A polydopamine-based molecularly imprinted polymer was deposited on the surface of magnetite (ferroferric oxide) nanoparticles (Fe3O4@PDA MIPs) and is shown to be an efficient and fairly specific sorbent for the extraction of various ochratoxins. The MIPs were characterized by IR spectroscopy and transmission electron microscopy. The adsorption capacities, evaluated through the langmuir adsorption isotherm model, are 1.8, 0.23 and 0.17 mg·g?1 for ochratoxin A, ochratoxin B and ochratoxin C, respectively. Parameters such as the amount of magnetic MIPs, pH value, time for ultrasonication, elution solvent and volume were optimized. Following desorption from the MIP with acetonitrile, the ochratoxins were quantified by HPLC with fluorometric detection. Under optimal experimental conditions, the calibration plots are linear in the range of 0.01–1.0 ng·mL?1 of OTA, 0.02–2.0 ng·mL?1 of OTB, and 0.002–0.2 ng·mL?1 of OTC. The LODs are between 1.8 and 18 pg·mL?1, and the recoveries from spiked samples are 71.0% - 88.5%, with RSDs of 2.3–3.8% in case of rice and wine samples. The MIPs can be re-used for at least 7 times.
Graphical abstract Schematic of the preparation of a magnetic molecularly imprinted polymer based on self-polymerization of dopamine in weakly alkaline solution. Ochratoxins are recognized owing to homologous cavities in the MIPs, and quantified by HPLC after desorption with acetonitrile.
CdTe quantum dots (QDs) were integrated with polyethyleneimine-coated carbon dots (PEI-CDs) to form a dually emitting probe for heparin. The red fluorescence of the CdTe QDs is quenched by the PEI-CDs due to electrostatic interactions. In the presence of heparin, the blue fluorescence of PEI-CDs remains unaffected, while its quenching effect on the fluorescence of CdTe QDs is strongly reduced. A ratiometric fluorometric assay was worked out. The ratio of the fluorescences at 595 and 436 nm serves as the analytical signal. Response is linear in the concentration range of 50–600 ng·mL?1 (0.1–1.2 U·mL?1) of heparin. The limit of detection is 20 ng·mL?1 (0.04 U·mL?1). This makes the method a valuable tool for heparin monitoring during postoperative and long-term care. This assay is relatively free from the interference by other analogues which commonly co-exist with heparin in samples, and it is more robust than single-wavelength based assays.
Graphical abstract In the presence of heparin, the fluorescence of polyethyleneimine-coated carbon dots (PEI-CDs) at 436 nm remains unaffected, while its quenching effect on the fluorescence of CdTe at 595 nm is strongly reduced.
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 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.
This work describes the preparation of carbon dots doped with terbium(III) (Tb-CDs) via a hydrothermal method, starting from terbium ion and ethylenediamine. The size, composition and spectral properties of the Tb-CDs were characterized by transmission electron microscopy, infrared spectra, and fluorescence spectra. The results show that doping of the CDs with Tb(III) reduces the particle size and results in more uniform particles, while fluorescence (at excitation/emission peaks of 380/475 nm) is strongly enhanced. The interaction between Tb-CDs and ct-DNA results in fluorescence quenching of Tb-CDs. The findings were exploited to design a quenchometric method for the determination of ct-DNA. The signal drops linearly in the 80 ng·mL?1 to 50 μg·mL?1 ct-DNA concentration range, and the detection limit is 53 ng·mL?1. The method was applied to the determination of ct-DNA in spiked samples and gave satisfactory results. The possible fluorescence quenching mechanism (which is mainly static) was investigated using the Stern–Volmer equation and thermodynamic equations.
Graphical abstract A kind of carbon dots doped with terbium(III) (Tb-CDs) were prepared via a hydrothermal method, using terbium ion and ethylenediamine as precursor. Doping with Tb(III) reduced the particle size of CDs and results in uniform particle size and stronger fluorescence. The interaction between the Tb-CDs and dsDNA results in quenching of the fluorescence of Tb-CDs and can be applied to determination of dsDNA.
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 a method for the extraction of the herbicide 2-methyl-4-chlorophenoxyacetic acid (MCPA) from agricultural products. The metal organic framework (MOF) HKUST-1 (a copper(II) benzene-1,3,5-tricarboxylate) was used as a sorbent for efficient clean-up and preconcentration of MCPA. The effects of pH value, stirring time, amount of sorbent on extraction were optimized by central composite design. Ultrasonic waves were used for desorption procedure and its advantage was demonstrated for an increase in extraction recovery. Corona discharge ion mobility spectrometry (IMS) was then applied for fast and sensitive determination of MCPA. The method was validated in terms of sensitivity, recovery and reproducibility. Under the optimum conditions the calibration plot is linear between 0.035–0.200 μg. L?1. The detection limit is 10 ng L?1, with relative standard deviations of <5%. Real samples (water, soil and agricultural product) were spiked and then analyzed by this method, and the results revealed efficient solid phase extraction and recovery.
Graphical abstract Schematic presentation of a procedure for extraction of an organochlorine pesticide (2-methyl-4-chlorophenoxyacetic acid) from agriculture products using the HKUST-1 metal-organic framework prior to determination by ion mobility spectrometry based on its ionization in drift cell.
The authors describe a zinc(II) benzenetricarboxylate (Zn-BTC) based metal-organic framework (MOF) with chrysanthemum-like structure, and its application to the adsorption of pesticides from real water samples. The Zn-BTC MOF was characterized by XRD, TGA, SEM, nitrogen adsorption-desorption analysis and FT-IR spectroscopy. The MOF was used in dispersive solid-phase extraction of six aromatic pesticides from various wastewater samples prior to their quantification by HPLC. Extraction times, extraction temperature, amount of adsorbent, and oscillation rate were optimized. Under the optimal conditions, the method has relative standard deviations (RSDs) of 6.1–10.1%, and good linearity (correlation coefficients higher than 0.9974). The LODs and LOQs for seven pesticides are found to be 0.20–1.60 μg·L?1 and 0.66–5.28 μg·L?1, respectively. The RSDs of within batch extraction are 1.6–9.5% and 3.9–12%.
Graphical abstract Schematic of a zinc-benzenetricarboxylate (Zn-BTC) based metal-organic framework (MOF) for use as an adsorbent of dispersive solid phase extraction (DSPE) of pesticides prior to their determination by HPLC.
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.
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.
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.
CdSe:Eu nanocrystals were successfully synthesized and characterized by transmission electron microscopy, X-ray powder diffraction, and X-ray photoelectric spectroscopy. The CdSe:Eu nanocrystals showed enhanced green electrochemiluminescence (ECL) intensity when compared to pure CdSe nanocrystals. Further, the nanocrystals were used to design an ECL immunosensor for the detection of carcinoembryonic antigen (CEA) that has a linear response over the 1.0 fg·mL?1 to 100 ng·mL?1 CEA concentration range with a 0.4 fg·mL?1 detection limit. The assay was applied to the determination of CEA in human serum samples.
Graphical abstract Schematic of the assay: GCE-glassy-carbon electrode, Ab- Antibody, BSA- Bovine serum albumin, Ag- Antigen. CdSe:Eu nanocrystals were used to design an ECL immunosensor for the detection of carcinoembryonic antigen.
We describe a label-free electrochemical immunosensor for the carcinoembryonic antigen (CEA). It is based on a nanocomposite consisting of electrochemically reduced graphene oxide, gold nanoparticles (AuNPs), and poly(indole-6-carboxylic acid). Coupled to nanoparticle-amplification techniques and modified with ionic liquid (IL), this immunoassay shows high sensitivity and good selectivity for CEA. At the best working voltage of 0.95 V (vs. Ag/AgCl), the lower detection limit is 0.02 ng·mL?1, and the response to CEA is linear in the range from 0.02 to 90 ng·mL?1. The method was applied to the determination of CEA in spiked serum samples and gave recoveries in the range from 98.5 % to 102 %.
Graphical abstract A label-free electrochemical immunosensor was fabricated for the carcinoembryonic antigen (CEA) with a detection limit of 0.02 ng·mL?1. It is based on a nanocomposite consisting of electrochemically reduced graphene oxide (erGO), gold nanoparticles (Au NP), and poly(indole-6-carboxylic acid) (PICA).
A method is described for the determination of the pesticide chlorothalonil (CLT). It is based on the finding that citrate-capped gold nanoparticles (AuNPs) undergo aggregation on exposure to chlorothalonil. This is accompanied by a visually detectable color change from wine red to blue. The effect is due to the interaction of the cyano group of chlorothalonil with gold nanoparticles. The assay may also be performed by using a spectrometer. The ratio of absorbances at 700 nm and 520 nm (A700/A520) linearly drops in the 5 to 100 ng·mL?1 CLT concentration range, with a 3.6 ng·mL?1 detection limit. This is below the Chinese guideline value for cucumber. The method is rather simple and does not require any modification of the AuNPs or the utilization of antibody. It was successfully applied to the determination of CLT in (spiked) cucumber samples. Recoveries ranged from 80.4 to 97.4%, and the analytical results compared well with those obtained by HPLC.
Graphical abstract Schematic of the assay. The strong interaction of the cyano group of acetamiprid with gold nanoparticles (AuNPs) via Au-N bond induces the aggregation of gold nanoparticles, and this is accompanied by a color change from red to purple.
The article describes the synthesis of core-shell magnetic nanoparticles (MNPs) of the type Fe3O4@MIL-100 (MIL standing for Material Institut Lavoisier), and their application as sorbent for magnetic solid-phase extraction (MSPE) of triclosan. The MNPs were prepared via circular self-assembly of ferric chloride and benzenetricarboxylic acid. The functionalized MNPs were characterized by transmission electron microscopy, FTIR and thermogravimetry. Following extraction, triclosan was eluted with ammoniacal methanol and then submitted to HPLC with UV detection. The amount of magnetic microspheres, sample pH and ionic strength, adsorption time, desorption time, desorption solvent and the volume of the eluent were optimized. Under optimum conditions, the method showed good linearity in the 0.1 to 50 mg·kg?1 triclosan concentration range in toothpaste samples. Other features include (a) intra-day and inter-day relative standard deviations (RSD, for n = 4) of <5.5 %, (b) a 30 μg·kg?1 limit of detection, and (c) extraction recoveries between 90.86 % and 101.1 %. The method was successfully applied to the determination of triclosan in children’s toothpaste.
Graphical abstract The article describes the synthesis of core-shell magnetic nanoparticles (MNPs) of the type Fe3O4@MIL-100, and their application as sorbent for magnetic solid-phase extraction (MSPE) of triclosan.
The authors describe an immunoassay for the determination of carcinoembryonic antigen (CEA) tumor markers by depositing a polydopamine-Pb(II) nanocomposite on the surface of a glassy carbon electrode. The nanocomposite acts as a redox system that displays a large specific surface and provides a strong current signal at ?0.464 V (vs. Ag/AgCl). After the deposition of PDA-Pb2+ on glassy carbon electrode, the electrode was additionally coated with a chitosan-gold nanocomposite. The immunoassay platform was obtained by immobilization of antibodies against carcinoembryonic antigens by using glutaraldehyde and blocking with bovine albumin. Owing to its large surface, good electrical conductivity and powerful current response, the immunoassay has a wide linear range that extends from 1 fg·mL?1 to 100 ng·mL?1, with a detection limit as low as 0.26 fg·mL?1. The results obtained with this immunoassay when determining CEAs in human serum were found to be consistent with those obtained by ELISAs.
Graphical abstract Schematic of an ultrasensitive electrochemical immunosensor for the carcinoembryonic antigen. It is based on a glassy carbon electrode modified with a polydopamine-Pb(II) nanocomposite acting as a signal-inherent substrate.
Europium(III)-doped carbon dots (Eu-CDs) were prepared from citric acid and europium nitrate via a one-pot pyrolytic method. The Eu-CDs emit intense blue fluorescence (with excitation/emission peaks at 365/465 nm), are water soluble and biocompatible. On addition of 2,6-dipicolinic acid (DPA; an anthrax biomarker), ligand-to-ion energy transfer occurs from DPA to Eu(III) which has a red emission peaking at 615 nm. This results in an increase of the intensity of the red fluorescence. DPA can be detected by the ratio of fluorescence intensities at 616 and 475 nm. The method has an analytical range that extends from 5 to 700 nmol·L?1, with a 5 nmol·L?1 detection limit. The Eu-CDs also were incorporated into a test paper for visual detection of DPA with a portable UV lamp and a smartphone. In this case, the detection limit is 1 μmol·L?1. The Eu-CDs internalize well into HeLa cells, and this paves the way to bioimaging.
Graphical abstract Schematic of a method for visual detection of 2,6-dipicolinic acid (DPA, an anthrax biomarker) by using a test stripe impregnated with europium(III)-doped carbon dots (Eu-CDs).
A metal-organic framework nanocomposite was synthesized and applied to speciation analysis of Se(IV) and Se(VI). The sorbent is composed of MIL-101(Cr) and magnetite nanoparticles modified with dithiocarbamate. It is capably of selectively extracting Se(IV) at pH?=?1.85, while Se(VI) remains in solution. The total amount of selenium can then be determined by reducing Se(VI) to Se(IV) and also extracting it. The extraction parameters were optimized by employing design-of-experiments methodology. Selenium was then quantified by electrothermal AAS. Figures of merit include (a) a 10 ng·L?1 limit of detection, (b) a linear response in the 30 ng·L?1 to 10 μg·L?1 concentration range, and (a) a relative standard deviation of <11.5% for Se(IV). The method was validated by analyzing certified reference materials (water and tomato leaves). It was also applied to the speciation analysis of Se(IV) and Se(VI) in (spiked) water samples and of total selenium in agricultural samples.
Graphical abstract Schematic of the synthesis of a metal-organic framework nanocomposite for speciation analysis of Se(IV) and Se(VI). The sorbent is composed of MIL-101(Cr) and magnetite nanoparticles modified with dithiocarbamate. Selenium can be quantified by electrothermal AAS with a 10 ng L?1 detection limit.
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 SERS-based aptasensor for ochratoxin A (OTA) is described. It is making use of Fe3O4@Au magnetic nanoparticles (MGNPs) and of Au@Ag nanoprobes modified with the Raman reporter 5,5-dithiobis-(2-nitrobenzoic acid; DTNB). Au-DTNB@Ag NPs were modified with the OTA aptamer (aptamer-GSNPs) and used as Raman signal probes. The SERS peak of DTNB at 1331 cm?1 was used for quantitative analysis. MGNPs modified with cDNA (cDNA-MGNPs) were used as capture probes and reinforced substrates. When the Au-DTNB@Ag-Fe3O4@Au complexes are formed through oligonucleotide hybridization, the Raman signal intensity of the Raman probe is significantly enhanced. If the OTA concentration in samples increases, more Raman signal probes (aptamer-GSNPs) will dissociate from the cDNA-MGNPs because more OTA aptamer is bound by OTA. This leads to a lower Raman signal after magnetic separation. Under the optimal conditions, the detection limit for OTA is 0.48 pg·mL?1 based on 3σ criterion. This is attributed to the multiple Raman signal enhancement and the good performance of the OTA aptamer. The good recovery and accuracy of the assay was confirmed by evaluating spiked samples of wine and coffee.
Graphical abstract Schematic of an aptamer based SERS assay for OTA by integrating Fe3O4@AuNPs (MGNPs) with Au-DTNB@Ag NPs with multiple signal enhancement. Aptamer modified Au-DTNB@Ag NPs are used as Raman probes, and MGNPs modified with cDNA are used as capture probes and reinforced substrates.
