To provide a fast, simple, and reliable way of identifying unwanted compounds present in the water systems aboard ISS and other crewed spacecrafts, we aim to develop a robust, portable and easy-to-use sensor system based on solid-state nanopore technology, a.k.a. SWAN. The current water monitoring capability in the ISS is only limited to electrical conductivity, total organic carbon and selected ions of iodine and silver. Any other analyte must be brought back to Earth for analysis. The solid-state nanopore system presents an inherently single-molecule sensor system that works on the principle of pore occlusion by the molecule which then can be registered as a change of the electrical current. Each analyte establishes its unique electrical signal upon passing through the nanopore of tailored characteristics. Previously we reported the detection of mercury and lead ions using 2-5 nm- diameter and 20-nm thick nanopores at concentrations down to 5 nM and 0.5 nM, respectively, both of which are below both EPA requirements and SWEGs. We continued to mature the sensor platform by using it to detect silver ions at concentrations down to 0.5 µM. This is lower than the detection limit of 75 ppb (~ 0.7 µM) found with the standard technique of atomic absorption spectrometry (AAS). Silver ion is the current forerunner for a future disinfection system in the US segment of the ISS water supply. It is of great importance to ensure the amount of silver is anti-microbially effective at levels that are also safe for human consumption. This detection is enabled by identification of highly specific aptamers for silver ions and innovative thin (~15 nm) nanopores. SWAN will allow the detection of low-concentration analytes in water and is thus a promising tool for a miniaturized analytical laboratory for future NASA missions, together with other analytical tools available.
Xia et al. (Sun,) studied this question.