Johan Drott

Porous silicon as the carrier matrix in microstructured enzyme reactors yielding high enzyme activities

Miniaturization and silicon integration of micro enzyme reactors for applications in micro total analysis systems (mu TASs) require new methods to achieve structures with a large surface area onto ...

Enhanced enzyme activity in silicon integrated enzyme reactors utilizing porous silicon as the coupling matrix

Abstract The performance of porous silicon as a coupling matrix for silicon integrated enzyme reactors has been investigated. A porous silicon layer in a water is expected to yield an increased catalytic activity when coupling an enzyme to the wafer due to the surface enlargement of the porous structure. The porous silicon layer is obtained by anodizing a 1 cm x 1 cm silicon die in a hydrofluoric acid/ethanol mixture at a constant current density of 10, 50 or 100 mA cm−2 for 50 min. Glucose oxidase is immobilized on the porous matrix of three dice and the enzyme activity of the silicon samples is monitored using a colorimetric assay. As a reference sample a polished die is also submitted to the enzyme immobilization. The three porous dice display higher glucose turn-over rates than the unetched reference die. Samples etched at lower current densities show increased turn-over rates. The maximum rise in turn-over rate is more than 30 times for the 10 mA cm−2 sample compared with the reference die. Porous silicon has the potential of being incorporated in a micro total analysis system (μTAS) to give highly efficient enzyme reactors.

Silicon wafer integrated enzyme reactors

Abstract Enzyme reactors were fabricated on silicon wafers using microstructuring technologies. The reactors were made of several parallel vertically-cut flow channels. The reactor structure occupied a wafer area of 3 ∗ 15 mm. Reactors with two different channel densities were fabricated: 10 channels/ mm, 165 μm deep; and 25 channels/mm, 235 μm deep. Glucose oxidase was immobilised on the reactors and their corresponding enzyme activities were monitored by a colourimetric assay. It was shown that a reactor surface are increase of 3 times gave rise to a proportional enzyme activity increase in the reactor. The maximum glucose turnover rate for the reactor with 25 channels/ mm was approximately 35 nmol/minute and the corresponding apparent K m was approximately 17 mM. A wafer integrated enzyme reactor was also operaed in a microdialysis-based system for continuous glucose monitoring, showing a linear response up to 4 mM glucose.

Rat sciatic nerve regeneration through a micromachined silicon chip.

The capacity of regenerating nerve fibres to grow through a perforated silicon chip was tested using the silicone chamber model for nerve regeneration. The chips were fabricated as circular membranes, 4 mm in diameter, thickness 60 microns, with a perforated area, 2 mm in diameter, in the centre. Three types of chips were fabricated utilizing anisotropic etching. The chips were glued with silicone adhesive between two halves of silicone rubber tubing (total length 8 mm, inner diameter 1.8 mm, outer diameter 3.0 mm) which was used to bridge a 4 mm gap between the proximal and distal nerve stumps of a transected rat sciatic nerve. The capacity of regenerating nerve fibres to grow through the holes of the chip was analysed by light and scanning electron microscopy after 4 or 16 weeks of regeneration. Furthermore, the muscle contractility force of the gastrocnemius muscle was measured after 16 weeks of regeneration and compared as a percentage of the contralateral uninjured side. Nerves generated through chips with hole diameters of 10 or 50 microns were morphological and functional failures. The nerve structures distal to chips with hole diameters of 100 microns contained many myelinated nerve fibres in a minifascicular pattern after both 4 and 16 weeks of regeneration. The muscle contractility force was 56% of that of contralateral control muscles.

Pore morphology influence on catalytic turn-over for enzyme activated porous silicon matrices

Abstract The enzyme glucose oxidase (GOx) was coupled to porous silicon of different morphologies and the catalytic turn-over of glucose was recorded for the samples. The recorded catalytic turn-over of the samples clearly indicated the influence of morphology, with respect to dopant concentration and current density, of the porous silicon carrier matrix. The highest rise in catalytic turn-over (350 times), when compared to a non-porous surface, was recorded for a sample with an n-type epilayer on an n+-type substrate anodised at 100 mA/cm2. A storage and operational stability measurement was performed on the sample showing the highest catalytic efficiency. After 5 months of refrigerated storage a 2% loss of activity was noted, and after 4 days of constant glucose load (0.5 mM) a 56% loss of activity was recorded. A BET (Brunauer, Emmet, and Teller) nitrogen adsorption analysis was performed on one of the substrate types, p+-type (0.001–0.025 Ω cm). In spite of the fine porous morphology with a high surface area the recorded enzyme activities were moderate. The pore morphology achieved on this substrate most likely comprised too small pores in a too dense porous matrix giving poor diffusion conditions to give efficient access for the enzyme during the coupling procedure and for the reactant transport during operation to fully utilise the surface enlargement of the porous layer.

Regeneration of axons from central neurons into microchips at the level of the spinal cord

AXONS from central neurons can regenerate into the tissue matrix formed within a silicone tube capped with two pieces of peripheral nerve, one of which had been sutured to a lesion in the spinal cord. Such axons can grow through a transversely positioned microchip in the tube. These observations suggest that it is feasible to establish functional contact between external electronic equipment and regenerating central nervous axons making it possible to monitor and control their electrical activity. The findings open new perspectives for restoration of motor and sensory functions following spinal cord lesions.

Improvements of silicon integrated GOx micro enzyme reactors by the use of porous silicon as a surface enlarging matrix

Micro flow-through cells were fabricated in silicon and were designed to work as micro enzyme reactors (columns) for glucose monitoring. The reactor design comprised a parallel channel structure with 32 channels, 50 /spl mu/m wide. A reactor with vertical channels yields a much larger surface area than a corresponding v-groove channel structure. Therefore, [110] silicon was used to allow the fabrication of channels with vertical walls (channel depth was 250 /spl mu/m). Glucose oxidase (GOx) can be immobilized to the silicon surface and earlier measurements have shown that the increase in enzyme activity corresponded to the surface area increase of such a channel structure. A new approach to surface enlargement was investigated. Planar silicon surfaces were anodised in an HF/ethanol etchant, yielding a spongious nanoporous silicon surface. Dice with three different porosities were fabricated and GOx was coupled to the porous dice. The increase in enzyme activity due to surface enlargement of the nanoporous structure was 33 times compared to a planar surface. The two surface enlarging strategies (vertical channel reactors and porous silicon) were subsequently combined, giving a parallel vertical channel structure covered by a porous silicon layer. This reactor structure displayed an enzyme activity increase of 100 times when compared to a non-porous channel structure.

A Micromachined Flow-through Cell For Continuous Pico Volume Sampling In An Analytical Flow

A micromashined flow-through cell for liquid sampling is presented. The flow channel is formed by two 350 pin deep silicon basins facing each other with a 60 pm diameter orifice in the Centre of one of the basins. A piezo-ceramic disc glued to the silicon basin opposite the orifice controls,the drop ejection in a drop-on-demand fashion. The ejected drops have a diameter of 40 prit, i.e. a drop volume of 34 pl. At an ejection frequency of 100 Hz, a sample flow of 0.2 0/min is obtained.

Porous silicon as an inherent surface enlarging layer for improved electrode performance in stimulation and recording applications

The performance of doped silicon and porous silicon as a new electrode material in neurophysiological applications is investigated. By increasing the surface area of adopted silicon region through anodisation in hydrofluoric acid it was found that the impedance parameters of the electrode were considerably improved. Impedance spectra of bare silicon electrodes, porous electrodes and platinum electroplated porous silicon electrodes are presented. It was found that porous silicon electrodes display a 2.5 times higher capacitance and the platinum electroplated porous silicon electrode displayed a 5 times higher capacitance when compared to the corresponding planar doped silicon electrode.

Porous Silicon as the Carrier Martix in a Micro Enzyme Reactor to Achieve a Highly Efficient and Long-Term Stable Glucose Sensor

Porous silicon with its spongious structure and vast surface enlargement was investigated as the carrier matrix for immobilised enzymes in micro enzyme reactors.