Smartphone‐assisted Colorimetric Detection of Nickel (II), Copper (II), and Zinc (II) in Water

ABSTRACT The development of portable analytical tools for detecting and quantifying heavy metals has attracted increasing interest in environmental and food safety monitoring. In this work, we developed a smartphone‐assisted colorimetric sensor for the detection of nickel(II), copper(II), and zinc(II) ions using a film‐shaped biopolymer composed of starch and gelatin, incorporating Xylenol Orange (XO) as the chromogenic agent. Upon contact with aqueous solutions containing these metal ions, the film exhibited distinct color changes—blue for Ni(II), purple for Cu(II), and pink for Zn(II)—enabling both visual detection and digital quantification. Color data were extracted from digital images using red–green–blue (RGB) analysis and reduced to principal components to construct calibration curves. The method demonstrated high analytical performance, particularly for Ni(II), with a linear range of 0–5 mg·L −1 , a correlation coefficient (R 2 ) of 0.9968, and limits of detection and quantification of 0.17 ± 0.02 and 0.21 ± 0.02 mg·L −1 , respectively. Although naked‐eye detection of Zn(II) and Cu(II) was not possible at their drinking‐water limits, the method remains suitable for monitoring higher concentrations relevant to industrial water and beverages. This simple, low‐cost, and portable sensing approach represents a promising tool for on‐site detection of heavy metals in water.