The applicability of two potential-sensitive dyes (PSDs) for optical sensing of ions is reported. In particular, nitrate and nitrite-responsive as well as potassium and mercury-sensitive polymer membranes have been developed. In general, membranes are composed of a plasticized polymer, an ion carrier and a fluorescent dye which optically transduces the extraction of the analyte ion in the polymer matrix. The nitrate sensor membrane is composed of rhodamine B octadecylester and the anion-exchange catalyst is tridodecylmethylammonium chloride. Both are dissolved in plasticized PVC. The nitrite sensor is based on the same dye and the same polymer matrix but with benzylbis (triphenylphosphine) palladium(II) chloride acting as the nitrite-selective carrier. The potassium sensor membrane consists of the carbocyanine dye DiOC16(3), valinomycin and a lipophilic borate salt. The mercury ‘sensor’ is based on the irreversible decomposition of borate by mercury ions and is composed of DiOC16(3) and borate only. All sensor membranes have been investigated in terms of signal change, sensitivity, stability, limits of detection and the selectivity for the analyte over interferent ions. The mechanism of the sensor membranes is discussed on the basis of changes of the microenvironment of solvatochromic dyes, which result in analyte-dependent signal changes.