A highly sensitive and selective assay of doxycycline by dualwavelength overlapping resonance Rayleigh scattering.

A dual-wavelength overlapping resonance Rayleigh scattering (DWO-RRS) method was developed and validated for highly sensitive and selective assay of doxycycline residues in several meat samples. The response signals were dependent on the specific multi-site coordination between lanthanum(III) and doxycycline (DOTC). And La(III)-DOTC complex would further aggregate to form [La(III)-DOTC]n nanoparticles, resulting in the occurrence of two new scattering peaks. Notably, with the addition of DOTC, the increments of both of these two wavelengths were proportional to the concentration of DOTC over the ranges of 3.9-4.0×10(3) nmol L(-1) (1.7-1.8×10(3) μg/kg). The detection limit of DWO-RRS was 1.1 nmol L(-1) (0.5 μg/kg), which was lower than or comparable to most of the published methods. Additionally, the generating mechanisms of multi-response RRS signals were discussed and a semi-empirical principle was established for better design of multi-response RRS probes.