In this work, a short direct current (dc) discharge that lacks a positive column for the measurement of the densities of plasma and ambient gas particles is demonstrated and studied. It is shown that a sensor based on the discharge can provide the absolute measurement of the densities of plasma and ambient gas particles at low-pressures (between 0.3 and 7 Torr). This sensor may work for afterglow plasma and active dc discharge. It also has a wide dynamic range of measurements and, depending on the studied species, its resolution can be in the range of a fraction of 1 ppb to a fraction of 1 ppm. The sensor is able to survive and function in harsh environments, including at cryogenic and high temperatures, in the presence of toxic substances, and at elevated ionizing radiation and vibration levels.