Selective lead ion sensing via cotton pad-based Na₂EDTA capped AuNPs: A smartphone-assisted colorimetric method

Herein, Na₂EDTA-capped AuNPs specifically designed for selective smartphone-assisted colorimetric detection are synthesized and characterized. Na₂EDTA-capped AuNPs was synthesized and characterized by UV-Visible spectroscopy, ATR, Raman, XRD, SEM and EDX. The calculated activation energy of the produced nanoparticles was 0.2 eV. Using XRD and SEM, the average crystallite size was found to be approximately 25 nm. Only Pb²⁺ and Cd²⁺, among the following metal ions: Mg²⁺, K⁺, Ca²⁺, Co²⁺, Ni²⁺, Ba²⁺, Hg⁺, Bi²⁺, Pb²⁺, and Cd²⁺, caused the AuNa₂EDTA solution's hue to shift from reddish in color to blue. Pb²⁺ and Cd²⁺ were distinguished using a Na₂S solution. Cotton pad with AuNa₂EDTA integrated served as the substrate for metal ion adsorption. The GIMP software-supported smartphone was used to implement the color contrast (R) method. In the 10-2000 μM range, a straight line represented the relationship between 1/R and Pb²⁺ ion concentrations, with a limit of detection (LOD) of 0.28 μM was revealed. Real water sample collected from Rupsa River, Khulna, Bangladesh was tested by the developed colorimetric method to be 80 μM of Pb²⁺ ion. Combining the prevalence of smartphones and the potential of nanotechnology, a cotton-pad based platform functionalized with AuNa₂EDTA may be a ground-breaking method for the detection of Pb²⁺ ions in various media.