Gold/silver bimetallic nanoclusters stabilized by immunoprotein: Tuning the selectivity for identification of kynurenine pathway metabolites

Template-assisted green chemistry protocol for production of bimetallic gold/silver nanoclusters (Au/Ag NCs) with controlled noble metal composition is presented for the first time, where the synthesis of orange-emitting (λem = 634 nm) ultrasmall NCs, which exhibit outstanding kinetic stability in physiological conditions, has been carried out by γ-globulin (γG) immunoprotein as reducing and stabilizing agent. In addition to the optimization of the fabrication protocol, detailed optical and structural characteristics are also presented. In our previous work we demonstrated the applicability of γG-stabilized NCs with pure gold content for identification of the kynurenine pathway metabolites and a paper-based quick test was also designed for L-kynurenine (Kyn). In present work, we confirmed that the selectivity of the pure γG-Au NCs can be systematically shifted to the detection of kynurenic acid (Kyna) by controlled silver doping (∼10 %). Sensing measurements were carried out in both phosphate buffer saline (PBS) solution and artificial cerebrospinal fluid (aCSF), where the calculated detection limits are 64.0 and 80.0 µM, respectively. Both the quenching process and the thermodynamic nature of the interaction between the Kyna and γG-Au/Ag NCs were interpreted, which confirm the electron-induced charge transfer between them.