Spectrophotometric determination of Fe(III) by using casein-functionalized gold nanoparticles
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The preparation and application of casein-capped gold nanoparticles (AuNPs) as a specific probe for ferric ions Fe(III) is reported. The functionalized AuNPs exhibit narrow size distribution and form stable dispersions in water of different ionic strengths and basicity. The presence of diverse functional groups from the side chain of peptides warrants colloidal stability of AuNPs and also assists recognition of Fe(III) in versatile conditions. Fe(III) ion reportedly causes the aggregation of AuNPs and a red-shift in absorbance toward longer wavelength (660 nm). A spectrophotometric method is appropriate for selective detection of Fe(III) and the spectral shift is also accompanied by a color change from red to blue. The aggregation of AuNPs is not suppressed after the addition of NaOH or at moderate ionic strength. The resulting spectrophotometric method works for Fe(III) in the concentration range of 0.1 to 0.9 μM and has a detection limit of 450 nM. The AuNP probe can also detect Fe(III) ion content in real samples at the same detection limit, which is much lower than the maximum contaminant level allowed for Fe(III) in drinking water (5.37 μM) by the U.S. Environmental Protection Agency.
KeywordsDrinking water Metal ions Ferric ions Aggregation assay Ionic strength effect Capping FTIR HR-TEM SAED
This research was supported by National Research Foundation South Korea under the project number 2017R1C1B-5017360. This research was also supported by Dongguk University-Seoul research fund 2016-2017. The authors extend their appreciation to the Deanship of Scientific Research at King Saud University for partly funding this work under research group No (RG-1438-078).
Compliance with ethical standards
The authors declare that they have no financial and competing interest.
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