A ratiometric sensor for selective detection of Hg ions by combining second-order scattering and fluorescence signals of MIL-68(In)-NH.

Ratio fluorescence has attracted much attention because of its self-calibration properties. However, it is difficult to obtain suitable fluorescent materials with well-resolved signals simultaneously under one excitation. In this work, we report a different strategy, using MIL-68(In)-NH as both the fluorescence element and the scattered light unit, and coupling the fluorescence and the scattered light to construct the fluorescence and scattered light ratio system. Based on the optical properties and the second-order scattering (SOS) of the material nanoparticles, the synthesized MIL-68(In)-NH can be used to realize the ratio detection of Hg. Because the scattering intensity of small particle MIL-68(In)-NH is weak, SOS is not obvious. When Hg is introduced the coordination reaction between the amino nitrogen atoms of MIL-68(In)-NH and Hg make the particles larger, resulting in the decrease of fluorescence and the enhancement of SOS. As a result, a novel Hg ratiometric detection method is developed by using the dual signal responses of the fluorescence and scattering. Under the optimal conditions (pH = 6, reaction time 5 min, room temperature, and the maximum excitation wavelength 365 nm), the linear range of the method is 0-100 μM, and the detection limit is 5.8 nM (Ksv = 9.89 × 10 M). In addition, the probe is successfully used to evaluate Hg in actual water samples. Compared with the traditional method of recording only the fluorescence signal, the proposed fluorescence-scattering method provides a new strategy for the design of ratiometric sensors.