Chromogenic vesicles for aqueous detection and quantification of Hg ²⁺ /Cu ²⁺ in real water samples

Mercury and copper are toxic environmental pollutants, which pollutes air, water and land posing a sever threat to the human health. For instant valuation, a qualitative method (colorimetric) for recognition of these analytes can be a better choice. However, for precise measurement, below the threshold value, a quantitative method is needed. Herein, we present the aqueous and visual detection of these analytes through the polymer vesicles functionalized with rhodamine based chemical sensor 2-(6-bromobenzo[d]thiazol-2-yl)-3′,6′-bis(diethylamino)spiro[isoindoline-1,9′-xanthen]-3-one (BTDX). The synthesized vesicular sensor exploits the self-assembling nature of the alternating copolymer followed by robust coordination of metallic ions with highly electronegative atoms i.e. oxygen nitrogen and Sulphur. During the sensing process, this interaction leads to the spirolactam ring opening of xanthene moiety attached to the surface of the polymeric vesicular sensor. This ring opening owes to the substantial increase in the spectral pattern (fluorescence and UV–Visible) of the vesicular sensor. Consequently, this binding behavior leads to the competitive cation study which result into the transformation of P(DO-a-DTODT)-g-BTDX@ vesicles (colorless) to the P(DO-a-DTODT)-g-BTDX-Hg ²⁺ /Cu ²⁺ complexed vesicle (pink colored) solutions. This colorimetric transition evidence the naked eye detection of these analytes. Additionally, the lower limit of detection was calculated as low as 20 nM for Hg ²⁺ and 30 nM for Cu ²⁺ . Finally, seawater was employed to quantify these environmental pollutants. The findings reveal that the vesicular sensor has excellent ability to quantify these pollutants in terms of %age recovery. The calculated value was not less than 95%.