Highly sensitive colorimetric determination of nitrite based on the selective etching of concave gold nanocubes

Concave gold nanocubes are viable optical nanoprobes for the determination of nitrite ions. Herein, a novel approach was developed, based on the measurement of localized surface plasmon resonance absorption. The addition of nitrite ions selectively induced the etching of concave gold nanocubes, abrading the sharp vertices to spherical corners, which resulted in blue-shifted absorption accompanied by a color change from sapphire blue to light violet. The mechanism of selective etching of concave gold nanocube tips was elucidated by using X-ray photoelectron spectroscopy and atom probe tomography. The optimized detection of NO2- via the concave gold nanocube-based probe occurred at pH 3.0 and in 20 mM NaCl concentration at 40 degrees C. The absorption ratios (A(550 nm)/A(640 nm)) were proportional to the NO2- concentrations in the range 0.0-30 mu M, with a detection limit of 38 nM (limit of quantitation of 0.12 mu M and precision of 2.7%) in tap water. The highly selective and sensitive colorimetric assay has been successfully applied to monitor the nitrite ion concentrations in spiked tap water, pond water, commercial ham, and sausage samples.

Automated summary

Concave gold nanocubes are used as optical nanoprobes for the determination of nitrite ions by measuring localized surface plasmon resonance absorption, where the blue-shifted color change after selective etching provides a rapid assessment of concentration. The method showed high selectivity and sensitivity in detecting nitrite ions under different conditions, and has been successfully applied to various water and food samples.