Fabrication and characterisation of a porous silicon membrane for an improved optical detection of bacteria

Bacteria are ubiquitous microorganisms of our daily life, and some of them, which are pathogenic, can cause dramatic events such as media contaminations and human infections. It is therefore of paramount importance to detect these pathogens in order to act accordingly. Current standard methods used for bacteria detection are mostly biological and require a long time and laboratory equipment. To be able to respond fast, a rapid and on-site mean of detection would be ideal. In this context, biosensors have garnered increasing attention these last 20 years due to their great potential for sensitivity and selectivity, as well as rapidity of detection. The different types of biosensors developed so far differ in the biorecognition elements (antibodies, DNA, proteins ...) and the transduction modes (optical, electrochemical, mass-based ...). In this work a transverse porous silicon (PSi) membrane for the detection of Staphylococcus epidermidis in synthetic solution using lytic selectivity is fabricated. S. epidermidis is an opportunistic bacterium commonly present on human skin and mucous membranes which can sometimes lead to skin, nasal and urinary tract infections. Several manufacturing processes were considered, which include electrochemical etching, reactive-ion etching and passivation. The PSi membrane was exposed to bacteria which were thereafter lysed by lysostaphin and its reflectance spectrum was recorded in real-time. The detection is based on changes in the reflectance spectrum upon bacteria exposure and lysate penetration into the pores. The first part of this work is about the membrane fabrication using mainly microfabrication techniques carried out in a cleanroom environment and characterisation tools such as scanning electron microscopy and light spectrometry for optical characterisation. The second part concerns sensing experiments with bacteria in solution performed in a microbiology laboratory. The different fabrication processes tested are described and assessed through the characterisation of the resulting membranes. The reflectance spectrum of the fabricated porous silicon membranes displays Fabry-Pérot fringes that were exploited in a fast Fourier transform analysis to detect changes in the position and intensity of the resulting frequency peak upon bacteria exposure. After fabrication, the membranes were too fragile to withstand the passivation step and ended up caved in. A preliminary bacteria detection experiment however suggests that the sensitivity of the membrane is increased in comparison to lateral structures, but more work still needs to be carried out. Several suggestions to conduct further study are proposed at the end of this work.