A novel, gold-nanocluster-based fluorescent sensor for cyanide in aqueous solution, which is based on the cyanide etching-induced fluorescence quenching of gold nanoclusters, is reported. In addition to offering high selectivity due to the unique Elsner reaction between cyanide and the gold atoms of gold nanoclusters, this facile; environmentally friendly and cost-effective method provides high sensitivity&-With-zthis'sensor, the lowest concentration to quantify cyanide ions ccould be down to 200 x 10(-9) M, which. is approximately 14 times lower tharr-the..moxotim, level (2.7 x 10(-6) M) of cyanide in drinking water permitted by the World Health Organization (WHO). Furthermore, several real water samples spiked with cyanide, including local groundwater, tap water, pond water, and lake water, are analyzed using the sensing system, and experimental results show that this fluorescent sensor exhibits excellent recoveries (over 93%). This highly sensitive and selective detection of cyanide in food, soil, water, and biological samples.