טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentUrmann Katharina
SubjectAptamer-based optical biosensors
(The research and thesis were conducted at
Technion and Leibniz Univ.
Hannover, Germany)
DepartmentDepartment of Biotechnology and Food Engineering
Supervisor Professor Ester H. Segal


Abstract

This work describes a novel label-free optical biosensing platform based on aptamers and nanostructured porous silicon (PSi). Aptamers are single-stranded DNA or RNA oligonucleotides which can bind their target structure with high anity and specificity. Aptamers can be selected against a wide range of analytes, from small molecules, proteins to whole cells, thus making them excellent recognition elements for the design of biosensors for numerous applications e.g., environmental monitoring, food safety and medical diagnostics.

Our biosensors are constructed from an oxidized PSi thin films, used as the optical transducer element, and target-specific aptamers, which are immobilized onto the porous nanostructure. Exposure of these biosensors to their target analytes results in predictable changes in their reflectivity spectra, which are induced by selective capture of the respective analyte i.e., specific proteins or cells, within the porous nanostructure or its surface, respectively. These binding events can easily be monitored in real time using a simple spectrometer. The biosensors’ concept is generic and they can be tailored to detect and quantify many highly relevant targets. By conjugation of an appropriate aptamer to the PSi via facile immobilization routes, we have designed biosensors for targeting his-tagged proteins, protein A (secreted from Staphylococcus aureus) and live Lactobacillus acidophilus bacteria. In addition, we present a through comparison of an aptamer-PSi biosensor and its analogue antibody-based biosensor.

The biosensors developed in this work are characterized by a prolonged shelf-life and outstanding stability in complex biological samples, allowing for reproducible consecutive biosensing cycles. Thus, the superior properties of aptamers as recognition elements, mainly their availability for various targets and their excellent selectivity and stability, combined with the advantages of PSi-optical transducers, can be exploited for construction of simple, flexible, inexpensive, robust, and portable biosensing platforms.