Ph.D Thesis


Ph.D StudentNaama Ivanir
SubjectDevelopment and Characterization of Porous Silicon/Hydrogel
Hybrids for Biosensing Applications
DepartmentDepartment of Biotechnology and Food Engineering
Supervisor Professor Segal Ester H.
Full Thesis textFull thesis text - English Version


Abstract

The objective of this multidisciplinary research effort is to design and construct porous Silicon-based biosensing platforms, capable of rapid and label-free detection of bacteria. Food and waterborne pathogens pose a risk to food safety and are a threat to the food supply chain. The detection and identification of these pathogens in drinking water, raw food, food products, and processing lines continue to rely on conventional culturing techniques, which typically require several days to obtain results, making ‘real-time’ assessment of food safety unfeasible. Therefore, there is a great need for rapid, non-destructive, accurate, cost effective, reliable, and portable methods to evaluate ‘real-time’ quality and safety of food products. The present research is designed as a response to this important challenge. We develop a new class of nanomaterials for biosensing applications, based on porous Si/hydrogel hybrids. These hybrids combine oxidized porous Si optical nanostructures e.g., Fabry-Pérot thin films, used as the optical transducer element, and a soft porous organic component (hydrogel). The hydrogel is synthesized in situ within the inorganic template and conjugated with appropriate capture probes, with specific binding to the target bacteria (E. coli, as a model bacteria), to provide the active component of the biosensor. The corresponding biorecognition events to be monitored rely on antibody-antigen interactions. These binding events are detected by monitoring the intensity changes in the reflectivity spectra of the hybrids. We show that monitoring changes in the thin film optical interference spectrum of the hybrid enables for the first time a simple and sensitive detection scheme of bacteria via a “direct-cell-capture” approach. Our studies demonstrate the applicability of these biosensors for the detection of low bacterial concentrations, in the range of 103-105 cell ml-1, within minutes.

A second biosensor based on neat oxidized porous Si (no hydrogel) functionalized with a similar capture probe, is designed as a reference system to the previous hybrid-based platform. We show that the presence of the hydrogel in the porous nanostructure offers many advantageous properties to the biosensing platform, including: stabilization of porous Si in aqueous environments, introduction of numerous immobilization modes for different biological probes, and a cellular-like environment to optimize steric crowding effects of immobilized biomolecules. Our experiments show that the hybrid-based biosensors outperform the porous Si platforms in terms of both, sensitivity and signal stability.

The biosensors presented in this study are generic and could be potentially applied for rapid detection and identification of a variety of microorganisms.