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Porous Silicon -an enzyme coupling matrix for micromachined reactors

Drott, Johan LU (1997)
Abstract (Swedish)
Popular Abstract in Swedish

<i>Avhandlingen beskriver forskningen kring miniatyriserade enzymreaktorer - nyckelkomponenter i system för diabetsövervakning. Målet är att systemet kontinuerligt och under flera dagar skall kunna mäta glukosstatus hos bäraren. Provtagningstekniken för systemet är mikrodialys; en prob instucken i bukfettvävnaden ger ett prov som innehåller glukos. Analysen av detta prov sker i en "mikrofabrik" tillverkad i kisel. För att öka effekten i "fabriken" har poröst kisel utnyttjats. Det porösa ytskiktet ger en ytförstorande effekt vilket leder till en långtidsstabil sensor.</i>



Med hjälp av mikrostruktureringsteknik, eller mikromekanik, är det möjligt att skapa strukturer... (More)
Popular Abstract in Swedish

<i>Avhandlingen beskriver forskningen kring miniatyriserade enzymreaktorer - nyckelkomponenter i system för diabetsövervakning. Målet är att systemet kontinuerligt och under flera dagar skall kunna mäta glukosstatus hos bäraren. Provtagningstekniken för systemet är mikrodialys; en prob instucken i bukfettvävnaden ger ett prov som innehåller glukos. Analysen av detta prov sker i en "mikrofabrik" tillverkad i kisel. För att öka effekten i "fabriken" har poröst kisel utnyttjats. Det porösa ytskiktet ger en ytförstorande effekt vilket leder till en långtidsstabil sensor.</i>



Med hjälp av mikrostruktureringsteknik, eller mikromekanik, är det möjligt att skapa strukturer i mikrometerskala. Dessa strukturer kan byggas samman till små fabriker, där t ex biokemisk analys kan utföras. Vinsten med att miniatyrisera är i detta fall de små provvolymerna och därmed den låga åtgången av analyter. Detta passar utmärkt samman med kraven som ställs av ett mätsystem som kopplas till mikrodialys och således för en användning inom bärbar diabeteskontroll.



Analysmetoden i "fabriken", eller reaktorn, bygger på att ett enzym bryter ned glukos och under denna process förbrukas syre. Genom att mäta syrgasförbrukningen kan glukoskoncentrationen i provet fastställas. Yven om enzymet endast är en katalysator till glukosnedbrytningen, förbrukas en viss del av enzymet. För att uppnå målet med en långtidsstabil sensor trots förlusten av enzym måste därför ett överskott av enzym vara tillgängligt i reaktorn.



Avhandlingen visar att poröst kisel är ett mycket lämpligt material att binda enzymer vid. Genom att använda poröst kisel i en miniatyriserad enzymreaktor ökar effektiviteten minst en faktor 170 jämfört med en liknande reaktor utan poröst kisel. Avhandlingen visar också hur det porösa kislets morfologi och djupet av det porösa skiktet påverkar reaktorns effektivitet.



Tillverkningsprocessen för att framställa poröst kisel kan kombineras med andra mikrostruktureringstekniker varför det nu är möjligt att tillverka en helt integrerad högeffektiv mikroenzymreaktor på ett enda kiselchips. Alltså en hel kemisk mikrofabrik stor som ett frimärke med möjlighet att ge information om glukosstatus. (Less)
Abstract
The development of a miniaturised silicon wafer integrated enzyme reactor is described. The reactor was micromachined by anisotropic wet etching of (110) silicon. The enzyme glucose oxidase (GOx) was coupled to the reactor surface with standard methods of immobilising enzyme to silica. The glucose turn-over rate was monitored following a colourimetric assay. The advantage, in terms of high surface area per volume ratio, of utilising (110) silicon for microreactor fabrication compared to (100) silicon was demonstrated. Two reactors with different channel widths (50 and 20 µm) and channel densities (10 and 25 per millimetre) were compared, yielding a proportionally increased enzyme activity, for the reactor with the highest surface area (20... (More)
The development of a miniaturised silicon wafer integrated enzyme reactor is described. The reactor was micromachined by anisotropic wet etching of (110) silicon. The enzyme glucose oxidase (GOx) was coupled to the reactor surface with standard methods of immobilising enzyme to silica. The glucose turn-over rate was monitored following a colourimetric assay. The advantage, in terms of high surface area per volume ratio, of utilising (110) silicon for microreactor fabrication compared to (100) silicon was demonstrated. Two reactors with different channel widths (50 and 20 µm) and channel densities (10 and 25 per millimetre) were compared, yielding a proportionally increased enzyme activity, for the reactor with the highest surface area (20 µm channels, 25 channels per millimetre).



A novel method, utilising porous silicon as a coupling matrix, to increase the surface area for enzyme coupling was investigated. A porous silicon layer was fabricated on samples by anodic dissolution of silicon in hydrofluoric acid. Three different pore morphologies were generated by anodisation at (10, 50 and 100 mA cm<sup>-2</sup>). Glucose oxidase was coupled to the samples and a non porous reference sample. The sample anodised at 10 mA cm<sup>-2</sup> displayed a 30-fold increased catalytic efficiency, compared to the non porous reference sample. The possibility of generating porous silicon on vertical channel type silicon reactors were also demonstrated. A porous silicon layer was generated on an anisotropically preetched vertical channel type microreactor. GOx was immobilised in the reactors and the glucose turn-over rate was monitored. A more than 100-fold increase in catalytic efficiency was recorded for a reactor anodised at 50 mA cm<sup>-2</sup>, compared to a non porous reference reactor.



The applicability of micro enzyme reactors was demonstrated by immobilising ß-fructose onto a porous channel type reactor. Sucrose monitoring was performed utilising Fourier transform infrared (FTIR) spectroscopy system with the micro enzyme reactor as a key component, the dissociation of sucrose into glucose and fructose. The miniaturised FTIR spectroscopy system was used for sucrose analysis of crude real samples from commercial soft drinks showing results in accordance with standardised sucrose test-kits.



The influence of pore morphology was investigated to further improve the catalytic efficiency of enzyme activated porous silicon carrier matrices. Porous silicon was generated on substrates of p- and n-type silicon with different dopant concentrations. For each type of substrate, the porous layer was generated at three current densities (10, 50 and 100 mA cm<sup>2</sup>). The porous samples and a non porous reference sample was enzyme activated with GOx. A 350-fold increase in glucose turn-over rate, compared to the reference, was recorded for an n-type epilayer on n<sup>+</sup>-type substrate anodised at 100mAcm<sup>-2</sup>. The influence of the porous silicon matrix depth was also investigated, for planar samples and vertical channel type reactors. In this investigation porous silicon layers were fabricated at two current densities and for three depths at each current density. A 170-fold increase in catalytic turn-over, compared to a non porous reference, was recorded for a reactor with an average porous depth of 10 µm. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • van den Berg, Albert, MESA Research Institute, University of Twente, The Netherlands
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Instrumentation technology, glucose, biosensor, immobilised enzyme, porous silicon, microreactor, Mät- och instrumenteringsteknik
pages
137 pages
defense location
E:1406, Sweden
defense date
1997-12-18 10:15
external identifiers
  • Other:ISRN: LUTEDX/TEEM--1062--SE
ISSN
0346-6221
language
English
LU publication?
yes
id
4aabfc55-a65a-4884-9305-0935447ecd8b (old id 29759)
date added to LUP
2007-06-14 09:02:20
date last changed
2016-09-19 08:45:00
@misc{4aabfc55-a65a-4884-9305-0935447ecd8b,
  abstract     = {The development of a miniaturised silicon wafer integrated enzyme reactor is described. The reactor was micromachined by anisotropic wet etching of (110) silicon. The enzyme glucose oxidase (GOx) was coupled to the reactor surface with standard methods of immobilising enzyme to silica. The glucose turn-over rate was monitored following a colourimetric assay. The advantage, in terms of high surface area per volume ratio, of utilising (110) silicon for microreactor fabrication compared to (100) silicon was demonstrated. Two reactors with different channel widths (50 and 20 µm) and channel densities (10 and 25 per millimetre) were compared, yielding a proportionally increased enzyme activity, for the reactor with the highest surface area (20 µm channels, 25 channels per millimetre).<br/><br>
<br/><br>
A novel method, utilising porous silicon as a coupling matrix, to increase the surface area for enzyme coupling was investigated. A porous silicon layer was fabricated on samples by anodic dissolution of silicon in hydrofluoric acid. Three different pore morphologies were generated by anodisation at (10, 50 and 100 mA cm&lt;sup&gt;-2&lt;/sup&gt;). Glucose oxidase was coupled to the samples and a non porous reference sample. The sample anodised at 10 mA cm&lt;sup&gt;-2&lt;/sup&gt; displayed a 30-fold increased catalytic efficiency, compared to the non porous reference sample. The possibility of generating porous silicon on vertical channel type silicon reactors were also demonstrated. A porous silicon layer was generated on an anisotropically preetched vertical channel type microreactor. GOx was immobilised in the reactors and the glucose turn-over rate was monitored. A more than 100-fold increase in catalytic efficiency was recorded for a reactor anodised at 50 mA cm&lt;sup&gt;-2&lt;/sup&gt;, compared to a non porous reference reactor.<br/><br>
<br/><br>
The applicability of micro enzyme reactors was demonstrated by immobilising ß-fructose onto a porous channel type reactor. Sucrose monitoring was performed utilising Fourier transform infrared (FTIR) spectroscopy system with the micro enzyme reactor as a key component, the dissociation of sucrose into glucose and fructose. The miniaturised FTIR spectroscopy system was used for sucrose analysis of crude real samples from commercial soft drinks showing results in accordance with standardised sucrose test-kits.<br/><br>
<br/><br>
The influence of pore morphology was investigated to further improve the catalytic efficiency of enzyme activated porous silicon carrier matrices. Porous silicon was generated on substrates of p- and n-type silicon with different dopant concentrations. For each type of substrate, the porous layer was generated at three current densities (10, 50 and 100 mA cm&lt;sup&gt;2&lt;/sup&gt;). The porous samples and a non porous reference sample was enzyme activated with GOx. A 350-fold increase in glucose turn-over rate, compared to the reference, was recorded for an n-type epilayer on n&lt;sup&gt;+&lt;/sup&gt;-type substrate anodised at 100mAcm&lt;sup&gt;-2&lt;/sup&gt;. The influence of the porous silicon matrix depth was also investigated, for planar samples and vertical channel type reactors. In this investigation porous silicon layers were fabricated at two current densities and for three depths at each current density. A 170-fold increase in catalytic turn-over, compared to a non porous reference, was recorded for a reactor with an average porous depth of 10 µm.},
  author       = {Drott, Johan},
  issn         = {0346-6221},
  keyword      = {Instrumentation technology,glucose,biosensor,immobilised enzyme,porous silicon,microreactor,Mät- och instrumenteringsteknik},
  language     = {eng},
  pages        = {137},
  title        = {Porous Silicon -an enzyme coupling matrix for micromachined reactors},
  year         = {1997},
}