Noble metal nanoclusters allow for the atomically-precise control of their composition. However, to create nanoclusters with pre-defined optical properties, comprehensive description of their structure-property relation is required. Here, we report the gold atom doping impact on one-photon and two-photon absorption (TPA) and luminescence properties of ligated silver nanoclusters via combined experimental studies and time-dependent density functional theory simulations (TD-DFT). We synthesized a series of Ag 25À x Au x -(DMBT) 18 nanoclusters where x = 0, 1 and 5-10. For Ag 24 Au 1 (DMBT) 18 we demonstrate that the presence of the central Au dopant strongly influences linear and non-linear optical properties, increasing photoluminescence quantum yield and two-photon brightness, with respect to undoped silver nanoclusters. With improved TPA and luminescence, atomically-precise AuAg alloys presented in our work can serve as robust luminescent probes e.g. for bioimaging in the second biological window.

Atomically precise gold nanoclusters are a fascinating class of nanomaterials that exhibit molecule-like properties and have outstanding photoluminescence (PL). Their ultrasmall size, molecular chemistry, and biocompatibility make them extremely appealing for selective biomolecule labeling in investigations of biological mechanisms at the cellular and anatomical levels. In this work, we report a simple route to incorporate a preformed Au 25 nanocluster into a model bovine serum albumin (BSA) protein. A new approach combining small-angle X-ray scattering and molecular modeling provides a clear localization of a single Au 25 within the protein to a cysteine residue on the gold nanocluster surface. Attaching Au 25 to BSA strikingly modifies the PL properties with enhancement and a redshift in the second near-infrared (NIR-II) window. This study paves the way to conrol the design of selective sensitive probes in biomolecules through a ligand-based strategy to enable the optical detection of biomolecules in a cellular environment by live imaging.

Cancer is one of the leading causes of premature death, and, as such, it can be prevented by developing strategies for early and accurate diagnosis. Cancer diagnostics has evolved from the macroscopic detection of malignant tissues to the fine analysis of tumor biomarkers using personalized medicine approaches. Recently, various nanomaterials have been introduced into the molecular diagnostics of cancer. This has resulted in a number of tumor biomarkers that have been detected in vitro and in vivo using nanodevices and corresponding imaging techniques. Atomically precise ligand-protected noble metal quantum nanoclusters represent an interesting class of nanomaterials with a great potential for the detection of tumor biomarkers. They are characterized by high biocompatibility, low toxicity, and suitability for controlled functionalization with moieties specifically recognizing tumor biomarkers. Their non-linear optical properties are of particular importance as they enable the visualization of nanocluster-labeled tumor biomarkers using non-linear optical techniques such as two-photon-excited fluorescence and second harmonic generation. This article reviews liganded nanoclusters among the different nanomaterials used for molecular cancer diagnosis and the relevance of this new class of nanomaterials as non-linear optical probe and contrast agents.

Atomically precise, ligand-protected gold nanoclusters (AuNCs) attract considerable attention as contrast agents in the biosensing field. However, the control of their optical properties and functionalization of surface ligands remain challenging. Here we report a strategy to tailor AuNCs for the precise detection of protein carbonylation—a causal biomarker of ageing. We produce Au15SG13 (SG for glutathione) with atomic precision and functionalize it with a thiolated aminooxy moiety to impart protein carbonyl-binding properties. Mass spectrometry and molecular modelling reveal the key structural features of Au15SG12-Aminooxy and its reactivity towards carbonyls. Finally, we demonstrate that Au15SG12-Aminooxy detects protein carbonylation in gel-based 1D electrophoresis by one- and two-photon excited fluorescence. Importantly, to our knowledge, this is the first application of an AuNC that detects a post-translational modification as a nonlinear optical probe. The significance of post-translational modifications in life sciences may open avenues for the use of Au15SG13 and other nanoclusters as contrast agents with tailored surface functionalization and optical properties.

We report the chemical substitution mediated doping of silver atoms into the Au10SG10 (SG: glutathione) catenane nanoclusters in a controllable manner. Two levels of doping were conducted leading to two silver-doped Au10-xAgxSG10 nanoclusters (with x=0-2 and x=1-4). Optical studies reveal that nanoclusters with high level of doping (x=1-4) feature a blue shift in absorption and a significant red shift of ~ 50 nm in the two-photon excited emission spectrum with respect to pristine Au10SG10. The preservation of the catenane structure is confirmed by comparing experimental and computational X-ray diffraction patterns and absorption spectra of Au10SG10 and its silver-doped analogues. In order to better address the structure-property relationship in such catenane clusters, further theoretical investigations were performed at DFT level. A high-energy shift of the S1 state is evidenced in the calculated one-photon absorption spectra due to a larger s to d gap in silver caused by smaller relativistic effects in comparison to the gold atoms. Furthermore, the red-shift in the two-photon excited emission band of the clusters is due to significantly larger calculated relaxation of the first excited state in nanoclusters with high level of silver doping.