Synthesis of MUC1 aptamer-stabilized gold nanoclusters for cell-specific imaging

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.

Aptamer functionalized gold nanoclusters as an emerging nanoprobe in biosensing, diagnostic, catalysis and bioimaging

DNA nanostructures, with their fascinating luminescent and detecting capabilities, provide a basis that can accommodate a wide range of applications. The unique electronic configurations, and physical and chemical properties of aptamer-assembled gold nanoclusters (apt-AuNCs) as a novel type of fluorophore have gradually piqued the interest of the scientific community. Bending DNA sequences and other templates/legends as a stabilizing agent with Au metal has produced an abundance of biosensors, along with catalytic and imaging properties. This review article summarizes the synthesis, conjugation tactics, advantages, and sensing mechanisms of AuNCs aptasensor after providing a brief introduction to the topic. Moreover, the application of DNA/aptamer functionalization has been briefly discussed in the fields of food safety and quality, catalysis, clinical diagnosis, cancer cell bioimaging, detection of cancer cell indicators, and therapy. We also concluded the current obstacles and made recommendations about the future prospects of AuNCs for fundamental research and applications in line with the developments in DNA/aptamer-AuNCs.

Carbon dots@noble metal nanoparticle composites: research progress report

Carbon dots@noble metal nanoparticle composites are formed by combining carbon dots and metal nanoparticles using various strategies. Carbon dots exhibit a reducing ability and function as stabilisers; consequently, metal-ion solutions can be directly reduced by them to synthesise gold, silver, and gold-silver alloy particles. Carbon dots@gold/silver/gold-silver particle composites have demonstrated the potential for several practical applications owing to their superior properties and simple preparation process. Until now, several review articles have been published to summarise fluorescent carbon dots or noble metal nanomaterials. Compared with metal-free carbon dots, carbon dots@noble metal nanoparticles have a unique morphology and structure, resulting in new physicochemical properties, which allow for sensing, bioimaging, and bacteriostasis applications. Therefore, to promote the effective development of carbon dots@noble metal nanoparticle composites, this paper primarily reviews carbon dots@gold/silver/gold-silver alloy nanoparticle composites for the first time in terms of the following aspects. (1) The synthesis strategies of carbon dots@noble metal nanoparticle composites are outlined. The principle and function of carbon dots in the synthesis strategies are examined. The advantages and disadvantages of these methods and composites are analysed. (2) The characteristics and properties of such composites are described. (3) The applications of these composite materials are summarised. Finally, the potentials and limitations of carbon dots@noble metal nanoparticle composites are discussed, thus laying the foundation for their further development.

Engineered aptamers for molecular imaging

Molecular imaging, including quantification and molecular interaction studies, plays a crucial role in visualizing and analysing molecular events occurring within cells or organisms, thus facilitating the understanding of biological processes. Moreover, molecular imaging offers promising applications for early disease diagnosis and therapeutic evaluation. Aptamers are oligonucleotides that can recognize targets with a high affinity and specificity by folding themselves into various three-dimensional structures, thus serving as ideal molecular recognition elements in molecular imaging. This review summarizes the commonly employed aptamers in molecular imaging and outlines the prevalent design approaches for their applications. Furthermore, it highlights the successful application of aptamers to a wide range of targets and imaging modalities. Finally, the review concludes with a forward-looking perspective on future advancements in aptamer-based molecular imaging.

Biological Interaction and Imaging of Ultrasmall Gold Nanoparticles

The ultrasmall gold nanoparticles (AuNPs), serving as a bridge between small molecules and traditional inorganic nanoparticles, create significant opportunities to address many challenges in the health field. This review discusses the recent advances in the biological interactions and imaging of ultrasmall AuNPs. The challenges and the future development directions of the ultrasmall AuNPs are presented.

Title: Advances of Gold Nanoclusters for Bioimaging

Gold nanoclusters (AuNCs) have become a promising material for bioimaging detection because of their tunable photoluminescence, large Stokes shift, low photobleaching, and good biocompatibility. Last decade, great efforts have been made to develop AuNCs for enhanced imaging contrast and multimodal imaging. Herein, an updated overview of recent advances in AuNCs was present for visible fluorescence (FL) imaging, near-infrared fluorescence (NIR-FL) imaging, two-photon near-infrared fluorescence (TP-NIR-FL) imaging, computed tomography (CT) imaging, positron emission tomography (PET) imaging, magnetic resonance imaging (MRI), and photoacoustic (PA) imaging. The justification of AuNCs applied in bioimaging mentioned above applications was discussed, the performance location of different AuNCs were summarized and highlighted in an unified parameter coordinate system of corresponding bioimaging, and the current challenges, research frontiers, and prospects of AuNCs in bioimaging were discussed. This review will bring new insights into the future development of AuNCs in bio-diagnostic imaging.

Mesoporous silica@chitosan@gold nanoparticles as "on/off" optical biosensor and pH-sensitive theranostic platform against cancer

A cancer nanotheranostic system was fabricated based on mesoporous silica@chitosan@gold (MCM@CS@Au) nanosystem targeted by aptamer toward the MUC-1 positive tumor cells. Subsequently, curcumin as an efficient herbal anticancer drug was first encapsulated into chitosan-triphosphate nanoparticles and then the resulted nanoparticle was loaded into the nanosystem (MCM@CS@Au-Apt). The nanosystem successful fabrication was approved at each synthesis step through FTIR, XRD, BET, DLS, FE-SEM, HRTEM, and fluorescence spectroscopy. Besides, the interaction between aptamer and curcumin was evaluated using full atomistic molecular dynamics simulations. The mechanism of curcumin release was likewise investigated through different kinetic models. Afterwards, the potential of the designed nanosystem in targeted imaging, and drug delivery was evaluated using fluorescence microscopy and flow cytometry. It was found that the energy transfer between the base pairs in the hairpin of double strands of DNA aptamer acts as a quencher for MCM@CS@Au fluorescence culminating in an "on/off" optical biosensor. On the other hand, the presence of pH-sensitive chitosan nanoparticles creates smart nanosystem to deliver more curcumin into the desired cells. Indeed, when the aptamer specifically binds to the MUC-1 receptor, its double strands separate under the low pH condition, leading to the drug release and the recovery of the fluorescence ("On" state). Based on the toxicity results, this nanosystem had more toxicity toward the MUC-1-positive tumor cells than MUC-1-negative cells, representing its selective targeting. Therefore, this nanosystem could be introduced as a smart anticancer nanotheranostic system for tracing particular biomarkers (MUC-1), non-invasive fluorescence imaging, and targeted curcumin delivery.

MUC1 detection and in situ imaging method based on aptamer conformational switch and hybridization chain reaction

Mucin 1 (MUC1) overexpression in tumor cells is related to various cancers, including breast, stomach, and lung cancer. MUC1 detection and imaging are important for cancer localization in tissue sections to support histopathological diagnosis. In this study, we developed a simple, enzyme-free MUC1 detection and in situ imaging method. Three hairpin probes, Apt-trigger, HP1-FAM, and HP2, were designed for MUC1 recognition and hybridization chain reaction (HCR). The Apt-trigger probe was composed of two sequences: the MUC1 aptamer and HCR trigger sequence. The 5' end of the HP1-FAM probe was modified with a FAM signal molecule. In the presence of MUC1, the aptamer sequence is activated and bound to MUC1, which opens the hairpin structure. Then, the trigger sequence gets exposed and, complementary to HP1-FAM, triggers a continuous HCR process. This method was successfully used to detect MUC1 of 200 pM-25 nM and MUC1 in situ imaging in specific cells, such as human breast carcinoma (MCF-7) and human colon cancer (HT-29) cells.

Synthesis of Exosome-Based Fluorescent Gold Nanoclusters for Cellular Imaging Applications

In recent years, fluorescent metal nanoclusters have been used to develop bioimaging and sensing technology. Notably, protein-templated fluorescent gold nanoclusters (AuNCs) are attracting interest due to their excellent fluorescence properties and biocompatibility. Herein, we used an exosome template to synthesize AuNCs in an eco-friendly manner that required neither harsh conditions nor toxic chemicals. Specifically, we used a neutral (pH 7) and alkaline (pH 11.5) pH to synthesize two different exosome-based AuNCs (exo-AuNCs) with independent blue and red emission. Using field-emission scanning electron microscopy, energy dispersive X-ray microanalysis, nanoparticle tracking analysis, and X-ray photoelectron spectroscopy, we demonstrated that AuNCs were successfully formed in the exosomes. Red-emitting exo-AuNCs were found to have a larger Stokes shift and a stronger fluorescence intensity than the blue-emitting exo-AuNCs. Both exo-AuNCs were compatible with MCF-7 (human breast cancer), HeLa (human cervical cancer), and HT29 (human colon cancer) cells, although blue-emitting exo-AuNCs were cytotoxic at high concentrations (≥5 mg/mL). Red-emitting exo-AuNCs successfully stained the nucleus and were compatible with membrane-staining dyes. This is the first study to use exosomes to synthesize fluorescent nanomaterials for cellular imaging applications. As exosomes are naturally produced via secretion from almost all types of cell, the proposed method could serve as a strategy for low-cost production of versatile nanomaterials.

"Turn-off" sensing probe based on fluorescent gold nanoclusters for the sensitive detection of hemin

Balanced level of hemin in the body is fundamentally important for normal human organ function. Therefore, environmentally benign, stable, and fluorescent metal nanoclusters (NCs) for selective and sensitive detection of hemin have been investigated and reported. Herein, highly orange red emissive gold NCs are successfully synthesized using glutathione as a reducing and stabilizing agent (GSH-Au NCs). The clusters are characterized using various techniques like Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), UV-vis spectroscopy, and fluorescence spectrometer. The fluorescence intensity of as-synthesized Au NCs strongly quenched upon addition of different concentrations of hemin. The decrease in fluorescence intensity of GSH-Au NCs has been applied for determination of hemin concentration in the linear range from 1 to 25 nM with a low limit of detection (LOD) of 0.43 nM. The method was also successfully applied for quantification of hemin in human serum sample. In view of this reality, the system can be considered as a possible strategy and excellent platform for determination of hemin in various areas of application.

Extended gate field-effect-transistor for sensing cortisol stress hormone

Cortisol is a hormone released in response to stress and is a major glucocorticoid produced by adrenal glands. Here, we report a wearable sensory electronic chip using label-free detection, based on a platinum/graphene aptamer extended gate field effect transistor (EG-FET) for the recognition of cortisol in biological buffers within the Debye screening length. The device shows promising experimental features for real-time monitoring of the circadian rhythm of cortisol in human sweat. We report a hysteresis-free EG-FET with a voltage sensitivity of the order of 14 mV/decade and current sensitivity up to 80% over the four decades of cortisol concentration. The detection limit is 0.2 nM over a wide range, between 1 nM and 10 µM, of cortisol concentrations in physiological fluid, with negligible drift over time and high selectivity. The dynamic range fully covers those in human sweat. We propose a comprehensive analysis and a unified, predictive analytical mapping of current sensitivity in all regimes of operation.

Carbohydrate-protein template synthesized high mannose loading gold nanoclusters: A powerful fluorescence probe for sensitive Concanavalin A detection and specific breast cancer cell imaging

Protein-encapsulated gold nanoclusters (Au NCs) have recently gained much attention in biosensing and bioimaging applications owing to their remarkable fluorescence properties, nontoxicity and good biocompatibility. In this work, the mannose was grafted onto the bovine serum albumin (BSA) encapsulated Au NCs (BSA-Au NCs) to produce a mannose functionalized BSA-Au NCs (Man-BSA-Au NCs) as a new fluorescence probe for Concanavalin A (Con A) detection and human breast cancer cell imaging. A new strategy with mannose-BSA conjugates as template was firstly applied for the synthesis of Man-BSA-Au NCs, leading to a high loading of mannose (767.6 ± 7.2 mg/L) onto BSA-Au NCs. The as-prepared Man-BSA-Au NCs showed advantages of facile preparation, good monodispersity and strong red-emission. Notably, aggregation-induced fluorescence quenching of Man-BSA-Au NCs was triggered by Con A due to the multivalent cooperative interactions between mannose and Con A, which was subsequently confirmed by MALDI-TOF MS. Hence highly selective and sensitive fluorescence detection of Con A was achieved by using Man-BSA-Au NCs as a fluorescence sensor. A good linear relationship was obtained over the range of 0.01-1 μM (R² = 0.994) with a detection limit of 0.62 nM (S/N = 3). The developed sensor was then applied to determine Con A in human serum with acceptable recoveries of 93.70-104.8%. Moreover, based on the specific recognition between mannose and overexpressed mannose receptors on human breast cancer cells, the Man-BSA-Au NCs were successfully utilized for cancer cell imaging with good specificity.