An array of micro-chambers (220) with individual ion sensitive field effect transistors (ISFETs) (300) disposed therein for monitoring single cell activity in the microarray to determine the presence or absence of microorganisms in a sample (390). In addition to the presence or absence of a single cell, certain further embodiments contemplate monitoring cell behavior. Cell behavior includes the entire range of cell activity as well as cell response to changes in environmental conditions of changes in response due to the addition of sample constituents.