Highly selective, sensitive and simpler colorimetric sensor for Fe2+ detection based on biosynthesized gold nanoparticles

Abstract

Herein, we describe the fabrication of green bell pepper, Capsicum annuum L. extract capped gold nanoparticles (CA-AuNPs) in aqueous medium using tetrachloroaurate (HAuCl₄·3H₂O) 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 Fe²⁺ in the presence of several interfering cations including Fe³⁺. Importantly, the fabricated CA-AuNPs based colorimetric sensor functioned linearly in the range of 0.3-7.0 ppb Fe²⁺, based on increasing absorption intensity with R² value of 0.9938 using UV-Vis spectrometry. The limit of detection (LOD) and limit of quantification (LOQ) for Fe²⁺ were estimated as 0.036 and 0.12 ppb, respectively. Finally, the sensor was effectively tested for determination of Fe²⁺ in some locally collected real water samples.

Keywords: Capsicum annuum L.; Characterization; Fe(2+) sensing; Gold nanoparticles; Real water samples.