Analytical Sciences

Alpha-Lipoic Acid Functionalized Silver Nanoparticles for Colorimetric Detection of Copper Ion

Kosin TEEPARUKSAPUN, Nicha PRASONGCHAN, and Auttachai THAWONSUWAN

Science Program, Department of General Education, Faculty of Liberal Arts, Rajamangala University of Technology Srivijaya, Songkhla 90000, Thailand

A facile, low cost, rapid and easy-to-use colorimetric sensor for the detection of Cu²⁺ ion is described using alpha-lipoic acid (ALA) functionalized AgNPs. The prepared ALA-AgNPs are yellow, and spherical with an average particle size of 9.23 ± 3.36 nm. The addition of Cu²⁺ ion resulted in the aggregation of ALA-AgNP solution and caused a visible color change from yellow to orange-brown, which could be detected by the naked eye and UV-vis spectrophotometer. Parameters affecting the sensitivity of the sensor were investigated, including ALA concentrations, reaction times, reaction volumes and pH. Under optimal conditions, the colorimetric sensor could detect Cu²⁺ ion in the range of 0.625 × 10⁻⁵ to 10 × 10⁻⁵ M with a linear coefficient (r) of 0.9978. The limit of detection (LOD) and limit of quantification (LOQ) were 0.43 × 10⁻⁵ M (4.3 μM) and 1.45 × 10⁻⁵ M (14.5 μM), respectively, which is lower than the limit set by the U.S. Environmental Protection Agency (EPA). This proposed method showed good selectivity and could detect Cu²⁺ within 5 min. Finally, the proposed method could be successfully applied for the analysis of Cu²⁺ ion in tap water samples.

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