Synthesis of AuNPs using a biogenic synthesis approach and its application in colorimetric quantification of cyanide in soil samples and toxicological evaluation using Daphnia magna.

Cyanide (CN⁻) is a highly toxic anion that can accumulate in air, soil, and water, posing severe risks to living organisms even at trace levels. Therefore, the development of an accurate and sensitive analytical method is crucial for the quantitation of cyanide. In this study, a simple, effective and reliable analytical method for the quantitative determination of cyanide in soil samples was developed using UV-Vis spectrophotometry and smartphone-based colorimetry methods with gold nanoparticles (AuNPs) synthesized from rosehip extract. UV-Vis absorption spectra indicated that the interaction between cyanide ions and AuNPs led to a significant decrease in the surface plasmon resonance (SPR) band at 524 nm. The experimental results demonstrated a linear relationship between cyanide concentrations and absorbance values within the range of 1.0-30 mg/L. Additionally, the linear range for the developed smartphone-based colorimetry method was found to be between 2.0 and 20 mg/L. Recovery experiments were conducted with the spiked soil samples to assess the applicability and accuracy of developed methods. Acceptable recovery results in the range of 78-128% showed that the proposed analytical methods can be used to determine CN- content in soil samples. Additionally, toxicological evaluation revealed that gold nanoparticles produced from rosehip exhibited dose-dependent toxicity against Daphnia magna (96-h LC₅₀ = 1.58 µM, 95% CI 0.90-3.60 µM) and caused DNA damage despite biogenic synthesis. A decreasing trend in cell viability with increasing concentration was observed, indicating potential biological risks.