Slow and controlled visible photo-reduction of AgNO 3 by synthetic azo food-dyes in aqueous media produces spherical silver nanoparticles (Ag NPs). These show excellent selectivity toward inorganic anions (sulfide (S 2− ) and cyanide (CN − ) with lowest detection limit (LOD) of ∼60ppb. Complete photo-degradation of these dyes during nanoparticle formation can be very useful for environmental remediation and removal of dye toxicity. Detection of water soluble S 2− and CN − is achieved by spectroscopic technique (fluorescence turn-on process), based on the etching of Ag NPs. Selectivity with respect to either of these two ions (S 2− or CN − ) is achieved by using suitable masking agents. This simple, rapid, and significantly low-cost sensing protocol can be employed at ease.