Red-emitting gold nanoclusters for rapid fluorescence sensing of tryptophan metabolites

In this work, we first present a simple “green” preparation procedure of red-emitting (λemission = 645 nm, d = 1.5 ± 0.3 nm) fluorescent gold nanoclusters (Au NCs) using only γ-globulin (γG) immunoprotein as reducing and stabilizing agent. The γG-Au NCs are potent candidate for rapid detection of L-kynurenine (Kyn) which is a dominant molecule of the kynurenine pathway (KP) of the tryptophan (Trp) metabolism. Sensing of Kyn has been carried out in phosphate buffer (PBS) solution and in artificial cerebrospinal fluid (aCSF) with the calculated detection limit of 15 and 22 μM, respectively. Beyond the definition of the dynamic range of 15–100 μM and analytical parameters (KSV, k0, kq) the nature as well as the proposed mechanism of the quenching process was also suggested based on temperature-dependent spectrofluorometric studies. Moreover, a paper-based sensor technology was also successfully developed for rapid detection of Kyn with 5 μM detection limit.