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Development of Dextran-Based Hydrogel Layers for Biosensor Applications = = Dextran-alapu Hidrogel Retegek Fejlesztese Bioszenzorikai Alkalmazasokhoz /

Record Type:	Electronic resources : Monograph/item
Title/Author:	Development of Dextran-Based Hydrogel Layers for Biosensor Applications =/ Andras Saftics.
Reminder of title:	Dextran-alapu Hidrogel Retegek Fejlesztese Bioszenzorikai Alkalmazasokhoz /
Author:	Saftics, Andras,
Description:	1 electronic resource (134 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 85-07, Section: B.
Contained By:	Dissertations Abstracts International85-07B.
Subject:	Biocompatibility. -
Online resource:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=30776278
ISBN:	9798381197716

Development of Dextran-Based Hydrogel Layers for Biosensor Applications = = Dextran-alapu Hidrogel Retegek Fejlesztese Bioszenzorikai Alkalmazasokhoz /
Saftics, Andras,

Development of Dextran-Based Hydrogel Layers for Biosensor Applications =Dextran-alapu Hidrogel Retegek Fejlesztese Bioszenzorikai Alkalmazasokhoz /Andras Saftics. - 1 electronic resource (134 pages)

Source: Dissertations Abstracts International, Volume: 85-07, Section: B.

In the present thesis, the development of ultrathin (CMD-ut) and spin-coated (CMD-sc) carboxymethyl dextran layers was demonstrated. The composition, structure as well as proteinand cell repellent-ability of the developed heavily hydrated coatings were characterized by various analytical methods. While the CMD-ut layers were developed to use later in classical biosensor measurements for biomolecule detection, the CMD-sc layers were developed for future cell-based biosensor experiments.All the layer preparation experiments were performed using CMD stock material that was synthetized according to the adapted method described in Section 4.2.1.The synthetized CMDs were characterized by FTIR and acidimetric titration which were successfully used to detect the presence of carboxylic groups and determine the degree of carboxymethylation (DS).For the fabrication of CMD-ut layers, two different surface chemistries were applied, including CMD grafting to aminosilane coating using EDC/NHS linking chemistry with the formation of amide bonds (CMD-ut-Am layers) as well as direct grafting to epoxysilane coatings forming ester and ether bonds (CMD-ut-Ep layers). The layer fabrications were performed on oxide-based surfaces, including the SiO2-TiO2-type waveguide surface of OWLS biosensor chips and SiO2surface of standard Si substrates.The CMD-ut coatings were analyzed in their dry state using ATR-FTIR, XPS as well AFM techniques. The ATR-FTIR and XPS measurements proved the presence of CMD layer on Si substrates by detecting the signal of carboxylic groups and obtaining the elemental composition of the specimen surfaces. The topography of CMD surfaces was analyzed by AFM measurements and the surface roughness (RRMS) was determined to be 1.1 nm. According to the results of XPS depth analysis, the separate thickness of aminosilane and CMD layers was 2.30 nm and 0.73 nm, respectively, correlating well with the AFM result that provided 4 nm as a collective thickness of the aminosilane and CMD layers. Control XPS measurements performed on unsilylated Si substrates resulted in one order of magnitude lower CMD thickness (0.07 nm) than on silylated surfaces, demonstrating the success of covalent grafting. Water CA measurements showed that the grafting of CMD-ut layer on aminosilylated surface accompanies with significant decrease in the CA data (65 - 80° → 20 - 40°), proving the presence and hydrophilic characteristic of CMD-ut coatings.Since even the uncrosslinked CMD layers behave like hydrogels and due to the fact that the high water content and swelling ability are essential properties determining several applications, the characterization of CMD-ut layers under aqueous conditions was of high importance. In the corresponding experiments, the formation of CMD-ut layers was in situmonitored by OWLS and QCM-I measurements, allowing to collect kinetic data about the CMD grafting process.The in situ grafting experiments proved that the CMD molecules form stable coating on the SiO2-TiO2waveguide surface. The deposited layer could not be washed even by a concentrated solution of NaCl, confirming that the chains were covalently grafted to the surface.Revealed by the analysis of deviations between the OWLS apparent layer refractive index data and realistic CMD refractive index values (quasi-isotropic analysis), it was found that there is the possibility to tune the nanostructure of CMD-ut layers both by the composition of the silane coating and the pH of CMD grafting solution. In case of CMD-ut-Ep coatings, the OWLS measurements revealed that the layer structure was strongly pH-dependent: while the dominant chain conformation was parallel with the surface in neutral and basic conditions, at acidic pH, the structure was found more open with larger number of loops perpendicular to the surface. In case of CMD-ut-Am layers, an intermediate structure was observed which could be characterized by a structure that was between the two pH extremes of CMD-ut-Ep layers. The pH-dependent nanostructure of CMD-ut-Ep layers was explained by the varying efficiency of the grafting reaction at different pH values resulting in a significant variation in the number of surface grafting points.

English

ISBN: 9798381197716Subjects--Topical Terms:

656157
Biocompatibility.

Development of Dextran-Based Hydrogel Layers for Biosensor Applications = = Dextran-alapu Hidrogel Retegek Fejlesztese Bioszenzorikai Alkalmazasokhoz /
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520 $a In the present thesis, the development of ultrathin (CMD-ut) and spin-coated (CMD-sc) carboxymethyl dextran layers was demonstrated. The composition, structure as well as proteinand cell repellent-ability of the developed heavily hydrated coatings were characterized by various analytical methods. While the CMD-ut layers were developed to use later in classical biosensor measurements for biomolecule detection, the CMD-sc layers were developed for future cell-based biosensor experiments.All the layer preparation experiments were performed using CMD stock material that was synthetized according to the adapted method described in Section 4.2.1.The synthetized CMDs were characterized by FTIR and acidimetric titration which were successfully used to detect the presence of carboxylic groups and determine the degree of carboxymethylation (DS).For the fabrication of CMD-ut layers, two different surface chemistries were applied, including CMD grafting to aminosilane coating using EDC/NHS linking chemistry with the formation of amide bonds (CMD-ut-Am layers) as well as direct grafting to epoxysilane coatings forming ester and ether bonds (CMD-ut-Ep layers). The layer fabrications were performed on oxide-based surfaces, including the SiO2-TiO2-type waveguide surface of OWLS biosensor chips and SiO2surface of standard Si substrates.The CMD-ut coatings were analyzed in their dry state using ATR-FTIR, XPS as well AFM techniques. The ATR-FTIR and XPS measurements proved the presence of CMD layer on Si substrates by detecting the signal of carboxylic groups and obtaining the elemental composition of the specimen surfaces. The topography of CMD surfaces was analyzed by AFM measurements and the surface roughness (RRMS) was determined to be 1.1 nm. According to the results of XPS depth analysis, the separate thickness of aminosilane and CMD layers was 2.30 nm and 0.73 nm, respectively, correlating well with the AFM result that provided 4 nm as a collective thickness of the aminosilane and CMD layers. Control XPS measurements performed on unsilylated Si substrates resulted in one order of magnitude lower CMD thickness (0.07 nm) than on silylated surfaces, demonstrating the success of covalent grafting. Water CA measurements showed that the grafting of CMD-ut layer on aminosilylated surface accompanies with significant decrease in the CA data (65 - 80° → 20 - 40°), proving the presence and hydrophilic characteristic of CMD-ut coatings.Since even the uncrosslinked CMD layers behave like hydrogels and due to the fact that the high water content and swelling ability are essential properties determining several applications, the characterization of CMD-ut layers under aqueous conditions was of high importance. In the corresponding experiments, the formation of CMD-ut layers was in situmonitored by OWLS and QCM-I measurements, allowing to collect kinetic data about the CMD grafting process.The in situ grafting experiments proved that the CMD molecules form stable coating on the SiO2-TiO2waveguide surface. The deposited layer could not be washed even by a concentrated solution of NaCl, confirming that the chains were covalently grafted to the surface.Revealed by the analysis of deviations between the OWLS apparent layer refractive index data and realistic CMD refractive index values (quasi-isotropic analysis), it was found that there is the possibility to tune the nanostructure of CMD-ut layers both by the composition of the silane coating and the pH of CMD grafting solution. In case of CMD-ut-Ep coatings, the OWLS measurements revealed that the layer structure was strongly pH-dependent: while the dominant chain conformation was parallel with the surface in neutral and basic conditions, at acidic pH, the structure was found more open with larger number of loops perpendicular to the surface. In case of CMD-ut-Am layers, an intermediate structure was observed which could be characterized by a structure that was between the two pH extremes of CMD-ut-Ep layers. The pH-dependent nanostructure of CMD-ut-Ep layers was explained by the varying efficiency of the grafting reaction at different pH values resulting in a significant variation in the number of surface grafting points.
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