Strategies of Luminescent Gold Nanoclusters for Chemo-/Bio-Sensing

EXPAR for biosensing: recent developments and applications

Emerging as a promising novel amplification technique, the exponential amplification reaction (EXPAR) offers significant advantages due to its potent exponential amplification capability, straightforward reaction design, rapid reaction kinetics, and isothermal operation. The past few years have witnessed swift advancements and refinements in EXPAR-based technologies, with numerous high-performance biosensing systems documented. A deeper understanding of the EXPAR mechanism has facilitated the proposal of novel strategies to overcome limitations inherent to traditional EXPAR. Furthermore, the synergistic integration of EXPAR with diverse amplification methodologies, including the use of a CRISPR/Cas system, metal nanoparticles, aptamers, alternative isothermal amplification techniques, and enzymes, has significantly bolstered analytical efficacy, aiming to enhance specificity, sensitivity, and amplification efficiency. This comprehensive review presents a detailed exposition of the EXPAR mechanism and analyzes its primary challenges. Additionally, we summarize the latest research advancements in the biomedical field concerning the integration of EXPAR with diverse amplification technologies for sensing strategies. Finally, we discuss the challenges and future prospects of EXPAR technology in the realms of biosensing and clinical applications.

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.

Gold Nanoclusters Synthesized within Single-Chain Nanoparticles as Catalytic Nanoreactors in Water

Metalloenzymes are able to catalyze complex biochemical reactions in cellular (aqueous) media with high efficiency. In recent years, a variety of metal-containing single-chain nanoparticles (SCNPs) have been synthesized as simplified metalloenzyme-mimetic nano-objects. However, most of the metal-containing SCNPs reported so far contained complexed metal ions but not metal nanoclusters (NCs) with diameter <5 nm, which could be used as powerful, emerging catalysts. Herein, we report the synthesis of gold nanoclusters (Au-NCs) within SCNPs and the further use of Au-NCs/SCNPs as catalytic nanoreactors in water. We demonstrate that a common motif contained in several drugs (i.e., the aminophenyl-oxazolidinone fragment present in Rivaroxaban, Sutezolid, and Linezolid) can be efficiently prepared in water from a hydrophobic precursor compound by using the Au-NCs/SCNPs as efficient catalytic nanoreactors. In summary, this work paves the way forthe synthesis of metal-NCs/SCNPs for advanced catalysis in aqueous media.

Calixarene-based supramolecular assembly with fluorescent gold-nanoclusters for highly selective determination of perfluorooctane sulfonic acid

The present study developed an efficient fluorescent approach, based on a supramolecular assembly between gold nanoclusters and calix[4]arene derivatives (C4A-Ds), to detect sever pollutant of perfluorooctane sulfonic acid (PFOS). For that, a series of C4A-Ds with different chain lengths and positive charges at the wider rim were designed and synthesized. Cytidine-5' phosphate protected gold nanoclusters (AuNCs@CMP) were then assembled with calix[4]arene (LC4AP) to form AuNCs/LC4AP assembly, leading to 8-fold luminescence enhancement via the AIEE effect. However, further binding with PFOS reconstituted the as-formed assembly hrough a competitive effect, generating a fluorescence quenching. Particularly, the linear fluorescence response of AuNCs/LC4AP to PFOS realized a highly sensitive determination of the pollutant PFOS in a wide range (2.0-100 μM). In addition, the developed method successfully detected PFOS in pool water near a fire drill field, being good enough for the practical PFOS determination. The calixarene mediated method, based on the fluorescence "on-off" strategy of metal nanoclusters, is sensitive, rapid-responsive, economical, particularly, suitable for the PFOS determination in practice. It takes full advantage of the molecular recognition and self-assembly of artificial macrocyclic host molecules as a promising strategy for the PFOS determination, and will be highlight to develop new detection methods for PFOS and other poisonous compounds in environments.

Ratiometric Fluorescence Probe of Vesicle-like Carbon Dots and Gold Clusters for Quantitation of Cholesterol

We report a facile method for the preparation of vesicle-like carbon dots (VCDs) via dry-heating of surfactant solutions. Like most reported CDs, the VCDs possess interesting fluorescence properties. Entrapment of enzymes and gold nanoclusters (AuNCs) inside the VCDs allows for the development of fluorescent probes for the quantitation of various substrates, with the advantages of high sensitivity and selectivity. The AuNCs act as a probe, and the VCDs as an internal standard confine the AuNCs, enzyme, and analyte to provide high local concentrations to enhance the assay sensitivity. In this study, we employed cholesterol oxidase (ChOX) as a model enzyme for the quantitation of cholesterol. The as-formed hydrogen peroxide through the enzyme reaction inside the VCDs causes fluorescence quenching of AuNCs (excitation/emission wavelengths of 320/670 nm), but not that of the VCDs (excitation/emission wavelengths of 320/400 nm). To improve the sensitivity and linearity, the fluorescence ratios of AuNCs/VCDs are plotted against analyte concentration. The present ratiometric fluorescent method allows for the detection of hydrogen peroxide over the concentration range of 1–100 μM, with a detection limit of 0.673 μM, and cholesterol concentrations ranging from 5 to 100 μM, with a detection limit of 2.8 μM. The practicality of this fluorescent method has been further validated by evaluating cholesterol levels in human serum samples with sufficient accuracy and recovery, revealing its great prospective in diagnosis and biomedical applications.

Gold nanoclusters encapsulated into zinc-glutamate metal organic frameworks for efficient detection of H2O2

Gold nanoclusters (AuNCs) have large Stokes shifts and long fluorescence life, which make them have high application value in bioanalytical applications. However, the quantum yield (QY) of AuNCs was lower, which hinders their wide application. Herein, a facile, novel and one-pot approach was developed to synthesize AuNCs@zinc-glutamate metal organic frameworks (AuNCs@ZnGlu-MOFs (product)). The product was easily prepared via mixing the glutathione (GSH) protected AuNCs with ZnGlu-MOF precursors. Compared with GSH-AuNCs, the ultrahigh QY (33.18%) of the AuNCs@ZnGlu-MOF is nearly 6 times higher. In addition, the product possesses better water stability and longer luminescence life (9.86 μs) due to the protective and confinement effects of the ZnGlu-MOF. Particularly, the product has a unique spatial structure, which can effectively prevent the interaction between large-size biothiols (such as cysteine and homocysteine) and the product, thus significantly improving the selectivity of it. Based on the excellent optical advantages of this product, it was capable of being applied as a selectable and sensitive fluorescence probe to detect H₂O₂ and H₂O₂-related analytes. This method has also been further employed in the precise H₂O₂-monitoring in serum, which is promising in the application of clinical bioassay.

Nanostructured Antimicrobial Peptides: Crucial Steps of Overcoming the Bottleneck for Clinics

The security issue of human health is faced with dispiriting threats from multidrug-resistant bacteria infections induced by the abuse and misuse of antibiotics. Over decades, the antimicrobial peptides (AMPs) hold great promise as a viable alternative to treatment with antibiotics due to their peculiar antimicrobial mechanisms of action, broad-spectrum antimicrobial activity, lower drug residue, and ease of synthesis and modification. However, they universally express a series of disadvantages that hinder their potential application in the biomedical field (e.g., low bioavailability, poor protease resistance, and high cytotoxicity) and extremely waste the abundant resources of AMP database discovered over the decades. For all these reasons, the nanostructured antimicrobial peptides (Ns-AMPs), based on a variety of nanosystem modification, have made up for the deficiencies and pushed the development of novel AMP-based antimicrobial therapies. In this review, we provide an overview of the advantages of Ns-AMPs in improving therapeutic efficacy and biological stability, reducing side effects, and gaining the effect of organic targeting and drug controlled release. Then the different material categories of Ns-AMPs are described, including inorganic material nanosystems containing AMPs, organic material nanosystems containing AMPs, and self-assembled AMPs. Additionally, this review focuses on the Ns-AMPs for the effect of biological activities, with emphasis on antimicrobial activity, biosecurity, and biological stability. The "state-of-the-art" antimicrobial modes of Ns-AMPs, including controlled release of AMPs under a specific environment or intrinsic antimicrobial properties of Ns-AMPs, are also explicated. Finally, the perspectives and conclusions of the current research in this field are also summarized.

Free Radical Polymerization of Gold Nanoclusters and Hydrogels for Cell Capture and Light-Controlled Release

Gold nanocluster (AuNC) decorated hydrogels have attracted considerable attention as versatile biomaterials. To date AuNCs and hydrogels have mainly been mixed as independent components. Here, we report the use of AuNCs as reactive monomers in the polymerization of hydrogels. We used a free radical polymerization to copolymerize AuNCs with acrylamide and N-acryloyl glycinamide to prepare stimuli-responsive smart hydrogels. Multiple C═C bonds were decorated on the surface of the AuNCs as active sites for polymerization. These C═C bonds not only protected the structure of the AuNCs from oxidation by free radicals during polymerization but also covalently connected the AuNCs with the polymer chains. This structure ensured good photothermal performance of the AuNCs while preserving the thermoresponsive hydrogen bonds of polymers. Moreover, the copolymerized AuNCs acted as cross-linkers, which improved the mechanical properties of the hydrogels. These smart hydrogels had good stability, efficient photothermal conversion, and a sensitive thermoresponsive. We examined their potential for capture of MDA-MB-231 cells with hyaluronic acid as target molecules. The captured cells were released under 660 nm irradiation. This process of targeted capture and light-controlled remote release could be repeatedly applied. These results suggest that systems based on AuNCs copolymerized with hydrogels have great potential for biomedical applications.

Bioresponsive Functional Phenylboronic Acid-Based Delivery System as an Emerging Platform for Diabetic Therapy

The glucose-sensitive self-adjusting drug delivery system simulates the physiological model of the human pancreas-secreting insulin and then precisely regulates the release of hypoglycemic drugs and controls the blood sugar. Thus, it has good application prospects in the treatment of diabetes. Presently, there are three glucose-sensitive drug systems: phenylboronic acid (PBA) and its derivatives, concanavalin A (Con A), and glucose oxidase (GOD). Among these, the glucose-sensitive polymer carrier based on PBA has the advantages of better stability, long-term storage, and reversible glucose response, and the loading of insulin in it can achieve the controlled release of drugs in the human environment. Therefore, it has become a research hotspot in recent years and has been developed very rapidly. In order to further carry out a follow-up study, we focused on the development process, performance, and application of PBA and its derivatives-based glucose-sensitive polymer drug carriers, and the prospects for the development of this field.

Stimuli-responsive polymer/nanomaterial hybrids for sensing applications

Chemical and biological/biochemical sensors are capable of generating readout signals that are proportional to the concentration of specific analytes of interest. Signal sensitivity and limit of detection/quantitation can be enhanced through the use of polymers, nanomaterials, and their hybrids. Of particular interest are stimuli-responsive polymers and nanomaterials due to their ability to change their physical and/or chemical characteristics in response to their environment, and/or in the presence of molecular/biomolecular species of interest. Their individual use for sensing applications have many benefits, although this review focuses on the utility of stimuli-responsive polymer and nanomaterial hybrids. We discuss three main topics: stimuli-responsive nanogels, stimuli-responsive network polymers doped with nanomaterials, and nanoparticles modified with stimuli-responsive polymers.

Diphenylalanin nanofibers-inspired synthesis of fluorescent gold nanoclusters for screening of anti-amyloid drugs

Protein misfolding and aggregation into amyloid structures is linked with a number of pathophysiological disorders. In the past decade, significant progresses have been made in the drug discovery strategies against toxic aggregates. Although lack of specificity and high sensitivity for in vitro screening system still seen. Here we demonstrate a new targeting probe based on FF diphenylalanine peptide -protected gold nanoclusters (FF AuNCs). Diphenylalanine peptide has previously been shown to self-assemble into well-ordered fiber like the fibers that are observed in amyloid aggregates. We used of the self-assembly properties along with the ability of FF dipeptide in reduction of gold ions for synthesis of novel Au nanoclusters. We used FF AuNCs for monitoring of effectiveness of anti-amyloid drugs. Fluorescence was considerably diminished when drugs at different concentrations added, due to destruction of the amyloid fibers. Furthermore, the analysis of several components demonstrates significant selectivity against the amyloid disrupting molecules. Prepared FF AuNCs will gain possible strategy for in vitro screening of amyloid disrupting molecules.

Fluorescent Gold Nanoclusters for Biosensor and Bioimaging Application

With the rapid development of materials technology, fluorescent gold nanoclusters (AuNCs) are emerging as novel functional materials for diagnostic applications including the detection of biomarkers and bioimaging due to the advantages of their ultra-small size, tunable emissions, size-dependent fluorescence and excellent biocompatibility. In this review, we introduced the synthetic methods, and physical and chemical properties of AuNCs. Subsequently, we described the AuNCs-based design strategies for the detection of biomarkers including small molecules, DNA and proteins. The applications of AuNCs for tumor imaging in vitro and in vivo were also presented. Finally, we discussed the challenges and potential solutions of AuNCs-based nanosensors.

Luminescent gold nanoclusters for bioimaging applications

Luminescent nanomaterials have emerged as attractive candidates for sensing, catalysis and bioimaging applications in recent years. For practical use in bioimaging, nanomaterials with high photoluminescence, quantum yield, photostability and large Stokes shifts are needed. While offering high photoluminescence and quantum yield, semiconductor quantum dots suffer from toxicity and are susceptible to oxidation. In this context, atomically precise gold nanoclusters protected by thiol monolayers have emerged as a new class of luminescent nanomaterials. Low toxicity, bioavailability, photostability as well as tunable size, composition, and optoelectronic properties make them suitable for bioimaging and biosensing applications. In this review, an overview of the sensing of pathogens, and of in vitro and in vivo bioimaging using luminescent gold nanoclusters along with the limitations with selected examples are discussed.