Abstract: A self-contained apparatus and methods for detecting the presence of any specified substance in any medium. A sample of the medium is placed in a capsule, along with a solvent and a sensor configured to test for a target analyte. The solvent comes into contact with the medium in the capsule, and the capsule is agitated to create a dispersion in the solvent of a portion of any target analyte present in the medium. A release mechanism configured to cause conduction of the dispersion to the sensor, so that the sensor produces an indication of presence of the target analyte if the target analyte is present in the medium. The apparatus uses a disposable capsule where the medium in question is placed and the disposable capsule is placed inside a reader and analyzed for presence of the harmful substance.