Individually actuated cantilever arrays for cell force spectroscopy

The design, fabrication and characterization of thermally actuated, parallelizable cantilevers is presented. Thermal simulations of operation in liquid give indications regarding displacement range in such an environment

Integrated long-range thermal bimorph actuators for parallelizable bio-AFM applications

AFM-based cell force spectroscopy is an emerging research method that already has enhanced our understanding of the structural changes that take place in a cell as it becomes cancerous. However, the method is limited as it is not time-efficient in its current state of development. This paper presents the fabrication of an integrated long-range thermal bimorph actuator that controls the z-position of an AFM cantilever in liquid. Multiplied in arrays, such individually actuated probes can parallelize cell force spectroscopy measurements, thereby drastically reducing the time per measured cell. The need to accommodate differences in tip-sample distance implies an individual device actuation range of ≥10 µm out of plane. In addition, any cross-talk, i.e. between actuators or between the actuator and the force sensor, must be minimized. To meet these requirements, we designed and fabricated a novel thermal bimorph actuator that was incorporated with force sensing cantilevers. In order to keep temperatures in a bio-friendly range, the design was optimized for high thermo-mechanical sensitivity. FEM simulations confirmed that the surrounding liquid constitutes a large thermal reservoir that absorbs the generated heat. Furthermore, given that a cell substrate material of high thermal conductivity is chosen, in our case silicon, the thermal coupling between the cell and the substrate dominates over that between the cell and the actuator. Suspended silicon nitride structures with platinum electrodes were micro-fabricated through standard techniques. The finalized actuator was able to displace the cantilever out of plane by 17 µm in air

Integrated MEMS actuation for force spectroscopy in liquid

This work aims to develop arrays of individually actuated cell force spectroscopy probes. Cross et al. (Nat. Nanotech. 2007) have shown that human cells undergo substantial mechanical changes as they become cancerous. Cell force spectroscopy using AFM has emerged as a promising candidate to measure those changes. It is believed that this method will lead to an increased understanding of the disease and potentially also to new diagnosis technologies. In order to collect a sucient amount of data, several cells must be measured. In the current state of the technology, iterations are very time-consuming. The PATLiSci project aims to parallelize these measurements by developing arrays of probes. Our task is to develop such arrays with the additional feature of individual actuation, allowing tuning of the applied force exerted by each probe

Compound fabrication for in-liquid selective Self-Assembly

Passing from millimeter to micrometer scale, the traditional pick and place method for assembling large amount of compounds be- comes difficult and time consuming. At micrometer scale it is then very important to have other assembling methods. This work presents the ability to perform selective and pairwise serial self-assembly of more than 500 immersed compounds, using hydropho- bic interaction [1]. To show the selectivity of the assembly, bicolor 100 μm SU-8 filled cylinders have been fabricated by photolithogra- phy techniques. Inducing selective hydrophilic interaction, a yield higher than 60% of correctly assembled parts has been achieved

Hydrodynamic Trap for Directed Self-Assembly of MEMS

This paper presents the realization of a hydrodynamic microfluidic trap with the goal of sorting MEMS for self-assembly experiments in liquid. A simplified analytical design rule has been compiled and numerically verified. Microfluidic devices have been fabricated in PDMS and PMMA beads have been trapped in a controlled way, validating the concept

Characterization of Hydrophobic Forces for in Liquid Self-Assembly of Micron-Sized Functional Building Blocks

This paper presents the experimental and numerical study of hydrophobic interaction forces at nanometer scale in the scope of engineering micron-sized building blocks for self-assembly in liquid. The hydrophobic force distance relation of carbon, Teflon and dodeca-thiols immersed in degassed and deionized water has been measured by atomic force microscopy. Carbon and dodeca-thiols showed comparable attractive and binding forces in the rage of pN/nm2. Teflon showed the weakest binding and no attractive force. Molecular dynamic simulations were performed to correlate the molecular arrangement of water molecules and the hydrophobic interactions measured by atomic force microscopy. The simulations showed a depletion zone of 2Å followed by a layered region of 8Å in the axis perpendicular to the hydrophobic surface