We report a rapid test strip based on mesoporous silica nanoparticles functionalized with a specific GABAB receptor agonist to selectively detect γ-hydroxybutyric acid (GHB) in urine samples. The sensing mechanism involves rhodamine B-loaded MCM-41 silica nanoparticles whose pores are capped with a GABA-derived ligand (baclofen) acting as a gatekeeper via supramolecular interactions with the GABAB receptor protein. In the presence of GHB, competitive binding produces GABA<s