Electron Compensation Effect Suppressed Silver Ion Release and Contributed Safety of Au@Ag Core-Shell Nanoparticles

Enrofloxacin‑silver composite nano-emulsion as a scalable synergetic antibacterial platform for accelerating infected wound healing

The colonization of bacterial pathogens is a major concern in wound infection and becoming a notable medical issue. Enrofloxacin (ENR) can be applied to treat skin infections, while poor water solubility and bioavailability limit its clinical application. Nanostructured lipid carriers (NLCs) enhance the solubility and bioavailability of drugs by encapsulating them, making them effective for the topical treatment of skin wound infections. Additionally, to enhance treatment efficacy and further improve wound healing, silver nanoparticles (AgNPs) were attached to the aforementioned matrix, which also improved its colloidal stability and reduced toxicity. Herein, a scalable poly (vinyl alcohol) modified NLCs-based antibacterial platform was fabricated by high-pressure homogenization method, to co-load ENR and AgNPs for treating the bacterial-infected wounds. The growth of common wound bacterial pathogens (Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa) was synergistically inhibited by released ENR and Ag+ from the poly (vinyl alcohol) modified enrofloxacin‑silver composite nano-emulsion (ENR@PVA-NLCs/AgNPs). In the in vivo wound model, the Staphylococcus aureus-infected wound in rat almost completely disappeared after treatment with ENR@PVA-NLCs/AgNPs, and no suppuration symptom was observed. Importantly, this nanoplatform had negligible side effects in vivo. Taken together, the above results strongly demonstrate the promising potential of ENR@PVA-NLCs/AgNPs as a synergistic therapeutic agent for clinical wound infections.

Au-Ag controllable composition nanoalloying of hexagonal nanoplates: heterogeneous interfacial nanogaps enhance near-field focusing

In this study, we present a novel strategy for fabricating binary-array surface-enhanced Raman scattering (SERS) substrates composed of gold (Au) and silver (Ag) plasmonic hexagonal nanoplates (h-NPLs), functioning as a "nanoalloy" system. Using Au h-NPLs as scaffolds, we synthesized Ag h-NPLs of closely identical sizes and shapes, facilitating the construction of a mixed plasmonic system. The flat morphology of h-NPLs enables their face-to-face assembly into parallel "wire-like string" arrays, referred to as "columnar superpowders (SPs)", which expose nanogaps perpendicular to the incident light and maximize near-field focusing. We achieved anisotropic superstructures of Au-Ag core-shell h-NPLs through epitaxial Ag growth on Au surfaces, controlled by the interplay of halide ions and surface crystal energy differences. Free-standing columnar SPs were fabricated via an upside-down assembly method, forming dense face-to-face nanogaps that act as hotspots for SERS enhancement. The thickness of the Ag shell was critical in optimizing plasmonic coupling between the Au core and Ag shell, thereby enhancing near-field effects. The observed strong near-field focusing originates from synergistic intra- and inter-interface plasmonic coupling, which induces a mirror charge effect, amplifying near-field polarization and SERS sensitivity. Theoretical simulations and experimental bulk SERS analyses validated these effects, underscoring the potential of binary-component nanoalloy structures for advanced optical sensing technologies. This work highlights the critical role of heterogeneous interfacial nanogaps in enhancing both near- and far-field plasmonic effects, paving the way for next-generation SERS applications.

Photo-enhanced synergistic sterilization and self-regulated ion release in rGO-Ag nanocomposites under NIR irradiation

Silver ions (Ag+) released from silver nanoparticles (Ag NPs) can help to improve the inhibition and killing ability of particles to bacteria. The leakage of Ag+ ions released from Ag NPs will lead to possible risks in cytotoxicity and environmental damage. It is still a challenge to balance particles' ions release and leakage to environment. Here, a nanocomposite of Ag NPs combined with reduced graphene oxide (rGO), labeled as rGO-Ag, was prepared by laser-induced photoreduction of Ag+ ions in solution. This composite exhibits not only a synergistic effect of Ag NPs and rGO in sterilization under normal circumstances, but also another synergistic effect from photothermal function under the 808 nm near-infrared (NIR) laser irradiation and the subsequent enhanced Ag+ ions release at high temperature. In experiments, rGO works as photothermal converter, which can directly cause the death of bacteria and force Ag+ ions to leave particle surface to assist in killing bacteria, and also as a catcher to intercepts the leakage of the released ions. After treating a 50 mg/L rGO-Ag solution with an NIR laser for 30 min, the concentration of released Ag+ ions increased, but these ions were subsequently adsorbed back onto the rGO. Compared with the no-light treatment group, the mortality rates of E. coli and S. aureus exposed to rGO-Ag under NIR irradiation increased by 39.06 % and 17.48 %, respectively. The clever combination between Ag NPs and rGO makes their composite exhibit a photo-enhanced synergistic sterilizing function, as well as a self-controlled ion release capability under NIR stimulation.

Single-Molecule-Sensitive Three-Dimensional Atomic Heterostructures with Extreme Light-Matter Coupling

Three-dimensional heterostructures (3DHS) with controlled compositions and tuned properties are highly desired for fundamental studies and applications in optoelectronics, nanocatalysis, clean energy, and biomedicine. However, conventional nanostructure engineering is hindered by challenges such as poor structural control, time- and energy-intensive processes, the use of hazardous and expensive chemicals, and harsh conditions. Here, we report plasma-assisted epitaxy (PAE) engineering of a metal-organic 3DHS with extreme light-matter interaction for rapid single-molecule-level sensing. Plasmonic-active 3DHS composed of structure-tuned gold-silver core-shell nanoparticles (AuAgCSNPs) was precisely engineered using stable and scalable microplasma-enabled nanofabrication under ambient conditions. The engineered AuAgCSNP-based 3DHS possessed exceptional Raman enhancement under suitable laser excitation, leading to single-molecule detection of SARS-CoV-2 spike proteins in simulated human saliva via surface-enhanced Raman scattering (SERS). The developed plasma fabrication method allows the production of centimeter-scale SERS-active metal-organic 3DHS on disposable, flexible, lightweight, and cost-effective substrates, thereby opening a new avenue for next-generation biosensing, nanoelectronics, nanocatalysis, and biomedical applications.

Synergistic Enhancement of Fluorescence Through Plasmon Resonance and Interfacial Charge Transfer by AgNC@AgAux Core-Shell Quantum Dots

Bimetallic core-shell quantum dots (QDs) hold great promise in elucidating the bimetallic synergism and optoelectronic devices. The synthesis and properties of AgNC@AgAux QDs of core-shell heterostructure are reported. Significantly enhanced photoluminescence emission on these heterostructures is observed. These enhancements are attributed to electron injection and the surface plasmon-induced strong local electric field, which are observed through time-resolved transient absorption spectroscopy. X-ray absorption near edge structure spectra and density functional theory confirms the electron injection from the Ag core to the AgAux shell. On the other hand, the plasmon resonance of the AgNC@AgAux QDs has been studied by finite-element method analysis and time-resolved photoluminescence spectra. There are 94.06 times fluorescence enhancement and 32.40 times quantum yield improvement of oxygen content correlation compared to AgAu3 QDs. It shows a perfect correlation coefficient of 98.85% for the detection of heavy metal Cu2+ ions. Such Bimetallic core-shell heterostructures have great potential for future optoelectronic devices, optical imaging, and other energy-environmental applications.

β-Cyclodextrin Functionalized Au@Ag Core-Shell Nanoparticles: Plasmonic Sensors for Cysteamine and Efficient Nanocatalysts for Nitrobenzene-to-Aniline Conversion

We reported the gold/silver core-shell nanoparticles (Aucore@Agshell NPs) functionalized with β-cyclodextrin (β-CD) as versatile nano-agents demonstrated for human urine-based biosensing of cysteamine and catalytic conversion from nitrobenzene (NB) to aniline. First, the hybrid bimetallic nanoparticles, i.e., β-CD-Aucore@Agshell NPs, constituted a colorimetric sensing platform based on localized surface plasmons, enabling cysteamine (Cyst) to be detected in a remarkably rapid manner, i.e., within 2 min, which was greatly shortened in comparison with that of our previous report. This was due largely to use of β-CD being effectively replaceable by Cyst. The detection of Cyst was demonstrated using human urine specimens in the linear range of 25-750 nM with a limit of detection of 1.83 nM. Excellent specificity in detecting Cyst was also demonstrated against potential interfering molecules. Meanwhile, the β-CD-Aucore@Agshell NPs were demonstrated as nanocatalysts for converting NB to aniline with efficiency enhanced by more than three-fold over the pure gold nanoparticles previously reported, due to the dual functions of the structural core-shell. The demonstrated versatile features of the hybrid nanoparticles can find applications in human urine-based biosensors for Cyst detection, and in the screening of Cyst-containing drugs, while detoxicating NB for ecological protection in aqueous media.

Trimetallic nanocomposites developed for efficient in vivo bimodal imaging via fluorescence and magnetic resonance

Despite several attempts, in vivo bimodal imaging still represents a challenge. Generally, it is accepted that dual-modality in imaging can improve sensitivity and spatial resolution, namely, when exploiting fluorescence (FI) and magnetic resonance imaging (MRI), respectively. Here, a newly developed combination of (i) protein-protected luminescent Au-Ag nanoclusters (LGSN) manifesting themselves by fluorescent emission at 705 nm and (ii) superparamagnetic iron oxide nanoparticles (SPION) embedded within the same protein and creating contrast in MR images, has been investigated in phantoms and applied for in vivo bimodal imaging of a mouse as a proof of principle. Unique LGSN-SPION nanocomposites were synthesized in a specific sequential one-pot green preparation procedure and characterized thoroughly using many physicochemical experimental techniques. The influence of LGSN-SPION samples on the viability of healthy cells (RPE-1) was tested using a calcein assay. Despite the presence of Ag (0.12 mg mL-1), high content of Au (above 0.75 mg mL-1), and moderate concentrations of Fe (0.24 mg mL-1), LGSN-SPION samples (containing approx. 15 mg mL-1 of albumin) were revealed as biocompatible (cell viability above 80%). Simultaneously, these concentration values of all components in the LGSN-SPION nanocomposite were used for achieving both MRI and fluorescence signals in phantoms as well as in a living mouse with sufficiently high resolution. Thus, the LGSN-SPION samples can serve as new efficient bimodal FI and MRI probes for in vivo imaging.

Constructing Isoreticular Metal-Organic Frameworks by Silver-Carbon Bonds

The incorporation of new coordinate bonds and the development of universal methods for new structures have always been of major interest in metal-organic framework (MOF) research. The poor reversibility makes metal-carbon (M-C) bonds a great challenge to adopt as linkages to construct crystalline MOFs. Herein, three isoreticular microcrystalline MOFs connected by silver-carbon (Ag-C) bonds are presented for the first time and named AgC-MOFs. Their structures contain a double coordination mode (σ and π) between Ag(I) and alkynyl. The three AgC-MOFs all exhibit three-dimensional (3D) frameworks with uniform one-dimensional (1D) hexagonal channels, and the pore width could be tuned from 1.1 to 1.8 nm. The construction of crystalline MOFs using poorly reversible Ag-C coordinate bonds extends the nexuses for the MOF structure and lights up more possibilities for the systematic design of MOFs.

Morphology and optical properties of Au-Ag hybrid nanoparticles regulation and its ultra-sensitive SERS immunoassay detection in carbohydrate antigen 19-9

The development of an ultra-sensitive detection method for carbohydrate antigen 19-9 (CA19-9) is very important for the early diagnosis of pancreatic cancer. In this work, we developed a new strategy to achieve a variety of Au-Ag hybrid nanoparticles from janus to core-satellite which is controlled by the volume of AgNO3 and the concentration of benzimidazolecarboxylic acid (MBIA). With the volume of AgNO3 increased, Au-Ag hybrid nanoparticles changed from janus to core-satellite and the characteristic absorption peak showed two opposite trends. The size and number of Ag islands were determined by the concentration of MBIA. Au-Ag core-satellites nanoparticles with a large number of small-sized Ag have the highest SERS intensity. Then we used them as SERS nanotags and Au-Polystyrene nanospheres modified by captured anti-CA19-9 antibody as solid substrates to realize the ultra-sensitive detection of CA19-9 with a low limit of detection of 1.25 × 10-6 IU/mL and a wide linear range of 1.00 × 10-5 -1.00 × 104 IU/mL. This work not only demonstrates that MBIA and AgNO3 were the key factors in the growth of Au-Ag hybrid nanoparticles from 2D to 3D structure but also supplies an ultra-sensitive detection method for CA19-9 which has a potential practicability in the clinical early diagnoses of pancreatic cancer.

Medical Applications of Silver and Gold Nanoparticles and Core-Shell Nanostructures Based on Silver or Gold Core: Recent Progress and Innovations

Nanoparticles (NPs) of noble metals such as silver (Ag NPs) or gold (Au NPs) draw the attention of scientists looking for new compounds to use in medical applications. Scientists have used metal NPs because of their easy preparation, biocompatibility, ability to influence the shape and size or modification, and surface functionalization. However, to fully use their capabilities, both the benefits and their potential threats should be considered. One possibility to reduce the potential threat and thus prevent the extinction of their properties resulting from the agglomeration, they are covered with a neutral material, thus obtaining core-shell nanostructures that can be further modified and functionalized depending on the subsequent application. In this review, we focus on discussing the properties and applications of Ag NPs and Au NPs in the medical field such as the treatment of various diseases, drug carriers, diagnostics, and many others. In addition, the following review also discusses the use and potential applications of Ag@SiO2 and Au@SiO2 core-shell nanostructures, which can be used in cancer therapy and diagnosis, treatment of infections, or tissue engineering.

Self-Assembled Bimetallic Au-Ag Nanorod Vertical Array for Single Molecule Plasmonic Sensing

Ordered plasmonic nanoparticle arrays are highly desirable for optical sensing, as they provide uniformly distributed plasmonic hotspots due to their periodic order and near-field coupling. Anisotropic-shaped bimetallic nanoparticles are of particular interest as their hybridized plasmonic modes enable precise tuning of plasmonic resonance and optical responses. However, the controlled assembly of large-scale arrays of bimetallic nanoparticles with uniformly distributed hotspots remains a challenge. In this study, we present a highly robust and reproducible method for creating large-area vertically aligned arrays of bimetallic Au-Ag nanorods by epitaxially growing Ag over preassembled Au nanorods. Structural characterization using electron microscopy and X-ray photoelectron spectroscopy confirms the formation of a uniform thin layer of Ag, creating a bimetallic Au-Ag nanorod array. We also demonstrate the efficacy of the designed nanoarrays for Surface-Enhanced Raman Scattering (SERS) spectroscopy. Our experimental and computational studies show considerably enhanced optical responses of bimetallic Au-Ag nanorods compared to their monometallic counterparts. The scalability, cost-effectiveness, and reproducibility of this method make it a versatile platform for creating various structures by varying guest nanoparticles in suspensions, with broad applications in biomedical research, food safety surveillance, and environmental monitoring.

Photo-enhanced dehydrogenation of formic acid on Pd-based hybrid plasmonic nanostructures

Coupling visible light with Pd-based hybrid plasmonic nanostructures has effectively enhanced formic acid (FA) dehydrogenation at room temperature. Unlike conventional heating to achieve higher product yield, the plasmonic effect supplies a unique surface environment through the local electromagnetic field and hot charge carriers, avoiding unfavorable energy consumption and attenuated selectivity. In this minireview, we summarized the latest advances in plasmon-enhanced FA dehydrogenation, including geometry/size-dependent dehydrogenation activities, and further catalytic enhancement by coupling local surface plasmon resonance (LSPR) with Fermi level engineering or alloying effect. Furthermore, some representative cases were taken to interpret the mechanisms of hot charge carriers and the local electromagnetic field on molecular adsorption/activation. Finally, a summary of current limitations and future directions was outlined from the perspectives of mechanism and materials design for the field of plasmon-enhanced FA decomposition.

A novel electrochemical aptasensor for ultrasensitive detection of herbicide prometryn based on its highly specific aptamer and Ag@Au nanoflowers

Herbicide prometryn has become a common pollutant in aquatic environments and caused adverse impacts on ecosystems. This study developed an ultrasensitive electrochemical aptasensor for prometryn based on its highly affinitive and specific aptamer and Ag@Au nanoflowers (Ag@AuNFs) for signal amplification. Firstly, this study improved the Capture-SELEX strategy to screen aptamers and obtained aptamer P60-1, which had a high affinity (Kd: 23 nM) and could distinguish prometryn from its structural analogues. Moreover, the typical stem-loop structure in aptamer P60-1 was found to be the binding pocket for prometryn. Subsequently, an electrochemical aptasensor for prometryn was established using multiwalled carbon nanotubes and reduced graphene oxide as electrode substrate, Ag@Au NFs as signal amplification element, and aptamer P60-1 as recognition element. The aptasensor had a detection range of 0.16-500 ng/mL and a detection limit of 60 pg/mL, which was much lower than those of existing detection methods. The aptasensor had high stability and good repeatability, and could specifically detecting prometryn. Furthermore, the utility of the aptasensor was validated by measuring prometryn in environmental and biological components. Therefore, this study provides a robust and ultrasensitive aptasensor for accurate detection for prometryn pollution.

Oxidative Stress-Induced Silver Nano-Carriers for Chemotherapy

Recently, silver nanoparticles (AgNPs) have been extensively explored in a variety of biological applications, especially cancer treatment. AgNPs have been demonstrated to exhibit anti-tumor effects through cell apoptosis. This study intends to promote cell apoptosis further by increasing oxidative stress. AgNPs are encapsulated by biocompatible and biodegradable polyaspartamide (PA) (PA-AgNPs) that carries the anti-cancer drug Doxorubicin (Dox) to inhibit cancer cells primarily. PA-AgNPs have an average hydrodynamic diameter of 130 nm, allowing them to move flexibly within the body. PA-AgNPs show an excellent targeting capacity to cancer cells when they are conjugated to biotin. In addition, they release Dox efficiently by up to 88% in cancer environments. The DCFDA experiment demonstrates that the Dox-carried PA-AgNPs generate reactive oxidation species intensively beside 4T1 cells. The MTT experiment confirms that PA-AgNPs with Dox may strongly inhibit 4T1 cancer cells. Furthermore, the in vivo study confirms that PA-AgNPs with Dox successfully inhibit tumors, which are about four times smaller than the control group and have high biosafety that can be applied for chemotherapy.

Potential application of Au core labeling for tracking Ag nanoparticles in the aquatic and biological system

The entering of silver nanoparticles (Ag NPs) in natural environments constantly increases due to their widespread production and application. While the environmental behavior, impacts, and fate of Ag NPs were critically assessed, the main challenge represents continuous tracking and quantification of Ag NPs in environmental and biological matrices. A group of labeled Ag NPs with gold cores (Au@Ag NPs) was developed for distinguishing between pristine Ag NPs and their other forms, and we comprehensively compared their physicochemical properties, environmental behavior, and biological effects with unlabeled Ag NPs. The electron transfer process from the Au core to the Ag shell gradually decreased with the increase of Ag shell thickness, then the inhibition of Ag⁺ release induced by the Au core was gradually alleviated, but the generation of superoxide radicals was intensified sharply. Then, the effect of the Au core on the dissolution capacity and free radicals' generation significantly altered the biological toxicity of Ag NPs, and the influence degree was related to the test organism's species. Nevertheless, the Au core retained the surface properties of Ag NPs, leading to the uptake of Au@Ag NPs, entirely consistent with the behavior of unlabeled Ag NPs. These findings confirmed that Au core labeling provides new opportunities for tracking Ag NPs in environmental and biological systems, and the exposure conditions and test organisms should be carefully assessed before employing the Au core labeling technology.

Property-activity relationship between physicochemical properties of PM2.5 and their activation of NLRP3 inflammasome

Air pollution is becoming severe environment factor affecting human health. More and more research has indicated that fine particulate matter (PM_2.5) plays a critical role in causing pulmonary inflammation or fibrosis, which potentially is ascribed to the activation of nucleotide-binding domain and leucine-rich repeat protein 3 (NLRP3) inflammasome. However, the underlying property-activity relationship between the physicochemical properties of PM_2.5 and their activation of NLRP3 inflammasome remains unclear. Herein, various ways, such as metal chelation, organic extraction, ROS consumption, charge neutralization and particle dispersion, were applied to interfere with the effects of metal ion, polycyclic aromatic hydrocarbons (PAHs), reactive oxygen species (ROS), charge and size. It was found that aggregated size and PAHs could activate the NLRP3 inflammasome through lysosome rupture and potassium efflux, respectively. Metal ion, PAHs and surface ROS could also activate the NLRP3 inflammasome through mitochondrial ROS production. However, neutralization of PM_2.5 with the negative surface charge could not relieve the activation of NLRP3 inflammasome. Furthermore, oropharyngeal aspiration of various modified PM_2.5 were adopted to explore their effects on lung fibrosis, which showed the consistent results with those in cellular levels. Removal of metal ion, PAHs and ROS as well as reduction of size of PM_2.5 could reduce collagen deposition in the lung tissue of mice, while the charge neutralization of PM_2.5 increased this collagen deposition. This study provides great insights to clarify the property-activity relationship of PM_2.5.

DNA Origami-Templated Bimetallic Nanostar Assemblies for Ultra-Sensitive Detection of Dopamine

The abundance of hotspots tuned via precise arrangement of coupled plasmonic nanostructures highly boost the surface-enhanced Raman scattering (SERS) signal enhancements, expanding their potential applicability to a diverse range of applications. Herein, nanoscale assembly of Ag coated Au nanostars in dimer and trimer configurations with tunable nanogap was achieved using programmable DNA origami technique. The resulting assemblies were then utilized for SERS-based ultra-sensitive detection of an important neurotransmitter, dopamine. The trimer assemblies were able to detect dopamine with picomolar sensitivity, and the assembled dimer structures achieved SERS sensitivity as low as 1 fM with a limit of detection of 0.225 fM. Overall, such coupled nanoarchitectures with superior plasmon tunability are promising to explore new avenues in biomedical diagnostic applications.

Specific sensing of resorcin based on the hierarchical porous nanoprobes constructed by cuttlefish-derived biomaterials through differential pulse voltammetry

The specific detection of resorcin from its isomers is a current research hotspot. Thus in our work, a ternary hierarchical porous nanoprobe has been constructed based on the combination of cuttlefish ink and bimetallic Au@Ag nanoclusters for the specific sensing of resorcin. Briefly, through electrostatic interaction, Au@Ag core-shell nanoclusters are immobilized on the surface of polydopamine extracted from cuttlefish, which is turned into nitrogen-doped porous carbon functionalized by bimetallic Au@Ag by topological transformation subsequently. Afterward, an electrochemical sensor is fabricated based on the nanoprobes for specifically determining resorcin in solution by differential pulse voltammetry, and the linear detection ranges of the sensor are 1-100 μM and 1.2-4 mM while the detection limit reaches 0.06 μM. Meanwhile, the sensing mechanism of resorcin by the pre-fabricated sensor is detailedly studied by density functional theory to obtain a clear electrochemical process. Besides, the selectivity, stability, plus reproducibility of the pre-fabricated sensor have been also tested, and the determinations for resorcin in real environmental water samples have also been performed with good recoveries, revealing the auspicious application potential in the environmental monitoring.

A Smartphone Optical Device for Point-of-Care Testing of Glucose and Cholesterol Using Ag NPs/UiO-66-NH2-Based Ratiometric Fluorescent Probe

Point-of-care testing (POCT) with the advantages of simplicity, rapidity, portability, and low-cost is of great importance to improve healthcare, especially in resource-limited settings and home healthcare settings. Moreover, it is a great challenge to quantitative POCT of multiplexed biomarkers within a single accessible assay but provides enhanced diagnostic accuracy and improved diagnostic efficiency. Herein, a smartphone optical device has been designed for POCT of glucose and cholesterol in metabolic syndrome patients using a ratiometric fluorescent sensor. The sensing system of Ag NPs/UiO-66-NH₂ and o-phenylenediamine presents a dual-emission response to H₂O₂ (the main product of glucose and cholesterol catalyzed by glucose oxidase and cholesterol oxidase) on account of the inner filter effect, resulting in an increase in the response of the fluorescence intensity ratio (F_555 nm/F_425 nm) accompanied by a distinguishable color transition from blue to yellow green. After compositing probes with a flexible substrate, the obtained test strip can be integrated with a smartphone-based portable platform to read RGB values for accurate testing of glucose and cholesterol with both detection limits of 10 μmol L^-1, which are hundreds of times lower than their concentrations in human serum. With the advantages of low-cost, ease of operation, and broad adaptability, this smartphone optical device holds great potential for portable detection of numerous targets in personalized healthcare and clinical diagnosis.

In situ immobilization of silver nanocrystals in carbon nanoparticles for intracellular fluorescence imaging and hydroxyl radicals detection

Silver nanoparticles (Ag NPs) have attracted extensive research interest in bioimaging and biosensing due to their unique surface plasmon resonance. However, the potential aggregation and security anxiety of Ag NPs hinder their further application in biomedical field due to their high surface energy and the possible ionization. Here, binary heterogeneous nanocomplexes constructed from silver nanoparticles and carbon nanomaterials (termed as C-Ag NPs) were reported. The C-Ag NPs with multiple yolk structure were synthesized via a one-step solvothermal route using toluene as carbon precursor and dispersant. The hydrophilic functional groups on the carbon layer endowed the C-Ag NPs excellent chemical stability and water-dispersity. Results showed that C-Ag NPs demonstrated excellent safety profile and excellent biocompatibility, which could be used as an intracellular imaging agent. Moreover, the C-Ag NPs responded specifically to hydroxyl radicals and were expected to serve as a flexible sensor to efficiently detect diseases related to the expression of hydroxyl radicals in the future.

Au@Ag Core@Shell Nanoparticles Synthesized with Rumex hymenosepalus as Antimicrobial Agent

In this work, we used a sequential method of synthesis for gold-silver bimetallic nanoparticles with core@shell structure (Au@AgNPs). Rumex hymenosepalus root extract (Rh), which presents high content in catechins and stilbenes, was used as reductor agent in nanoparticles synthesis. Size distribution obtained by Transmission Electron Microscopy (TEM) gives a mean diameter of 36 ± 11 nm for Au@AgNPs, 24 ± 4 nm for gold nanoparticles (AuNPs), and 13 ± 3 nm for silver nanoparticles (AgNPs). The geometrical shapes of NPs were principally quasi-spherical. The thickness of the silver shell over AuNPs is around 6 nm and covered by active biomolecules onto the surface. Nanoparticles characterization included high angle annular dark field images (HAADF) recorded with a scanning transmission electron microscope (STEM), Energy-Dispersive X-ray Spectroscopy (EDS), X-Ray Diffraction (XRD), UV-Vis Spectroscopy, Zeta Potential, and Dynamic Light Scattering (DLS). Fourier Transform Infrared Spectrometer (FTIR), and X-ray Photoelectron Spectroscopy (XPS) show that nanoparticles are stabilized by extract molecules. A growth kinetics study was performed using the Gompertz model for microorganisms exposed to nanomaterials. The results indicate that AgNPs and Au@AgNPs affect the lag phase and growth rate of Escherichia coli and Candida albicans in a dose-dependent manner, with a better response for Au@AgNPs.

Comparative Study of In Situ Techniques to Enlarge Gold Nanoparticles for Highly Sensitive Lateral Flow Immunoassay of SARS-CoV-2

Three techniques were compared for lowering the limit of detection (LOD) of the lateral flow immunoassay (LFIA) of the receptor-binding domain of severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) based on the post-assay in situ enlargement of Au nanoparticles (Au NPs) on a test strip. Silver enhancement (growth of a silver layer over Au NPs-Au@Ag NPs) and gold enhancement (growth of a gold layer over Au NPs) techniques and the novel technique of galvanic replacement of Ag by Au in Au@Ag NPs causing the formation of Au@Ag-Au NPs were performed. All the enhancements were performed on-site after completion of the conventional LFIA and maintained equipment-free assay. The assays demonstrated lowering of LODs in the following rows: 488 pg/mL (conventional LFIA with Au NPs), 61 pg/mL (silver enhancement), 8 pg/mL (galvanic replacement), and 1 pg/mL (gold enhancement). Using gold enhancement as the optimal technique, the maximal dilution of inactivated SARS-CoV-2-containing samples increased 500 times. The developed LFIA provided highly sensitive and rapid (8 min) point-of-need testing.

Titanium Nanotube Modified With Silver Cross-Linked Basic Fibroblast Growth Factor Improves Osteoblastic Activities of Dental Pulp Stem Cells and Antibacterial Effect

Titanium modifications with different silver loading methods demonstrate excellent antibacterial properties. Yet pure silver nanoparticles with limited bioactive properties may delay regeneration of bone surrounding the dental implant. Therefore, loading silver with bioactive drugs on titanium surfaces seems to be a very promising strategy. Herein, we designed a silver (Ag) step-by-step cross-linking with the basic fibroblast growth factor (bFGF) by polydopamine (PDA) and heparin on titanium nanotube (TNT) as its cargo (TNT/PDA/Ag/bFGF) to improve the implant surface. Our results showed that TNT/PDA/Ag/bFGF significantly enhanced the osteogenic differentiation of dental pulp stem cells (DPSCs). It also showed an excellent effect in bacterial inhibition and a reduction of pro-inflammatory factors through inhibition of M1 macrophage activity. These results showed that bFGF cross-linked silver coating on TNTs presented good osteogenic differentiation and early anti-infiammatory and antibacterial properties. Together, this novel design on titanium provides a promising therapeutic for dental implants.

DNA-Origami-Based Assembly of Au@Ag Nanostar Dimer Nanoantennas for Label-Free Sensing of Pyocyanin

Early-stage detection of diseases caused by pathogens is a prerequisite for expedient patient care. Due to the limited signal-to-noise ratio, molecular diagnostics needs molecular signal amplification after recognition of the target molecule. In this present study, we demonstrate the design of plasmonically coupled bimetallic Ag coated Au nanostar dimers with controlled nanogap using rectangular DNA origami. We further report the utility of the designed nanostar dimer structures as efficient SERS substrate for the ultrasensitive and label-free detection of the pyocyanin molecule, which is a biomarker of the opportunistic pathogenic bacteria, Pseudomonas aeruginosa. The experimental results showed that the detection limit of pyocyanin with such nanoantenna based biosensor was 335 pM, which is much lower than the clinical range of detection. Thus, fast, sensitive and label-free detection of pyocyanin at ultralow concentration in an infected human body can pave a facile route for early stage warning for severe bacterial infections.

Synergistic Modulation at Atomically Dispersed Fe/Au Interface for Selective CO2 Electroreduction

The electrocatalytic carbon dioxide reduction reaction (CO₂RR) offers an attractive route to fuels and feedstocks from renewable energy. Gold is active for the electrochemical CO₂RR to CO, while the competing hydrogen evolution reaction is unavoidable. Here, we report a synergistic strategy, via introducing atomically dispersed Fe to tune the electronic structure of the Au nanoparticle, to improve the CO selectivity. By using operando X-ray absorption and infrared spectroscopies, we reveal the dynamic structural evolution and the adsorption of reactant intermediates at the single-atom Fe₁/Au interface. During the reaction, the interaction between Fe and Au atoms becomes stronger, and the Fe₁/Au synergies affect the adsorption of reaction intermediates, thus improving the selectivity of CO up to 96.3% with a mass activity of 399 mA mg^-1. These results highlight the significant importance of synergistic modulation for advancing the single-atom decorated nanoparticle catalysis.

Highly Biocompatible Plasmonically Encoded Raman Scattering Nanoparticles Aid Ultrabright and Accurate Bioimaging

Plasmonically engineered nanomaterials based on Au-Ag for surface-enhanced Raman scattering (SERS)-based biomedicine is of great importance but is still far behind clinical needs because of the poor compatibility between sensitivity and safety. Here, robust plasmonically encoded Raman scattering nanoparticles, named Au core-Raman-active molecule-Ag shell-Au shell nanoparticles (CMSS NPs), were synthesized. The as-developed CMSS NPs possess a unique exterior ultrathin Au shell (∼2.2 nm thickness) that plays double key roles as an effective wrapping layer as well as a plasmonic enhancing layer, thereby showing not only extraordinary stability against oxidative damages and bioerosion but also outstanding SERS sensitivity because of the stronger in-built electromagnetic field, achieving a significant SERS enhancement factor of 3.3 × 108. The results confirm that the individual CMSS NPs show ultrahigh brightness, reproducibility, selectivity, and biocompatibility in single-cell Raman imaging. Moreover, ultrabright in vivo tumor imaging with 1 × 1 mm2 area can be quickly achieved within 35 s under open-air condition. Furthermore, by secondary plasmonic encoding, the CMSS NPs flexibly serve as nanobeacon to monitor single-cell autophagy with improved accuracy. The CMSS NPs are expected as versatile SERS probes that enable ultrabright, fast, and precise Raman-based bioimaging and clinical bioapplications.

Photothermally Modulatable and Structurally Disintegratable Sub-8-nm Au1Ag9 Embedded Nanoblocks for Combination Cancer Therapy Produced by Plug-in Assembly

As well as the exploration of translatable delivery nanosystems for cancer therapeutic agents, the development of automatable continuous-flow manufacturing technology comprising digitally controlled reactions for the on-demand production of pharmaceuticals is an important challenge in anticancer nanomedicine. Most attempts to resolve these issues have involved the development of alternative reactions, formulations, or constructs containing stimulus components aimed at producing multiple approaches for highly efficacious combination cancer therapies. However, there has been no report of a platform based on plug-in execution that enables continuous-flow manufacture in a compact, reconfigurable manner, although an optimal platform technology may be a prerequisite for the timely translation of recently developed nanomedicines. To this end, we describe the development of a platform toward digitizable, continuous manufacture by a serial combination of plug-in reactionwares (heating plates, a spraying cup, and a photochamber) for single-pass flow fabrication. Specifically, we fabricated three different composite nanoblocks consisting of Au₁Ag₉ (<8 nm; stimulus component), docetaxel (an anticancer drug), and bovine serum albumin (a protective and targeting agent) using our system, with the result of producing nanoblocks with photothermally modulatable and structurally disintegratable properties. These were examined for effectiveness in near-infrared-induced chemothermal cancer therapy and renal excretion of Au₁Ag₉ particles and exhibited high anticancer efficacy and warrantable biosafety.

Molecular Mechanisms, Characterization Methods, and Utilities of Nanoparticle Biotransformation in Nanosafety Assessments

It is a big challenge to reveal the intrinsic cause of a nanotoxic effect due to diverse branches of signaling pathways induced by engineered nanomaterials (ENMs). Biotransformation of toxic ENMs involving biochemical reactions between nanoparticles (NPs) and biological systems has recently attracted substantial attention as it is regarded as the upstream signal in nanotoxicology pathways, the molecular initiating event (MIE). Considering that different exposure routes of ENMs may lead to different interfaces for the arising of biotransformation, this work summarizes the nano-bio interfaces and dose calculation in inhalation, dermal, ingestion, and injection exposures to humans. Then, five types of biotransformation are shown, including aggregation and agglomeration, corona formation, decomposition, recrystallization, and redox reactions. Besides, the characterization methods for investigation of biotransformation as well as the safe design of ENMs to improve the sustainable development of nanotechnology are also discussed. Finally, future perspectives on the implications of biotransformation in clinical translation of nanomedicine and commercialization of nanoproducts are provided.

Hyaluronic Acid-Modified Au-Ag Alloy Nanoparticles for Radiation/Nanozyme/Ag+ Multimodal Synergistically Enhanced Cancer Therapy

Gold nanoparticles (AuNPs) have been widely documented as tumor radiosensitizers via enhanced energy deposition of ionizing radiation. However, the sensitization efficiency of AuNPs is still far from satisfactory owing to the irradiation on nontarget tissues and the tumor radio-resistance. To address these issues, we report herein the rational design and development of hyaluronic acid-modified Au-Ag alloy nanoparticles (Au-Ag@HA NPs) with effective tumor radiosensitization by receptor mediated tumor targeting as well as microenvironment-activated hydroxyl radicals (•OH) generation. In our work, Au-Ag@HA NPs were synthesized by the coreduction of HAuCl₄ and AgNO₃ in the presence of trisodium citrate, followed by surface modification of HA to the Au-Ag alloy NPs. HA modification affords the alloy NPs with specific targeting to 4T1 breast cancer cells overexpressing CD44 receptor, while the introduction of Ag atom imparts the alloy NPs with superior multienzyme-like activities to the monometallic AuNPs for efficient tumor catalytic therapy. More importantly, the ionizing radiation and peroxidase-like activity of Au-Ag@HA NPs boost the production of •OH and the release of toxic Ag⁺ in the tumor sites, thereby leading to effective tumor therapeutic outcome. This work provides a promising treatment paradigm for radiation/nanozyme/Ag⁺ combined therapy against cancer and will advance the design and development of multifunctional nanoplatforms for synergetically enhanced tumor therapy.

Safety-by-Design of Metal Oxide Nanoparticles Based on the Regulation of their Energy Edges

The safety of metal oxide (MOx) nanoparticles (NPs) has been highly concerned because of their wide application and potential toxicological injury. The safe-by-design strategy is usually developed to make safer MOx NPs based on regulation of their physicochemical properties. In the present study, manganese oxide (Mn₃ O₄ ) NPs, as a representative of insoluble toxic MOx NPs, are doped with a series of transition metal to regulate their conduction band energy (E_c ) out of biological redox potential range (BRPR) or Fermi energy (E_f ) far away from valence band energy (E_v ), aiming at completely eliminating the toxicity or significantly reducing the toxicity. It is found that all these M-doping cannot move E_c of Mn₃ O₄ NPs out of the BRPR but zinc (Zn)-, copper (Cu)-, and chromium (Cr)-doping do move E_f far away from E_v , where Zn-doping results in the largest |E_f - E_v | value. Various abiotic, in vitro and in vivo assessments reveal that Zn-, Cu-, and Cr-doped Mn₃ O₄ NPs can generate lower amount of •OH and trigger weaker injury than Mn₃ O₄ NPs, where Zn-doped Mn₃ O₄ NPs show the lowest toxicity. Regulating E_f far away from E_v becomes a feasible safe-by-design approach to achieve safe MOx NPs.

Initiation of protective autophagy in hepatocytes by gold nanorod core/silver shell nanostructures

The high reactivity of silver nanoparticles leads to their broad applications in the anti-bacterial field; however, the safety of silver nanoparticles has attracted increasing public attention. After exposure to silver nanoparticles in vivo, the liver serves as their potential deposition site; however the potential biological effects of such nanoparticles on hepatocytes at low dosages are not well understood. Here, we study the interaction between gold nanorod core/silver shell nanostructures (Au@Ag NRs) and human hepatocytes, HepG2 cells, and determine that Au@Ag NRs at sub-lethal doses can induce autophagy. After uptake, Au@Ag NRs mainly localize in the lysosomes where they release silver ions and promote the production of reactive oxygen species (ROS). The ROS then suppress the AKT-mTOR signaling pathway and activate autophagy. In addition, oxidative stress results in lysosomal impairment, causing decreased ability for lysosomal digestion. Moreover, oxidative stress also affects the structure and function of mitochondria, leading to the initiation of protective autophagy to eliminate the damaged mitochondrion. Our study shows that at sub-lethal dosages, silver nanomaterials may alter the physiological functions of hepatic cells by activating protective autophagy and cause potential health risks, indicating that cautious consideration of the safety of nanomaterials for certain applications is necessary.

Selenium Nanoparticles as an Efficient Nanomedicine for the Therapy of Huntington's Disease

Huntington's disease (HD) is an incurable disease with progressive loss of neural function, which is influenced by epigenetic, oxidative stress, metabolic, and nutritional factors. Targeting inhibition of huntingtin protein aggregation is a strategy for HD therapy, but the efficacy is unsatisfactory. Studies found that selenium (Se) levels in the brain are insufficient for HD disease individuals, while improvement in Se homeostasis in the brain may attenuate neuronal loss and dysfunction. In this study, we applied selenium nanoparticles (NPs) (Nano-Se) for the HD disease therapy by regulating HD-related neurodegeneration and cognitive decline based on transgenic HD models of Caenorhabditis elegans (C. elegans). At low dosages, Nano-Se NPs significantly reduced neuronal death, relieved behavioral dysfunction, and protected C. elegans from damages in stress conditions. The molecular mechanism further revealed that Nano-Se attenuated oxidative stress, inhibited the aggregation of huntingtin proteins, and downregulated the expression of histone deacetylase family members at mRNA levels. The results suggested that Nano-Se has great potential for Huntington's disease therapy. In conclusion, the mechanism about how Nano-Se NPs protect from damages in stress conditions and how they repair neural functions will benefit HD disease therapy. This study will also guide rational design of Nano-Se NPs or other selenium compounds to improve HD therapy in the future.