Integrated 3-D silicon electrodes for electrochemical sensing in microfluidic environments: Application to single-cell characterization

A microtechnology allowing the integration of thin metal electrodes and three dimensional highly doped bulk silicon electrodes on a hybrid PDMS/glass fluidic microchip has been developed. The fabrication involved anodic bonding of a silicon wafer onto glass substrate, deep reactive ion etching of 3-D bulk silicon electrodes, and plasma bonding of a PDMS microfluidic structure on a silicon/gold/glass substrate. The devices realized using this technology have been used for electrical impedance characterization of chemical and biological material. Microdevices with typical dimensions of hundreds of micrometers have been fabricated and tested in the determination of the conductivity of NaCl solutions. Smaller sensors, with critical dimensions under 10 μm, have been achieved for single-cell characterization. Human hepatocellular liver carcinoma cells have been introduced in the microimpedance sensors. Measurements show the interfacial relaxation of the cellular membrane in the 10³ -10 ⁶ Hz range. It is expected that other electrochemical sensors and electrokinetic actuators can benefit from this technology.