Microfabrication of a high sensitivity fluidic AFM probe
Schoenwald, David Kipp
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This dissertation presents significant advancements in AFM probe fabrication technologies toward an AFM based assay that combines a spectrum of AFM capabilities into a comprehensive multimodal single cell analysis. The objective of this work is the fabrication of the world’s softest hollow cantilever with a beam stiffness, k, less than 100 pN/nm that is two orders of magnitude smaller than previously published. In pursuit of this objective, the intellectual contributions of this work include: 1) formation of the first high resolution (1.87 pN noise floor), low stiffness (k = 53.54 pN/nm) nano-channel cantilever made from thermally decomposable sacrificial polymer; 2) a parametric analysis of the hollow cantilever that highlights critical design features to minimize beam stiffness; 3) two new methods of interfacing a bulk microfluidic channel to a surface nanofluidic channel via a thermally decomposable polymer; and 4) a microfluidic side entry glass capillary interconnect to a bulk microfluidic channel. The technology incorporates the ability to manipulate the internal fluid pressure at the cantilever terminus to enable controlled aspiration of single cells. This work could enable the simultaneous measurement of cell mechanical properties, including mass, compressive modulus, viscoelasticity, tensile modulus, and adhesion in a single experiment. Further, an integrated analogue pressure control system is developed, using an original side-entry interconnect structure for direct-to-chip connection of glass capillary for fluidic probes as well as other lab on chip applications. The low stiffness nano-channel cantilever was fabricated, tested, and found to be more than two orders of magnitude more force sensitive than that published to date, and is comparable to standard COTS probes for the application of cell stiffness measurements. Within the scope of this thesis, fabrication of an integrated liquid cell was developed that integrates a 50 nL microfluidic channel around a cantilever for atomic force microscopy in aqueous environment. This is a reduction is over 3-5 orders of magnitude compared to commercial liquid cells. This device facilitates testing at high shear rates and laminar flow conditions coupled with full AFM functionality in microfluidic aqueous environments, including execution of both force displacement curves and high-resolution imaging.