Dye nanoparticle or nanocomposite- coated test papers for detection at ppb levels of harmful ions

We have proposed a next-generation simple method for water analysis with high sensitivity to trace ions at ppb levels, named "dye nanoparticle-coated test strip" (DNTS). The DNTS is loaded with a thin layer (400 nm ~ 3 μm) of indicator dye nanoparticles or nanocomposites on the top surface of a membrane filter and provides a remarkably concentrated color signaling surface. Therefore, almost all signals are available efficiently, but in contrast to conventional test papers, indicator dyes are distributed over the entire support. The DNTS is applicable not only to immersion test but also to filtration enrichment in which target metal ions are concentrated by passing sample solutions through it. In addition, we designed two fabrication methods of DNTSs for the purpose of producing a large number of test strips with various organic indicator dyes. One method is ideal for hydrophobic indicators and is based on nanoparticle preparation by reprecipitation method. The other is suitable for hydrophilic dyes and is based on the preparation of nanocomposite composed of a water-soluble dye and nanoadsorbent through electrostatic interaction and the following aggregation. By simple filtration of the respective nano-dispersions with a fine membrane filter having microscopic pores, various kinds of DNTSs are available.