In this study, a versatile sensing platform based on a commercially available filter paper for the development of a colorimetric sensor using label-free gold nanoparticles (AuNPs) for the detection of cyanide in water is presented. The developed sensor can be applied for the direct detection of cyanide from an aqueous sample efficiently in a wide concentration range. The synthesised AuNPs were found to have an average size of about 13.2 ± 2.65 nm with a surface plasmon resonance peak at around 525 nm. Successful integration of AuNPs on the WFP substrate was observed through the FESEM-EDX analysis and supported by the presence of an absorbance peak at about 528 nm on the spectrum of the WFP-AuNPs composite. The colour of the WFP-AuNPs composite changed from purple-red to white in the presence of cyanide. Using the paper-based sensor, the limit of detection is calculated to be 7.68 × 10−6 M (0.5 ppm). The said sensitivity is good enough for the determination of cyanide in industrial wastewater samples. The developed sensor also showed excellent selectivity towards cyanide over other ions, demonstrating its practical applicability to monitor cyanide contamination in different environmental samples. Furthermore, the applicability of the sensor was demonstrated using several real water samples spiked with cyanide, including creek and tap water. Notably, the sensor showed great promise for the rapid, cost-effective, and versatile monitoring of cyanide contamination in various aqueous samples.

This work presents the synthesis of silver nanoparticles (AgNPs) capped with polyvinylpyrrolidone (PVP) via a simple chemical reduction approach. A route in controlling the optical absorbance of the AgNPs by varying the concentration of silver precursors, as reflected by the shifts and broadening of the UV-vis spectra of the AgNPs is also highlighted. Dynamic Light Scattering results revealed the narrow and small hydrodynamic size for AgNPs synthesized at low precursor concentration, while multiple hydrodynamic size peaks were observed for AgNPs produced at high precursor concentration. Likewise, Fourier transform-infrared spectroscopy confirmed the successful capping of PVP on the AgNPs through the O and N atoms as potential binding sites. Transmission electron micrographs revealed the formation of spherical PVP-capped AgNPs, having no apparent aggregation observed. A closer inspection of the micrograph showed the subsequent formation of rod-like growth template of the AgNPs, that might lead to the formation of non-spherical silver nanostructures.