Colorimetric and visual detection of cyanide ions based on the morphological transformation of gold nanobipyramids into gold nanoparticles

In this study, we developed a facile, rapid, selective and sensitive colorimetric method for the detection of cyanide ions (CN-) by using gold nanobipyramids (Au NBPs). The structure and morphology of the as-prepared Au NBPs are characterized by UV-visible spectroscopy, high-resolution transmission electron microscopy (HR-TEM) and zeta potential measurements. Upon addition of increasing concentrations of CN- ions, the absorption intensity pertaining to the longitudinal localized surface plasmon resonance band of the Au NBPs decreased drastically with a blue shift. The spectral changes associated with an obvious visible color transition from wine red to pale red color are further utilized to determine the trace amount of CN- ions by the naked eyes. The observed spectral evolution and color changes are attributed to the morphological transformation of the Au NBPs into gold nanoparticles (Au NPs) upon CN- ion etching. The relative shift in the localized surface plasmon resonance (LSPR) band position of the Au NBPs is found to be proportional to the concentration of CN- ions ranging from 1 mu M to 15 mu M. The Au NBP colorimetric probe exhibited a detection limit as high as 1.58 nM. The selectivity of the Au NBP probe toward CN- ions is ascertained by performing the sensing assay in the presence of different anions. The proposed colorimetric assay provided a promising platform for the sensitive determination of CN- ions in different water samples with good recoveries.