A biological sterilization indicator device is provided. The device comprises a body, a plurality of test microorganisms, and an oxygen-modulated first fluorescent sensor. The body comprises a first layer attached to a second layer, forming at least one isolatable microchamber and at least one primary passageway that provides fluidic communication between ambience and the at least one microchamber. The microchamber has an isolated volume of about 0.5 microliters to about 9.5 microliters. The plurality of test microorganisms and the oxygen-modulated first fluorescent sensor are disposed in the microchamber. A method of using the device to determine the effectiveness of a sterilization process is also provided.