The authors describe a composite material prepared from carbon nanohorns and poly(2-aminopyridine) that was obtained by electrochemical polymerization of 2-aminopyridine on carbon nanohorns. The material was used to modify a glassy carbon electrode (GCE) to obtain a sensor for non-enzymatic determination of hydrogen peroxide. The modified GCE was characterized by cyclic voltammetry, electrochemical impedance spectroscopy and chronoamperometry. The modified electrode is shown to display excellent electrical conductivity and catalytic activity towards hydrogen peroxide, mainly due to the large specific surface area of carbon nanohorns, the good electron charge transfer properties resulting from the use of poly(2-aminopyridine), and their synergistic effect. The response of the modified GCE (best operated at a working potential of ?0.45 V vs. SCE) to H2O2 is linear in the 0.05 to 8 mM concentration range. The limits of detection (LOD) and quantitation (LOQ) are 3.6 μM and 12.4 μM, respectively. The electrode is selective, stable and reproducible, this making it a promising tool for non-enzymatic determination of hydrogen peroxide.
The authors describe an electrochemical sensor for hydrogen peroxide (H2O2). It was constructed by consecutive, selective modification of a glassy carbon electrode (GCE) with Prussian Blue (PB), layered molybdenum disulfide (MoS2), and reduced graphene oxide (rGO). The properties of the modified GCE were characterized via high-resolution transmission electron microscopy, UV-vis spectroscopy and X-ray diffraction. The electrochemical properties of the electrode were studied using cyclic voltammetry and electrochemical impedance spectroscopy. The sensor exhibits excellent electrocatalytic activity for the reduction of hydrogen peroxide in comparison to GCEs modified with MoS2-rGO or PB only. Response is linear in the 0.3 μM to 1.15 mM H2O2 concentration range at a working analytical voltage of 0.1 V, with a 0.14 μM detection limit. The electrochemical sensitivity is 2883.5 μA·μM?1·cm?2, and response is fast (<10 s). The sensor is selective, stable and reproducible. This is attributed to the efficient electron transport properties of the MoS2-rGO composite and the high loading with PB.
Graphic abstract Prussian Blue nanoparticles were deposited on MoS2-rGO modified glassy carbon electrode by electrochemical method. This sensor was used for the detection of H2O2 in tap water and river water.
Iron sulfides with different atomic ratios were synthesized by a hydrothermal method and used to modify a glassy carbon electrode. The various sulfides were compared to each other for their amperometric response to H2O2. It is found that FeS is the most adequate material. Operated in 0.1 M NaOH solution at 0.4 V (vs. Ag/AgCl), the sensor based on FeS displays a linear response that extends from 0.50 μM to 20.5 mM of H2O2, with a sensitivity of 36.4 μA mM?1 cm?2 and a detection limit of 0.15 μM (at an S/N ratio of 3). The sensor is selective, stable and reproducible.
Graphical abstract Schematic of the synthesis of pomegranate flower-like FeS by a hydrothermal route using ferric chloride and thiourea (SC(NH2)2) as the precursors, and ethanolamine (EA) as the structure-guiding auxiliary agent. A glassy carbon electrode (GCE) modified with this material allows for amperometric sensing of hydrogen peroxide in 0.1 M NaOH solution with a 0.15 μM detection limit.
A glassy carbon electrode (GCE) was modified with gold nanoparticles (AuNPs) coated on monolayer graphene (AuNP/MG) by direct in situ sputtering of AuNPs on CVD-generated graphene. This process avoids complicated polymer transfer and polymer cleaning processes and affords AuNPs with a clean surface. The monolayer graphene is ductile and well dispersed. The clean surface of the AuNPs renders this sensor superior to GCEs modified with AuNPs on reduced graphene oxide in terms of the amperometric non-enzymatic determination of hydrogen peroxide. The detection limit is 10 nM (S/N = 3) at 0.55 V (vs. SCE), which is lower than that for similar methods, and the response time is as short as 2 s. Another attractive feature of the sensor is its feasibility for large-scale production via CVD and sputtering.
Graphical abstract Gold nanoparticles deposited onto monolayered graphene generated by chemical vapor deposition (CVD) are used for electrochemical sensing of H2O2, with the detection limit of 10 nM (S/N = 3) and response time of less than 2 s.
The work describes a hybrid electrochemical sensor for highly sensitive detection of the anesthetic lidocaine (LID). Porous carbon (PC) was synthesized from an isoreticular metal-organic framework-8 (IRMOF-8) and drop cast onto a glassy carbon electrode (GCE). A layer of a molecularly imprinted polymer (MIP) layer was then fabricated in situ on the modified GCE by electro-polymerization, with LID acting as the template and resorcinol as the functional monomer. Hexacyanoferrate is used as an electrochemical probe. The electrical signal (typically acquired at 0.335 V vs. SCE) increases linearly in the 0.2 pM to 8 nM LID concentration range, with a remarkable 67 fM detection limit (at an S/N ratio of 3). The sensor is stable and selective. Eventually, rapid and accurate detection of LID in spiked real samples was successfully realized.
The authors report on the preparation of a hollow-structured cobalt ferrite (CoFe2O4) nanocomposite for use in a non-enzymatic sensor for hydrogen peroxide (H2O2). Silica (SiO2) nanoparticles were exploited as template for the deposition of Fe3O4/CoFe2O4 nanosheets, which was followed by the removal of SiO2 template under mild conditions. This leads to the formation of hollow-structured Fe3O4/CoFe2O4 interconnected nanosheets with cubic spinel structure of high crystallinity. The material was placed on a glassy carbon electrode where it acts as a viable sensor for non-enzymatic determination of H2O2. Operated at a potential of ?0.45 V vs. Ag/AgCl in 0.1 M NaOH solution, the modified GCE has a sensitivity of 17 nA μM?1 cm?2, a linear response in the range of 10 to 1200 μM H2O2 concentration range, and a 2.5 μM detection limit. The sensor is reproducible and stable and was applied to the analysis of spiked urine samples, where it provided excellent recoveries.
Graphical abstract Schematic of a cobalt ferrite (CoFe2O4) hollow structure for use in electrochemical determination of H2O2. The sensor shows a low detection limit, a wide linear range, and excellent selectivity for H2O2.
A nanocomposite consisting of cetyltrimethylammonium bromide (CTAB), Fe3O4 nanoparticles and reduced graphene oxide (CTAB-Fe3O4-rGO) was prepared, characterized, and used to modify the surface of a glassy carbon electrode (GCE). The voltammetric response of the modified GCE to 4-nonylphenol (NPh) was investigated by cyclic voltammetry and revealed a strong peak at around 0.57 V (vs. SCE). Under optimum conditions, the calibration plot is linear in the ranges from 0.03 to 7.0 μM and from 7.0 to 15.0 μM, with a 8 nM detection limit which is lower that that of many other methods. The modified electrode has excellent fabrication reproducibility and was applied to the determination of NPh in spiked real water samples to give recoveries (at a spiking level of 1 μM) between 102.1 and 99.1%.
Graphical abstract A nanocomposite consisting of cetyltrimethylammonium bromide (CTAB), Fe3O4 nanoparticles and reduced graphene oxide (CTAB-Fe3O4-rGO) was prepared and used to modify the surface of a glassy carbon electrode (GCE) for the differential pulse voltammetric (DPV) determination of 4-nonylphenol (NPh).
A temperature-responsive biosensing film consisting of the temperature-responsive block co-polymer poly (N-isopropylacrylamide)-b-poly(2-acrylamidoethyl benzoate) (referred to as PNIPAM-b-PAAE), graphene oxide (GO), and hemoglobin (Hb) was fabricated and used to modify a glassy carbon electrode (GCE). The film provides a favorable micro-environment for Hb to facilitate the electron transfer to the GCE. Hb at PNIPAM-b-PAAE/GO/Hb (PGH) film exhibits a couple of well-defined redox peaks with a formal potential of ?0.371 V (vs. SCE) and displays intrinsic electro-catalytic activity toward H2O2. The sensing film also shows temperature-tunable catalytic activity toward H2O2 that can be stimulated by temperature. Large peak currents can be seen in amperometry at 0.4 V (vs. SCE) in pH 7.0 phosphate buffer only if the temperature is above the lower critical solution temperature (LCST) of 32 °C. The response of the modified GCE is linear in the 0.1 to 3.7 μmol L?1 concentration range if operated at above 32 °C, but in the 0.2 to 3.7 μmol L?1 concentration range at below 30 °C. This behavior is attributed to the temperature-dependent phase transition of PNIPAM-b-PAAE and cooperative effect of GO. The strategy presented here in our perception meets the requirements of switchable sensors for use in bioscience and biotechnology.
Graphical abstract A temperature-responsive biosensing film consisting of temperature-responsive polymer, graphene oxide and hemoglobin has been fabricated. This film displays favorable electrochemical property and good electro-catalytic activity toward H2O2. It also exhibits catalytic activity change upon temperature stimuli.
A bimetallic metal-organic framework of the type MOF(Co/2Fe), synthesized by a hydrothermal method, is demonstrated to exhibit peroxidase-like activity and oxidase-like activity. The material catalyzes the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) to produce a blue product both in the absence and presence of H2O2. Its catalytic activity strongly depends on temperature and the solution pH value. With its dual enzyme mimetic activity, MOF(Co/2Fe) has the advantages of low cost, good stability, ease of preparation, and attractive Michaelis-Menten behavior. The mechanisms and kinetics of the pseudo-enzymatic activity were studied in some detail. A colorimetric method was developed for determination of H2O2 that is based on the peroxidase-like activity of MOF(Co/2Fe). Under the optimal conditions, the absorbance of oxidized TMB at 652 nm increases linearly in the 10 to 100 μM H2O2 concentration range, with a 5 μM limit of detection.
Graphical Abstract A bimetallic metal-organic framework of the type MOF(Co/2Fe) exhibits peroxidase-like activity and oxidase-like activity. The material catalyzes the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) to produce a blue product in the presence and absence of H2O2.
The electrogenerated chemiluminescence (ECL) of methionine stabilized gold nanoclusters (Met-AuNCs) is presented. The Met-AuNCs were used to modify a glassy carbon electrode (Met-AuNC/GCE) which is shown to exhibit a stable and strong cathodic ECL signal (at ?1.86 V) when using potassium peroxodisulfate (K2S2O8) as the coreactant in aqueous solution of pH 7.4. Compared to a GCE modified with BSA-AuNCs, the ECL intensity of Met-AuNCs is 5-fold enhanced. The possible ECL reaction mechanism of the ECL system was studied, and a method for the determination of dopamine (DA) was worked out. The modified GCE has a linear response in the 0.1 to 4 μM DA concentration range, with a detection limit of 32 nM (at an S/N ratio of 3). The method was applied to the determination of DA released by PC12 cells. In our perception, the Met-AuNC/GCE provides a viable new tool in ECL based bioanalysis that also paves new routes to the design and application of new sensors.
Graphical abstract The electrochemiluminescence (ECL) sensor based on methionine stabilized gold nanocluster modified glassy carbon electrode (Met-AuNC/GCE) using potassium peroxodisulfate (K2S2O8) as the coreactant in aqueous solution was fabricated for the highly sensitive detection of dopamine (DA) released by cells.
The β1 receptor blocker metoprolol targets the hypertension-carrying adrenergic receptor gene (ADRB1), but therapy is often hindered by a lack of evidence-based medical information. The authors describe an assay for the ADRB1 gene. It is based on the electrocatalytic oxidation of H2O2 by a nanocomposite consisting of hemin and platinum nanoparticles in an amino-modified metal-organic framework of the type Fe-MIL-88-NH2 and heavily loaded with Cu(II) ions. The nanocomposite was placed on a glassy carbon electrode (GCE), and the resulting sensor displays increased electrocatalytic activity with the addition of H2O2 because of the synergistic effects of hemin and the platinum nanoparticles (Pt NPs). Next, a capture DNA probe for the target ADRB1 gene was immobilized on the modified GCE. Binding of the target gene results in a distinct change in the electrocatalytic activity of H2O2. The amperometric i–t curves were recorded at ?0.4 V in 5 mL of phosphate buffered saline at room temperature. The electrode responds to ADRB1 in the 1 f. to 10 nM concentration range and has a 0.21 f. detection limit (at a S/N ratio of 3). In our perception, this detection scheme can simplify and accelerate the identification of drug response and therapeutic efficacy. Conceivably, it may be applied to other mutations, and it may enable a more precise clinical prognosis and thus facilitate personalized medical diagnostics.
Graphical abstract Schematic presentation of an electrode for the determination of the adrenergic receptor gene (ADRB1). The assay is based on the electrooxidation of added H2O2 by using a glassy carbon electrode (GCE) coated with a composite prepared from platinum nanoparticles (Pt NPs), hemin and a metal-organic framewok of type Fe-MIL-88NH2 loaded with Cu(II). This versatile platform simplifies studies on the response of hypertension drugs and the effectiveness of therapy.
An electrochemical sensor for H2O2 was developed based on electrochemically deposited Prussian blue (PB) nanoparticles doped poly(3,4-ethylenedioxythiophene) (PEDOT). The PEDOT/PB composite was composed of PEDOT wrapped PB nanoparticles, where the conducting polymer PEDOT not only protected the PB particles to warrant high stability, but also connected them to enhance the electron transfer. Owing to the excellent conductivity of PEDOT and unique electrocatalytic activity of PB, the PEDOT/PB modified electrode exhibited good catalytic activity toward the electrochemical reduction of H2O2, and was used for the detection of H2O2 in concentrations ranging from 0.5 to 839 μM, with a detection limit of 0.16 μM. Moreover, the sensor also demonstrated excellent reproducibility, selectivity and long-term stability, showing great promise for the fabrication of electrochemical sensors and H2O2 related biosensors.
Graphical abstract An electrochemical non-enzymatic sensor for hydrogen peroxide with excellent stability was developed. It is based on conducting polymer PEDOT doped with Prussian blue nanoparticles.
This study describes an amperometric sensor for hydrogen peroxide (H2O2) that uses an ITO glass electrode which was modified with a nanocomposite consisting of electrochemically reduced graphene oxide and gold nanoclusters (AuNCs). The sensor was used to quantify extracellular H2O2 released from human neuroblastoma cells of type SH-SY5Y. The calibration plot, established best at a working voltage of ?0.4 V (vs. Ag/AgCl) is linear in the 40 nmol?L?1 to 2 μmol?L?1 concentration range, and the detection limit is 20 nmol?L?1 (at a signal-to-noise ratio of 3). The method was further applied to study bupivacaine-induced cell damage and the protective effects of α-lipoic acid. The study indicated that pretreatment of the cells with lipoic acid retards cell damage induced by bupivacaine. The sensor can be easily fabricated, is disposable and highly sensitive. The sensor is perceived to represent an alternative for studying the interactions of drugs with cells, and as an effective tool to quantify cell-secreted H2O2.
Graphical abstract One-step electrochemical synthesis of graphene oxide and gold nanoclusters on an ITO electrode for studying the release of H2O2 from SH-SY5Y cells and for evaluation of drug-induced cell damage
A composite material obtained by ultrasonication of graphene oxide (GO) and multi-walled carbon nanotubes (MWCNTs) was loaded with manganese dioxide (MnO2), poly(diallyldimethylammonium chloride) and gold nanoparticles (AuNPs), and the resulting multilayer hybrid films were deposited on a glassy carbon electrode (GCE). The microstructure, composition and electrochemical behavior of the composite and the modified GCE were characterized by transmission electron microscopy, Raman spectra, energy-dispersive X-ray spectroscopy, electrochemical impedance spectroscopy and cyclic voltammetry. The electrode induces efficient electrocatalytic oxidation of dopamine at a rather low working voltage of 0.22 V (vs. SCE) at neutral pH values. The response is linear in the 0.5 μM to 2.5 mM concentration range, the sensitivity is 233.4 μA·mM￣1·cm￣2, and the detection limit is 0.17 μM at an SNR of 3. The sensor is well reproducible and stable. It displays high selectivity over ascorbic acid, uric acid and glucose even if these are present in comparable concentrations.
Graphical abstract Gold nanoparticles were self-assembled onto the surface of the MnO2 decorated graphene oxide-carbon nanotubes composites with poly(diallyldimethylammonium chloride) (PDDA) as a coupling agent. Further, a sensitive electrochemical sensor of dopamine was developed via immobilizing this nanocomposite on a glassy carbon electrode (GCE).
We report on a non-enzymatic hydrogen peroxide (H2O2) sensor which makes use of a nanocomposite consisting of platinum nanoparticles (PtNPs) and chitosan-encapsulated graphite (graphite-CS). The composite was prepared by sonication of pristine graphite in chitosan (CS) in 5 % acetic acid. The PtNP decorated graphite-CS (graphite-CS/PtNPs) composite was prepared by electrodeposition of PtNPs on the graphite-CS modified glassy carbon electrode. The graphite-CS/PtNP composite was characterized by scanning electron microscopy, elemental analysis and FTIR spectroscopy. The modified electrode displays an enhanced reduction peak current for H2O2 when compared with electrodes modified with graphite/PtNPs and PtNPs. The modified electrode exhibits excellent electrocatalytic activity towards the reduction of H2O2, and the amperometric response is linear over the concentration range from 0.25 to 2890 μM. The sensitivity and the detection limit are 0.465 μA?μM￣1 ? cm￣2 and 66 nM, respectively. The sensor shows fast response (3 s) in detecting H2O2. It is also highly selective in the presence of potentially interfering compounds, and may therefore be used as a feasible platform for sensing H2O2 in real samples.
A method is described for ratiometric fluorometric assays of H2O2 by using two probes that have distinct response profiles. Under the catalytic action of ferrous ion, the 615 nm emission of protein-stabilized gold nanoclusters (under 365 nm photoexcitation) is quenched by H2O2, while an increased signal is generated with a peak at 450 nm by oxidizing coumarin with the H2O2/Fe(II) system to form a blue emitting fluorophore. These decrease/increase responses give a ratiometric signal. The ratio of the fluorescences at the two peaks are linearly related to the concentration of H2O2 in the range from 0.05 to 10 μM, with a 7.7 nM limit of detection. The detection scheme was further coupled to the urate oxidase catalyzed oxidation of uric acid which proceeds under the formation of H2O2. This method provides an simple and effective means for the construction of ratiometric fluorometric (enzymatic) assays that involve the detection of H2O2.
Graphical abstract Under catalysis by ferrous ion, hydrogen peroxide quenches the luminescence of gold nanoclusters (AuNCs) and oxidizes coumarin into a fluorescent derivative, which rendered fluorescence ON and OFF at two distinct wavelengths for ratiometric measurements.
A nanostructured material of the type Au-ZnO-SiO2 is described that consists of ZnO and gold nanoparticles (NPs) dispersed into a silica matrix and used to construct a voltammetric sensor for 4-nitrophenol. The AuNPs and ZnO NPs are anchored onto the silica network which warrants the nanostructures to be stable in various environments. It also facilitates the electron transfer between the electrolyte and the glassy carbon electrode (GCE). The properties of the nanostructure as a modifier for the GCE were investigated by energy dispersive spectrometry, X-ray diffraction spectroscopy, and transmission electron microscopy. It is shown that the nanostructure increases the surface area. Hence, the cathodic and anodic current in differential pulse voltammetry of 4-nitrophenol are considerably enhanced in comparison to a bare GCE. Under optimum conditions, the currents for oxidation and reduction are proportional to the concentration of 4-nitrophenol in the 0.05–3.5 μM and 0.01–1.2 μM concentration ranges, with 13.7 and 2.8 nM detection limits, respectively. The sensor has excellent sensitivity, fast response, long-term stability, and good reproducibility. It is perceived to be a valuable tool for monitoring 4-nitrophenol in real water samples.
Graphical abstract Schematic of voltammetric sensor for 4-nitrophenol. It is based on GCE modified with gold-ZnO-SiO2 nanostructure. It exhibited the improvement in performance for both oxidation and reduction peaks in terms of linearity, concentration range, detection limit, and sensitivity.
Nanocomposites consisting of gold nanoclusters and graphene oxide (AuNC/GO) were prepared and investigated with respect to the design of new sensors for hydrogen peroxide (H2O2). The AuNC/GO hybrid nanomaterials were deposited on a gold electrode by the layer-by-layer assembly method, where they showed enhanced photoelectrical and sensing properties. The presence of graphene oxide improves the photoinduced electron separation efficiency of the AuNCs, as well as the catalytic effect of AuNCs on the electroreduction of H2O2. Compared to an electrode modified with AuNCs only, the new electrodes display a more than ten-fold enhanced photocurrent at a working voltage of -500 mV (vs. Ag/AgCl), higher sensitivity for H2O2 (25.76 nA?mM?1), lower LOD (2 μM) and extended linear range (from 30 μM to 5 mM). The sensors were applied to the determination of H2O2 extracted from living human umbilical vein endothelial cells stimulated by angiotensin II.
Graphical abstract Graphene oxide (GO) not only improves the photoinduced charge separation efficiency of fluorescent gold nanoclusters (AuNCs) based photoelectrochemical sensors, but also enhances the catalytic property of AuNCs on the detection of hydrogen peroxide (H2O2).
A binary nanocomposite of type copper tungstate and polyaniline (CuWO4@PANI) is described that was obtained by single step polymerization on the surface of a glassy carbon electrode (GCE). The resulting electrode is shown to be a viable tool for voltammetric sensing of quercetin (Qn) in blood, urine and certain food samples. The nanocomposite was characterized by UV-visible absorption spectroscopy, Fourier-transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction and high-resolution transmission electron microscopy. Differential pulse voltammetry was applied to quantify Qn, typically at the relatively low working potential of 0.15 V (vs. Ag/AgCl). The modified GCE has a wide analytical range (0.001–0.500 μM) and a low detection limit (1.2 nM). The sensor is reproducible, selective and stable. This makes it suitable for determination of Qn in real samples without complicated sample pretreatment.
Graphical abstract Schematic of a copper tungstate and polyaniline nanocomposite modified glassy carbon electrode for voltammetric determination of quercetin in real samples.
The authors describe a method for signal amplification of label-free voltammetric immunosensors. A glassy carbon electrode (GCE) was modified with Prussian Blue-platinum nanoparticles (PB-PtNPs) as a redox-active species that gives a strong amperometric signal at 0.18 V (vs. Ag/AgCl). Benefitting from the excellent electrical conductivity and the strong catalytic activity to H2O2, the modified GCE gives a strongly enhanced signal. The PB-PtNPs were incorporated into a polyaniline (PANI) hydrogel to further enhance the signal. The signal response of the PB-PtNP-PANI/GCE is larger by a factor of 7.6 than that of PB-PtNP/GCE. In order to further improve electrical conductivity and immobilize antibody, gold nanoparticles (AuNPs) were deposited on the surface of the PB-PtNP-PANI hydrogel. The AuNP-PB-PtNP-PANI hydrogel nanocomposite on the GCE was used in an immunosensor for the model analyte carcinoma antigen 125 (CA125), a biomarker for epithelial ovarian cancer, by immobilizing the respective antibody on the modified GCE. A linear response found for the 0.01 to 5000 U mL?1 CA125 concentration range, with a detection limit of 4.4 mU mL?1 (at an S/N ratio of 3). The electrochemical sensitivity is as high as 119.76 μA·(U/mL)?1·cm?2. The detection of CA125 in human serum showed satisfactory accuracy compared to a commercial chemiluminescent microparticle immunoassay (CMIA).
Graphical abstract Schematic of a nanocomposites consisting of gold nanoparticles, Prussian Blue, platinum nanoparticles and polyaniline hydrogel as a signal multi-amplification sensing substrate for the ultrasensitive immuno detection of carcinoma antigen 125 (CA125).
