DNA Nanoribbon-Assisted Intracellular Biosynthesis of Fluorescent Gold Nanoclusters for Cancer Cell Imaging

Glutathione: a naturally occurring tripeptide for functional metal nanomaterials

Glutathione (GSH), a naturally occurring tripeptide, plays an important role as an intracellular antioxidant in the physiological microenvironment and participates in redox balance, detoxification, and cellular and disease regulation. The unique structural features of GSH, including the reductive thiol and multiple coordination sites (carboxyl and amino group), make it a significant molecule not only in the physiological context but also as a ligand in the development of functional metal nanomaterials. In this context, GSH's role as a protective ligand and reducing agent in surface etching and ligand exchange reactions has been explored at the molecular level, expanding the diversity of GSH-protected metal nanomaterials. With photoluminescence (PL) as one of its most intriguing properties, investigations into GSH's influence on PL properties emphasize its multifaceted coordination capabilities in surface coating, charge transfer from electron-rich functional groups, chirality arising from its unique structure, and available conjugation sites. Moreover, the biocompatibility of GSH, combined with the synergistic effect of metal components, renders GSH-protected nanomaterials an "Inseparable Duo" highly suited for applications in bio-sensing, bio-imaging via PL radiative decay and anti-cancer bio-therapies through photothermal therapy, photodynamic therapy, and radiotherapy. By exploring the multifaceted roles of GSH, this Perspective aims to highlight pathways including the encouragement of deeper synthetic exploration, innovative design at the bio-nano interface, and expanded nanobiomedical applications.

Intensive near-infrared emitting Au7Cu10 nanoclusters for both energy and electron harvesting

Triplet excitons have gained increasing recognition as inherent characteristics of various nanomaterials. However, the practical application of triplet excitons is limited due to their confinement within the material where they originate, posing significant challenges to harnessing their potential. In this work, we report direct extraction of both triplet energy and electrons from newly synthesized atomically precise Au7Cu10 nanoclusters (NCs). These NCs exhibit intensive near-infrared (NIR) emission with a quantum yield of 31% at room temperature. They also display near-unity quantum yield of intersystem crossing (ISC) with strong spin-orbit coupling (SOC) up to 864 cm-1. Consequently, Au7Cu10 NCs can act as triplet sensitizers, facilitating efficient triplet-triplet annihilation and achieving upconverted emission with an efficiency of 18.4% in perylene. Furthermore, rapid electron injection from Au7Cu10 NCs in the triplet state to methyl viologen was clearly observed. This study represents the first direct extraction of both triplet energy and electrons from the same metal NCs, indicating their potential as molecular triplet energy and electron surrogates in optoelectronics, photocatalysis, and solar energy conversion.

Proximity-induced DNA Ag NC enhancement with a DNA-fueled molecule machine for lung cancer-associated miRNA detection

Hairpin DNA-templated Ag NCs are atypically synthesized. Intriguingly, these dark Ag NCs can be activated to emit strong red fluorescence when their hairpin structure is opened by complementary DNA. Building on this exciting finding, an unprecedented and proximity-induced Ag NC enhancement system with a DNA-fueled molecule machine is built for the detection of lung cancer-associated miRNA. Importantly, this detection system can discriminate lung cancer patients from healthy donors with high accuracy (AUC = 1).

DNA origami-templated individual gold nanoclusters: probing their photophysical dynamics using single-molecule fluorescence spectroscopy

Single-molecule fluorescence microscopy demands ultrahigh stability of single fluorophores with less photobleaching and essentially no intensity fluctuations on experimentally relevant time scales. In this respect, there is a need to design fluorescent probes with excellent photostability and long-lived dark transient states. Herein, we report the site-specific synthesis of gold nanoclusters (Au NCs) on DNA origami. Rectangular DNA origami bearing a poly-cytosine sequence in the centre was used as a template to guide the in situ synthesis of Au NCs. The photophysical properties of DNA-templated AuNCs were extensively studied using single-molecule confocal fluorescence microscopy, which revealed the average on-time and off-time of 0.08 seconds and 0.05 seconds, respectively. Photon antibunching measurements confirmed the existence of single Au NCs in the confocal volume and fluorescence transient studies revealed their excellent brightness and remarkable photostability with long survival times and less blinking. Such DNA-templated Au NCs with ultrahigh photostability, intense brightness, and low toxicity have tremendous potential to be used as probes in single-molecule dynamics measurements on biologically relevant timescales. The precise addressability of DNA origami nanostructures provides the controlled attachment of various biomolecules specifically at a predesigned location on the origami template, allowing such platforms to be used for single nanocatalysis as well as performing imaging and sensing studies at the single-molecule level.

Biomolecular ligands as tools to modulate the optical and chiroptical properties of gold nanoclusters

Biomolecule-stabilized gold nanoclusters (AuNCs) have become functional nanomaterials of interest because of their unique optical properties, together with excellent biocompatibility and stability under biological conditions. In this review, we explore the recent advancements in the application of biomolecular ligands for synthesizing AuNCs. Various synthesis approaches that are employing amino acids, peptides, proteins, and DNA as biomolecular scaffolds are reviewed. Furthermore, the influence of the synthesis conditions and nature of the biomolecule on the emerging optical (absorption and photoluminescence) and chiroptical properties of AuNCs is discussed. Finally, the latest research on the applications of biomolecule-stabilized AuNCs for biosensing, bioimaging, and theranostics is presented.

Ultrasmall metal nanoclusters as efficient luminescent probes for bioimaging

Ultrasmall metal nanoclusters (NCs, <2 nm) have emerged as a novel class of luminescent probes due to their atomically precise size and tailored physicochemical properties. The rapid advancements in the design and utilization of metal NC-based luminescent probes are facilitated by the atomic-level manipulation of metal NCs. This review article explores (i) the engineering of metal NCs' functions for bioimaging applications, and (ii) the diverse uses of metal NCs in bioimaging. We begin by presenting an overview of the engineering functions of metal NCs as luminescent probes for bioimaging applications, highlighting key strategies for enhancing NCs' luminescence, biocompatibility and targeting capabilities towards biological specimens. Our discussion then centers on the bioimaging applications of metal NCs in subcellular organelles, individual cells, tissues, and entire organs. Finally, we offer a perspective on the challenges and potential developments in the future use of metal NCs for bioimaging applications.

DNA-templated fluorescent metal nanoclusters and their illuminating applications

After the discovery of DNA during the mid-20th century, a multitude of novel methodologies have surfaced which exploit DNA for its various properties. One such recently developed application of DNA is as a template in metal nanocluster formation. In the early years of the new millennium, a group of researchers found that DNA can be adopted as a template for the binding of metal nanoparticles that ultimately form nanoclusters. Three metal nanoclusters have been studied so far, including silver, gold, and copper, which have a plethora of biological applications. This review focuses on the synthesis, mechanisms, and novel applications of DNA-templated metal nanoclusters, including the therapies that have employed them for their wide range of fluorescent properties, and the future perspectives related to their development by exploiting machine learning algorithms and molecular dynamics simulation studies.

Functional structures assembled based on Au clusters with practical applications

The advancement of gold nanoclusters (Au NCs) has given rise to a new era in fabricating functional materials due to their controllable morphology, stable optical properties, and excellent biocompatibility. Assemblies based on Au NCs demonstrate significant potentiality in constructing multiple structures as acceptable agents in applications such as sensing, imaging technology, and drug delivery systems. In addition, the assembled strategies illustrate the integration mechanism between each component while facing material requirement. It is necessary to provide supplementary and comprehensive reviews on the assembled functional structures (based Au NCs), which hold promise for applications and could expand their functional range and potential applications. This review focuses on the assembled structures of Au NCs in combination with metals, metal oxides, and non-metal materials, which are intricately arranged through various interaction forces including covalent bonds and metal coordination, resulting in a diverse array of multifunctional Au NC assemblies. These assemblies have widespread applications in fields such as biological imaging, drug delivery, and optical devices. The review concludes by highlighting the challenges and future prospects of Au NC assemblies, emphasizing the importance of continued research to advance nanomaterial assembly innovation.

Leveraging Concentration Imbalance-Driven DNA Circuit as an Operational Amplifier to Enhance the Sensitivity of Hepatitis B Virus DNA Detection with Hybridization-Responsive DNA-Templated Silver Nanoclusters

Hepatitis B virus (HBV) infection remains a major global health concern, necessitating the development of sensitive and reliable diagnostic methods. In this study, we propose a novel approach to enhance the sensitivity of HBV DNA detection by leveraging a concentration imbalance-driven DNA circuit (CIDDC) as an operational amplifier, coupled with a hybridization-responsive DNA-templated silver nanocluster (DNA-AgNCs) nanoprobe named Q·C6-AgNCs. The CIDDC system effectively converts and amplifies the input HBV DNA into an enriched generic single-stranded DNA output, which subsequently triggers the fluorescence of the DNA-AgNCs reporter upon hybridization, generating a measurable signal for detection. By incorporating the DNA circuit, we not only achieved enhanced sensitivity with a lower detection limit of 0.11 nM but also demonstrated high specificity with single-base mismatch discriminability for HBV DNA detection. Additionally, this mix-and-detect assay format is simple, user-friendly, and isothermal. This innovative strategy holds promise for advancing molecular diagnostics and facilitating the effective management of HBV-related diseases.

Upgraded and Light-Up Biosensing Platform: Entropy-Driven Catalysis Circuit Manipulates the Configuration Transformation of Novel DNA Silver Nanoclusters on the Graphene Oxide Surface

To tackle the predicament of the traditional turn-off mechanism, exploring an activated turn-on system remains an intriguing and crucial objective in biosensing fields. Herein, a dark DNA Ag nanocluster (NC) with hairpin-structured DNA containing a six-base cytosine loop (6C loop) as a template is atypically synthesized. Intriguingly, the dark DNA Ag NCs can be lit to display strong red-emission nanoclusters. Building upon these exciting findings, an unprecedented and upgraded turn-on biosensing system [entropy-driven catalysis circuit (EDCC)-Ag NCs/graphene oxide (GO)] has been created, which employs an EDCC to precisely manipulate the conformational transition of DNA Ag NCs on the GO surface from adsorption to desorption. Benefiting from the effective quenching of GO and signal amplification capability of the EDCC, the newly developed EDCC-Ag NCs/GO biosensing system displays a high signal-to-background (S/B) ratio (26-fold) and sensitivity (limit of detection as low as 0.4 pM). Meanwhile, it has good specificity, excellent stability, and reliability in both buffer and biological samples. To the best of our knowledge, it is the first example that adopts an EDCC to precisely modulate the configuration transformation of DNA Ag NCs on the GO surface to obtain a biosensor with low background, strong fluorescence, high contrast, and sensitivity. This exciting finding may provide a new route to fabricate a novel turn-on biosensor based on hairpin-templated DNA Ag NCs in the optical imaging and bioanalytical fields.

The roles of templates consisting of amino acids in the synthesis and application of gold nanoclusters

Gold nanoclusters (AuNCs) with low toxicity, high photostability, and facile synthesis have attracted great attention. The ligand is of great significance in stabilizing AuNCs and regulating their properties. Ligands consisting of amino acids (proteins and peptides) are an ideal template for synthesizing applicative AuNCs due to their inherent bioactivity, biocompatibility, and accessibility. In this review, we summarize the correlation of the template consisting of amino acids with the properties of AuNCs by analyzing different peptide sequences. The selection of amino acids can regulate the fluorescence excitation/emission and intensity, size, cell uptake, and light absorption. By analyzing the role played by AuNCs stabilized by proteins and peptides in the application, universal rules and detailed performances of sensors, antibacterial agents, therapeutic reagents, and light absorbers are reviewed. This review can guide the template design and application of AuNCs when selecting proteins and peptides as ligands.

Recent Advances in Gold Nanocluster-Based Biosensing and Therapy: A Review

Gold nanoclusters (Au NCs) with bright emission and unique chemical reactivity characters have been widely applied for optical sensing and imaging. With a combination of surface modifications, effective therapeutic treatments of tumors are realized. In this review, we summarize the recently adopted biosensing and therapy events based on Au NCs. Homogeneous and fluorometric biosensing systems toward various targets, including ions, small molecules, reactive oxygen species, biomacromolecules, cancer cells, and bacteria, in vitro and in vivo, are presented by turn-off, turn-on, and ratiometric tactics. The therapy applications are concluded in three aspects: photodynamic therapy, photothermal therapy, and as a drug carrier. The basic mechanisms and performances of these systems are introduced. Finally, this review highlights the challenges and future trend of Au NC-based biosensing and therapy systems.

Visualization and Quantification of Drug Release by GSH-Responsive Multimodal Integrated Micelles

Using molecular imaging techniques to monitor biomarkers and drug release profiles simultaneously is highly advantageous for cancer diagnosis and treatment. However, achieving the accurate quantification of both biomarkers and drug release with a single imaging modality is challenging. This study presents the development of a glutathione (GSH)-responsive polymer-based micelle, PEG-SS-FCy7/PEG-SS-GEM (PSFG), which can precisely localize the tumor using bimodal imaging and prevent drug leakage. These PSFG micelles exhibit a small particle size of 106.3 ± 12.7 nm with a uniform size distribution, and the drug loading efficiency can also be easily controlled by changing the PEG-SS-FCy7 (PSF) and PEG-SS-GEM (PSG) feeding ratio. The PSFG micelles display weak fluorescence emission and minimal drug release under physiological conditions but collapse in the presence of GSH to trigger near-infrared fluorescence and the 19F magnetic resonance imaging signal, allowing for real-time monitoring of intracellular GSH levels and drug release. GSH could synergistically promote the disassembly of the micellar structure, resulting in accelerated probe and drug release of up to about 93.1% after 24 h. These prodrug micelles exhibit high in vitro and in vivo antitumor abilities with minimal side effects. The GSH-responsive drug delivery system with dual-modal imaging capability provides a promising imaging-guided chemotherapeutic platform to probe the tumor microenvironment and quantify real-time drug release profiles with minimal side effects.