Highly selective and sensitive nanoprobes for cyanide based on gold nanoclusters with red fluorescence emission

We report a novel and environmentally friendly fluorescent probe for detecting the cyanide ion (CN⁻) using L-amino acid oxidase (LAAOx)-protected Au nanoclusters (LAAOx@AuNCs) with red emission. The fluorescence-based sensing behaviour of LAAOx@AuNCs towards anions was investigated in buffered aqueous media. Among the anions studied, CN⁻ was found to effectively quench the fluorescence emission of AuNCs based on CN⁻ induced Au core decomposition. Excellent sensitivity and selectivity toward the detection of CN⁻ in aqueous solution were observed. The CN⁻ detection limit was determined to be approximately 180 nM, which is 15 times lower than the maximum level (2700 nM) of CN⁻ in drinking water permitted by the World Health Organization (WHO). A linear relationship between the fluorescence intensity and CN⁻ concentration was observed in two ranges of CN⁻ concentration, including 3.2 × 10⁻⁶ to 3.4 × 10⁻⁵ mol L⁻¹ and 3.81 × 10⁻⁵ to 1.04 × 10⁻⁴ mol L⁻¹. The high sensitivity and selectivity to CN⁻ among the 17 types of anions make the AuNCs good candidates for use in fluorescent nanoprobes of CN⁻.