Colorimetric detection of hypochlorite based on the morphological changes of silver nanoprisms to spherical nanoparticles

Abstract

In this work, we have developed a simple, rapid, sensitive and selective colorimetric method for the quantitative determination of hypochlorite (ClO⁻) ions by using triangular silver nanoprisms (AgNPRs) as a colorimetric probe. The synthesized AgNPRs were characterized by UV-visible absorption and high resolution transmission electron microscopy (HR-TEM) measurements. Upon the successive addition of increasing concentrations of ClO⁻ to AgNPRs, the absorption intensity of AgNPRs at 716 nm showed a gradual decrease with a significant blue shift. This phenomenon was accompanied by simultaneous enhancement in the absorption intensity near the in-plane quadrupole band at 470 nm along with a rapid color change of the AgNPR solution from blue to yellow. The observed spectral and color changes are attributed to ClO⁻ induced morphological transformation from triangular AgNPRs to spherical particles. The physiochemical and morphological characteristics of AgNPRs in the absence and presence of ClO⁻ were evidenced by HR-TEM, DLS and zeta potential measurements. The selectivity of the proposed assay was tested for its performance in the presence of other relevant interfering common anions and cations. It was observed that the presence of other interfering ions did not evoke any change in the color and absorption spectral profile of AgNPRs. The limit of detection (LOD) of the present method was calculated to be 2.50 × 10⁻¹⁰ mol dm⁻³ with a wide linear range of 2.00 × 10⁻⁷ mol dm⁻³ to 12.00 × 10⁻⁷ mol dm⁻³. The applicability of the proposed method was ascertained by performing the colorimetric assay for ClO⁻ in real water samples such as tap water and swimming pool water.