Plasmon-based colorimetric assay using green synthesized gold nanoparticles for the detection of bisphenol A.

Herein, we report a green synthesized gold nanoparticle (AuNPs) based colorimetric detection of bisphenol A (BPA). The AuNPs were synthesized using khat leaf extract as a reducing agent by optimizing factors affecting the AuNPs synthesis, including gold precursor concentration (1 mM), and reaction temperature (60 °C). The AuNPs characterization was carried out using ultraviolet-visible spectrophotometry and transmission electron microscopy, and it was found spherical with an average particle size of 17.3 ± 3.7 nm. A colorimetric nanosensor was developed by conjugation of bio-inspired AuNPs with BPA-specific aptamer for a quick and easy detection of BPA in plastic bottled water. The colorimetric assay relies on the strong affinity of BPA for aptamer, which causes detachment of the aptamer from the AuNPs surface in the presence of BPA inducing AuNPs aggregation. To achieve the colorimetric detection of BPA, the concentrations of NaCl and aptamer were optimized. The detection of BPA was monitored visually using a naked eye, as well as quantitatively using an ultraviolet-visible spectrophotometer. The method visual limit of detection (LOD) was determined to be 0.1 ng/mL and reached 0.09 ng/mL using ultraviolet-visible spectrophotometer. The method demonstrated very good linearity (R 2  = 0.9986) in the range of 0.1-100 ng/mL. The proposed method showed high sensitivity to BPA detection in plastic bottled water with 86.7-98.0%, recovery. Therefore, the proposed colorimetric nanosensor can be used for determination of BPA in plastic bottled waters with reliable performance at lower concentrations.