The authors describe a dye-sensitized photoelectrochemical immunoassay for the tumor marker carcinoembryonic antigen (CEA). The method employs the rhodamine dye Rh123 with red color and absorption maximum at 500 nm for spectral sensitization, and a 3D nanocomposite prepared from graphene oxide and MoS2 acting as the photoelectric conversion layer. The nanocomposite with flower-like 3D architectures was characterized by transmission electron microscopy, scanning electron microscopy, X-ray powder diffraction, and UV-vis diffuse reflectometry. A photoelectrochemical sandwich immunoassay was developed that is based on the use of the nanocomposite and based on the specific binding of antibody and antigen, and by using a secondary antibody labeled with Rh123 and CdS (Ab2-Rh123@CdS). Under optimal conditions and at a typical working voltage of 0 V (vs. Hg/HgCl2), the photocurrent increases linearly 10 pg mL?1 to 80 ng mL?1 CEA concentration range, with a 3.2 pg mL?1 detection limit.
Graphical abstract Flower-like GO-MoS2 complex with high efficiency of electron transport was synthesized to construct photoelectrochemical platform. The sandwich-type immunoassay was built on this platform based on specific binding of antigen and antibody. Carcinoembryonic antigen in sample was detected sensitively by using sensitization of rhodamine dye Rh123 as signal amplification strategy.
A nanocomposite consisting of a few layers of graphene (FLG) and tin dioxide (SnO2) was prepared by ultrasound-assisted synthesis. The uniform SnO2 nanoparticles (NPs) on the FLG were characterized by X-ray diffraction in terms of lattice and phase structure. The functional groups present in the composite were analyzed by FTIR. Electron microscopy (HR-TEM and FE-SEM) was used to study the morphology. The effect of the fraction of FLG present in the nanocomposite was investigated. Sensitivity, selectivity and reproducibility towards resistive sensing of liquid propane gas (LPG) was characterized by the I-V method. The sensor with 1% of FLG on SnO2 operated at a typical voltage of 1 V performs best in giving a rapid and sensitive response even at 27 °C. This proves that the operating temperature of such sensors can be drastically decreased which is in contrast to conventional metal oxide LPG sensors.
Graphical abstract Schematic of a room temperature gas sensor for liquefied petroleum gas (LPG). It is based on the use of a few-layered graphene (1 wt%)/SnO2 nanocomposite that was deposited on an interdigitated electrode (IDEs). A sensing mechanism for LPG detection has been established.
Tungsten disulfide (WS2) nanosheets were obtained by exfoliating WS2 bulk crystals in N-methylpyrrolidone by ultrasonication. Gold nanoparticles (GNPs) were synthesized by in-situ ultrasonication of sodium citrate and HAuCl4 while fabricating the WS2 nanosheets. In this way, the GNPs were self-assembled on WS2 nanosheets to form a GNPs/WS2 nanocomposite through interaction between sulfur and gold atoms. The photoelectrochemical response of WS2 nanosheets is significantly enhanced after integration of the GNPs. The GNPs/WS2 nanocomposite was coated onto a glassy carbon electrode (GCE) to construct a sensing interface which then was modified with an antibody against the carcinoembryonic antigen (CEA) to obtain a photoelectrochemical immunosensor for CEA. Under optimized conditions, the decline in relative photocurrent is linearly related to the logarithm of the CEA concentration in the range from 0.001 to 40 ng mL?1. The detection limit is 0.5 pg mL?1 (at S/N =?3). The assay is sensitive, selective, stable and reproducible. It was applied to the determination of CEA in clinical serum samples.
Graphical abstract Schematic presentation of the fabrication of Au/WS2 nanocomposites by in-situ ultrasonication and the procedure for the CEA photoelectrochemical immunosensor preparation, and the photocurrent response towards the carcinoembryonic antigen.
The paper describes a nonenzymatic amperometric H2O2 sensor that uses a nanocomposite consisting of Co3O4 nanoparticles (NPs) and mesoporous carbon nanofibers (Co3O4-MCNFs). The Co3O4 NPs were grown in situ on the MCNFs by a solvothermal procedure. The synergetic combination of the electrocatalytic activity of the Co3O4 NPs and the electrical conductivity of MCNFs as an immobilization matrix enhance the sensing ability of the hybrid nanostructure. The oxidation current, best measured at 0.2 V (vs. SCE) is linear in the 1 to 2580 μM H2O2 concentration range, with a 0.5 μM lower detection limit (at an S/N ratio of 3). The sensor is highly selective even in the presence of common electroactive interferents. It was applied to the determination of H2O2 in spiked milk samples.
Graphical abstract Schematic of the synthesis of a nanocomposite consisting of Co3O4 nanoparticles (NPs) and mesoporous carbon nanofibers (Co3O4-MCNFs) by a solvothermal procedure. It was used as electrocatalyst for direct oxidation of H2O2.
We report on the synthesis of cobalt dihydroxide [Co(OH)2] nanorods and their deposition on a 3-dimensional graphene network via chemical bath deposition. The structural characterization reveals deposited Co(OH)2 to consist of flower-like nanorods on a 3-dimensional graphene foam. The nanocomposite was used for glucose sensing by electrocatalytic oxidation of glucose in 1 M KOH solution. Cyclic voltammetry and amperometric studies revealed a high sensitivity for glucose (3.69 mA mM?1 cm?2) and a 16 nM detection limit. The nanocomposite offers a large effective surface (11.4 cm2) and is very selective for glucose over potentially interfering materials such as dopamine, ascorbic acid, lactose, fructose and urea, not the least due to a relatively low working potential of 0.6 V (vs. Ag/AgCl). The high sensitivity, low detection limit and very good selectivity of free-standing nanocomposite electrodes are attributed to the synergistic effect of (a) the good electrocatalytic activity of the NRs, and (b) the large surface area with high conductivity offered by the 3D graphene foam.
Graphical Abstract Cobalt hydroxide [Co(OH)2] nanorods were deposited on three dimensional graphene (3DG) by a chemical bath deposition method, and the resulting material was used as an electrode for non-enzymatic and specific sensing of glucose in 1 M KOH solution.
The authors describe the synthesis of a multifunctional nanocomposite with an architecture of type Fe3O4@SiO2@graphene quantum dots with an average diameter of about 22 nm. The graphene quantum dots (GQDs) were covalently immobilized on the surface of silica-coated magnetite nanospheres via covalent linkage to surface amino groups. The nanocomposite displays a strong fluorescence (with excitation/emission peaks at 330/420 nm) that is fairly selectively quenched by Hg2+ ions, presumably due to nonradiative electron/hole recombination annihilation. Under the optimized experimental conditions, the linear response to Hg2+ covers the 0.1 to 70 μM concentration range, with a 30 nM lower detection limit. The high specific surface area and abundant binding sites of the GQDs result in a good adsorption capacity for Hg2+ (68 mg?g?1). The material, due to its superparamagnetism, can be separated by using a magnet and also is recyclable with EDTA so that it can be repeatedly used for simultaneous detection and removal of Hg2+ from contaminated water.
Graphical abstract A schematic view of preparation process for the Fe3O4@SiO2@graphene quantum dots nanocomposite (denoted as Fe3O4@SiO2@GQDs). The graphene quantum dots were covalently immobilized on the surface of silica-coated magnetite nanospheres (Fe3O4@SiO2) via covalent linkage to surface amino groups.
The authors report on a low temperature method for large-scale fabrication of cuprous oxide nanocubes deposited on nitrogen-doped reduced graphene oxide (Cu2O/N-RGO). The material was deposited in a glassy carbon electrode (GCE) where it is found to display enhanced electrocatalytic activity for oxidation of diethylstilbestrol (DES). The morphology and composition of Cu2O/N-RGO were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and energy-dispersive spectroscopy. The results demonstrate that the RGO is doped with 3.5% of nitrogen (atomic ratio), and that nanostructured Cu2O particles with controlled cubical morphology and an average size of about 450 nm have been homogeneously deposited on the surface of N-RGO sheets. The oxidation peak of DES was recorded at 0.315 V (vs. saturated calomel electrode) using differential pulse voltammetry. Under the optimal conditions, the modified GCE displays a linear response in the 0.3 to 150 μM DES concentration range, and the limit of detection is 10 nM. The method was applied to the determination of DES in spiked milk, meat and urine samples and gave excellent selectivity, stability and reproducibility.
Graphic abstract A nanocomposite consisting of Cu2O nanocubes/N-doped reduced graphene oxide (Cu2O/N-RGO) for the electrochemical determination of diethylstilbestrol (DES). The Cu2O/N-RGO modified electrode displays a linear response in the 0.3 to 150 μM DES concentration range. The method was applied to the determination of DES in spiked milk, meat and urine samples
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 molecularly imprinted polymer (MIP) and a nanocomposite prepared from gold nanoparticles (AuNP) and poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate) (PEDOT:PSS) were deposited on a screen-printed carbon electrode (SPCE). The nanocomposite was prepared by one-pot simultaneous in-situ formation of AuNPs and PEDOT:PSS and was then inkjet-coated onto the SPCE. The MIP film was subsequently placed on the modified SPCE by co-electrodeposition of o-phenylenediamine and resorcinol in the presence of the antibiotic nitrofurantoin (NFT). Using differential pulse voltammetry (DPV), response at the potential of ~ 0.1 V (vs. Ag/AgCl) is linear in 1 nM to 1000 nM NFT concentration range, with a remarkably low detection limit (at S/N?=?3) of 0.1 nM. This is two orders of magnitude lower than that of the control MIP sensor without the nanocomposite interlayer, thus showing the beneficial effect of AuNP-PEDOT:PSS. The electrode is highly reproducible (relative standard deviation 3.1% for n?=?6) and selective over structurally related molecules. It can be re-used for at least ten times and was found to be stable for at least 45 days. It was successfully applied to the determination of NFT in (spiked) feed matrices and gave good recoveries.
Graphical abstract Schematic representation of a voltammetric sensor for the determination of nitrofurantoin. The sensor is based on a screen-printed carbon electrode (SPCE) modified with an inkjet-printed gold nanoparticles-poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) nanocomposite and a molecularly imprinted polymer.
Thin films of La2O3 were deposited onto glass substrates by ultrasonic spray pyrolysis. Their structural and morphological properties were characterized by X-ray diffraction, Fourier transform Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray photo-electron spectroscopy, Brunauer-Emmett-Teller and optical absorption techniques. The sensor displays superior CO2 gas sensing performance at a low operating temperature of 498 K. The signal change on exposure to 300 ppm of CO2 is about 75%, and the signal only drops to 91% after 30 days of operation.
Graphical abstract Schematic diagram of the CO2 gas sensing mechanism of an interconnected web-like La2O3 nanostructure in presence of 300 ppm of CO2 gas and at an operating temperature of 498 K.
An Al-doped ZnO@Fe3O4 nanocomposite was synthesized and used as a magnetic sorbent for solid-phase extraction of Cd(II) prior to its determination by flame atomic absorption spectrometry (FAAS). The size and morphology of the nano-sorbent were characterized via X-ray diffraction analysis, scanning electron microscopy and FTIR. Following its desorption with acetic acid, cadmium was quantified by FAAS. Factors affecting the extraction of the Cd(II) were optimized. Under optimized experimental conditions, the calibration graph is linear in the 0.6 to 60 ng mL?1 concentration range. The limit of detection is 0.17 ng mL?1 and the pre-concentration factor is 50. The inter- and intra-day relative standard deviations for six replicate determinations at a Cd(II) level of 40 ng mL?1 are 3.8% and 2.5%, respectively. The method was successfully applied to the trace determination of Cd(II) in spiked water samples. The accuracy of the method was confirmed by analyzing the certified reference material NIST SRM 1643e.
Graphical abstract Schematic of the synthesis of an Al-doped ZnO@Fe3O4 nanocomposite and its application as a magnetic sorbent for solid-phase extraction of Cd(II) prior to its determination by flame atomic absorption spectrometry (FAAS).
Cuprous oxide (Cu2O) thin films have been deposited onto fluorine doped tin oxide (FTO) glass substrates by using electrochemical route. The structural, morphological, and chemical composition of the deposited films have been studied by using X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Energy dispersive x-ray spectroscopy (EDAX) techniques respectively. The optical studies have been carried out by using UV-Vis spectroscopy. The effect of potential, pH and bath temperature onto absorption and band gap of Cu2O thin films have been studied. The highest sensitivity 6.25 mA·mM·cm-2 is observed for the thin films which shows glucose concentration 7 mM in 0.1 M NaOH solution. The results indicates Cu2O is promising material for glucose sensor with high sensitivity, high stability, and repeatability.
Graphical abstract The surface morphology of Cu2O thin films was found to be tip-truncated octahedral. The films were prepared by electrodeposition. The Cu2O thin films were used to construct low cost, highly sensitive and stable glucose sensor.
We describe a highly sensitive glucose probe based on carbon dots modified with MnO2. A strong reduction of the green fluorescence of the carbon dots (CDs) happened due to the surface energy transfer (SET) from CDs to the deposited MnO2. In the presence of H2O2 (formed via enzymatic oxidation of glucose), fluorescence is restored because the MnO2 nanosheets are reduced to form colorless Mn(II) ions. These findings were used to design a fluorometric glucose assay that has a detection limit as low as 44 nM (at an S/N ratio of 3).
Graphical Abstract A strong reduction of the green fluorescence of the carbon dots (CDs) occurs due to surface energy transfer (SET) from CDs to the deposited MnO2. In the presence of H2O2 (formed by enzymatic action of glucose oxidase) the MnO2 nanosheets are reduced to form colorless Mn(II) ions, and glucose can be quantified by the fluorescence restored.
Hetero-dimeric magnetic nanoparticles of the type Au-Fe3O4 have been synthesised from separately prepared, differently shaped (spheres and cubes), monodisperse nanoparticles. This synthesis was achieved by the following steps: (a) Mono-functionalising each type of nanoparticles with aldehyde functional groups through a solid support approach, where nanoparticle decorated silica nanoparticles were fabricated as an intermediate step; (b) Derivatising the functional faces with complementary functionalities (e.g. amines and carboxylic acids); (c) Dimerising the two types of particles via amide bond formation. The resulting hetero-dimers were characterised by high-resolution TEM, Fourier transform IR spectroscopy and other appropriate methods.
Graphical Abstract Nano-LEGO: Assembling two types of separately prepared nanoparticles into a hetero-dimer is the first step towards complex nano-architectures. This study shows a solid support approach to combine a gold and a magnetite nanocrystal.
A glassy carbon electrode (GCE) was modified with a nanocomposite consisting of tetraoctylammonium bromide (TOAB), C60 fullerene, and palladium nanorods (PdNRs). The PdNRs were hydrothermally prepared and had a typical width of 20 ± 2 nm. The nanocomposite forms stable films on the GCE and exhibits a reversible redox pair for the C60/C60? system while rendering the surface to be positively charged. The modified GCE was applied to fabricate an electrochemical biosensor for detecting acetylcholinesterase (AChE) by measurement of the amount of thiocholine formed from acetylthiocholine, best at a working voltage of ?0.19 V (vs. SCE). The detection scheme is based on (a) measurement of the activity of ethyl paraoxon-inhibited AChE, and (b) measurement of AChE activity after reactivation with pralidoxime (2-PAM). Compared to the conventional methods using acetylthiocholine as a substrate, the dual method presented here provides data on the AChE activity after inhibition and subsequent reactivation, thereby yielding credible data on reactivated enzyme activity. The linear analytical range for AChE activity extends from 2.5 U L?1 to 250 kU·L?1, and the detection limit is 0.83 U L?1.
Graphical abstract Cyclovoltammetric acetylcholinesterase (AChE) activity assay is constructed based on the palladium nanorods composited with functionalized C60 fullerene (PdNR/C60 + TOAB), which aims to measure the signal change between ethyl paraoxon-inhibited and subsequent pralidoxime (2-PAM)-reactivated AChE activity.
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).
The authors describe a disposable electrochemical immunosensor strip for the detection of the Japanese encephalitis virus (JEV). The assay is based on the use of a screen printed carbon electrode (SPCE) modified with carbon nanoparticles (CNPs) that were prepared from starch nanoparticles and deposited on the SPCE working electrode whose surface was functionalized with 3-aminopropyl triethoxysilane. Next, antibody of JEV was immobilized on the surfaces of the CNPs. The analytical performance of immunosensor strip was characterized using cyclic voltammetry (with hexacyanoferrate as the redox probe) and electrochemical impedance spectroscopy. The deposition of CNPs enhances the electron transfer kinetics and current intensity of the SPCE by 63% compared to an unmodified SPCE. Under optimized conditions, the calibration plot is linear within the 5–20 ng·mL?1 JEV concentration range, the limit of detection being 2 ng·mL?1 (at an S/N ratio of 3), and the assay time is 20 min. This immunosensor strip was successfully applied to the detection of JEV in human serum samples. It represents a cost-effective alternative to conventional diagnostic tests for JEV.
Graphical abstract A disposable carbon nanoparticles modified screen printed carbon electrode (SPCE) immunosensor strip for Japanese encephalitis virus (JEV) detection is described. A limit of detection of 2 ng·mL?1 and an assay time of 20 min were achieved.
The incorporation of nanomaterials into electrochemical sensors is an attractive approach towards the improvement of the sensitivity of amperometry and also can provide improved sensor selectivity and stability. This review (with 137 references) details the current state of the art and new trends in nanomaterial-based electrochemical sensing of hydrogen peroxide (H2O2), hydrogen sulfide (H2S) and nitric oxide (NO) in cells or released by cells. The article starts with a discussion of the significance of the three analytes, and this is followed by three sections that summarize the electrochemical detection schemes for H2O2, H2S and NO. Each section first summarizes the respective physiological roles, and then reviews electrochemical sensors based on the use of carbon nanomaterials, noble metal nanomaterials, metal oxide nanomaterials, and layered doubled hydroxides. The materials are compiled in three tables along with figures of merit for the various sensors.
Graphical abstract Nanomaterial-based electrochemical sensors for Reactive oxygen species (H2O2), Reactive nitrogen species (NO) and Reactive hydrogen sulfide species (H2S) inside cells or released by cells.
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.
An electrochemical microsensor for chloramphenicol (CAP) was fabricated by introducing magnetic Fe3O4 nanoparticles (NPs) onto the surface of activated carbon fibers. This microsensor exhibited increased electrochemical response toward CAP because of the synergetic effect of the Fe3O4 NPs and the carbon fibers. Cyclic voltammograms were acquired and displayed three stable and irreversible redox peaks in pH 7.0 solution. Under optimized conditions, the cathodic current peaks at ?0.67 V (vs. Ag/AgCl). The calibration plot is linear in the 40 pM to 1 μM CAP concentration range, with a 17 pM detection limit (at a signal-to-noise ratio of 3). The sensor was applied to the determination of CAP in spiked sediment samples. In our perception, this electrocatalytic platform provided a useful tool for fast, portable, and sensitive analysis of chloramphenicol.
Graphical abstract A sensitive carbon fiber microsensor modified with Fe3O4 nanoparticles is found to display two cathodic peaks when detecting chloramphenicol at 100 mV·s?1 and at pH 7.0. The sensor was applied to the determination of chloramphenicol in sediment samples.
