Abstract
Classical dye absorption-based pH test papers are widely used to measure the degree of acidity of media for quantification or semi-quantification by the observation of the naked eye on the variation of colour. However, it remains a challenging task to extend portable and cheap methods to a wide range of analytes for accurate quantification. Here, we report a dosage-sensitive test paper for the assay of mercury ions (Hg2+) with wide colour evolution. The ratiometric fluorescent probe was prepared by mixing blue-emission silicon nanocrystals (Si NCs) and red-emission carbon dots (r-CDs). The Si NCs serve as the reaction site and the r-CDs as the internal reference. Upon the addition of Hg2+, the blue fluorescence of the Si NCs was quenched, while the red fluorescence of the r-CDs remained constant, resulting in the consecutive fluorescence colour changes from blue to orange red. The probe demonstrates high selectivity and sensitivity of the visualization assay of Hg2+ with a detection limit of 7.63 nM. Moreover, we printed the ratiometric fluorescence probe result onto a piece of filter paper to prepare a test paper, which represents an on-site, sensitive, rapid and cost-effective method for the visual determination of Hg2+ by the naked eye.
Highlights
Heavy metal pollution has always been a serious environmental concern across the world for decades, being widely distributed in air, water, food and soil
The properties of the Si NCs and r-carbon dots (CDs) were characterized by fluorescence spectroscopy, Fourier transform infrared (FT-IR) spectra and transmission electron microscopy (TEM)
A higher magnification image of a single Si NC clearly revealed the interplanar spacing of 0.31 nm corresponding to the (111) lattice planes of Si [19,20], while the as-prepared red-emission carbon dots (r-CDs) possessed a good monodispersity with a diameter of approximately 20 nm
Summary
Heavy metal pollution has always been a serious environmental concern across the world for decades, being widely distributed in air, water, food and soil. The widely used methods for the determination of mercuric ions include atomic absorption spectroscopy [4], inductively coupled plasma mass spectroscopy [5], X-ray fluorescence spectrometry [6] and anodic stripping voltammetry [7]. These assays are of high sensitivity and selectivity, they are usually expensive and time-consuming, and require tedious sample pretreatments and expensive equipment operated by well-trained technicians. There is a great demand to develop a fast, sensitive and reliable assay of Hg2+ to improve food safety and environmental protection
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