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排序方式: 共有591条查询结果,搜索用时 15 毫秒
91.
92.
Limbikani Matumba Christof Van Poucke Emmanuel Njumbe Ediage Sarah De Saeger 《Critical reviews in food science and nutrition》2017,57(8):1584-1592
Following the discovery of aflatoxins in the early 1960s, there have been many studies leading to the uncovering of many mycotoxins and the understanding of associated health effects in animals and humans. Consequently, there has been a global increase in the number of countries with mycotoxin regulations in foods. However, many African countries have only regulations for aflatoxins (or a few other mycotoxins) in specific foods, or no regulations at all. This paper critically reviews the challenges thwarting the establishment of mycotoxin regulations and their impacts on human dietary mycotoxin exposure in Africa. Mycotoxin regulatory limits for different countries are compared with mycotoxin tolerable daily intakes established by international food safety bodies taking into account consumption patterns. The agrarian setup, food insecurity, and mycotoxin analytical challenges in African countries are discussed; and more feasible mycotoxin dietary exposure reduction strategies are proposed. 相似文献
93.
Giuseppe Arrabito Stephanie Reisewitz Leif Dehmelt Philippe I. Bastiaens Bruno Pignataro Hendrik Schroeder Christof M. Niemeyer 《Small (Weinheim an der Bergstrasse, Germany)》2013,9(24):4243-4249
A general methodology for patterning of multiple protein ligands with lateral dimensions below those of single cells is described. It employs dip pen nanolithography (DPN) patterning of DNA oligonucleotides which are then used as capture strands for DNA‐directed immobilization (DDI) of oligonucleotide‐tagged proteins. This study reports the development and optimization of PEG‐based liquid ink, used as carrier for the immobilization of alkylamino‐labeled DNA oligomers on chemically activated glass surfaces. The resulting DNA arrays have typical spot sizes of 4–5 μm with a pitch of 12 μm micrometer. It is demonstrated that the arrays can be further functionalized with covalent DNA‐streptavidin (DNA‐STV) conjugates bearing ligands recognized by cells. To this end, biotinylated epidermal growth factor (EGF) is coupled to the DNA‐STV conjugates, the resulting constructs are hybridized with the DNA arrays and the resulting surfaces used for the culturing of MCF‐7 (human breast adenocarcinoma) cells. Owing to the lateral diffusion of transmembrane proteins in the cell's plasma membrane, specific recruitment and concentration of EGF receptor can be induced specifically at the sites where the ligands are bound on the solid substrate. This is a clear demonstration that this method is suitable for precise functional manipulations of subcellular areas within living cells. 相似文献
94.
Katrin Vogel Maximilian Glettenberg Hendrik Schroeder Christof M. Niemeyer 《Small (Weinheim an der Bergstrasse, Germany)》2013,9(2):255-262
A novel bioorthogonal method for the modification of cells with single‐stranded DNA oligomers is compared to five alternative methods with respect to labeling efficacy, specificity, and effects on cell viability. The new method is based on oxime ligation of aminooxybiotin to aldehyde groups installed by periodate cleavage of cell‐surface glycans, followed by the coupling of preformed DNA–streptavidin conjugates. As compared with two literature‐reported methods based on direct coupling of N‐hydroxysuccinimidyl (NHS)–DNA or NHS–biotinylation as well as with techniques based on strain‐promoted alkyne‐azide cycloaddition, this method shows the highest labeling densities and is sufficiently mild to avoid cell damage. Functionality of the DNA tags is demonstrated by DNA‐directed immobilization on solid substrates and assembly of small cell aggregates. 相似文献
95.
Christof Vockenhuber Marcus ChristlCornelia Hofmann Johannes LachnerArnold Milenko Müller Hans-Arno Synal 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2011,269(24):3199-3203
The performance of the compact ETH-TANDY system for accelerator mass spectrometry measurements of 236U is presented. Despite the low ion energies of around 1.2 MeV we can demonstrate a background level that is comparable to larger facilities. The careful ion-optical design of the high-energy spectrometer leads to a high suppression of neighboring isotopes sufficient to measure samples with isotopic ratios of 236U/238U > 10-11 the ion chamber only, as demonstrated by systematic investigations with different slit settings and time-of-flight measurements. Additionally, a high overall efficiency is achieved due to a high transmission through the accelerator. 相似文献
96.
Object
Two approaches of reconstructing undersampled partial k-space data, acquired with multiple coils are compared: homodyne detection combined with SENSE (HM_SENSE) and analytic image reconstruction combined with SENSE (AI_SENSE). The latter overcomes limitations of HM_ SENSE by considering aliased images as analytic thus avoiding the need for phase correction required for HM_SENSE. 相似文献97.
Dana E Gheorghe Lili Cui Christof Karmonik Audrius Brazdeikis Jose M Penaloza Joseph K Young Rebekah A Drezek Malavosklish Bikram 《Nanoscale research letters》2011,6(1):554
We have developed novel gold-silver alloy nanoshells as magnetic resonance imaging (MRI) dual T1 (positive) and T2 (negative) contrast agents as an alternative to typical gadolinium (Gd)-based contrast agents. Specifically, we have doped iron oxide nanoparticles with Gd ions and sequestered the ions within the core by coating the nanoparticles with an alloy of gold and silver. Thus, these nanoparticles are very innovative and have the potential to overcome toxicities related to renal clearance of contrast agents such as nephrogenic systemic fibrosis. The morphology of the attained nanoparticles was characterized by XRD which demonstrated the successful incorporation of Gd(III) ions into the structure of the magnetite, with no major alterations of the spinel structure, as well as the growth of the gold-silver alloy shells. This was supported by TEM, ICP-AES, and SEM/EDS data. The nanoshells showed a saturation magnetization of 38 emu/g because of the presence of Gd ions within the crystalline structure with r1 and r2 values of 0.0119 and 0.9229 mL mg-1 s-1, respectively (Au:Ag alloy = 1:1). T1- and T2-weighted images of the nanoshells showed that these agents can both increase the surrounding water proton signals in the T1-weighted image and reduce the signal in T2-weighted images. The as-synthesized nanoparticles exhibited strong absorption in the range of 600-800 nm, their optical properties being strongly dependent upon the thickness of the gold-silver alloy shell. Thus, these nanoshells have the potential to be utilized for tumor cell ablation because of their absorption as well as an imaging agent. 相似文献
98.
Dominiczak M Otubo L Alamarguy D Houzé F Volz S Noël S Bai J 《Nanoscale research letters》2011,6(1):335
Using an atomic force microscope (AFM) at a controlled contact force, we report the electrical signal response of multi-walled carbon nanotubes (MWCNTs) disposed on a golden thin film. In this investigation, we highlight first the theoretical calculation of the contact resistance between two types of conductive tips (metal-coated and doped diamond-coated), individual MWCNTs and golden substrate. We also propose a circuit analysis model to schematize the «tip-CNT-substrate» junction by means of a series-parallel resistance network. We estimate the contact resistance R of each contribution of the junction such as Rtip-CNT, RCNT-substrate and Rtip-substrate by using the Sharvin resistance model. Our final objective is thus to deduce the CNT intrinsic radial resistance taking into account the calculated electrical resistance values with the global resistance measured experimentally. An unwished electrochemical phenomenon at the tip apex has also been evidenced by performing measurements at different bias voltages with diamond tips. For negative tip-substrate bias, a systematic degradation in color and contrast of the electrical cartography occurs, consisting of an important and non-reversible increase of the measured resistance. This effect is attributed to the oxidation of some amorphous carbon areas scattered over the diamond layer covering the tip. For a direct polarization, the CNT and substrate surface can in turn be modified by an oxidation mechanism. 相似文献
99.
Hendrik Schröder Linda Hoffmann Joachim Müller Petra Alhorn Markus Fleger Andreas Neyer Christof M. Niemeyer 《Small (Weinheim an der Bergstrasse, Germany)》2009,5(13):1547-1552
A microfluidic polymer chip for the self‐assembly of DNA conjugates through DNA‐directed immobilization is developed. The chip is fabricated from two parts, one of which contains a microfluidic channel produced from poly(dimethylsiloxane) (PDMS) by replica‐casting technique using a mold prepared by photolithographic techniques. The microfluidic part is sealed by covalent bonding with a chemically activated glass slide containing a DNA oligonucleotide microarray. The dimension of the PDMS–glass microfluidic chip is equivalent to standard microscope slides (76 × 26 mm2). The DNA microarray surface inside the microfluidic channels is configured through conventional spotting, and the resulting DNA patches can be conveniently addressed with compounds containing complementary DNA tags. To demonstrate the utility of the addressable surface within the microfluidic channel, DNA‐directed immobilization (DDI) of DNA‐modified gold nanoparticles (AuNPs) and DNA‐conjugates of the enzymes glucose oxidase (GOx) and horseradish peroxidase (HRP) are carried out. DDI of AuNPs is used to demonstrate site selectivity and reversibility of the surface‐modification process. In the case of the DNA–enzyme conjugates, the patterned assembly of the two enzymes allows the establishment and investigation of the coupled reaction of GOx and HRP, with particular emphasis on surface coverage and lateral flow rates. The results demonstrate that this addressable chip is well suited for the generation of fluidically coupled multi‐enzyme microreactors. 相似文献
100.