Hybrid nanoparticles based on magnetic multiwalled carbon nanotube-nanoC18SiO2 composites for solid phase extraction of mycotoxins prior to their determination by LC-MS

Mycotoxins are a group of compounds produced by various fungi and excreted into the matrices on which they grow, often food intended for human consumption or animal feed. The high toxicity and carcinogenicity of these compounds and their ability to cause various pathological conditions has led to widespread screening of foods and feeds potentially polluted with them. Maximum permissible levels in different matrices have also been established for some toxins. As these are quite low, analytical methods for determination of mycotoxins have to be both sensitive and specific. In addition, an appropriate sample preparation and pre-concentration method is needed to isolate analytes from rather complicated samples. In this article, an overview of methods for analysis and sample preparation published in the last ten years is given for the most often encountered mycotoxins in different samples, mainly in food. Special emphasis is on liquid chromatography with fluorescence and mass spectrometric detection, while in the field of sample preparation various solid-phase extraction approaches are discussed. However, an overview of other analytical and sample preparation methods less often used is also given. Finally, different matrices where mycotoxins have to be determined are discussed with the emphasis on their specific characteristics important for the analysis (human food and beverages, animal feed, biological samples, environmental samples). Various issues important for accurate qualitative and quantitative analyses are critically discussed: sampling and choice of representative sample, sample preparation and possible bias associated with it, specificity of the analytical method and critical evaluation of results.

The alignment of multiwalled carbon nanotubes (MWNTs) has been accomplished through deposition of uniform layers of magnetite/maghemite nanoparticles (diameter = 6-10 nm) and use of an external magnetic field. The coating of CNTs with magnetic nanoparticles was performed by combining the polymer wrapping and layer-by-layer (LbL) assembly techniques. The particle-coated MWNTs are superparamagnetic and can be aligned at room temperature on any substrate by deposition from an aqueous solution in an external field B = 0.2 T. The volume magnetization of the particle coated MWNTs is found to be enhanced by 17% compared to the pure particles in a powder indicating that either the adsorption process onto the CNTs changes the particle magnetization, or the MWNTs carry an intrinsic magnetization due to remaining Ni used as a catalyst for the growth process.

Magnetic multiwalled carbon nanotubes (MWNTs) were facilely prepared by the electrostatic self-assembly approach. Poly(2-diethylaminoethyl methacrylate) (PDEAEMA) was covalently grafted onto the surfaces of MWNTs by MWNT-initiated in situ atom transfer radical polymerization (ATRP) of 2-diethylaminoethyl methacrylate (DEAEMA). The PDEAEMA-grafted MWNTs were quaternized with methyl iodide (CH(3)I), resulting in cationic polyelectrolyte-grafted MWNTs (MWNT-PAmI). Magnetic iron oxide (Fe(3)O(4)) nanoparticles were loaded onto the MWNT surfaces by electrostatic self-assembling between MWNT-PAmI and Fe(3)O(4), affording magnetic nanotubes. The assembled capability of the nanoparticles can be adjusted to some extent by changing the feed ratio of Fe(3)O(4) to MWNT-PAmI. The obtained magnetic nanotubes were characterized with TEM, EDS, STEM, and element mapping analyses. TEM and EDS measurements confirmed the nanostructures and the components of the resulting nanoobjects. The magnetic nanotubes were assembled onto sheep red blood cells in a phosphate buffer solution, forming magnetic cells. The blood cells attached with or without magnetic nanotubes can be selectively manipulated in a magnetic field. These results promise a general and efficient strategy to magnetic nanotubes and the fascinating potential of such magnetic nanoobjects in applications of bionanoscience and technology.