Janus Gold Nanoparticles Research Articles

Fabrication of Densely-Packed Janus Gold Nanoparticles Layer by Self-Assembly for a Potential Molecular Sensing Probe

Localized surface plasmon phenomena of metallic nanoparticles could be utilized for sensing applications. As the particles in the vicinity results in a near-field coupling phenomenon, a higher field enhancement factor increases the sensing sensitivity. In this research, we propose a self-assembled and closely-packed Janus gold nanoparticle (AuNP) structure for application in molecular sensing. We utilize three-phase interfacial trapping and Langmuir-Schaefer method for the fabrication of Janus AuNP layer. In our case, dodecylamine (DDA) was used as the analyte for sensing assay. We found that the color of our AuNP changes from red-wine to blue in conjunction with the phase changes from colloidal to closely-packed layer that results in a red-shift absorbance peak. In the application of sensing assay, the absorbance peak is revealed blue-shifted up to ~40 nm from pristine AuNP layer due to the adsorption of DDA on the particle surfaces. Sensitivity enhancement is also expected due to the hotspot arises from the plasmonic particles in vicinity. This research could be further developed to a sensitive and quantitative molecular sensor up to colorimetric specific biosensor.

Janus nanozyme based satellite structure immunosandwich colorimetric strategy for glycoproteins visual detection

Glycoproteins are reliable biomarkers for early cancer detection, and the timely response to these biomarkers could improve the survival rate and reduce the medical care burden. However, conventional detection technologies such as immune-based assays often need natural antibody, complex sample pretreatments and long analysis time, which failing to provide the rapid turnaround times. To address this problem, a janus gold nanoparticles nanozyme (J-GNPsNE) linked magnetic titanium dioxide molecularly imprinted particles (MTi-MIP) satellite structure immunosandwich colorimetric strategy (SS-ICS) is proposed to rapid detect glycoproteins in human serum for the first time. The unique detection mode of the strategy relies on the sandwich-like assembly of molecularly imprinted nanoparticles, glycoprotein and nanozyme. This enabled to establish a point-of-care, labor-saving, easy-to-use and noninvasive serum glycoprotein biomarkers detection tool for efficient early diagnosis of cancer. By taking transferrin (TrF) as an example, the proposed strategy can exhibits great performance with a low detection limit (0.052 μg/mL) and a short analysis time (40 min), which is much better than most of the previous methods. Our presented strategy can be easily generalized for specific detection other types of glycoproteins by changing the template, thereby facilitating the serum screening for early cancer diagnosis in non-specialized laboratory infrastructure.

Systemic Immune Modulation Alters Local Bone Regeneration in a Delayed Treatment Composite Model of Non-Union Extremity Trauma.

Bone non-unions resulting from severe traumatic injuries pose significant clinical challenges, and the biological factors that drive progression towards and healing from these injuries are still not well understood. Recently, a dysregulated systemic immune response following musculoskeletal trauma has been identified as a contributing factor for poor outcomes and complications such as infections. In particular, myeloid-derived suppressor cells (MDSCs), immunosuppressive myeloid-lineage cells that expand in response to traumatic injury, have been highlighted as a potential therapeutic target to restore systemic immune homeostasis and ultimately improve functional bone regeneration. Previously, we have developed a novel immunomodulatory therapeutic strategy to deplete MDSCs using Janus gold nanoparticles that mimic the structure and function of antibodies. Here, in a preclinical delayed treatment composite injury model of bone and muscle trauma, we investigate the effects of these nanoparticles on circulating MDSCs, systemic immune profiles, and functional bone regeneration. Unexpectedly, treatment with the nanoparticles resulted in depletion of the high side scatter subset of MDSCs and an increase in the low side scatter subset of MDSCs, resulting in an overall increase in total MDSCs. This overall increase correlated with a decrease in bone volume (P = 0.057) at 6 weeks post-treatment and a significant decrease in mechanical strength at 12 weeks post-treatment compared to untreated rats. Furthermore, MDSCs correlated negatively with endpoint bone healing at multiple timepoints. Single cell RNA sequencing of circulating immune cells revealed differing gene expression of the SNAb target molecule S100A8/A9 in MDSC sub-populations, highlighting a potential need for more targeted approaches to MDSC immunomodulatory treatment following trauma. These results provide further insights on the role of systemic immune dysregulation for severe trauma outcomes in the case of non-unions and composite injuries and suggest the need for additional studies on targeted immunomodulatory interventions to enhance healing.

Synthesis of amphiphilic Janus gold nanoparticles stabilized with triphenylphosphine and D-penicillamine by ligand exchange at toluene/water emulsion interface

Ligand exchange was triggered at toluene/water emulsion interface between homogeneous gold nanoparticles (Au NPs) with triphenylphosphine (PPh3) and D-penicillamine (D-PA), resulted in amphiphilic Janus Au NPs with both phosphine and thiolate ligands. TEM and XRD analyses indicate that the product is composed of Au nanocrystals in an average diameter of about 3.7 nm. XPS, FTIR, Raman, and 1H NMR analyses demonstrate that the Au NPs are protected with hydrophilic D-PA molecules and lipophilic PPh3 ligands in a molecular ratio of ca. 1.8. The NOESY analysis and contact angle measurement further suggest that the D-PA and PPh3 molecules are spontaneously separated to form compartmentalized hydrophilic and lipophilic regions on the individual Au NPs, which exhibit good catalytic performance and recyclability on the reduction of 4-nitrophenol. The results demonstrate that amphiphilic Janus Au NPs can be synthesized by partly exchange of PPh3 with D-PA at toluene/water emulsion interface and are potentially applicable for other phosphine/thiolate pairs to modify Au NPs.

Free-Standing 2D Janus Gold Nanoparticles Monolayer Film with Tunable Bifacial Morphologies via the Asymmetric Growth at Air-Liquid Interface.

Large scaled two-dimensional free-standing monolayer films of gold nanoparticles show distinctive optical, electrical, and chem-physical propertie making them a new class of advanced plasmonic materials differing from bulk materials and individual nanoparticles in solution. The conventional 2D gold nanoparticle films usually possess symmetric structures and identical properties of gold nanoparticles on both sides. Herein, we developed an easy and efficient approach to construct a new type of free-standing 2D gold nanoparticle monolayer film with asymmetric gold nanoparticle structures and functions, called a 2D Janus gold nanoparticle film. The remarkable feature of our method is the subsequent asymmetric growth on one side of the interfacial self-assembled gold nanoparticle monolayer film at the air-liquid interface. It is very easy to control the morphology of the Janus film by simply and precisely adjusting the size and shape of the gold nanoparticles on the top side, and selectively tuning the structure and composition on the bottom side of the film by growing gold nanoparticles or other noble metals such as Ag, Pt, and Pd. Unlike the conventionally prepared Janus films at solid substrate that require long-time etching and transfer procedures, other features of our method include the short time in which the interfacial self-assembly and the subsequent asymmetric growth are completed as well as the easily transferable property of the Janus film onto different substrates, such as quartz glass sheets, silicon wafers, and PDMS. The obtained Janus gold nanoparticle film shows asymmetric wettabilities, optical properties, and surface-enhanced Raman scattering (SERS) effects, which is promising for a range of potential applications in optical devices, sensors, and asymmetric catalysis.

One-pot synthesis of amphiphilic Janus gold nanoparticles with d-penicillamine and benzyl mercaptan ligands by toluene/water emulsion reaction

Amphiphilic Janus Au NPs were synthesized by emulsion reaction with presence of d-penicillamine (D-PA) and benzyl mercaptan (BM) molecules at water and toluene phases, respectively. TEM and XRD characterizations indicate that the reaction product is composed of Au nanocrystals in size of 2.9 nm. XPS, FTIR, Raman and 1H NMR analyses suggest that the capping ligands on the Au NPs are D-PA and BM, where the ratio of D-PA to BM is ca. 1.7. Contact angle measurement and NOESY analysis further reveal that the hydrophilic D-PA and lipophilic BM are separated into two distinct hemispheres on the individual Au NPs. The simple and efficient approach allows large scale preparation of amphiphilic Janus Au NPs at low cost for versatile applications, such as drug delivery, vapor sensors and heterogeneous catalysts.

Direct colorimetric detection of aspartic acid in rat brain based on oriented aggregation of Janus gold nanoparticle

We report a colorimetric assay based on oriented Janus gold nanoparticles (AuNPs) aggregation for highly selective and sensitive detection of aspartic acid (Asp) in rat brain. Initially, the Janus AuNPs with relatively large size was prepared, during which the stabilizing agent polyethylene glycol (PEG) and highly selective recognition agent cysteine (Cys) were attached to the selected area at the surface. The addition of Asp causes the oriented and controllable aggregation due to the specific recognition between Cys and Asp. Such a way of aggregation leads to significantly improved long-term stability and an at least 2 orders of magnitude wider dynamic range (1.8 nM–180 μM) compared with conventional colorimetric sensors. In addition, the strategy to increase the size of AuNPs (13–45 nm) enables to efficiently increase the limit of detection (18 μM–1.8 nM). Surprisingly, such a sensor can be applied to direct sensing of cerebral Asp in rat brain, which is determined round 33.9 ± 1.3 μM with satisfactory spiked recovery (86.5 ± 7.5%) due to the excellent anti-interference ability. This work provides a direct and reliable method to evaluate the Asp involved physiological and pathological process and opens a new avenue for real sample detection.

Ligands Exchange Process on Gold Nanoparticles in Acetone Solution

The ligands exchange process on gold nanoparticles (GNPs) was proceeded by using hydrophobic group (PPh3) and hydrophilic group (THPO) in acetone solution. The FTIR and XPS results demonstrated that part of THPO was replaced by PPh3 which was dissolved in polar solution (acetone); the results were in accordance with the electrochemical analysis where the differential capacity decreased with increasing exchange time. After 12 h, the exchange process terminated and the final ratio of PPh3 and THPO was about 1.4: 1. This ratio remained unchanged although the PPh3 and THPO modified GNPs re-dispersed in the PPh3 acetone solution demonstrating the stable adsorption of both ligands after exchanging for 12 h. The TEM images showed that the gold nanoparticles were self-assembled from scattered to arranged morphology due to the existence of hydrophilic and hydrophobic ligands and led to Janus gold nanoparticles.

Tuning Metamaterials Nanostructure of Janus Gold Nanoparticle Film for Surface-Enhanced Raman Scattering

Large-area metamaterial nanostructures of a Janus gold nanoparticle (AuNP) film decorated with thiol-terminated polymers have been fabricated and tuned at an oil/water interface by a facile and innovative process. The results show that AuNPs had been arrayed with ultrasmall gaps between neighboring particles laminated with polymer which is called a Janus film. This film exhibits a sensitive property for surface-enhanced Raman scattering (SERS) for determination of both hydrophilic methylene blue and hydrophobic thiram. The structure-dependent SERS of the Janus AuNP film has also been confirmed by a finite-difference time domain (FDTD) method.

Infrared external reflection spectra of Janus gold nanoparticle monolayers prepared at the air–water interface

Abstract. Nanoparticle monolayers at the air–water interface have received broad attention because of their potential applications owing to the tunability of their surface properties. We prepared gold nanoparticle monolayers by adsorption of hydrophilized nanoparticles from solution onto Langmuir monolayers of amphiphilic organic molecules (polyion complexes of deuterated stearic acid and polyallylamine) at the air–water interface, followed by adsorption of dodecyltrimethylammonium bromide onto the underside of these particles. The infrared external reflection spectra of the monolayers recorded both during and after preparation showed that the adsorption of gold nanoparticles on the Langmuir monolayers and that of dodecyltrimethylammonium bromide on the nanoparticles occurred in several tens of minutes. The infrared spectra also showed that both stearic acid and dodecyltrimethylammonium bromide molecules were highly ordered on the gold nanoparticles at the air–water interface. These results suggested that this preparation procedure is a useful fabrication method for Janus particles.

One-pot synthesis of ultrafine amphiphilic Janus gold nanoparticles by toluene/water emulsion reaction

Spontaneous phase separation of capping ligands at emulsion interfaces was used to synthesize amphiphilic Janus gold nanoparticles in batch.

Catalysis-Driven Self-Thermophoresis of Janus Plasmonic Nanomotors.

It is highly demanding to design active nanomotors that can move in response to specific signals with controllable rate and direction. A catalysis-driven nanomotor was constructed by designing catalytically and plasmonically active Janus gold nanoparticles (Au NPs), which generate an asymmetric temperature gradient of local solvent surrounding NPs in catalytic reactions. The self-thermophoresis behavior of the Janus nanomotor is monitored from its inherent plasmonic response. The diffusion coefficient of the self-thermophoresis motion is linearly dependent on chemical reaction rate, as described by a stochastic model.

Catalysis‐Driven Self‐Thermophoresis of Janus Plasmonic Nanomotors

AbstractIt is highly demanding to design active nanomotors that can move in response to specific signals with controllable rate and direction. A catalysis‐driven nanomotor was constructed by designing catalytically and plasmonically active Janus gold nanoparticles (Au NPs), which generate an asymmetric temperature gradient of local solvent surrounding NPs in catalytic reactions. The self‐thermophoresis behavior of the Janus nanomotor is monitored from its inherent plasmonic response. The diffusion coefficient of the self‐thermophoresis motion is linearly dependent on chemical reaction rate, as described by a stochastic model.

Molecular tilt-dependent and tyrosine-enhanced electron transfer across ITO/SAM/[DPPC–Au NP–Tyrosine] Janus nanoparticle junction

Enhanced interfacial electron transfer (ET) across the otherwise insulating indium tin oxide/alkanethiol self-assembled monolayer (SAM)/redox molecule junction was accomplished when a Janus gold nanoparticle (JNP) protected by bioinspired phosphatidylcholine (DPPC) lipid and tyrosine amino acid ligands was anchored on it. In addition to the most theoretical and experimental investigations on the distance-dependent ET across Metal–Organic SAM–Nanoparticle (NP) architectures, the current results succinctly illustrate molecular tilt angle of the SAM and the characteristic of JNP as key factors in expediting the ET rate via electron tunneling. In the absence of JNP, electron tunneling with a tunneling factor β = 1.1 A−1 across the SAM was the rate-limiting step, evidenced from electrochemical impedance spectroscopy (EIS). The apparent electron transfer rate constant (k app 0 ) for anchored SAM was enhanced by at least one order of magnitude than the DPPC-only protected nanoparticle, suggesting the potential role of tyrosine towards the enhanced ET. The asymmetric and biogenic nature of the construct sheds light on a potential bioelectronic device for novel electronic attributes. Entry of TOC .

Multiple-Sized Amphiphilic Janus Gold Nanoparticles by Ligand Exchange at Toluene/Water Interface

Amphiphilic Janus gold nanoparticles (GNPs) are prospected to encapsulate drug molecules in cancer therapy and to serve as heterogeneous catalysts at oil/water interfaces, where Janus GNPs with different sizes are required. In this work, multiple-sized precursor GNPs were synthesized by seeded growth method protected with tris(hydroxymethyl)phosphine oxide (THPO) ligand molecule, and a ligand exchange reaction with triphenylphosphine (PPh3) at the toluene/water interface was employed to prepare amphiphilic Janus GNPs. UV-vis and transmission electron microscopy (TEM) analyses indicate that the as-prepared GNPs are nanocrystals with average diameters of 2.3 nm, 9.5 nm, 16.1 nm and 18.8 nm, respectively. Contact angle, Raman and X-ray photonic spectroscopy (XPS) analyses reveal that the self-assembled GNP films exhibit hydrophilic on one side and hydrophobic on another, owing to the adsorption of hydrophilic ligands (THPO and THP) and a similar amount of hydrophobic ligands (PPh3 and PPh3O). Angle-resolved XPS analysis further demonstrates that the individual GNPs actually possess hydrophilic and hydrophobic compartments on the surface, which regularly packed by supramolecular interactions at toluene/water interface to form the self-assembled GNP films.

Thermoswitchable Janus Gold Nanoparticles with Stimuli-Responsive Hydrophilic Polymer Brushes.

Well-defined thermoswitchable Janus gold nanoparticles with stimuli-responsive hydrophilic polymer brushes were fabricated by combining ligand exchange reactions and the Langmuir technique. Stimuli-responsive polydi(ethylene glycol) methyl ether methacrylate was prepared by addition-fragmentation chain-transfer polymerization. The polymer brushes were then anchored onto the nanoparticle surface by interfacial ligand exchange reactions with hexanethiolate-protected gold nanoparticles, leading to the formation of a hydrophilic (polymer) hemisphere and a hydrophobic (hexanethiolate) one. The resulting Janus nanoparticles showed temperature-switchable wettability, hydrophobicity at high temperatures, and hydrophilicity at low temperatures, due to thermally induced conformational transition of the polymer ligands. The results further highlight the importance of interfacial engineering in the deliberate functionalization of nanoparticle materials.

Directed Self-Assembly and Infrared Reflection Absorption Spectroscopy Analysis of Amphiphilic and Zwitterionic Janus Gold Nanoparticles.

Here, we report an approach to use infrared reflection absorption spectroscopy (IRRAS) for the unambiguous proof of the presence as well as the spatial distribution of organic ligands on the Janus gold nanoparticle (AuNP) surface. For this purpose we synthesized amphiphilic and zwitterionic Janus AuNPs and immobilized these on pretreated gold surfaces by directed self-assembly, exploiting hydrophilic/hydrophobic or electrostatic interactions, respectively. Thus, we obtained macroscopic two-dimensional arrays of Janus AuNPs exhibiting a specific orientation. These arrays were investigated by IRRAS, and the obtained spectra revealed only peaks of the ligands facing the IR beam, while the ligands facing the gold substrate were not detected due to reflection of the IR beam on the AuNP cores. Thus, we describe a straightforward spectroscopic procedure to prove the Janus character of zwitterionic and amphiphilic AuNPs in the size range of 10-15 nm.

Janus gold nanoparticles obtained via spontaneous binary polymer shell segregation.

Janus gold nanoparticles are of high interest because they allow directed self-assembly and display plasmonic properties. We succeeded in coating gold nanoparticles with two different polymers that form a Janus shell. The spontaneous segregation of two immiscible polymers at the surface of the nanoparticles was verified by NOESY NMR and most importantly by electron microscopy analysis in two and three dimensions. The Janus structure is additionally shown to affect the aggregation behavior of the nanoparticles.

A simple strategy to improve the interfacial activity of true Janus gold nanoparticles: a shorter hydrophilic capping ligand.

Janus gold nanoparticles (JPs) of ∼4 nm-diameter half functionalized with 1-hexanethiol as a hydrophobic capping ligand exhibit significantly higher interfacial activity, reproducibility and rheological response when the other half is functionalized with 1,2-mercaptopropanediol (JPs-MPD) than with 2-(2-mercaptoethoxy)ethanol (JPs-MEE), both acting as hydrophilic capping ligands. The interfacial pressure measured by pendant drop tensiometry reaches 50 mN m(-1) and 35 mN m(-1) for the JPs-MPD at the water/air and water/decane interface, respectively. At the same area per particle, the JPs-MEE reveal significantly lower interfacial pressure: 15 mN m(-1) and 5 mN m(-1) at the water/air and water/decane interface, respectively. Interfacial dilatational rheology measurements also show an elastic shell behaviour at higher compression states for JPs-MPD while the JPs-MEE present near-zero elasticity. The enhanced interfacial activity of JPs-MPD is explained in terms of chemical and hydration differences between the MPD and MEE ligands, where MPD has a shorter hydrocarbon chain and twice as many hydroxyl terminal groups as MEE.

Synthesis of Janus-like gold nanoparticles with hydrophilic/hydrophobic faces by surface ligand exchange and their self-assemblies in water.

This study aims at the synthesis of Janus gold nanoparticles (Janus GNPs) with hydrophilic/hydrophobic faces by a simple ligand exchange reaction in an homogeneous system and at the elucidation of the self-assembled structures of the Janus GNPs in water. As hydrophilic surface ligands, we synthesized hexaethylene glycol (E6)-terminated thiolate ligands with C3, C7, or C11 alkyl chains, referred to as E6C3, E6C7, and E6C11, respectively. As a hydrophobic ligand, a butyl-headed thiolate ligand C4-E6C11, in which a C4 alkyl was introduced on the E6C11 terminus, was synthesized. The degree of segregation between the two ligands on the GNPs (5 nm in diameter) was examined by matrix-assisted laser desorption/ionization time-of fright mass spectrometry (MALDI-TOF MS) analysis. We found that the choice of immobilization methods, one-step or two-step addition of the two ligands to the GNP solution, crucially affects the degree of segregation. The two-step addition of a hydrophilic ligand (E6C3) followed by a hydrophobic ligand (C4-E6C11) produced a large degree of segregation on the GNPs, providing Janus-like GNPs. When dispersed in water, these Janus-like GNPs formed assemblies of ∼160 nm in diameter, whereas Domain GNPs, in which the two ligands formed partial domains on the surface, were precipitated even when the molar ratio of the hydrophilic ligand and the hydrophobic ligand on the surface of the NPs was almost 1:1. The assembled structure of the Janus-like GNPs in water was directly observed by pulsed coherent X-ray solution scattering using an X-ray free-electron laser, revealing irregular spherical structures with uneven surfaces.