Abstract
We combined a multi-sensor glass-chip with a microfluidic channel grid for the characterization of cellular behavior. The grid was imprinted in poly-dimethyl-siloxane. Mouse-embryonal/fetal calvaria fibroblasts (MC3T3-E1) were used as a model system. Thin-film platinum (Pt) sensors for respiration (amperometric oxygen electrode), acidification (potentiometric pH electrodes) and cell adhesion (interdigitated-electrodes structures, IDES) allowed us to monitor cell-physiological parameters as well as the cell-spreading behavior. Two on-chip electro-thermal micro-pumps (ETμPs) permitted the induction of medium flow in the system, e.g., for medium mixing and drug delivery. The glass-wafer technology ensured the microscopic observability of the on-chip cell culture. Connecting Pt structures were passivated by a 1.2 μm layer of silicon nitride (Si3N4). Thin Si3N4 layers (20 nm or 60 nm) were used as the sensitive material of the pH electrodes. These electrodes showed a linear behavior in the pH range from 4 to 9, with a sensitivity of up to 39 mV per pH step. The oxygen sensors were circular Pt electrodes with a sensor area of 78.5 μm2. Their sensitivity was 100 pA per 1% oxygen increase in the range from 0% to 21% oxygen (air saturated). Two different IDES geometries with 30- and 50-μm finger spacings showed comparable sensitivities in detecting the proliferation rate of MC3T3 cells. These cells were cultured for 11 days in vitro to test the biocompatibility, microfluidics and electric sensors of our system under standard laboratory conditions.
Highlights
Cell-based in vitro systems such as Micro Total Analysis Systems or lab-on-chip systems are commonly used for cell monitoring, cell sorting, or as micro-bioreactors [1,2,3,4]
Most of the systems are based on 2D-cell cultures of adherent cells and their monitoring by microscopic techniques and different types of assays, like ELISAs or life-death assays [20,21]
Bubble injection and contamination usually led to strong distortions of the cell culture
Summary
Cell-based in vitro systems such as Micro Total Analysis Systems or lab-on-chip systems are commonly used for cell monitoring, cell sorting, or as micro-bioreactors [1,2,3,4]. Chip-based cell-culture systems are a growth market because miniaturization reduces the costs for the systems by reducing the amount of cells and chemical compounds required while enabling the parallelization of investigations in. Most of the systems are based on 2D-cell cultures of adherent cells and their monitoring by microscopic techniques and different types of assays, like ELISAs or life-death assays [20,21]. A few commercial systems are available for the on-line monitoring of cell physiological parameters. A glass substrate was chosen to permit microscopic observation of the cell culture. The glass substrate carried platinum (Pt) structures, which were covered by Si3N4 in most chip areas.
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