Microfabricated nanomotion detectors for rapid cells viability tests

The widespread use of antibiotics and antifungal drugs has provoked an increasing numberof multi-resistant bacteria and fungi. The emergence of multiresistance to antibiotics hasbeen now recognized as a very serious public health issue. In order to target infections withthe appropriate antibiotics as soon as possible, there is an urgent need of rapid diagnostictools. Presently, the conventional antimicrobial testing techniques require between 24 h andone month depending on the replication speed of the microorganism, which leads to the useof broad-spectrum antibiotics treatments and further favors the development of resistantpathogens.This thesis proposes a rapid nanomechanical sensing - based diagnostic technique for studyingthe viability of living organisms. This instrument is a nanomechanical sensor borrowed fromthe 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 thediagnostic apparatus. This thesis shows a first use of the microfabricated optomechanicalsensors for monitoring activity of living cells.Its working principle is the following. The organism of interest is attached onto a cantilever andits 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 isrecorded with a camera or a 4-quadrants photodiode. This allows to monitor the viability ofthe microorganisms, that were previously attached to the cantilever surface.The first part of this thesis briefly introduces the basic operating principle of the Atomic ForceMicroscope, discusses the importance of the problem of the antimicrobial resistance as oneof 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 antimicrobialsensors, and optomechanical mass sensors are discussed.The second chapter introduces the methods for calculating the mechanical properties of thecantilever beams, as well as discusses the fundamental sources of the noise in nanomotiondetectors, that limits their sensitivity. This chapter also includes calculations and finite elementssimulations of the mechanical properties of SU-8 - based cantilevers, as well asestimations of the electronic and thermal noise of the system.Third chapter explains in details the proposed sensing devices and elaborates on its designand different strategies for the microfabrication of SU-8 - based optomechanical sensors.It also describes the developed experimental setup for optomechanical measurements, thelight-coupling procedure and data acquisition.The fourth chapter reports the optomechanical measurements conducted by actuating ananomechanical motion of the cantilever chips, and describes the preparation of the yeastcells and cantilevers for the nanomotion experiments. Subsequently, the results of the viabilitytest are presented, along with a discussion of the mechanical and optical origins of it.Finally, the thesis ends with a conclusion of this work and outlook of the presented results.