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Self Assembled Monolayers for Quartz Crystal Microbalance based Biosensing
Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular Physics . Linköping University, The Institute of Technology.
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The work in this thesis has been focused on developing surfaces for use in biosensor systems, especially for quartz crystal microbalances. The surfaces were prepared by adsorption of organosulfur molecules onto gold substrates, so called self assembled monolayers (SAMs). By chemical synthesis these thiols can be specifically tailored to provide surfaces with desired properties. The investigated surfaces were all based on thiols terminated with carboxylic acid groups to render hydrophilic surfaces onto which desired proteins can be covalently attached.

In order to increase the performance of two dimensional carboxyl surfaces, a method for improving the immobilization of proteins to the surface was investigated. The immobilization levels of antibodies were increased by using N-hydroxysulfo-succinimide (sulfo-NHS), instead of N-hydroxy-succinimide (NHS), as stabilizer of the amine reactive intermediate formed by reaction of the carboxyl groups with 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC). The negatively charged sulfo-NHS intermediate promotes the attraction of overall positively charged proteins and enables immobilization also at low pH. In addition, the orientation of the immobilized antibodies was shown to be dependent on the pI of the antibody and to have a profound effect on the subsequent interaction with the antigen.

The organization of carboxyl terminated SAMs can be poor due to the repellation between the polar terminal groups. By using acidified ethanol as solvent during the assembly step of monolayer formation, the organization in carboxyl terminated alkyl and oligo(ethylene glycol) SAMs was improved. However, the carboxyl groups were found to be converted to ethyl esters, the rate being related to the acid strength. Furthermore, the long-term stability of carboxyl oligo(ethylene glycol) SAMs was investigated. Here, the effect of alkyl chain length on the storage stability was of interest. A short alkyl chain was shown to have a profound negative effect on the storage stability of the SAM, resulting in decomposition and loss of functionality over time compared to when thiols with longer alkyl chains were studied.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2009. , 31 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1408
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-19679Local ID: LiU-TEK-LIC-2009:16ISBN: 987-91-7393-587-6 OAI: oai:DiVA.org:liu-19679DiVA: diva2:227244
Presentation
2009-08-17, Planck, Fysikhuset, Campus Valla, Linköpings Universitet, Linköping, 13:15 (English)
Opponent
Supervisors
Available from: 2009-07-14 Created: 2009-07-10 Last updated: 2009-07-14Bibliographically approved
List of papers
1. Optimizing immobilization conditions on a two dimensional carboxylbiosensor surface: pH dependence of antibody orientation andantigen binding capacity
Open this publication in new window or tab >>Optimizing immobilization conditions on a two dimensional carboxylbiosensor surface: pH dependence of antibody orientation andantigen binding capacity
2009 (English)In: Analytical Biochemistry, ISSN 0003-2697, E-ISSN 1096-0309Article in journal (Other academic) Submitted
Abstract [en]

The performance of immunosensors is highly dependent on the amount of immobilized antibodies and their remaining antigen binding capacity. In this work, a method for immobilization of antibodies on a two dimensional carboxyl surface has been optimized using quartz crystal microbalance biosensors. We have shown that successful immobilization is highly dependent on surface pKa, antibody pI and pH of immobilization buffer. By use of EDC/sulfo-NHS activation reagents, the effect of the intrinsic surface pKa is avoided and immobilization also at very low pH has been made possible which is of importance for immobilization of acidic proteins. Generic immobilization conditions were demonstrated on a panel of antibodies which resulted in an average coefficient of variation of 4% for the immobilization of these antibodies.

Antigen binding capacity as a function of immobilization pH was studied. In most cases the antigen binding capacity followed the immobilization response. However, the antigen to antibody binding ratio differed between the antibodies investigated, and for one of the antibodies, the antigen binding capacity was significantly lower than expected from immobilization in a certain pH range. Tests with anti-Fc and anti-Fab antibodies on different antibody surfaces showed that the orientation of the antibodies on the surface had a profound effect on the antigen binding capacity of the immobilized antibodies.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-19690 (URN)
Available from: 2009-07-14 Created: 2009-07-14 Last updated: 2017-12-13Bibliographically approved
2. Esterification of self-assembled carboxylic acid-terminated thiolmonolayers in acid environment: A time dependent study
Open this publication in new window or tab >>Esterification of self-assembled carboxylic acid-terminated thiolmonolayers in acid environment: A time dependent study
2010 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, no 2, 821-829 p.Article in journal (Refereed) Published
Abstract [en]

This contribution reports on the influence of acids on the quality of carboxylic acid terminated self-assembled monolayers (SAMs) on gold prepared from ethanolic solution of HS-(CH2)15-COOH and HS-(CH2)11CONH–(EG)6CH2-COOH. Null ellipsometry, contact angle goniometry and infrared reflection-absorption spectroscopy are used to monitor the physical and chemical changes occurring within the SAMs upon acid post treatment; after incubation with acids present in the solution; and after incubation in aged acid containing solutions. The presence of acid has a positive effect on the crystallinity, packing and orientation of the supporting alkyl and ethylene glycol subunits of the SAM. Our studies also confirm previous findings stating that the carboxylic groups are rapidly converted into ethyl ester groups in the presence of hydrochloric acid in the incubation solution. It is also evident that the conversion occurs in the presence of the weaker acid, acetic acid, although at a much slower rate than for hydrochloric acid. This is a new observation that has not been reported on before. The physical and chemical characterization is also complemented with a functional bioaffinity study. The functional evaluation revealed that the present model system was surprisingly insensitive to the degree of esterification of the carboxylic acid SAMs, but that 4 weeks of storage of the two investigated thiols in hydrochloric acid containing ethanol resulted in SAMs that were completely inactive with respect to immobilization and subsequent binding of the antigen. It was encouraging to note that the non-specific binding of both antigen and antibody was extremely low on the two SAMs, regardless of the relative amount of ethyl esters on the surface.

Place, publisher, year, edition, pages
ACS, 2010
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-19691 (URN)10.1021/la902255j (DOI)
Available from: 2009-07-14 Created: 2009-07-14 Last updated: 2017-12-13Bibliographically approved
3. On the stability of carboxylic acid-terminated self-assembled monolayers: Influence of varying alkyl chain length
Open this publication in new window or tab >>On the stability of carboxylic acid-terminated self-assembled monolayers: Influence of varying alkyl chain length
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The physio-chemical properties and storage stability of three carboxyl-terminated selfassembled monolayers (SAMs), prepared from ethanolic and acidified ethanolic thiolssolutions of HS-(CH2)nCONH-EG6CH2-COOH, n=3, 11 or 15 on gold, have been correlated to their performance as potential biosensor surfaces. The SAMs of the two longer thiols (n=11, 15) prepared from acidified thiol solutions displayed highly organized and crystallinelike alkyl and ethylene glycol portions. The length of the supporting alkyl chain also influenced the storage stability of the SAMs in nitrogen gas, water and acidified water/ethanol solutions. The two long alkyl chain SAMs exhibited excellent storage characteristics, whereas the short chain thiol resulted in a less storage stable SAM as revealed by increased molecular decomposition and desorption, and a significantly reduced biofunctionality.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-19692 (URN)
Available from: 2009-07-14 Created: 2009-07-14 Last updated: 2010-01-14Bibliographically approved

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Myrskog, Annica

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