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Magnetic beads play an important role in the miniaturization of clinical diagnostics systems. In lab-on-chip platforms, beads can be made to link to a target species and can then be used for the manipulation and detection of this species. Current bead actuation systems utilize complex on-chip coil systems that offer low field strengths and little versatility. We demonstrate a novel system based on an external rotating magnetic field and on-chip soft-magnetic structures to focus the field locally. These structures were designed and optimized using finite element simulations in order to create a number of local flux density maxima. These maxima, to which the magnetic beads are attracted, move over the chip surface in a continuous way together with the rotation of the external field, resulting in a mechanism similar to that of a conveyor belt. A prototype was fabricated using PDMS molding techniques mixed with iron powder for the magnetic structures. In the subsequent experiments, a quadrupole electromagnet was used to create the rotating external field. We observed that beads formed agglomerates that rolled over the chip surface, just above the magnetic structures. Field rotation frequencies between 0.1-50 Hz were tested resulting in magnetic bead speeds of over 1 mm s -1 for the highest frequency. With this, we have shown that our novel concept works, combining a simple design and simple operation with a powerful and versatile method for bead actuation. This makes it a promising method for further research and utilization in lab-on-chip systems.

In this tutorial review, an overview of the why, what and how of enzyme immobilisation for use in biocatalysis is presented. The importance of biocatalysis in the context of green and sustainable chemicals manufacture is discussed and the necessity for immobilisation of enzymes as a key enabling technology for practical and commercial viability is emphasised. The underlying reasons for immobilisation are the need to improve the stability and recyclability of the biocatalyst compared to the free enzyme. The lower risk of product contamination with enzyme residues and low or no allergenicity are further advantages of immobilised enzymes. Methods for immobilisation are divided into three categories: adsorption on a carrier (support), encapsulation in a carrier, and cross-linking (carrier-free). General considerations regarding immobilisation, regardless of the method used, are immobilisation yield, immobilisation efficiency, activity recovery, enzyme loading (wt% in the biocatalyst) and the physical properties, e.g. particle size and density, hydrophobicity and mechanical robustness of the immobilisate, i.e. the immobilised enzyme as a whole (enzyme + support). The choice of immobilisate is also strongly dependent on the reactor configuration used, e.g. stirred tank, fixed bed, fluidised bed, and the mode of downstream processing. Emphasis is placed on relatively recent developments, such as the use of novel supports such as mesoporous silicas, hydrogels, and smart polymers, and cross-linked enzyme aggregates (CLEAs)., Biotechnology, Applied Sciences

Contains fulltext : 103489.pdf (publisher's version ) (Open Access), Many aspects of brain processing are intimately linked to brain rhythms. Essentially all classical brain rhythms, i.e., delta, theta, alpha, beta, and sleep waves, are highly heritable. This renders brain rhythms an interesting intermediate phenotype for cognitive and behavioral traits. One brain rhythm that has been particularly strongly linked to cognition is the gamma rhythm: it is involved in attention, short- and long-term memory, and conscious awareness. It has been described in sensory and motor cortices, association and control structures, and the hippocampus. In contrast to most other brain rhythms, the gamma frequency highly depends on stimulus and task conditions, suggesting a low heritability. However, the heritability of gamma has not been assessed. Here, we show that visually induced gamma-band synchronization in humans is strongly genetically determined. Eighty twin subjects (20 monozygotic and 20 dizygotic twin pairs) viewed a moving sinusoidal grating while their brain activity was recorded using magnetoencephalography. The stimulus induced spectrally confined gamma-band activity in sensors over visual cortex in all subjects, with individual peak frequencies ranging from 45 to 85 Hz. Gamma-band peak frequencies were highly correlated across monozygotic twins (r = 0.88), but not across dizygotic twins (r = 0.32) or unrelated subjects (r = 0.02). This implies a heritability of the gamma-band frequency of 91%. This strong genetic determination suggests that gamma-related cognitive functions are under close genetic control.

Contains fulltext : 89971.pdf (publisher's version ) (Closed access)

Nitrile hydratases (NHases, E.C. 4.2.1.84) catalyse the transformation of nitriles into the corresponding amides and were first discovered 30 years ago in studies on the microbial degradation of toxic cyano-group-containing compounds. The use of NHases in synthetic chemistry is especially interesting in conversions where the substrate or the product is labile at the high temperature or extreme pH employed in chemical nitrile hydration. However, also in the production of bulk chemicals like acrylamide, NHases offer a green alternative to chemical hydration. Besides mild reaction conditions, the potential advantage of using a nitrile hydratase as a catalyst is a high chemo-, regio-, and enantioselectivity. In this thesis new NHase containing organisms from soda lakes and soda soils in Mongolia and Russia were isolated. One of the NHases from these organisms was characterized in detail and subsequently it was demonstrated that it was possible to significantly increase the stability of this NHase by immobilisation in the form of a cross-linked enzyme aggregate (CLEA). Combining the aforementioned NHase CLEA with a CLEA of the hydroxynitrile lyase (HnL, E.C. 4.1.2.37) from Manihot esculenta enabled an efficient one-pot bienzymatic cascade for the production of enantiomerically enriched aliphatic ?-hydroxycarboxylic amides from the corresponding aldehydes and HCN. Finally, a small library of five purified NHases was screened on their enantioselectivity for several structurally different chiral nitriles. Some of these NHases were shown to have promising enantioselectivities (E > 100)., Biotechnology, Applied Sciences

An enrichment culture from saline soda soils, using acetate as carbon and energy source and 2- phenylpropionitrile as nitrogen source (PPN) at pH 10, resulted in the isolation of strain ANL-?CH3. The strain was identified as a representative of the genus Halomonas in the Gammaproteobacteria. The bacterium was capable of PPN utilization as a nitrogen source only, while phenylacetonitrile (PAN) served both as carbon, energy and nitrogen source. This capacity was not described previously for any other haloalkaliphilic bacteria. Apart from the nitriles mentioned above, resting cells of ANL- ?CH3 also hydrolyzed mandelonitrile, benzonitrile, acrylonitrile, and phenylglycinonitrile, presumably using nitrilase pathway. Neither nitrile hydratase nor amidase activity was detected. The isolate showed a capacity to grow with benzoate and salicylate as carbon and energy source and demonstrated the ability to completely mineralize PAN. These clearly indicated a potential to catabolize aromatic compounds. On the basis of unique phenotype and distinct phylogeny, strain ANL-?CH3 is proposed as a novel species of the genus Halomonas—Halomonas nitrilicus sp. nov., Biotechnology, Applied Sciences

DelftChemTech, Applied Sciences