Silica-based functional materials: recognition and detection of viruses

Sykora, Sabine. Silica-based functional materials: recognition and detection of viruses. 2018, Doctoral Thesis, University of Basel, Faculty of Science.


Official URL: http://edoc.unibas.ch/diss/DissB_13017

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Millions of people falling ill annually due to viral infections caused after the consumption of con- taminated water or food. The fact that industrialized countries with high hygienic standards are also affected by water- and food-borne viral diseases indicates that the water purification and food control systems that are implemented are not sufficient to combat all viruses or do not cover all transmitting pathways. The advancing globalization and increased exchange of goods has further elevated the risk of contamination. For instance, there was a huge outbreak of norovirus in German schools due to infected strawberries imported from China. Food vehicles that were earlier in contact with contaminated water suppliers transmit most of the Norovirus. Considering this transmission pathway, there is a high interest for such materials or systems that can effi- ciently bind viruses with high affinity directly from environmental water or from the food vehicle. Besides the removal of the virus from water and food, the detection of viruses during the food preparation or in the water source will help determine the source of contamination, leading to an improvement in safety. For both the removal and detection, binding of the viruses is required. The best known way to bind viruses is using antibodies. However, their application is limited due to their fragility. Therefore, the solution would be to use materials with the binding properties of antibodies based on organically functional groups and the stability of inorganic materials. Such a material can be acquired from the so-called organic-inorganic hybrid materials.
Organic-inorganic hybrid materials are most suitable to provide a system for rapid and specific detection of viral contaminants directly in the environment. They are provided with a surface that has the properties of (bio)-organic molecules for specific binding, while their core substance is inorganic, providing the required stability to resist environmental factors over a long period of time. Among the large number of hybrid materials, silica, with organic functional groups, is one of the few that come closest to having the properties of antibodies in terms of binding. Furthermore, there are a number of ways to modify silica. On the one side, silica can be easily synthe- sized in different forms. On the other side, silica can be easily equipped with a broad range of compounds, from organic molecules to complete biomolecules. These modifications in silica are possible by controlled building-up of silica at the molecular level. The desired building blocks can be linked like Lego blocks to form various sophisticated and functionalized silica structures. This principle allows us to synthesize multi-functional silica that specifically binds viral contaminants as well as generates a signal that visualizes the binding directly. Such multi-functional silica was prepared in the frame of this work.
By applying different well-known techniques for functionalizing silica, such as molecular imprinting and entrapment, it was demonstrated the preparation of an artificial virus-recognition material with an integrated detection system, allowing the direct visualization of the virus binding. Molecular imprinting is suited to generate artificial recognition surfaces that overtake antibodies in terms of stability. By combining surface imprinting with nanoparticles, the high surface-area-to-volume ratio of nanoparticles provides a high number of recognition sites, also called imprints, for the specific binding of the previously imprinted virus.
In the frame of this work, norovirus-like particles as safe replacement for the human pathogen norovirus were successfully imprinted and thereby, also provided crucial information for further development of silica-based molecular imprinting in general.
To use these imprinted particles for detection as well, they were equipped with two different de- tection systems that were integrated with the binding site, generating a visible signal accordingly to target concentration.
First, silica particles were equipped with a biocatalytic layer that contained a signal-generating enzyme, which was covered by a recognition layer. It was assumed that covering the biocatalytic layer with the recognition layer would form a connection between the enzymatic activity and the virus binding. This connection was based on the concept that the recognition layer limits the transport of substrate to the enzyme except where the imprints are. As a result of this, occupa- tion of the imprints causes a decrease in the enzymatic activity. This concept was demonstrated using acid phosphatase as the signal-generating enzyme and norovirus-like particles for imprinting. The activity of the biocatalytic layer could be followed via colorimetric assay and depended on the amount of bound norovirus-like particles. This result proves this read-out system over steric inhibition of the substrate uptake, which represents a straightforward detection system for viruses.
The second detection system was based on a fluorescence signal emitted by a dye that was site-specifically integrated in the binding site. The relation between the fluorescence intensity and virus binding was based on the concept that the bound viruses quench the signal of the fluorescent dye, allowing a direct display of the virus binding over the quenching intensity. To enable sufficient quenching, an inactive version of the dye was first integrated and then activated site-selectively, mainly in the imprints. This concept was demonstrated using fluorescein and its inactivated version, fluorescein diacetate, as the signal-generating dye and norovirus-like par- ticles for imprinting. The so-prepared imprinted fluorescent particles showed a fluorescent sig- nal depending on the amount of bound norovirus-like particles. This result proves this read-out system over fluorescent without the addition of external compounds, such as substrate, which represents another straightforward detection system for viruses.
In summary, the application of different tools was demonstrated to prepare multi-functional silica for detection, and which is not limited to silica particles but could be used to functionalize different surfaces for the purpose of detection and in water-purification systems.
Advisors:Meier, Wolfgang and Shahgaldian, Patrick and Pieles, Uwe
Faculties and Departments:05 Faculty of Science > Departement Pharmazeutische Wissenschaften > Pharmazie > Clinical Pharmacy (Meier)
UniBasel Contributors:Pieles, Uwe
Item Type:Thesis
Thesis Subtype:Doctoral Thesis
Thesis no:13017
Thesis status:Complete
Number of Pages:1 Online-Ressource (VII, 115 Seiten)
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edoc DOI:
Last Modified:07 May 2019 04:30
Deposited On:06 May 2019 08:47

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