Zeptoampere electric current measurements with molecular tagging

A novel method of measuring concentrations of ionized molecules in gases that enables detection of individual ionized molecules by means of tagging them with readily detectable nano-objects has been recently discovered and developed. The femtoampere detection level of this method has been demonstrated. Here we confirm that this detection level is caused by cosmic rays and suggest ways to reduce it. The method was shown to be able to detect 1 ion in 104 cm3 of air in an underground laboratory where the cosmic rays level is negligible. This is an extremely low electric current down to zeptoampere level (1 zA = 10−21 A). This concept opens doors for advances in detection sensitivity in chemistry, biology, medicine and physics. For example for mass spectrometry this method may increase sensitivity of the absolute current detection (for Faraday collector detectors) by two to three orders of magnitude.