Aggregation Of Metal Nanoparticles Research Articles

Nanocavity in hollow sandwiched catalysts as substrate regulator for boosting hydrodeoxygenation of biomass-derived carbonyl compounds.

Hydrodeoxygenation of oxygen-rich molecules toward hydrocarbons is attractive yet challenging in the sustainable biomass upgrading. The typical supported metal catalysts often display unstable catalytic performances owing to the migration and aggregation of metal nanoparticles (NPs) into large sizes under harsh conditions. Here, we develop a crystal growth and post-synthetic etching method to construct hollow chromium terephthalate MIL-101 (named as HoMIL-101) with one layer of sandwiched Ru NPs as robust catalysts. Impressively, HoMIL-101@Ru@MIL-101 exhibits the excellent activity and stability for hydrodeoxygenation of biomass-derived levulinic acid to gamma-valerolactone under 50°C and 1-megapascal H2, and its activity is about six times of solid sandwich counterparts, outperforming the state-of-the-art heterogeneous catalysts. Control experiments and theoretical simulation clearly indicate that the enrichment of levulinic acid and H2 by nanocavity as substrate regulator enables self-regulating the backwash of both substrates toward Ru NPs sandwiched in MIL-101 shells for promoting reaction with respect to solid counterparts, thus leading to the substantially enhanced performance.

Interfacial galvanic replacement strategy for Pd-doped NiFe MOF nanosheets with highly efficient dopamine detection.

Aninterfacial galvanic replacement strategy to controllable synthesize palladium nanoparticles (Pd NPs)-modified NiFe MOF nanocomposite on nickel foam, which served as an efficient sensing platform for quantitative determination of dopamine (DA). Pd NPs grown in situ on the nanosheets of NiFe MOF via self-driven galvanic replacement reaction (GRR) and well uniform distribution was achieved. This method effectively reduced the aggregation of metallic nanoparticles and significantly promoted the electron transfer rate during the electrochemical process, leading to improved electrocatalytic activity for DA oxidation. Remarkably, the precisely constructed biosensor achieved a low detection limit (LOD) of 0.068µM and recovery of 94.1% (RSD 6.7%, N = 3) for simulated real sample detection and also exhibited superior selectivity and stability. The results confirmed that the as-fabricated Pd-NiFe/NF composite electrode could realize the quantitative determination of DA and showed promising prospects in real sample biosensing.

Integrating PtCo nanoparticles on N, S doped pore carbon nanosheets as high-performance bifunctional catalysts for oxygen reduction and hydrogen evolution reactions

The development of low-Pt bifunctional electrocatalysts with excellent performance for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is critical for the advancement of the hydrogen economy. Here, we have integrated low-loading Pt and Co metals into N, S doped porous carbon nanosheets to obtain composite catalysts encapsulating PtCo alloy nanoparticles (PtCo2@Co9S8/N-CNS and PtCo2@N-CNS). The acquired PtCo nanoparticles, with dimensions of about 2.5 nm, are uniformly distributed and firmly anchored in N, S doped carbon nanosheets with large specific surface areas and rich pore structure, forming multiple active centers and effectively preventing the aggregation of metal nanoparticles. The PtCo2@Co9S8/N-CNS and PtCo2@N-CNS display high ORR catalytic mass activity of 1.65 A mgPt-1 and 1.01 A mgPt-1 in 0.1 M HClO4. The PtCo2@N-CNS catalyst exhibits excellent HER performance in 0.5 M H2SO4, with a mass activity (at 50 mV) 4.3 times higher than that of Pt/C. The PtCo2@Co9S8/N-CNS and PtCo2@N-CNS also exhibit stronger ORR and HER stability than Pt/C after accelerated durability tests. The superior catalytic activity performance of catalysts can be attributed to the synergistic effect of multiple active centers of PtCo, Co9S8 and Co-N in the catalysts. The confinement of PtCo nanoparticles by Co metal and N, S doped porous nanosheets derived from graphitic carbon nitride (g-C3N4) as the template, which can effectively prevent the corrosion and migration of the catalysts under acidic conditions, enhances the catalytic stability of the materials. This study provides a new perspective for the development of economical and efficient bifunctional low-Pt catalysts.

Assessing the catalytic performance of Cu@Ln (Eu, Sm)-N-C composites as bifunctional electrocatalysts using mesoporous silica-protected calcination

Synthesis of a composite with high technical performance and low cost instead of Platinum-based electrocatalysts has become an investigation hotspot to develop fuel cells and storage technologies. So, in the current investigation, three new bifunctional electrocatalysts incorporating lanthanides into Zeolitic Imidazolate Framework (ZIF)-8 are fabricated and assessed. First, by using a facile protocol, three trimetallic composites consisting of Europium (Eu), Samarium (Sm), Copper (Cu), and ZIF-8 are prepared, and the fabricated samples are labeled as EuCu-ZIF, SmCu-ZIF, and SmEuCu-ZIF. Next, in order to eliminate the irreversible fusion and quick aggregation of metal nanoparticles through the high-temperature carbonization process, the mesoporous-silica-protected calcination technique is investigated. After the Hydrofluoric (HF) etching process, the Cu@Ln (Eu, Sm)-N-C electrocatalysts are formed. Based on the fabricated samples, the Cu@Eu-N-C electrocatalyst exhibited the best Oxygen Reduction Reaction (ORR) performance with an onset potential of −0.06 V vs Ag/AgCl. Additionally, the electron transfer number for this composite is found to be 3.68. The GCD experiments show that the Cu@Eu-N-C electrode has the greatest specific capacitance, measuring 431 F g−1 when tested at 1 A g−1. It is deduced that the introduction of Eu3+ and Sm3+ as metal ions in the ZIF-8 catalyst led to an improvement in defects in the carbon matrix and mass transfer, illustrating the fabricated catalysts have an acceptable efficiency for ORR and storage applications. Indeed, due to the use of metallic ions (Ln and Cu), highly effective active sites were formed, resulting in an outstanding improvement in ORR efficiency. Also, it was found that with the use of mesoporous-silica protection for the fabricated samples, there is a remarkable improvement in the onset potential and specific capacitance parameters.

Confined covalent organic framework anchored Fe sites derived highly uniform electrocatalysts for rechargeable aqueous and solid-state Zn-air batteries

Exploiting clean, highly efficient energy storage and conversion device like Zn-air battery is of significance for alleviating the energy and environmental crises of this society. Metal organic coordination polymers/frameworks have been regarded as ideal templates to synthesize non-noble metal catalysts for a long time. However, the high density of metal nodes inevitably leads to the heavy aggregation of metal nanoparticles during thermolysis transformation process, which greatly hinders the maximizing of electrochemical performances. Herein, covalent organic framework (COF) has been employed to anchor the quantificational Fe ions (COF-Fe) and then confined into the macropores of g-C3N4 to improve the dispersion of metal active sites and avoid severe aggregation during high temperature pyrolysis. After calcination, the metal nanoparticles highly dispersed Fe-CFN catalysts can be obtained. The optimal Fe-CFN-800 catalysts exhibit excellent ORR and OER performances with the potential difference between ORR and OER of merely 0.723 V. Moreover, experimental way and DFT theoretical calculations are also employed to disclose the reaction mechanism. Finally, the all-solid-state and aqueous Zn-air batteries assembled with the optimized Fe-CFN-800 as cathode present excellent performances with high peak power density, flexible rate performance, strong discharge stability and long-term charge–discharge cycling performance.

Co-assembly of Ag nanowires and nanocubes mediated by adhesive tape in hydrophilic and hydrophobic pattern for SERS-based determination of gefitinib and ritonavir in serum

Controlled aggregation of noble metal nanoparticles is incredibly crucial for obtaining reliable surface-enhanced Raman scattering (SERS) properties. Here, a rational agglomeration of large Ag nanowires (NWs) and small Ag nanocubes (NCs) was readily facilitated by simply utilizing the intrinsic viscosity of adhesive tape, leading to the generation of abundant electromagnetic “hotspots” around the numerous crossed nanotips and ultra-small nanogaps. After the molecular enrichment efficiency was further promoted by exploiting a hydrophilic-hydrophobic strategy, an ultra-low limit of detection as 8.8 × 10−11 M was demonstrated for rhodamine 6 G. Benefiting from the high sensitivity of the SERS chip, its application in the determination of clinical sample containing mixed gefitinib and ritonavir was finally proved, facilitating impressive specificity and accuracy. Considering the simplicity and reliability, our strategy has great potentials to be applied in clinical blood drug identification and concentration monitoring.

Size-controllable colloidal Ag nano-aggregates with long-time SERS detection window for on-line high-throughput detection

Making metal nanoparticle aggregates is a common way to improve surface-enhanced Raman scattering (SERS) enhancement via the formation of hot spots between nanoparticles. Here, we propose a “freeze-thaw-ultrasonication” method to obtain stable colloidal Ag nano-aggregates (AgNAs) with controllable sizes, which can remain stable for a few days. Compared with other method using aggregation reagents (e.g., organic molecules and salt), this method can maintain metal surface charges and adsorption affinity, which ensures the excellent SERS stability and sensitivity. The SERS detection window during the experiment can reach more than 25 min, which makes it a prerequisite for accurate SERS detection during a long-time range. Combining the obtained stable AgNAs with microfluidic devices, we established a sequential SERS on-line continuous detection method for the high-throughput detection of multiplex samples. The UV-Fenton degradation process of methylene blue (MB) is continuously on-line monitored through this platform, which is more sensitive than the UV–Vis Spectrum. Moreover, we have realized the sensitive and accurate detection of 5-nitro-8-hydroxyquinoline (5-NQ) with antibacterial and anticancer activities based on chloride-functionalized silver, which paved a way for SERS high-throughput analysis in bioanalysis and other fields.

A general method for precise chain assembly of noble metal nanoparticles

We report a general method for obtaining precise chain aggregates of noble metal nanoparticles, which could be generally applied to AuNPs, AgNPs and PtNPs of various sizes, giving single long chains.

Interface Optimization of Metal Quantum Dots/Polymer Nanocomposites and their Properties: Studies of Multi-Functional Organic/Inorganic Hybrid.

Nanomaterials filled polymers system is a simple method to produce organic/inorganic hybrid with synergistic or complementary effects. The properties of nanocomposites strongly depend on the dispersion effects of nanomaterials in the polymer and their interfaces. The optimized interface of nanocomposites would decrease the barrier height between filler and polymer for charge transfer. To avoid aggregation of metal nanoparticles and improve interfacial charge transfer, Pt nanodots filled in the non-conjugated polymer was synthesized with an in situ method. The results exhibited that the absorbance of nanocomposite covered from the visible light region to NIR (near infrared). The photo-current responses to typical visible light and 808 nm NIR were studied based on Au gap electrodes on a flexible substrate. The results showed that the size of Pt nanoparticles was about 1-2 nm and had uniformly dispersed in the polymer matrix. The resulting nanocomposite exhibited photo-current switching behavior to weak visible light and NIR. Simultaneously, the nanocomposite also showed electrical switching responses to strain applied to a certain extent. Well-dispersion of Pt nanodots in the polymer is attributable to the in situ synthesis of metal nanodots, and photo-current switching behavior is due to interface optimization to decrease barrier height between metal filler and polymer. It provided a simple way to obtain organic/inorganic hybrid with external stimuli responses and multi-functionalities.

THE CHEMICAL SYNTHESIS AND CHARACTERIZATION OF COBALT (Co), NICKEL (Ni) AND COPPER (Cu) NITROGEN-DOPED GRAPHENE NANOCOMPOSITES

Nitrogen-doped graphene (NGr) and metal nitrogen-doped graphene nanocomposites (MNGr) were synthesized employing chemical reduction method. The synthesized nanocomposites and graphene oxide (GO) were characterized via conventional characterization techniques. UV-Vis spectra of the synthesized metal nanocomposites indicated that cobalt (Co), nickel (Ni) and (Cu) copper nanoparticles (NPs) exhibited surface plasmon resonance peaks at 515 nm, 230 nm and 770 nm respectively, indicating the formation of the respective metal nanoparticles (MNPs) on NGr. The EDXRF analysis showed that the synthesized nanocomposites of the metals are very pure. SEM indicated the appearance of wrinkles and crumples, confirming the structural morphology of NGr. It also showed the attachment of smaller and white spherically shaped spots with insubstantial aggregation of MNPs on NGr. FTIR analysis showed the C=C stretching frequency in the GO that has shifted to a higher wavenumber from 1632.6-1640 cm- 1, indicating successful reduction of the nanocomposites. XRD analysis revealed the presence of the face-centred cubic crystalline lattices (fcc) for Ni, Co and Cu nanoparticles. The Scherrer equation was used to calculate the mean particle sizes of the MNPs formed on the NGr support.

Co/N nanoparticles supported on a C3N4/polydopamine framework as a bifunctional electrocatalyst for rechargeable zinc-air batteries

• An electrocatalyst with Co NPs on a graphitized N -doped carbon framework are prepared. • The synthetic strategy avoids the excessive growth and aggregation of metal nanoparticles. • The catalyst has an improved ORR and OER activity compared with Pt/C and Ir/C, respectively. • The synthetic catalyst-containing ZABs present an outstanding discharging performance. Metal N -doped carbons (M N C) and specifically cobalt-based N -doped carbons (Co N C) have attracted extensive attention as suitable multifunctional catalysts. Their high catalytic activity, originating from the strong coupling effect of Co with N, lead to the formation of active sites with suitable binding energies for promoting the discharging and charging reactions. Herein, we propose the synthesis of an efficient bifunctional electrocatalyst (ZIFCNDA) prepared by the introduction of Co ions during the polymerisation of dopamine, which lead to the direct doping of a carbon framework and the localized growth of Co-based MOFs polyhedrons, generating Co-based nanoparticles (Co NPs) upon pyrolysis. The C 3 N 4 -controlled polydopamine growth formed thin graphitized carbon nanosheets which can facilitate the transfer of electrons to the catalytically active sites. The ZIFCNDA catalyst was able to efficiently catalyse both the oxygen reduction (ORR) and oxygen evolution (OER) reactions). The ZAB containing the developed catalyst presented a stable discharge voltage of 1.1 V at a high current density of 10 mA cm −2 with higher stability and longer cycle life compared to their counterparts constructed using Pt/C and Ir/C in air–cathode. This study illustrates a platform to enhance the catalytic activity of the ORR and OER catalyst via promoting the formation of well distributed cobalt active sites, achieved due to the insertion of cobalt ions during the polymerization process of dopamine, instead of on a previously prepared framework and their application for rechargeable metal–air batteries.

Gold Nanocone Array with Extensive Electromagnetic Fields for Highly Reproducible Surface-Enhanced Raman Scattering Measurements.

Surface-enhanced Raman scattering (SERS) is a technique used to distinguish the constitution of disease-related biomarkers in liquid biopsies, such as exosomes and circulating tumor cells, without any recognition elements. Previous studies using metal nanoparticle aggregates and angular nanostructures have achieved the detection of various biomarkers owing to strong hot spots and electromagnetic (EM) fields by localized surface plasmon resonance (LSPR). Although these SERS platforms enable significant enhancement of Raman signals, they still have some problems with the fabrication reproducibility of platforms in obtaining reproducible SERS signals. Therefore, highly reproducible fabrication of SERS platforms is required. Here, we propose the application of a polymer-based gold (Au) nanocone array (Au NCA), which extensively generates an enhanced EM field near the Au NCA surface by LSPR. This approach was experimentally demonstrated using a 785 nm laser, typically used for SERS measurements, and showed excellent substrate-to-substrate reproducibility (relative standard deviation (RSD) < 6%) using an extremely simple fabrication procedure and very low laser energy. These results proved that a Au NCA can be used as a highly reproducible SERS measurement to distinguish the constitution of biomarkers.

Efficient catalysis using honeycomb-like N-doped porous carbon supported Pt nanoparticles for the hydrogenation of cinnamaldehyde in water

The construction of three dimensionally nitrogen-doped honeycomb-like porous carbon (3D-NHPC) materials for metal based heterogeneous catalysts has received substantial attention. However, tailoring these morphologies while retaining catalytic activity and avoiding aggregation of metal nanoparticles (NPs) is still challenging. Herein, we report a synthesis of 3D-NHPC supported Pt NPs (Pt@3D-NHPC (1.6 nm)) through a combination of hyper-crosslinking mediated self-assembly and subsequent in situ pyrolysis reduction. The prepared Pt@3D-NHPC (1.6 nm) catalysts possess a high surface area and hierarchically interconnected porous framework, which can provide more active sites of Pt NPs and short transport paths for substrates. Especially, after a H2O2 post-treatment, the obtained superhydrophilicity of the Pt@3D-NHPCH2O2 (1.6 nm) catalyst presents significant increase of catalytic activity towards efficient hydrogenation of cinnamaldehyde in aqueous solutions. Moreover, owing to the coordination effect by nitrogen-doping and confinement of the porous framework, the as-prepared Pt@3D-NHPCH2O2 (1.6 nm) showed excellent stability and durability.

Unraveling a role of molecular linker in nanoparticles self-organization by SERS spectroscopy: Comparative study of three aromatic diamines

The preparation of controllable small noble metal nanoparticle (NP) aggregates is required for plasmon-enhanced spectroscopy and metamaterials development. In this work, we present a systematic study of three aromatic diamines as possible linkers of silver NPs. Symmetric 4,4′-derivatives of bibenzyl, stilbene and tolane have been selected to reveal the effect of linker rigidity and conjugation degree on the morphology and optical properties of the obtained aggregates. Surface-enhanced Raman scattering spectra of colloidal solutions with different aromatic amine additives have been acquired to assess the surface equilibria and adsorbate state. The non-monotonic concentration profiles have been obtained in the case of effective NPs linking and can be considered as its feature. Transmission electron microscopy and absorption spectroscopy have been involved for the analysis of size and morphology of NPs aggregates. Effective linking of silver NPs is established for stilbene and tolane compounds, which give quasi-spherical aggregates and elongated dimers/trimers. Surface-initiated azo conversion is revealed for bibenzyl compound instead of NPs bridging. The tendency to decrease the degree of NP aggregation with increasing aromaticity and “springiness” of molecular linker is observed. The capability of rigid diamines to assemble the nanoparticles with a finite degree of aggregation, even at high concentrations, distinguishes them advantageously from aliphatic bifunctional linkers. Highly stable plasmonic aggregates can be obtained in this way and implemented further as building blocks for nano- and meta-materials, as well as for tags in imaging applications.

Harnessing Strong Metal-Support Interaction to Proliferate the Dry Reforming of Methane Performance by In Situ Reduction.

The strong bonding at the interface between the metal and the support, which can inhibit the undesirable aggregation of metal nanoparticles and carbon deposition from reforming of hydrocarbon, is well known as the classical strong metal-support interaction (SMSI). SMSI of nanocatalysts was significantly affected by heat treatment and reducing conditions during catalyst preparation.the heat treatment and reduction conditions during catalyst preparation. SMSI can be weakened by the decrement of metal-doped sites in the supporting oxide and can often deactivate catalysts by the encapsulation of active sites through these processes. To retain SMSI near the active sites and to enhance the catalytic activity of the nanocatalyst, it is essential to increase the number of surficial metal-doped sites between nanometal and the support. Herein, we propose a mild reduction process using dry methane (CH4/CO2) gas that suppresses the aggregation of nanoparticles and increases the exposed interface between the metal and support, Ni and cerium oxide. The effects of mild reduction on the chemical state of Ni-cerium oxide nanocatalysts were specifically investigated in this study. As a result, mild reduction led to form large amounts of the Ni3+ phase at the catalyst surface of which SMSI was significantly enhanced. It can be easily fabricated while the dry reforming of methane (DRM) reaction is on stream. The superior performance of the catalyst achieved a considerably high CH4 conversion rate of approximately 60% and stable operation up to 550 h at a low temperature, 600 °C.

Influence of Random Plasmonic Metasurfaces on Fluorescence Enhancement.

One of the strategies employed to increase the sensitivity of the fluorescence-based biosensors is to deposit chromophores on plasmonic metasurfaces which are periodic arrays of resonating nano-antennas that allow the control of the electromagnetic field leading to fluorescence enhancement. While artificially engineered metasurfaces realized by micro/nano-fabrication techniques lead to a precise tailoring of the excitation field and resonant cavity properties, the technological overhead, small areas, and high manufacturing cost renders them unsuitable for mass production. A method to circumvent these challenges is to use random distribution of metallic nanoparticles sustaining plasmonic resonances, which present the properties required to significantly enhance the fluorescence. We investigate metasurfaces composed of random aggregates of metal nanoparticles deposited on a silicon and glass substrates. The finite difference time domain simulations of the interaction of the incident electromagnetic wave with the structures reveals a significant enhancement of the excitation field, which is due to the resonant plasmonic modes sustained by the nanoparticles aggregates. We experimentally investigated the role of these structures in the fluorescent behaviour of Rhodamine 6G dispersed in polymethylmethacrylate finding an enhancement that is 423-fold. This suggests that nanoparticle aggregates have the potential to constitute a suitable platform for low-cost, mass-produced fluorescent biosensors.

Interface modulation and physical properties of heterostructure of metal nanoparticles and two-dimensional materials

&lt;sec&gt;Two-dimensional (2D) material has atomic smooth surface, nano-scale thickness and ultra-high specific surface area, which is an important platform for studying the interface interaction between metal nanoparticles (NPs) and 2D materials, and also for observing the surface atomic migration, structural evolution and aggregation of metal NPs in real time and &lt;i&gt;in situ&lt;/i&gt;. By rationally designing and constructing the interfaces of metal NPs and 2D materials, the characterization of the interface structure on an atomic scale is very important in revealing the structure-property relationship. It is expected that the investigation is helpful in understanding the mechanism of interaction between metal and 2D materials and optimizing the performance of the devices based on metal-2D material heterojunctions.&lt;/sec&gt;&lt;sec&gt;In this review, the recent progress of interface modulation and physical properties of the heterostructure of metal NPs and 2D materials are summarized. The nucleation, growth, structural evolution and characterization of metal NPs on the surface of 2D materials are reviewed. The effects of metal NPs on the crystal structure, electronic state and energy band of 2D materials are analyzed. The possible interfacial strain and interfacial reaction are also included. Because of the modulation of electrical and optical properties of 2D materials, the performance of metal NPs-2D material based field effect transistor devices and optoelectronic devices are improved. This review is helpful in clarifying the physical mechanism of microstructure affecting the properties of metal NPs-2D material heterostructures on an atomic scale, and also in developing the metal-2D material heterostructures and their applications in the fields of electronic devices, photoelectric devices, energy devices, etc.&lt;/sec&gt;

Remarkable reduction ability towards p-nitrophenol by a synergistic effect against the aggregation and leaching of palladium nanoparticles in dendritic supported catalysts

The aggregation and leaching of noble metal nanoparticles (NPs) in supported catalysts can decrease or even deactivate the catalytic activity. It is crucial but still challengeable to circumvent these drawbacks. Herein, we facilely synthesize a novel kind of composite nanocatalyst system to conquer these issues of palladium (Pd) NPs. To be specific, nanochannels of dendritic mesoporous silica&titania nanospheres (DMSTNs) could confine Pd NPs. Anatase titania (TiO2) and the coupled mercapto groups (-SH) on the surface could remarkably disperse and robustly anchor Pd. The as-prepared DMSTNs-SH-Pd displays outstanding performance in p-nitrophenol reduction, where a synergistic effect of the chemical composition and surface functionality on the catalytic activity can be further confirmed by photocatalytic water splitting and Suzuki coupling reaction. The strategy for Pd NPs spatially confined in nanochannels and finely decorated on chemically functionalized supports might be versatile for other noble metals like gold (Au), platinum (Pt), etc.

Dicyandiamide-assisted HKUST-1 derived Cu/N-doped porous carbon nanoarchitecture for electrochemical detection of acetaminophen

MOFs-derived metal/carbon materials have been considered as promising candidates for the electrochemical detection of micropollutants. However, the aggregation of metal nanoparticles and structure collapse of precursor MOFs during pyrolysis significantly hamper the improvement on detecting performance. Herein, a dicyandiamide-assisted strategy is utilized to synthesize well-dispersed Cu/N-doped porous carbon nanoarchitecture (CuNC) for the electrochemical detection of acetaminophen (AP). The constructed CuNC sensor exhibits excellent electro-analytical performance for monitoring AP with linear range from 0.01μM to 921.2μM, and the low detection limit of 2.46nM (S/N=3). The improved performance of CuNC sensor is ascribed to the introduction of dicyandiamide, which can prevent HKUST-1 framework breakage and reduce the aggregation tendency of Cu, leading to the evenly distributed small Cu nanoparticles, abundant N species, hierarchical channel structure, and high conductivity carbon framework. These advantages endow predominant repeatability, stability, and selectivity of CuNC sensor. This strategy provided a novel approach to preparing MOFs-derived carbon nanoarchitectures with excellent electroanalysis performance to monitor micropollutants.

Colloidal dendritic nanostructures of gold and silver for SERS analysis of water pollutants

Surface-Enhanced Raman Scattering (SERS) using colloidal metal (Ag, Au) nanoparticles has been regarded as a powerful method for detecting organic pollutants at vestigial levels. Although less investigated, the controlled synthesis of binary nanostructures comprising two metals provides an alternative route to SERS platforms with tuned surface plasmon resonances. Here, we demonstrate that the use of dendrimers allows the formation of distinct combinations of Ag:Au nanostructures that are composed of smaller metal nanocrystals. Our research highlights the role of the dendrimer macromolecules as a multipurpose ligand in the generation of such hybrid nanostructure, including as a reducing agent, an effective long-term colloidal stabilizer and as a molecular glue for interconnecting the primary metal nanocrystals. Noteworthy, the dendrimer-based Ag:Au hybrid nanostructures are more SERS sensitive as compared to the corresponding colloidal blends or to the single-phase metals, as revealed by using molecular pesticides as analytes in spiked water samples. We suggest that the high SERS sensitivity of the hybrid nanostructures is due to interparticle plasmonic coupling occurring between the primary metal nanoparticle aggregates, whose arrangement is templated by the presence of the dendrimer macromolecules.