Gold Nanoparticle Based Colorimetric Sensors for Heavy Metal Lons Detection

Abstract

Contamination of water by toxic metal ions can lead to serious environmental and health problems. Therefore, monitoring of toxic metal ions in water is very important in terms of improving public health and water quality. Common methods for toxic metal ion detection are often based on chromatographic and spectroscopic techniques such as inductively coupled plasma mass spectrometry (ICP-MS), atomic absorption spectrometry (AAS), and high performance liquid chromatography (HPLC). These methods are highly sensitive but they require intense technical training because of their complicated procedures, and they are expensive and time-consuming. Therefore, low cost, simple, rapid, and portable methods for metal ion detection are still highly desired. In this context, this thesis seeks development of facile colorimetric based methods for detection of toxic metal ion contaminated water using gold nanoparticles and amino acids. In this thesis, we report the preparation of two different gold nanoparticle based colorimetric method for this purpose. In the first approach, we demonstrate the preparation of a simple yet very sensitive (detection limit is 2.9 nM) colorimetric assay for rapid detection of Hg2+ in water using as-prepared citrate-capped gold nanoparticles and amino acid lysine. In addition, the assay showed good selectivity against Hg2+ and the analysis can be completed within only a few minutes. In the second approach, we report a facile colorimetric sensor array for detection of multiple toxic heavy metal ions (Hg2+, Cd2+, Fe3+, Pb2+, Al3+, Cu2+, and Cr3+) in water using 11-mercaptoundecanoic acid-capped gold nanoparticles and five amino acids (lysine, cysteine, histidine, tyrosine, and arginine). The presence of amino acids (which have functional groups that can form complexes with metal ions and gold nanoparticles) regulates the aggregation of the particles; it can either enhance or diminish the particle aggregation. Therefore, the color change enables naked-eye discrimination of all of the tested metal ions.