The Interaction of Amines with Gold Nanoparticles

N-Heterocyclic Carbene-Based Copolymers for Templated Synthesis and Stabilization of Gold Nanoparticles

Surface functionalization and colloidal stability are pivotal for numerous applications of gold nanoparticles (Au-NPs). Over the past decade, N-heterocyclic carbenes (NHCs) have emerged as promising ligands for stabilizing Au-NPs owing to their ease of synthesis, structural diversity, and strong metal-ligand bonds. Here, we introduce new Au(I)-NHCcopolymer scaffolds as precursors to multidentate NHC-protected Au-NPs. Ring-opening metathesis copolymerization of a norbornene-appended Au(I)-NHC complex with another functionalized norbornene comonomer provides NHC-Au(I) copolymers with modular compositions and structures. Upon reduction, these copolymers yield multidentate polyNHC-coated Au-NPs with varied properties and corona functionalities dictated by the secondary monomer. These nanoparticles exhibit excellent size homogeneity and stability against aggregation in various buffers, cell culture media, and under exposure to electrolytes, oxidants, and exogenous thiols over extended periods. Moreover, we demonstrate post-synthetic surface functionalization reactions of polyNHC-Au-NPs while maintaining colloidal stability, highlighting their robustness and potential for applications such as bioconjugation. Overall, these findings underscore the potential of ROMP-derived NHC-containing copolymers as highly tunable and versatile multidentate ligands that may be suitable for other inorganic colloids and flat surfaces.

An electrochemical biosensor for the detection of BRCA1 based on MOF-derived CeO2@CuS nanosheets with high electrocatalytic H2O2 reduction performance

BACKGROUND

Since the incidence of breast cancer ranks first among female malignant tumors, early diagnosis and treatment of breast cancer are crucial to women's health. Therefore, the detection and monitoring of breast cancer susceptibility gene (BRCA1) is particularly important. In this paper, an electrochemical biosensor was developed to detect BRCA1 based on MOF-derived CeO2@CuS nanosheets with efficient electrocatalytic activity of H2O2 reduction.

RESULTS

CeO2 nanotube derived from MOF possessed excellent charge transfer ability and high specific surface area, making it an ideal substrate for loading CuS nanosheets. The combination of CeO2 and CuS enhanced the electrocatalytic activity and conductivity of H2O2 redox reaction. Then gold nanoparticles (Au) were introduced to synthesize Au@CeO2@CuS to further improve conductivity and electrocatalytic activity. Based on the excellent properties of the above synthetic materials, the non-enzymatic electrochemical sensing platform for detecting BRCA1 were constructed. The proposed method demonstrated wide linearity ranges and low detection limits for detecting BRCA1 (0.1 pmol/L - 10 nmol/L, 0.02 fmol/L), respectively.

SIGNIFICANCE

These showed that the sensing strategy provides a new approach for the detection of BRCA1 and has important significance for the early diagnosis and treatment of breast cancer.

A surface chemistry perspective on SERS: revisiting the basics to push the field forward

Surfaces are well known to be complex entities that are extremely difficult to study, and any phenomenon that is related to them is consequently challenging to approach. Moving from the bulk to the nanoscale adds a further layer of complexity to the problem. Because SERS relies on surfaces at the nanoscale, a rigorous understanding of the chemical phenomena that concur in the observation of the SERS signal is still limited or disorganized at best. Specifically, the lack of understanding of the chemical properties of nanoparticle surfaces has direct consequences on the development of SERS-based devices, causing a widespread belief that SERS is an inherently unreliable and fundamentally irreproducible analytical technique. Herein, we discuss old and new literature from SERS and related fields to accompany the reader through a journey that explores the chemical nature and architecture of colloidal plasmonic nanoparticles as the most popular SERS-active surfaces. By examining the chemistry of the surface landscape of the most common SERS colloids and the thermodynamic equilibria that characterize it, we aim to paint a chemically realistic picture of what a SERS analyst deals with on a daily basis. Thus, our goal for this review is to provide a centralized compilation of key, state-of-the-art surface chemistry information that can guide the rational development of analytical protocols and contribute an additional path through which our community can continue to advance SERS as a reliable and robust analytical tool.

Localization of fluorescent gold nanoparticles throughout the eye after topical administration

The human eye is a highly intricate sensory organ. When a condition requiring treatment occurs, eyedrops, which represent 90% of all ophthalmic treatments, are most frequently used. However, eyedrops are associated with low bioavailability, with less than 0.02% of therapeutic molecules reaching the anterior chamber. Thus, new delivery systems are required to ensure sufficient drug concentration over time at the target site. Gold nanoparticles are a promising avenue for drug delivery; however, they can be difficult to track in biological systems. Fluorescent gold nanoparticles, which have the same ultrastability and biocompatibility as their nonfluorescent counterpart, could act as an effective imaging tool to study their localization throughout the eye after administration. Thus, this study (1) synthesized and characterized fluorescent gold nanoparticles, (2) validated similar properties between nonfluorescent and fluorescent gold nanoparticles, and (3) determined their localization in the eye after topical application on ex vivo rabbit eyes. The fluorescent gold nanoparticles were synthesized, characterized, and identified in the cornea, iris, lens, and posterior segment of rabbit eyeballs, demonstrating tremendous potential for future drug delivery research.

Combined Esculentin-2CHa Fusion Protein-Coated Au Nanoparticles for Effective Against Non-Alcoholic Fatty Liver Disease in Mice Model

Introduction

Extensive research has focused on identifying effective treatments for NAFLD, with numerous bioactive peptide candidates showing significant promise. In this research, a long-acting esculentin-2CHa(1-30)-coated AuNPs (ESC-ABD-AuNPs) was developed and the applicability was evaluated for their use in the treatment of non-alcoholic fatty liver disease (NAFLD).

Methods

ESC-ABD-AuNPs were synthesized by adopting a 1-step reduction process and the successful preparation of the nanoparticles (NPs) was assessed by various physical characterizations including transmission electron microscopy (TEM), ultraviolet-visible (UV-VIS) absorption spectra, dynamic light scattering (DLS), and Fourier Transform Infrared Spectroscopy (FT-IR). After the ESC-ABD-AuNPs were prepared, cytotoxicity, pharmacokinetics (PK), and biodistribution profiles were identified. Then, with a high-fat diet (HFD)-fed obese mice model, efficacy studies were carried out focused on their effects for anti-hyperglycemia and anti-NAFLD. Furthermore, the feasibility of loading a small molecule onto the NPs was evaluated for potential combination therapy.

Results

ESC-ABD-AuNPs were synthesized with an average hydrodynamic size of 120 (±10) nm and demonstrated good stability and an extended plasma half-life of 28.3 h. The NPs exhibited high liver accumulation and were well tolerated in cell viability tests. In PK and biodistribution studies, ESC-ABD-AuNPs showed prolonged retention in major organs, such as the pancreas and the liver. Therapeutic efficacy was demonstrated in the HFD-fed obese mice, where the ESC-ABD-AuNPs significantly reduced blood glucose levels, improved glucose tolerance, and mitigated liver fat accumulation. The ESC-ABD-AuNPs platform also showed potential for combination therapies, demonstrated by its ability to load obeticholic acid (OCA), a farnesoid X receptor (FXR) agonist, found effective for the treatment of NAFLD in clinical studies.

Conclusion

Overall, this study has demonstrated the promising potential of ESC-ABD-AuNPs as a novel treatment for NAFLD. This research suggests that ESC-ABD-AuNPs could be a significant advancement in drug delivery and liver disease treatment, particularly for combination therapies.

Mechanistic understanding of pH as a driving force in cancer therapeutics

The development of pH-directed nanoparticles for tumor targeting represents a significant advancement in cancer biology and therapeutic strategies. These innovative materials have the ability to interact with the unique acidic microenvironment of tumors. They enhance drug delivery, increase therapeutic efficacy, and reduce systemic toxicity. The acidic conditions within tumors trigger the release of drugs from pH-responsive nanoparticles, ensuring targeted and controlled delivery directly to cancer cells while minimizing damage to healthy tissues. This review comprehensively explores the design, synthesis, and application of pH-stabilized nanoparticles in cancer therapy. It delves into the mechanisms of pH-responsive behavior, such as the use of pH-sensitive polymers and cleavable linkages that respond to the acidic tumor environment. Current strategies for nanoparticle stabilization, including surface coating, core-shell nanostructures, and hybrid nanoparticles, are discussed in detail, highlighting how these approaches enhance the stability and functionality of the nanoparticles in biological systems. Recent advancements in nanoparticle-based drug delivery systems are examined, showcasing multi-functional nanoparticles that combine therapeutic and diagnostic functions, as well as those designed for combination therapy to overcome drug resistance. This review identifies future directions in the field, such as the need for improved stability and biocompatibility, controlled and predictable drug release, and overcoming regulatory and manufacturing hurdles. Herein, we have highlighted the transformative potential of pH-stabilized nanoparticles in cancer therapy, offering a pathway towards more effective and targeted cancer treatments.

Magnetic-Plasmonic Core-Shell Nanoparticles: Properties, Synthesis and Applications for Cancer Detection and Treatment

Nanoparticles have been widely used in cancer diagnostics and treatment research due to their unique properties. Magnetic nanoparticles are popular in imaging techniques due to their ability to alter the magnetization field around them. Plasmonic nanoparticles are mainly applied in cancer treatments like photothermal therapy due to their ability to convert light into heat. While these nanoparticles are popular among their respective fields, magnetic-plasmonic core-shell nanoparticles (MPNPs) have gained popularity in recent years due to the combined magnetic and optical properties from the core and shell. MPNPs have stood out in cancer theranostics as a multimodal platform capable of serving as a contrast agent for imaging, a guidable drug carrier, and causing cellular ablation through photothermal energy conversion. In this review, we summarize the different properties of MPNPs and the most common synthesis approaches. We particularly discuss applications of MPNPs in cancer diagnosis and treatment based on different mechanisms using the magnetic and optical properties of the particles. Lastly, we look into current challenges they face for clinical applications and future perspectives using MPNPs for cancer detection and therapy.

Thermally and Electrically Regulated Plasmonic Devices Based on VO2-Covered Gold Nanoplate Arrays with SiO2 Interface Layer for Large Plasmon Shifts

Integrating metal nanoparticles with vanadium dioxide (VO2) is an effective means to realize active plasmonic regulation which has great application potential in optical devices that respond in real-time to external stimuli. However, the high temperature necessary for VO2 growth severely reshapes the metal nanoparticles, causing reduced refractive index (RI) sensitivity and degraded modulation performance. Herein, we construct a large-area dynamically tunable plasmonic system composed of a VO2-covered array of hexagonal gold nanoplates (AuNPLs). By introducing a SiO2 interface layer, the thermal tolerance of the AuNPLs is effectively improved, making the high RI sensitivity (∼368.3 nm/RIU at 855 nm) survive the subsequent VO2 deposition. Through tuning the localized surface plasmon resonance (LSPR) of the AuNPL array and the thickness of the VO2 film, the LSPR-related transmission dip can be tailored to the near-infrared region where VO2 shows a large two-phase RI contrast, a dip shift up to 272 nm is therefore realized upon VO2 phase transition. Furthermore, electro-optic modulation is demonstrated through electrically triggered VO2 partial phase transition which is accompanied by a gradually changed effective dielectric permittivity, and a continuous shift of the transmission dip from 1070 to 860 nm is achieved by varying the applied electrical current flowing through the film. This work provides a feasible route for controllably constructing stimuli-response optical devices with large wavelength modulation amplitude.

Detection of low-level fentanyl concentrations in mixtures of cocaine, MDMA, methamphetamine, and caffeine via surface-enhanced Raman spectroscopy

Surface-enhanced Raman spectroscopy (SERS) was utilized to measure low-level fentanyl concentrations mixed in common cutting agents, cocaine, 3,4-methylenedioxymethamphetamine (MDMA), methamphetamine, and caffeine. Mixtures were prepared with a fentanyl concentration range of 0-339 μM. Data was initially analyzed by plotting the area of a diagnostic peak (1026 cm-1) against concentration to generate a calibration model. This method was successful with fentanyl/MDMA samples (LOD 0.04 μM) but not for the other mixtures. A chemometric approach was then employed. The data was evaluated using principal component analysis (PCA), partial least squares (PLS1) regression, and linear discriminant analysis (LDA). The LDA model was used to classify samples into one of three designated concentration ranges, low = 0-0.4 mM, medium = 0.4-14 mM, or high >14 mM, with fentanyl concentrations correctly classified with greater than 85% accuracy. This model was then validated using a series of "blind" fentanyl mixtures and these unknown samples were assigned to the correct concentration range with an accuracy >95%. The PLS1 model failed to provide accurate quantitative assignments for the samples but did provide an accurate prediction for the presence or absence of fentanyl. The combination of the two models enabled accurate quantitative assignment of fentanyl in binary mixtures. This work establishes a proof of concept, indicating a larger sample size could generate a more accurate model. It demonstrates that samples, containing variable, low concentrations of fentanyl, can be accurately quantified, using SERS.

Exploring the anticancer and antioxidant potential of gold nanoparticles synthesized from Pterocarpus marsupium bark extract against oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) is a disease of significant concern with higher mortality rates. Conventional treatment approaches have several drawbacks, leading to the opening of new research avenues in the field of nanoparticle-based cancer therapeutics. The study aimed at the synthesis of gold nanoparticles (Pm-AuNPs) from the aqueous bark extract of Pterocarpus marsupium, followed by its characterization and in vitro anticancer evaluation against OSCC. The synthesized Pm-AuNPs were characterized using UV-visible spectroscopy, particle size analyser, zeta potential, FTIR and SEM techniques. The anticancer potential of the Pm-AuNPs was evaluated against OSCC cell lines (SCC29b, SSC154 and OECM-1) through in vitro assays. The IC50 value was found to be 25 ± 1.2, 45 ± 1.5 and 75 ± 2.1 µg/mL for the three OSCC cell lines, elucidating Pm-AuNPs cytotoxic effects and mechanism of action. Intracellular ROS and SOX detection, mitochondrial transmembrane potential analysis and apoptosis detection were used to confirm the activity of Pm-AuNPs against OSCC. Acute toxicity studies on Wistar rats confirmed the non-toxic nature of the Pm-AuNPs at a higher dose concentration up to 2000 mg/kg body weight. The findings underscore Pm-AuNPs as promising candidates for future anticancer therapeutics, providing insights into their mechanism of action and therapeutic efficacy against OSCC.

Atomically Precise Ternary Cluster: Polyoxometalate Cluster Sandwiched by Gold Clusters Protected by N-Heterocyclic Carbenes

Coinage metal (Au, Ag, Cu) cluster and polyoxometalate (POM) cluster represent two types of subnanometer "artificial atoms" with significant potential in catalysis, sensing, and nanomedicine. While composite clusters combining Ag/Cu clusters with POM have achieved considerable success, the assembly of gold clusters with POM is still lagging. Herein, we first designedly synthesized two cluster structural units: an Au3O cluster stabilized by diverse N-heterocyclic carbene (NHC) ligands and an amine-terminated POM linker. The subsequent reaction involved amine substitution in the POM linker for the central O atom in the Au3O cluster, resulting in the first ternary composite cluster-a POM cluster sandwiched by two Au clusters protected by NHCs. Single-crystal X-ray diffraction and other characteristic methods characterized their atomically precise structures. Furthermore, altering the NHC ligands decreased the number of gold atoms in the sandwich structures, accompanying the different protonated degrees of amine ligand in the terminal end of the POM linker. These composite clusters showed excellent performances in catalytic H2O2 conversion through the synergistic effect between gold clusters and POM clusters. This work opens a new avenue to functional composite metal clusters and would promote their enhanced catalysis applications through intercluster synergistic interactions within composite systems.

Robust Metal Oxide Adhesion Layers for Cellulose Nanofiber-Based QCM Sensors

Here, we demonstrate the significant role of robust metal oxide adhesion layers on the cellulose nanofiber (CNF)-based quartz crystal microbalance (QCM) humidity sensor characteristics including sensitivity and stability. In this study, we deposited various metal oxide films (NiO, TiO2, ZnO, and WO3) onto QCM Au electrodes as adhesion layers before drop-casting CNF dispersion water. These metal oxide adhesion layers significantly enhanced the stability of CNF films on QCM sensors even in a high-humidity environment where a conventional adhesion layer (polyethylenimine) for CNF could not maintain stable adhesion. There was a significant difference between different metal oxide layers in the QCM data for humidity sensing. We found a negative correlation between the QCM sensitivity and the water wettability of metal oxide surfaces. Morphology analysis of the deposited CNF films revealed that the center-concentrated CNF microstructures on the metal oxide adhesion layers rigorously explained the observed negative correlation between the sensitivity and the wettability of metal oxide surfaces. This trend was further confirmed by gradually changing the hydrophobicity of the NiO adhesion surfaces. Thus, the proposed strategy using robust metal oxide adhesion layers will be a foundation for further development of various CNF-based QCM gas sensors.

Seed-Mediated Growth and Advanced Characterization of Chiral Gold Nanorods

The controlled growth of gold nanostructures with complex shapes and reduced symmetry, exemplified by chiral gold nanorods and nanoparticles, is one of the most dynamic fields of nanochemistry. A timely summary of underlying concepts, including growth mechanisms and redefined chirality measures, would further promote this research area. In this perspective, we aim to establish qualitative connections between the chiral shapes and growth conditions, specifically for the seed-mediated synthesis of chiral gold nanorods as a convenient case of chiral morphogenesis. The crystallographic and morphological features of achiral nanorods used as seeds, the experimental conditions during chiral growth, and the symmetry of the chiral inducers, can all be exploited to obtain nanorods with intricate chiral shapes. Chirality characterization (such as electron tomography techniques) and quantification (including chirality measures) emerge as critical aspects to comprehensively explore and understand such structures, enabling optimization of their geometric and optical features. We conclude by discussing relevant challenges to be addressed toward a better controlled synthesis of chiral plasmonic nanostructures.

Nano- and Micro-Platforms in Therapeutic Proteins Delivery for Cancer Therapy: Materials and Strategies

Proteins have emerged as promising therapeutics in oncology due to their great specificity. Many treatment strategies are developed based on protein biologics, such as immunotherapy, starvation therapy, and pro-apoptosis therapy, while some protein biologics have entered the clinics. However, clinical translation is severely impeded by instability, short circulation time, poor transmembrane transportation, and immunogenicity. Micro- and nano-particles-based drug delivery platforms are designed to solve those problems and enhance protein therapeutic efficacy. This review first summarizes the different types of therapeutic proteins in clinical and research stages, highlighting their administration limitations. Next, various types of micro- and nano-particles are described to demonstrate how they can overcome those limitations. The potential of micro- and nano-particles are then explored to enhance the therapeutic efficacy of proteins by combinational therapies. Finally, the challenges and future directions of protein biologics carriers are discussed for optimized protein delivery.

Highly sensitive multiplexed colorimetric lateral flow immunoassay by plasmon-controlled metal-silica isoform nanocomposites: PINs

Lateral flow assay (LFA) systems use metal nanoparticles for rapid and convenient target detection and are extensively studied for the diagnostics of various diseases. Gold nanoparticles (AuNPs) are often used as probes in LFAs, displaying a single red color. However, there is a high demand for colorimetric LFAs to detect multiple biomarkers, requiring the use of multicolored NPs. Here, we present a highly sensitive multiplexed colorimetric lateral flow immunoassay by multicolored Plasmon-controlled metal-silica Isoform Nanocomposites (PINs). We utilized the localized surface plasmon resonance effect to create multi-colored PINs by precisely adjusting the distance between the NPs on the surface of PINs through the controlled addition of reduced gold and silver precursors. Through simulations, we also confirmed that the distance between nanoparticles on the surface of PINs significantly affects the color and colorimetric signal intensity of the PINs. We achieved multicolored PINs that exhibit stronger colorimetric signals, offering a new solution for LFA detection with high sensitivity and a 33 times reduced limit of detection (LOD) while maintaining consistent size deviations within 5%. We expect that our PINs-based colorimetric LFA will facilitate the sensitive and simultaneous detection of multiple biomarkers in point-of-care testing.

Surface-enhanced Raman scattering enhancement using a hybrid gold nanoparticles@carbon nanodot substrate for herbicide detection

The widespread distribution of herbicides in the environment poses a significant risk to human health and wildlife. Surface-enhanced Raman scattering (SERS) has emerged as a powerful technique for detecting and analyzing herbicides. However, developing a low-cost, highly sensitive, reproducible, stable, and Raman-active nanostructured substrate for herbicide detection remains a particular challenge. In this research, a nanohybrid substrate consisting of gold nanoparticles@carbon nanodots (AuNPs@CNDs) was synthesized by reducing HAuCl4 in the presence of CNDs at 100 °C. The optical, chemical, and physical properties of CNDs, AuNPs, and the hybrid AuNPs@CND substrates were thoroughly investigated using various techniques including UV-vis spectrometry, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and CytoViva darkfield and hyperspectral imaging. The SERS effect of the substrates was evaluated using rhodamine 6G (Rh6G), a Raman-active probe, and two groups of herbicides containing mesotrione or S-metolachlor. The results demonstrated a significant signal amplification in the SERS spectra of Rh6G and herbicide molecule detection using the AuNPs@CND substrate compared to bare CNDs and AuNPs alone. This suggests that the nanohybrid AuNPs@CND SERS substrate holds promise for the detection of herbicides and other organic compounds in environmental applications.

A plasmonic biosensor pre-diagnostic tool for Familial Mediterranean Fever

Familial Mediterranean Fever (FMF) is an autosomal recessive genetic disorder, primarily observed in populations around the Mediterranean Sea, linked to MEFV gene mutations. These mutations disrupt inflammatory responses, increasing pyrin-protein production. Traditional diagnosis relies on clinical symptoms, family history, acute phase reactants, and excluding similar syndromes with MEFV testing, which is expensive and often inconclusive due to heterozygous mutations. Here, we present a biosensor platform that detects differences in pyrin-protein levels between healthy and affected individuals, offering a cost-effective alternative to genetic testing. Our platform uses gold nanoparticle-based plasmonic chips enhanced with anti-pyrin antibodies, achieving a detection limit of 0.24 ng/mL with high specificity. The system integrates an optofluidic system and visible light spectroscopy for real-time analysis, with signal stability maintained for up to six months. Our technology will enhance FMF diagnosis accuracy, enabling early treatment initiation and providing a cost-effective alternative to genetic testing, thus improving patient care.

Engineering Core/Ligands Interfacial Anchors of Nanoparticles for Efficiently Inhibiting Both Aβ and Amylin Fibrillization

Accurate construction of artificial nano-chaperones' structure is crucial for precise regulation of protein conformational transformation, facilitating effective treatment of proteopathy. However, how the ligand-anchors of nano-chaperones affect the spatial conformational changes in proteins remains unclear, limiting the development of efficient nano-chaperones. In this study, three types of gold nanoparticles (AuNPs) with different core/ligands interface anchor structures (Au─NH─R, Au─S─R, and Au─C≡C─R, R = benzoic acid) are synthesized as an ideal model to investigate the effect of interfacial anchors on Aβ and amylin fibrillization. Computational results revealed that the distinct interfacial anchors imparted diverse distributions of electrostatic potential on the nanointerface and core/ligands bond strength of AuNPs, leading to differential interactions with amyloid peptides. Experimental results demonstrated that all three types of AuNPs exhibit site-specific inhibitory effects on Aβ40 fibrillization due to preferential binding. For amylin, amino-anchored AuNPs demonstrate strong adsorption to multiple sites on amylin and effectively inhibit fibrillization. Conversely, thiol- and alkyne-anchored AuNPs adsorb at the head region of amylin, promoting folding and fibrillization. This study not only provided molecular insights into how core/ligands interfacial anchors of nanomaterials induce spatial conformational changes in amyloid peptides but also offered guidance for precisely engineering artificial-chaperones' nanointerfaces to regulate the conformational transformation of proteins.

Tunable Nanoislands Decorated Tapered Optical Fibers Reveal Concurrent Contributions in Through-Fiber SERS Detection

Creating plasmonic nanoparticles on a tapered optical fiber (TF) tip enables a remote surface-enhanced Raman scattering (SERS) sensing probe, ideal for challenging sampling scenarios like biological tissues, site-specific cells, on-site environmental monitoring, and deep brain structures. However, nanoparticle patterns fabricated from current bottom-up methods are mostly random, making geometry control difficult. Uneven statistical distribution, clustering, and multilayer deposition introduce uncertainty in correlating device performance with morphology. Ultimately, this limits the design of the best-performance remote SERS sensing probe. Here we employ a tunable solid-state dewetting method to create densely packed monolayer Au nanoislands with varied geometric parameters in direct contact with the silica TF surface. These patterns exhibit analyzable nanoparticle sizes, densities, and uniform distribution across the entire taper surface, enabling a systematic investigation of particle size, density, and analyte effects on the SERS performance of the through-fiber detection system. The study is focused on the SERS response of a widely employed benchmark molecule, rhodamine 6G (R6G), and serotonin, a highly relevant neurotransmitter for the neuroscience field. The numerical simulations and limit of detection (LOD) experiments on R6G show that the increase of the total near-field enhancement volume promotes the SERS sensitivity of the probe. However, we observed a different behavior for serotonin linked to its interaction with the nanoparticle's surface. The obtained LOD is as low as 10-7 M, a value not achieved so far in a through-fiber detection scheme. Therefore, our work offers a strategy to design nanoparticle-based remote SERS sensing probes and provides new clues to discover and understand intricate plasmonic-driven chemical reactions.

Enantioselective Surface-Enhanced Raman Scattering by Chiral Au Nanocrystals with Finely Modulated Chiral Fields and Internal Standards

The chiral discrimination of enantiomers is crucial for drug screening and agricultural production. Surface-enhanced Raman scattering (SERS) is proposed for discriminating enantiomers benefiting from chiral plasmonic materials. However, the mechanism of enantioselective SERS is unclear, and fluctuating SERS intensities may result in errors. Herein, this work demonstrates a reliable SERS substrate using chiral Au nanocrystals with finely modulated chiral fields and internal standards. Chiral electromagnetic fields are enhanced after modulation, which is conducive to increasing the difference in the enantiomeric SERS intensity, as evidenced by the experimental and simulation results. Furthermore, the SERS stability is improved by the corrective effect of the internal standards, and the relative standard deviation is significantly reduced. Using finely modulated chiral fields and internal standards, L- and D-phenylalanine exhibit a stable six times difference in SERS ratio. Theoretical simulations reveal that linearly polarized light can also excite the chiral fields of chiral Au nanocrystals, indicating non-chiral far-field light is converted into chiral near-field sources by chiral Au nanocrystals. Thus, the mechanism of enantioselective SERS can be elucidated by the scattering difference of chiral molecules in chiral near fields. This study will pave the way for the development of enantioselective SERS and related chiroptical technologies.

Hydrolysis of Nerve Agent Simulants Accelerated by Stimuli-Responsive Dinuclear Catalysts

The ability to control the catalytic activity of enzymes in chemical transformations is essential for the design and development of artificial catalysts. Herein, we report the synthesis and characterization of functional ligands featuring two 1,4,7,10-tetraazacyclododecane units linked by an azobenzene group and their corresponding dinuclear Zn(II) complexes. We show that the configuration switching (E/Z) of the azobenzene spacer in the ligands and their dinuclear Zn(II) complexes is reversibly controlled by irradiation with UV and visible light. The Zn(II)-metal complexes are light-responsive catalysts for the hydrolytic cleavage of nerve agent simulants, i.e., p-nitrophenyl diphenyl phosphate and methyl paraoxon. The catalytic activity of the Z-isomers of the dinuclear Zn(II) complexes outperformed that of the E-counterparts. Moreover, combining the less active E-isomers with gold nanoparticles induced an enhancement in the hydrolysis rate of p-nitrophenyl diphenyl phosphate. Kinetic analysis has shown that the catalytic site appears to involve a single metal ion. We explain our results by considering the different desolvation effects occurring in the catalyst's configurations in the solution and the catalytic systems involving gold nanoparticles.

An Unconventional Immunosensor for Biomolecule Detection via Nonspecific Gold Nanoparticle-Antibody Interactions

Immunogold, that is, gold nanoparticles (AuNPs) conjugated with biomolecules such as antibodies and peptides, have been widely used to construct sandwiched immunosensors for biodetection. Two main challenges in these immunoassays are difficulties in finding and validating a suitable antibody, and the nonspecific interaction between the substrate and immunogold, which lowers the detection sensitivity and even causes false results. To avoid these issues, we took advantage of the nonspecific interaction between AuNPs and capture antibodies and proposed a new sensing mechanism. That is, after the capture of analyte targets by the capture antibodies on the substrate, AuNPs of certain chemical functionality would preferably bind to the free capture antibodies. Consequently, the amount of deposited AuNPs will inversely depend on the concentration of the analytes. As a proof-of-concept, we designed a mass-based sensor where anti-IgG antibodies were coated on a quartz crystal microbalance substrate. After IgG was introduced, tannic acid-capped AuNPs were applied to bind with the free anti-IgG antibody molecules. A frequency change (Δf) of the quartz substrate was induced by the increased mass loading. To further amplify the loading mass, an Ag enhancer solution was added, and Ag growth was catalyzed by the bound AuNPs. The Δf response showed a concentration-dependent decrease when increasing IgG concentration with a detection limit of 2.6 ng/mL. This method relies on the nonspecific interaction between AuNPs and anti-IgG antibodies to realize sensitive detection of IgG and eliminates the use of detection antibodies. The concept is an alternative to many existing immunoassay technologies.

Antimicrobial peptide-conjugated phage-mimicking nanoparticles exhibit potent bactericidal action against Streptococcus pyogenes in murine wound infection models

Streptococcus pyogenes is a causative agent for strep throat, impetigo, and more invasive diseases. The main reason for the treatment failure of streptococcal infections is increased antibiotic resistance. In recent years, infectious diseases caused by pyogenic streptococci resistant to multiple antibiotics have been rising with a significant impact on public health and the veterinary industry. The development of antibiotic resistance and the resulting emergence of multidrug-resistant bacteria have become primary threats to the public health system, commonly leading to nosocomial infections. Many researchers have turned their focus to developing alternative classes of antibacterial agent based on various nanomaterials. We have developed an antibiotic-free nanoparticle system inspired by naturally occurring bacteriophages to fight antibiotic-resistant bacteria. Our phage-mimicking nanoparticles (PhaNPs) display structural mimicry of protein-turret distribution on the head structure of bacteriophages. By mimicking phages, we can take advantage of their evolutionary constant shape and high antibacterial activity while avoiding the immune reactions of the human body experienced by biologically derived phages. We describe the synthesis of hierarchically arranged core-shell nanoparticles, with a silica core conjugated with silver-coated gold nanospheres to which we have chemisorbed the synthetic antimicrobial peptide Syn-71 on the PhaNPs surface, and increased the rapidity of the antibacterial activity of the nanoparticles (PhaNP@Syn71). The antibacterial effect of the PhaNP@Syn71 was tested in vitro and in vivo in mouse wound infection models. In vitro, results showed a dose-dependent complete inhibition of bacterial growth (>99.99%). Cytocompatibility testing on HaCaT human skin keratinocytes showed minimal cytotoxicity of PhaNP@Syn71, being comparable to the vehicle cytotoxicity levels even at higher concentrations, thus proving that our design is biocompatible with human cells. There was a minimum cutoff dosage above which there was no evolution of resistance after prolonged exposure to sub-MIC dosages of PhaNP@Syn71. Application of PhaNP@Syn71 to a mouse wound infection model exhibited high biocompatibility in vivo while showing immediate stabilization of the wound size, and infection free wound healing. Our results suggest the robust utility of antimicrobial peptide-conjugated phage-mimicking nanoparticles as a highly effective antibacterial system that can combat bacterial infections consistently while avoiding the emergence of resistant bacterial strains.

Ligand Decomposition Differences during Thermal Sintering of Oleylamine-Capped Gold Nanoparticles in Ambient and Inert Environments: Implications for Conductive Inks

Gold nanoparticles (GNPs) are essential in creating conductive inks vital for advancing printable electronics, sensing technologies, catalysis, and plasmonics. A crucial step in fabricating useful GNP-based devices is understanding the thermal sintering process and particularly the decomposition pathways of ligands in different environments. This study addresses a gap in the existing research by examining the sintering of oleylamine (OA)-capped GNPs in both ambient (air) and inert (N2) environments. Through a series of analyses including TGA/MS, Raman spectroscopy, and XPS, distinctive OA decomposition behaviors were identified in air and nitrogen environments. The research delineates two OA decomposition pathways resulting in different porosity, microstructure, and electrical conductivity of GNP films sintered in air and nitrogen environments. The study offers some insights that can steer the sintering and utilization of the GNP sintering process and promises to aid the future development of nanoparticle-based printable electronics.

A colorimetric sensor with dual-ratio and dual-mode for detection of nicotine in tobacco samples

Nicotine (NIC) is a harmful substance, drug, pesticide and chemical that is widely found in tobacco. It has carcinogenic, teratogenic and neurotoxic effects that have raised serious concerns. Herein, a colorimetric sensor with dual-ratio and dual-mode for the detection of NIC in tobacco samples was reported. The localized surface plasmon resonance signals of gold nanoparticles (AuNPs) and AuNPs-NIC are used as dual-ratio signals. The absorbance ratio of NIC to AuNPs or the absorbance ratio of NIC to AuNPs-NIC and the wavelength shift value of AuNPs-NIC are applied as dual-mode. Transmission electron microscopy, energy dispersive spectroscopy, dynamic light scattering spectroscopy, ultraviolet-visible spectrophotometry, cyclic voltammetry, and potentiostatic methods were used to characterize the sensor. Further analysis of NIC was conducted through morphological fitting and theoretical calculations. Under optimal conditions, the sensor shows a wide linear range of 5-500 μM. The detection limits for NIC are 2.48 μM, 1.63 μM and 1.34 μM, respectively. The experimental result shows that the dual-ratio signal of AuNPs and AuNPs-NIC has good selectivity and sensitivity, and can effectively reduce the interference of impurities on NIC detection. And the dual-mode of detection for NIC improves the accuracy and comparability of the result significantly. In addition, the proposed sensor was also applied to test NIC in tobacco samples with satisfactory recovery.