Showing papers in "Mikrochimica Acta in 2016"
TL;DR: This review summarizes the commonly used methods for the preparation of C-dots, their surface functionalization, physical and chemical properties, characterization as well as applications and recent advances in the fields of biology and anticancer therapy.
Abstract: Carbon dots (C-dots) are a kind of fluorescent nanoparticles that are strongly fluorescent, non-blinking, and can be easily synthesized at low cost. Their emission color can be tuned by varying the excitation wavelength. Their properties make them strong competitors to semiconductor quantum dots. Synthetic approaches for C-dots can be classified into two categories, viz. top-down and bottom-up methods. Surface passivated and functionalized C-dots can be utilized to sense pH values, metal ions and organic molecules. Owing to their low cytotoxicity, biocompatibility and impressive photostability, long-term observations become possible. C-dots also show promise as labels and for bioimaging. This review (with 142 refs.) is divided into several sections. The first covers commonly used methods for preparation of C-dots including laser ablation, arc discharge, electrochemical methods, pyrolytic processes, template based methods, microwave assisted methods, chemical oxidation methods, reverse micelle based methods, etc. The first section also covers methods for surface functionalization and passivation. We continue by discussing the spectroscopic properties and other physical and chemical properties of C-dots (fluorescence, up-conversion fluorescence, methods for enhancing photoluminescence, effects of pH value, cytotoxicity, etc.). Another section covers the characterization including TEM and XRD. Applications in biology are summarized and subdivided into in vitro imaging, in vivo imaging, chemical probe, quantitation of biomacromolecules, but also in drug delivery, photoacoustic imaging and anticancer therapy. We finally discuss current challenges and perspectives in this promising field.
478 citations
TL;DR: This review summarises recent advances in oriented immobilization of proteins based on strategies via bio−/chemical affinity, covalent bonding, and molecular imprinting techniques and describes methods for characterization of oriented immobilized proteins.
Abstract: Immobilization of proteins on a solid support is critical with respect to the fabrication and performance of biosensors and biochips. Protein attachment with a preferable orientation can effectively avoid its denaturation and keeps its active sites fully exposed to solution, thus maximally preserving the bioaffinity or bioactivity. This review (with 140 refs.) summarises the recent advances in oriented immobilization of proteins with a particular focus on antibodies and enzymes. Following an introduction that describes reasons for oriented immobilization on (nano)surfaces, we summarize (a) methods for (bio)chemical affinity-mediated oriented immobilization (with sections on immunoglobulin G (IgG)-binding protein as the capture ligand, DNA-directed immobilization, aptamer- and peptide-mediated immobilization, affinity ligand and fusion tag-mediated immobilization, material-binding peptide-assisted immobilization); (b) methods for covalent oriented immobilization (with sections on immobilization via cysteine residues or cysteine tags, via carbohydrate moieties; via enzyme fusion or enzymatic catalysis, and via nucleotide binding sites of antibodies); (c) methods based on molecular imprinting techniques; (d) methods for characterization of oriented immobilized proteins; and then make conclusions and give perspectives.
223 citations
TL;DR: In this article, a review of screen-printed electrodes (SPEs) as transducers for detecting heavy metal ions in water samples is presented, which reveals the significance of SPEs in terms of decentralized and in situ analysis of heavy metal ion in environmental monitoring.
Abstract: Heavy metals such as lead, mercury, cadmium, zinc and copper are among the most important pollutants because of their non-biodegradability and toxicity above certain thresholds. Here, we review methods for sensing heavy metal ions (HMI) in water samples using screen-printed electrodes (SPEs) as transducers. The review (with 107 refs.) starts with an introduction into the topic, and this is followed by sections on (a) mercury-coated SPEs, (b) bismuth-coated SPEs, (c) gold-coated SPEs (d) chemically modified and non-modified carbon SPEs, (e) enzyme inhibition-based SPEs, and (f) an overview of commercially available electrochemical portable heavy metal analyzers. The review reveals the significance of SPEs in terms of decentralized and of in situ analysis of heavy metal ions in environmental monitoring.
216 citations
TL;DR: In this article, the progress made between 2010 and 2015 in the field of nanomaterial based electrochemical biosensors for pesticides in food is discussed, and the main focus is on strategies to analyze real samples.
Abstract: This overview (with 114 refs.) covers the progress made between 2010 and 2015 in the field of nanomaterial based electrochemical biosensors for pesticides in food. Its main focus is on strategies to analyze real samples. The review first gives a short introduction into the most often used biorecognition elements. These include (a) enzymes (resulting in inhibition-based and direct catalytic biosensors), (b) antibodies (resulting in immunosensors), and (c) aptamers (resulting in aptasensors). The next main section covers the various kinds of nanomaterials for use in biosensors and includes carbonaceous species (carbon nanotubes, graphene, carbon black and others), and non-carbonaceous species in the form of nanoparticles, rods, or porous materials. Aspects of sample treatment and real sample analysis are treated next before discussing vanguard technologies in tailor-made food analysis.
155 citations
TL;DR: A review of recent trends in core-shell surface molecular imprinting can be found in this paper, where the imprinting sites are located on the surface of the cores or shells of nanoparticles (NPs).
Abstract: Core-shell surface molecular imprinting technology represents a rather new trend in analytical sciences. In this kind of material, the imprinting sites are located on the surface of the cores or shells of nanoparticles (NPs). This material can improve the capability of recognizing target molecules (analytes), reduce nonspecific adsorption, increase the relative adsorption capacity and selectivity, and accelerate the rate of mass transfer. This review (with 158 references) focuses on recent trends in core-shell MIPs. Following an introduction into the field, a first main section covers common core-materials including silica, magnetic NPs, quantum dots (including semiconductor quantum dots and carbon dots), gold and silver nanoclusters, and up-conversion materials. A further section covers the materials and reagents required for preparing MIPs (with subsections on templates, functional monomers, cross-linkers, initiators, and effects of solvent). A next main section covers synthetic approaches such as precipitation polymerization, emulsion polymerization, and grafting approach. A final section gives examples for applications of core-shell MIPs in analytical assays and in sensing.
154 citations
TL;DR: In this paper, a review of surface functionalizaton of metal oxides by gold nanoparticles and the application of the resulting nanomaterials in resistive gas sensors is presented.
Abstract: This review (with 170 refs.) discusses approaches towards surface functionalizaton of metal oxides by gold nanoparticles, and the application of the resulting nanomaterials in resistive gas sensors. The articles is subdivided into sections on (a) methods for modification of metal oxides with gold nanoparticles; (b) the response of gold nanoparticle-modified metal oxide sensors to gaseous species, (c) a discussion of the limitations of such sensors, and (d) a discussion on future tasks and trends along with an outlook. It is shown that, in order to achieve significant improvements in sensor parameters, it is necessary to warrant a good control the size and density of gold nanoparticles on the surface of metal oxide crystallites, the state of gold in the cluster, and the properties of the metal oxide support. Current challenges include an improved reproducibility of sensor preparation, better long-term stabilities, and a better resistance to sintering and poisoning of gold clusters during operation. Additional research focused on better understanding the role of gold clusters and nanoparticles in gas-sensing effects is also required.
131 citations
TL;DR: In this article, the authors report on the hydrothermal synthesis of boron-doped carbon dots (B-CDs) starting from glucose and boric acid.
Abstract: We report on the hydrothermal synthesis of boron-doped carbon dots (B-CDs) starting from glucose and boric acid. Doping of the CDs with boron was confirmed by Fourier transform infrared and X-ray photoelectron spectroscopy. The B-CDs have an average diameter of about 4 nm and display blue fluorescence which is dynamically quenched by Fe(III) ions. This finding was exploited to design a method for the determination of Fe(III) in water. The relative fluorescence intensity at 359 nm in the presence and of absence ions is inversely proportional to the concentration of Fe(III) ions, and a Stern-Volmer calibration plot is linear in the concentration range of 0–16 μM, with a 242 nM detection limit. The assay is sensitive, robust and selective.
125 citations
TL;DR: Fe3S4 magnetic nanoparticles (MNPs) are shown to act as peroxidase mimetics and this was used to design a glucose oxidase (GOx) based glucose assay where the H2O2 formed during oxidation of glucose oxidizes tetramethylbenzidine to give a blue product which can be quantified by photometry.
Abstract: Greigite magnetic nanoparticles (Fe3S4-MNPs) were prepared and reveal a peroxidase-like activity. Kinetic studies revealed a pseudo-enzymatic activity that is much higher than that of other magnetic nanomaterial-based enzyme mimetics. This finding was exploited to design a photometric enzymatic glucose assay based on the formation of H2O2 during enzymatic oxidation of glucose by glucose oxidase, and the formation of a blue product from an enzyme substrate that is catalytically oxidized by H2O2 in the presence of Fe3S4-MNPs. Glucose can be detected in the 2 to 100 μM concentration range, and the low detection limit is 0.16 μM. The method was applied to quantify glucose in human serum. In our perception, this enzyme mimetic has a large potential in that it may be used in other oxidase based assays, but also in ELISAs.
108 citations
TL;DR: In this paper, a hybrid material consisting of molybdenum sulfide flowers placed on graphene nanosheets and multiwalled carbon nanotubes (GNS-CNTs/MoS2) was deposited on a glassy carbon electrode (GCE) which was well suited for sensitive and selective determination of dopamine.
Abstract: We describe a hybrid material that consists of molybdenum sulfide flowers placed on graphene nanosheets and multiwalled carbon nanotubes (GNS-CNTs/MoS2) It was deposited on a glassy carbon electrode (GCE) which then is well suited for sensitive and selective determination of dopamine The GNS-CNTs/MoS2 nanocomposite was prepared by a hydrothermal method and characterized by scanning electron and transmission emission microscopies, energy-dispersive X-ray spectroscopy, cyclic voltammetry, differential pulse voltammetry and electrochemical impedance spectroscopy Electrochemical studies show the composite to possess excellent electrochemical properties such as a large electrochemically active surface, high capacitance current, a wide potential window, high conductivity and large porosity The electrode displays excellent electrocatalytic ability to oxidize dopamine The modified GCE, best operated at a working potential as low as 015 V (vs Ag/AgCl), responds linearly to dopamine in the 100 nM to 100 μM concentration range The detection limit is 50 nM, and the sensitivity is 1081 (± 026) μA⋅μM−1⋅cm−2 The sensor has good selectivity, appreciable stability, repeatability and reproducibility It was applied to the determination of dopamine in (spiked) biological and pharmaceutical samples
106 citations
TL;DR: In this article, carbon dots were prepared from citric acid and urea, and their fluorescence was found to be quenched by hypochlorite and peroxynitrite.
Abstract: Carbon dots (CDs) were prepared from citric acid and urea, and their fluorescence was found to be quenched by hypochlorite and peroxynitrite. Microwave based synthesis gives CDs with excitation/emission wavelength-dependent quantum yields (8 % at 400/520 nm; 10 % at 360/451 nm; 12 % at 350/420 nm). Quenching of fluorescence depends on pH values, and response is most selective and sensitive to hypochlorite at pH 4, and to peroxynitrite at pH 9. The lower detection limits are 0.5 and 1.5 μM, respectively. The method was successfully applied to quantify hypochlorite and peroxynitrite in standard solutions and in spiked dilute serum samples.
106 citations
TL;DR: In this paper, the synthesis of a hybrid nanocomposite consisting of MoS2 and reduced graphene oxide (MoS2/rGO) by a one-pot hydrothermal process, and the use of the material in an amperometric sensor was described.
Abstract: We describe the synthesis of a hybrid nanocomposite consisting of MoS2 and reduced graphene oxide (MoS2/rGO) by a one-pot hydrothermal process, and the use of the material in an amperometric sensor. Scanning electron microscopy and nitrogen adsorption-desorption tests revealed that the nanocomposite possesses a porous and flower-like structure and a large specific surface. Cyclic voltammetry and differential pulse voltammetry demonstrated the nanocomposite to perform excellently in the electrochemical oxidation of ascorbic acid (AA), dopamine (DA), and uric acid (UA), respectively. The oxidation potentials are well separated (oxidation peaks at −64, 168 and 320 mV vs. Ag/AgCl) for AA, DA, and UA, and the respective detection sensitivities are strongly enhanced (0.12, 4.11 and 1.59 μA μM−1 cm−2). The sensor was applied to the detection of the three species in spiked human serum samples where it gave recoveries ranging from 98.9 to 104.1 % (for n = 3).
TL;DR: In this paper, the synthesis of fluorescent carbon dots doped with nitrogen and sulfur (N,S-CDs) via a hydrothermal process in pure water and starting from a mixture of alfalfa and garlic was reported.
Abstract: We report on the synthesis of fluorescent carbon dots doped with nitrogen and sulfur (N,S-CDs) via a hydrothermal process in pure water and starting from a mixture of alfalfa and garlic. Compared to N-doped CDs, the N,S-CDs exhibit a high fluorescence quantum yield (10 %) and a more longwave emission maximum (at 481 nm). The results also pave the way to tune the luminescence of CDs. The fluorescence of the N,S-CDs is quenched by Cu(II) ions but is recovered by addition of any of the biothiols cystein, glutathione or homocysteine. This turn-on effect was exploited to design a method for the quantification of these thiols in concentrations as low as 86 nM. The method was successfully applied to the determination of Cys in (spiked) human serum samples.
TL;DR: This review gives comprehensive and critical insights into the development of materials and techniques for lab-on-paper chips, focusing on materials and methods for fabrication, modification and detection.
Abstract: Paper-based chips (PB-chips; also referred to as lab-on-paper chips) are using patterned paper as a substrate in a lab-on-a-chip platform. They represent an outstanding technique for fabrication of analytical devices for multiplex analyte assays. Typical features include low-cost, portability, disposability and small sample consumption. This review (with 211 refs.) gives a comprehensive and critical insight into current trends in terms of materials and techniques for use in fabrication, modification and detection. Following an introduction into the principles of PB-chips, we discuss features of using paper in lab-on-a-chip devices and the proper choice of paper. We then discuss the versatile methods known for fabrication of PB-chips (ranging from photolithography, plasma treatment, inkjet etching, plotting, to printing including flexographic printing). The modification of PB-chips with micro- and nano-materials possessing superior optical or electronic properties is then reviewed, and the final section covers detection techniques (such as colorimetry, electrochemistry, electrochemiluminescence and chemiluminescence) along with specific (bio)analytical examples. A conclusion and outlook section discusses the challenges and future prospectives in this field.
TL;DR: In this paper, an eco-friendly molecularly imprinted material based on carbon dots (C-dots) via a facile and efficient sol-gel polymerization for selective fluorescence detection of 4-nitrophenol (4-NP) was presented.
Abstract: We on report an eco-friendly molecularly imprinted material based on carbon dots (C-dots) via a facile and efficient sol–gel polymerization for selective fluorescence detection of 4-nitrophenol (4-NP). The amino-modified C-dots were firstly synthesized by a hydrothermal process using citric acid as the carbon source and poly(ethyleneimine) as the surface modifier, and then after a sol–gel molecular imprinting process, the molecularly imprinted fluorescence material was obtained. The material (MIP-C-dots) showed strong fluorescence from C-dots and high selectivity due to the presence of a molecular imprint. After the detection conditions were optimized, the relative fluorescence intensity (F0/F) of MIP-C-dots presented a good linearity with 4-NP concentrations in the linear range of 0.2 − 50 μmol L-1 with a detection limit (3σ/k) of 0.06 μmol L-1. In addition, the correlation coefficient was 0.9978 and the imprinting factor was 2.76. The method was applicable to the determination of trace 4-NP in Yangtze River water samples and good recoveries from 92.6–107.3 % were obtained. The present study provides a general strategy to fabricate materials based on C-dots with good fluorescence property for selective fluorescence detection of organic pollutants.
TL;DR: In this article, nitrogen and phosphorus co-doped carbon dots (N,P-C-dots) were prepared by microwave assisted thermolysis of N-phosphonomethyl aminodiacetic acid and ethylenediamine.
Abstract: Nitrogen and phosphorus co-doped carbon dots (N,P-C-dots) were prepared by microwave-assisted thermolysis of N-phosphonomethyl aminodiacetic acid and ethylenediamine. N,P-C-dots exhibit bright blue fluorescence with an emission maximum at 418 nm. Experimental results show that they have uniform dispersion with the average size of 3.3 nm, a fluorescence decay time of 7.8 ns, a quantum yield of 17.5 %, low toxicity, and good stability. All these make them an excellent choice as a fluorescent nanomaterial for use in cellular imaging.
TL;DR: In this article, a chemical exfoliation method for the preparation of MoS2 nanosheets was described and incorporated into poly(3,4-ethylenedioxythiophene) (PEDOT) by electrodeposition on a glassy carbon electrode (GCE) to form a nanocomposite.
Abstract: 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.
TL;DR: In this article, a conjugate composed of silver nanoparticles and graphene oxide (Ag@GO) via chemical reduction of silver precursors in the presence of graphene oxide while sonicating the solution was described.
Abstract: The article describes a facile method for the preparation of a conjugate composed of silver nanoparticles and graphene oxide (Ag@GO) via chemical reduction of silver precursors in the presence of graphene oxide (GO) while sonicating the solution. The Ag@GO was characterized by X-ray photoelectron spectroscopy, X-ray powder diffraction, and energy-dispersive X-ray spectroscopy. The nanocomposite undergoes a color change from yellow to colorless in presence of Hg(II), and this effect is based on the disappearance of the localized surface plasmon resonance absorption of the AgNPs due to the formation of silver-mercury amalgam. The presence of GO, on the other hand, prevents the agglomeration of the AgNPs and enhances the stability of the nanocomposite material in solution. Hence, the probe represents a viable optical probe for the determination of mercury(II) ions in that it can be used to visually detect Hg(II) concentrations as low as 100 μM. The instrumental LOD is 338 nM.
TL;DR: A microfluidic and surface-enhanced Raman scattering substrate integrated biosensing platform involving silver nanoparticles is demonstrated for rapid and on-site detection and discrimination of polymicrobial food-borne pathogenic bacteria.
Abstract: The authors have developed a microfluidic platform for improved detection of pathogenic bacteria by using silver nanoparticles and new platforms for chemometric data analysis, viz. a combination of principle component analysis and linear discriminant analysis. The method can distinguish eight key foodborne pathogens (E. coli, S. typhimirium, S. enteritis, Pseudomonas aeruginosa, L. monocytogenes, L. innocua, MRSA 35 and MRSA 86) and, hence, holds good promise for use in the food industry.
TL;DR: In this paper, a colorimetric method for the determination of ascorbic acid was proposed based on the finding that nanosheets of reduced graphene oxide that were functionalized with poly(styrene sulfonate) (PSS-rGO) possess peroxidase-like activity that catalyzes the oxidization of the substrate 3,3',5,5'-tetramethylbenzidine (TMB) by H2O2 to form a blue product (oxidized TMB; oxTMB).
Abstract: The authors describe a highly sensitive colorimetric method for the determination of ascorbic acid. It is based on the finding that nanosheets of reduced graphene oxide that were functionalized with poly(styrene sulfonate) (PSS-rGO) possess peroxidase-like activity that catalyzes the oxidization of the substrate 3,3’,5,5’-tetramethylbenzidine (TMB) by H2O2 to form a blue product (oxidized TMB; oxTMB) that can be quantified by photometry or visually. If ascorbic acid is present, a fraction of H2O2 will be consumed and hence less oxTMB (with an absorption peak at 652 nm) will be formed. Ascorbic acid can be quantified by photometry in the 0.8 to 60 μM concentration range with a 0.15 μM detection limit. The method was successfully applied to the determination of ascorbic acid in vitamin C tablets and orange juice.
TL;DR: In this paper, a Salmonella biosensor was obtained by electrochemical immobilization of a nanocomposite consisting of reduced graphene oxide (rGO) and carboxy-modified multi-walled carbon nanotubes (MWCNTs) directly on the surface of a glassy carbon electrode.
Abstract: We describe a Salmonella biosensor that was obtained by electrochemical immobilization of a nanocomposite consisting of reduced graphene oxide (rGO) and carboxy-modified multi-walled carbon nanotubes (MWCNTs) directly on the surface of a glassy carbon electrode (GCE). An amino-modified aptamer specific for Salmonella was covalently bound to the rGO-MWCNT composite via amide bonds. The morphology of the rGO-MWCNT nanocomposite was characterized by transmission electron microscopy and scanning electron microscopy. Cyclic voltammetry and electrochemical impedance spectroscopy were used to monitor all steps during assembly. When exposed to samples containing Salmonella, the anti-Salmonella aptamer on the electrode captures its target. Hence, electron transfer is blocked, and this results in a large increase in impedance. Salmonella can be quantified by this aptasensor, typically operated at a working voltage of 0.2 V (vs. Ag/AgCl), in the range from 75 to 7.5 × 105 cfu⋅mL−1 and detection limit of 25 cfu⋅mL−1 (at an S/N of 3). The method is perceived to have a wide scope in that other bacteria may be detected by analogy to this approach and with very low limits of detection by applying respective analyte-specific aptamers.
TL;DR: In this paper, a carbon paste electrode (CPE) was modified with Pt-Co nanoparticles and 2-(3,4-dihydroxyphenethyl)isoindoline-1,3-dione (3, 4-DHPID) and then used for determination of N-acetylcysteine (N-AC) in the presence of paracetamol (PC) and folic acid (FA).
Abstract: A carbon paste electrode (CPE) was modified with Pt-Co nanoparticles and 2-(3,4-dihydroxyphenethyl)isoindoline-1,3-dione (3,4-DHPID) and then used for determination of N-acetylcysteine (N-AC) in the presence of paracetamol (PC) and folic acid (FA). The Pt-Co nanoparticles were synthesized by the polyol method and characterized by X-ray diffraction, energy dispersive X-ray analysis and transmission electron microscopy. The modified CPE displays good electrocatalytic activity towards the electrooxidation of N-AC in solution of pH 7.0. It was applied to the determination of N-AC in the presence of PC and FA (with well separated signals peaking at 0.2, 0.55 and 0.86 V vs. Ag/AgCl) by using square wave voltammetry. The peak currents are linearly dependent on the concentrations of N-AC, PC and FA in the respective ranges from 0.07 to 500, 1.0 to 850, and 2.0 to 550 μmol·L−1, with detection limits of 0.009, 0.6 and 0.8 μmol·L−1. The modified CPE was applied to the determination of N-AC, PC and FA in (spiked) pharmaceutical and biological samples.
TL;DR: In this article, a method for synthesis of water-soluble photoluminescent carbon dots (CDs) by one-pot hydrothermal treatment of adipic acid and triammonium citrate was described.
Abstract: We describe a new method for synthesis of water-soluble photoluminescent carbon dots (CDs) by one-pot hydrothermal treatment of adipic acid and triammonium citrate. The CDs have excitation/emission maxima of 340/440 nm, a quantum yield of 0.13, and are shown to be a viable fluorescent probe for the determination of Hg(II). It shows a linear relationship in the 4 to 18 μM mercury ion concentration range. The detection limit is as low as 2.47 μM. The CDs were applied to intracellular sensing and imaging of Hg(II) where they showed low toxicity.
TL;DR: In this article, the authors described the preparation of a magnetic metal organic framework of type MOF-199 containing magnetite (Fe3O4) nanoparticles carrying covalently immobilized 4-(thiazolylazo) resorcinol.
Abstract: The author describes the preparation of a magnetic metal organic framework of type MOF-199 containing magnetite (Fe3O4) nanoparticles carrying covalently immobilized 4-(thiazolylazo) resorcinol (Fe3O4@TAR). This material is shown to represent a viable sorbent for separation and preconcentration of Cd(II), Pb(II), and Ni(II) ions. Box-Behnken design was applied to optimize the parameters affecting preconcentration. Following elution with 0.6 mol L−1 EDTA, the ions were quantified by FAAS. The capacity of the sorbent ranged between 185 and 210 mg g−1. The limits of detection are 0.15, 0.40, and 0.8 ng mL−1 for Cd(II), Ni(II), and Pb(II) ions, respectively. The relative standard deviations are <8.5 %. The method was successfully applied to the rapid extraction of trace amounts of these ions from sea food and agri food.
TL;DR: A novel solid phase sorbent synthesized by coupling graphene oxide (GO) to ethylenediamine (EDA) is capable of adsorbing the ions of iron, cobalt, nickel, copper, zinc and lead and was successfully applied to the determination of trace amounts of these metal ions in water samples.
Abstract: We describe a novel solid phase sorbent that was synthesized by coupling graphene oxide (GO) to ethylenediamine (EDA). This nanomaterial (referred to as GO-EDA) is capable of adsorbing the ions of iron, cobalt, nickel, copper, zinc and lead. The ethylenediamine-modified graphene oxide was characterized by X-ray photoelectron spectroscopy, scanning electron microscopy and Fourier transform infrared spectroscopy. The analytical procedure relies on (a) sorption of metal ions on GO-EDA dispersed in aqueous samples; (b) filtering, and (c) direct submission of the filter paper to energy-dispersive X-ray fluorescence spectrometry. This kind of dispersive micro-solid phase extraction was optimized with respect to pH values, concentration of GO-EDA, contact time, and the effects of interfering ions and humic acid on recovery of determined elements. Under optimized conditions, the recoveries of spiked samples range from 90 to 98 %. The detection limits are 0.07, 0.10, 0.07, 0.08, 0.06 and 0.10 ng mL−1 for Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Pb(II), respectively. The method has a relative standard deviation of <6 %, and its accuracy was verified by analysis of two standard reference materials [LGC6016 (estuarine water) and BCR-610 (groundwater)]. It was successfully applied to the determination of trace amounts of these metal ions in water samples.
TL;DR: In this paper, a nanocomposite consisting of bismuth nanoparticles and amorphous carbon was synthesized by a combined one-step sol-gel and pyrolysis process and milled down to a specific particle size distribution as required for the preparation of an ink formulation to be used in screen printing.
Abstract: This work reports on the simplified fabrication and on the characterization of bismuth-based screen-printed electrodes (SPEs) for use in heavy metal detection. A nanocomposite consisting of bismuth nanoparticles and amorphous carbon was synthesized by a combined one-step sol-gel and pyrolysis process and milled down to a specific particle size distribution as required for the preparation of an ink formulation to be used in screen printing. The resulting electrochemical devices were applied to the detection of Pb(II) and Cd(II) ions in water samples. The porous structure of carbon and the high surface area of the bismuth nanoparticles allow for the detection of Pb(II) and Cd(II) at concentration levels below 4 ppb. The application of the SPEs was demonstrated by quantifying these ions in tap drinking water and wastewater collected from an influent of an urban wastewater treatment plant.
TL;DR: In this article, a composite consisting of gold nanoparticles and reduced graphene oxide (AuNPs@rGO) was electrochemically prepared in-situ on a screen printed electrode (SPE) which then was used as an immunosensor for the cardiac biomarker myoglobin.
Abstract: A composite consisting of gold nanoparticles and reduced graphene oxide (AuNPs@rGO) was electrochemically prepared in-situ on a screen printed electrode (SPE) which then was used as an immunosensor for the cardiac biomarker myoglobin. The nanocomposite was characterized by transmission electron microscopy (TEM, scanning electron microscopy (SEM), atomic force microscopy, FTIR and electrochemical impedance spectroscopy. For FTIR, TEM and SEM, the deposition was done on indium tin oxide coated glass plates. The immunosensor was obtained by immobilization of in-house generated antibody against cardiac myoglobin on the electrode surface. The immunosensing response was monitored using differential pulse voltammetry, which showed a reduction peak at ~ −0.5 V (vs. Ag/AgCl). The reduction peak arises from the reduction of iron moiety present in the heme group of myoglobin. The immunosensor exhibited dynamic linearity range from 1 ng.mL−1 to 1400 ng.mL−1 with the detection limit of ~0.67 ng.mL−1 for cardiac myoglobin. The obtained result was almost eight times better (in terms of detection limit) than that obtained with ELISA tests (with detection limit of ~4 ng.mL−1) using the same antibodies. The immunosensor was applied to analyze spiked serum samples also.
TL;DR: In this article, a fast and sensitive method for sequential speciation and separation of chromium (VI) and chromium(III) using dispersive magnetic solid phase extraction prior to determination by FAAS is described.
Abstract: We describe a fast and sensitive method for sequential speciation and separation of chromium(VI) and chromium(III) using dispersive magnetic solid phase extraction prior to determination by FAAS. The sorbent (mf-GO) was obtained by functionalizing a graphene oxide decorated with magnetite which was modified with triethylenetetramine. The sorbent was characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray analysis, FTIR and elemental analysis. The use of mf-GO results in fast removal of chromium(VI) (10 min) and of Cr(III) (30 min). The sorption capacity is 16.4 mg∙g‾1 for Cr(VI) and 9.6 mg∙g‾1 for Cr(III). Effective chromium speciation is demonstrated by simply tuning the pH value of the solution. Following batch sorption, the particles can be magnetically separated. The method was validated under optimized conditions. Linear dynamic range of calibration plot extends from 5 to 100 μg L−1, and their detection and quantification limits are 1.4 and 4.5 μg L−1 for Cr(VI) and 1.6 and 5.2 μg L−1 for Cr(III), respectively. Accuracy was established by analyzing the SRM JSS (513–4) chromium steel Standard Reference Material. Recoveries of (spiked) analyte range from 96 to 102 %. The method was applied to speciate and quantifies chromium in tannery wastewater, electroplating wastewater, and (spiked) river water.
TL;DR: A review of the recent advances in the preparation and application of magnetic micro/nanoparticles can be found in this article, where the authors discuss the existing challenges and possible trends in the field.
Abstract: This review (with 144 refs.) focuses on the recent advances in the preparation and application of magnetic micro/nanoparticles. Specifically, it covers (a) methods for preparation (such as by coprecipitation, pyrolysis, hydrothermal, solvothermal, sol-gel, micro-emulsion, sonochemical, medium dispersing or emulsion polymerization methods), and (b) applications such as magnetic resonance imaging, magnetic separation of biomolecules (nucleic acids; proteins; cells), separation of metal ions and organic analytes, immobilization of enzymes, biological detection, magnetic catalysis and water treatment. Finally, the existing challenges and possible trends in the field are addressed.
TL;DR: In this article, a single-step wet-chemical approach using metformin as a growth-directing agent was used for the formation of bimetallic gold-copper nanochain networks (AuCu NCNs).
Abstract: Bimetallic gold-copper nanochain networks (AuCu NCNs) were prepared by a single-step wet-chemical approach using metformin as a growth-directing agent. The formation mechanism was investigated in detail, and the AuCu NCNs were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The nanocrystals were deposited on glassy carbon electrode and this resulted in a highly sensitive sensor for nitrite. Features include a low working potential (best at 0.684 V vs. SCE), fair sensitivity (17.55 μA mM−1), a wide linear range (0.01 to 4.0 mM), a low detection limit (0.2 μM, S/N = 3), and superior selectivity as compared to other sensors.
TL;DR: In this article, dual-emission carbon nanodots containing blue emitters and yellow emitters were used for direct and indirect determination of tetracyclines (TCs).
Abstract: The authors describe dual-emission carbon nanodots containing blue emitters (BE; peak emission at 385nm under 315 nm excitation) and yellow emitters (YE; peak emission at 530 nm under 365nm excitation), and how they can be applied to direct and indirect determination of tetracyclines (TCs). The direct detection scheme is based on the finding that tetracycline (TET), oxytetracycline, chlortetracycline and doxycycline quench the two emissions of the carbon dots. While direct determination is rapid and convenient, it cannot differentiate between TCs. The indirect detection scheme, in contrast, is based on the finding that Al (III) ions enhance the fluorescence of the YE in the carbon dots, and that they cause a blue shift in emission. It is, however, known that TET forms a strong complex with Al (III), and this can inhibit the interaction between Al (III) and the YE, so that the fluorescence of YE is not enhanced and blue-shifted by Al (III) in the presence of TET. This finding is exploited in a fluorescence turn-on/off assay for TET that can distinguish TET from other TCs. The linear range of indirect determination for TET extends from 1 nM to 30 μM, and the limit of detection is 0.52 nM. The indirect method was successfully applied to the determination of TET in spiked milk, fish and pork, and recoveries ranged from 91.7 to 102 %.