A packed microcolumn approach to a cell-based biosensor

We present and evaluate a new approach to cell immobilization for use in cell-based biosensors. We have fabricated a microfluidic channel using poly(dimethylsiloxane) (PDMS) with cell entrapment posts for the gentle packing and immobilization of yeast cells. This method of immobilization allows for a density of metabolically active cells greater than 8.0 × 106 cells/mm3. The packed microcolumn approach addresses simple diffusional limitations inherent in traditional suspension and membrane entrapment techniques. By utilizing genetically engineered whole cells, rather then cellular components, the sensor is capable of detecting and responding to a wide range of biologically active compounds. In this study, Saccharomyces cerevisiae was genetically engineered to produce yellow fluorescent protein (YFP) when exposed to galactose. Fluorescence response of packed cells (G1 phase) to galactose required 40% longer than the fluorescent response of cells grown in suspension. To address concerns of long-term viability (>60 days) and cell overgrowth, stationary phase cells were also tested in the microfluidic channel. Response time required approximately 50% longer than non-stationary phase cells packed inside the microfluidic channel. Additionally, cellular response as a function of the target analyte concentration was investigated and response time versus analyte concentration is reported. This report demonstrates proof-of-concept of using protein expression-based biosensors, based upon a packed, microcolumn architecture, as a dependable long-term storage platform.