An Analytical Method for Detecting Toxic Metal Cations Using Cyclotriveratrylene Derivative Capped Gold Nanoparticles
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Due to the environmental and biological impact of metal ion contamination, the development of sensitive and selective detection systems for colorless metal ions is of great importance. The toxicity of heavy metals is well known, yet even essential metals are toxic at higher concentrations including zinc and also copper, which is implicated in neurodegenerative diseases. A variety of analytical devices have been developed for the detection of metal ions, including systems based on direct chemosensors, atomic fluorescence spectrometry (AFS), inductively coupled plasma mass spectrometry (ICP-MS), and atomic absorption spectroscopy (AAS). Although these techniques offer sensitive and selective analytical approaches, they are expensive, require sophisticated equipment, and lack the portability for on-site detection.
Unlike traditional organic fluorescent dyes, gold nanoparticles (AuNPs) have much stronger molar absorptivities that are 3–5 orders of magnitude higher than organic fluorescent dyes and are of great interest in chemical and biological sensingas well as for in vitro diagnostics. The optical properties of AuNPs are due to their unique surface plasmon resonance (SPR) where electrons on the surface of a AuNP are in collective oscillation and become in resonance with incident electro-magnetic radiation. Modified AuNPs make excellent colorimetric analytical platforms because AuNP aggregation due to analyte detection results in a distinct color change from red to blue.AuNPs with various surface-bound ligands have been previously employed to detect K+, and Ca2+, divalent heavy metals (Hg2+, Pb2+, Cd2+), Cr3+, and trivalent lanthanide ions. Herein we describe cyclotriveratrylene (CTV)-functionalized AuNPs that provide the basis for the design of an analytical tool that can be used for the detection of di- and trivalent metal ions in solution for the detection of metal ions of environmental concern.
Cyclotriveratrylene is a bowl-shaped supramolecular scaffold that we have previously employed through apex derivatization to provide a supramolecular scaffold with the concave bowl receptor pointed away from the surface, enabling CTV to function as a gold surface-bound host molecule. The crown and saddle conformers are comparable in energy and interconvert in solution