Biothiols as Chelators for Preparation of N‑(aminobutyl)-N-(ethylisoluminol)/Cu<sup>2+</sup> Complexes Bifunctionalized Gold Nanoparticles and Sensitive Sensing of Pyrophosphate Ion

In this work, chemiluminescence (CL) reagent and catalyst metal ion complexes bifunctionalized gold nanoparticles (BF-AuNPs) with high CL efficiency were synthesized via an improved synthesis strategy. Biothiols, such as cysteine (Cys), cysteinyl-glycine (Cys-Gly), homocysteine (Hcy), and glutathione (GSH), instead of 2-[bis­[2-[carboxymethyl-[2-oxo-2-(2-sulfanylethylamino)­ethyl]­amino]­ethyl]­amino]­acetic acid (DTDTPA), were used as new chelators. N-(aminobutyl)-N-(ethylisoluminol) (ABEI) was used as a model of CL reagents and Cu<sup>2+</sup> as a model of metal ion. In this strategy, biothiols were first grafted on the surface of ABEI-AuNPs by Au–S bond. Then, Cu<sup>2+</sup> was captured onto the surface of ABEI-AuNPs by the coordination reaction to form BF-AuNPs. The CL intensity of Cu<sup>2+</sup>-Cys/ABEI-AuNPs was 1 order of magnitude higher than that of DTDTPA/Cu<sup>2+</sup>-ABEI-AuNPs synthesized by the previous work. Moreover, strong CL emission of Cu<sup>2+</sup>-Cys/ABEI-AuNPs was also observed in neutral pH conditions. In addition, the present BF-AuNPs synthesis method exhibited advantages over the previous method in CL efficiency, simplicity, and synthetic rate. Finally, by virtue of Cu<sup>2+</sup>-Cys/ABEI-AuNPs as a platform, a simple CL chemosensor for the sensitive and selective detection of pyrophosphate ion (PPi) was established based on the competitive coordination interactions of Cu<sup>2+</sup> between Cys and PPi. The method exhibited a wide detection range from 10 nM to 100 μM, with a low detection limit of 3.6 nM. The chemosensor was successfully applied to the detection of PPi in human plasma samples. It is of great application potential in clinical analysis. This work reveals that BF-AuNPs could be used as ideal nanointerface for the development of novel analytical methods.