Au Nanostars Research Articles

Plasmon-enhanced electrocatalytic ethanol oxidation over Au@Pd nanostars

Hybrid noble-metal nanostructures, which integrate plasmonic characteristics and electrocatalytic performance, have garnered significant interest recently. In this study, Au@Pd nanostars were synthesized and employed as an advanced electrocatalyst for the ethanol oxidation reaction (EOR), which suffers from the kinetic limitations of the anodic half-reaction of direct ethanol fuel cells. Leveraging the superior surface plasmon resonance (SPR) property of Au nanostars, the synthesized Au@Pd nanostars exhibited superior plasmon-enhanced EOR activity of 4191.63 A g−1 under laser illumination, noting a 9.40-fold increase compared to dark conditions (445.99 A g−1). The influences of Pd loading and laser power on EOR activity were explored. The impact of Pd loading on EOR activity demonstrates a volcano-shaped correlation, where optimal Pd coverage enhances catalysis but excessive amounts dampen SPR performance, crucial for maximizing EOR activity. Within a specified range, EOR activity linearly increases with laser power due to its influence on SPR performance. Mechanistic investigation suggests the critical roles of photothermal effect and hot carriers’ separation in boosting EOR kinetics. The repeated experiments show little difference, ensuring the accuracy and reproducibility of the reported activity of Au@Pd nanostars for EOR. During the long-term stability estimation, the Au@Pd nanostars display the best durability over three electrocatalysts. Overall, our findings highlight the potential of plasmon-enhanced catalysis in advancing the performance of electrocatalysts for EOR and other conventional electrocatalytic reactions.

Selective deposition of a MOF at the spikes of Au nanostars for SERS detection

Selective deposition of a MOF at the spikes of Au nanostars for SERS detection

"Three-in-One" Plasmonic Au@PtOs Nanocluster Driven Lateral Flow Assay for Multimodal Cancer Exosome Biosensing.

Exploiting the multiple properties of nanozymes for the multimode lateral flow assay (LFA) is urgently required to improve the accuracy and versatility. Herein, we developed a novel plasmonic Au nanostar@PtOs nanocluster (Au@PtOs) as a multimode signal tag for LFA detection. Based on the PtOs bimetallic nanocluster doping strategy, Au@PtOs can indicate both excellent SERS enhancement and nanozyme catalytic activity. Meanwhile, Au@PtOs displays a better photothermal effect than that of Au nanostars. Therefore, catalytic colorimetric/SERS/temperature three-mode signals can be read out based on the Au@PtOs nanocomposite. The Au@PtOs was combined with LFA and applied for breast cancer exosome detection. The detection limit for the colorimetric/SERS/temperature mode was 2.6 × 103/4.1 × 101/4.6 × 102 exosomes/μL, respectively, which was much superior to the common Au nanoparticles LFA (∼105 exosomes/μL). Moreover, based on the fingerprint molecular recognition ability of the SERS mode, exosome phenotypes derived from different breast cancer cell lines can be discriminated easily. Based on the convenient visual colorimetric mode and sensitive SERS/temperature quantitative modes, Au@PtOs driven LFA can satisfy the requirements of accurate and flexible multimodal sensing in different application scenarios.

Metal-Organic Framework-Based Surface-Enhanced Raman Scattering Sensing Platform for Trace Malondialdehyde Detection in Tears.

Disease biomarkers in tears are crucial for clinical diagnosis and health monitoring. However, the limited volume of tear samples, low concentration of tear biomarkers, and complex tear composition present challenges for precise testing. We introduce a spot-on testing platform of metal-organic framework (MOF)-based surface-enhanced Raman scattering (SERS) capillary column, which is capable of target molecules selective separation and enrichment for tear biomarkers in situ detection. It consists of Au nanostars for effective SERS signal and a porous MOF shell for separating impurities through molecular sieving effect. This platform allows for simultaneous collection and detection of tear, capturing the disease biomarker malondialdehyde in tears with a 9.38 × 10-9 mol/L limit of detection. Moreover, we designed a hand-held device based on this tubular SERS sensor, successfully diagnosing patients with dry eye disease. This functional capillary column enables noninvasive and rapid diagnosis of biomarkers in biofluids, providing potential for disease diagnosis and healthcare monitoring.

Hydrogen Bonding-Induced Aggregation of Chiral Functionalized AuNS@Ag NPs for Photothermal Enantioanalysis.

Toward the challenges of signaling transduction amplified in enantioselective recognition, we herein devised an innovative strategy for highly selective recognition of amino acids and their derivatives, leveraging photothermal effects. In this approach, bifunctional l-ascorbic acid is employed to reduce silver ions in situ on Au nanostars. Simultaneously, its oxidate (l-dehydroascorbic acid) is bonded to the silver shell as a chiral selector to prepare chiral nanoparticles (C-AuNS@Ag NPs) with the ability to recognize stereoisomers and sensitively modulate the photothermal effect. l-Dehydroascorbic acid can selectively capture one of the enantiomers of the two forms through hydrogen bonding and drive aggregation of the nanoparticles, which sharply enhances the photothermal effect. Consequently, the two forms of the system exhibit a significant temperature difference, which enables the discrimination and quantification of enantiomers. Our strategy verifies that six chiral amino acids and their derivatives can be discriminated with enantioselective response values of up to 79. Additionally, the chiral recognition mechanism was revealed through density functional theory (DFT) calculations, providing a paradigm shift in the development of enantiomeric recognition strategies.

Two Birds with one Stone: Dual-mode immunoassay constructed using a novel emitter ethylene glycol-induced perylene diimide and a multifunctional ANS probe

Perylene diimide (PDI) is a readily reducible electron-deficient dye that exhibits strong photoluminescent properties, providing new opportunities for synthesizing novel electrochemiluminescence (ECL) emitters. In this study, ethylene glycol (EG) was used to induce the self-assembly of PDI supramolecules for the preparation of ultrathin EG-PDI nanosheets characterized by low crystallinity and weak stacking interaction. Notably, EG-PDI integrates luminescent and catalytic functions into one device, accelerating the interfacial electron transfer and the faster charge transfer kinetics of EG-PDI with K2S2O8. Furthermore, the narrow band gap of EG-PDI facilitates its excitation at an ultra-low potential (−0.3 V). To improve the efficiency of tumor marker analysis, multifunctional Au nanostars (ANS) was introduced both as an energy acceptor of the ECL system and a probe for the photothermal system. Dual-mode immunoassay have demonstrated superior analytical performance in detecting alpha-fetoprotein (AFP), meeting the requirements of modern clinical diagnostics in resource-limited environments.

Au Nanostars Coated with a Thin Film of MIL-100 (Fe) for SERS-Based Sensing of Volatile Organic Compound Indicators in Saliva

Au Nanostars Coated with a Thin Film of MIL-100 (Fe) for SERS-Based Sensing of Volatile Organic Compound Indicators in Saliva

Detection of Psychoactive N,N-Dimethyltryptamine Alkaloid Based on Surface‑Enhanced Raman Scattering Using Gold Nanostars in Flexible Inkjet‑Printing Paper Substrates

N,N-Dimethyltryptamine (DMT) is a serotonergic psychedelic that, when combined with monoamine oxidase enzyme inhibitors in the hallucinogenic beverage commonly known as ayahuasca, surpasses most common orally administered psychoactive drugs. There is a growing interest in the therapeutic potential of DMT due to recent clinical data showing the improvement of cognitive deficits associated with depression and Alzheimer’s disease. The development of analytical methodology for the monitoring of concentrations of DMT molecules to control the appropriate dosage for their use is essential for the treatment of patients. For this, we propose a novel flexible inkjet-printed paper substrate based on Au nanostars as proof of concept for DMT detection by surface-enhanced Raman scattering (SERS). The substrate was applied to detect DMT in water as a first approach to more complex matrices like ayahuasca beverages or blood samples. The optimization and performance of SERS substrates with different print cycles indicate that one print is enough to achieve the great performance of the flexible paper substrates. The SERS analyses for DMT in different concentrations, 10-3 to 10-10 mol L-1, reveal a high sensitivity of the sensors with a silhouette coefficient of 0.84 obtained by principal component analysis (PCA) statistical projections.

SERS Immunoassay Based on an Enzyme-Catalyzed Cascade Reaction and Metal-Organic Framework/Alkaline Phosphatase for Ultrasensitive Detection of Adenosine Triphosphate.

Herein, an adenosine triphosphate (ATP)-induced enzyme-catalyzed cascade reaction system based on metal-organic framework/alkaline phosphatase (MOF/ALP) nanocomposites was designed to establish a surface-enhanced Raman spectroscopy (SERS) biosensor for use in rapid, sensitive ATP detection. Numerous ALP molecules were first encapsulated using ZIF-90 to temporarily deactivate the enzyme activity, similar to a lock. Au nanostars (AuNSs), as SERS-enhancing substrates, were combined with o-phenylenediamine (OPD) to form AuNSs@OPD, which could significantly improve the Raman signal of OPD. When the target ATP interacted with the MOF/ALP nanocomposites, ATP could act as a key to open the MOF structure, releasing ALP, which should further catalyze the conversion of OPD to oxOPD with the aid of ascorbic acid 2-phosphate. Therefore, with the increasing concentrations of ATP, more ALP was released to catalyze the conversion of OPD, resulting in the reduced intensity of the Raman peak at 1262 cm-1, corresponding to the level of OPD. Based on this principle, the ATP-induced enzyme-catalyzed cascade reaction SERS biosensor enabled the ultrasensitive detection of ATP, with a low detection limit of 0.075 pM. Consequently, this study provides a novel strategy for use in the ultrasensitive, rapid detection of ATP, which displays considerable potential for application in the fields of biomedicine and disease diagnosis.

SERS detection of foodborne pathogens in beverage with Au nanostars.

The aim of this study is to develop a simple but rapid method for the determination of foodborne pathogens in complex matrices (beverages) by surface enhanced Raman spectroscopy (SERS) combined with Au nanostar solid-phase substrates. The star-shaped singlet Au nanostructure was formed on the surface of astainless steel sheetby chemical replacement reaction. Rhodamine 6G verified the sensitivity and reproducibility of this substrate, and the relative standard deviations of the SERS intensity at 1312 cm-1, 1364 cm-1, and 1510 cm-1 displacements were 3.40%, 5.64%, and 3.48%, respectively. By detecting four pathogens in beverage samples on Au nanostar substrates, the utility of the SERS assay was demonstrated, while the combination of principal component analysis (PCA) and hierarchical cluster analysis (HCA) further enabled the isolation and identification of pathogens. The results of spiked beverages were validated in conventional culture identification and Vitek 2 Compact biochemical identification system experiments. Thus, this research demonstrated that Au nanostar substrates can be effectively utilized for the recognition of pathogenic bacteria and have immense promise to advance the progress of quick detection of foodborne pathogens and food safety.

Chiral Au nanostars for SERS sensing of enantiomers discrimination, multibacteria recognition and photothermal antibacterial application

The recognition and detection of chirality is of great significance in the fields of chemistry, pharmacy and biomedicine. In this work, we fabricated a chiral Au nanostars (C-AuNSs) with intense chiroptical responses and surface-enhanced Raman scattering (SERS) features by controlling chiral ligand D-/L-cysteine (Cys) concentration. The proposed chiral AuNSs can be applied for the enantiodiscrimination of amino acid based on SERS-chiral anisotropy (SERS-ChA) effect, in which homochiral amino acid has distinct affinities to the C-AuNSs of homogeneous handedness. By demonstrating selective affinity of D-AuNSs with D-glutamic acid (D-Glu) on bacterial peptidoglycan, we further realized effective identification of multiple bacteria according to SERS specific bacterial “fingerprints” by discriminant analysis (DA). More importantly, D-AuNSs can also be carried out to classify two bacterial pathogens (E. coli and S. aureus) in serum samples, as well as differentiate the infected patients from healthy subjects successfully with great accuracy. Benefiting from intrinsic photothermal capability, chiral AuNSs exhibited high efficiency in killing of bacteria and disrupting of biofilms through a synergistic chemotherapy and phototherapy (PTT) functions. Altogether, the chiral AuNSs provides a novel strategy for SERS discrimination of enantiomer and bacteria, as well as incorporation of photothermal bacterial elimination, contributing to further broaden the chiral nanomaterials-based application.

Design of Silica@Au Hybrid Nanostars for Enhanced SERS and Photothermal Effect.

Core-shell nanostructures of silicon oxide@noble metal have drawn a lot of interest due to their distinctive characteristics and minimal toxicity with remarkable biocompatibility. Due to the unique property of localized surface plasmon resonance (LSPR), plasmonic nanoparticles are being used as surface-enhanced Raman scattering (SERS) based detection of pollutants and photothermal (PT) agents in cancer therapy. Herein, we demonstrate the synthesis of multifunctional silica core - Au nanostars shell (SiO2 @Au NSs) nanostructures using surfactant free aqueous phase method. The SERS performance of the as-synthesized anisotropic core-shell NSs was examined using Rhodamine B (RhB) dye as a Raman probe and resulted in strong enhancement factor of 1.37×106 . Furthermore, SiO2 @Au NSs were also employed for PT killing of breast cancer cells and they exhibited a concentration-dependent increase in the photothermal effect. The SiO2 @Au NSs show remarkable photothermal conversion efficiency of up to 72 % which is unprecedented. As an outcome, our synthesized NIR active SiO2 @Au NSs are of pivotal importance to have their dual applications in SERS enhancement and PT effect.

Tailor-made yolk-shell nanocomposites of star-shape Au and porous organic polymer for nitrogen electroreduction to ammonia

Electrocatalytic nitrogen (N2) reduction reaction (NRR) is an energy-saving approach to synthesize ammonia (NH3), which significantly depends on the development of high-efficiency electrocatalysts. Inspired by the catalytic microenvironment of enzymes, a series of yolk-shell nanostructures of monodispersed Au nanostars within porous organic polymers (POPs) have been successfully prepared via a self-sacrificing template strategy. The obtained yolk-shell nanocomposites have highly active Au nanostar cores and permeable POP shells for ambient electrocatalytic NRR to NH3. The hydrophobic properties of yolk-shell nanoreactors can be tailored accurately by engineering the POP shells at an atomic level, which greatly improves the N2 fixation performance by inhibiting the hydrogen evolution reaction, resulting in the unprecedented NH3 yield rate (∼109.1 μg h−1 mgcat.−1) and Faradaic efficiency (∼68.3 %). This work pioneers an effective strategy to construct tailor-made electrocatalysts for the N2-to-NH3 fixation.

Gold-Based Nanostructures for Antibacterial Application.

Bacterial infections have become a fatal threat because of the abuse of antibiotics in the world. Various gold (Au)-based nanostructures have been extensively explored as antibacterial agents to combat bacterial infections based on their remarkable chemical and physical characteristics. Many Au-based nanostructures have been designed and their antibacterial activities and mechanisms have been further examined and demonstrated. In this review, we collected and summarized current developments of antibacterial agents of Au-based nanostructures, including Au nanoparticles (AuNPs), Au nanoclusters (AuNCs), Au nanorods (AuNRs), Au nanobipyramids (AuNBPs), and Au nanostars (AuNSs) according to their shapes, sizes, and surface modifications. The rational designs and antibacterial mechanisms of these Au-based nanostructures are further discussed. With the developments of Au-based nanostructures as novel antibacterial agents, we also provide perspectives, challenges, and opportunities for future practical clinical applications.

Defect Damping-Enhanced Plasmonic Photothermal Conversion.

Significantly increasing the photothermal conversion of plasmonic nanostructured particles (PNPs) is a common goal for all applications of thermoplasmonics, but it is still in challenge, especially for PNPs with the morphology and composition required for a specific photothermal application. Here, we present a concept of defect-induced damping-enhanced photothermal conversion, which favors PNP intrinsic properties. A model of a defect-damped harmonic oscillator is established to depict photothermal conversion correlation with the structure of PNPs and is capable of accurately reproducing the optical performance of the PNPs with the local surface plasmon resonance far from the interband transition. The theoretical model analyses demonstrate that the defect-induced damping can significantly suppress the light scattering of the PNPs and effectively improve their photothermal conversion efficiency. Especially for the PNPs with a sufficiently large size (larger than ∼100 nm for Au and Ag), we show that defect-induced damping can significantly enhance their light absorption and photothermal performances. These are experimentally confirmed. Typically, defect-enriched Au nanostars with ∼100-150 nm profile size were fabricated and showed much higher photothermal performance and a big increment by 23% in photothermal conversion efficiency, compared with the normal (or defect-impoverished) counterpart. Furthermore, the in vitro and in vivo biological experiments demonstrate that this defect-enriched PNP can indeed exhibit significantly higher photothermal performance than the normal counterpart in cells and mouse tumors, which confirms the validity of the presented strategy in typical practical applications. This work provides a strategy to intrinsically and significantly enhance plasmonic photothermal conversion of PNPs with a sufficiently large size, which is not only suitable for PNPs with the morphology and composition required for specific applications but also can be combined with existing strategies to further increase their photothermal performance.

LoC-SERS Platform Integrated with the Signal Amplification Strategy toward Parkinson's Disease Diagnosis.

Multiplexed detection of Parkinson's disease (PD) biomarkers is of great significance for early diagnosis and personalized treatment. In this study, we fabricated a robust surface-enhanced Raman scattering-enabled lab-on-a-chip (LoC-SERS) platform for simultaneous quantification of α-synuclein, phosphorylated tau protein 181, osteopontin, and osteocalcin. Herein, the antibody-DNA conjugate was designed to introduce the catalytic hairpin self-assembly (CHA) amplification into the protein detection. Au nano-stars (AuNSs) modified with Raman reporter molecules and hairpin-structure DNA 1 were applied as the SERS nanotags. Au-coated silicon nanocone array (Au/SiNCA) fabricated based on the maskless plasma etching-prepared high-density Si nanocone array (SiNCA) and surface ion sputtering was used as the capture substrate after the modification of hairpin-structure DNA 2. Benefitting from the antibody-DNA conjugate-induced CHA amplification, numerous AuNSs can be connected to the Au/SiNCA surface, which significantly amplify the plasmonic coupling effect for ultrasensitive SERS detection, and the limit of detection was less than the pg/mL level. The application of highly uniform Au/SiNCA and antibody-DNA conjugate endows the LoC-SERS platform excellent analytical performance, including superior reproducibility, satisfactory universality, and high sensitivity. In addition, a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD mice model was established, and satisfactory results were obtained in real sample analysis with the LoC-SERS platform, which may be enlightening for exploiting protein biomarkers in PD monitoring.

Nanomaterial-decorated micromotors for enhanced photoacoustic imaging

Micro-and nanorobots have the potential to perform non-invasive drug delivery, sensing, and surgery in living organisms, with the aid of diverse medical imaging techniques. To perform such actions, microrobots require high spatiotemporal resolution tracking with real-time closed-loop feedback. To that end, photoacoustic imaging has appeared as a promising technique for imaging microrobots in deep tissue with higher molecular specificity and contrast. Here, we present different strategies to track magnetically-driven micromotors with improved contrast and specificity using dedicated contrast agents (Au nanorods and nanostars). Furthermore, we discuss the possibility of improving the light absorption properties of the employed nanomaterials considering possible light scattering and coupling to the underlying metal-oxide layers on the micromotor’s surface. For that, 2D COMSOL simulation and experimental results were correlated, confirming that an increased spacing between the Au-nanostructures and the increase of thickness of the underlying oxide layer lead to enhanced light absorption and preservation of the characteristic absorption peak. These characteristics are important when visualizing the micromotors in a complex in vivo environment, to distinguish them from the light absorption properties of the surrounding natural chromophores.

Fabrication of flexible SERS substrate based on Au nanostars and PDMS for sensitive detection of Thiram residue in apple juice

We developed a novel fabrication of flexible surface-enhanced Raman scattering (SERS) substrate to perform selective and sensitive determination of thiram residue in fruits and juices. Au nanostars (Au NSs) with multi-branching structure were self-assembled on aminated Polydimethylsiloxane (PDMS) slides by electrostatic interaction. By measuring the Thiram’s characteristic peak intensity at 1371 cm−1, the SERS method could distinguish Thiram from other pesticide residues. A good linear relationship between the peak intensity at 1371 cm−1 and thiram’s concentration was established at the range from 0.01 ppm to 100 ppm and the Limit of detection is 0.0048 ppm. We directly used this SERS substrate to detect Thiram in apple juice. By standard addition method, recoveries varied in the range of 97.05% to 106.00% and the RSD were from 3.26% to 9.35%. The SERS substrate exhibited a good sensitivity, stability and selectively for the detection of Thiram in food samples, which can be spread as a common method for the detection of pesticides in food samples.

Photothermal Effect and Phase Transition in VO2 Enhanced by Plasmonic Particles

Phase change metasurfaces based on VO2, which are pre-heated with electric current and optically addressed by projected structured light hologram, are considered to become a new paradigm in programmed THz/middle IR flat optics. Macroscopic quasi-homogeneous arrays of Au nanoparticles show large near IR absorption and a significant photothermal effect capable of boosting a light-triggered switching of VO2 and are to be carefully examined. We propose a new approach to simultaneously probe the altered temperature and electric conductivity of a hybrid Au particle-VO2 film composite by monitoring a phase shift and attenuating a surface acoustic wave in a YX128° cut LiNbO3 substrate. The method shows a temperature resolution of 0.1 °C comparable with the best existing techniques for studying nanoobjects and surfaces. The laser-induced photothermal effects were characterized in a macroscopic array of Au nanostars (AuNSts) with different surface coverage. In a monolayer of 10 nm Au, coupled plasmonic nanoparticles were deposited on the LiNbO3 substrate. An optically triggered insulator-metal transition assisted by photothermal effect in AuNSts/VO2/TiO2/LiNbO3 composites was studied at varied light power. We believe that the proposed SAW-based method is of significant importance for the characterization and optimization of radiation absorbing or/and electrically heated elements of metasurfaces and other devices for lab-on-chip and optical communication/processor technology.

Optical Printing of Single Au Nanostars.

Obtaining arrays of single nanoparticles with three-dimensional complex shapes is still an open challenge. Current nanolithography methods do not allow for the preparation of nanoparticles with complex features like nanostars. In this work, we investigate the optical printing of gold nanostars of different sizes as a function of laser wavelength and power. We found that tuning the laser to the main resonances of the nanostars in the near-infrared makes it possible to avoid nanoparticles reshaping due to plasmonic heating, enabling their deposition at the single particle level and in ordered arrays.