Microfabricated nanomotion detectors for rapid cells viability tests

The widespread use of antibiotics and antifungal drugs has provoked an increasing number of multi-resistant bacteria and fungi. The emergence of multiresistance to antibiotics has been now recognized as a very serious public health issue. In order to target infections with the appropriate antibiotics as soon as possible, there is an urgent need of rapid diagnostic tools. Presently, the conventional antimicrobial testing techniques require between 24 h and one month depending on the replication speed of the microorganism, which leads to the use of broad-spectrum antibiotics treatments and further favors the development of resistant pathogens. This thesis proposes a rapid nanomechanical sensing - based diagnostic technique for studying the viability of living organisms. This instrument is a nanomechanical sensor borrowed from the Atomic Force Microscopy-based technology that uses a SU-8 lever as an optical fiber. This combination is a promising approach for further integration and miniaturization of the diagnostic apparatus. This thesis shows a first use of the microfabricated optomechanical sensors for monitoring activity of living cells. Its working principle is the following. The organism of interest is attached onto a cantilever and its nanoscale movements induce the oscillations of the cantilever. To detect the oscillations, a laser light is coupled into the SU-8 structure and travels to the free end of the cantilever. The displacement of the output light spot induced by the oscillations of the cantilever is recorded with a camera or a 4-quadrants photodiode. This allows to monitor the viability of the microorganisms, that were previously attached to the cantilever surface. The first part of this thesis briefly introduces the basic operating principle of the Atomic Force Microscope, discusses the importance of the problem of the antimicrobial resistance as one of the major health threats, and lists available alternative solutions to fight the resistance. Then the state of the art, working principle, applications of the nanomechanical antimicrobial sensors, and optomechanical mass sensors are discussed. The second chapter introduces the methods for calculating the mechanical properties of the cantilever beams, as well as discusses the fundamental sources of the noise in nanomotion detectors, that limits their sensitivity. This chapter also includes calculations and finite elements simulations of the mechanical properties of SU-8 - based cantilevers, as well as estimations of the electronic and thermal noise of the system. Third chapter explains in details the proposed sensing devices and elaborates on its design and different strategies for the microfabrication of SU-8 - based optomechanical sensors. It also describes the developed experimental setup for optomechanical measurements, the light-coupling procedure and data acquisition. The fourth chapter reports the optomechanical measurements conducted by actuating a nanomechanical motion of the