Green synthesis of highly luminescent gold nanoclusters and their application in sensing Cu(II) and Hg(II)

Abstract

A novel synthetic strategy for high luminescent gold nanoclusters (AuNCs) based on coffee Arabica seeds extract (CASE) is presented in this work. We have designed and developed a green technique that enhanced the selectivity of gold nanoclusters towards Cu(II) and Hg(II) ions. The coffee extract was used as a stabilizer and reducing agent in the synthesis process of AuNCs. The as-prepared AuNCs were characterized in terms of size, surface modification, and composition utilizing different advanced techniques. The CASE-AuNCs responded to these significant metal ions through the quenching phenomenon of the AuNCs fluorescence. EDTA and sodium borohydride were utilized as masking agents. Further, EDTA is bind to Cu(II) ion forming a metal complex and shielding the quenching effect of Cu(II) ions on CASE-AuNCs fluorescence through electron or energy transfer. Besides, Hg(II) is reduced to mercury Hg0 in the presence of sodium borohydride and prevents the quenching effect of Hg(II)-CASE-AuNCs system. Thus, considerable selectivity of AuNCs was achieved towards these two metal ions allowing sensitive determination even one of these metal ions coexists in the environment. The AuNCs have detection limits for Cu(II) and Hg(II) in nanomolar level. The as-prepared CASE-AuNCs were used successfully to detect Cu(II) and Hg(II) ions in real samples.