The authors describe magnetic nanoparticles consisting of an Fe3O4 core and a poly(methacrylic acid) coating for dispersive solid phase extraction (DSPE) of arsenic prior to its determination by hydride-generation microwave plasma AES (HG-MP-AES). The particles have an average size of 25 nm, can be prepared at low costs, and provide improved operational safety in combination with plasma generation. The methods allows arsenic to be determined with detection limits (at 3σ/m) of 3.0 ng?L?1 for As(III) and of 10.0 ng?L?1 of As(V). Recoveries of (spiked) samples range from 99.0 to 102%. This is the first report on the use of HG-MP-AES for speciation and preconcentration of arsenic using DSPE. The method displays detection limits that come close to those of ICP-OES and ICP-MS.
Graphical abstract A core/shell Fe3O4@poly(methacrylic acid) coated sorbent was synthesised and employed to the speciation of arsenic prior to its determination by hydride-generation microwave plasma atomic emission spectrometry.
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.
The authors report that the peroxidase-like activity of Au@Pt core-shell nanohybrids (Au@PtNHs) is selectively inhibited by cysteine. This finding has led to a highly sensitive colorimetric assay for cysteine that is based on the nanohybrid-catalyzed oxidation of TMB by H2O2 to form a blue product. The method has a detection limit of 5.0 nM and a linear range from 10 nM to 20 μM. The assay is highly selective over other amino acids. It was successfully applied to the determination of cysteine in an injection containing a mixture of amino acids.
Graphical abstract The peroxidase-like activity of Au@Pt core-shell nanohybrids (Au@PtNHs) is selectively inhibited by cysteine, enabling the determination of cysteine.
A photoelectrochemical wire microelectrode was constructed based on the use of a TiO2 nanotube array with electrochemically deposited CdSe semiconductor. A strongly amplified photocurrent is generated on the sensor surface. The microsensor has a response in the 0.05–20 μM dopamine (DA) concentration range and a 16.7 μM detection limit at a signal-to-noise ratio of 3. Sensitivity, recovery and reproducibility of the sensor were validated by detecting DA in spiked human urine, and satisfactory results were obtained.
Graphical abstract Schematic of a sensitive photoelectrochemical microsensor based on CdSe modified TiO2 nanotube array. The photoelectrochemical microsensor was successfully applied to the determination of dopamine in urine samples.
A highly selective electrochemical sensor was fabricated based on a modified carbon paste electrode with zinc ferrite nanoparticles (ZnFe2O4 NPs). The nanocomposite has attractive properties such as high surface-to-volume ratio and good electrocatalytic activity towards the drugs acetaminophen (AC), epinephrine (EP), and melatonin (MT), best at working voltages of 0.35, 0.09 and 0.55 V (vs. Ag/AgCl), respectively. The linear ranges (and detection limits) are 6.5–135 (0.4) μmol L?1 for AC, 5–100 (0.7) μmol L?1 for EP, and 6.5–145 (3) μmol L?1 for MT.
Graphical abstract A novel electrochemical sensor based on a modified carbon paste electrode with zinc ferrite nanoparticles (ZnFe2O4) for the simultaneous detection of the acetaminophen, epinephrine and melatonin was fabricated
A method is described for the determination of the polarity of mixed organic solvents by using the fluorescent probe Hostasol Red (HR) desposited on the outer surface of nanosized zeolite L. Organic solvents and their mixtures can be roughly classified according to their polarity with bare eyes and fluorometrically. Emission peaks range from 520 to 640 nm. Some solvents act as quenchers. The method is studied with series of protic and nonprotic solvents, and with selected mixtures of organic solvents.
Graphical abstract The dye Hostalene Red adsorbed on nanosized zeolite shows strong fluorescence solvatochromism. This can be exploited to quickly assess the polarity of solvents and solvent mixtures.
The authors report that sulfide ions are capable of inhibiting the peroxidase-like activity of copper nanoclusters (CuNCs). The catalytic activity of CuNCs toward the oxidation of the chromogenic substrate 3,3′,5,5′-tetramethylbenzidine by H2O2 is remarkably decreased in the presence of sulfide. Based on this finding, a colorimetric assay was developed for the rapid determination of sulfide. Best operated at a wavelength of 652 nm, it has a 0.5 μM detection limit. The method is highly selective and has been successfully applied to the quantification of sulfide in environmental water samples.
Graphical abstract The catalytic activity of CuNCs toward the oxidation of 3,3′,5,5′-tetramethylbenzidine by H2O2 is remarkably decreased in the presence of sulfide ions. This finding has been applied to design a method for colorimetric quantification of sulfide ions in environmental samples.
The authors describe an ethylene glycol assisted precipitation method for synthesis of Er(III)/Yb(III)-doped BiF3 nanoparticles (NPs) at room temperature. Under 980-nm light irradiation, the NPs emit upconversion (UC) emission of Er(III) ions as a result of a two-photon absorption process. The temperature-dependent green emissions (peaking at 525 and 545 nm) are used to establish an unambiguous relationship between the ratio of fluorescence intensities and temperature. The NPs have a maximum sensitivity of 6.5?×?10?3 K?1 at 619 K and can be applied over the 291–691 K temperature range. The results indicate that these NPs are a promising candidate for optical thermometry.
Graphical abstract Schematic of the room-temperature preparation of Er(III)/Yb(III)-doped BiF3 nanoparticles with strongly temperature-dependent upconversion emission.
This review (with 85 refs.) summarizes the recent literature on the adsorption of common aromatic pollutants by using modified metal-organic frameworks (MOFs). Four kinds of aromatic pollutants are discussed, namely benzene homologues, polycyclic aromatic hydrocarbons (PAHs), organic dyes and their intermediates, and pharmaceuticals and personal care products (PPCPs). MOFs are shown to be excellent adsorbents that can be employed to both the elimination of pollutants and to their extraction and quantitation. Adsorption mechanisms and interactions between aromatic pollutants and MOFs are discussed. Finally, the actual challenges of existence and the perspective routes towards future improvements in the field are addressed.
Graphical abstract Recent advance on adsorption of common aromatic pollutants including benzene series, polycyclic aromatic hydrocarbons, organic dyes and their intermediates, pharmaceuticals and personal care products by metal-organic frameworks.
This review (with (318) refs) describes progress made in the design and synthesis of morphologically different metal oxide nanoparticles made from iron, manganese, titanium, copper, zinc, zirconium, cobalt, nickel, tungsten, silver, and vanadium. It also covers respective composites and their function and application in the field of electrochemical and photoelectrochemical sensing of chemical and biochemical species. The proper incorporation of chemical functionalities into these nanomaterials warrants effective detection of target molecules including DNA hybridization and sensing of DNA or the formation of antigen/antibody complexes. Significant data are summarized in tables. The review concludes with a discussion or current challenge and future perspectives.
A fluorescence assay is described for the fluorometric determination of dopamine (DA). It based on the use of silica-coated CdTe quantum dots (QD@SiO2). These were fabricated through a hydrothermal process. When DA is added to a solution of the QD@SiO2 and then oxidized by oxygen under catalytic action of tyrosinase to form dopamine quinone, the fluorescence of QD@SiO2 (acquired at excitation/emission wavelengths of 310/525 nm) decreases due to an electron transfer quenching processes. The assay has a linear calibration plot in the 0.05 to 30 μM DA concentration range and a 12.5 nM detection limit (at an S/N ratio of 3). The method was applied to the determination of DA in spiked human serum samples.
Graphical abstract Schematic presentation of a fluorometric dopamine (DA) assay by using silica-coated CdTe QDs (QD@SiO2). DA is oxidized by oxygen under catalytic action of tyrosinase to form dopamine quinone, and this causes the quenching of fluorescence of QD@SiO2 at excitation/emission wavelengths of 310/525 nm.
This article reviews the progress made in the past 5 years in the field of direct and non-enzymatic electrochemical sensing of glucose. Following a brief discussion of the merits and limitations of enzymatic glucose sensors, we discuss the history of unraveling the mechanism of direct oxidation of glucose and theories of non-enzymatic electrocatalysis. We then review non-enzymatic glucose electrodes based on the use of the metals platinum, gold, nickel, copper, of alloys and bimetals, of carbon materials (including graphene and graphene-based composites), and of metal-metal oxides and layered double hydroxides. This review contains more than 200 refs.
Figure This article reviews the history of unraveling the mechanism of direct electrochemical glucose oxidation and the attempts to successfully develop non-enzymatic electrochemical glucose sensors over the past 5 years.
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.
A voltammetric sensor is described for the quantitation of propyl gallate (PG). A screen-printed carbon electrode (SPCE) was modified with reduced graphene sheets that were decorated with cobalt diselenide nanoparticles (CoSe2@rGO). The material was hydrothermally prepared and characterized by several spectroscopic techniques. The modified SPCE displays excellent electrocatalytic ability towards PG. Differential pulse voltammetry, with a peak voltage at 0.34 V (vs. Ag/AgCl) has a sensitivity of 12.84 μA·μM?1·cm?2 and a detection limit as low as 16 nM. The method is reproducible, selective, and practical. This method was applied to the determination of PG in spiked meat samples, and the result showed an adequate recovery.
A highly selective and sensitive aptasensor is described for voltammetric determination of the pesticide chlorpyrifos (CPS). The sensor was constructed by modifying a glassy carbon electrode (GCE) with gold nanorods and a polymer that was molecularly imprinted with an aptamer against CPS. This results in double specific recognition. Under optimal conditions and a working potential as low as 0.22 V (vs. Ag/AgCl), the nanotools has a dynamic range that covers the 1.0 fM - 0.4 pM CPS concentration range, and the detection limit is 0.35 fM. This is lower than any of the previously reported methods. This MIP-aptasensor is selective over structural analogs, stable, and adequately reproducible. It was successfully applied to the determination of CPS in spiked food samples.
Graphical abstract Impedimetric detection of Chlorpyrifos by using a Fe(CN)63?/4- probe based on double recognition of aptamer-molecular imprinted polymer onto a glassy carbon electrode modified with gold nanorod nanocomposite. The incubation with Chlorpyrifos lead to an increase of electron transfer resistance.
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.
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.
A magnetic glassy carbon electrode (mGCE) was modified with a ternary composite prepared from Prussian blue (PB), magnetite (Fe3O4) nanoparticles, and reduced graphene oxide (rGO) in order to obtain an amperometric sensor for hydrazine. The utilization of Fe3O4 facilitates the magnetic immobilization and separation of sensing material, while the use of rGO enhances sensitivity. The surface coverage and the stability of the PB on the modified electrode were considerably improved. The electro-oxidative response to hydrazine was investigated with this modified mGCE using cyclic voltammetry and amperometric. The sensor, typically operated at a voltage of 0.2 V (vs. SCE), displays superior response hydrazine, with a response time of 4 s, a sensitivity of 97.73 μA μM?1 cm?2 and a 13.7 nM detection limit.
Graphical abstract A magnetic glassy carbon electrode was modified with a ternary composite prepared from Prussian blue, magnetite nanoparticles, and reduced graphene oxide to obtain a selective amperometric sensor for dissolved hydrazine.
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 paper describes a voltammetric method for the quantitation of the activity of telomerase extracted from cancer cells. A thiolated single-stranded telomerase substrate primer was firstly immobilized on a gold electrode. In the presence of a mixture of telomerase and deoxynucleotide triphosphates, the primer becomes elongated and contains repetitive nucleotide sequences (TTAGGG)n. After hybridization with blocker DNA, gold nanoparticles are added and captured by the elongated single-stranded DNA. This reduces the charge transfer resistance of the gold electrode. The telomerase activity is then quantified via differential pulse voltammetry, typically at 0.12 V (vs. SCE). The method is PCR-free, rapid, and convenient. It was applied to the detection of HeLa cells via the telomerase activity of lysed cells. The detection range was from 500 to 50,000 cells/mL and the detection limit was as low as 500 cells/mL.
Graphical abstract A telomerase substrate (TS) primer is immobilized on a gold electrode as the sensing interface to detect the activity of telomerase extracted from cancer cells. Unmodified gold nanoparticles (AuNPs) are utilized which change the electrochemical responses.
