Thomas Steen Hansen

Synergy of boric acid and added salts in the catalytic dehydration of hexoses to 5-hydroxymethylfurfural in water

In combination with various salts boric acid, B(OH)3, was shown to be an efficient, weak Lewis acid catalyst in the aqueous dehydration of fructose to 5-hydroxymethylfurfural (HMF) due to strong complexation between the boron atom and the hexoses. In the dehydration of a highly concentrated aqueous fructose solution (30 wt%), a HMF yield of 60% was achieved at 92% fructose conversion and a HMF selectivity of 65% with 100 g L−1B(OH)3 and 50 g L−1sodium chloride in the aqueous phase and methyl-isobutylketone (MIBK) as extracting solvent. Furthermore, the dehydration of glucose resulted in a yield of 14% HMF at 41% glucose conversion after 5 h at similar conditions. These results are highly competitive with currently reported aqueous HMF dehydration systems. In combination with the non-corrosive and non-toxic nature of the boric acid, compared to other well known homogeneous catalysts applicable for the dehydration process (e.g., H2SO4 and HCl), clearly, the boric acid-salt mixture is a very attractive catalyst system.

Injection molded chips with integrated conducting polymer electrodes for electroporation of cells

We present the design-concept for an all polymer injection molded single use microfluidic device. The fabricated devices comprise integrated conducting polymer electrodes and Luer fitting ports to allow for liquid and electrical access. A case study of low voltage electroporation of biological cells in suspension is presented. The working principle of the electroporation device is based on a focusing of the electric field by means of a constriction in the flow channel for the cells. We demonstrate the use of AC voltage for electroporation by applying a 1 kHz, ±50 V square pulse train to the electrodes and show delivery of polynucleotide fluorescent dye in 46% of human acute monocytic leukemia cells passing the constriction.

An all-polymer micropump based on the conductive polymer poly(3,4-ethylenedioxythiophene) and a polyurethane channel system

An all-polymer micropump was realized using the conductive polymer poly(3,4-ethylenedioxythiophene) (PEDT) as the active component. The pumping effect originated from an ac potential applied to an asymmetric array of interdigitated electrodes. The PEDT electrodes were fabricated using optical lithography and reactive ion etching, and dimensions down to 2 ?m could be successfully realized. The channel system was made from a flexible thermoplastic polyurethane. The chosen polyurethane exhibited good sealing without the possible contamination issues of silicones, adequate wetting without plasma treatment, and has the potential for mass production, e.g., by injection moulding. The assembled micropump showed a pumping speed of 150 ?m s?1 at a frequency of 10 kHz and an amplitude of 5 V. Higher potentials resulted in permanent damage to the pump electrodes. Encapsulation of the conducting polymer electrodes by an insulating polymer layer prevented electrode break-down at the cost of pumping efficiency. Continuous pumping for 40 min at 20 ?m s?1 without detectable pump degradation was demonstrated in this configuration.

Fast prototyping of injection molded polymer microfluidic chips

We present fast prototyping of injection molding tools by the definition of microfluidic structures in a light-curable epoxy (SU-8) directly on planar nickel mold inserts. Optimized prototype mold structures could withstand injection molding of more than 300 replicas in cyclic olefin copolymer (COC) without any signs of failure or release. The key parameters to avoid mold failure are maximum adhesion strength of the epoxy to the nickel insert and minimum interfacial energy of the epoxy pattern to the molded polymer. Optimal molding of microstructures with vertical sidewalls was found for nickel inserts pre-coated by silicon oxide before applying the structured epoxy, followed by coating of the epoxy by a fluorocarbon layer prior to injection molding. Further improvements in the mold stability were observed after homogeneous coating of the patterned epoxy by a second reflowed layer of epoxy, likely due to the resulting reduction in sidewall steepness. We employed the latter method for injection molding bondable polymer microfluidic chips with integrated conducting polymer electrode arrays that permitted the culture and on-chip analysis of cell spreading by impedance spectroscopy.

Multiferroic clusters: a new perspective for relaxor-type room-temperature multiferroics

Multiferroics are promising for sensor and memory applications, but despite all efforts invested in their research no single-phase material displaying both ferroelectricity and large magnetization at room-temperature has hitherto been reported. This situation has substantially been improved in the novel relaxor ferroelectric single-phase (BiFe0.9Co0.1O3)0.4-(Bi1/2K1/2TiO3)0.6, where polar nanoregions (PNR) transform into static-PNR (SPNR) as evidenced by piezoresponse force microscopy (PFM) and simultaneously enable congruent multiferroic clusters (MFC) to emerge from inherent strongly magnetic Bi(Fe,Co)O3 rich regions as verified by magnetic force microscopy (MFM) and secondary ion mass spectrometry (SIMS). The material’s exceptionally large Neel temperature TN = 670 ± 10 K, as found by neutron diffraction, is proposed to be a consequence of ferrimagnetic order in MFC. On these MFC, exceptionally large direct and converse magnetoelectric coupling coefficients, α ≈ 1.0 x 10-5 s/m at room-temperature, were measured by PFM and MFM respectively. We expect the non-ergodic relaxor properties which are governed by the Bi1/2K1/2TiO3 component to play a vital role in the strong ME coupling, by providing an electrically and mechanically flexible environment to MFC. This new class of non-ergodic relaxor multiferroics bears great potential for applications. Especially the prospect of a ME nanodot storage device seems appealing.

Efficient large volume electroporation of dendritic cells through micrometer scale manipulation of flow in a disposable polymer chip

We present a hybrid chip of polymer and stainless steel designed for high-throughput continuous electroporation of cells in suspension. The chip is constructed with two parallel stainless steel mesh electrodes oriented perpendicular to the liquid flow. The relatively high hydrodynamic resistance of the micrometer sized holes in the meshes compared to the main channel enforces an almost homogeneous flow velocity between the meshes. Thereby, very uniform electroporation of the cells can be accomplished. Successful electroporation of 20 million human dendritic cells with mRNA is demonstrated. The performance of the chip is similar to that of the traditional electroporation cuvette, but without an upper limit on the number of cells to be electroporated. The device is constructed with two female Luer parts and can easily be integrated with other microfluidic components. Furthermore it is fabricated from injection molded polymer parts and commercially available stainless steel mesh, making it suitable for inexpensive mass production.

Increased adsorption of histidine-tagged proteins onto tissue culture polystyrene

In this study we compare histidine-tagged and native proteins with regards to adsorption properties. We observe significantly increased adsorption of proteins with an incorporated polyhistidine amino acid motif (HIS-tag) onto tissue culture polystyrene (TCPS) compared to similar proteins without a HIS-tag. The effect is not observed on polystyrene (PS). Adsorption experiments have been performed at physiological pH (7.4) and the effect was only observed for the investigated proteins that have pI values below or around 7.4. Competitive adsorption experiments with imidazole and ethylenediaminetetraacetic acid (EDTA), as well as adsorption performed at different pH and ionic strength indicates that the high adsorption is caused by electrostatic interaction between negatively charged carboxylate groups on the TCPS surface and positively charged histidine residues in the proteins. Pre-adsorption of bovine serum albumin (BSA) does not decrease the adsorption of HIS-tagged proteins onto TCPS. Our findings identify a potential problem in using HIS-tagged signalling molecule in assays with cells cultured on TCPS, since the concentration of the molecule in solution might be affected and this could critically influence the assay outcome.

New junction materials by the direct growth of ZnO NWs on organic semiconductors

Ordered hetero-junctions using one dimensional inorganic nanostructures have been widely studied to develop devices such as high efficiency photovoltaic devices, light emitting diodes, catalysts, supercapacitors, lithium ion batteries and nanogenerators. High quality Schottky contacts can be obtained by the spin coating of conducting polymer dispersions/solutions onto inorganic nanostructures; however, the interaction of polar surfaces of the nanostructures with chemically active materials in the spin coating solution makes the junctions less reliable. In the present work, we show that high quality junctions can be fabricated by either directly growing the nanostructures onto the vapour phase polymerised (VPP) poly(3,4-ethylenedioxythiophene) (PEDOT) substrates or sandwiching VPP polymerised substrates, thereby avoiding any unwanted interactions with the acidic additives from the polymer solution at the organic–inorganic interfaces. The I–V measurements proved that the direct growth of ZnO NWs on PEDOT coated substrates creates an ohmic contact, whereas the PEDOT layer on top surface produces a Schottky contact due to the dipole moment with the polar ends.