A Reversible Dual-Response Fluorescence Switch for the Detection of Multiple Analytes

This paper reports a reversible dual fluorescence switch for the detection of a proton target and 2,4,6-trinitrotoluene (TNT) with opposite-response results, based on fluorophore derivatization of silica nanoparticles. Fluorescent silica nanoparticles were synthesized through modification of the surface with a nitrobenzoxadiazole (NBD) fluorophore and an organic amine to form a hybrid monolayer of fluorophores and amino ligands; the resultant nanoparticles showed different fluorescence responses to the proton target and TNT. Protonation of the ammo ligands leads to fluorescence enhancement due to inhibition of photoinduced electron transfer (PET) between the amine and fluorophore. By contrast, addition of TNT results in fluorescence quenching because a fluorescence resonance energy transfer (FRET) happens between the NBD fluorophore and the formed TNT-amine complex. The fluorescence signal is reversible through washing with the proper solvents and the nanoparticles can be reused after centrifugal separation. Furthermore, these nanoparticles were assembled into chips on an etched silicon wafer for the detection of TNT and the proton target. The assembled chip can be used as a convenient indicator of herbicide (2,4-dichlorophenoxyacetic acid) and TNT residues with the use of only 10 mu L of sample. The simple NBD-grafted silica nanoparticles reported here show a reversible signal and good assembly flexibility; thus, they can be applied in multianalyte detection.