A sample monitoring structure includes fluorescently-labeled hydrogel that is size-responsive to changes in one or more properties of aqueous liquid medium contacted with the sample monitoring structure. An intensity of a fluorescent emission from the sample monitoring structure changes with changes in the size of the fluorescently-labeled hydrogel. The sample monitoring structure is advantageously used in automated processing and analytical evaluation of large numbers of fluid samples over extended periods of time analytical evaluation systems, including flow cytometry systems, live cell imaging and analysis systems and parallel bioreactor system. The sample monitoring structure may be in a form of sample monitoring beads for addition to liquid media of fluid samples subjected to analytical evaluation.