Micromanipulator-resonator system for selective weighing of individual microparticles
Over the past decade, MEMS-based cantilever sensors have been widely used in the detection of biomolecules, environmental pollutants, chemicals and pathogens. Cantilever-based sensors rely on attachment of target entities on their surface. The attachment causes either change in surface stress or resonance frequency of the cantilever, which is detected using various schemes that range from optical to piezoelectric. The majority of these sensors rely on probabilistic attachment of multiple target entities to the sensor surface. This introduces uncertainties since the location of the adsorbed target entity can modify the signal generated by the sensor. In addition, it does not allow the measurement of individually selected target entities. The goal of this dissertation is to exploit the cantilever-based sensors' mass sensing capability to develop a "supermarket weight scale" for the micro world: a scheme that can enable the user to pick an individual target entity and weigh only that particular entity by precisely positioning it on a micro- weight scale. The system is composed of a manually operated micromanipulator and a cantilever-based micro-resonator. The micromanipulator is able to pick, move and place a xiv micro-particle of interest, and the micro-resonator can determine the mass of the target particle. During a measurement, an individual target particle selected under a microscope is picked up by the micromanipulator and then placed on the tip of one of the two cantilevers beam for weighing. The differential motion between the two cantilevers is measured by means of a diffraction grating that allows picogram level mass resolutions. Although the main goal of the study is not to develop the world's most sensitive mass detector, we demonstrate that the current resolution of the sensor is sufficient to weigh a wide range of microparticles. We present the capability of the system to select and weigh various individual microparticles from a single red blood cell (~10-11 g) to the eye-brain complex of an insect (~10-6 g), covering a 5-order-of-magnitude mass range. In addition, we are also able to measure the mass and density responses of stem cells to pathological treatments. We also demonstrate that this weighing scheme can work in conjunction with other experimental practices, such as immunomagnetic separation and focused ion beam milling processes, to provide complementary mass information. We believe this versatile and user-friendly system will be useful to a wide range of users, including biologists and bioengineers.
Savran, Purdue University.
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