Fast and selective colorimetric detection of Fe<SUP>3+</SUP> based on gold nanoparticles capped with ortho-hydroxybenzoic acid

A fast and selective colorimetric sensor for detecting Fe3+ was developed using gold nanoparticles capped with ortho-hydroxybenzoic acid (o-HBA AuNPs). This sensor was characterized using UV-Vis spectroscopy, FTIR spectroscopy, XRD, and TEM. The absorbance of surface plasmon resonance (SPR) at 534 nm increased after the addition of Fe3+. It was confirmed by FTIR, XRD, and TEM data indicating that Fe3+ acted as a bridge among the capping agents of AuNPs. The bridges blocked AuNPs from aggregation and caused an increase in the uniformity distribution of o-HBA AuNPs. Under the optimized condition, this sensor had a good calibration curve linearity at 534 nm. The value of R-2 obtained was 0.9994 with LoD of 9.19 mu M and LoQ of 30.57 mu M. This sensor exhibited good precision and accuracy for Fe3+ detection in rice field, river, and sea waters and has been successfully used to detect Fe3+ in the real water samples collected from various locations of Code River, Yogyakarta, Indonesia.