Porous silicon flow-through membrane : application to the optical detection of bacteria from their lysate

It has been predicted that by 2050, bacteria will make more victims than cancer. One way to combat pathogenic bacteria and their growing danger is to develop tools that enable an early diagnosis and allow for an effective treatment to eliminate the microbes. Fast bacterial detection methods not only have an impact on the public and preventive health, but also on the food industry and the environment. In this thesis, we developed a biosensor for the indirect detection of bacteria from their lysate. The developed sensor is based on porous silicon membranes, which are known for their many attractive optical and physical properties. Porous silicon has indeed been widely studied for sensing applications, mainly because of its large surface area, rendering it sensitive to minute changes in its environment. Unlike traditional porous silicon biosensors, the selectivity of our bioassay does not rely on bio-probes attached to the sensor's surface; the selectivity is added in the analyte itself, by the insertion of lytic enzymes that target only the desired bacteria. The resulting bacterial lysate is then able to penetrate into the porous silicon sensor and affects its optical properties, while intact bacteria accumulate on top of the sensor. We started this thesis with the design of the sensor, studying both the analyte and the sensor. This was followed by the fabrication and characterisation of a first prototype using Bacillus cereus and Staphylococcus epidermidis as model strains. This first prototype was then optimised, enabling the fabrication of a sensitive, selective and versatile optical biosensor for the indirect detection of bacteria, even in complex media.