Design and development of portable colorimetric sensor integrated with low-code smartphone application for rapid...

Heavy metal contamination of surface water, particularly lead, poses a severe global threat to aquatic ecosystems and public health. Conventional detection techniques, including Atomic Absorption Spectroscopy (AAS) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS), offer high sensitivity yet remain constrained by elevated operational costs, laboratory dependency, and inability to support real-time field monitoring. Although portable colorimetric alternatives exist, they frequently rely on toxic extraction solvents and lack cloud-integrated frameworks for field data management. This study presents the design and development of a portable, low-cost, green colorimetric sensor coupled with a smartphone application for rapid and accurate quantification of lead in surface water. The method exploits complexation of lead with 1,5-diphenylthiocarbazone (dithizone), with optimization identifying acetone as a superior monophasic solvent, eliminating chloroform-based extraction in accordance with Green Analytical Chemistry (GAC) principles. Optimal conditions were established at 0.05% w/v dithizone, a Pb:Dz volume ratio of 2:1, pH 2, and an absorbance wavelength of 600 nm, yielding a strong linear correlation (R² = 0.9925). To support field deployment, a low-code smartphone application was developed using Canva AI for interface design and Google Apps Script for cloud-based data processing via Google Sheets. Validation following international guidelines yielded a limit of detection (LOD) of 0.131 mg L^-1 and a limit of quantification (LOQ) of 0.260 mg L^-1. Bias assessment produced a Mean Absolute Error (MAE) of 8.68% and Root Mean Square Error (RMSE) of 11.08%. Recovery tests in real surface water matrices ranged from 82.00% to 117.75%, and a paired t-test confirmed no significant difference from AAS results.