Development of an array of ion-selective microelectrodes aimed for the monitoring of extracellular ionic activities

In this study, we present the development and the characterization of a generic platform for cell culture able to monitor extracellular ionic activities (K+, NH4+) for real-time monitoring of cell-based responses, such as necrosis, apoptosis, or differentiation. The platform for cell culture is equipped with an array of 16 silicon nitride micropipet-based ion-selective microelectrodes with a diameter of either 2 or 6 microm. This array is located at the bottom of a 200-microm-wide and 350-microm-deep microwell where the cells are cultured. The characterization of the ion-selective microelectrode arrays in different standard and physiological solutions is presented. Near-Nernstian slopes were obtained for potassium- (58.6 +/- 0.8 mV/pK, n = 15) and ammonium-selective microelectrodes (59.4 +/- 3.9 mV/pNH4, n = 13). The calibration curves were highly reproducible and showed an average drift of 4.4 +/- 2.3 mV/h (n = 10). Long-term behavior and response after immersion in physiological solutions are also presented. The lifetime of the sensors was found to be extremely long with a high recovery rate.

MeV ion beam lithography of biocompatible halogenated Parylenes using aperture masks

Parylenes are poly(p-xylylene) polymers that are widely used as moisture barriers and in biomedicine because of their good biocompatibility. We have investigated MeV ion beam lithography using 16O+ ions for writing defined patterns in Parylene-C, which is evaluated as a coating material for the Cochlear Implant (CI) electrode array, a neuroprosthesis to treat some forms of deafness. Parylene-C and -F on silicon and glass substrates as well as 50 μm thick PTFE were irradiated to different fluences (1×1013-1×10161×1013-1×1016 1 MeV 16O+ ions cm−2) through aperture masks under high vacuum and a low pressure (<10−3 mbar) oxygen atmosphere. Biocompatibility of the irradiated and unirradiated surfaces was tested by cell-counting to determine the proliferation of murine spiral ganglion cells. The results reveal that an oxygen ion beam can be used to pattern Parylene-C and -F without using a liquid solvent developer in a similar manner to PTFE but with a ∼25× smaller removal rate. Biocompatibility tests showed no difference in cell adhesion between irradiated and unirradiated areas or ion fluence dependence. Coating the Parylene surface with an adhesion-promoting protein mixture had a much greater effect on cell proliferation.