Smartphone-assisted lateral flow nanosensor for the selective detection of GHB in urine

We report a rapid test strip based on mesoporous silica nanoparticles functionalized with a specific GABA_B 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 GABA_B receptor protein. In the presence of GHB, competitive binding produces GABA_B receptor protein displacement, leading to pore opening and fluorophore release, which is detected via fluorescence readout. The nanosensor demonstrated high sensitivity, with a limit of detection (LOD) of 168 μM in buffer solution and 41 μM in diluted urine. Selectivity assays showed highly specific sensor response over common drugs such as cocaine, morphine, MDMA, heroin, scopolamine, 1,4-butenediol (1,4-BD), γ-aminobutyric acid (GABA), and γ-butyrolactone (GBL). The sensing material was also incorporated into a lateral flow assay (LFA) platform with a smartphone-assisted fluorescence readout, providing a rapid, portable, and low-cost analysis of GHB. The resulting test strip exhibited high sensitivity, with a LOD of 0.28 μM in diluted urine, which is low enough to clearly distinguish between physiological endogenous GHB levels (∼96 μM) and exogenous intake within only 1 min, a crucial requirement in forensic and clinical toxicology. This portable, cost-effective method holds strong potential for on-site forensic and clinical GHB screening.