Nanoscale probe system for cell-organelle analysis

By Bai, Seoung-Jai; Fabian, Tibor; Prinz, Fritz B. & Fasching, Rainer J.
Published in Sensors and Actuators B: Chemical NULL 2008

Abstract

Planar and bended needle shaped probes with a dual electrode system in submicron size have been developed for electrochemical analyses of living single cells. The probe system is designed for local probing of the cytosolic cell environment and cell organelles using amperometric, potentiometric and impedance spectroscopic methods. Silicon nitride cantilevers with an electrode metal layer system are fabricated on 4-in. wafers using conventional micro-fabrication techniques. The probe needle structures with a tip in submicron scale are patterned using focus ion beam (FIB) technology. A focused ion beam is utilized to write the probe needle shape into the pre-shaped cantilever and, for a dual electrode system, the probe is divided into two parts to create two separate electrodes. Subsequently, the planar needle structures are released from the supporting bulk silicon during a wet etching step, and a silicon nitride layer is deposited to isolate and embed the electrode metal layer. Finally, FIB milling is used for a precise exposure of the buried metal layer by cutting the top of the tip. Bended nano-probes for simultaneous AFM analyses were fabricated by combining this process with pre-structured wafers. This way AFM probe systems with high aspect ratio silicon nitride tips with single and dual electrochemical transducers can be manufactured. Electrochemical and mechanical characterization of planar and bended probes showed full functionality. The sharpness of the probe tip with a radius of smaller than 50 nm and the mechanical robustness of the needle structure allow for a reliable scanning as well as penetration of cell membranes. Initial measurements of cell membrane potentials and cell membrane impedances of rat fibroblast cells using Ag/AgCl transducer probes demonstrate the analytical capability of these probes in biological environments.

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