Nucleic acid separation is an increasingly important tool for molecular biology. Before modern technologies could be used, nucleic acid separation had been a time- and work-consuming process based on several extraction and centrifugation steps, often limited by small yields and low purities of the separation products, and not suited for automation and up-scaling. During the last few years, specifically functionalised magnetic particles were developed. Together with an appropriate buffer system, they allow for the quick and efficient purification directly after their extraction from crude cell extracts. Centrifugation steps were avoided. In addition, the new approach provided for an easy automation of the entire process and the isolation of nucleic acids from larger sample volumes. This review describes traditional methods and methods based on magnetic particles for nucleic acid purification. The synthesis of a variety of magnetic particles is presented in more detail. Various suppliers of magnetic particles for nucleic acid separation as well as suppliers offering particle-based kits for a variety of different sample materials are listed. Furthermore, commercially available manual magnetic separators and automated systems for magnetic particle handling and liquid handling are mentioned.

Owing to their chemical and magnetic properties, magnetite nanoparticles are an interesting adsorbing material for biomolecules. The understanding of the interactions of simple biomolecules with inorganic nanoparticles is an important approach for research on the bio-nano interface and can constitute the fundamentals to manifold applications in biotechnology, medicine and catalysis. The aim of the work presented here is to compare the interaction of seven different amino acids (L-alanine, L-cysteine, Lglutamic acid, glycine, L-histidine, L-lysine, and L-serine) with magnetite nanoparticles in a colloidal system at pH 6. We investigate the influence of the side chain on the adsorption at a magnetite−water interface with incubation experiments. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and simultaneous thermal analysis (STA) reveal deeper insights into the interactions of amino acids with magnetite nanoparticles. The amino acids that contain polar side chains adsorb on the nanoparticles to a high degree. Cysteine demonstrates the highest adsorption capacity and the formation of cystine is observed. ATR-FTIR spectroscopy results indicate a strong influence of the carboxyl group and side chains on the binding mechanism of amino acids at the iron oxide surface. Our investigation offers novel knowledge into adsorption behavior at the bio-nano interface.

Iron oxide nanoparticles are of great scientific interest due to their huge versatility of applications. The oxidation process of magnetite to maghemite is difficult to monitor as both iron oxide polymorphs possess connatural chemical properties. Especially the surface composition and reactivity of these nanosystems, which are most relevant for interactions with their environment, are not completely understood. Here, the oxidation of magnetite is investigated under mild and harsh conditions in order to understand the oxidation behaviour and the chemical stability of transition forms. Therefore, the oxidation process, is investigated with Raman, Mössbauer and X-ray photoelectron spectroscopy as well as X-ray diffraction and magnetometry. The multi-analytical approach allows new insights into surface composition and rearrangement according to respective different depth profiles. For both conditions investigated, the ferrous iron components are oxidised prior to structural changes in the Fe-O vibrations and crystal structure. The process starts from the outer layers and is acid catalysed. Oxidation leads to a decrease of magnetisation which still remains higher than 54 emu g −1. The charge and surface reactivity can be affected by the different oxidation methods and the irreversible adsorption of acid molecules. Biocompatibility and catalytic properties of iron oxide nanoparticles open doors to future applications.

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During the last few decades, increasing interest in biological surfactants led to an intensification of research for the cost-efficient production of biosurfactants compared with traditional petrochemical surface-active components. The quest for alternative production strains also is associated with new demands on biosurfactant analysis. The present paper gives an overview of existing analytical methods, based on the example of rhamnolipids. The methods reviewed range from simple colorimetric testing to sophisticated chromatographic separation coupled with detection systems like mass spectrometry, by means of which detailed structural information is obtained. High-performance liquid chromatography (HPLC) coupled with mass spectrometry currently presents the most precise method for rhamnolipid identification and quantification. Suitable approaches to accelerate rhamnolipid quantification for better control of biosurfactant production are HPLC analysis directly from culture broth by adding an internal standard or Fourier transform infrared attenuated total reflectance spectroscopy measurements of culture broth as a possible quasi-online quantification method in the future. The search for alternative rhamnolipid-producing strains makes a structure analysis and constant adaptation of the existing quantification methods necessary. Therefore, simple colorimetric tests based on whole rhamnolipid content can be useful for strain and medium screening. Furthermore, rhamnolipid purification from a fermentation broth will be considered depending on the following application.

The purification of porcine gastric mucin was optimized and key properties such as gel formation at acidic pH, lubrication behavior and interactions of mucins with charged molecules were preserved.

Superparamagnetic nanoparticles have recently gained much attention due to their broad range of applicability including medical in vivo technologies, sensors, and as supports for catalysts. As magnetic affinity materials, they can be utilized for the development of new purification strategies for pharmaceuticals and other target molecules from crude lysates. Here, a short peptide tag based on a glutamate sequence is introduced and the adsorption of pure protein as well as protein from crude cell lysate at different conditions is demonstrated. Fused to a model protein this tag can be used to recognize and purify this protein from a fermentation broth by bare iron oxide nanoparticles (BIONs). Binding of up to 0.2 g protein per g nanoparticles can be achieved and recovered easily by switching to a citrate buffered system. For a deeper understanding of the separation process, the aggregation and agglomeration of the nanoparticle protein systems were monitored for binding and elution steps. Furthermore, an upscaling of the process to the liter scale and the separation of a green fluorescent protein (GFP) containing the affinity tag to purities of 70% from Escherichia coli fermentation broth was possible in a one step process by means of high gradient magnetic separation (HGMS).

Today, magnetic nanoparticles are present in multiple medical and industrial applications. We take a closer look at the synthesis of magnetic iron oxide nanoparticles through the co-precipitation of iron salts in an alkaline environment. The variation of the synthesis parameters (ion concentration, temperature, stirring rate, reaction time and dosing rate) change the structure and diameter of the nanoparticles. Magnetic iron oxide nanoparticles are characterized by X-ray diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM). Magnetic nanoparticles ranging from 5 to 16 nm in diameter were synthesized and their chemical structure was identified. Due to the evaluation of Raman spectra, TEM and XRD, the magnetite and maghemite nanoparticles can be observed and the proportion of phases and the particle size can be related to the synthesis conditions. We want to highlight the use of Raman active modes A 1g of spinel structured iron oxides to determine the content of magnetite and maghemite in our samples. Magnetite nanoparticles can be derived from highly alkaline conditions even without establishing an inert atmosphere during the synthesis. The correlation between the particle properties and the various parameters of the synthesis was modelled with linear mixture models. The two models can predict the particle size and the oxidation state of the synthesized nanoparticles, respectively. The modeling of synthesis parameters not only helps to improve synthesis conditions for iron oxide nanoparticles but to understand crystallization of nanomaterials.Crystals 2020, 10, 214 2 of 12 For these applications, an understanding and development of effective and low-cost synthesis routes are necessary. The size, stability and composition of magnetic nanoparticles need to be controlled in order to affect magnetic, optic and surface properties [5,14]. Since these physical and chemical properties are often related to the dimension of nanomaterials, the most simple approach is to investigate the size of nanoparticles for distinct synthesis conditions [2,[15][16][17]. Forge et al. and Roth et al. investigated the influence of several parameters on the particle size of iron oxide nanoparticles based on the alkaline co-precipitation synthesis [17][18][19]. Other studies focus on the formation pathways of iron oxide nanoparticles depending on the synthesis conditions and especially on the reaction time [20]. Such studies include the formation, which can be quite versatile for multiple synthesis routes [2,14,[20][21][22][23][24][25][26]. Although some works approach parameter studies by design of experiments, multiple questions concerning the co-precipitation are not understood [17,18]. For these nanoscale particles, it is quite challenging to characterize and predict their structure, especially at the surface [14,27]. Multiple approaches exist on classifying magnetic iron oxide nanoparticles and describing them according to their properties, which are strongly dependent on their environment, synthesis conditions...