Highly selective, sensitive and simpler colorimetric sensor for Fe detection based on biosynthesized gold nanoparticles.

Herein, we describe the fabrication of green bell pepper, Capsicum annuum L. extract capped gold nanoparticles (CA-AuNPs) in aqueous medium using tetrachloroaurate (HAuCl·3HO) as precursor salt and sodium hydroxide (NaOH) solution as accelerator as well as pH adjuster. Formation of CA-AuNPs was verified via colour change from yellowish to ruby red with further confirmation through surface plasmon resonance (SPR) band at 519 nm using ultraviolet violet-visible (UV-Vis) spectroscopy. Other characterizations techniques include, Fourier transform infra-red (FTIR) spectroscopy, atomic force microscopy (AFM), dynamic light scattering (DLS) with Zeta-potential analysis (ZPA) and X-ray diffraction (XRD) method. The resulting AuNPs were efficaciously implemented as highly sensitive colorimetric sensor for selective detection of Fe in the presence of several interfering cations including Fe. Importantly, the fabricated CA-AuNPs based colorimetric sensor functioned linearly in the range of 0.3-7.0 ppb Fe, based on increasing absorption intensity with R value of 0.9938 using UV-Vis spectrometry. The limit of detection (LOD) and limit of quantification (LOQ) for Fe were estimated as 0.036 and 0.12 ppb, respectively. Finally, the sensor was effectively tested for determination of Fe in some locally collected real water samples.