A nanosystem composed of upconversion nanoparticles and N, N-diethyl-p-phenylenediamine for fluorimetric determination of ferric ion Microchim. Acta (IF 5.705) Pub Date : 2018-07-17 Min Chen, Felix Y. H. Kutsanedzie, Wu Cheng, Akwasi Akomeah Agyekum, Huanhuan Li, Quansheng Chen
A system composed of upconversion nanoparticles (UCNPs) and N,N-diethyl-p-phenylenediamine (EPA) is shown to be a useful probe for highly sensitive and selective fluorometric determination of ferric ion. The fluorescence of the UCNPs (under the 980 nm excitation) has peaks at 546, 657, 758 and 812 nm. EPA is readily oxidized by Fe(III) to generate a dye with a peak at 552 nm. This causes an inner filter effect on the fluorescence peaks at 546 nm, whereas the emissions at 657, 758 and 812 nm remained unchanged. Therefore, the iron concentration can be quantified by measurement of the ratio of fluorescence at 546 and 758. Under optimal condition, the ratio drops linearly in the 0.25 to 50 μM. Fe(III) concentration ranges, with a detection limit of 0.25 μM. The method is highly selective and was applied to the analysis of spiked samples (wastewater) where it gave recoveries of between 100.9 and 107.3%; and RSD values between 0.8 and 1.4%. Results are approximately the same as those obtained by AAS.
Aptamer based voltammetric biosensor for Mycobacterium tuberculosis antigen ESAT-6 using a nanohybrid material composed of reduced graphene oxide and a metal-organic framework Microchim. Acta (IF 5.705) Pub Date : 2018-07-17 Linlin Li, Yonghua Yuan, Yongjie Chen, Pu Zhang, Yan Bai, Lijuan Bai
The 6-kDa early secretory antigenic target referred to as ESAT-6 is a virulence factor secreted by Mycobacterium tuberculosis (MTB). This work describes a voltammetric aptasensor for ultrasensitive detection of ESAT-6. Reduced graphene oxide doped with metal-organic framework (MOF-rGO) was deposited on a glassy carbon electrode (GCE). This increases the immobilization of electroactive Toluidine Blue (TB) and facilitates the electron transfer from TB to the modified GCE. Platinum/gold core/shell (Pt@Au) nanoparticles were used to assemble thiolated ESAT-6 binding aptamer (EBA) on a modified electrode and to further amplify the response to TB. The modified GCE, typically operated at −0.36 V (vs. SCE), has a linear response in 1.0 × 10−4 to 2.0 × 102 ng⋅mL-1 ESAT-6 concentration range, and the limit of detection (LOD) for ESAT-6 is as low as 3.3 × 10−5 ng⋅mL-1. It exhibits satisfactory specificity and reproducibility when analyzing spiked human serum.
Selective capture and sensitive fluorometric determination of Pseudomonas aeruginosa by using aptamer modified magnetic nanoparticles Microchim. Acta (IF 5.705) Pub Date : 2018-07-16 Zitao Zhong, Xiaomei Gao, Ran Gao, Li Jia
A fluorometric assay is described for the detection of the food pathogen Pseudomonas aeruginosa (P. aeruginosa). It is based on the hybridization of aptamer and fluorescein-labeled complementary DNA (FAM-cDNA) in combination with magnetic separation. In the absence of P. aeruginosa, FAM-cDNA is assembled on the surface of aptamer modified magnetic particles (MNPs) via hybridization between aptamer and cDNA. Upon addition of P. aeruginosa, FAM-cDNA is replaced by the bacteria and released from the MNPs since the aptamer preferentially binds to bacteria. After magnetic separation, the amount of bacteria can be quantified by determination of the fluorescence intensity (λexc/em = 494/525 nm) of the supernatant containing the released FAM-cDNA. This kind of assay allows for both selective enrichment and sensitive fluorometric determination of bacteria in a single step. The assay has a response to the logarithm of P. aeruginosa concentration that is linear in the range between 10 and 108 cfu·mL−1, with a detection limit as low as 1 cfu·mL−1. The detection process can be finished within <1.5 h. The feasibility of the assay was verified by detecting P. aeruginosa in spiked food samples.
A chemiluminescence-based catalase assay using H 2 O 2 -sensitive CdTe quantum dots Microchim. Acta (IF 5.705) Pub Date : 2018-07-16 Fahimeh Ghavamipour, Reza H. Sajedi, Khosro Khajeh
A method is described for the chemiluminescence based determination of the activity of catalase (CAT) using H2O2-sensitive CdTe quantum dots (QDs). It is based on the finding that the chemiluminescence (CL) of the CdTe/H2O2 system is reduced due to the consumption of H2O2 by the catalytic action of CAT. The Michaelis constant is calculated to be 519 ± 27 mM, showing the potential of the method to accurately measure the Km compared to the standard method. The method does not require QDs to be conjugated to biological/organic molecules and therefore is considered to be a rapid and convenient method for determination of CAT in real samples. At an incubation time of 2 s, the LOD was calculated to be 4.5 unit/mL, with a linear range from 6 to 400 unit/mL. The assay is sensitive, simple, and suitable for practical applications.
RNase H meets molecular beacons: an ultrasensitive fluorometric assay for nucleic acids Microchim. Acta (IF 5.705) Pub Date : 2018-07-14 Shao-Xiang Wang, Kai-Sheng Liu, Yi-Fei Lou, Shao-Qi Wang, Yong-Bo Peng, Jian-Ping Chen, Jia-Hao Huang, Shou-Xia Xie, Liang Cui, Xiao Wang
An innovative signal amplification strategy assisted by RNase H is described here for the detection of DNA targets in a universal fashion. A tailor-made RNA molecular beacon (RMB) conjugated with a fluorescence resonance energy transfer (FRET) pair (fluorophore and quencher) was designed, characterized, and combined with the employment of RNase H. Its performance is compared to that of other nucleases including Exonuclease III and T7 exonuclease. Fluorometry, performed best at excitation/emission wavelengths of 490/520 nm, gives an amazingly low detection limit of 23 fM for target DNA. The method was verified by the determination of human hemochromatosis (HFE) gene. It is perceived that the method represents a versatile tool for the detection of a wide range of targets.
A paper-based optical probe for chromium by using gold nanoparticles modified with 2,2′-thiodiacetic acid and smartphone camera readout Microchim. Acta (IF 5.705) Pub Date : 2018-07-13 Shadab Faham, Gholamreza Khayatian, Hamed Golmohammadi, Raouf Ghavami
A paper based analytical device is presented for the determination of Cr(III) and Cr(VI) using gold nanoparticles (AuNPs) modified with 2,2′-thiodiacetic acid. The modified AuNPs were characterized using UV-Vis spectrophotometry, Fourier transform infrared, dynamic light scattering, zeta potential, energy dispersive spectroscopy and transmission electron microscopy. Cr(III) ions induce the aggregation of the modified AuNPs, and the color of the nanoprobe changes from red to blue. This can be detected visually, or by colorimetry, or with a camera. No interference is observed in the presence of 19 other cations and anions. Cr(VI) (chromate) can be determined by after reduction to Cr(III) by using ascorbic acid and then quantified total Cr(III). The concentration of Cr(VI) is obtained by subtracting the concentration of Cr(III) from that of total chromium. Under optimal conditions, the ratio of the absorbances measured at 670 (blue) and 522 (red) increases linearly in the 1.0 nM to 22.1 μM chromium concentration range, with 0.66 nM (0.034 ppb) limit of detection (LOD) in solution. In case of the paper device, the linear range extends from 1.0 nM to 0.1 mM, and the LOD is 0.64 nM (0.033 ppb). The method was applied to the determination of chromium in spiked water, urine and dilutes human plasma, and results were confirmed by GF-AAS analysis. This method is highly selective, fast and portable, requires minimum volume of reagents and samples and no washing steps.
Computer-aided design of magnetic dummy molecularly imprinted polymers for solid-phase extraction of ten phthalates from food prior to their determination by GC-MS/MS Microchim. Acta (IF 5.705) Pub Date : 2018-07-12 Chunxia Lu, Zonggui Tang, XiaoXu Gao, Xiaomei Ma, Changbin Liu
Magnetic dummy molecularly imprinted polymers (MDMIPs) were prepared by combining the surface imprinting technique with computer simulation for selective recognition of phthalate esters (PAEs). A computational study based on the density functional theory was performed to evaluate the template–monomer geometry and interaction energy in the prepolymerization mixture. The MDMIPs were characterized by transmission electron microscopy, scanning electron microscopy, vibrating sample magnetometry, X-ray diffraction, and Fourier transform infrared spectroscopy. They exhibited (a) high saturation magnetization of 53.14 emu g−1 (leading to fast separation), and (b) large adsorption capacity, fast binding kinetics, and high selectivity for PAEs. Subsequently, a molecularly imprinted solid-phase extraction procedure followed by GC-MS was established for selective extraction and determination of 10 PAEs in food samples. Under the optimal experimental conditions, the response (peak area) was linear in the 0.5–100 ng mL−1 concentration range. The limits of detection ranged from 0.15 to 1.64 ng g−1. The method was applied to the determination of PAEs in spiked real samples. The recoveries for 10 PAEs from various foods were in the range of 73.7%–98.1%, with relative standard deviations of 1.7%–10.2%.
Fluorometric determination of microRNA-155 in cancer cells based on carbon dots and MnO 2 nanosheets as a donor-acceptor pair Microchim. Acta (IF 5.705) Pub Date : 2018-07-11 Somayeh Mohammadi, Abdollah Salimi
A fluorometric method is presented for sensitive deternination of microRNA. It is making use of carbon dots (C-dots) loaded with a DNA probe as fluorophore and MnO2 nanosheets as the quenching agent. The blue-green fluorescence of the DNA-loaded C-dots is quenched by the MnO2 nanosheets, but restored on binding target microRNA-155. The maximum excitation wavelength and the maximum emission wavelength of C-dots are at 360 nm and 455 nm, respectively. Fluorescence correlates linearly with the log of the microRNA-155 concentration in two ranges, viz. from 0.15 to 1.65 aM and from 1.65 to 20 aM. The detection limit is as low as 0.1 aM. The assay can discriminate between fully complementary and single-base mismatch microRNA. The assay displayed high specificity when used to detect MCF-7 breast cancer cells which can be detected in concentrations from 1000 to 45,000 cells·mL−1, with a 600 cells·mL−1 detection limit. The method was applied to the analysis of serum samples spiked with microRNA, and satisfactory results were acquired.
Hydrothermal and plasma nitrided electrospun carbon nanofibers for amperometric sensing of hydrogen peroxide Microchim. Acta (IF 5.705) Pub Date : 2018-07-10 Yuan-Ping Lyu, Yi-Shan Wu, Tzu-Pei Wang, Chien-Liang Lee, Meng-Yin Chung, Chieh-Tsung Lo
Nitrogen-doped carbon nanofibers (CNFs) were prepared by an electrospinning method, this followed by a hydrothermal reaction or nitrogen plasma treatment to obtain electrode for non-enzymatic amperometric sensing of H2O2. The hydrothermally treated electrode performs better. Its electrochemical surface is 3.7 × 10−3 mA cm−2, which is larger than that of a nitrogen plasma treated electrode (8.9 × 10−4) or a non-doped CNF (2.45 × 10−4 mA cm−2). The hydrothermally treated CNF with rough surface and a complex profile with doped N has a higher sensitivity (357 μA∙mM−1∙cm−2), a lower detection limit (0.62 μM), and a wider linear range (0.01–0.71 mM) than N-CNFP at a working potential of −0.4 V (vs. Ag/AgCl). The electrode gave high recoveries when applied to the analysis of milk samples spiked with H2O2.
Simultaneous voltammetric determination of acetaminophen and dopamine using a glassy carbon electrode modified with copper porphyrin-exfoliated graphene Microchim. Acta (IF 5.705) Pub Date : 2018-07-09 Xinjian Song, Ju Fu, Juan Wang, Chunya Li, Zhihong Liu
Graphene nanosheets (GSs) were prepared via liquid-phase non-covalent exfoliation of graphite powder in N,N-dimethylformamide under the assistance of copper(II) meso-tetra(4-carboxyphenyl)porphyrin tetrasodium salt Na4(CuTCPP). A glassy carbon electrode (GCE) was modified with a film of such GSs which, due to the good electrical conductivity of graphene and the electrocatalytic properties of Na4(CuTCPP), is capable of simultaneous determination of acetaminophen (AC) and dopamine (DA). The peak currents, best measured at voltage of 0.2 V (for DA) and 0.4 V (for AC; both vs. SCE), increase linearly in the 0.0024–3.6 μM and 0.004–7.6 μM concentration ranges, respectively. The detection limits are 0.8 nM for DA and 0.7 nM for AC. The sensor was successfully applied to the simultaneous determination of AC and DA in pharmaceutical preparations and spiked human serum. The results were in good agreement with those obtained for the same samples by HPLC.
Synthesis of tellurium nanosheet for use in matrix assisted laser desorption/ionization time-of-flight mass spectrometry of small molecules Microchim. Acta (IF 5.705) Pub Date : 2018-07-09 Ya-Shun Chen, Jun Ding, Xiao-Mei He, Jing Xu, Yu-Qi Feng
Two-dimensional tellurium nanosheets were prepared by a hydrothermal method and characterized by scanning electron microscopy, powder X-ray diffractometry, and UV-vis spectroscopy. The nanosheets were explored as a novel matrix for desorption/ionization of small molecules including nucleobases, fatty acids and amino acids by matrix assisted laser desorption/ionization time-of-flight mass spectrometry. The results show that the tellurium nanosheets have good UV light absorption, cause low matrix ion interference in the low-molecule-mass region, and have high desorption/ionization efficiency in the negative ion mode. Hence, they are a viable matrix for negative ion desorption/ionization in MALDI-TOF MS of small molecules. In order to investigate the desorption/ionization mechanisms, benzylpyridinium salt and bisphenol A were adopted as probes. The results show that both of the electronic transitions mechanism and laser-induced thermal mechanism play important roles in desorption/ionization process.
A magnetic adsorbent grafted with pendant naphthyl polymer brush for enrichment of the nonsteroidal anti-inflammatory drugs indomethacin and diclofenac Microchim. Acta (IF 5.705) Pub Date : 2018-07-09 Ya’nan Deng, Jiwei Shen, Jiawei Liu, Yinmao Wei, Chaozhan Wang
Poly(2-naphthyl acrylate) was first grafted onto silica-coated magnetic nanoparticles by surface-initiated atom transfer radical polymerization to prepare a reversed-phase magnetic adsorbent. The resulting polymer brush displays enhanced extraction efficiency by offering active sites on the surfaces of adsorbent. It was applied to the preconcentration of the non-steroidal antiinflammatory drugs (NSAIDs) indomethacin (InDo) and diclofenac (DIC). These drugs interact with the sorbent through hydrophobic and π-interactions, and via electrostatic attraction. By coupling the magnetic solid-phase extraction with HPLC, a method for analysis of InDo and DIC in the environmental water samples was established. The limits of detection range from 0.62 to 0.64 ng·mL−1, and the relative standard deviations for intra-and inter-day analyses of spiked water samples are <11.9%, and relative recoveries are between 62.1 and 96.7%.
Electrochemical dopamine sensor using a nanoporous gold microelectrode: a proof-of-concept study for the detection of dopamine release by scanning electrochemical microscopy Microchim. Acta (IF 5.705) Pub Date : 2018-07-09 Henry Steven Catota Sáenz, Lucas Patricio Hernández-Saravia, Jéssica S. G. Selva, Anandhakumar Sukeri, Patricio Javier Espinoza-Montero, Mauro Bertotti
Nanoporous gold (NPG) structures were prepared on the surface of a gold microelectrode (Au-μE) by an anodization-reduction method. Cyclic voltammetry and field emission scanning electron microscopy were used to study the electrochemical properties and the morphology of the nanostructured film. Voltammetry showed an improved sensitivity for dopamine (DA) oxidation at this microelectrode when compared to a bare gold microelectrode, with a peak near 0.2 V (vs. Ag/AgCl) at a scan rate of 0.1 V s−1. This is due to the increased surface area and roughness. Square wave voltammetry shows a response that is linear in the 0.1–10 μmol L−1 DA concentration range, with a 30 nmol L-1 detection limit and a sensitivity of 1.18 mA (μmol L−1)−1 cm−2. The sensor is not interfered by ascorbic acid. The reproducibility, repeatability, long-term stability and real sample analysis (spiked urine) were assessed, and acceptable performance was achieved. The “proof-of-concept” detection of dopamine release was demonstrated by using scanning electrochemical microscopy (SECM) with the aim of future applications for single cell analysis.
Aptamer-based fluorometric lateral flow assay for creatine kinase MB Microchim. Acta (IF 5.705) Pub Date : 2018-07-07 Jing Zhang, Xuefei Lv, Wei Feng, Xiaoqiong Li, Kunjie Li, Yulin Deng
A group of aptamers possessing high specificity and affinity for creatine kinase MB (CKMB) was obtained by magnetic systematic evolution of ligands by exponential enrichment. Two aptamers (referred to as C.Apt.21 and C.Apt.30) were found to possess adequately low Kd values. They form a well suited pair for CKMB binding. By using fluorescent microspheres, an aptamer-based lateral flow assay was developed. It is portable, economical, and sensitive. The limit of detection for CKMB is as low as 0.63 ng·mL-1, and the assay works in the 0.005 - 2 μg·mL-1 CKMB concentration range. The method is specific for CKMB, and biomarkers for AMI (such as cardiac troponin I and myoglobin) and serum do not interfere. The strip is highly accurate as shown by analysis of spiked serum samples which gave recoveries ranging between 88 and 117%.
Speciation analysis of Tl(I) and Tl(III) after magnetic solid phase extraction using a magnetite nanoparticle composite modified with aminodibenzo-18-crown-6 functionalized MIL-101(Cr) Microchim. Acta (IF 5.705) Pub Date : 2018-07-07 Soheyla Rezabeyk, Mahboobeh Manoochehri
The authors describe a magnetic metal-organic framework nanocomposite consisting of aminodibenzo-18-crown-6 magnetite nanoparticles and MIL-101(Cr). It was employed to the speciation analysis of Tl(I) and Tl(III) ions. The sorbent is capable of selectively extracting Tl(I) while Tl(III) remains in solution. The total amount of thallium was then determined by reducing Tl(III) to Tl(I) by hydroxylamine hydrochloride and also extracting it. The extraction parameters were optimized by employing design of experiments methodology. Thallium was quantified by ET-AAS. Under optimized conditions, the detection limit is as low as 1.5 ng L−1, the quantification limit is 5.0 ng L−1, the linear range extends from 5 to 400 ng L−1, and the relative standard deviation is <12% (for n = 5 at levels of 5, 50 and 250 ng L−1). The recoveries of real samples analysis were in the range of 90–106%. The method was successfully applied to the analysis of a certified reference material (NIST SRM 1643d water sample) and to various real water samples.
A fluorometric clenbuterol immunoassay based on the use of organic/inorganic hybrid nanoflowers modified with gold nanoclusters and artificial antigen Microchim. Acta (IF 5.705) Pub Date : 2018-07-07 Tao Peng, Jianyi Wang, Sijun Zhao, Sanlei Xie, Kai Yao, Pimiao Zheng, Sihan Wang, Yuebin Ke, Haiyang Jiang
Organic/inorganic hybrid nanoflowers were synthesized from calcium phosphate and protein modified fluorescent gold nanoclusters and antigens. These nanoflowers are shown to be well suited labels for bioassay because they fulfill the functions of biological recognition and signal output. A fluorometric immunoassay was developed that was combined with immunomagnetic separation. In the detection system, the red fluorescence of the supernatant (measured at excitation/emission wavelengths of 360/640 nm) is found to be proportional to the clenbuterol (Clen) concentration after two immunomagnetic separations. The assay has a linear response in the 0.5 μg L−1 to 40 μg L−1 Clen concentration range, and 0.167 μg L−1 limit of detection. This makes it well suited for food safety monitoring. The average recoveries from spiked samples range from 92.7 to 109.1% (intra-assay) and 101.2 to 125.7% (inter-assay) with relative standard deviations of <11.6%. Spiked swine urine samples were analyzed by this method, and the results correlated well with data obtained by LC-MS/MS.
Tunable composites prepared from graphene oxide and zeolitic imidazolate framework-8 for improved selective isolation of hemoglobin Microchim. Acta (IF 5.705) Pub Date : 2018-07-05 Jiawei Liu, Yixun Liang, Qingmei Liang, Hailin Yan, Jiwei Shen, Chaozhan Wang, Quan Bai
The authors report on the preparation of composites made from graphene oxide (GO) and zeolitic imidazolate framework-8 (ZIF-GO), with various fractions of GO. GO acts as the template and as a modulator for the surface properties of the composites. It also improves the selective adsorption of specific proteins, i.e. hemoglobin (Hb) in this case. The adsorption capacity for Hb is as high as 436 mg g−1 when using a composite containing 20% of GO as sorbent, and 95% of specific activity is maintained for the Hb recovered. The sorbent is applied to selectively isolate Hb from human whole blood.
Sensitive determination of Hg(II) based on a hybridization chain recycling amplification reaction and surface-enhanced Raman scattering on gold nanoparticles Microchim. Acta (IF 5.705) Pub Date : 2018-07-05 Ruiyuan Zhang, Shaoping Lv, Yan Gong, Yunxia Li, Caifeng Ding
A method was developed for the determination of mercuric ion Hg(II). It is based on hybridization chain reaction (HCR) and surface-enhanced Raman scattering (SERS). Raman signal DNA and streptavidin were self-assembled on gold nanoparticles as a novel signal nanoprobe (AuNP-sDNA). A thymine-mercury(II)-thymine structure was immobilized on magnetic beads (MBs). The HCR makes use of two hairpin probes that are initiated by the trigger DNA to form a stable nicked dsDNA structure (MB-TS-hDNAs). A large number of the binding sites is provided to connect the signal nanoprobe. The stable sandwich structure (MB-TS-hDNA/AuNP-sDNA) was isolated by applying a magnetic field and used in the amplification step. In this way, Hg(II) can be determined sensitively after multiple signal amplification. The SERS signal, measured at 1499 cm−1, increases linearly in the 0.1 pM to 10 nM Hg(II) concentration range, and the limit of detection is 0.08 pM (at an S/N ratio of 3). The method was applied to the detection of Hg(II) in spiked environment water samples, with recoveries ranging from 96 to 119%.
A terbium-based metal-organic framework@gold nanoparticle system as a fluorometric probe for aptamer based determination of adenosine triphosphate Microchim. Acta (IF 5.705) Pub Date : 2018-07-05 Fei Qu, Chao Sun, Xiaoxia Lv, Jinmao You
This study reports on a method for fluorometric aptasensing of adenosine triphosphate (ATP). It is based on the interaction of dispersed (red) and agglomerated (blue) gold nanoparticles (AuNPs) with a water-dispered terbium(III) based metal-organic framework (Tb-MOF). The dispersed AuNPs quench the emissions of the Tb-MOF, while the aggregated AuNPs have little effect. Under the condition of high salt concentration, the free aptamer against ATP does not stabilize the AuNPs against aggregation. This causes a color change from red to blue and weak quenching of the fluorescence of the Tb-MOF (with peaks at 489 nm and 544 nm after excitation at 290 nm). On addition of ATP, it will be bound by its aptamer to form a complex that is adsorbed on the AuNPs. This protects the AuNPs from salt-induced aggregation and the color (with a peak at 525 nm) remains red. The two fluorescence bands of the Tb-MOF are therefore suppressed by fluorescence resonance energy transfer (FRET) between Tb-MOF and the dispersed AuNPs. Fluorescence drops linearly in the 50 nM to 10 μM ATP concentration range, and the detection limit is 23 nM. ATP analogs such as guanosine triphosphate, uridine triphosphate, cytidine triphosphate, adenosine monophosphate and cyclic adenosine monophosphate have no obvious interference. The method was successfully applied to the determination of ATP in (spiked) human plasma samples and gave satisfactory recoveries.
Fluorometric determination of sulfide ions via its inhibitory effect on the oxidation of thiamine by Cu(II) ions Microchim. Acta (IF 5.705) Pub Date : 2018-07-05 Pengjuan Ni, Chuanxia Chen, Yuanyuan Jiang, Zhenlu Zhao, Yizhong Lu
A fluorometric assay is described for sulfide ions determination. It is based on the finding that the oxidation of the non-fluorescent substrate thiamine (TH) by Cu(II) in basic solution to form fluorescent thiochrome is inhibited by sulfide ions. This results in a decrease in fluorescence intensity which is proportional to the concentration of sulfide ions. Under the optimized conditions, the decrease in fluorescence, best measured at excitation/emission wavelengths of 370/440 nm, decreases linearly in the 0.03 to 2.5 μM sulfide ions concentration range. The detection limit is 20 nM. The method shows excellent selectivity over many potentially interfering ions and has been successfully applied to the determination of sulfide ions in spiked tap water, lake water and the synthetic wastewater samples. The method is time-saving and environmentally friendly, and in our perception shows a great potential in water quality inspection and environmental monitoring.
Colorimetric immunoassay for Listeria monocytogenes by using core gold nanoparticles, silver nanoclusters as oxidase mimetics, and aptamer-conjugated magnetic nanoparticles Microchim. Acta (IF 5.705) Pub Date : 2018-07-05 Yushen Liu, Juan Wang, Xiuling Song, Kun Xu, Huisi Chen, Chao Zhao, Juan Li
The authors describe a rapid colorimetric assay for Listeria monocytogenes (L. monocytogenes) based on the o-phenylenediamine-mediated deaggregation of gold nanoparticles. Silver nanoclusters are used as an artificial enzyme that can oxidize o-phenylenediamine to form o-benzoquinone diamine. Aptamer and IgY antibodies were chosen to conjugate with magnetic beads and silver nanoclusters, respectively, which can recognize and bind L. monocytogenes at different specific binding sites. This results in the disassembly of colloidal gold nanoparticles which is accompanied by a color change from blue to red, with peaks at 730 and 525 nm, respectively. The method allows L. monocytogenes to be colorimetrically determined in the 10 to 106 cfu·mL−1 concentration range without pre-enrichment, and the limit of detection is as low as 10 cfu·mL−1. Recoveries ranging from 97.4 to 101.3% are found when analyzing spiked food samples. The assay is rapid, sensitive and specific.
Colorimetric and visual detection of mercury(II) based on the suppression of the interaction of dithiothreitol with agar-stabilized silver-coated gold nanoparticles Microchim. Acta (IF 5.705) Pub Date : 2018-07-04 Qiang Da, Yuanyuan Gu, Xiafeng Peng, Liying Zhang, Shuhu Du
A colorimetric and visual method is described for the determination of mercury(II) ion. A gel consisting of agar-stabilized silver-coated gold nanoparticles (Au@Ag NPs) was prepared. The reaction with dithiothreitol (DTT) via thiol-Ag chemistry results in an orange to purple color change of the gel. However, in the presence of Hg(II), the reaction of DTT with the silver shells is suppressed due to the strong thiophilicity of Hg(II). The color of the gel changes from purple to red to orange in the presence of increasing concentrations of Hg(II). The Au@Ag NPs therefore are a viable optical probe for Hg(II) which can be detected in concentration as low as 78 nM via dual-wavelength ratiometric absorbance (A390/A520), and at 1 μM levels with bare eyes. The use of agar as a support is mandatory to prevent the aggregation of the NPs and also improves selectivity. The method was applied to the analysis of spiked samples, and recoveries ranged between 96.3 and 104%. The assay is easy, inexpensive, and in our perception represents an attractive tool for on-site visual detection of Hg(II).
A cathodic photoelectrochemical sensor for chromium(VI) based on the use of PbS quantum dot semiconductors on an ITO electrode Microchim. Acta (IF 5.705) Pub Date : 2018-07-04 Panpan Wang, Ling Cao, Ying Wu, Junwei Di
Under visible-light irradiation, a cathodic photoelectrochemical (PEC) sensor is presented for highly sensitive determination of Cr(VI) at a potential of −0.25 V (vs SCE). PbS quantum dots (QDs) were capped with mercaptoacetic acid and assembled on the surface of an indium tin oxide (ITO) electrode via the linker poly(diallyl dimethyl ammonium chloride) providing a photoactive sensor. Cr(VI) accepts the photoelectrons generated by the PbS QDs. This promotes the separation of electron holes and enhances the cathodic photocurrent generated by a 470-nm LED. The sensor has 10 pM detection limit and a linear working range from 0.02 nM to 2 μM of chromate. The method was successfully applied to the determination of Cr(VI) and total chromium in spiked environmental water samples.
Metal oxide nanoparticles in electrochemical sensing and biosensing: a review Microchim. Acta (IF 5.705) Pub Date : 2018-07-04 Jaise Mariya George, Arun Antony, Beena Mathew
This review (with (318) refs) describes progress made in the design and synthesis of morphologically different metal oxide nanoparticles made from iron, manganese, titanium, copper, zinc, zirconium, cobalt, nickel, tungsten, silver, and vanadium. It also covers respective composites and their function and application in the field of electrochemical and photoelectrochemical sensing of chemical and biochemical species. The proper incorporation of chemical functionalities into these nanomaterials warrants effective detection of target molecules including DNA hybridization and sensing of DNA or the formation of antigen/antibody complexes. Significant data are summarized in tables. The review concludes with a discussion or current challenge and future perspectives.
Synthesis of Au@Ag core-shell nanostructures with a poly(3,4-dihydroxy-L-phenylalanine) interlayer for surface-enhanced Raman scattering imaging of epithelial cells Microchim. Acta (IF 5.705) Pub Date : 2018-07-03 Haibin Wen, Peichun Jiang, Yuling Hu, Gongke Li
Poly(3,4-dihydroxy-L-phenylalanine) (polyDOPA) is a stable and biocompatible reducing agent. A versatile strategy is described here for the synthesis of core-shell Au@Ag nanostructures containing a polyDOPA interlayer. The latter provides abundant sites for deposition of nanocomposites, to immobilize molecules and to grow shells. The Au@polyDOPA@Ag nanoparticles are shown to generate strong and stable surface-enhanced Raman spectroscopy (SERS) signals compared to bare AuNPs and bare AgNPs. Folic acid was then immobilized on Au@polyDOPA@Ag nanoparticles and then applied to SERS imaging of human lung adenocarcinoma cell line A549 by the specific recognition of the folic acid receptor. The folic acid-conjugated SERS tags were promising to be nanoplatforms for imaging of cancer cells.
Colorimetric determination of ofloxacin using unmodified aptamers and the aggregation of gold nanoparticles Microchim. Acta (IF 5.705) Pub Date : 2018-07-03 Xiaotong Zhou, Lumei Wang, Guoqing Shen, Dongwei Zhang, Jialun Xie, Abdureyim Mamut, Weiwen Huang, Shanshan Zhou
A colorimetric method is presented for the determination of the antibiotic ofloxacin (OFL) in aqueous solution. It is based on the use of an aptamer and gold nanoparticles (AuNPs). In the absence of OFL, the AuNPs are wrapped by the aptamer and maintain dispersed even at the high NaCl concentrations. The solution with colloidally dispersed AuNPs remains red and has an absorption peak at 520 nm. In the presence of OFL, it will bind to the aptamer which is then released from the AuNPs. Hence, AuNPs will aggregate in the salt solution, and color gradually turns to blue, with a new absorption peak at 650 nm. This convenient and specific colorimetric assay for OFL has a linear response in the 20 to 400 nM OFL concentration range and a 3.4 nM detection limit. The method has a large application potential for OFL detection in environmental and biological samples.
Colorimetric determination of the pesticide chlorothalonil based on the aggregation of gold nanoparticles Microchim. Acta (IF 5.705) Pub Date : 2018-07-03 Qingju Liu, Ping Han, Wenwen Gong, Hui Wang, Xiaoyuan Feng
A method is described for the determination of the pesticide chlorothalonil (CLT). It is based on the finding that citrate-capped gold nanoparticles (AuNPs) undergo aggregation on exposure to chlorothalonil. This is accompanied by a visually detectable color change from wine red to blue. The effect is due to the interaction of the cyano group of chlorothalonil with gold nanoparticles. The assay may also be performed by using a spectrometer. The ratio of absorbances at 700 nm and 520 nm (A700/A520) linearly drops in the 5 to 100 ng·mL−1 CLT concentration range, with a 3.6 ng·mL−1 detection limit. This is below the Chinese guideline value for cucumber. The method is rather simple and does not require any modification of the AuNPs or the utilization of antibody. It was successfully applied to the determination of CLT in (spiked) cucumber samples. Recoveries ranged from 80.4 to 97.4%, and the analytical results compared well with those obtained by HPLC.
Dialysis assisted ligand exchange on gold nanorods: Amplification of the performance of a lateral flow immunoassay for E. coli O157:H7 Microchim. Acta (IF 5.705) Pub Date : 2018-07-02 Yingzhou Tao, Jiao Yang, Lijuan Chen, Youju Huang, Bin Qiu, Longhua Guo, Zhenyu Lin
Ligand exchange on the surface of gold nanorods (AuNRs) is widely used, but conventional methods usually require multiple centrifugation cycles to completely remove cetyltrimethylammonium bromide (CTAB). This can lead to undesired aggregation of AuNRs. A dialysis-assisted protocol is described here for ligand exchange on AuNRs. Dialysis driven by a concentration gradient is shown to be a powerful tool to separate CTAB from aqueous solutions. The concentration gradient of CTAB in a dialysis bag can avoid the possible aggregation of AuNRs that can be caused by drastic environmental changes. It also supports the rate of ligand exchange on the surfaces of the AuNRs. The modified AuNRs were employed in a lateral-flow test strip immunoassay (LFTS-IAs) for the food pathogen E. coli O157:H7 in order to study of efficiency of ligand exchange. Compared to AuNRs where ligand exchange was performed via multiple centrifugation cycles, the AuNRs prepared by dialysis-assisted ligand exchange show improved conjugation to antibody and enhanced visual signals in the test line of the LFTS-IAs. A portable strip reader (absorption wavelength = 525 nm) is used to records the testing results. The sensitivity of AuNRs modified by dialysis has been achieved even as low as 1 × 102 cfu·mL−1 in a short time (within 15 min), and the working range is 1 × 102 to 1 × 106 cfu·mL−1, which is superior over the detection performance of conventional test strip using AuNRs modified by centrifugation.
Colorimetric determination of Hg(II) via the gold amalgam induced deaggregation of gold nanoparticles Microchim. Acta (IF 5.705) Pub Date : 2018-07-02 Yonghong Xie
A method is described for the colorimetric determination of mercury(II). In the absence of Hg(II), aminopropyltriethoxysilane (APTES) which is positively charged at pH 7 is electrostatically absorbed on the surface of gold nanoparticles (AuNPs). This neutralizes the negative charges of the AuNPs and leads to NP aggregation and a color change from red to blue-purple. However, in the presence of Hg(II), reduced Hg (formed through the reaction between Hg(II) and citrate on the AuNP surface) will replace the APTES on the AuNPs. Hence, the formation of aggregates is suppressed and the color of the solution does not change. The assay is performed by measuring the ratio of absorbances at 650 and 520 nm and can detect Hg(II) at nanomolar levels with a 10 nM limit of detection. The specific affinity between mercury and gold warrants the excellent selectivity for Hg(II) over other environmentally relevant metal ions.
Extraction-free colorimetric determination of thymol and carvacrol isomers in essential oils by pH-dependent formation of gold nanoparticles Microchim. Acta (IF 5.705) Pub Date : 2018-07-02 Natalia Verónica Tonello, Fabiana D’Eramo, Juan Miguel Marioli, Agustín G. Crevillen, Alberto Escarpa
An extraction-free method is described for the colorimetric determination of thymol (TY) and carvacrol (CA) isomers in essential oils by making use of the pH-dependent formation of gold nanoparticles (AuNPs). In solutions of pH 12, TY and CA form gold nanoparticles, while at pH ≤ 11 only CA does so. By taking advantage of this finding, two different approaches based on colorimetric assay (absorption at 550 nm) were developed: one at pH 12 for the determination of total CA and TY, and other at pH 9 and pH 12 for differential quantification of TY and CA. The former agrees with the well-established Folin-Ciocalteu method, and the latter provides a simple way for calculation of TY/CA ratio. The linear ranges are from 100 to 1000 μM at pH 9, and from 50 to 200 μM at pH 12. The limits of detection are 0.09 μM at pH 9, and 0.02 μM at pH 12. These features make this method simple, fast and reliable. Conceivably, it can be used to assess the quality of essential oils and may become a valuable alternative to more sophisticated, laborious and high time-consuming methods.
Nanosensing of ATP by fluorescence recovery after surface energy transfer between rhodamine B and curcubituril-capped gold nanoparticles Microchim. Acta (IF 5.705) Pub Date : 2018-07-02 Riham El Kurdi, Digambara Patra
The authors describe a method for functionalization of gold nanoparticles (AuNPs) with the supramolecular host molecule, curcubituril (CB) which can bind rhodamine B (RhB). The fluorescence of RhB is quenched by the AuNPs via surface energy transfer. On addition of ATP, a dimeric RhB-ATP complex is formed and RhB is pushed out of CB. Hence, fluorescence increases by a factor of 8. This fluorescence recovery effect has been utilized to develop a new detection scheme for ATP. The assay, measured at fluorescence excitation and emission wavelengths of 500 nm and 574 nm respectively, works in the 0.5–10 μM concentration range and has a 100 nM detection limit. The method is not interfered by UTP, GTP, CTP, TTP, ascorbic acid and glutathione.
Selective, fast and semi-automatic enrichment of nucleosides by using a phenylboronic acid modified hybrid material composed of graphene oxide and melamine sponge Microchim. Acta (IF 5.705) Pub Date : 2018-06-30 Ting Cheng, Zhijuan Jiao, Xiaoyan Liu, Haixia Zhang
A hybrid material was prepared from graphene oxide and melamine sponge, and modified with phenylboronic acid to obtain a sorbent for the enrichment of the nucleosides cytidine, uridine, inosine, guanosine and adenosine. The loading capacity typically is around 27.8 mg g−1 which is comparable to other sorbents, and highly selectivity for cis-diols is observed even if the concentration of potential interferents is 1500-fold higher. The sorbent was placed in an injector, and the process was operated semiautomatically by using a peristaltic pump. The sorbent is stable and can be re-used six times without decrease in efficiency. It was applied to the selective extraction of the cis-diols (cytidine, uridine, inosine, guanosine, adenosine) from HepG2 cells. It presents good linear between 3 to 5000 μg L−1 and the limits of detection (in HPLC analysis with UV detection) are 1–4 μg L−1. Good recoveries of 85–101% were obtained with spiked HepG2 cells samples, with relative standard deviation of ≤9.9%.
Fluorometric aptamer-based determination of ochratoxin A based on the use of graphene oxide and RNase H-aided amplification Microchim. Acta (IF 5.705) Pub Date : 2018-06-30 Changbei Ma, Kefeng Wu, Han Zhao, Haisheng Liu, Kemin Wang, Kun Xia
The authors describe a fluorometric assay for ochratoxin A (OTA) that is based on the use of graphene oxide and RNase H-aided amplification. On addition of OTA, cAPT is replaced from the APT/cAPT hybridization complex and then hybridizes with RNA labeled with a fluorophore at the 5′-end. Eventually, the fluorophore is released by RNase H cleavage. As the concentration of OTA increases, more cAPTs are displaced, this leading to fluorescence enhancement (best measured at excitation/emission wavelengths of 495/515 nm). This RNase H-assisted cycle response results in strong signal amplification. The limit of detection, calculated on the basis of a signal to noise ratio of 3, is 0.08 ng·mL−1. Response is linear in the 0.08–200 ng·mL−1 OTA concentration range. The method is highly selective for OTA over ochratoxin B and aflatoxin B1. It was applied to the determination of OTA in red wine samples spiked at levels of 1, 7, and 50 ng·mL−1, and the recoveries ranged from 90.9 to 112%.
Voltammetric immunoassay for α-fetoprotein by using a gold nanoparticle/dendrimer conjugate and a ferrocene derived ionic liquid Microchim. Acta (IF 5.705) Pub Date : 2018-06-30 Youming Shen, Guangyu Shen, Youyu Zhang
An immunosensor is described for the voltammetric determination of α-fetoprotein. It is making use of an AuNP-dendrimer conjugate and an ionic liquid. A gold electrode was first modified with chitosan. Then, the AuNP-dendrimer conjugate was covalently immobilized on the electrode. Following this, an ionic liquid was placed on the electrode via formation of a covalent bond between the amino groups of PAMAM and the aldehyde groups of an ionic liquid containing ferrocene. Thus, the redox probe ferrocene becomes immobilized on the electrode surface. PAMAM increases the amount of ferrocene immobilized on the electrode due to its globular shape and rich amino groups. The use of AuNPs improves the conductivity of the electrode. The modified electrode was applied to the determination of α-fetoprotein in human serum and has a linear response that covers the 0.05 to 30 ng mL−1 α-fetoprotein concentration range, with a detection limit of 0.02 ng mL−1. This assay is stable, selective and reproducible. It is perceived to provide a powerful tool for the early detection of cancer markers.
Photoelectrochemical aptasensor for sulfadimethoxine using g-C 3 N 4 quantum dots modified with reduced graphene oxide Microchim. Acta (IF 5.705) Pub Date : 2018-06-29 Xueming Dang, Huimin Zhao, Xiaona Wang, Tangnuer Sailijiang, Shuo Chen, Xie Quan
A novel photoelectrochemical (PEC) aptasensor with graphitic-phase carbon nitride quantum dots (g-C3N4; QDs) and reduced graphene oxide (rGO) was fabricated. The g-C3N4 QDs possess enhanced emission quantum yield (with an emission peak at 450 nm), improved charge separation ability and effective optical absorption, while rGO has excellent electron transfer capability. Altogether, this results in improved PEC performance. The method is making use of an aptamer against sulfadimethoxine (SDM) that was immobilized on electrode through π stacking interaction. Changes of the photocurrent occur because SDM as a photogenerated hole acceptor can further accelerate the separation of photoexcited carriers. Under optimized conditions and at an applied potential of +0.2 V, the aptasensor has a linear response in the 0.5 nM to 80 nM SDM concentration range, with a 0.1 nM detection limit (at S/N = 3). The method was successfully applied to the analysis of SDM in tap, lake and waste water samples.
Sandwich electrochemical thrombin assay using a glassy carbon electrode modified with nitrogen- and sulfur-doped graphene oxide and gold nanoparticles Microchim. Acta (IF 5.705) Pub Date : 2018-06-28 Baoshan He
Graphene oxide doped with nitrogen and sulfur was decorated with gold nanoparticles (AuNP-SN-GO) and applied as a substrate to modify a glassy carbon electrode (GCE). An aptamer against the model protein thrombin was self-assembled on the modified GCE which then was exposed to thrombin. Following aptamer-thrombin interaction, biotin-labeled DNA and aptamer 2 are immobilized on another AuNP-SN-GO hybrid and then are reacted with the thrombin/AuNP-SN-GO/GCE to form a sandwich. The enzyme label horseradish peroxidase (HRP) was then attached to the electrode by biotin–avidin interaction. HRP catalyzes the oxidation of hydroquinone by hydrogen peroxide. This generates a strong electrochemical signal that increases linearly with the logarithm of thrombin concentration in the range from 1.0 × 10−13 M to 1.0 × 10−8 M with a detection limit of 2.5 × 10−14 M (S/N = 3). The assay is highly selective. It provides a promising strategy for signal amplification. In our perception, it has a large potential for sensitive and selective detection of analytes for which appropriate aptamers are available.
Preconcentration of Pb(II) by using Mg(II)-doped NiFe 2 O 4 nanoparticles as a magnetic solid phase extraction agent Microchim. Acta (IF 5.705) Pub Date : 2018-06-28 Hossein Abdolmohammad-Zadeh, Arezu Salimi
Magnesium(II)-doped nickel ferrite (Mg–NiFe2O4) nanoparticles are introduced as a new adsorbent for magnetic solid phase extraction of lead(II) ions from aqueous solutions. The structure and morphology of the adsorbent was characterized by FTIR, X-ray diffraction and scanning electron microscopy. The effects of pH value, amount of adsorbent, type, concentration and volume of the eluent and adsorption/desorption time on the extraction efficiency were studied. Following elution with hydrochloric acid, Pb(II) ions were quantified by flame atomic absorption spectrometry. Under optimized conditions, the calibration graph is linear in the 0.5–125 ng mL−1 Pb(II) ion concentration range. Other figures of merit include (a) a 0.2 ng mL−1 limit of detection, (b) an enrichment factor of 200, (c) an intra-day relative standard deviation (for n = 6 at 50 ng mL−1) of 1.6%, and (d) an inter-day precision of 3.8%. The method was validated by the analysis of the certified reference material, NIST SRM 1566b. It was successfully applied to the determination of Pb(II) ion in spiked water samples, industrial wastewater and acidic lead battery waters.
Recent advances in metal-organic frameworks for adsorption of common aromatic pollutants Microchim. Acta (IF 5.705) Pub Date : 2018-06-27 Chang Liu, Li-Qing Yu, Ya-Ting Zhao, Yun-Kai Lv
This review (with 85 refs.) summarizes the recent literature on the adsorption of common aromatic pollutants by using modified metal-organic frameworks (MOFs). Four kinds of aromatic pollutants are discussed, namely benzene homologues, polycyclic aromatic hydrocarbons (PAHs), organic dyes and their intermediates, and pharmaceuticals and personal care products (PPCPs). MOFs are shown to be excellent adsorbents that can be employed to both the elimination of pollutants and to their extraction and quantitation. Adsorption mechanisms and interactions between aromatic pollutants and MOFs are discussed. Finally, the actual challenges of existence and the perspective routes towards future improvements in the field are addressed.
Inorganic iron-sulfur clusters enhance electron transport when used for wiring the NAD-glucose dehydrogenase based redox system Microchim. Acta (IF 5.705) Pub Date : 2018-06-26 Aishwarya Mahadevan, Sandun Fernando
Wiring the active site of an enzyme directly to an electrode is the key to ensuring efficient electron transfer for the proper performance of enzyme-based bioelectronic systems. Iron-sulfur complexes, the first link between proteins and mediating molecules in the biological electron transport chain(s), possess an intrinsic electron transport capability. The authors demonstrate the application of inorganic iron-sulfur clusters (Fe-S) viz. FeS, FeS2, Fe2S3, and Fe3S4, as molecular wires to mediate electron transport between a glucose-selective redox enzyme and the gold electrode. It is shown that Fe-S can emulate the functionality of the natural electron transport chain. Voltammetric studies indicate a significant improvement in electron transport, surface coverage, and resilience achieved by the Fe-S-based glucose anodes when compared to a conventional pyrroloquinoline quinone (PQQ)-based electrode. The Fe-S-based glucose anodes showed glucose oxidation at a potential of +0.5 V vs. Ag/AgCl with Tris-HCl buffer (pH 8) acting as a carrier. The current densities positively correlated with the concentrations of glucose in the range 0.1–100 mM displaying detection limits of 0.77 mM (FeS), 1.22 mM (FeS2), 2.95 mM (Fe2S3), and 14.57 mM (Fe3S4). The metal-anchorable sulfur atom, the strong π-coordinating iron atom, the favorable redox properties, low cost, and natural abundance make Fe-S an excellent electron-mediating relay capable of wiring redox active sites to electrode surfaces.
Non-enzymatic electrochemical glucose sensor based on monodispersed stone-like PtNi alloy nanoparticles Microchim. Acta (IF 5.705) Pub Date : 2018-06-26 Rulei Wang, Xinyi Liang, Haiyan Liu, Land Cui, Xiaoyue Zhang, Changjiang Liu
Monodisperse stone-like PtNi alloy nanoparticles (NPs) were synthesized at room temperature using an inverse microemulsion method. The results of XRD, HRTEM, and EDS demonstrate that these NPs consist of a disordered alloy that has (a) a face-centered cubic structure, (b) Pt/Ni atomic ratios of ∼5:1, and (c) a large number of atoms exposed on the NP surface and enclosed by low index facets. The material was placed on a glassy electrode which then displayed superior response to glucose. Best operated at a potential of 0.43 V (vs. SCE), the electrode has the following features: (a) a wide linear range (from 0.5 mM to 40 mM), (b) rapid response (<1 s), (c) a low detection limit (0.35 μM) and (d) a sensitivity of 40.17 μA mM−1cm−2). The NP sensor also is fairly selective over ascorbic acid, uric acid and fructose. The sensor has repeatability and durability for up to 30 days after manufacture.
Protein-templated Fe 2 O 3 microspheres for highly sensitive amperometric detection of dopamine Microchim. Acta (IF 5.705) Pub Date : 2018-06-26 Xiaoyu Chen, Qingquan Liu, Minghuan Liu, Xiaoyan Zhang, Suying Lin, Yisong Chen, Junyang Zhuang, Da-Peng Yang
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.
Hyaluronic acid-grafted three-dimensional MWCNT array as biosensing interface for chronocoulometric detection and fluorometric imaging of CD44-overexpressing cancer cells Microchim. Acta (IF 5.705) Pub Date : 2018-06-26 Minghuan Liu, Yanan Xu, Chusen Huang, Ti Jia, Xiaoyan Zhang, Da-Peng Yang, Nengqin Jia
A sandwich-type electrochemical cytosensor is described for quantitative determination of CD44-overexpressing HeLa cells. Hyaluronic acid (HA) acts as a targeting molecule that was in-situ incorporated into the sensor based on the use of an indium tin oxide (ITO) electrode modified with multi-walled carbon nanotubes (MWCNTs). The 3D-MWCNT structure is shown to strongly improve the electronic properties and surface chemical reactivities. The HA-modified sensor exhibits a highly sensitive response to HeLa cells. A sandwiched hybridization protocol was then established using BIO [an N-butyl-4-(6′-aminohexyl)amino-1,8-naphthalimide probe modified with HA] as the tracing labels of the fluorescent probes for targeting CD44-positive tumor cells. The signal amplification was thereby maximized and measured by chronocoulometry. The binding of CD44-positive HeLa cells to the HA modified sensing layer causes a decrease in chronocoulometric response. The signal decreases linearly in the 2.1 × 102 to 2.1 × 107 HeLa cells·mL−1 concentration range with a detection limit of 70 cells·mL−1. Such a sandwich-type assay may be tailored as a sensitive candidate for detecting low levels of tumor cells.
Silver nanoparticles supported onto a stainless steel wire for direct-immersion solid-phase microextraction of polycyclic aromatic hydrocarbons prior to their determination by GC-FID Microchim. Acta (IF 5.705) Pub Date : 2018-06-26 Adrián Gutiérrez-Serpa, Patricia I. Napolitano-Tabares, Verónica Pino, Francisco Jiménez-Moreno, Ana I. Jiménez-Abizanda
The authors describe a new coating for use in solid-phase microextraction (SPME). Silver nanoparticles (AgNPs) were prepared by using gallic acid or glucose as the reducing agents, and then supported onto a stainless steel wire that was previously coated with a silver mirror. Coating with AgNPs was performed by a layer-by-layer approach of up to eight cycles of consecutive deposition of AgNPs and the thiol linker 1,8-octanedithiol. This procedure allows proper control of the coating thickness. Thicknesses are 3.2 μm and 3.5 μm with AgNPs obtained with gallic acid and glucose, respectively. This is in agreement with theoretical estimations (3.8 μm). The fibers were used in the direct-immersion SPME-GC-FID determination of 16 polycyclic aromatic hydrocarbons (PAHs) from different waters. The performance of the method was compared to the one using polydimethylsiloxane fibers (100 μm), which is the most suitable commercial SPME fiber for PAHs. Despite the low thickness of the AgNP coatings (compared to PDMS), the analytical features of the method using the most adequate coating (AgNPs prepared with gallic acid) include: (a) limits of detection down to 0.6 ng·mL−1; (b) intra-day, inter-day, and inter-fiber precisions (expressed as RSDs) lower than 22, 26 and 25%, respectively; and (c) an operational lifetime of ~150 extractions/desorption cycles. The analysis of various spiked environmental waters using these fibers resulted in adequate analytical performance.
Packed hybrids of gold nanoparticles and layered double hydroxide nanosheets for microextraction of triazine herbicides from maize Microchim. Acta (IF 5.705) Pub Date : 2018-06-23 Xinpei Li, Ying Sun, Liming Yuan, Li Liang, Yanxiao Jiang, Huilan Piao, Daqian Song, Aimin Yu, Xinghua Wang
This work describes a nanohybrid material consisting of gold nanoparticles (AuNPs) and nanosheets of layered double hydroxides (NLDHs) of Mg(II) and Al(III). Mono-disperse AuNPs were immobilized on the surface of the LDHs via Au-O bonding. The nanohybrid sorbent was packed in an organic filter along with a syringe and applied to the microextraction of triazine herbicides with the help of an injection pump. The collected hexane eluate was concentrated and directly injected into a HPLC column for quantification. The effects of the amount of Au/LDH nanohydrobrids, type, flow rate, volume of washing and eluting solvent were optimized. The method was validated by detecting four triazine herbicides (prometryn, atrazine, terbumeton and secbumeton) in spiked maize. The limits of detection range between 35 and 108 pg g−1. The relative standard deviations range from 1.0–6.9% for repeatability and 4.6–7.8% for reproducibility (for n = 5).
Coupling antibody based recognition with DNA based signal amplification using an electrochemical probe modified with MnO 2 nanosheets and gold nanoclusters: Application to the sensitive voltammetric determination of the cancer biomarker alpha fetoprotein Microchim. Acta (IF 5.705) Pub Date : 2018-06-23 Wen Xiang, Guanwu Wang, Shuang Cao, Qiuguo Wang, Xiangyue Xiao, Ting Li, Minghui Yang
The authors describe a sensitive electrochemical immunoassay for the cancer biomarker α-fetoprotein (AFP). It is based on a combination of an immunoassay with DNA-based signal amplification. Two-dimensional MnO2 nanosheets modified with gold nanoclusters (AuNC-MnO2) were synthesized through one-pot process and utilized as an electrochemical probe. Bovine serum albumin served as templating agent to guide the formation and assembly of the modified sheets. The detection antibody against AFP and a polycytosine DNA sequence (dC20) were immobilized onto the modified nanosheets. The electrochemical assay follows the usual sandwich protocol. The antibodies on the nanosheets then bind to AFP, while dC20 causes signal amplification. The reaction of the phosphate backbone of dC20 with molybdate leads to the formation of redox-active molybdophosphate which generates an electrochemical current, typically measured at 0.20 V (vs. Ag/AgCl). The method allows AFP to be determined in the 0.01 to 10 ng·mL−1 concentration range, and the detection limit is as low as 5 pg·mL−1. This strategy overcomes the drawbacks of conventional immunoassays whose sensitivity is often limited because many immunoassays are rather difficult to amplify. The method has a wide scope in that various other DNA signal amplification methods such as rolling circle amplification and hybridization chain reactions may also be applied.
Synergistic effect of MoS 2 and diamond nanoparticles in electrochemical sensors: determination of the anticonvulsant drug valproic acid Microchim. Acta (IF 5.705) Pub Date : 2018-06-22 María Dolores Petit-Domínguez, Carmen Quintana, Luis Vázquez, María del Pozo, Isabel Cuadrado, Ana María Parra-Alfambra, Elena Casero
The authors describe an electrochemical sensor based on the use of diamond nanoparticles (DNPs) and molybdenum disulfide (MoS2) platelets. The sensor was applied to the voltammetric determination of the anticonvulsant valproic acid which was previously derivatized with ferrocene. The MoS2 platelets were obtained by an exfoliation method, and the DNPs were directly dispersed in water and subsequently deposited on a glassy carbon electrode (GCE). The sensor response was optimized in terms of the solvent employed for dispersing the MoS2 nanomaterial and the method for modifying the GCE. Sensors consisting of a first layer of MoS2 dispersed in ethanol/water and a second layer of DNPs give better response. The single steps of sensor construction were characterized by atomic force microscopy and electrochemical impedance spectroscopy. The differential pulse voltammetric response of the GCE (measured at +0.18 V vs. Ag/AgCl) was compared to that of sensors incorporating only one of the nanomateriales (DNPs or MoS2). The formation of a hybrid MoS2-DNP structure clearly improves performance. The GCE containing both nanomaterials exhibits high sensitivity (740 µA ⋅ mM−1 ⋅ cm−2), a 0.27 μM detection limit, and an 8% reproducibility (RSD). The sensor retained 99% of its initial response after 45 days of storage.
Nanostructured aptamer-based sensing platform for highly sensitive recognition of myoglobin Microchim. Acta (IF 5.705) Pub Date : 2018-06-21 Neda Ghafori Nia, Azadeh Azadbakht
A composite was prepared from PtSn nanoparticles and carbon nanotubes (PtSnNP/CNTs) and applied to the electrochemical determination of myoglobin (Mb). An Mb-aptamer was immobilized on a glassy carbon electrode (GCE), and hexcyanoferrate was used as an electrochemical probe. The PtSnNP/CNTs were synthesized by a microwave-aided ethylene glycol reduction method. Detection is based on electron transfer inhibition that is caused by the folding and conformational change of the Mb-aptamer in the presence of Mb. The amperometric signal for hexacyanoferrate, best measured at 0.2 V vs. Ag/AgCl depends on the concentration of Mb that interacts with the aptamer on the GCE. This approach is selective and sensitive for Mb due to (a) the highly specific recognition ability of the aptamer for Mb, (b) the powerful electronic properties of carbon nanotubes, (c) the arranged decoration of CNTs with PtSnNPs, and (d), the superior electron transfer to hexacyanoferrate. The assay is highly selective, with linear relationships from 0.01–1 nM and 10 nM–200 nM, and a limit of detection as low as 2.2 ± 0.1 pM. The modified GCE was applied to the quantitation of Mb in spiked human serum samples.
Ultrasensitive detection of heparin by exploiting the silver nanoparticle-enhanced fluorescence of graphitic carbon nitride (g-C 3 N 4 ) quantum dots Microchim. Acta (IF 5.705) Pub Date : 2018-06-20 Qiao Cheng, Yu He, Yili Ge, Jiangang Zhou, Gongwu Song
A composite (Ag-g-CNQDs) was prepared from graphitic carbon nitride quantum dots and silver nanoparticles by water phase synthesis. Aided by metal-enhanced fluorescence, the composite exhibits excitation-dependent red emission with a peak at 600 nm with a quantum yield of 21%. If the composite is coated with polyethylenimine (PEI) to form the Ag-g-CNQD/PEI complexe, fluorescence is strongly reduced. Upon addition of heparin, the fluorescence of the system is enhanced because PEI has a higher affinity for heparin than Ag-g-CNQDs. The effect was used to design a fluorometric assay for heparin. The emission at 600 nm increases linearly in the 0.025 to 2.5 μM heparin concentration range, with a 8.2 nM limit of detection.
Gold nanoparticle enhanced hybridization chain reaction as a method for signal amplification. Application to electrochemical immunodetection of the ovarian cancer biomarker carbohydrate antigen 125 Microchim. Acta (IF 5.705) Pub Date : 2018-06-18 Yanting Nie, Mengyuan Yang, Yiling Ding
The authors describe a method for enhancing the hybridization chain reaction (HCR) by using gold nanoparticles (AuNPs). This can considerably improve the sensitivity of electrochemical immunoassays as demonstrated for the carbohydrate antigen 125 (CA125), a biomarker for ovarian cancer. Compared to previous HCR based assays, the DNA acting as fuel strands were immobilized onto AuNPs, so that dendrimeric like chains were formed on the electrode after HCR. The improved signal is due to the reaction of DNA on the electrode. Specifically, the reaction of the phosphate groups of DNA with molybdate forms redox-active molybdophosphate, and this generates a strong electrochemical current. The immunosensor was prepared by sequential capturing, on the electrode, (a) antibody against CA125, (b) analyte (CA125), and (c) an aptamer against CA125 to form a sandwich structure. The primer on the aptamer sequence initiates HCR by annealing to one strand of DNA on the AuNPs and to another DNA in solution. The increased loading of DNA molecules onto the electrode increases the amount of phosphate groups and subsequently increases the electrical signal. The sensitivity of the assay is found to be significantly improved compared to assays without HCR and when using conventional HCR. The immunosensor was successfully applied to the determination of CA125 in human serum samples. The detection limit (based on an S/N ratio of 3) is 50 μU.mL−1. This indicates that this signal amplification strategy has a large potential in terms of clinical applications. It may be modified such that it also can be applied to the determination of other analytes for which proper aptamers are available.
Determination of trichloroethylene by using self-referenced SERS and gold-core/silver-shell nanoparticles Microchim. Acta (IF 5.705) Pub Date : 2018-06-18 Zhao Yu, Michael E. Smith, Jinnan Zhang, Yan Zhou, Peng Zhang
A surface-enhanced Raman scattering (SERS) method has been developed to determine the concentration of trichloroethylene (TCE) in environmental water. Au-core/Ag-shell nanoparticles containing 4-mercaptophenylboronic acid (4-MPBA) between the core and shell are used as the SERS substrate. 4-MPBA serves as an internal reference with a Raman shift at 534 cm−1. TCE reacts with 4-mercaptopyridine (4-MPy) in a so-called Fujiwara reaction. With the presence of TCE in water, the consumption of 4-MPy results in a change in the intensity of its Raman signal at 1220 cm−1. The ratio of the Raman shift at 1220 cm−1 and 534 cm−1 decreases linearly in the 0.2 to 1.0 μM TCE concentration range, and the detection limit of TCE is as low as 8 ppb (60 nM). The method has been successfully applied to the determination of TCE in spiked lake water.
A nonfouling voltammetric immunosensor for the carcinoembryonic antigen based on the use of polyaniline nanowires wrapped with hyaluronic acid Microchim. Acta (IF 5.705) Pub Date : 2018-06-16 Jiasheng Wang, Ni Hui
A non-fouling electrochemical immunosensor is described for determination of the tumor biomarker carcinoembryonic antigen (CEA). It is based on the use of composite wires made by chemical grafting of hyaluronic acid onto polyaniline nanowires. The modified nanowires possess excellent antifouling property both in single protein solutions and in dilute serum samples. The current of immunoelectrode exhibits a linear response in the 0.01 pg mL−1 to 10,000 pg mL−1 CEA concentration range and 0.0075 pg mL−1 detection limit. This work demonstrates that coating an electrode with hyaluronic acid can largely reduce unspecific adsorption of proteins on the electrode surface.
Advances in the use of functional composites of β-cyclodextrin in electrochemical sensors Microchim. Acta (IF 5.705) Pub Date : 2018-06-16 Xiaohui Niu, Zunli Mo, Xing Yang, Mingyuan Sun, Pan Zhao, Zhenliang Li, Meixuan Ouyang, Zhenyu Liu, Huhu Gao, Ruibin Guo, Nijuan Liu
β-Cyclodextrin (β-CD) possess a hydrophobic inner cavity and a hydrophilic exterior surface. They exhibit excellent inclusion properties with the guest molecules that match cavity size, and β-CD-based materials drew widespread attention in electrochemical sensors. The hydroxy groups at the edge of the cavity can form hydrogen bonds and undergo electrostatic and dipole-dipole interactions with other molecules. This review (with 109 refs.) reveals β-CD-based detection mechanisms from the viewpoint of the size/shape-fit concept, and summarizes the current state of multiple electrochemical sensors based on the use of β-CD and functionalized β-CD such as carboxymethyl-β-CD, mono-(6-ethanediamine-6-deoxy)-β-CD, hydroxypropyl-β-CD, thio-β-cyclodextrin, and others.
Aptamer based SERS detection of Salmonella typhimurium using DNA-assembled gold nanodimers Microchim. Acta (IF 5.705) Pub Date : 2018-06-12 Xumin Xu, Xiaoyuan Ma, Haitao Wang, Zhouping Wang
The authors describe a surface-enhanced Raman scattering (SERS) based aptasensor for Salmonella typhimurium (S. typhimurium). Gold nanoparticles (AuNPs; 35 nm i.d.) were functionalized with the aptamer (ssDNA 1) and used as the capture probe, while smaller (15 nm) AuNPs were modified with a Cy3-labeled complementary sequence (ssDNA 2) and used as the signalling probe. The asymmetric gold nanodimers (AuNDs) were assemblied with the Raman signal probe and the capture probe via hybridization of the complementary ssDNAs. The gap between two nanoparticles is a “hot spot” in which the Raman reporter Cy3 is localized. It experiences a strong enhancement of the electromagnetic field around the particle. After addition of S. typhimurium, it will be bound by the aptamer which therefore is partially dehybridized from its complementary sequence. Hence, Raman intensity drops. Under the optimal experimental conditions, the SERS signal at 1203 cm−1 increases linearly with the logarithm of the number of colonies in the 102 to 107 cfu·mL−1 concentration range, and the limit of detection is 35 cfu·mL−1. The method can be performed within 1 h and was successfully applied to the analysis of spiked milk samples and performed very well and with high specificity.
A nanohybrid composed of Prussian Blue and graphitic C 3 N 4 nanosheets as the signal-generating tag in an enzyme-free electrochemical immunoassay for the neutrophil gelatinase-associated lipocalin Microchim. Acta (IF 5.705) Pub Date : 2018-06-12 Fengling Zhang, Hongbin Zhong, Ying Lin, Miaoxuan Chen, Qingshui Wang, Yao Lin, Jiyi Huang
An enzyme-free electrochemical immunoassay is described for the neutrophil gelatinase-associated lipocalin (NGAL; a biomarker of kidney disease). Prussian Blue (PB) nanoparticles with redox activity were deposited on graphitic C3N4 nanosheets (g-C3N4) by in-situ reduction. A screen printed electrode (SPCE) was modified with antibody against NGAL, and the PB-g-C3N4 nanohybrid was used as the signal-generating tag for the secondary antibody against NGAL. Upon addition of target NGAL and of secondary antibody, a sandwich is formed on the SPCE. At an applied potential of typically 0.13 V (vs. Ag/AgCl), a well-defined voltammetric peak is observed that results from the presence of PB on the secondary antibody. Under optimal conditions, the peak current increases linearly in the 0.01 to 10 ng·mL−1 NGAL concentration range, and the detection limit is 2.8 pg·mL−1. An average precision of <12% was accomplished in the batch-to-batch mode. Other disease-related biomarkers do not interfere. The accuracy and inter-laboratory validation of this method were evaluated for target NGAL detection in spiked human serum by using a commercial ELISA. The results obtained by the two methods are in good accordance.
Affinity capture of aflatoxin B 1 and B 2 by aptamer-functionalized magnetic agarose microspheres prior to their determination by HPLC Microchim. Acta (IF 5.705) Pub Date : 2018-06-12 Hongmei Liu, Anxiang Lu, Hailong Fu, Bingru Li, Meihua Yang, Jihua Wang, Yunxia Luan
A novel adsorbent is described for magnetic solid-phase extraction (MSPE) of the aflatoxins AFB1 and AFB2 (AFBs). Magnetic agarose microspheres (MAMs) were functionalized with an aptamer to bind the AFBs which then were quantified by HPLC and on-line post-column photochemical derivatization with fluorescence detection. Streptavidin-conjugated MAMs were synthesized first by a highly reproducible strategy. They possess strong magnetism and high surface area. The MAMs were characterized by transmission electron microscopy, scanning electron microscopy, optical microscopy, laser diffraction particle size analyzer, Fourier transform infrared spectrometry, vibrating sample magnetometry and laser scanning confocal microscopy. Then, the AFB-aptamers were immobilized on MAMs through biotin–streptavidin interaction. Finally, the MSPE is performed by suspending the aptamer-modified MAMs in the sample. They are then collected by an external magnetic field and the AFBs are eluted with methanol/buffer (20:80). Several parameters affecting the coupling, capturing and eluting efficiency were optimized. Under the optimized conditions, the method is fast, has good linearity, high selectivity, and sensitivity. The LODs are 25 pg·mL−1 for AFB1 and 10 pg·mL−1 for AFB2. The binding capacity is 350 ± 8 ng·g−1 for AFB1 and 384 ± 8 ng·g−1 for AFB2, and the precision of the assay is <8%. The method was successfully applied to the analysis of AFBs in spiked maize samples.
Anodic stripping voltammetric determination of total arsenic using a gold nanoparticle-modified boron-doped diamond electrode on a paper-based device Microchim. Acta (IF 5.705) Pub Date : 2018-06-11 Kingkan Pungjunun, Sudkate Chaiyo, Issarapong Jantrahong, Siriwan Nantaphol, Weena Siangproh, Orawon Chailapakul
A multistep paper-based analytical device (mPAD) was designed and applied to the voltammetric determination of total inorganic arsenic. The electrodeposition of gold nanoparticles on a boron-doped diamond (AuNP/BDD) electrode and the determination of total inorganic arsenic is accomplished with a single device. Total inorganic arsenic can be determined by first reducing As(V) to As(III) using thiosulfate in 1.0 mol L−1 HCl. As(III) is then deposited on the electrode surface, and total inorganic arsenic is quantified as As(III) by square-wave anodic stripping voltammetry the potential range between −0.25 V and 0.35 V (vs. Ag/AgCl), best at around 0.05 V. Under optimal conditions, the voltammetric response for As(III) detection is linear in the range from 0.1 to 1.5 μg mL−1 and the limit of detection (3SD/slope) is 20 ng mL−1. The relative standard deviation at 0.3, 0.7 and 1.0 μg mL−1 of As(III) are 3.6, 4.3 and 3.3, respectively (10 different electrodes). The results show that the assay has high precision, a rather low working potential, and excellent sensor-to-sensor reproducibility. The method was employed to the determination of total inorganic arsenic in rice samples. Results agreed well with those obtained by inductively coupled plasma-optical emission spectroscopy (ICP-OES).
Amperometric immunoassay for the obesity biomarker amylin using a screen printed carbon electrode functionalized with an electropolymerized carboxylated polypyrrole Microchim. Acta (IF 5.705) Pub Date : 2018-06-09 Gonzalo Martínez-García, Esther Sánchez-Tirado, Araceli González-Cortés, Paloma Yáñez-Sedeño, José M. Pingarrón
Amylin (the islet amyloid polypeptide) is a hormone related to adiposity, hunger and satiety. It is co-secreted with insulin from pancreatic B-cells. An amperometric immunosensor is presented here for the determination of amylin. It is making use of a screen printed carbon electrode (SPCE) functionalized with electropolymerized poly(pyrrole propionic acid) (pPPA) with abundant carboxyl groups that facilitate covalent binding of antibody against amylin. A competitive immunoassay was implemented using biotinylated amylin and streptavidin labeled with horse radish peroxidase (HRP-Strept) as the enzymatic tracer. The amperometric detection of H2O2 mediated by hydroquinone was employed as an electrochemical probe to monitor the affinity reaction. The variables involved in the preparation and function of the immunosensor were optimized and the electrodes were characterized by electrochemical impedance spectroscopy and cyclic voltammetry. The calibration graph for amylin, obtained by amperometry at −200 mV vs Ag pseudo-reference electrode, showed a range of linearity extending from 1.0 fg∙mL−1 to 50 pg∙mL−1, with a detection limit of 0.92 fg∙mL−1. This is approximately 7000 times lower than the minimum detectable concentration reported for the ELISA immunoassays available for amylin. The assay has excellent reproducibility and good selectivity over potential interferents.
Three-dimensional nanofiber scaffolds are superior to two-dimensional mats in micro-oriented extraction of chlorobenzenes Microchim. Acta (IF 5.705) Pub Date : 2018-06-08 Habib Bagheri, Faranak Manshaei, Omid Rezvani
Three-dimensional (3D) polyamide scaffolds were fabricated by applying a solvent bath as the collecting element. Electrospun nanofibers were immersed into the solvent bath to give a material with a laminated 3D texture. In parallel, 2D nanofibers were synthesized and utilized as microextractive phases in a needle trap device to compare the capabilities of 2D and 3D materials in terms of headspace extraction of various chlorobenzenes (chlorobenzene, 1,2-dichlorobenzene, 1,4-dichlorobenzene, 1,2,4-trichlorobenzene and 1,2,3,4-tetrachlorobenzene). The results demonstrate the superiority of 3D nanofibrous scaffolds over 2D mats. The porosity, morphology, and thermal stability of the 3D scaffolds were characterized using FT-IR, scanning electron microscopy, confocal laser scanning microscopy and thermogravimetric analysis. The CLSM images were reconstructed and analyzed by Image J software, and eventually the enhancement of porosity using 3D scaffolds was confirmed. The type of solvent bath, polyamide solution concentration and other parameters were optimized. Following thermal desorption of the chlorobenzenes, they were quantified by GC-MS. Under optimum conditions, the calibration plots cover the 0.004–1.0 pg μL−1 concentration range and the limits of detection are in the range from 0.8–3 pg mL−1. The relative standard deviations (RSDs) are between 3 and 8% and 3–10% (n = 3) at spiking levels of 200 and 1000 ng L−1, respectively. The RSDs for the needle-to-needle repeatability are <15% (for n = 3). This needle trap microextraction method was applied to the analysis of river water, sea water, and of inlet water of a water treatment plant.
Polystyrene nanofibers capped with copper nanoparticles for selective extraction of glutathione prior to its determination by HPLC Microchim. Acta (IF 5.705) Pub Date : 2018-06-08 Lanlan Wei, Yuan Song, Ping Liu, Xuejun Kang
Polystyrene nanofibers were coated with copper nanoparticles (CuNPs) by a combination of electrospinning and in-situ reduction of Cu(II) using sodium borohydride as the reductant. The CuNPs on the nanofibers were characterized by energy dispersive spectrometry, scanning electron microscopy and transmission electron microscopy. A cartridge was packed with the nanofibers which then were activated with methanol and water. Glutathione (GSH) is found to quantitatively adsorbed by the packed cartridge at pH 3.0, and then can be desorbed with aqueous 2-mercaptoethanol and detected, after derivatization with ortho-phthalaldehyde, via high performance liquid chromatography with fluorometric detection. Under optimized conditions, the method has a 1.1 ng·mL−1 detection limit and a response that is linear in the 10–1000 ng·mL−1 GSH concentration range. The recoveries of GSH from artificial urine spiked at three levels (80, 400 and 800 ng·mL−1) are in the range of 94.6–98.6% with relative standard deviations (RSD) of <4.5% (n = 5). The method was applied to assessing the differences in urinary GSH between high-risk infants and healthy infants. The results show that the levels of GSH of normal infants are significantly higher than those of high-risk infants (P < 0.05).
Voltammetric aptasensor for bisphenol A based on the use of a MWCNT/Fe 3 O 4 @gold nanocomposite Microchim. Acta (IF 5.705) Pub Date : 2018-06-07 Mehdi Baghayeri, Reza Ansari, Marzieh Nodehi, Iman Razavipanah, Hojat Veisi
The present study describes an electrochemical aptamer-based method for the determination of bisphenol A (BPA). It is making use of gold nanoparticles (AuNPs) immobilized on a conjugate between multiwalled carbon nanotubes and thiol-functionalized magnetic nanoparticles (MWCNT/Fe3O4-SH) that are modified with an aptamer. The nanocomposite was characterized by Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometry, elemental mapping analysis and energy dispersive X-ray diffraction. The aptasensor, typically operated at 0.20 V (vs. Ag/AgCl), has a linear response in the 0.1 to 8 nM BPA concentration range, a low detection limit (0.03 nM), and high sensitivity (86.43 μA nM−1 cm−2). Voltammetric experiments were performed by using the hexacyanoferrate redox system as an electrochemical probe. The results indicate that the presence of AuNPs, magnetic nanoparticles and MWCNTs results a synergistic electrochemical augmentation. The method is highly selective, sensitive, efficient and environmentally friendly. The method was successfully applied to the determination of BPA in spiked real samples.
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