•Novel electrochemical sensor was fabricated facilely by NH2-MIL-88-rGO composite.•NH2-MIL-88-rGO/GCE showed enhanced sensing performance for Cu2 +, Pb2 + and Cd2 +.•Detection of Cu2 +, Pb2 + and Cd2 + by this sensor with satisfactory recoveries.A novel electrochemical sensor was developed for the sensitive and selective detection of Cu2 +, Pb2 + and Cd2 +, which was based on NH2-MIL-88(Fe)-rGO composite modified glass carbon electrode (NH2-MIL-88(Fe)-rGO/GCE). The NH2-MIL-88(Fe)-rGO composite was facilely prepared by a one-step method and characterized by SEM, XRD, Raman spectrum and electrochemical methods. The stepwise GCE modified process was investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The electrochemical behaviors of Cu2 +, Pb2 + and Cd2 + ions on the NH2-MIL-88(Fe)-rGO/GCE were explored by differential pulse anodic stripping voltammetry (DPASV). It was found that NH2-MIL-88(Fe)-rGO was capable of adsorbing Cu2 +, Pb2 + and Cd2 + ions from aqueous solutions and the NH2-MIL-88(Fe)-rGO/GCE could enhance the electrochemical responses of Cu2 +, Pb2 + and Cd2 + effectively. Important operational parameters such as electrolyte pH and deposition time were investigated and optimized for the determination of trace Cu2 +, Pb2 + and Cd2 + ions. Under the optimum conditions, the proposed electrochemical sensor had a linear range of 0.005––0.3 μM for Cd2 +, 0.01–0.3 μM for Pb2 + and 0.005–0.05 μM for Cu2 +, respectively. The limits of detection (LODs) are 4.9 nM for Cd2 +, 10 nM for Pb2 + and 3.6 nM for Cu2 +, respectively. The proposed method has been successfully applied to determine three metal ions in water samples. The developed sensor promises simple preparation, fast operation, good sensitivity and excellent reusability, showing great potential for monitoring of water quality.Download high-res image (177KB)Download full-size image

Nitrogen and sulfur codoped graphene quantum dots (N,S-GQDs) were facilely fabricated by a one-step hydrothermal treatment of citric acid as the carbon source in the presence of cysteine as the doping agent. The resulting N,S-GQDs were characterized by TEM, AFM, Raman, FT-IR, UV-vis, XPS and fluorescence spectroscopy. The N,S-GQDs display a luminescence quantum yield of 35.4%, which was about 14 times greater than that of the undoped graphene quantum dots (GQDs). The AFM image showed a typical topographic height of 0.5 to 1.5 nm with 1–4 graphene layers. The fluorescent emission spectra of N,S-GQDs display an excitation-dependent behavior, and the emission peaks shift from 413 to 440 nm on increasing the excitation wavelength from 310 to 380 nm. The N,S-GQDs possess a storage stability of at least 2 months and are stable in the presence of high concentrations of salt. Due to the strong specific reactivity between Au3+ and amine groups on the N,S-GQDs, the addition of Au3+ ions to the N,S-GQDs suspension results in the formation of gold nanoparticles, which strongly quench the fluorescence of N,S-GQDs. While, other common cations and anions result in negligible changes in the fluorescence of N,S-GQDs. On this basis, a sensitive fluorometric method for the detection of Au3+ was developed that has a 50 nM detection limit and a linear range that extends from 0.1 μM to 50 μM. The method has been successfully used for the determination of Au3+ in real aqueous samples and for gold content in auranofin.

The octahedral structure of MIL-53(Fe) was facilely prepared by a microwave (MW)-assisted approach, and confirmed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The MIL-53(Fe) MOFs were further characterized by thermo gravimetric (TG) analysis and fourier transform infrared (FTIR) spectroscopy. It is found that the as-prepared MIL-53(Fe) exhibits intrinsic peroxidase-like activity, and could catalytically oxidize 3,3′,5,5′-tetramethylbenzidine (TMB), ABTS and OPD by H2O2 to produce a typical coloured reaction. The Michaelis–Menten behavior of the as-prepared MIL-53(Fe) was studied. The Km value of the as-prepared MIL-53(Fe) with H2O2 as the substrate was 0.03 mM, which was at least seven times lower than that of Fe-MIL–88NH2 and hemin@MIL-53(Al)–NH2. Interesting, the Km values of the as-prepared MIL-53(Fe) with H2O2 and TMB as the substrates were both lower than those of the MIL-53(Fe) obtained by conventional electric (CE) heating-based solvothermal method. This is probably attributed to the purely octahedral structure and small sized crystals of the MIL-53(Fe) obtained by MW-based synthesis method, confirming that the MW-based synthesis method promised advantages of simplicity, fast crystallization and good phase selectivity. Results of electron spin resonance (ESR) experiments indicated that the as-prepared MIL-53(Fe) exhibited catalytic ability to decompose H2O2 into ˙OH radicals. On this basis, a simple, sensitive and selective method for glucose detection was developed by coupling the oxidation of glucose catalyzed by glucose oxidase (GOx). As low as 0.25 μM glucose could be detected with a linear range from 0.25–20 μM. The proposed method was successfully used to determine glucose in real human serum samples.

In this paper, we successfully synthesized novel Mn3O4 nano-octahedrons using a simple hydrothermal method and demonstrated that the prepared Mn3O4 nanoparticles (NPs) exhibited highly intrinsic oxidase-like activity and could catalyze the reaction of TMB, ABTS and OPD to produce a typical color reaction in the absence of H2O2 within minutes. Compared with other non-noble metal NPs oxidase nanozymes, the affinity of Mn3O4 NPs to TMB was increased by at least 35% according to the Km values. It was deduced that O2˙− and few OH˙ radicals were produced during the catalytic reaction. Then, the addition of twelve phenols to the TMB–Mn3O4 NP system led to the fading of the solution by different degrees based on the antioxidant activity of the phenols. Thus, preliminary assessment of the antioxidant ability of twelve phenols using TMB decolorization assays was realized based on the excellent oxidase-like properties of the Mn3O4 NPs. Finally, under the optimum conditions, visual determination of tannic acid (TA) was realized and the detection limit was 19 nM with a linear range from 0.05 to 1.4 μM. The proposed method was successfully used to determine TA in tea samples.

Mesoporous material supported CoFe2O4 magnetic nanoparticles possess unique peroxidase/oxidase-like activity, and react with luminol to yield a novel chemiluminescence without the need of H2O2. Their oxidase-like activity shows pH and support dependence, and could be reversibly controlled by their pH. This offers a new method for manipulating the enzyme-like activity of nanoparticles.

•Carbon dots (CDs) and reduced state carbon dots (r-CDs) can react with potassium permanganate (KMnO4) in a strong acid to generate chemiluminescence (CL).•With different surface groups, the CL intensity of r-CDs-KMnO4 system is different from that of CDs-KMnO4 system.•The CL mechanisms of the two systems were investigated.Potassium permanganate (KMnO4) can react with two different carbon nanoparticles, i.e., carbon dots (CDs) and reduced state carbon dots (r-CDs), in a strong acid medium to generate chemiluminescence (CL). Furthermore, the different CL intensities and CL behaviors due to the different surface groups on these two kinds of carbon nanoparticles were confirmed. CL spectra, fluorescence spectra, UV–vis absorption spectra, and electron paramagnanetic resonance spectra were applied to investigate the CL mechanism. The main reaction pathways were proposed as follows: for the CL reaction between CDs and KMnO4, the excited states of CDs (CDs⁎) and Mn(II) (Mn(II)⁎) emerged as KMnO4 could inject holes into CDs, then, the CDs⁎ and Mn(II)⁎ acted as luminophors to yield CL; in the r-CDs-KMnO4 system, r-CDs were oxidized by KMnO4 directly, and CDs⁎ and Mn(II)⁎ were produced, at the same time, CL occurred. What is more interesting is that the CL intensity of the r-CD system is stronger than that of the CD system, which confirms that functional groups have strong effect on the CL behavior. It inspired us that new carbon nanoparticles with excellent luminous performance can be designed by tuning their surface groups.

A new method for selective determination of Cr(VI) in environmental water samples was developed based on its quenching effect on the fluorescent N-doping graphene quantum dots (N-GQDs). The N-GQDs were synthesized by a simple one-step method using citric acid as the carbon source and ammonia as the nitrogen source with a 65% yield, showing that mass production of the N-GQDs is possible. The obtained N-GQDs with oxygen-rich functional groups exhibited a strong blue emission with a quantum yield of 18.6%, which was 7 times greater than that of graphene quantum dots (GQDs). Due to the selective coordination to Cr(VI), the N-GQDs can be used as a green and facile sensing platform for label-free sensitive and selective detection of Cr(VI) ions in aqueous solution and real water samples. Compared to GQDs, the N-GQDs as a fluorescent probe promises much improved selectivity for sensing of Cr(VI). The N-GQDs fluorescence probe shows a sensitive response to Cr(VI) in a wide concentration range of 0–140 μM with a detection limit of 40 nM. The N-GQDs-based fluorescence method was successfully used to selectively detect Cr(VI), and discriminate it and Cr(III) as well in aqueous samples.

The Fenton-based reaction is powerful enough to decompose refractory organic pollutants, but it is limited by having a low pH range and it is necessary to have a secondary disposal of the iron sludge. This study demonstrates that Fe3O4–multi-walled carbon nanotube (Fe3O4–MWCNT) magnetic hybrids can be used as an efficient peroxidase mimic catalyst that could overcome such pH limitations in a Fenton-like reaction and could be reused after a simple magnetic separation. The Fe3O4–MWCNT hybrid was prepared using a simple one-pot strategy via in situ growth of Fe3O4 magnetic nanoparticles onto the surface of the MWCNTs. In this process, MWCNTs act as an excellent dispersant, which ensures that the Fe3O4 is well dispersed. The Fe3O4–MWCNT hybrid was characterized by X-ray diffractometry, Fourier transform infrared spectrometer, thermogravimetric analysis and vibrating sample magnetometry, which indicated that the Fe3O4 nanoparticles were successfully deposited on to the surface of MWCNTs. Furthermore, it was revealed that the Fe3O4–MWCNTs could catalyze H2O2 decomposition by acting as a peroxidase mimic catalyst. Then heterogenous Fenton-like reactions were performed using the Fe3O4–MWCNT nanocomposites as a catalyst to degrade methylene blue (10.0 mg L−1; MB) in aqueous solution. The results showed that MB could be efficiently removed in a broad pH range of 1.0–10.0, with a degradation efficiency of 88.13% to 98.68% in two hours, and a highest total organic carbon removal efficiency of 35.6% in 12 hours. Furthermore, the magnetic nanocomposites exhibited an enhanced removal efficiency for MB compared with the Fe3O4 magnetic nanocomparticles and MWCNTs used individually. In addition, Fe3O4–MWCNT nanocomposites exhibited strong magnetism, and thereby could be easily separated from aqueous solution using an external magnetic field. Therefore, the as-prepared Fe3O4–MWCNT nanocomposites could be used as a promising and effective catalyst in Fenton-like reactions for the purification of MB polluted water in a wide pH range.

This article presents a new enzyme-mimic activity of non-noble metal-based bimetallic Fe–Co NPs. This type of enzyme-mimic exhibits much higher affinity to H2O2 over other NPs-based peroxidase mimetics by at least one order of magnitude due to the synergistic effects between the two metals.

We investigated the suitability of dithiocarbamate (DTC) capped Ag nanoparticles (NPs) as resonance light scattering (RLS) probes for the simultaneous sensing of Pb2+ and cysteine. The DTC capping ligands are generated by a very simple in situ method through reaction of carbon disulfide with diethanolamine as primary precursor molecules under ultrasonic irradiation. This strategy was based on the fact that Pb2+ could induce the aggregation of DTC–Ag NPs due to the strong metal affinity of DTC along with an enhanced RLS signal. After optimizing some experimental conditions (including the pH value of the solution, concentration of DTC–Ag NPs, and ion strength), a very simple and facile sensing system has been developed for the detection of Pb2+ in water based on RLS technology. The proposed system promises excellent selectivity, a wide linear response range and high sensitivity for Pb2+. The linear response range for Pb2+ was from 0.01 μM to 60 μM. The limit of detection (S/N = 3σ) for Pb2+ was as low as 4 nM. The proposed method was successfully used to detect Pb2+ in river and tap water samples, indicating the potential of this new, sensitive and selective method in water quality monitoring. Meanwhile, due to the strong binding preference of cysteine toward Pb2+ by the formation of Pb2+–S bonds, Pb2+ was removed from the surfaces of the DTC–Ag NPs, leading to redispersion of DTC–Ag NPs, along with a decreased RLS signal. The possibility of the proposed system for the sensing of cysteine was also investigated.

We reported a new application of silver nanoparticles (NPs) for the visual sensing of aromatic polyphenols, such as gallic acid, pyrogallol and tannic acid, which is based on the intensified plasmon absorbance signals and visual changes from yellow to orange due to hydrogen-bonding recognition and subsequent catalytic oxidation of the target phenols by chitosan-capped Ag NPs (Ch–Ag NPs). The Ch–Ag NPs are generated by the well-known reaction of AgNO3 with NaBH4 and stabilized with chitosan which is a polysaccharide biopolymer with excellent dispersive properties and stability in aqueous media. After optimizing some experimental conditions, a very simple and facile sensing system has been developed for the detection of gallic acid, pyrogallol and tannic acid in water samples. The proposed system promises high selectivity toward gallic acid, pyrogallol and tannic acid, and other phenolic compounds including p-aminobenzoic acid, pentachlorophenol, 2,4,6-trinitrophenol, 2,4-dinitrophenol, p-nitrophenol, 1-naphthol, β-naphthol, p-aminophenol, catechol, hydroquinone, m-dihydroxybenzene, phloroglucin and phenol could not induce a color change even at 0.1 mM. The outstanding selectivity property of the proposed method for gallic acid, pyrogallol and tannic acid resulted from the Ch–Ag NPs-mediated reduction of Ag+ by the target phenols. Also, a wide linear response range was obtained for the three targets. The linear response ranges for gallic acid, pyrogallol, and tannic acid were from 1 × 10−5 to 1 × 10−3 M, 1 × 10−5 to 1 × 10−2 M and 1 × 10−6 to 1 × 10−4 M with a respective detection limit (DL) of 1 × 10−5, 1 × 10−5, and 1 × 10−6 M. The proposed method was successfully applied to detect target phenols in environmental water samples. Furthermore, because the color change from yellow to orange is observable by the naked eye, it is easy to realize visual detection of the target phenols without any instrumentation or complicated design. The experimental results reported here open up an innovative application of the catalytic reactivity of Ag NPs.

Polyethyleneimine (PEI) can selectively capture trace-level free copper ions (Cu2+), from which the true toxic effects of copper originate. Thus, PEI-functionalized eggshell membrane (ESM) may serve as a green, economical, easily available, and selective solid phase extraction (SPE) adsorbent material for Cu2+ enrichment. In this paper, the potential of the PEI-functionalized ESM (PEI–ESM) as a biosorbent for the selective solid phase extraction and preconcentration of trace Cu2+ in environmental water samples and food samples in combination with flame atomic absorption spectrometry (FAAS) was investigated. After modification, the dynamic uptake capacity of PEI–ESM increased by about 20-fold compared with ESM. Various factors affecting Cu2+ extraction by SPE were investigated. Under the optimal conditions, Cu2+ could be easily extracted by the PEI–ESM packed cartridge. The favorable limit of detection (LOD) for Cu(II) was 0.15 μg L−1 with an enrichment factor of 100, and the relative standard deviation (RSD) was 2.0% for 50 μg L−1 Cu(II) (n = 11). The reproducibility among columns was satisfactory (RSD among the columns is less than 5%). Stability testing demonstrated that the PEI–ESM maintained over 92.0% recovery for Cu(II) even after a run of 45 adsorption and desorption cycles, showing its operational stability. The proposed method has been applied successfully to the analysis of copper in environmental water samples and food samples, which demonstrated that PEI–ESM could be an excellent SPE adsorbent for copper pretreatment and enrichment from real water samples and food samples.

In recent years, nanoparticles, particularly magnetic nanoparticles (MNPs), have been emerging as a new type of important functional solid phase extraction (SPE) material. However, there has been no report on the direct application of Fe3O4 MNPs for the extraction of trace Sudan dyes as a SPE material in food and environmental analysis. In this work, Fe3O4 MNPs from a one-pot chemical coprecipitation route were prepared under ultrasound irradiation. The as-obtained Fe3O4 MNPs showed good adsorbability to the four Sudan dyes and were successfully applied as a SPE material coupled with high-performance liquid chromatography (HPLC) for the simultaneous isolation and determination of four Sudan dyes from foodstuff and water samples. Compared to the traditional SPE adsorbents, such as neutral alumina and C18, the Fe3O4 MNPs adsorbents provided simple, fast and easy operation with an effective purification effect. The results on the water matrix suggest that such purification can be considered a practicable solution for sample preparation in the routine analysis of Sudan dyes in environmental samples with good anti-interference ability to natural organic matter, and can detect Sudan dyes down to 0.02 μg L−1 when sample volumes of 750 mL and 500 mg Fe3O4 MNPs adsorbents were adopted. Also, the proposed method could be potentially applied to the rapid isolation and determination of Sudan dyes in complicated matrices, such as food samples, and can detect Sudan dyes down to 10 μg kg−1 when 1 g foodstuff and 500 mg Fe3O4 MNPs adsorbents were used. The as-obtained Fe3O4 MNPs showed operational stability and retained excellent adsorption and magnetic properties, even after an eight-cycle run for the adsorption and desorption of Sudan dyes.

The magnetic multiwalled carbon nanotubes (MMWCNTs) have been successfully prepared using a one-pot chemical coprecipitation method, in which magnetic nanoparticles (MNPs) were deposited onto multiwalled carbon nanotubes (MWCNTs) by in situ high temperature decomposition of the magnetic precursor of iron(III) in ethylene glycol media. A novel procedure for extraction of linear alkylbenzene sulfonates (LAS) as a model compound was thus developed in an off-line extraction system with detection by HPLC. The procedure includes the separation and preconcentration of LAS homologues onto MMWCNTs at pH 7.0 and their subsequent detection after sonication elution, followed by the separation of the MMWCNTs from the aqueous phase by external magnetic field and washing with ultra pure water. With a sample volume of 500 mL and 100 mg MMWCNTs sorbents, an enrichment factor of about 500, and a detection limit of 0.013–0.021 μg L−1 were obtained within a linear range of 0.5–100 μg L−1, together with a correlation coefficient of 0.9938–0.9998 for four LAS homologues. A precision of 2.4–5.6% was obtained for six replicate determinations of 50 μg L−1LAS. The recoveries of LAS homologues spiked in environmental water samples ranged from 87.3 to 106.3%, demonstrating the utility of the MMWCNTs adsorbents in a series of water samples. Stability testing demonstrated that the MMWCNTs remained 95.0% recovery for the target LAS even after a run of 50 adsorption and desorption cycles, showing their super operational stability. The MMWCNTs are promising adsorbents, suitable for the long-term repetitive sorption/desorption of target compounds in environmental water samples.

Here, we report a highly simple and general protocol for functionalization of the CoFe2O4 NPs with chitosan polymers in order to make CoFe2O4 NPs disperse and stable in solution. The functionalized CoFe2O4 NPs (denoted as CF-CoFe2O4 NPs) were characterized by scanning electron microscope (SEM), thermogravimetric (TG), X-ray diffraction (XRD) and FT-IR spectra. It was found that the CoFe2O4 NPs were successfully decorated and uniformly dispersed on the surface of chitosan without agglomeration. The CF-CoFe2O4 NPs were found to increase greatly the radiation emitted during the CL oxidation of luminol by hydrogen peroxide. Results of ESR spin-trapping experiments demonstrated that the CF-CoFe2O4 NPs showed catalytic ability to H2O2 decomposition into ˙OH radicals. On this basis, a highly sensitive and rapid chemiluminescent method was developed for hydrogen peroxide in water samples and glucose in blood samples. Under optimum conditions, the proposed method allowed the detection of H2O2 in the range of 1.0 × 10−9 to 4.0 × 10−6 M and glucose in the range of 5.0 × 10−8 to 1.0 × 10−5 M with detectable H2O2 as low as 500 pM and glucose as low as 10 nM, respectively. This proposed method has been successfully applied to detect H2O2 in environmental water samples and glucose in serum samples with good accuracy and precision.

Chitosan stabilized silver nanoparticles (Ch-Ag NPs) were successfully synthesized by a one-step method and were found to possess intrinsic peroxidase-like activity, could catalytically oxidize substrates, such as TMB, and OPD, by H2O2 to produce a typical colour reaction such as from colorless to blue for TMB and from colorless to red for OPD. Our results demonstrate that the Ch-Ag NPs exhibit higher thermal and pH durance than HRP, thus could be suitable in a wider range of harsh conditions. Results of electron paramagnetic resonance (ESR) suggest that the catalyse-mimic activity of the Ch-Ag nanostructures effectively catalyzed the decomposition of H2O2 into ˙OH radicals. Based on this finding, a simple, sensitive and selective visual and colorimetric method with TMB as substrate has been designed for glucose detection when combined with glucose oxidase (GOx). This colorimetric method can be used for detection of glucose in biological samples with a detection limit as low as 100 nM and a dynamic range from 5.0 × 10−6 to 2.0 × 10−4 M.

The polyethyleneimine (PEI) functionalized biosorbent which uses an eggshell membrane (ESM) as a model was synthesized based on the cross linking reaction between aldehydes in glutaraldehyde and functional groups such as amines and amides in ESM. The as-prepared biosorbent (PEI–ESM) strongly interacted with chromium(VI). After modification, the dynamic uptake capacity of the PEI–ESM increased by 105% compared with the control, and the maximum equilibrium adsorption capacity for Cr(VI) can reach about 160 mg g−1 with an initial pH of 3.0. The Langmuir adsorption isotherm was applicable to fit the removal process. Kinetics of the Cr(VI) removal were found to follow a pseudo-second-order rate equation. The results obtained by Raman spectroscopy and X-ray photoelectron spectroscopic analysis (XPS), performed on the as-prepared biosorbent before and after Cr(VI) adsorption, suggested that some of adsorbed Cr(VI) anions were reduced to Cr(III) in Cr2O3 or Cr(OH)3 during the sorption process, demonstrating that the PEI–ESM could detoxify Cr(VI). The developed biosorbent promises advantages such as low cost, high adsorption capacity, Cr(VI) detoxification, and environmental friendliness.

This communication presents a new peroxidase mimic of CoFe2O4 nanoparticles evaluated by the luminol-based chemiluminescent (CL) reaction. This offers a new method for evaluation and screening of the nanoparticles-based enzyme mimetics.

Carbon nanodots (C-Dots) were found to possess intrinsic peroxidase-like activity, and could catalytically oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) by H2O2 to produce a colour reaction. This offers a simple, sensitive and selective colorimetric method for glucose determination in serum.

It was found that Cu2+ has a great catalytic effect on p-cresol oxidation by hydrogen peroxide under alkaline conditions, leading to an intense fluorescence signal due to the fast formation of 2,2′-dihydroxy-5,5′-dimethylbiphenyl, an oxidation product of p-cresol. Investigation of the fluorescence spectra of the p-cresol–hydrogen peroxide system demonstrated the catalytic behavior of Cu2+. On this basis, a very simple, sensitive, and selective fluorescent method was established for the determination of trace copper in this study. Under the optimal conditions, the proposed system could respond down to 1.0 × 10−8 mol L−1 of Cu2+ with a linear calibration range of 3.0 × 10−7 mol L−1 to 5.0 × 10−5 mol L−1. The relative standard deviation (RSD) was 2.1% for 7.0 × 10−6 mol L−1Cu2+ (n = 15). The proposed method was successfully applied in the determination of trace Cu2+ in lake, river and swimming pool water samples with satisfactory results. The results obtained by the proposed method are in good agreement with those obtained by a conventional atomic absorption spectroscopy method.

Multiwalled carbon nanotubes (MWCNTs) were used as a novel kind of solid-phase extraction adsorbents in this work as well as an analytical method based on MWCNTs solid-phase extraction (SPE) combined with high-performance liquid chromatography (HPLC) was established for the determination of polycyclic aromatic hydrocarbons (PAHs), some of which belong to typical persistent organic pollutants (POPs) owing to their carcinogenicity and endocrine disrupting activity. Several conditions that probably affected the extraction efficiency including the eluent volume, sample flow rate, sample pH and the sample volume were optimized in detail. The characteristic data of analytical performance were determined to investigate the sensitivity and precision of the method, and the method was applied to the determination of PAHs in environmental water samples such as river water sample, tap water sample and wastewater sample from the constructed wetland effluent. The experimental results indicated that there were excellent linear relationship between peak area and the concentration of PAHs over the range of 0.04–100 μg L−1, and the precisions (RSD) were 1.7–4.8% under the optimal conditions. The detection limits of proposed method for the studied PAHs were 0.005–0.058 μg L−1 (S/N = 3). The recoveries of PAHs spiked in environmental water samples ranged from 78.7 to 118.1%. It was concluded that MWCNTs packed cartridge coupled with HPLC was an excellent alternative for the routine analysis of PAHs at trace level.

Mesoporous material supported CoFe2O4 magnetic nanoparticles possess unique peroxidase/oxidase-like activity, and react with luminol to yield a novel chemiluminescence without the need of H2O2. Their oxidase-like activity shows pH and support dependence, and could be reversibly controlled by their pH. This offers a new method for manipulating the enzyme-like activity of nanoparticles.

In this paper, we successfully synthesized novel Mn3O4 nano-octahedrons using a simple hydrothermal method and demonstrated that the prepared Mn3O4 nanoparticles (NPs) exhibited highly intrinsic oxidase-like activity and could catalyze the reaction of TMB, ABTS and OPD to produce a typical color reaction in the absence of H2O2 within minutes. Compared with other non-noble metal NPs oxidase nanozymes, the affinity of Mn3O4 NPs to TMB was increased by at least 35% according to the Km values. It was deduced that O2˙− and few OH˙ radicals were produced during the catalytic reaction. Then, the addition of twelve phenols to the TMB–Mn3O4 NP system led to the fading of the solution by different degrees based on the antioxidant activity of the phenols. Thus, preliminary assessment of the antioxidant ability of twelve phenols using TMB decolorization assays was realized based on the excellent oxidase-like properties of the Mn3O4 NPs. Finally, under the optimum conditions, visual determination of tannic acid (TA) was realized and the detection limit was 19 nM with a linear range from 0.05 to 1.4 μM. The proposed method was successfully used to determine TA in tea samples.

This article presents a new enzyme-mimic activity of non-noble metal-based bimetallic Fe–Co NPs. This type of enzyme-mimic exhibits much higher affinity to H2O2 over other NPs-based peroxidase mimetics by at least one order of magnitude due to the synergistic effects between the two metals.

Carbon nanodots (C-Dots) were found to possess intrinsic peroxidase-like activity, and could catalytically oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) by H2O2 to produce a colour reaction. This offers a simple, sensitive and selective colorimetric method for glucose determination in serum.

The polyethyleneimine (PEI) functionalized biosorbent which uses an eggshell membrane (ESM) as a model was synthesized based on the cross linking reaction between aldehydes in glutaraldehyde and functional groups such as amines and amides in ESM. The as-prepared biosorbent (PEI–ESM) strongly interacted with chromium(VI). After modification, the dynamic uptake capacity of the PEI–ESM increased by 105% compared with the control, and the maximum equilibrium adsorption capacity for Cr(VI) can reach about 160 mg g−1 with an initial pH of 3.0. The Langmuir adsorption isotherm was applicable to fit the removal process. Kinetics of the Cr(VI) removal were found to follow a pseudo-second-order rate equation. The results obtained by Raman spectroscopy and X-ray photoelectron spectroscopic analysis (XPS), performed on the as-prepared biosorbent before and after Cr(VI) adsorption, suggested that some of adsorbed Cr(VI) anions were reduced to Cr(III) in Cr2O3 or Cr(OH)3 during the sorption process, demonstrating that the PEI–ESM could detoxify Cr(VI). The developed biosorbent promises advantages such as low cost, high adsorption capacity, Cr(VI) detoxification, and environmental friendliness.

This communication presents a new peroxidase mimic of CoFe2O4 nanoparticles evaluated by the luminol-based chemiluminescent (CL) reaction. This offers a new method for evaluation and screening of the nanoparticles-based enzyme mimetics.

It was found that Cu2+ has a great catalytic effect on p-cresol oxidation by hydrogen peroxide under alkaline conditions, leading to an intense fluorescence signal due to the fast formation of 2,2′-dihydroxy-5,5′-dimethylbiphenyl, an oxidation product of p-cresol. Investigation of the fluorescence spectra of the p-cresol–hydrogen peroxide system demonstrated the catalytic behavior of Cu2+. On this basis, a very simple, sensitive, and selective fluorescent method was established for the determination of trace copper in this study. Under the optimal conditions, the proposed system could respond down to 1.0 × 10−8 mol L−1 of Cu2+ with a linear calibration range of 3.0 × 10−7 mol L−1 to 5.0 × 10−5 mol L−1. The relative standard deviation (RSD) was 2.1% for 7.0 × 10−6 mol L−1Cu2+ (n = 15). The proposed method was successfully applied in the determination of trace Cu2+ in lake, river and swimming pool water samples with satisfactory results. The results obtained by the proposed method are in good agreement with those obtained by a conventional atomic absorption spectroscopy method.

Polyethyleneimine (PEI) can selectively capture trace-level free copper ions (Cu2+), from which the true toxic effects of copper originate. Thus, PEI-functionalized eggshell membrane (ESM) may serve as a green, economical, easily available, and selective solid phase extraction (SPE) adsorbent material for Cu2+ enrichment. In this paper, the potential of the PEI-functionalized ESM (PEI–ESM) as a biosorbent for the selective solid phase extraction and preconcentration of trace Cu2+ in environmental water samples and food samples in combination with flame atomic absorption spectrometry (FAAS) was investigated. After modification, the dynamic uptake capacity of PEI–ESM increased by about 20-fold compared with ESM. Various factors affecting Cu2+ extraction by SPE were investigated. Under the optimal conditions, Cu2+ could be easily extracted by the PEI–ESM packed cartridge. The favorable limit of detection (LOD) for Cu(II) was 0.15 μg L−1 with an enrichment factor of 100, and the relative standard deviation (RSD) was 2.0% for 50 μg L−1 Cu(II) (n = 11). The reproducibility among columns was satisfactory (RSD among the columns is less than 5%). Stability testing demonstrated that the PEI–ESM maintained over 92.0% recovery for Cu(II) even after a run of 45 adsorption and desorption cycles, showing its operational stability. The proposed method has been applied successfully to the analysis of copper in environmental water samples and food samples, which demonstrated that PEI–ESM could be an excellent SPE adsorbent for copper pretreatment and enrichment from real water samples and food samples.

In recent years, nanoparticles, particularly magnetic nanoparticles (MNPs), have been emerging as a new type of important functional solid phase extraction (SPE) material. However, there has been no report on the direct application of Fe3O4 MNPs for the extraction of trace Sudan dyes as a SPE material in food and environmental analysis. In this work, Fe3O4 MNPs from a one-pot chemical coprecipitation route were prepared under ultrasound irradiation. The as-obtained Fe3O4 MNPs showed good adsorbability to the four Sudan dyes and were successfully applied as a SPE material coupled with high-performance liquid chromatography (HPLC) for the simultaneous isolation and determination of four Sudan dyes from foodstuff and water samples. Compared to the traditional SPE adsorbents, such as neutral alumina and C18, the Fe3O4 MNPs adsorbents provided simple, fast and easy operation with an effective purification effect. The results on the water matrix suggest that such purification can be considered a practicable solution for sample preparation in the routine analysis of Sudan dyes in environmental samples with good anti-interference ability to natural organic matter, and can detect Sudan dyes down to 0.02 μg L−1 when sample volumes of 750 mL and 500 mg Fe3O4 MNPs adsorbents were adopted. Also, the proposed method could be potentially applied to the rapid isolation and determination of Sudan dyes in complicated matrices, such as food samples, and can detect Sudan dyes down to 10 μg kg−1 when 1 g foodstuff and 500 mg Fe3O4 MNPs adsorbents were used. The as-obtained Fe3O4 MNPs showed operational stability and retained excellent adsorption and magnetic properties, even after an eight-cycle run for the adsorption and desorption of Sudan dyes.