Simultaneous measurement of Cr(III) and Cu(II) based on indicator-displacement assay using a colorimetric nanoprobe

Abstract High-performance analysis of heavy metal ions is great importance in both environment and food safety. In this work, a facile and reliable colorimetric sensor was presented for simultaneous detection of Cu2+ and Cr3+ based on indicator-displacement assay (IDA). As a typical silicate nanomaterials, ZnSiO3 hollow nanosphere (ZSHS) exhibited an outstanding ion exchange capacity. Zincon was incorporated with the ZSHS to form a zincon/ZSHS hybrid ionophore with a blue color. Upon the addition of Cr3+, IDA reaction and selective ion exchange occurred with the color change of zincon/ZSHS ionophore from blue to yellow. With such a design, colorimetric measurement of Cr3+ was realized. The linear concentration for Cr3+ detection ranged from 0.5 μM to 75 μM with the LOD of 83.2 nM. Furthermore, we also screened different kinds of complexing agents that may respond with zincon/ZSHS ionophore and various metal ions. It was found that tartaric acid (TA) showed the chelation capability of Zn2+-TA is stronger than that of Zn2+-zincon. Thus zincon/ZSHS/TA presented a yellow color due to the chelation reaction of Zn2+-TA, releasing the zincon as a free state. After addition of Cu2+, a stronger chelation reaction of Cu2+-zincon occurred. This process involved in the color change from yellow to blue and realized colorimetric measurement of Cu2+. The detection limit of Cu2+ was calculated to be 43.7 nM with linear range from 0.1 to 20 μM. In addition, the zincon/ZSHS nanoprobe was successfully applied for simultaneous measurement of Cu2+ and Cr3+ in sorghum and river water, indicating that the zincon/ZSHS nanoprobe provided a promising sensing platform in environment and food safety.