Characterization of Dynamic Response of AFM Cantilevers for Microscale Thermofluidic and Biophysical Sensors

My doctoral research has focused on the characterization of dynamic response of atomic force microscope (AFM) cantilevers for thermofluidic and biophysical sensors, a novel scanning thermal microscopy technique development using a tipless microcantilever to investigate micro/nanoscale transport properties in liquid, and the characterization of the surface nanomechanical properties of biocompatible polyelectrolyte hydrogels with AFM for biomedical applications.

The temperature effects on Sader‟s viscous model for multilayered microcantilevers immersed in an aqueous medium were experimentally verified as a preliminary work. Next, temperature dependence of the near-wall oscillation of microcantilevers submerged in an aqueous medium was investigated to explore the possibility of a near-wall thermometry sensor. By correlating the frequency response of a microcantilever immersed in an aqueous medium near a solid surface (within the width of a microcantilever) with the surrounding liquid temperature, the near-wall region microscale temperature distributions at the probing site were successfully determined. For biological applications, this work has been extended to examine the effect of adsorption-induced surface stress change on the stiffness of a microcantilever immersed in saline solution with varying salt concentrations. It was found that adsorption-induced surface stress change increased the stiffness of a microcantilever in saline solution with increasing salt concentration ranging from 0 to 2 molality.

The surface nanomechanical properties of 2-hydroxyethyl methacrylate (HEMA) and 2-methacryloxyethyl trimethyl ammonium chloride (MAETAC) copolymer hydrogels were probed using AFM. The HEMA-MAETAC polyelectrolyte hydrogels with increasing positive charge concentrations ranging from 0 to 400 mM in increments of 40 mM, were fabricated using different proportions of HEMA and MAETAC monomers. Increasing proportions of positively charged MAETAC monomers produced hydrogels with increasingly swollen states and correspondingly decreasing measures of surface elasticity, or Young‟s modulus. The attachment of porcine pulmonary artery endothelial cells (PPAECs) increased with increasing prepared hydrogel charge concentration and subsequently decreasing surface elasticity.

Keywords: Atomic Force Microscope (AFM), Microcantilever, Thermofluidic sensor, Hydrogel, Surface elasticity