A fuel cell assembly includes a fuel cell, a fuel cell housing, and a diaphragm. The fuel cell housing includes an endwall and an inlet port extending through said endwall. The inlet port is for admitting a breath sample into the housing. The diaphragm is coupled within the housing such that a cavity is defined between the housing and the diaphragm. The fuel cell is positioned within the cavity and is substantially concentrically aligned with respect to the inlet port.