Thin films of LiMn2O4 with the spinel structure have been deposited by the laser ablation method onto various substrates. The composition of the films has been obtained through Rutherford Backscattering methods and Nuclear Reaction Analysis. The Li/Mn ratio strongly decreases with the temperature of the substrate and increases with the oxygen pressure. Pure LiMn2O4 films are obtained under 0.2 mbar at 500 degrees C. For lower oxygen pressures, mixed LiMn2O4 and Mn3O4 crystalline phases are obtained. The films are polycrystalline when deposited onto Si and Pt whereas they are strongly textured when deposited onto MgO. They exhibit high reversible intercalation properties with very good cycling behaviour as shown by cyclic voltammetry. We demonstrate the potential application of such films as very rapid and selective sensors of the Li concentration in aqueous solutions.