An ion detection device has a strip of carbon-based nanomaterial (CNM) film and a chamber enclosing the CNM film. A low bias voltage is applied at the ends of the CNM film strip, and ions present in the chamber are detected by a change in the magnitude of current flowing through the CNM film under the bias. Also provided are methods for fabricating the device, methods for measuring pressure of a gas, and methods for monitoring or quantifying an ionizing radiation using the device.