Red gum-capped gold nanoparticles for electrochemical sensing of bromocresol purple in water

Bromocresol purple (BCP) dye changes the chemical and physical properties of water, thereby affecting the aquatic organisms. Therefore, it is highly necessary to assess BCP in water samples. Herein, gold nanoparticles (AuNPs) capped with red gum were used for assessing BCP in river water. First, AuNPs were synthesized via the reduction of Au(iii) using red gum as a reducing and stabilizing agent. The synthesized AuNPs were then optically identified by ultraviolet-visible (UV-Vis) spectroscopy, which showed the characteristic absorption peak of AuNPs at 530 nm. Additionally, they were electrochemically identified using the square-wave voltammetry (SWV) technique, which monitored the characteristic oxidation peak of AuNPs at 1 V. Furthermore, transmission electron microscopy (TEM) revealed that AuNPs are spherical with an average size of 25 nm. Moreover, X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy were used to characterize the surface functionalization of the synthesized AuNPs. Next, a glassy carbon electrode (GCE) was immersed in a suspension of red gum-AuNPs for 30 min. Then, red gum-AuNPs/GCE was electrochemically characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results of CV and EIS confirmed the catalytic activity of AuNPs and a 1.5-fold increase in the active surface area of the GCE after modification. The red gum-AuNPs/GCE sensor was used for detecting BCP via its oxidation through one-proton and one-electron transfer. The described SWV method was optimized and validated. The sensor showed detection and quantification limits of 0.015 and 0.05 ppm, respectively. Moreover, the sensor was applied for detecting BCP in river water samples over a wide linear range with an acceptable recovery value of 99%, which denotes the high sensitivity of the elucidated SWV method for the assay of BCP dye. Red gum-capped gold nanoparticles showed higher catalytic activity for the electrochemical oxidation of bromocresol purple dye.