Highly sensitive ratiometric quantification of cyanide in water with gold nanoparticles via Resonance Rayleigh Scattering

A highly sensitive and selective ratiometric sensor for the quantification of cyanide (CN⁻) in aqueous samples has been developed using spherical gold nanoparticles (AuNPs) stabilized by polysorbate 40 (PS-40). Three different AuNP sizes (14, 40 and 80 nm mean diameters) were used to evaluate the response of the sensor using both colorimetric and Resonance Rayleigh Scattering (RRS) detection schemes. The best results were obtained for the sensor using 40 nm AuNPs, for which the limits of detection (LODs) were found to be 100 nmol L⁻¹ in a benchtop instrument and 500 nmol L⁻¹ by the naked eye, values well below the maximum acceptable level for drinking water (1.9 µmol L⁻¹) set by the World Health Organization (WHO). The practical use of the 40 nm-AuNPs RRS sensor was demonstrated with the determination of CN⁻ in drinking and fresh waters. Finally, the sensor was successfully implemented in a compact portable device consisting of two light-emitting diodes (LEDs) and a miniature spectrometer, turning this sensor into a very potent tool for its application as a quick routine field-deployable analytical method.