A ratiometric sensor for selective detection of Hg2+ ions by combining second-order scattering and fluorescence signals of MIL-68(In)-NH2

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)-NH2 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)-NH2 can be used to realize the ratio detection of Hg2+. Because the scattering intensity of small particle MIL-68(In)-NH2 is weak, SOS is not obvious. When Hg2+ is introduced the coordination reaction between the amino nitrogen atoms of MIL-68(In)-NH2 and Hg2+ make the particles larger, resulting in the decrease of fluorescence and the enhancement of SOS. As a result, a novel Hg2+ 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 × 109 M-1). In addition, the probe is successfully used to evaluate Hg2+ 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.