496d Development of a Platform for the Monitoring of Extracellular Ionic Activities

Olivier T. Guenat1, Silvia Generelli2, Nico De Rooij2, Milena Koudelka-Hep2, Francois Berthiaume3, and Martin L. Yarmush3. (1) Physics Department, Ecole Polytechnique de Montréal, 2900, boul. Édouard-Montpetit, Montréal, QC H3C 3A7, Canada, (2) Institute of Microtechnology, University of Neuchâtel, Rue Jaquet-Droz 1, Neuchâtel, Switzerland, (3) Center for Engineering in Medicine, Harvard Medical School, 51 Blossom St, Boston, MA 02114

In the past few years, there has been great interest in using micro- and nanostructures for the analysis of complex biological systems such as living cells. In this study we present the development of a generic platform for cell culture able to monitor extracellular ionic activities (K+, NH4+, Ca2+,…) for real-time monitoring of cell-based responses, such as necrosis and apoptosis, differentiation, etc. Here we focused on the development of potassium- and ammonium-selective microelectrodes. Potassium, which is present at high levels in intact viable cells, leaks out of dying cells and elevated extracellular potassium can be used as a marker of cell death. Ammonium is taken up by differentiated hepatocytes and a decrease in extracellular ammonium can be used as a marker of stem cell differentiation into hepatocytes. For this purpose, we developed a platform for cell culture that is equipped with an array of 16 silicon nitride micropipettes (with a diameter of either 2 or 6 um) housing ion-selective microelectrodes. This array consist of two rows of 8 micropipettes separated by 150 um located at the bottom of a 200 um wide and 350 um deep microchannel where the cells are cultured. The micropipettes are individually connected with a network of 50 um wide microchannels etched in a Pyrex substrate aligned and bonded at the bottom side of the silicon substrate. Extended characterization of the ion-selective microelectrodes arrays in different standard and physiological solutions was carried out. Near Nernstian slopes were obtained for potassium-selective microelectrodes (58.6 ± 0.8 mV/pK, n=15) and for ammonium-selective microelectrodes (59.4 ± 3.9 mV/pNH4, n=13), both after more than one week of use. The calibration curves were highly reproducible and showed very little drift (in average 4 mV/h, n=10). Long-term behavior as well as response after immersion in physiological solutions will also be presented.