Reminder: PhD defense, Tomorrow - Friday (Jan 7), 2 pm, CISX 101

Nanoscale metallic electrodes for intracellular electrical measurements
Piyush Verma

Stanford University PhD Oral Defense – Department of Materials Science and Engineering

Advisor: Prof. Nicholas A. Melosh

Date: Friday, January 7^th, 2011

Time: 2 pm (Refreshments start at 1:45pm)

Location: CISX Auditorium (101X)

http://campus-map.stanford.edu/index.cfm?ID=04-055

Interfacing living matter to electronics with the ability to monitor and deliver spatio-temporal signals to cells or cell networks is promising for various fundamental biophysical studies and also for applications such as high resolution neural prosthetics, on-chip electrically addressed artificial neuronal networks and chip based patchclamps. The main challenge in developing such interfaces is controlling the structure and properties of the junction between the device and cell membrane. Recent advances in nanoscale materials have enabled interactions at length scales natural to biology, thus providing an opportunity to control the structure of such junctions. In this presentation, the design and development of nanoscale intracellular electrodes and their application as powerful tools for the life sciences will be discussed.

By utilizing the design principles of transmembrane proteins that span the cell membrane, biomimetic metallic electrodes were fabricated for intracellular electrical measurements. The stacked hydrophilic-hydrophobic-hydrophilic domain architecture of transmembrane proteins was replicated in nanoscale post electrodes by evaporating and selectively functionalizing different metal layers. These metal layers were put down using e-beam evaporation following their definition using e-beam lithography. To enhance the electrical signal from the electrode, the tip of the post was made electrochemically active by depositing a thin layer of platinum. Thorough electrical passivation of the device was achieved through oxidation, atomic layer deposition and polymer coating.

The formation of a well controlled junction between the post electrode and cell membrane was demonstrated by testing the device with red blood cells. The electrical properties of the device were determined by performing cyclic voltammetry in a buffer solution with electrochemically active species. A giga-ohm seal was observed to form spontaneously as the cell was brought close to the post, confirming intracellular access. The formation of giga-ohm seal is critical for patchclamping, a technique used extensively in the pharmaceutical industry. To elucidate the molecular structure of the electrode-membrane interface, coarse grained molecular dynamics (MD) simulations were carried out. A methodology was developed to calculate the energetics of interface formation. In addition to these simulations, a physical model of cell deformation was developed to understand the mechanics of cell-post interaction. Together, MD simulations and cell deformation model provide a powerful approach to optimize the electrode design.

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Piyush Verma
Geballe Laboratory for Advanced Materials
McCullough Building, Rm. 203
Stanford University, Stanford, CA 94305-4045
(650) 892 4909
http://www.stanford.edu/group/melosh/