We performed quantum chemistry density functional theory calculations to provide insight and to calculate the response of nanographene (or molecular-graphene)-based sensors using Eu(III) complexes as a cold surrogate of trivalent actinide ions. We found that the electronic structure of graphene can be affected by its interaction with europium ions as well as with water molecules. We found an increase in electron transfer through the graphene-based device when exposed to a liquid sample of europium nitrate, Eu(NO<inf>3</inf>)<inf>3</inf>, and a decrease when Eu<inf>2</inf>O<inf>3</inf> approaches a graphene oxide surface. Because the detection mechanism of these nanosensors is based on changes in electron transfer when a trivalent europium complex approaches the graphene-based nanosensors, fabricating arrays of these nanosensors is encouraged.