Aggregation-based fluorescence amplification strategy: "turn-on" sensing of aminoglycosides using near-IR carbocyanine dyes and pre-micellar surfactants.

This study is aimed at developing sensing schemes without obtaining selective receptors. A series of simple carbocyanine dyes was synthesized, whose emission was quenched in water with formation of nanoparticles in the range of 20-100 nm. Fluorescence in near-IR region is "turned on" in the presence of a drug cation of middle molecular weight (400-700 Da) and sodium dodecyl sulfate (SDS), as well as anionic drugs and a cationic surfactant (cetyltrimethylammonium bromide, CTAB). Aggregates (clusters) up to 100-200 nm in size were detected using dynamic light scattering (DLS) and Rayleigh light scattering (RLS) techniques in the systems: cationic analyte-SDS, carbocyanine dye-CTAB, and in all brightly fluorescent ternary systems dye-surfactant-analyte. Small ions (<200 Da) incapable of multi-point binding do not form the aggregates or cause the emission enhancement. The "turn-on" signal is only observed at the surfactant submicellar concentrations insufficient to solubilize the dye nanoparticles. Based on these findings, we suggest a rapid and simple method for the detection of ≥4·10-5 mol/L of neomycin in urine. The proposed strategy paves the way for developing more selective methods.