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Optical Detection Using Computer Screen Photo-assisted Techniques and Ellipsometry
Linköping University, Department of Physics, Chemistry and Biology, Applied Optics . Linköping University, The Institute of Technology.
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Two main subjects, ellipsometry and computer screen photo-assisted techniques (CSPT), form the main line in this thesis. Ellipsometry is an optical technique based on the detection of polarization changes of light upon interaction with a sample. As most optical detection techniques it is non-intrusive and an additional advantage is its high surface sensitivity: thickness resolution in the order of pm can in principle be achieved. Therefore, ellipsometry is widely used as a technique for determination of optical constants and layer thickness for thin-layer structures. Lately ellipsometry has also been proposed for sensing applications, utilizing the detection of changes in the properties of thin layers. One application is described in this thesis concerning the detection of volatile organic solvents in gas phase using modified porous silicon layers, fabricated by electrochemical etching of silicon to create nm-sized pores. This greatly increases the surface area, promoting gas detection because the number of adsorption sites increases. Other applications of ellipsometry discussed in this thesis are based on combination with CSPT.

CSPT is a way to exploit existing optical techniques for use in low-cost applications. In CSPT the computer screen itself is used as a (programmable) light source for optical measurements. For detection a web camera can be used and the whole measurement platform is formed by the computer. Since computers are available almost everywhere, this is a promising way to create optical measurement techniques for widespread use, for example in home-diagnostics. Since the only thing that needs to be added is a sample holder governing the physical or chemical process and directing the light, the cost can be kept very low. First, the use of CSPT for the measurement of fluorescence is described. Fluorescence is used in many detection applications, usually by chemically attaching a fluorescent marker molecule to a suitable species in the process and monitoring the fluorescent emission. The detection of fluorescence is shown to be possible using CSPT, first in a cuvette-based setup, then using a custom designed micro array. In the latter, polarizers were used for contrast enhancement, which in turn led to the implementation of an existing idea to test CSPT for ellipsometry measurements. In a first demonstration, involving thickness measurement of silicon dioxide on silicon, a thickness resolution in the order of nm was already achieved. After improvement of the system, gradients in protein layers could be detected, opening the door toward biosensor applications. Some further development will be needed to make the CSPT applications described here ready for the market, but the results so far are certainly promising.

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi , 2006.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1020
Keyword [en]
Optical sensing, Biohttps://www.diva-portal.org/liu/webform/form.jsp#paper0sensing, Ellipsometry, Computer Screen Photo-assisted Technique, Fluorescence, Immunoassays
National Category
Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:liu:diva-6392ISBN: 91-85523-70-4 (print)OAI: oai:DiVA.org:liu-6392DiVA: diva2:21799
Public defence
2006-06-02, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2006-05-04 Created: 2006-05-04 Last updated: 2013-10-14
List of papers
1. Improvement of porous silicon based gas sensors by polymer modification
Open this publication in new window or tab >>Improvement of porous silicon based gas sensors by polymer modification
2003 (English)In: Physica Status Solidi (A), ISSN 0031-8965, Vol. 197, no 2, 378-381 p.Article in journal (Refereed) Published
Abstract [en]

Gas sensing was performed using spectroscopic ellipsometry and porous silicon films. Modification of the porous layer by polymer deposition showed an increase in sensitivity to organic solvent vapor of up to 135%. The increase in sensitivity is strongly dependent on polymer concentration. At high concentrations, too much polymer is deposited, presumably blocking the pores, causing a decrease in sensitivity. At sufficiently low concentrations, the polymer causes a strong increase in sensitivity. This is assumed to be caused by the polymer being deposited inside the pores, where its interaction with the vapor influences the sensitivity. At very low concentration, the sensitivity approaches values obtained without polymer modification. The sensitivity increase is different for different vapors, pointing to possible selectivity enhancement.

Keyword
07.07.Df, 61.43.Gt, 78.67.Bf, 82.35.Gh
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-13772 (URN)10.1002/pssa.200306529 (DOI)
Available from: 2004-12-10 Created: 2004-12-10 Last updated: 2013-10-14
2. Enhancing classification capabilities of computer screen photo-assisted fluorescence fingerprinting
Open this publication in new window or tab >>Enhancing classification capabilities of computer screen photo-assisted fluorescence fingerprinting
2005 (English)In: Sensors and Actuators B: Chemical, ISSN 0925-4005, Vol. 110, no 2, 190-194 p.Article in journal (Refereed) Published
Abstract [en]

The separation of emission from transmitted light for the fingerprinting of fluorescent substances using a computer screen photo-assisted technique (CSPT) is demonstrated. CSPT is a technique for optical evaluation using a simple cell with just a standard computer set and a web camera as instrumentation. It has been demonstrated to be a versatile system for colorimetric and fluorescent fingerprinting. Here the omnidirectional property of fluorescent emission is utilized to separate it from the background, using a simple optical arrangement compatible with CSPT purposes. This enhances the classification capabilities and makes classification at sub-μM concentrations possible.

Keyword
Computer screen photo-assisted technique; Fluorescence; Spectral fingerprinting; Bioassays; Home tests
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-13774 (URN)10.1016/j.snb.2005.01.046 (DOI)
Available from: 2004-12-10 Created: 2004-12-10 Last updated: 2009-09-08
3. Two-dimensional micro array fluorescence fingerprinting with a computer screen photo-assisted technique
Open this publication in new window or tab >>Two-dimensional micro array fluorescence fingerprinting with a computer screen photo-assisted technique
2005 (English)In: Spectral Imaging: Instrumentation, Applications, and Analysis III, 2005, 9-15 p.Conference paper, Published paper (Other academic)
Abstract [en]

Detection and classification of fluorescent dyes are demonstrated using a computer screen photo-assisted technique (CSPT). This technique has previously been demonstrated for analyzing fluorescence from 96 wells microtiterplates (200 µl per well) and from a single cuvette with some optics to enhance sensitivity. In this work a custom designed array of wells with a volume of approximately 1 mu;l is used. In order to measure such small volumes without saturating the detector, the transmitted light is masked by placing the sample between two crossed polarizers. This arrangement blocks nearly all the transmitted light, while the emitted light, which is nearly unpolarized, can still be detected. The lowest amount (concentration x volume) of analyte detectable in this setup is about 40 times smaller than in the previous setups.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13835 (URN)10.1117/12.589586 (DOI)
Available from: 2006-05-04 Created: 2006-05-04 Last updated: 2009-04-28
4. Computer screen photo-assisted off-null ellipsometry
Open this publication in new window or tab >>Computer screen photo-assisted off-null ellipsometry
2006 (English)In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 45, no 30, 7795-7799 p.Article in journal (Refereed) Published
Abstract [en]

The ellipsometric measurement of thickness is demonstrated using a computer screen as a light source and a webcam as a detector, adding imaging off-null ellipsometry to the range of available computer screen photoassisted techniques. The results show good qualitative agreement with a simplified theoretical model and a thickness resolution in the nanometer range is achieved. The presented model can be used to optimize the setup for sensitivity. Since the computer screen serves as a homogeneous large area illumination source, which can be tuned to different intensities for different parts of the sample, a large sensitivity range can be obtained without sacrificing thickness resolution.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-13836 (URN)10.1364/AO.45.007795 (DOI)
Available from: 2006-05-04 Created: 2006-05-04 Last updated: 2017-12-13
5. Non-labeled immunodetection with a computer screen photo-assisted technique
Open this publication in new window or tab >>Non-labeled immunodetection with a computer screen photo-assisted technique
Manuscript (Other academic)
Identifiers
urn:nbn:se:liu:diva-13837 (URN)
Available from: 2006-05-04 Created: 2006-05-04 Last updated: 2010-01-13

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