Detection Limit For Glucose Research Articles

A sensitive and selective non-enzymatic glucose sensor with hollow Ni-Al-Mn layered triple hydroxide nanocomposites modified Ni foam

Hollow Ni-Al-Mn triple layered hydroxide (HLTH) nanocomposite is used for developing a sensitive nonenzymatic electrochemical glucose sensor. Electrochemical studies of HLTH modified nickel foam (NF) possess a remarkable sensing activity towards glucose oxidation with a wide range of detection from 0.015 mM to 8 mM. The sensors show a superior sensitivity of 2.253 mA mM−1 cm−2 with a low glucose detection limit of 1.49 μM (S/N = 3). The fast response time of electrode is <3 s was mainly attributed to the combined effects of metal ions results in the enhanced electrical conductivity of material originating from abundant electroactive cites and stable structure. The application of sensor in glucose detection from human serum is also confirmed. HLTH possess an excellent selectivity of glucose over ascorbic acid and uric acid. The fabricated sensor confirmed the suitable stability, better reproducibility, and extreme sensitivity. The proposed material can be effectively used to detect glucose level in real time application.

A non-enzymatic glucose sensor based on a CoNi2Se4/rGO nanocomposite with ultrahigh sensitivity at low working potential.

Uniform and porous CoNi2Se4 was successfully synthesized by electrodeposition onto a composite electrode comprising reduced graphene oxide (rGO) anchored on a Ni foam substrate (prepared hydrothermally). This CoNi2Se4-rGO@NF composite electrode has been employed as an electrocatalyst for the direct oxidation of glucose, thereby acting as a high-performance non-enzymatic glucose sensor. Direct electrochemical measurement with the as-prepared electrode in 0.1 M NaOH revealed that the CoNi2Se4-rGO nanocomposite has excellent electrocatalytic activity towards glucose oxidation in an alkaline medium with a sensitivity of 18.89 mA mM-1 cm-2 and a wide linear response from 1 μM to 4.0 mM at a low applied potential of +0.35 V vs. Ag|AgCl. This study also highlights the effect of decreasing the anion electronegativity on enhancing the electrocatalytic efficiency by lowering the potential needed for glucose oxidation. The catalyst composite also exhibits high selectivity towards glucose oxidation in the presence of several interferents normally found in physiological blood samples. A low glucose detection limit of 0.65 μM and long-term stability along with a short response time of approximately 4 seconds highlights the promising performance of the CoNi2Se4-rGO@NF electrode for non-enzymatic glucose sensing with high precision and reliability.

Synthesis, characterization of copper oxide-gold nanoalloys and their peroxidase-like activity towards colorimetric detection of hydrogen peroxide and glucose

Bimetallic copper oxide-gold nanoalloys (CuO-Au nanoalloys) have been prepared and characterized using various techniques confirming their successful synthesis. The peroxidase-like activity of CuO-Au nanoalloys have been investigated and applied towards the colorimetric detection of glucose. CuO-Au nanoalloys as nanoenzymes exhibited peroxidase-like properties which occurred by generating the reactive oxygen species (ROS) due to the catalytic properties of CuO-Au nanoalloys.The generation of ROS was confirmed using radical and/or reactive oxygen species quenching properties of 1,3‑diphenylisobenzofuran (DPBF). The rate of production of ROS was higher when CuO-Au nanoalloys were present in a solution containing DPBF and H2O2 (0.1092 min−1). The absorption peak of DPBF at 430 nm decreased confirming the generation of ROS. The CuO-Au nanoalloys were evaluated their potential use for colorimetric detection of glucose. The detection limit for glucose was obtained to be 6.75 μM. The detection of glucose took place in two steps and at different pH conditions, first glucose oxidation by glucose oxidase occurred in physiological pH (7.4) at 37 °C. The optimum conditions for the CuO-Au nanoalloys peroxidase-like activity were obtained at pH 4 and 25 °C. The chromogen, TMB (3,3′,5,5′‑tetramethylbenzidine) oxidation to blue coloured product TMBDI (3,5,3′,5′‑tetrabenzidinediimine) occurred with high intensity obtained after 6 min.

Sensitive and selective non-enzymatic glucose detection using electrospun porous CuO–CdO composite nanofibers

Porous CuO–CdO nanofibers with mean diameter of 463 nm and high surface-to-volume ratio were prepared by impregnating electrospun carboxylic-functionalized poly(arylene ether ketone) (PCA-PAEK) nanofibrous webs with metal acetate solution and subsequent calcination. The special morphology was demonstrated to be decided by ion exchange reaction between metal ions and functional groups on polymer. TGA and EDX analysis confirmed that Cd2+ was more readily to react with PCA-PAEK than Cu2+, and the amount of Cu2+ can be decreased by overloading of Cd2+, leading to the degradation of sensing performance. FT-IR proved the existence of the ion exchange reaction and demonstrated the products were highly pure CuO–CdO compounds with EDX and XRD spectra. The products detailedly investigated for direct electrocatalytic oxidation of glucose evaluated cyclic voltammetry and chronoamperometry. CuO–CdO nanofibers modified electrodes exhibited superiorities of good anti-interference, low detection limit and fast response of glucose, attributing to the enhanced conductivity brought by CdO, good electrocatalytic activity brought by CuO and large surface area brought by porous structure. The simple strategy of electrospinning porous nanofibers using PCA-PAEK as templates and combined CuO and CdO with good electrooxidation glucose functions opens a new route to generate novel conductive metal oxide hybrid nanofibers applied for glucose enzymeless sensors.

Au decorated core-shell structured Au@Pt for the glucose oxidation reaction

Core-shell structured Au@Pt nanoparticles (NPs) with Au cores and dendritic Pt shells have been synthesized using the sonochemical method. Then, the Au is electrochemically incorporated into nano-channels between the Pt shells on the Au@Pt NPs (Au@Pt/Au NPs) to form a non-enzymatic glucose sensor. The electrochemically active surface area (ECSA) of the obtained Au@Pt/Au NPs is enlarged compared with that of Au@Pt NPs, which leads to enhanced glucose sensing performance. The particle sizes of Au@Pt/Au NPs are in the range from 35 nm to 60 nm. The ECSA of Au@Pt/Au NPs is calculated to be 6.19 m2 g(Pt)−1 and 0.8 m2 g(Au)−1 by cyclic voltammetry. The Au incorporation into the Pt shell region can boost the glucose oxidation process even at neutral pH. The sensor performance under the optimized experimental conditions has been confirmed in phosphate buffered saline (PBSsal) solution, showing two wide dynamic ranges for glucose (0.5–10.0 μM and 0.01–10.0 mM) with the correlation coefficient of 0.99. The detection limit of glucose in PBS saline solution has been determined to be 445.7 (±10.3) nM.

A One-Step Extraction and Luminescence Assay for Quantifying Glucose and ATP Levels in Cultured HepG2 Cells.

A fluorescence-based enzymatic microplate intracellular glucose assay was designed and fully validated. The method was tested in a hepatocellular cancer cell line (HepG2). Our novel one-step extraction reagent gave stable cell lysates for glucose, adenosine triphosphate (ATP), and total protein determination from the same sample. Limit of detection for glucose was 0.13 µM (26 pmol/well), which is superior to commercially available glucose assays. Both intra- and interday assay imprecision in HepG2 cultures were less than 12% coefficient of variance (CV). In cell lysates spiked with glucose, recovery at two levels varied between 83.70% and 91.81%, and both linearity and stability were acceptable. HepG2 cells treated with agents affecting glucose uptake/metabolism (phloretin, quercetin, quercetin-3′-sulfate, NaF, 3-bromopyruvate, NaN3, oligomycin A, ochratoxin A, cytochalasin B, and anti-GLUT1 antibody) showed dose-dependent changes in glucose and ATP levels without total protein (cell) loss. Finally, we performed flow cytometric glucose uptake measurement in the treated cells using 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxyglucose fluorescent glucose analog. Glucose uptake did not always mirror the intracellular glucose levels, which most likely reflects the differences between the two methodologies. However, interpreting data obtained by both methods and taking ATP/protein levels at the same time, one can get information on the mode of action of the compounds.

Detecting Glucose Levels in Blood Plasma and Artificial Tear by Au(I) Complex on the Carbopol Polymer: A Microfluidic Paper-Based Method.

We report on a selective paper-based method and a microfluidic paper-based analytical device (μPAD) for the detection of human plasma glucose and tear glucose using carbopol polymer-encapsulated Au(I) complex (AuC2C6H4OMe)2(Ph2P(C6H4)3PPh2), (B5). To the best of our knowledge, this demonstrates for the first time the glucose sensing based on dual emission, i.e., fluorescence and phosphorescence, of a single type molecule on the carbopol polymer. Upon addition of human blood treated with anticoagulants to μPADs, plasma is separated from the blood and flows into the response region of the μPADs to react with carbopol polymer-encapsulated B5, in which the ratiometric luminescence is analyzed. The plasma glucose concentration can be quantitively detected at 1.0–50.0 mM on paper, and tear glucose can be detected at 0.1–4.0 mM on μPADs. Owing to the structural design, this device has superior ratiometric changes of dual emission over other Au(I) complexes for signal transduction. The encapsulation of carbopol polymer also offers long-term storage stability. In tear measurement, carbopol polymer is not only used to encapsulate enzyme to remain the enzyme’s activity, but also played as a glue (or media) to connect microfluidic channel and response region. This further improves the sensitivity and limit of detection for glucose. Moreover, this sensor provides a faster response time, a wider range for glucose sensing than reported previously, and no statistical difference of the data from a commercial glucometer, allowing for practical diagnosis of diabetes and healthy individuals.

Ni@carbon nanocomposites/macroporous carbon for glucose sensor

A novel Ni@carbon nanocomposites/three-dimensional kenaf stem-derived macroporous carbon (3D-KSCs)-integrated electrode was prepared by calcinating Ni-benzenetricarboxylic acid (Ni-BTC) metal–organic frameworks (MOFs) grown on 3D-KSCs under N2 atmosphere for electrochemical glucose sensor. Both Ni-BTC MOFs/3D-KSCs and Ni@carbon nanocomposites/3D-KSCs-integrated electrode were studied by scanning electron microscopy and X-ray powder diffraction. These results showed that many flowerlike Ni-BTC MOFs which were composed of sticklike nanostructures were grown on the surface of 3D-KSCs. After calcination under N2 atmosphere, lots of pearl chain-like nanostructures were formed and uniformly arrayed on 3D-KSC electrode. XRD results confirmed that the Ni-BTC MOFs were successfully transformed into pearl chain-like Ni@carbon nanocomposites. Both electrochemical behaviors and electrocatalytic performances of Ni@carbon nanocomposites/3D-KSCs-integrated electrode were explored. Thanks to its large specific surface area, 3D macropores and special structures, the Ni@carbon nanocomposites/3D-KSCs-integrated electrode showed wide linear range (0.024–1.2 mM) and low detection limit (7.85 μM, S/N = 3) for glucose sensing. Noteworthily, the MOFs/3D-KSCs might be proposed to prepare other nanocomposites for electrochemical biosensing.

Local hydrogel fabrication based on electrodeposition with a large-scale integration (LSI)-based amperometric device

Addressable electrode arrays are widely used in a number of applications, such as electrochemical imaging and high-throughput assays. Recently, large-scale integration (LSI) technologies have been used to prepare electrochemical devices containing signal amplifiers and switching elements, such that multiple highly sensitive sensors can be incorporated into these devices. Because these devices induce chemical reactions at the target electrodes, biomaterials such as hydrogels can be electrochemically fabricated. In this study, we present a new biofabrication strategy using the electrochemical device. We used an LSI device to locally electrodeposit chitosan hydrogels at the target electrodes, with the goal of fabricating the designed hydrogels. The hydrogels were fabricated via the generation of Cl2 at the anodes where a potential of 0.95 V was applied. The biofabrication method was utilized for three bioapplications. First, three-dimensionally designed chitosan hydrogels, for example apple-shaped and layered hydrogels were fabricated on this device by electrodepositing them for 10–30 s. In order to demonstrate biosensing, glucose oxidase and horseradish peroxidase were modified at the target electrodes through hydrogel electrodeposition; consequently, droplets containing glucose and H2O2 were electrochemically imaged at the same time using the electrochemicolor imaging technique we developed. Since this system can be used to fabricate hydrogels containing enzymes only at the target sensors, glucose and H2O2 were separately monitored. The detection limit of glucose was less than 0.5 mM. In addition, the chitosan hydrogels were electrodeposited only in the target areas such that cells only adhering at unmodified areas, resulting in cell patterning. We show that the LSI device is useful for the fabrication of local hydrogels for several bioapplications such as biosensing and cell culturing.

Enhanced photoeletrochemical biosensing performance from rutile nanorod/anatase nanowire junction array

In this work, a novel enzymatic glucose photoelectrochemical biosensor was successfully fabricated based on rutile/anatase TiO2 (R/A-TiO2) heterostructure which was composed of anatase nanowires and rutile nanorods. Compared to a rutile nanorod electrode, an obvious enhanced photocurrent was observed on R/A-TiO2 electrode in photoelectrochemical test. Excellent photoeletrochemical performance was obtained due to these follow points: higher optical absorptivity for the larger surface area, better separation of the photogenerated carriers related to the specific R/A-TiO2 heterostructure and faster electrical transmission stemmed from the unique conductive structure. This R/A-TiO2 heterostructure array was applied to glucose detection by loading glucose oxidase on R/A-TiO2 electrode. A remarkable performance with a 5.71 μA mM−1 cm−2 sensitivity, 1–20 mM linear range and a 0.019 mM glucose detection limit (S/N = 3) were obtained in the glucose detection.

MOF-808: A Metal-Organic Framework with Intrinsic Peroxidase-Like Catalytic Activity at Neutral pH for Colorimetric Biosensing.

Natural enzyme mimetics with high catalytic activity at nearly neutral pH values are highly desired for their applications in biological systems. Herein for the first time a stable MOF, namely MOF-808, has been shown to possess high intrinsic peroxidase-like catalytic activity under acidic, neutral, and alkaline conditions. As a novel peroxidase mimetic, MOF-808 can effectively catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine when H2O2 serves as oxidant, accompanied by a significant color variation in the solution. The catalytic activity and the color variation were greatly dependent on H2O2 concentration, and thus MOF-808 can be applied to the colorimetric sensing of H2O2. The H2O2 detection limit is 4.5 μM, and the linear range is 10 μM to 15 mM. In view of the significant inhibition effect produced by ascorbic acid, a facile and sensitive approach for colorimetric sensing of ascorbic acid was successfully established. The AA detection limit is 15 μM, and the linear range is 30-1030 μM. Further investigation found that the catalytic activity of MOF-808 could be mainly ascribed to the Zr-OH(OH2) groups. Such active Zr-OH(OH2) groups can be effectively shielded by gluconic acid, and subsequently the catalytic activity of MOF-808 was significantly suppressed. With these findings, a facile and selective colorimetric assay for glucose sensing has been successfully explored via combination of the glucose oxidation with the TMB oxidation. The glucose detection limit is 5.7 μM, and the linear range is 5.7-1700 μM. MOF-808 is one of the best colorimetric biosensors among the peroxidase mimics reported for H2O2, AA, and glucose detection.

Graphene Quantum Dots and Enzyme-Coupled Biosensor for Highly Sensitive Determination of Hydrogen Peroxide and Glucose.

In this paper, a simple and specific graphene quantum dots (GQDs)-based fluorescent biosensor adopted for the determination of glucose based on the combination of the enzyme-coupled method and fluorescence quenching mechanism is demonstrated. Glucose was oxidized by the enzyme glucose oxidase (GOx), forming hydrogen peroxide (HO) via the catalysis by horseradish peroxidase (HRP). HO was then employed to oxidize phenol to quinone, which led to effective quenching effect in the GQDs–GOx–HRP–phenol system. By optimizing the reaction conditions of the GQDs-enzyme system, a linear relationship between the concentration of glucose and the fluorescence intensity over a range of 0.2–10 mol/L was obtained. The limit of detection for glucose is 0.08 mol/L. The present biosensor for the determination of glucose showed satisfactory reproducibility and accuracy in human serum samples. Since the enzymes have high specificity and unique affinity to the certain substance, the enzyme-coupled system promises a sensitive way for further detection of those chemicals which could be oxidized by enzymes and generated HO or glucose. GQDs and other fluorescent materials coupled with several enzymes can be applied to extensive sensing field.

A simple automated microplate method for determining reducing sugars in food extracts and synthetic serum using cupric-neocuproine as reductant

In the present work, a simple automated microplate method based on cupric ion reduction is described for determining total reducing sugars in food extracts and synthetic serum. The reaction of Cu(II)-Nc (cupric-neocuproine) with reducing sugars was performed in alkaline medium in microplates, and the absorbance of the formed highly colored Cu(I)-Nc chelate in a plate reader at 450 nm was recorded. The proposed method was applied to reducing sugars (glucose, fructose, galactose, maltose, and lactose) and their linear calibration curves were constructed. The detection and quantification limits (LOD and LOQ) for glucose were 0.14 and 0.46 $\mu $M, respectively. Absorbances of glucose were linear within the concentration range 2.5-54.2 $\mu $M and the method showed high linearity (r = 0$.$9998) over a relatively broad concentration range of analyte. This automated microplate method was validated through linearity, additivity, precision (RSD%, 2.33-6.65), and recovery (101%-103%), revealing that the method is reliable and robust for determining reducing sugars. Total reducing sugar contents of synthetic sugar mixtures, fruit juices, milk, and synthetic serum samples were successfully determined with the proposed method. The results were compared to those of the conventional alkaline Cu(II)-Nc spectrophotometric method. The proposed method offers many advantages when compared to classical methods, such as (sample and reagent) volume reduction (20-fold), simplicity, multiple sample analysis (32 samples in 4 h), and environmental friendliness.

Green approach for in-situ growth of highly-ordered 3D flower-like CuS hollow nanospheres decorated on nitrogen and sulfur co-doped graphene bionanocomposite with enhanced peroxidase-like catalytic activity performance for colorimetric biosensing of glucose

We describe a green and facile hydrothermal route to synthesize highly ordered 3D flower-like hierarchical CuS hollow nanospheres@N-S-rGO bionanocomposite used to detect glucose. After synthesis and comprehensive characterization of all potential catalysts, the peroxidase-like activity of 3D CuS NSs@N-S-rGO is compared extensively with pure 3D CuS NSs, N-S-rGO, N-rGO, and GO to monitor the effect of each modification and treatment on their catalytic properties. The results indicate promising peroxidase activity of 3D CuS NSs@N-S-rGO by possessing the highest catalytic activity and the Michaelis constant of ~93.5 times lower and 9.7 times higher than that of reported for HRP, respectively. The bionanocomposite is used to detect glucose in serum with and without light. The results show a remarkable enhancement in the limit of detection for glucose from 0.3 μM to 0.075 μM (40 folds) with visible light that can be attributed to the fast electron transfer on the surface of 3D CuS NSs@N-S-rGO and the synergistic interaction of 3D CuS NSs and N-S-rGO. The method was further applied to the colorimetric detection of glucose in human serum and showed high selectivity. Our result also show that this method based on 3D CuS NSs@N-S-rGO is economical, reliable, feasible, and highly efficient.

A wearable electrochemical glucose sensor based on simple and low-cost fabrication supported micro-patterned reduced graphene oxide nanocomposite electrode on flexible substrate

In this study, a reduced graphene oxide (rGO)-based nanostructured composite working electrode of high quality was successfully microfabricated and micro-patterned on a flexible polyimide substrate using simple low-cost fabrication processes. Gold and platinum alloy nanoparticles were electrochemically deposited onto the microfabricated rGO surface and chitosan-glucose oxidase composites were integrated onto the modified surface of the working electrode to develop a human sweat-based wearable glucose sensor application. The fabricated biosensor exhibited excellent amperometric response to glucose at a detection range of 0–2.4 mM (covers the glucose range in sweat), with a sensitivity of 48 μA/mMcm2, a short response time (20 s), and high linearity (0.99). The detection limit for glucose was calculated as 5 µm. The human sweat/mixing glucose samples initially used for testing indicated acceptable detection performance and stability for low glucose concentrations. These results confirm that the proposed nanostructured composite flexible working electrode and fabrication process are highly promising for application as human sweat-based electrochemical glucose sensors.

Highly selective FET-type glucose sensor based on shape-controlled palladium nanoflower-decorated graphene

The glucose concentration in human body fluids is main marker for diagnose diabetes mellitus, which is a disease caused by insufficient insulin. Although diagnostic devices based on glucose level in the blood have been commercialized, a non-invasive detection methodology is required. Here, selectivity enhanced field-effect-transistor (FET)-type glucose sensor based on shape-controlled palladium nanoflower-decorated CVD graphene (SPNFG) with glucose oxidase (GOx) and nafion was fabricated using surface functionalization, electrodeposition and spin coating techniques. The surface-functionalized CVD graphene is used as substrate for electrodeposition and a p-type channel for FET-type sensor. The palladium nanoflower (PNF) shape was controlled by adjusting the sulfuric acid concentration in the electrolyte during the electrodeposition. Nafion and GOx layer were deposited onto SPNFG using spincoating method. The GOx/Nafion/SPNFG electrode within FET system was applied to high sensitive and selective glucose sensor. The GOx/Nafion/SPNFG based sensors exhibit high selectiviy for uric acid and ascorbic acid with low minimum detection limit for glucose (1 nM). and The high durability can be expected for the FET-type sensor by virtue of direct decoration of palladium on the CVD graphene surface.

Preparation of enzyme-functionalized carbon nanotubes and their application in glucose and Fe2+ detection through "turn on" and "turn off" approaches.

A versatile enzyme-functionalized carbon nanotube (CNT) platform was fabricated by covalently conjugating glucose oxidase (GOD) and/or horseradish peroxidase (HRP) on carboxyl-group-functionalized CNTs. The GOD and HRP co-conjugated CNTs were used for the detection of glucose through the chain reaction between glucose, GOD and HRP. The locally formed H2O2 originating from the oxidization of glucose by GOD is able to further oxidize the 3,3',5,5'-tetramethylbenzidine (TMB) substrate, resulting in the production of colorimetric products. The reaction between H2O2 and Fe2+ can deplete the amount of H2O2 in solution, which in turn decreases the oxidization extent of TMB and decreases the absorbance of the solution in the presence of HRP-conjugated CNTs. The hybrid materials can increase the number of active sites, thus increasing the amount of immobilized enzyme molecules on the surface. Electron transmission between different species is also accelerated and the co-conjugated enzymes can decrease the diffusion of intermediate products, further increasing the local concentrations of reactants. By utilizing these hybrid materials, glucose and Fe2+ were successfully detected. The linear dynamic range of glucose and Fe2+ was 1-100 μM, and the limits of detection for glucose and Fe2+ were 0.3 and 0.22 μM, respectively. The selectivity of glucose and Fe2+ was also studied by adding different kinds of interferents (e.g., sugars, metallic ions and biomolecules), and satisfactory results were obtained. In particular, Fe2+ can be distinguished from Fe3+. Meanwhile, the performance of these biosensors was also validated in biological samples (human serum and human serum albumin) using standard addition methods, and good recoveries were obtained.

Double-sided 3D printing on paper towards mass production of three-dimensional paper-based microfluidic analytical devices (3D-μPADs).

Recently, much effort has been focused on developing three-dimensional, paper-based microfluidic analytical devices (3D-μPADs) targeting in vitro diagnostics. However, 3D-μPAD fabrication typically requires tedious assembly that hinders mass production. Here, we report on a fabrication method for 3D-μPADs made of plastics without the need for additional assembly. Both sides of the paper were printed via liquid resin photopolymerization using a digital light processing (DLP) printer. The sample reservoir and detection zones are located on the top of the 3D-μPADs, and three microchannels are located on the bottom. The detection limits for glucose, cholesterol, and triglyceride (TG) in phosphate-buffered saline (PBS) were 0.3 mM, 0.2 mM, and 0.3 mM, respectively. The detectable ranges of glucose, cholesterol, and TG in human serum were 5-11 mM, 2.6-6.7 mM, and 1-2.3 mM. These results suggest that our fabrication method is suitable to mass produce 3D-μPADs with relative ease using simple fabrication processes.

Synergistic peroxidase-like activity of CeO2-coated hollow Fe3O4 nanocomposites as an enzymatic mimic for low detection limit of glucose

Abstract Fe3O4@CeO2 yolk–shell nanocomposites (NCs) were synthesized by growing CeO2 onto Fe3O4 hollow nanoparticles (NPs) as an artificial peroxidase for the purpose of elevated activity. The resultant NCs exhibited strong magnetic response with narrow size distribution and high surface area. Owing to the individual peroxidase-like catalytic activity of CeO2 onto Fe3O4 nanoparticles (NPs), Fe3O4@CeO2 NCs was investigated to achieve synergistic catalytic activity. As a result, the as-prepared Fe3O4@CeO2 NCs exhibited impressive peroxidase-like catalysis activity for 3, 3′, 5, 5′-tetramethylbenzidine (TMB). Moreover, comparing with natural enzymes, hollow Fe3O4 NPs and CeO2 NPs, the Fe3O4@CeO2 NCs displayed a lower Michaelis constant (Km) value or stronger affinity to H2O2 and TMB. A limit of detection of 8.5 µmol/L for H2O2 and 21 µmol/L for glucose was attained with acceptable stability and reproducibility. The activation mechanism was also studies using competitive radical tests and Electron spin resonance (ESR) analysis.

Preparation of bright fluorescent polydopamine-glutathione nanoparticles and their application for sensing of hydrogen peroxide and glucose

A novel water-soluble fluorescent polydopamine derivative, polydopamine-glutathione nanoparticles (PDA-G (-S-)NPs), was synthesized by the Michael addition reaction between dopamine (DA) and reduced glutathione (GSH). Compared to a direct polymerization of dopamine, the as-prepared PDA-G (-S-)NPs have stronger fluorescence emission intensity. Also, the synthesis does not need any hazardous organic solvents and the process is simple. Additionally, the roles of GSH and hydrogen peroxide (H2O2) in enhancing the fluorescence intensity are discussed in detail. The thioether in PDA-G (-S-)NPs is easily oxidized by hydrogen peroxide to sulfoxide and sulfone groups, accompanied by a decrease in fluorescence intensity. Therefore, the PDA-G (-S-)NPs can be applied to construct a fluorescent sensor for the sensitive detection of hydrogen peroxide. Based on the transformation of glucose into gluconic acid and H2O2 in the presence of glucose oxidase, the PDA-G (-S-)NPs system was further utilized to sensing glucose. The linear ranges and detection limits of hydrogen peroxide and glucose are (0.5–6 μM, 2–130 μM) and (0.15 μM, 0.6 μM), respectively.