The authors describe a 3-component nanoparticle system composed of a silica-coated magnetite (Fe3O4) core and a layered double (Cu-Cr) hydroxide nanoplatelet shell. The sorbent has a high anion exchange capacity for extraction anionic species. A simple online system, referred to as "on-line packed magnetic-in-tube solid phase microextraction" was designed. The nanoparticles were placed in a stainless steel cartridge via dry packing. The cartridge was then applied to the preconcentration acidic drugs including naproxen and indomethacin from urine and plasma. Extraction and desorption times, pH values of the sample solution and flow rates of sample solution and eluent were optimized. Analytes were then quantified by HPLC with UV detection. Under optimal conditions, the limits of detection range from 70 to 800 ng L?1, with linear responses from 0.1–500 μg L?1 (water samples), 0.6–500 μg L?1 (spiked urine), and 0.9–500 μg L?1 (spiked plasma). The inter- and intra-assay precisions (RSDs, for n?=?5) are in the range of 2.2–5.4%, 2.8–4.9%, and 2.0–5.2% at concentration levels of 5, 25 and 50 μg L?1, respectively. The method was applied to the analysis of the drugs in spiked human urine and plasma, and good results were achieved.
Graphical abstract Fe3O4@SiO2@CuCr-LDH magnetic nanoparticles were synthesized and packed in to a stainless steel column. The column was applied to solid phase microextraction of acidic drugs from biological samples.
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.
The authors report that carbon nitride quantum dots (CN QDs) exert a strong enhancing effect on the Cu(II)/H2O2 chemiluminescent system. Chemiluminescence (CL) intensity is enhanced by CN QDs by a factor of ~75, while other carbon nanomaterials have a much weaker effect. The possible mechanism of the effect was evaluated by recording fluorescence and CL spectra and by examining the effect of various radical scavengers. Emitting species was found to be excited-state CN QDs that produce green CL peaking at 515 nm. The new CL system was applied to the sensitive detection of H2O2 and glucose (via glucose oxidase-catalyzed formation of H2O2) with detection limits (3σ) of 10 nM for H2O2 and 100 nM for glucose. The probe was employed for glucose determination in human plasma samples with satisfactory results.
Graphical abstract The effect of carbon nitride quantum dots (CN QDs) on Cu(II)-H2O2 chemiluminescence reaction was studied and the new CL system was applied for sensitive detection of glucose based on the glucose oxidase (GOx)-catalyzed formation of H2O2.
Near infrared (NIR) emitting semiconductor quantum dots can be excellent fluorescent nanoprobes, but the poor biodegradability and potential toxicity limits their application. The authors describe a fluorescent system composed of graphene quantum dots (GQDs) as NIR emitters, and novel MnO2 nanoflowers as the fluorescence quenchers. The system is shown to be an activatable and biodegradable fluorescent nanoprobe for the “turn-on” detection of intracellular glutathione (GSH). The MnO2-GQDs nanoprobe is obtained by adsorbing GQDs onto the surface of MnO2 nanoflowers through electrostatic interaction. This results in the quenching of the NIR fluorescence of the GQDs. In the presence of GSH, the MnO2-GQDs nanoprobe is degraded and releases Mn2+ and free GQDs, respectively. This gives rise to increased fluorescence. The nanoprobe displays high sensitivity to GSH and with a 2.8 μM detection limit. It integrates the advantages of NIR fluorescence and biodegradability, selectivity, biocompatibility and membrane permeability. All this makes it a promising fluorescent nanoprobe for GSH and for cellular imaging of GSH as shown here for the case of MCF-7 cancer cells.
Graphical abstract A biodegradable NIR fluorescence nanoprobe (MnO2-GQDs) for the “turn-on” detection of GSH in living cell was established, with the NIR GQD as the fluorescence reporter and the MnO2 nanoflower as the fluorescence quencher.
The authors describe an aptamer-based fluorescent assay for adenosine (Ade). It is based on the interaction between silver nanoparticles (AgNPs) and CdTe quantum dots (QDs). The beacon comprises a pair of aptamers, one conjugated to Fe3O4 magnetic nanoparticles, the other to AgNPs. In the presence of Ade, structural folding and sandwich association of the two attachments takes place. After magnetic separation, the associated sandwich structures are exposed to the QDs. The AgNPs in sandwich structures act as the signaling label of Ade by quenching the fluorescence of QDs (at excitation/emission wavelengths of 370/565 nm) via inner filter effect, electron transfer and trapping processes. As a result, the fluorescence of QDs drops with increasing Ade concentration. The assay has a linear response in the 0.1 nM to 30 nM Ade concentration range and a 60 pM limit of detection. The assay only takes 40 min which is the shortest among the aptamer-based methods ever reported. The method was successfully applied to the detection of Ade in spiked biological samples and satisfactory recoveries were obtained.
Graphical abstract Schematic of a highly efficient and convenient adenosine (Ade) fluorometric assay. It is based on the interaction between Ag nanoparticles (NPs) and CdTe quantum dots (QDs). Ade aptamers (ABA1 and ABA2) are used as recognition unit and Fe3O4 magnetic nanoparticles act as magnetic separator. The assay exhibits superior sensitivity and speediness.
We report on the synthesis of Fe3O4@SiO2 nanoparticles incorporated poly(divinylbenzene) monolithic column via in situ polymerization. The monolith had larger specific surface area and relatively uniform porous structure and was characterized by scanning electron microscopy, nitrogen adsorption–desorption, and Fourier transform infrared spectroscopy. The monolith was then applied for the evaluation of gas chromatography separation properties. Here, an electromagnetic induction heating technique was employed to control the column temperature with the thermal effect of eddy current in ferromagnetic materials Fe3O4. The monolith offered good separation efficiency for benzene and toluene and a higher column efficiency was obtained up to 4481 and 9216 plates per meter, respectively. In addition, the injection volume and column capacity of the proposed system are as much as 5 µL and 100 ng. This makes it possible to use a UV detector. The fabricated Fe3O4@SiO2 nanoparticles incorporated poly(divinylbenzene) monolithic column has been shown to be very promising for gas chromatography separation.
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.
A nanocomposite composed of graphene oxide and magnetite (Fe3O4) was coated with the ionic liquid (IL) 1,3-didecyl-2-methylimidazolium chloride and used to capture and separate hemin from serum samples. The critical parameters affecting the extraction of analyte, such as pH, surfactant and adsorbent amounts, and desorption conditions were studied and optimized. Following magnetic separation and desorption with a 5:1 mixture of acetic acid and acetone, hemin (an iron porphyrin complex) was quantified by FAAS of iron. Under optimum conditions, the enrichment factor was 96. The calibration curve was linear in the 4.8 to 730 μg L?1 concentration range, the limit of detection was 3.0 μg L?1, and the relative standard deviations (RSDs) for single-sorbent repeatability and sorbent-to-sorbent reproducibility were less than 3.9 % and 10.2 % (n = 5), respectively. The adsorbent displayed adsorption capacity as high as 200 mg g?1, indicating IL-coated Fe3O4/GO to be a good sorbent for the adsorption of hemin. The method was validated by determining serum hemin in the presence of a large excess (480-fold) of Fe3+ without considerable interference. The results compare well to those obtained with a commercial hemin assay kit. The results show that this method can be successfully applied to the enrichment and determination of hemin in acid digested serum samples of breast cancer patients.
Graphical abstract Fe3O4/GO nanocomposites were coated with the ionic liquid 1,3-didecyl-2-methylimidazolium chloride and used as the sorbent for the separation and preconcentration of hemin from blood serum samples prior to determination using by flame AAS.
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).
The authors describe a new chemiluminescence (CL) system composed of Si-doped carbon dots (Si-CDs), Fe(II) ions, and K2S2O8. The Si-CDs were prepared by a hydrothermal method and characterized by fluorescence spectra, transmission electron microscopy, energy-dispersive X-ray and FTIR spectroscopy. The weak CL of the Fe(II)-K2S2O8 reaction is found to be intensified by a factor of ~125 in the presence of Si-CDs. The possible mechanism for CL and its enhancement was studied by recording fluorescence and CL spectra and by investigating the effect of some radical scavengers. It is found that norfloxacin exerts a strong enhancing effect on the CL intensity of the system. This finding was employed to design a CL-based norfloxacin assay that works in the 5.0 to 300 μg L?1 concentration range, with a limit of detection (3 σ) of 1.5 μg L?1. The method was applied to the determination of therapeutic levels of norfloxacin in spiked human plasma and gave satisfactory results.
Graphical Abstract Schematic of the new chemiluminescence system. It consists of silica-doped carbon dots, Fe(II) ions and K2S2O8 and was applied to the determination of norfloxacin which exerts a strong enhancement effect.
The synthesis of rattle-type nanostructured Fe3O4@SnO2 is described along with their application to dispersive solid-phase extraction of trace amounts of mercury(II) ions prior to their determination by continuous-flow cold vapor atomic absorption spectrometry. The voids present in rattle-type structures make the material an effective substrate for adsorption of Hg(II), and also warrant high loading capacity. The unique morphology, large specific surface, magnetism property and the synergistic effect of magnetic cores and SnO2 shells render these magnetic nanorattles an attractive candidate for solid-phase extraction of heavy metal ions.The sorbent was characterized by transmission electron microscopy, scanning electron microscopy, FTIR, energy-dispersive X-ray spectroscopy and by the Brunnauer-Emmett-Teller technique. The effects of pH value, adsorption time, amount of sorbent, volume of sample solutions, concentration and volume of eluent on extraction efficiencies were evaluated. The calibration plot is linear in the 0.1 to 40 μg·L?1 concentration range, and the preconcentration factor is 49. The detection limit is 28 ng·L?1. The sorbent was applied to the analysis of (spiked) river and sea water samples. Recoveries ranged from 97.2 to 100.5%.
Graphical abstract A yolk-shell structure based on a Fe3O4 core and SnO2 shell was developed as an efficient MSPE sorbent. A middle silica layer was etched by alkaline solution. The resulting sorbent was utilized for preconcentration of mercury ions from aqueous media.
The authors describe double-shell magnetic nanoparticles functionalized with 2-mercaptobenzothiazole (MBT) to give nanospheres of the type MBT-Fe3O4@SiO2@C). These are shown to be viable and acid-resistant adsorbents for magnetic separation of the heavy metal ions Ni(II), Cu(II) and Pb(II). MBT act as a binding reagent, and the carbon shell and the silica shell protect the magnetic core. Following 12 min incubation, the loaded nanospheres are magnetically separated, the ions are eluted with 2 M nitric acid and then determined by inductively coupled plasma-mass spectroscopy. The limits of detection of this method are 2, 82 and 103 ng L￣1 for Ni(II), Cu(II), and Pb(II) ions, respectively, and the relative standard deviations (for n = 7) are 6, 7.8, and 7.4 %. The protocol is successfully applied to the quantitation of these ions in tap water and food samples (mint, cabbage, potato, peas). Recoveries from spiked water samples ranged from 97 to 100 %.
Graphical abstract Mercaptobenzothiazole-functionalized magnetic carbon nanospheres of type Fe3O4@SiO2@C were synthesized. Then applied for magnetic solid phase extraction of Ni(II), Cu(II) and Pb(II) from water and food samples with LOD of 0.002, 0.082 and 0.103 μg L?1 respectively.
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).
The authors describe an amperometric sensor for dopamine (DA) by employing olive-like Fe2O3 microspheres (OFMs) as the electrocatalyst for DA oxidization. The OFMs were prepared by using a protein templated method. The structure and properties of the OFMs were characterized by scanning electron microscopy, X-ray powder diffraction, energy dispersive x-ray spectroscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The OFMs possess excellent catalytic activity towards DA oxidization due to their unique morphology. The sensor responds to DA within less than 5 s. The sensor, best operated at a voltage of +0.2 V (vs. SCE) responds linearly in the 0.2 to 115 μM DA concentration range and has a 30 nM detection limit. The selectivity, reproducibility and long-term stability of the sensor are acceptable. It performs well when applied to spiked human urine samples.
Graphical abstract Olive-like Fe2O3 microspheres (OFMs), synthesized using egg white as template, display excellent catalytic activity towards dopamine (DA) oxidization due to their unique morphology. They were applied for DA detection using the amperometric technique. The electrochemical sensor exhibited a high sensitivity and a 30 nM detection limit. DAQ: dopaquinone.
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.
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.
An amino acid derived ionic liquid, Fe3O4 nanoparticles and graphene oxide (GO) were used to prepare a material for the magnetic solid phase extraction (MSPE) of the ions Al(III), Cr(III), Cu(II) and Pb(II). The material was characterized by Fourier transform infrared spectral (FT-IR), scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), magnetic analysis and isoelectric point (pI) analysis. It is shown to be a viable sorbent for the separation of these metal ions. Single factor experiments were carried out to optimize adsorption including pH values, ionic strength, temperature and solution volume. Following desorption with 0.1 M HCl, the ions were quantified by inductively coupled plasma optical emission spectrometry. Under the optimum conditions, the method provides a linear range from 10 to 170 μg· L?1 for Al(III); from 4.0 to 200 μg· L?1 for Cr(III); from 5.0 to 170 μg· L?1 for Cu(II); and from 5.0 to 200 μg· L?1 for Pb(II). The limits of detection (LOD) are 6.2 ng L?1 for Al(III); 1.6 ng L?1 for Cr(III); 0.52 ng L?1 for Cu(II); and 30 ng L?1 for Pb(II). Method performance was investigated by determination of these ions in (spiked) environmental water and gave recoveries in the range of 89.1%–117.8%.
Graphical abstract The graph shows that Al(III), Cr(III), Cu(II), Pb(II) are not adsorbed quantitatively by Fe3O4-SiO2. On the other hand, Cr(III) and Pb(II) are adsorbed quantitatively by Fe3O4-SiO2-GO while Al(III) and Cu(II) are not quantitatively retained. However, 3D–Fe3O4-SiO2-GO-AAIL adsorb all these 4 metal ions quantitatively.
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.
The article describes a method for determination of tannic acid in extracts of medicinal plants. Tannic acid (TA) is an antioxidant and has anticancer and antimicrobial properties. Titanium dioxide nanoparticles (TiO2) were co-sensitized with 5-methylphenazinium methosulfate (PMS) and carboxy-functionalized cadmium telluride quantum dots (CdTe QDs), and immobilized on a fluorine-doped tin oxide electrode. The surface morphology and electrochemical properties of the modified electrode were investigated by scanning electron microscopy and amperometry, respectively. A composite consisting of TiO2, PMS and CdTe QDs in a nafion film has a response to TA under LED light higher than that observed for each separate component. Under optimized experimental conditions and at an applied voltage of +0.4 V vs Ag/AgCl, the photoelectrochemical sensor has a linear response in the 0.2 to 200 μmol L?1 TA concentration range and a detection limit of 60 nmol L?1. The sensor was successfully applied to the determination of TA in spiked extracts from three medicinal plants, with recovery values between 98.3 and 103.9 %.
Graphical abstract Schematic diagram for photoelectrochemical detection of tannic acid based on a fluorine doped tin oxide electrode modified with titanium oxide, 5-methylphenazinium methosulfate and carboxy-functionalized cadmium telluride quantum dots
The authors describe a cataluminescence (CTL) based sensing method via signals generated at the surface of In3LaTi2O10 nanoparticles for simultaneous determination of trimethylamine, formaldehyde and benzene in air. The analytical wavelengths are 340 nm, 440 nm and 600 nm, and the best surface temperature of the catalytic material is 275 °C. The limits of detection of this method are 0.3 mg?m?3 for trimethylamine, 0.07 mg?m?3 for formaldehyde, and 0.2 mg?m?3 for benzene. The linear ranges of CTL intensity versus gas/vapor concentration are from 1.0 to 65.1 mg?m?3 for trimethylamine, from 0.2 to 72.5 mg?m?3 for formaldehyde, and from 0.5 to 77.5 mg?m?3 for benzene. The recoveries after testing 10 standard samples ranged from 98.1% to 102.6% for trimethylamine, from 98.1% to 102.6% for formaldehyde, and from 97.7% to 103.8% for benzene. Gaseous ammonia, acetaldehyde, toluene, ethylbenzene, ethanol, sulfur dioxide and carbon dioxide do not interfere. The relative deviation of the CTL signals after 200 h of continuous detection of trimethylamine, formaldehyde and benzene is <3%.
Graphical abstract Schematic of a cataluminescence (CTL) based method for simultaneous determination of trimethylamine (TMA), formaldehyde (HCHO) and benzene (C6H6) in air. The linear ranges of CTL intensity versus gas/vapor concentration are from 1.0 to 65.1 mg?m?3 for TMA, from 0.2 to 72.5 mg?m?3 for HCHO, and from 0.5 to 77.5 mg?m?3 for C6H6.
