Etching-induced morphological evolution of concave gold nanocubes for enhanced colorimetric sensing of cobalt ions based on Fenton-like reactions

Abstract

Cobalt is an essential trace element for human growth and development, but both its deficiency and excess can cause adverse health effects. Herein, we develop a rapid, visual, and highly sensitive colorimetric sensor for Co²⁺ detection using concave gold nanocubes (CGNs) as a novel probe based on a Fenton-like reaction-mediated etching mechanism. In the presence of H₂O₂ and Co²⁺, a Fenton-like reaction occurs and generates abundant superoxide radicals, which oxidize Au⁰ on CGNs surface to generate Au(SCN)₂⁻, leading to a morphological transformation from concave to spherical shapes. This process causes a significant reduction in the absorbance at 690 nm in the UV-vis spectrum of the sensor, while the absorbance at 535 nm increases apparently. Under optimized conditions (2.0 mM KSCN, pH 9.0, and a reaction time of 18 min), the sensor exhibits a good linear relationship between the absorbance ratio (A₅₃₅/A₆₉₀) and Co²⁺ concentration over the range of 0.5–400 nM, with a linear regression equation of A₅₃₅/A₆₉₀ = 0.00798C_Co2+ + 0.6128 and R² = 0.9906. Its limit of detection is 0.3 nM, surpassing that of most reported sensors, because of the high chemical activity and morphology-dependent optical properties of CGNs. This sensor shows excellent selectivity against common interfering ions (e.g., Mn²⁺ and Hg²⁺) and detects Co²⁺ in real water samples with good recoveries. This study proves that CGNs are efficient probes for the development of sensitive assays, which hold great potential in food safety and environmental monitoring applications.