Sensitive detection of polymyxin B sulfate at the nanogram level using enhanced resonance scattering signals and decreased fluorescence signals with thioglycolic acid capped CdTe/CdS quantum dots as probe

Thioglycolic acid-capped (TGA-capped) CdTe/CdS quantum dots (QDs) were prepared in the water phase. The interaction of TGA-CdTe/CdS QDs with polymyxin B sulfate (POBS) was investigated by ultraviolet-visible (UV-vis) absorption, fluorescence (FL), resonance Rayleigh scattering (RRS) spectroscopy and the measurement of fluorescence lifetime. Under optimum conditions, not only the UV-vis absorption and fluorescence spectra were changed, but also the RRS intensity was greatly enhanced. These phenomena offered useful techniques for the determination of POBS with fluorescence quenching and RRS methods. The linear ranges and detection limits of POBS were 0.09-5.25 μg mL−1 and 27.5 ng mL−1 for the fluorescence quenching technique, 0.02-6.0 μg mL−1 and 6.36 ng mL−1 for the RRS technique. Among them, the RRS approach obtained the higher sensitivity. Accordingly, a novel rapid, convenient, and highly sensitive RRS method for the determination of POBS was proposed and applied to detect POBS in pharmaceutical preparations with satisfactory results. Furthermore, the suitable reaction conditions, affecting factors as well as the influence of coexisting substances were studied. Some possible reaction mechanisms were also discussed.