A stir foam composed of graphene oxide, poly(ethylene glycol) and natural latex (GO-PEG-NL) was prepared for use in micro-solid phase extraction sorbent of preservative agents and antioxidants from cosmetic products. The extracted analytes were quantified by GC-MS. Under the optimized conditions, the calibration plots are linear in the concentration ranges between 5.0 μg·L?1 to 1.0 mg·L?1 for benzoic acid, of 10.0 μg·L?1 to 1.0 mg·L?1 for 2-methyl-3-isothiazolinone (MI), and between 1.0 μg·L?1 and 1.0 mg·L?1 for both 3-tert-butyl-4-hydroxyanisole (BHA) and 2,6-di-tert-butyl-p-hydroxytoluene (BHT). The LODs are 1.0 μg·L?1 for benzoic acid, 5.0 μg·L?1 for MI and 0.5 μg·L?1 for both BHA and BHT. The stir-foam can be easily prepared, is inexpensive and well reproducible (RSDs <3%, for n?=?6). It can be re-used for up to 12 times after which extraction efficiency has dropped to 90%. The method was successfully applied to the determination of preservatives and antioxidants in cosmetic samples. Recoveries from spiked samples ranged between 94.5?±?2.1% and 99.8?±?1.8%.
Graphical abstract A stir foam was prepared from graphene oxide, poly(ethylene glycol) and natural latex (GO-PEG-NL) and is shown to be a most viable sorbent for the microextraction of trace amounts of preservative agents and antioxidants from cosmetic products.
A nanocomposite modified with dibenzo-18-crown-6 was synthesized and applied as a new sorbent for the preconcentration of thallium(I) via ultrasound assisted-solid phase extraction. This extraction step was combined with electrothermal atomic absorption spectrometry to determine ultra-trace amounts of thallium(I). The nanocomposite was characterized by Fourier transform infrared spectroscopy, X-ray diffraction spectrometry, field emission scanning electron microscopy and transmission electron microscopy. Under the optimized conditions, a dynamic linear range from 7.0 to 435 ng L?1, a detection limit of 1.8 ng L?1 and a quantification limit of 6.0 ng L?1 were obtained. Also, the intra- and inter-day relative standard deviations for 20.0 ng mL?1 Tl(I) were calculated as ±4.8% and ±5.1%, respectively. The adsorbent was applied to the determination of thallium(I) in the environmental, biological and standard samples with satisfactory results.
Graphical abstract A magnetic nanocomposite was synthesized as adsorbent from halloysite nanotubes and a crown ether. Tl(I) ions were extracted selectively and determined by electrothermal atomic absorption spectrometry.
A nanocomposite was prepared from graphene-like two-dimensional black phosphorene (BP, an allotrope of phosphorus) and nafion (Nf) treated with isopropanol (IP). A glassy carbon electrode (GCE) modified with this nanocomposite was found to be a viable sensor for voltammetric determination of clenbuterol (CLB). Unlike previously reported pure BP, the BP nanocomposite was stable towards water and oxygen. Its morphology, structure, electrochemically active surface area and electrochemical stability were investigated. The BP-Nf (IP) modified GCE displayed good electrochemical stability and electrocatalytic capacity with a low working potential of 0.94 V (vs. SCE), excellent peak current response for CLB in a linear concentration range of 0.06–24 μM with a detection limit of 3.7 nM (3σ/m) and a sensitivity of 0.14 μA·μM?1·cm?2 under optimal conditions. A sensing mechanism for the electro-oxidation of CLB was suggested and verified by density functional theory calculations under imitation of aqueous solution conditions. The sensor was successfully applied to the determination of CLB in bovine meat and bovine serum samples.
Graphical abstract Highly-stable black phosphorene (BP) nanocomposite based on Nafion (Nf) was used to modify a glassy carbon electrode (GCE). It is shonw to be a viable electrochemical platform for sensitive voltammetric determination of trace clenbuterol (CLB) in bovine beef and bovine serum.
An efficient approach is demonstrated for preparing particles consisting of a silver core and a shell of molecularly imprinted polymer (Ag@MIP). The MIP is prepared by using bisphenol A (BPA) as the template and 4-vinylpyridine as the functional monomer. The Ag@MIP fulfills a dual function in that the silver core acts as a SERS substrate, while the MIP allows for selective recognition of BPA. The Ag@MIP is characterized by scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, thermogravimetric analysis and Raman spectroscopy. The Raman intensity of Ag@MIP is higher than that of bare silver microspheres. The detection limit for BPA is as low as 10?9 mol·L?1.
Graphical abstract Schematic illustration of the preparation of silver microspheres coated with a molecularly imprinted polymer (Ag@MIPs) for detecting bisphenol A (BPA) by surface enhanced Raman scattering (SERS).
Diphenyl diselenide was immobilized on chitosan loaded with magnetite (Fe3O4) nanoparticles to give an efficient and cost-effective nanosorbent for the preconcentration of Pb(II), Cd(II), Ni(II) and Cu(II) ions by using effervescent salt-assisted dispersive magnetic micro solid-phase extraction (EA-DM-μSPE). The metal ions were desorbed from the sorbent with 3M nitric acid and then quantified via microflame AAS. The main parameters affecting the extraction were optimized using a one-at-a-time method. Under optimum condition, the limits of detection, linear dynamic ranges, and relative standard deviations (for n?=?3) are as following: Pb(II): 2.0 ng·mL?1; 6.3–900 ng·mL?1; 1.5%. Cd(II): 0.15 ng·mL?1; 0.7–85 ng·mL?1, 3.2%; Ni(II): 1.6 ng·mL?1,.6.0–600. ng·mL?1, 4.1%; Cu(II): 1.2 ng·mL?1, 3.0–300 ng·mL?1, 2.2%. The nanosorbent can be reused at least 4 times.
Graphical abstract Fe3O4-chitosan composite was modified with diphenyl diselenide as a sorbent for separation of metal ions by effervescent salt-assisted dispersive magnetic micro solid-phase extraction.
A carbon ceramic electrode (CCE) was fabricated from a composite consisting of sol-gel, ceramic graphite, multi-walled carbon nanotubes and the natural carotenoid crocin. The resulting sensor is shown to allow for the determination of NADH at a rather low working potential of 0.22 V (vs. Ag/AgCl). The heterogeneous electron transfer rate constant (ks) and the surface coverage of the modified electrode are 16.8 s?1 and 22 pmol·cm?2, respectively. The sensor shows excellent and linear response in solutions of pH 7.0 over the 0.5 to 100 μM NADH concentration range, a 0.1 μM detection limit, and a sensitivity of 251.3 nA·μM?1·cm?2.
Graphical abstract Schematic of the preparation of a carbon ceramic electrode modified with electropolymerized crocin on multi-walled carbon nanotubes. This sensor has a strongly decreased oxidation overpotential for NADH.
Melamine functionalized cellulose@carbon nanotubes were prepared by the following method: (a) Cellulose was dissolved in a mixture of urea and NaOH solutions and then mixed with multiwall carbon nanotubes; (b) the MWCT-modified cellulose was precipitated by addition of water; (c) the MWCNTs were activated with thionyl chloride, and finally reacted with melamine. The resulting sorbent was used in preconcentration of Co(II) ions prior to their determination by flame atomic absorption spectroscopy. The sorbent was characterized by FTIR and field emission scanning electron microscopy. The effects of the pH value of the medium, contact time, and elution conditions were optimized. The calibration plot is linear in the 3 to 200 μg·L￣1 Co(II) concentration range, the limit of detection is 0.8 μg·L￣1, and the relative standard deviation (at a concentration of 100 μg·L￣1) is 3.5 %. The maximum sorption capacity is 167 mg·g￣1. The method was applied to the preconcentration of cobalt ions from (spiked) food and water samples and gave recoveries between 96 and 102 %.
Disposable screen-printed carbon arrays modified with gold nanoparticles (AuNPs) are described. The AuNP-modified screen-printed carbon arrays, designated as AuNP-SPCE arrays, were characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The AuNP-SPCE arrays display excellent electrocatalytic activity towards lead and copper. Two well-defined and fully resolved anodic stripping peaks, at 20 mV for Pb(II) and at 370 mV for Cu(II), both vs. Ag/AgCl, can be seen. Square wave anodic stripping voltammetry was used to simultaneously analyze Pb(II) and Cu(II) in their binary mixtures in tap water. The linear working range for Pb(II) extends from 10 μg.L?1 to 100 μg.L?1 with a sensitivity of 5.94 μA.μg?1.L.cm?2. The respective data for Cu(II) are a working range from 10 μg.L?1 to 150 μg.L?1 with a sensitivity of 3.52 μA.μg?1.L.cm?2. The limits of detection (based on 3× the baseline noise) are 2.1 ng.L?1 and 1.4 ng.L?1, respectively. In our perception, this array is particularly attractive because Pb(II) and Cu(II) can be determined at rather low working potentials which makes the method fairly selective in that it is not significantly interfered by other electroactive species that require higher reduction potentials.
Graphical abstract Fabrication, characterization and electrochemical behavior of gold nanoparticles modified screen-printed carbon arrays towards lead and copper in tap water.
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.
Colloidal gold, quantum dots and polystyrene microspheres were used as labels in three kinds of lateral flow immunochromatographic assays (ICAs) for the detection of zearalenone (ZEN) in cereal samples. The assays allow ZEN to be quantified within 20 min. The LODs are 10 μg·L?1 of ZEN for the colloidal gold-based ICA, and 1 μg·L?1 for both the quantum dot and polystyrene microsphere based ICAs. The respective data are 60 μg·kg?1, 6 μg·kg?1 and 6 μg·kg?1, respectively, for spiked samples and cereals. Only minor cross-sensitivity occurred between ZEN and fusarium toxins, and no cross-sensitivity if found for aflatoxin B1, T-2 mycotoxin, ochratoxin A, deoxynivalenol, and fumonisin B1. LODs of the three assays are lower than the maximum limits of ZEN set by most standardization agencies.
Graphical abstract Schematic presentation of three lateral flow immunochromatographic assays (ICAs) based on the use of (a) colloidal gold (CG), (b) fluorescent quantum dots (QD), and (c) polystyrene microspheres (PMs) as signalling labels for the rapid and sensitive determination of zearalenone (ZEN) in cereal samples.
We describe a chemical exfoliation method for the preparation of MoS2 nanosheets. The nanosheets were incorporated into poly(3,4-ethylenedioxythiophene) (PEDOT) by electrodeposition on a glassy carbon electrode (GCE) to form a nanocomposite. The modified GCE is shown to enable simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA). Due to the synergistic effect of MoS2 and PEDOT, this electrode displays better properties in terms of electrocatalytic oxidation of AA, DA and UA than pure PEDOT, which is illustrated by cyclic voltammetry and differential pulse voltammetry (DPV). Under optimum conditions and at pH 7.4, the respective sensitivities and best working potentials are as follows: AA: 1.20 A?mM?1?m?2, 30 mV; DA: 36.40 A?mM?1?m?2, 210 mV; UA: 105.17 A?mM?1?m?2, 350 mV. The calculated detection limits for AA, DA and UA are 5.83 μM, 0.52 μM and 0.95 μM, respectively. The modified electrode was applied to the detection of the three species in human urine samples and gave satisfactory results.
Graphical abstract MoS2 nanosheets were prepared by a facile chemical exfoliation method. MoS2 and poly(3,4-ethylenedioxythiophene) nanocomposite modified glassy carbon electrodes were fabricated, which are shown to enable simultaneous determination of ascorbic acid, dopamine and uric acid with high sensitivity and selectivity.
A new type of carbon ceramic electrode modified with bismuth oxide nanoparticles (referred to as Bi-CCE) was fabricated via the sol-gel method. The Bi-CCE was applied to the determination of syringic acid by square wave adsorptive stripping voltammetry. The electrochemical properties of the Bi-CCE and the voltammetric response to syringic acid were investigated by cyclic voltammetry. The effects of the pH value of supporting electrolyte, of accumulation potential, accumulation time, SW mode parameters, and of possible interferents were tested. Under optimized conditions, the oxidation peak current (best measured at 0.8 V vs Ag/AgCl after an accumulation time of 20 s) increases linearly in the 0.4 to 24 μmol·L?1 syringic acid concentration range. Other figures of merit include an LOD of 47 nmol·L?1, a sensitivity of 3.3 μA·μmol?1·L·cm?2, and a relative standard deviation of 4.7% (for n = 5) at 2 μmol·L?1 of syringic acid. The method was successfully applied to the determination of syringic acid in red, white and rose wine as well as water samples.
Graphical abstract Schematic presentation of the preparation of carbon ceramic electrode (CCE) containing Bi2O3 nanoparticles and its application in square wave adsorptive stripping voltammetric (SW AdSV) determination of syringic acid.
The authors describe an electrochemical sensor for the breast cancer marker α-lactalbumin (αLA). It is based on the use of printed single-walled carbon nanotube (SWCNT) electrodes that were modified with polycatechol. Impedance-derived electrochemical capacitance spectroscopy (ECS) is applied for detection at an applied potential of ?0.14 V vs. Ag/AgCl reference electrode. The electrode was prepared in a two-step process. First, a dispersion of SWCNTs was drop-cast onto the surface of a poly(ethylene terephthalate) substrate to act as the working electrode. Next, catechol was electrochemically polymerized on the SWCNTs, prior to the immobilization of lysozyme. The strong interaction between lysozyme and αLA induced changes in the redox capacitance which are detected by ECS. The latter shows the device to be capable of detecting αLA in the 20 to 80 ng·mL?1 concentration range. The limit of detection is 9.7 ng·mL?1 at an S/N ratio of 3. The device was used to detect αLA in human blood serum with good recovery results.
Graphical abstract A sensitive biosensor for αLA was prepared by modifying SWCNT electrode with polycatechol and lysozyme. The electrochemical capacitance spectroscopy was used for the first time to selectively detect αLA in the blood in the range from 20 to 80 ng·mL?1.
A novel ZnO-graphene oxide nanocomposite was prepared and is shown to be a viable coating on fused silica fibers for use in solid phase microextraction (SPME) of diazepam and oxazepam from urine, this followed by thermal desorption and gas chromatographic quantitation using a flame ionization detector. A central composite design was used to optimize extraction time, salt percentage, sample pH and desorption time. Limits of detection are 0.5 μg·L?1 for diazepam and 1.0 μg·L?1 for oxazepam. Repeatability and reproducibility for one fiber (n?=?4), expressed as the relative standard deviation at a concentration of 50 μg·L?1, are 8.3 and 11.3% for diazepam, and 6.7 and 10.1% for oxazepam. The fiber-to-fiber reproducibility is <17.6%. The calibration plots are linear in the 5.0–1000 μg·L?1 diazepam concentration range, and from 1.0–1000 μg·L?1 in case of oxazepam. The fiber for SPME has high chemical and thermal stability (even at 280 °C) after 50 extractions, and does not suffer from a reduction in the sorption capacity.
Graphical abstract A hydrothermal method was introduced for preparation of ZnO- GO nano composite on a fused silica fiber as solid phase microextraction with high mechanical, chemical stability and long service life
The authors describe an upconversion nanoparticle-based (UCNP–based) fluorometric method for ultrasensitive and selective detection of Cu2+. The UCNPs show a strong emission band at 550 nm under near-infrared excitation at 980 nm. The principle of the strategy is that gold nanoparticles (AuNP) can quench the fluorescence of UCNP. In contrast, the addition of L-cysteine (Cys) can induce the aggregation of AuNP, resulting in a fluorescence recovery of the UCNPs. On addition of Cu2+, it oxidizes Cys to cystine and is reduced to Cu+. The Cu+ thusformed can be oxidized cyclically to Cu2+ by dissolved O2, which catalyzes and recycles the whole reaction. Thus, the aggregation of AuNP is inhibited and the fluorescence recovered by Cys is quenched. Under the optimal condition, the quenching efficiency shows a good linear response to the concentrations of Cu2+ in the 0.4–40 nM range. The limit of detection is 0.16 nM, which is 5 orders of magnitude lower than the U.S. Environmental Protection Agency limit for Cu2+ in drinking water (20 μM). The method has been further applied to monitor Cu2+ levels in real samples. The results of detection are well consistent with those obtained by atomic absorption spectroscopy.
Graphical abstract Gold nanoparticles (AuNP) as a high efficient fluorescence quenching reagent of upconversion nanoparticles (UCNP) were used in a fluorometric method for detection of Cu2+ based on a cyclic catalytic oxidation amplification strategy.
The family of zearalenones (ZENs) represents a major group of mycotoxins with estrogenic activity. They are produced by Fusarium fungi and cause adverse effects on human health and animal production. The authors describe here a label-free amperometric immunosensor for the direct determination of ZENs. A glassy carbon electrode (GCE) was first modified with polyethyleneimine-functionalized multi-walled carbon nanotubes. Next, gold and platinum nanoparticles (AuPt-NPs) were electro-deposited. This process strongly increased the surface area for capturing a large amount of antibodies and enhanced the electrochemical performance. In a final step, monoclonal antibody against zearalenone was orientedly immobilized on the electrode, this followed by surface blocking with BSA. The resulting biosensor was applied to the voltammetry determination of ZENs, best at a working voltage of 0.18 V (vs SCE). Under optimized conditions, the method displays a wide linear range that extends from 0.005 to 50 ng mL?1, with a limit of detection of 1.5 pg mL?1 (at an S/N ratio of 3). The assay is highly reproducible and selective, and therefore provides a sensitive and convenient tool for determination of such mycotoxins.
Graphical abstract An amperometric immunosensor for the direct determination of ZENs has been developed by immobilizing anti-ZEN monoclonal antibody on multi-walled carbon nanotubest hat were deposited, along with gold and platinum nanoparticles, on a glassy carbon electrode modified with Staphylococcus protein A.
The authors have developed an electrochemical sensor for cadmium(II) that is based on the use of a conventional fluorine doped tin oxide (FTO) electrode modified with polymeric electrospun nanofibers consisting of polyamide 6 (PA6) and chitosan which were further modified with gold nanoparticles (AuNPs). The materials were characterized by infrared spectroscopy, thermal analysis (DSC and TGA), and scanning electron microscopy. The modified electrode was applied to the detection of Cd(II) by square wave voltammetry. Response is linear in the 25 to 75 μg ? L?1 Cd(II) concentration range, with a detection limit of 0.88 μg ? L?1. The relative standard deviations are 4.6% and 8.2% for intra- and inter-electrode measurements, respectively. Mercury(II), lead(II), and copper(II) did not significantly interfere.
Graphical abstract The sensing platform developed can detect cadmium(II) with a detection limit of 0.88 μg L?1, with no significant interference by mercury(II) and lead(II).
The authors have prepared a super-hydrophilic polymer consisting of a poly-polyhedral oligomeric silsesquioxane (POSS)-formaldehyde (PPF) composite. The polymerization process does not require a catalyst and results in a material with excellent hydrophilic properties and abundant functional groups. The PFF composite, even if not chemically modified, can selectively bind glycoproteins due to strong hydrophilic interactions. It is shown that glycoproteins can be selectively captured by the composite that has a binding capacity as large as 542 mg g?1 for the model protein ovalbumin. The PPF was applied to the selective capture and isolation of ovalbumin from complex biological samples.
Graphical abstract Super-hydrophilic poly-polyhedral oligomeric silsesquioxane formaldehyde (PPF) is prepared via a catalyst-free polymerization route. PPF exhibits high capturing and adsorption selectivity towards glycoproteins due to its strong hydrophilic interaction with glycan groups. Favorable capturing capacity is also achieved.
Copper nanoclusters (Cu-NCs) were prepared by reducing CuCl2 with ascorbic acid in the presence of the short peptide template Cys-Cys-Cys-Asp-Leu. They were characterized by UV-vis absorption and fluorescence spectroscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The Cu-NCs have a size of ~2 nm, can be well dispersed in water and are photostable. Their fluorescence (peaking at 425 nm under 365-nm excitation) is quenched by Fe(III) ions. Based on this finding, a sensitive and selective fluorescence assay for the detection of Fe(III) was developed. Under optimized conditions and a pH value of 2.0, the assay displays a linear response in the 0.05 to 30 μM Fe(III) concentration range, with a detection limit of 20 nM based on an S/N ratio of 3. The assay was successfully applied to the determination of Fe(III) in spiked human serum where is gave recoveries that ranged from 96.2 % to 98.3 %.
Graphical abstract Copper nanoclusters (Cu-NCs) were prepared by reducing CuCl2 with ascorbic acid with peptide as the template. The fluorescence of Cu-NCs is quenched by Fe(III) ions with a linear response in the 0.05 to 30 μM of Fe(III) concentration range.
A voltammetric sensor is presented for the simultaneous determination of dopamine (DA) and uric acid (UA) in the presence of ascorbic acid (AA). It is based on a gold electrode (GE) modified with carboxyl-functionalized graphene (CFG) and silver nanocube functionalized DA nanospheres (AgNC@PDA-NS). The AgNC@PDA-NS nanocomposite was characterized by scanning electron microscopy and UV-Vis spectroscopy. The electrochemical behavior of the modified electrode was evaluated by electrochemical impedance spectroscopy, cyclic voltammetry and differential pulse voltammetry. The modified electrode displays good electrocatalytic activity towards DA (typically at 0.14 V vs. Ag/AgCl) and UA (typically at 0.29 V vs. Ag/AgCl) even in the presence of ascorbic acid. Response to DA is linear in the concentration range of 2.5 to 130 μM with a detection limit of 0.25 μM. Response to UA is linear in the concentration range of 10 to 130 μM with a detection limit of 1.9 μM. In addition, the sensitivity for DA and UA is 0.538 and 0.156 μA μM?1 cm?2, respectively. The modified electrode also displays good stability, selectivity and reproducibility.
Graphical abstract The gold electrode modified with polydopamine nanospheres functionalized with silver nanocube and carboxylated graphene is used for simultaneous determination of DA and UA in the presence of AA, with wide linear range and low detection limit.
