This paper reports the development of a microfluidic platform that utilizes arrays of normally closed (NC) microvalves, and its application in quantitative biological measurements, including microbial gene expression and stimulus-driven responses in living cells. The dimensions of the NC valves used in this platform were first optimized to actuate reliably at low negative pressures (-1 to -3 psig). The platform was then employed to investigate (i) inducible gene expression in Escherichia coli and (ii) the effect of an antibiotic (ampicillin) on cell growth and death. Copyright