Simple bare gold nanoparticles for rapid colorimetric detection of Cr³⁺ ions in aqueous medium with real sample applications

Facile bare gold nanoparticles (AuNPs) were synthesized via borohydride reduction method and evidenced the colorimetric sensor selectivity to Cr³⁺ ions among Na⁺, Ni²⁺, Fe³⁺, Cd²⁺, Cr³⁺, K⁺, Cu²⁺, Ca²⁺, Mg²⁺, Ga³⁺, Fe²⁺, Ba²⁺, Al³⁺ Ag⁺, Co²⁺, Zn²⁺, Pb²⁺, Mn²⁺ and Hg²⁺ ions. The color of bare AuNPs changed rapidly from red to blue via Cr³⁺ induced aggregation. These Cr³⁺-induced aggregation of bare AuNPs were monitored by naked eye and using UV-vis spectroscopy. The SPR absorbance (654 nm) of the reaction between bare AuNPs and Cr³⁺ showed a good linearity with a low detection limit of 13.42 nM. The optimal detection of Cr³⁺ was achieved between pH ranges from 5 to 11 and its reversibility was well established with EDTA. In addition, the bare AuNPs which were successfully applied for the detection of Cr³⁺ in tap and lake water displays low interference.