1. A method of monitoring a glucose level in a live subject, comprising the steps of: obtaining at least one stem cell from the subject; processing the at least one stem cell into a plurality of signal-generating cells that change their optical characteristics in response to changes in glucose concentration; forming the plurality of signal-generating cells into at least two cell clusters; determining, prior to implantation, for each of the at least two cell clusters, calibration data that relates responses of the respective cell cluster to glucose levels; implanting the at least two cell clusters into in the subject's body at locations that permit optical characteristics of the at least two cell clusters to be detected from outside the subject's body after implantation; illuminating the at least two implanted cell clusters; detecting reflected illumination from each of the at least two cell clusters; identifying changes in the optical characteristics of the cell clusters that correspond to the responses of the cell clusters, for each of the at least two cell clusters, based on changes in the amount of reflected illumination detected in the detecting step; mapping, for each of the at least two cell clusters, the identified change in optical characteristics to a glucose level based on the calibration data for the respective cell cluster; and outputting an indication of the glucose level in the subject based the glucose levels obtained in the mapping step.