A flow cytometry based high throughput screening system for glucose oxidase (GOx) gene libraries in double emulsions was developed. Firstly, encapsulation of yeast cells in double emulsion was optimized by changing the ABIL EM90 concentration in light mineral oil from 2.9% to 1.5%. This enabled formation of larger water droplets and more efficient yeast cell encapsulation. Several fluorescent assays for hydrogen peroxide were tested and the 3-carboxy-7-(4'-aminophenoxy)-coumarine (APCC) oxidation by horseradish peroxidase based assay best fit the requirements of the double emulsion technology. Using an optimized substrate solution consisting of 0.5 mM APCC, 40 mM glucose and 10 U/mL of horse radish peroxidase, a referent gene library containing 10~7 yeast cells was sorted in 30 min and enriched from 1% to 15% of yeast cells expressing wt GOx.
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