A rhodamine based nanosensor platform for Hg2+ sensing in near–perfect aqueous medium: Smartphone, test strip and real sample applications

Abstract

Herein, a rhodamine based nanosensor platform (RHD–NPs) was designed and prepared for the sensing of Hg2+ in the near–perfect aqueous medium (v/v, 0.01/99.99, acetone/water). The structure, aqueous stability, surface charge and particle size of RHD–NPs were analyzed by using zeta particle sizer, scanning electron microscopy (SEM) and UV–Vis spectrophotometry. The spherical shaped morphology ofRHD–NPshas 61.4 nm particule size. The interaction ability of RHD–NPstowards various heavy metal ions was evaluated with UV–Vis and fluorescence spectroscopies. After the transferring of Hg2+ to RHD–NPs, a new absorption band at 562 nm was observed due to the ring–opening mechanism of rhodamine structure. The remarkable emission enhancement at 582 nm was observed through the adding of Hg2+ because of chelation–enhanced fluorescence (CHEF) and aggregation–induced enhanced emission (AIEE) phenomena. RHD–NPs nanosensor system showed good selectivity for Hg2+ monitoring with a nanomolar–level detection limit of 6.56 nM. The binding constant ofRHD–NPswith Hg2+ was determined to be 10.06 × 103 M−1 based on the Benesi–Hildebrand graph and a maximum value of Job’s graph was about 0.5 ratio (1:1) between RHD–NPs and Hg2+.The smartphone–based technique revealed an outstanding potential of the RHD–NPsplatform for the sensing of Hg2+ without further device. A visual colorimetric strip based on papers with excellent selectivity towards Hg2+ without interfering competition ions, was produced with the white–to–pink color signal change. The RHD–NPswas also employed for the quantitative determination and real–time monitoring of Hg2+ in real samples.