An apparatus comprises a housing defining a chamber that has a liquid disposed therein, and a sensor submerged in the liquid. The sensor comprises a porous conductive film on a substrate, and the film comprises chemiresistive semiconducting metal oxide structures. The sensor also comprises an electrode pair operably connected to the porous conductive film for generating electric current in the film and for detecting a change in an electrical property of the film. The apparatus can be used to detect, identify, and quantify ions and molecules in a liquid sample. Molecules and ions, in a liquid sample, that interact with the porous conductive film can cause a change in an electrical property of the film. The change in electrical property of the film can be correlated with the presence and amount of the molecules or ions.