The fabrication and modeling of a microorganism separation stage for oceanographic investigations based on MEMS-grippers is targeted in this project. The microorganism viability must be guaranteed. The thermal, electrical and mechanical impact on microorganisms is investigated.
Final Report Abstract
Communities of cells are rarely homogenous with respect to species, size or cell viability. The observation of heterogeneous microorganism communities can produce misleading results with respect to the understanding of the correlation between specific microorganisms and their impact to human health or environmental changes. Microbiological investigations to separate and characterize single cells are extensively used in academic studies and industrial applications. Single cell investigations are also important in life science applications. Different techniques have been used to measure single cell biomechanical parameters including atomic force microscopy (AFM), micropipette aspiration, optical or laser traps (tweezers), magnetic beads and micro plate compression. These techniques are rather complicated for an implementation in automated systems. Therefore, the aim of this project was to investigate the capability to test single cells or microorganisms taken from the ocean in a MEMS environment and test how the interaction between cell and MEMS influence the cell physiology. The Dalhousie University MEMS Laboratory of Prof. Dr. Hubbard uses the Multi-User-MEMS process (PolyMUMPs) to design and test MEMS actuators in aqueous media. This project investigated for the first time usage of these devices in seawater. Devices failed in this harsh environment due to corrosion of the transmission line adhesion promoter. Therefore, a deposition process was developed using Atomic Layer Deposition to encapsulate the MEMS structures and transmission lines. Al 2O3 and TiO2 laminates were successfully deposited and tested in seawater. Devices were stored for 29 days in seawater and a constant displacement was measured for 51 actuation cycles during this time period. Displacements were optically measured with a phase sensitive FFT algorithm of series of static microphotographs. This technique was used for the first time in an aqueous environment. An initial displacement measurement repeatability of ±30 nm was improved to ±10 nm by using the blue and green color channel of a RGB picture. I developed a MEMS platform based on the PolyMUMPs fabrication method to estimate the biomechanical stiffness of single cells. A method of experimentally determining the mechanical stiffness of single cells by using differential displacement measurements in a two stage spring system was in particular evaluated. The spring system consisted of a known MEMS reference spring and an unknown cellular stiffness: the ratio of displacements was related to the ratio of stiffness. Tests were performed on saccharomyces cerevisiae in filtered tap water since oceanographic cells could not be tested in the beginning of the project. Tested cells showed stiffness values between 5.4 N/m and 8.4 N/m, which is in a good agreement with reported values. In addition, non-viable cells were tested by exposing viable cells to methanol. The resultant mean cell stiffness dropped by factor of 3 and an explicit discrimination between viable and non-viable cells based on mechanical stiffness was seen. I developed in this project a MEMS platform to measure single cell properties in harsh environments such as seawater. Only existing and well established MEMS fabrication processes were used which allows a repeatable investigation of single cells parameters in the future for several applications including environmental changes or human health.
Publications
- “MEMS Device for the determination of cell stiffness,” Proceedings of the 24th CANCAM, Saskatoon, June 2-5, 2013
R. Schwartz, S. Warnat, T. Hubbard, M. Kujath
- “Sub 50 nm optical measurements of th MEMS devices in various media.” Proceedings of the 24 CANCAM, Saskatoon, June 2-5, 2013
S. Warnat, R. Schwartz, T. Hubbard, M. Kujath
- “Submicron displacement measurements of MEMS using optical microphotographs in aqueous media: Enhancement using color image processing,” Mater. Res. Soc. Symp. Proc. Vol. 1659
S. Warnat, H. King, R. Schwartz, M. Kujath, T. Hubbard
(See online at https://doi.org/10.1557/opl.2014.58) - “Thermal MEMS actuator operation in aqueous media: Performance enhancement through ALD post processing,” 14th International Conference on Atomic Layer Deposition (ALD 2014), Kyoto, June 15-18, 2014
S. Warnat, A. Bertuch, G. Sundaram, T. Hubbard
(See online at https://doi.org/10.1116/1.4902081) - “Thermal MEMS actuator operation in aqueous media/seawater: Performance enhancement through atomic layer deposition post processing of PolyMUMPs devices,” Journal of Vacuum Science & Technology A 33, 01A126 (2015)
S. Warnat, C. Forbrigger, T. Hubbard, A. Bertuch, G. Sundaram
(See online at https://doi.org/10.1116/1.4902081)
