First ,the biomass of cells in the beads is sufficiently high before the copper detection step,
which avoids the negative effects of high or low copper ion concentrations on cell growth,as observed for free cells in liquid cultures.Moreover,the high cell density with in the beads results in much more intense and thus more easily detectable coloration than the coloration observed in sparse cell populations in liquid cultivation. The use of immobilized sensors thus leads to more precise readings