength of 420 nm. It was shown that the absorbance change in the case of polydopamine was about 2.5 times higher than that of catechol, where the background levels were similar. This confirms that the polymerization of dopamine significantly enhanced the photosignal.

Electrospinning carbon fibers based molecularly imprinted polymer self-supporting electrochemical sensor for sensitive detection of glycoprotein

For glycoprotein detection that is both specific and sensitive in clinical diagnosis and treatment, it is necessary to develop artificial bionic recognition materials. By integrating boronate affinity controllable oriented surface imprinting with carbon nanofibers (CNF) as self-supported electrodes, a simple and cost-effective method for preparing glycoprotein-imprinted self-supported electrochemical biosensors was presented in this paper. The molecular imprinted polymers (MIPs) electrode based on Co, Mo2C-CNF was prepared in the presence of horseradish peroxidase (HRP) as a model glycoprotein by cyclic voltammetry. The CNF mats, composed of Co and Mo2C nanoparticles encapsulated in carbon nanofibers (Co, Mo2C-CNF) via electrospinning, could offer more electrical conductivity and active sites for the detection process. The results demonstrated that the hybrid structure of Co, Mo2C-CNF and MIPs exhibited high specificity and excellent selective recognition efficiency for HRP. The detection limit was obtained as 7.4 fg mL−1. The developed biosensor was applied to detect HRP in human serum with a recovery ranging from 89.21 % to 116.68 %. The developed MIPs electrochemical sensor has great potential for developing highly sensitive and specific glycoprotein imprinting biosensors.

Contribution of the Fenton reaction to the degradation of carbon nanotubes by enzymes

The widespread use of carbon nanotubes (CNTs) has raised concerns about the human health and ecological effects of CNTs released into the environment. Bacteria play an important role in bioremediation and waste treatment, and their enzymes are mostly responsible for the degradation of contaminants. However, there are still only a few reports about the bacterial degradation of CNTs, and evidence showing the involvement of bacterial enzymes in CNT degradation with their mechanisms has never been reported. The purpose of this study is to clarify whether CNTs can be degraded by bacterial enzymes. In this study, the degradation of oxidized (carboxylated) single-walled CNTs (O-SWCNTs) by mt2DyP, a dye-decolorizing peroxidase of Pseudomonas putida mt-2, a common soil bacterium, was investigated. After incubation of O-SWCNTs with recombinant mt2DyP and its substrate H2O2 for 30 d, the optical absorbance and Raman spectra revealed the degradation of O-SWCNTs. However, inactivation of the enzyme was observed within 60 min of the start of incubation, suggesting that the degradation of O-SWCNTs occurred nonenzymatically. The inactivation of mt2DyP was accompanied by the release of iron, the active center metal, and degradation of O-SWCNTs was significantly inhibited in the presence of diethylenetriamine pentaacetic acid, a chelating agent, indicating that O-SWCNTs were degraded by the Fenton reaction with iron released from mt2DyP and H2O2. The same phenomenon was observed with P450, which is also a heme enzyme. Furthermore, we investigated the contribution of the Fenton reaction to the O-SWCNT degradation by horseradish peroxidase (HRP), which was reported to enzymatically and rapidly degrade O-SWCNTs. Our results revealed that the degradation of O-SWCNTs in the presence of HRP is also mainly due to the Fenton reaction, with negligible enzymatic degradation. This contradicts the report showing enzymatic degradation of O-SWCNTs by HRP but supports the subsequent report quantitatively showing very slow transformation of O-SWCNTs by HRP. The current results emphasize that the Fenton reaction, which has received little attention in CNT degradation by heme enzymes, must be taken into consideration and will contribute to the development of a simple disposal method for CNTs, utilizing the Fenton reaction with bacteria/bacterial enzymes and H2O2.

Micro‐Scaling Metal‐Organic Framework Films through Direct Laser Writing for Chemical Sensing

AbstractA zeolitic imidazolate framework (ZIF‐8) containing two enzymes that form a cascade biocatalyst has been integrated with 3D structures that are fabricated through a two‐photon polymerization using direct laser writing lithography. Glucose oxidase (GOx) and horseradish peroxidase (HRP) are encapsulated by the biomimetic self‐assembly process of ZIF‐8 to form the GOx/HRP/ZIF‐8 composite which grows in situ on the surface of microprinted carbon‐coated hexagonal substrates (cHS). The GOx/HRP/ZIF‐8/cHS film is applied to glucose detection through enzymatic oxidation of glucose to gluconic acid, forming H2O2, in the presence of GOx and the subsequent reduction of H2O2 to water in the presence of HRP and Amplex Red. This reaction is monitored using fluorimetry as the oxidation of Amplex Red with H2O2 catalyzed by HRP forms red‐emitting resorufin. The GOx/HRP/ZIF‐8/cHS film responds to glucose concentrations with a linear range of 10–200 µm, which correlates to the salivary glucose level in healthy humans. The GOx/HRP/ZIF‐8/cHS film shows more than eight times and 13 times enhanced activity than GOx/HRP/cHS (without ZIF‐8) and GOx/HRP/ZIF‐8 on a non‐3D patterned substrate, respectively. The GOx/HRP/ZIF‐8/cHS film retains more than 80% or 100% of its initial activity after being stored for over 2 months at ≤24 or 4 °C, respectively.

Glucose determination in human serum by applying inner filter effect quenching mechanism of upconversion nanoparticles.

Accurate blood glucose determination is essential to the clinical diagnosis and management of diabetes. This work establishes an inner filter effect (IFE) strategy between upconversion nanoparticles (UCNPs) and quinone-imine complex for glucose monitoring in human serum simply and efficiently. In this system, the enzyme glucose oxidase (GOx) catalyzes the reaction of glucose into hydrogen peroxide (H2O2) and gluconic acid when compulsion by oxygen. In the presence of horseradish peroxidase (HRP), the produced H2O2 can catalytically oxidize phenol and 4-amino antipyrine (4-AAP) to generate quinone-imine products. The purple-colored quinone-imine complex effectively absorbed the fluorescence of NaYF4:Yb3+, Er3+ UCNPs, leading to the strong fluorescence quenching of UCNPs through IFE. Thus, a new approach was established for glucose monitoring by determining the fluorescence intensity. Under the optimal condition, this approach shows better linearity to glucose from 2-240μmol/L with a low detection limit at 1.0μmol/L. Owing to the excellent fluorescence property and background-free interference of the UCNPs, the biosensor was applied for glucose measurements in human serum and got a satisfactory result. Furthermore, this sensitive and selective biosensor revealed great potential for the quantitative analysis of blood glucose or different kinds of H2O2-involved biomolecules for the application of clinical diagnosis.

The Peroxidase-Coupled Assay to Measure MAO Enzymatic Activity.

MAO activity measurement is generally performed following different spectroscopy methods, in most cases using peroxidase as a coupled reaction catalyst. In the presence of horseradish peroxidase (HRP), the assay follows the oxidation of the typical MAO substrate (aromatic amines) which generates hydrogen peroxide as a secondary product. There are several chromogens and fluorogens that, in the presence of hydrogen peroxide, are converted by HRP to detectable products. In the present chapter we describe the spectrophotometric 4-aminoantipyrine assay as well as the fluorogenic assay with the Amplex® Red chemical probe. These methods are applied on MAO activity and Michaelis-Menten curve determinations as well as inhibitory activity experiments.

An activatable Mn(II) MRI probe for detecting peroxidase activity in vitro and in vivo

Myeloperoxidase (MPO), a hallmark of the function and activation of innate immune cells, can act as a ‘double-edged sword’, contributing to clear infection as well as causing tissue oxidizing damage in various inflammatory diseases. In this study, an activatable Mn(II) chelate-based magnetic resonance imaging (MRI) contrast agent (CA), Mn-TyEDTA (TyEDTA = tyrosine derived ethylenediaminetetraacetic acid) structurally featuring a phenol group as the electron-donor, was developed to sense the activity of peroxidase in vitro and in vivo. Mn-TyEDTA demonstrated a peroxidase activity-dependent relaxivity in the presence of horseradish peroxidase (HRP)/H2O2 with more than a 2.6-fold increase in water proton relaxivity produced (HRP, 500 U; H2O2, 4.5 eq). A mechanism of peroxidase-mediated Mn(II) monomer radical polymerization was confirmed with those oligomers of Mn-TyEDTA such as dimer, trimer and tetramer were found in the LC-MS study. Dynamic MR imaging of normal mice revealed rapid blood clearance and mixed renal and hepatobiliary elimination of Mn-TyEDTA. Furthermore, compared to liver-specific and non-specific extracellular contrast agents (Mn-BnO-TyEDTA (BnO-TyEDTA = benzyl tyrosine-derived ethylenediaminetetraacetic acid) and Gd-DTPA (DTPA = diethylene triamine penta-acetic acid)), MRI on a monosodium urate (MSU) crystal-induced acute mice model of arthritis showed that inflamed tissues could be selectively enhanced by Mn-TyEDTA, suggesting that this peroxidase-activatable Mn(II) MRI probe could potentially be used for noninvasive detection of MPO activity in vivo.

Paper-Based Biosensor System for Fast and Sensitive Phenolic Compounds Detection

In this original paper, the development of a paper-based, sensitive, low-cost, quantitative and consistent biosensor system was demonstrated for the suitable “naked-eye” detection of phenolic compounds (specifical catechol). The Paper-based system depends on the enzymatic color-changing reaction that observed by using chromogenic agent of 4-AAP (4-aminoantipyrine) which has a specific color changing reaction in the presence of horseradish peroxidase (HRP) enzyme, phenol and H2O2. The visual result was associated with the catechol concentration by using image processing software to evaluate the quantitative detection. The developed biosensor system demonstrated a linear detection range from catechol between 2,5 µM to 100 µM with 2.6% to 9.3 % of sd results. The detection limit was also calculated as 2,25 µM. Specificity, selectivity, stability and direct real sample analysis demonstrated the potential applicability of the developed paper-based biosensor system for catechol detection in food samples with minimal investment and an easy-to-use method.

Anionic exopolysaccharide from Cryptococcus laurentii 70766 as an alternative for alginate for biomedical hydrogels

Alginates are widely used polysaccharides for biomaterials engineering, which functional properties depend on guluronic and mannuronic acid as the building blocks. In this study, enzymatically crosslinked hydrogels based on sodium alginate (Na-Alg) and the exopolysaccharide (EPS) derived from Cryptococcus laurentii 70766 with glucuronic acid residues were synthesized and characterized as a new potential source of polysaccharide for biomaterials engineering. The EPS was extracted (1.05 ± 0.57 g/L) through ethanol precipitation. Then the EPS and Na-Alg were functionalized with tyramine hydrochloride to produce enzymatically crosslinked hydrogels in the presence of horseradish peroxidase (HRP) and H2O2. Major characteristics of the hydrogels such as gelling time, swelling ratio, rheology, cell viability, and biodegradability were studied. The swelling ratio and degradation profile of both hydrogels showed negative values, indicating an increased crosslinking degree and a lower water uptake percentage. The EPS hydrogel showed similar gelation kinetics compared to the Alg hydrogel. The EPS and its hydrogel were found cytocompatible. The results indicate the potential of EPS from C. laurentii 70766 for biomedical engineering due to its biocompatibility and degradability. Further studies are needed to confirm this EPS as an alternative for Alg in tissue engineering applications, particularly in the development of wound dressing products.

Determination of glutamate using paper-based microfluidic devices with colorimetric detection for food samples

A paper-based device (PAD) capable of colorimetric detection was developed to determine the presence of glutamate in various food samples. The PAD employs an enzymatic reaction with glutamate followed by an oxidation reaction with N-benzoyl leucomethylene blue (BLMB) in the presence of horseradish peroxidase. The designed PAD consists of a sample introduction zone connected to a channel that transports a sample solution to three detection zones. The detection zones contain pre-deposited reagents: glutamate oxidase, horseradish peroxidase, BLMB, a phosphate buffer, and poly(acrylic acid). The PAD is perpendicularly immersed into a sample solution and bent at a right angle using a 3D-printed holder to allow the sample to simultaneously flow into three different detection zones. When the PAD is immersed into a sample containing glutamate, glutamate oxidase produces hydrogen peroxide, which changes the pale blue color of BLMB to a deep blue color in the presence of horseradish peroxidase. Under the optimum conditions, the calibration curve between the logarithm of the glutamate concentrations and the color intensity was linear within a range of from 5 × 10-6 mol L-1 to 10-2 and with a correlation coefficient of 0.994. Using this system, the PAD successfully determined glutamate in soup stocks, sauces, snacks, and tomato juice without the need of complicated sample pretreatment. These results agreed with those of a commercially available glutamate assay kit, which was employed as a certification method (tstat = 1.95, tcrit = 2.57). The developed PAD is simple, easy to fabricate, portable, and could be used outside of equipped laboratories to determine the presence of glutamate in food samples.

Preparation of pH-Responsive Poly(γ-glutamic acid) Hydrogels by Enzymatic Cross-Linking.

pH-responsive hydrogels are important for oral drug release applications, and they are increasingly demanded to reduce the adverse side effects of drug release and improve drug absorption. In this study, a new type of pH-responsive hydrogel comprised of poly(γ-glutamic acid) modified with tyramine (PGA-Tyr) was developed through enzymatic cross-linking in the presence of horseradish peroxidase (HRP) and hydrogen peroxide (H2O2). The gelation rate, stiffness, swelling behavior, and pore size of the resulting hydrogels were tuned by changing the concentrations of HRP and H2O2 or the degree of substitution (DS) of PGA-Tyr. The pH responsiveness of the hydrogels was evaluated by the swelling ratio in solutions with various pH values, and their pH responsiveness exhibited a good reversibility in pH 2.0 and 7.0 solutions. The degradation rate of the hydrogels in simulated intestinal fluid (SIF) was faster than that in simulated gastric fluid (SGF). Moreover, indomethacin (IM), a hydrophobic drug model, was encapsulated in the hydrogels by rapid in situ gelation, and the pH-dependent drug release of IM-loaded hydrogels was achieved in SGF and SIF. Importantly, when IM was entrapped in pluronic F-127 to form drug micelles, the burst release of the IM-micelle-loaded hydrogels with a high DS of PGA-Tyr was remarkably decreased in SGF, and sustained drug release was presented in SIF. Thus, pH-responsive PGA-based hydrogels have tremendous promise for biomedical applications, especially oral drug delivery.

Effect of Polymer Topology and Residue Chirality on Biodegradability of Polypeptide Hydrogels.

Polypeptide-based injectable hydrogels have attracted the attention of biomedical researchers due to their unique biocompatibility and biodegradability, tunable residue chirality, and secondary conformation of polypeptide chains. In the present study, four types of poly(ethylene glycol)-block-poly(glutamic acid)s with different topological structures and residue chirality of polypeptide segments were developed, which were grafted with tyramine side groups for further cross-linking. The results demonstrated that the covalent conjugation between the tyramine groups in the presence of horseradish peroxidase and hydrogen peroxide could form porous hydrogels rapidly. Additionally, the gelation time and mechanical strength of the hydrogels were measured. All the polymer precursors and hydrogels exhibited good cytocompatibility in vitro. Further assessment of the enzymatic degradability of the hydrogels and copolymers in vitro revealed that the degradation rate was influenced by the adjustment of polymer topology or residue chirality of polypeptide copolymers. Subsequently, the effect of copolymer topology and polypeptide chirality on in vivo biodegradability and biocompatibility was assessed. This study will provide insights into the relationship between copolymer structures and hydrogel properties and benefit future polypeptide-based hydrogel studies in biomedical applications.

Using bimetallic Au/Cu nanoplatelets for construction of facile and label-free inner filter effect-based photoluminescence sensing platform for sarcosine detection

Herein, we report a facile and label-free method for sensitive and specific determination of prostate cancer biomarker sarcosine via using photoluminescent bimetallic Au/Cu nanoplatelets (AuCu NPs) to construct an inner filter effect (IFE)-based photoluminescence (PL) sensing platform. The AuCu NPs were formed by the cysteine-induced co-reduction reaction, which displayed bright PL with an emission peak at 560 nm. Meanwhile, the Cu(I) doping caused a maximum 25-fold enhancement of quantum yield (QY), compared with the native Au(I) complexes, i.e., from 0.85 to 21.5%. By integrating the AuCu NPs with p-phenylenediamine (PPD) oxidation reaction, an IFE-based sensor for sarcosine detection was constructed. In this method, sarcosine is oxidized under the catalysis of sarcosine oxidase (SOx) to yield H2O2. The latter further oxidizes PPD to form 2,5-diamino-N,N′-bis(p-aminophenyl)-l,4-benzoquinone di-imine (PPDox) in the presence of horseradish peroxidase (HRP). The UV–vis absorption spectrum of the PPDox can overlap well with the excitation and emission spectra of the AuCu NPs, resulting in the efficient quenching of the AuCu NPs via the IFE effect. Therefore, this IFE-based AuCu NPs/SOx/PPD/HRP sensing platform can be used for highly sensitive and specific sensing of sarcosine. The sensing platform showed two linear regions of the PL intensity of the AuCu NPs versus the concentration of sarcosine in the range of 0.5–5 μM and 5–100 μM with a detection limit (LOD) of 0.12 μM (S/N = 3). Furthermore, this IFE-based sensing platform could be developed into a paper-based biosensor for simple, instrument-free, and visual detection of sarcosine.

Colorimetric detection and determination of glutathione based on superoxide radical-assisted etching approach

Rapid and ultrasensitive detection of biomarkers of diseases is of great importance in early diagnosis and monitoring the patient health conditions. Herein, we report a simple design for a naked-eye colorimetric biosensor for detection and determination of Glutathione (GSH) in human serum. In the presence of Horseradish peroxidase (HRP) and trace concentration of H2O2 and flavone apigenin, and of course GSH, oxidation of GSH results in generation of large amount of superoxide radicals (O2•−) which leads to etching of Au nanorods (AuNRs). The etching of AuNRs results in a blue-shift in the localized surface plasmon resonance (LSPR) of AuNRs, accompanied by a vivid color change from grey to blue then pink. The etching mechanism was well understood by carrying out a series of control experiments. The as-design naked-eye colorimetric biosensor possessed limit of detection of 34 nM, where the whole test was completed in only 5 min. Furthermore, proposed sensor showed an excellent selectivity toward interference substances. The practical tests were performed using human serum as a complex biological medium, where the as-designed biosensor was able to detect and determine GSH with an acceptable accuracy. Our findings suggest that the as-designed biosensor could be used for practical detection and determination of GSH level in for real samples, which could be a breakthrough in diagnosis of several GSH-related diseases.

NADH Regeneration Promoted by Solar Light Using Gold Nanoparticles/Layered Double Hydroxides as Novel Photocatalytic Nanoplatforms

AbstractNicotinamide adenine dinucleotide NAD(P)H is a prolific cofactor in oxidoreductases biochemistry, but its high cost and the stoichiometric amounts motivates significant research for establishing efficient solutions for regenerating NAD(P)H from NAD(P)+. This study presents nanoparticles of gold/layered double hydroxides (AuNPs/LDH) as nanoplatforms with highly efficient photocatalytic response for solar‐light promoted NADH regeneration. The novel photocatalysts are obtained via self‐assembling of ZnAlLDH and AuNPs by using the manifestation of the “structural memory” of the anionic clay in gold salt solution. The chemical composition, structural, optical and nanotextural features of AuNPs/LDH have been assessed by transmission electron microscopy (TEM), energy dispersive X‐Ray Spectroscopy (EDX), powder X‐ray diffraction (XRD), and UV‐Vis Spectroscopy (UV‐Vis). It was found that, at pH 8 and in the presence of flavin mononucleotide (FMN) as a mediator and using water as an electron donor, the regeneration the NADH under solar light is defined by a rate of 20.5 μM/h. Furthermore, the regenerated NADH cofactor is tested in presence of Horseradish Peroxidase (HRP) enzyme to promote the hydrogen peroxide reduction.

Cesium-Doped Graphene Quantum Dots as Ratiometric Fluorescence Sensors for Blood Glucose Detection

Developing a highly sensitive fluorescence probe for biomolecule detection has a significant meaning in clinical diagnosis and research. Tuning the optical property of fluorescent nanomaterials by heteroatom doping is generally feasible to improve the application performance. In this work, a kind of cesium-doped graphene quantum dots (Cs-GQDs) are synthesized, characterized, and explored as a fluorophore in ultrasensitive determination of H2O2 and glucose. The prepared Cs-GQDs with a quantum yield of 39.8% eradiate intense blue fluorescence under UV irradiation. The emission of Cs-GQDs is almost excitation-independent. Doping Cs into the GQDs leads to a clear blue shift of the fluorescence emission peak, probably related to the increased band gap. In addition, Cs-GQDs show a pH-sensitive behavior under acidic conditions. In the presence of horseradish peroxidase, o-phenylenediamine could react with H2O2 to form a yellow fluorescent compound of 2,3-diaminophenazine (DAP). A ratiometric fluorescence probe toward H2O2 and glucose is established using the fluorescence resonance energy transfer mechanism between DAP and Cs-GQDs. This sensing strategy shows high sensitivity for H2O2 and glucose detection with detection limits of 25 and 23 nM, respectively, and excellent selectivity toward glucose out of various interferences. This method is extended to glucose detection in human serum samples. The present method provides a robust, sensitive platform for detecting various biological metabolites participating in the H2O2-generation reaction and shows promising potential for clinical diagnostics and research.