Abstract: The present invention relates to a kit, device and method for detection of metals in aqueous media. The invention is based on complexation reactions of organic azo-dyes with heavy metals, utilizing a specially designed polymeric film matrix to which an organic azo-dye and an organic solvent are added. When submerged in water contaminated with heavy metals, the polymeric film changes its color. The azo-dyes are injected into the tested water, resulting in formation of nano-particles of insoluble complexes. The polymeric film embeds and dissolves these nano-particles and thus allows for spectral and/or visual analysis.