Abstract: A diagnostic test device to perform a test on a biological or environmental sample is provided. In one aspect, the diagnostic test device includes a sample preparation reservoir; a dispensing mechanism that includes a sealing member and a piercing member; and at least one diagnostic test reservoir separated from the sample preparation reservoir by a seal. A predetermined volume of fluid is defined between the sealing member, the piercing member, sides of at least one chamber defined by the sample preparation reservoir, and the seal when the sealing member engages the sides of the at least one chamber. The piercing member disrupts the at least one seal to dispense the predetermined volume of fluid to the at least one diagnostic test reservoir. The sealing member is configured to directly contact the sides of the at least one chamber as the seal is disrupted.