Ratiometric fluorescent nanoprobes based on Resonance Rayleigh Scattering and inner filter effect for detecting alizarin red and Pb.

A new ratiometric fluorescent strategy for detection of alizarin red (ARS) was designed based on the fluorescence of CDs and scattered light of scatterer. The CDs-ARS system can be used to detect Pb based on that the complexation between ARS and Pb. With the addition of ARS, the fluorescence of CDs was apparently quenched via inner filter effect (IFE). Resonance Rayleigh Scattering (RRS) at 350 nm was enhanced by an increase in the number of scatterer. The value of ln(I/I) was linearly correlated with ARS concentration in the range of 0-80 μM, and the detection limit for ARS was calculated to be 68.1 nM. When Pb was added to the CDs-ARS system, the complexation of ARS with Pb increased the size of the scatterer, resulting in the increase of the RRS intensity at 350 nm. Due to the affinity between ARS and Pb, the overlap of the emission spectra of CDs and the absorption spectra of ARS was reduced, resulting in the IFE effect was inhibited and the recovery of the fluorescence of CDs. The value of I/I linearly increased with the addition of Pb within the range of 10-50 μM, the limit of detection was 36.8 nM. As for practical application, CDs and CDs-ARS were applied to detect ARS and Pb in tap water and poor water, respectively. The recovery values were obtained to be 95.4-98.8% and 93.4-101.7%. Furthermore, the system of CDs-ARS has been successfully applied to H1299 cell imaging.