Tuning the Optical Properties of Au Nanoclusters by Designed Proteins

Gold nanoclusters (AuNCs) are nanomaterials with interesting photoluminescent properties that can be endowed with biomolecular recognition and biocompatibility when stabilized with proteins. The interplay between the optical features of AuNCs and the function added by the protein makes them perfect candidates for generating hybrid protein‐inorganic nanomaterials. Focusing on protein stabilized‐AuNCs, hitherto most of the work has covered the use of natural proteins for in situ growth of AuNCs. However, the exploitation of design proteins for such endeavors enables fine‐tuning of the photoluminescent assets of AuNCs. In this work, rational protein engineering of modular protein scaffolds is applied for capping of non‐emissive, non‐passivated naked AuNCs, resulting in a fast and easy method for the synthesis of customizable and emissive protein‐AuNC nanomaterials. Tuning of the photoluminescent properties of the final hybrid module is obtained by appropriate choice of the coordination residues grafted on the same protein scaffold. The effects of ligands and coordination bonds are studied using time‐resolved photoluminescence and X‐ray absorbance spectroscopies, shedding light on the mechanisms behind the emerging properties of these hybrid materials. Moreover, the described versatile strategy opens new avenues for the synthesis of on‐demand photoluminescent hybrids for a wide spectrum of optical applications. Natural proteins are commonly used for in situ synthesis of photoluminescent gold nanoclusters (AuNCs). However, designed proteins provide an extra level of control over photoluminescence and biological functionality. Employing X‐ray and photophysical spectroscopy, this work deepens the structural characterization of two different emissive engineered protein‐cluster hybrids produced by an easy protocol derived from standalone nonemissive AuNCs.