Sensitive determination of tobramycin using homocystine capped gold nanoclusters as probe by second-order scattering

A novel photoluminescent Hcy-AuNCs has been developed through one-pot reduction method, to establish a tobramycin sensing by second-order scattering (SOS). Hcy-AuNCs could spontaneously assemble to small-scaled aggregation, resulting in remarkable intensity enhancement of scattered luminescence signals. The luminescence of Hcy-AuNCs could be clearly observed under ultraviolet lamp, when excited at 365 nm, a significant luminescent intensity at 741 nm was monitored in SOS spectra. The introduction of AuNPs would cause large-scaled aggregation of Hcy-AuNCs that was rapidly settled in the solution, resulting in the decrease of SOS intensity. Besides, the non-radiative energy transfer between AuNPs and Hcy-AuNCs would also reduce the luminescent intensity. However, the addition of tobramycin would cause the aggregation of AuNPs due to the electrostatic and covalent bonding between AuNPs and tobramycin, thus eliminating the interference of AuNPs. The luminescence of Hcy-AuNCs reappeared, exhibiting an optical response toward tobramycin. The good linearity was obtained in a wide range from 4 nM to 300 nM with a low detection limit of 0.27 nM. The selectivity was acceptable toward different types of antibiotics. Finally, the proposed method was successfully applied to the widely used tobramycin eye drops.