Single AgNPs Research Articles

The collective photothermal effect of silver nanoparticles probed by a microbolometer

The collective photothermal effect of silver nanoparticles probed by a microbolometer

Surface-Enhanced Raman Scattering (SERS) Substrates Based on Ag-Nanoparticles and Ag-Nanoparticles/Poly (methyl methacrylate) Composites.

SERS substrates formed by spherical silver nanoparticles (Ag-NPs) with a 15 nm average diameter adsorbed on Si substrate at three different concentrations and Ag/PMMA composites formed by an opal of PMMA microspheres of 298 nm average diameter were synthesized. The Ag-NPs were varied at three different concentrations. We have observed from SEM micrographs, in the Ag/PMMA composites, the periodicity of the PMMA opals is slightly altered as the Ag-NP concentration is increased; as a consequence of this effect, the PBGs maxima shift toward longer wavelengths, decrease in intensity, and broaden as the Ag-NP concentration is increased in the composites. The performance of single Ag-NP and Ag/PMMA composites as SERS substrates was determined using methylene blue (MB) as a probe molecule with concentrations in the range of 0.5 µM to 2.5 µM. We found that in both single Ag-NP and Ag/PMMA composites as SERS substrates, the enhancement factor (EF) increases as the Ag-NP concentration is increased. We highlight that the SERS substrate with the highest concentration of Ag-NPs has the highest EF due to the formation of metallic clusters on the surface, which generates more "hot spots". The comparison of the EFs of the single Ag-NP with those of Ag/PMMA composite SERS substrates shows that the EFs of the former are nearly 10-fold higher than those of Ag/PMMA composites. This result is obtained probably due to the porosity of the PMMA microspheres that decreases the local electric field strength. Furthermore, PMMA exerts a shielding effect that affects the optical efficiency of Ag-NPs. Moreover, the metal-dielectric surface interaction contributes to the decrease in the EF. Other aspect to consider in our results is in relation to the difference in the EF of the Ag/PMMA composite and Ag-NP SERS substrates and is due to the existing mismatch between the frequency range of the PMMA opal stop band and the LSPR frequency range of the Ag metal nanoparticles adsorbed on the PMMA opal host matrix.

Toxicokinetics and Particle Number-Based Trophic Transfer of a Metallic Nanoparticle Mixture in a Terrestrial Food Chain.

Herein, we investigated to which extent metallic nanoparticles (MNPs) affect the trophic transfer of other coexisting MNPs from lettuce to terrestrial snails and the associated tissue-specific distribution using toxicokinetic (TK) modeling and single-particle inductively coupled plasma mass spectrometry. During a period of 22 days, snails were fed with lettuce leaves that were root exposed to AgNO3 (0.05 mg/L), AgNPs (0.75 mg/L), TiO2NPs (200 mg/L), and a mixture of AgNPs and TiO2NPs (equivalent doses as for single NPs). The uptake rate constants (ku) were 0.08 and 0.11 kg leaves/kg snail/d for Ag and 1.63 and 1.79 kg leaves/kg snail/d for Ti in snails fed with NPs single- and mixture-exposed lettuce, respectively. The elimination rate constants (ke) of Ag in snails exposed to single AgNPs and mixed AgNPs were comparable to the corresponding ku, while the ke for Ti were lower than the corresponding ku. As a result, single TiO2NP treatments as well as exposure to mixtures containing TiO2NPs induced significant biomagnification from lettuce to snails with kinetic trophic transfer factors (TTFk) of 7.99 and 6.46. The TTFk of Ag in the single AgNPs treatment (1.15 kg leaves/kg snail) was significantly greater than the TTFk in the mixture treatment (0.85 kg leaves/kg snail), while the fraction of Ag remaining in the body of snails after AgNPs exposure (36%) was lower than the Ag fraction remaining after mixture exposure (50%). These results indicated that the presence of TiO2NPs inhibited the trophic transfer of AgNPs from lettuce to snails but enhanced the retention of AgNPs in snails. Biomagnification of AgNPs from lettuce to snails was observed in an AgNPs single treatment using AgNPs number as the dose metric, which was reflected by the particle number-based TTFs of AgNPs in snails (1.67, i.e., higher than 1). The size distribution of AgNPs was shifted across the lettuce-snail food chain. By making use of particle-specific measurements and fitting TK processes, this research provides important implications for potential risks associated with the trophic transfer of MNP mixtures.

Periostracum of bivalve mollusk shells for sampling engineered metal nanoparticles: A case study of silver-based nanoparticles in Canada's experimental lake.

Given the ability of engineered metal nanoparticles to be transformed in natural waters in unpredictable manners, various sampling methods must be developed. Here, we took a novel approach to collection silver nanoparticles (AgNPs) that involved the use of the intact periostracum, the outer proteinaceous organic layer, of freshwater unionid mussels Pyganodon sp. Eight adult mussels were collected in August 2019 from a small boreal lake (L222) at the International Institute for Sustainable Development - Experimental Lakes Area (northwestern Ontario), which had been dosed with 15kg of poly(vinylpyrrolidone)-coated silver nanoparticles (PVP-AgNPs) in 2014-2015. Additionally, three adult mussels were collected from a control lake (L375). Numerous silica (SiO2) diatom frustules were adhered to periostracum of all mussels. Intact periostracum promotes the formation of layer composed of diatoms and sand grains. The Ag content in soft tissues and shells of the mussels from L375 was as low as ≤ 0.1 μg/g. In mussels from L222, Ag concentrations in the periostracum of five shells were in detectable amounts (1-4 μg/g); in three shells concentrations were as high as 86, 122, and 494 μg/g. The underlying mineral shell is depleted in Ag (<0.1 μg/g). The Ag content in soft tissue organs (whole body) ranged from 44 to 191 μg/g. AgNPs occur on the surface of both periostracum and diatoms. Single AgNPs (d=20-60nm) were partly sulfidized to Ag2S. The observed AgNPs often form aggregates with an average and a maximal size of circa 100nm and 1.5 μm, respectively. Scraping small fragments of intact periostracum of unionid shell is non-lethal to mussels, and is easy to do under field conditions. This simple sampling protocol could be used to detect metal-based nanoparticles (engineered or accidental) with the use of unionid and dreissenid bivalves.

Seeing Is Not Believing: Filtering Effects on Random Nature in Electrochemical Measurements of Single-Entity Collision.

To clarify the discrete nature of electrochemistry, single-entity electrochemistry of collision (SEEC) utilizes a confinement space in a nanoscale local electric field at a microscale electrode interface for characterizing single freely diffusing entities. This promising method provides new insights at the single entity level. However, the precise measurement is challenging because of the short residence time and wide current fluctuations caused by the dynamic and stochastic motion of a single entity at the interface of the electrode. Moreover, the enormous noise in the electrochemical system would submerge these weak transient electrochemical signals. To increase the signal-to-noise ratio, the low-pass filter (LPF) is often used but at the cost of lower temporal resolution. Therefore, a deeper understanding of the filtering effects on the electrochemical signal is required in SEEC. Here, we build a random walk model to simulate the dynamic electrochemical oxidation of individual silver nanoparticles (AgNPs) in the local electric field near the electrode. This model considers the effect of the effective potential during the interaction between NP and electrode. Results reveal that the shape of the signal is seriously distorted as the cutoff frequency (f c) of LPF is set at <20 kHz. Due to the filtering effects, hundreds of subpeaks originating from the dynamic motion of NP are merged in a simple peak, which muddies our "believing" from the "seeing" signals. However, the entire interaction time of single NPs with the electrodes can be acquired at f c ≥ 10 kHz. Moreover, an integral charge of the signal is conserved at any LPF, which enables quantitative analysis of SEEC. Our understanding of the filtering effect on single AgNPs oxidation is generally applicable to nano-electrochemical techniques (e.g., nanopore electrochemistry and nanopipette sensing) that generate transient current signals.

An approach to estimate the contribution of signal noise to the diameter uncertainty of individual silver nanoparticles and resolution of spICP-MS analysis

The factors influencing the signal noise and its contribution to the uncertainty of a single AgNP size in spICP-MS were investigated.

Hybrid nanocoatings of self-assembled organic-inorganic amphiphiles for prevention of implant infections

Antimicrobial coatings are one of the most promising strategies to prevent bacterial infections in orthopedic and dental implants. Combining antimicrobial agents with different antimicrobial mechanisms might have synergistic effects and be more potent. Others have shown that nanocomposites of silver nanoparticles (AgNPs) decorated with antimicrobial peptides (AMPs) show increased potency as free agents in solution. However, similar nanocomposites have not been explored to coat biomaterials through cooperative weak electrostatic attraction forces between AMP, AgNPs and substrates in need of protection against infection. In this work, we synthesized self-assembled antimicrobial amphiphiles of an AMP, GL13K. Then, we decorated the AMP nanostructures with AgNPs, which were finally used to coat etched Ti (eTi) surfaces. The strong hydrogen bonding between the AMP amphiphiles and the polar eTi yielded a robust and stable coating. When compared to single AgNP or single AMP coatings, our hybrid nanocoatings had notably higher in vitro antimicrobial potency against multiple bacteria strains related to implant infection. The hybrid coating also showed relevant antimicrobial activity in an in vivo subcutaneous infection model in rats. This work advances the application of AgNP/AMP nanocomposites as effective coatings for prevention of implant infections. Statement of significanceHigh morbidity, mortality and elevated costs are associated with orthopedic and dental implant infections. Conventional antibiotic treatment is ineffective due to barrier-like extracellular polymeric substances in biofilms and the increasing threat from antibiotic resistance. Antimicrobial coatings are one of the most promising strategies, but the performance is usually unsatisfactory, especially when tested in vivo. Here, we present a hybrid nanocoating with different modes of action to prevent implant infections using self-assembled antimicrobial peptide (AMP) amphiphiles decorated with silver nanoparticles (AgNPs). When compared to single AgNP or AMP coatings, our hybrid nanocoatings showed significant increases in antimicrobial potency against multiple implant infection-related bacterial strains in vitro and in an in vivo rat subcutaneous infection model.

An Envelope Algorithm for Single Nanoparticle Collision Electrochemistry†

Main observation and conclusionSingle nanoparticle collision has attracted great attention in the last several years to reveal the electron transfer and motion trajectories of individual particles at the electrode surface. An envelope algorithm is proposed for further reading and demonstrating the corresponding current signals, which integrates baseline correction, peak identification and Savitzky‐Golay filter. It is employed for data analysis of the single AgNPs collision on a wireless nanopore electrode to eliminate the current noise and accurately calculate the integrated charges in each current spike. The practicability and robustness of the algorithm are verified under additive Gaussian white noise with the signal‐to‐noise ratio higher than 5. By comparing with traditional Gaussian peak model, the algorithm here shows comparable performance for the peak identification and integrated charge calculation. These results signify a big step from manual Gaussian fitting to automatically data processing method, which facilitates a fast acquisition of intrinsic features in single entity electrochemistry.

Toward Vibrational Tomography of Citrate on Dynamically Changing Individual Silver Nanoparticles

This study explored changes in binding modes of the most common ligand, citrate on silver nanoparticles (AgNPs) using single-particle surface-enhanced Raman scattering (SP-SERS). Single AgNPs of 50 ± 10 nm diameter anchored on clean glass slides were monitored using time-dependent SP-SERS with 632.8 nm excitation at 1.3 μW incident (0.5 μW absorbed) power per nanoparticle. We observed several distinct spectra of citrate during time-dependent SP-SERS. Analysis of 1400 spectra showed the existence of two major groups termed as favorable (F) and probable (P) spectra based on their likelihood of appearance and intensities. These distinct spectra corresponded to a multitude of binding modes, structures, and variants of photocatalyzed products of citrate on the surface of dynamically changing AgNPs. Density functional theory (DFT) simulations were performed to model the structures and binding modes of citrate on an Ag(111) surface, and corresponding Raman spectra were computed and compared with distinct spectral types. Experiments performed with deuterated (2,2,4,4-d4) citrate-capped AgNPs provided additional evidence to understand the shifts in vibrational features obtained in SP-SERS of citrate-capped AgNPs. These systematic analyses of time-dependent SP-SERS spectra may be used for the reconstruction and vibrational tomography (VT) of ligands at the single-particle level. The proposed VT approach is similar to sectioning an object through a multitude of orientations and reconstructing its three-dimensional structure, although the structures reconstructed here are molecular orientations.

Collision-Based Electrochemical Detection of Lysozyme Aggregation.

Proteins are utilized across many biomedical and pharmaceutical industries; therefore, methods for rapid and accurate monitoring of protein aggregation are needed to ensure proper product quality. Although these processes have been previously studied, it is difficult to comprehensively evaluate protein folding and aggregation by traditional characterization techniques such as atomic force microscopy (AFM), electron microscopy, or X-ray diffraction, which require sample pre-treatment and do not represent native state proteins in solution. Herein, we report early tracking of lysozyme (Lyz) aggregation states by using single-particle collision electrochemistry (SPCE) of silver nanoparticle (AgNP) redox probes. The method relies on monitoring the rapid interaction of Lyz with AgNPs, which decreases the number of single AgNPs available for collisions and ultimately the frequency of oxidative impacts in the chronoamperometric profile. When Lyz is in a non-aggregated monomeric form, the protein forms a homogeneous coverage onto the surface of AgNPs, stabilizing the particles. When Lyz is aggregated, part of the AgNP surface remains uncoated, promoting the agglomeration of Lyz-AgNP conjugates. The frequency of AgNP impacts decreases with increasing aggregation time, providing a metric to track protein aggregation. Visualizations of integrated oxidation charge-transfer data displayed significant differences between the charge transfer per impact for AgNP samples alone and in the presence of non-aggregated and aggregated Lyz with 99% confidence using parametric ANOVA tests. Electrochemical results revealed meaningful associations with UV-vis, circular dichroism, and AFM, demonstrating that SPCE can be used as an alternative method for studying protein aggregation. This electrochemical technique could serve as a powerful tool to indirectly evaluate protein stability and screen protein samples for formation of aggregates.

Graphene on single Ag nanoparticles for nanoscale and quantum applications

Raman spectra of graphene on single Ag nanoparticles (Ag NPs) reveal promising features for quantum and imaging/sensing applications in the nanoscale regime. The active Raman modes of graphene monolayer act as a Raman Thermometry and Ag NPs act as plasmonic nanoheaters excited by the probe laser. The thermal probing resolution can reach the nanometer scale determined by the graphene area attached to the Ag NPs. In addition to the Raman shift and intensity enhancement, the G-peak half width (ΓG) decreases with increasing the laser power inferring the photo-induced electron transfer from AgNPs to the attached graphene area; we are the first to report ΓG reduction by thermal investigations. The proposed graphene/Ag NPs structure is exempt from power dissipation due to substrate effects such as the thermal coupling between graphene and substrate. Graphene plasmons bound to the surface at the nanoscale size driven by the photo-induced electron transfer from single Ag NPs are promising for quantum plasmonic applications that have been difficult to be achieved with conventional metal plasmonics.

Silver nanoparticles (Ag-NPs) in the central amygdala protect the rat conditioned by morphine from withdrawal attack due to naloxone via high-level nitric oxide.

Repeated injection of morphine during conditioned place preference (CPP) leads to spatial craving due to high-level nitric oxide (NO) in the central nucleus of amygdala (CeA). Silver nanoparticles (Ag-NPs) can produce oxygen-free radicals that lead to NO formation. We aimed to show the Ag-NPs protective effect on naloxone (NLX)-induced morphine withdrawal in the conditioned rats. Wistar rats (300-350g) were implanted with cannulae in the CeA. After recovery, they were randomly divided into experimental and saline groups. CPP was conducted by three-phase unbiased program. Morphine (0.5-7.5mg/kg) was injected subcutaneously (s.c.) once/per day during the conditioning phase. Naloxone (NLX) (0.05-0.4μg/rat) was given, intra-CeA, 10min before the CPP test. Ag-NPs (0.0001-0.01μg/rat) were administered alone or prior to the NLX effective dose (0.4μg/rat), intra-CeA. Conditioning score and withdrawal signs (wet dog shaking and scratching) were obtained and compared with saline group data. All rats' brains were collected in formalin 10% and after 48-72h stained with NADPH-diaphorase, the NO marker. All data were analyzed by one-way or two-way ANOVA. Morphine (2.5-7.5mg/kg, s.c.) induced a significant CPP vs. saline (1mL/kg, s.c.). The single Ag-NPs had no significant effect, whereas the NLX caused meaningful WDS and scratching. However, the NLX pre-treatment in combination with Ag-NPs eliminated these signs. Furthermore, the NO level increased in the CeA. The Ag-NPs may protect the morphine-conditioned rats against the NLX-induced withdrawal symptoms due to high-level NO in the CeA.

Plasmon-enhanced linear and second-order surface nonlinear optical response of silver nanoparticles fabricated using a femtosecond pulse

We present the plasmon-enhanced linear and second-order surface nonlinear optical response of silver nanoparticles (Ag NPs) fabricated using a femtosecond pulse. Theoretical analysis indicates Ag NPs with a diameter of ∼100 nm have excellent linear response within the visible band, and the electric field intensity enhancement factor reaches ∼105 under excitation of continuous light of 632.8 nm. Meanwhile, the simulation result of second-order surface nonlinear optical response shows that the second harmonic conversion efficiency of the Ag NPs dimer is two orders of magnitude higher than that of a single Ag NP, under excitation of a femtosecond pulse. In experiment, the linear response of Ag NPs is examined using surface-enhanced Raman spectroscopy (SERS) with a Raman enhancement factor of ∼1.7 × 1010, revealing the excellent linear optical response of Ag NPs. Moreover, the spectra of the second harmonic can be measured clearly under conditions of an average pump power of 40 μW, revealing the excellent second-order surface nonlinear optical response of Ag NPs.

Silver Nanoparticle Surface Enabled Self-Assembly of Organic Dye Molecules.

Fluorescence titration of methylene blue, rhodamine B and rhodamine 6G (R6G) by silver nanoparticle (AgNP) all resulted in an initial steep quenching curve followed with a sharp turn and a much flatter quenching curve. At the turn, there are about 200,000 dye molecules per a single AgNP, signifying self-assembly of approximately 36-layers of dye molecules on the surface of the AgNP to form a micelle-like structure. These fluorescence-quenching curves fit to a mathematical model with an exponential term due to molecular self-assembly on AgNP surface, or we termed it “self-assembly shielding effect”, and a Stern-Volmer term (nanoparticle surface enhanced quenching). Such a “super-quenching” by AgNP can only be attributed to “pre-concentration” of the dye molecules on the nanoparticle surface that yields the formation of micelle-like self-assembly, resulting in great fluorescence quenching. Overall, the fluorescence quenching titration reveals three different types of interactions of dye molecules on AgNP surface: 1) self-assembly (methylene blue, rhodamine B and R6G), 2) absorption/tight interaction (tryptamine and fluorescein), and 3) loose interaction (eosin Y). We attribute the formation of micelle-like self-assembly of these three dye molecules on AgNP to their positive charge, possession of nitrogen atoms, and with relatively large and flat aromatic moieties.

Monitoring Hydrogen Evolution Reaction Catalyzed by MoS2 Quantum Dots on a Single Nanoparticle Electrode.

Hydrogen evolution reaction (HER) catalyzed by molybdenum sulfide quantum dots (MoS2 QDs) has attracted extensive attention in the energy field. Monitoring HER catalyzed by MoS2 QDs based on a glass nanopore with an electrochemically confined effect was proposed for the first time. MoS2 QDs inside the glass nanopore is driven toward the orifice of the nanopore and bonded with the Ag nanoparticles (Ag NPs) to form a single nanocomposite. When enough voltage is applied across the orifice, the single Ag NP acts as a single nanoparticle electrode to conduct the electrochemically bipolar reaction on its two extremities. In the process, HER is catalyzed by MoS2 QDs, and Ag NPs are oxidized at the same time. The appearance of blockages on the elevated ionic current is attributed to the generation of a H2 bubble. Furthermore, by analyzing the modulations in the ionic current oscillation, the frequency of hydrogen bubble generation that is related to the catalytic efficiency of MoS2 QDs could be estimated. The results reveal the capability of the glass nanopore for the real-time monitoring electrocatalytic behavior, which makes the glass nanopore an ideal candidate to further reveal the heterogeneity of catalytic capability at the single particle level.

3D Droplet-Based Microfluidic Device Easily Assembled from Commercially Available Modules Online Coupled with ICPMS for Determination of Silver in Single Cell.

More recently, single-cell analysis based on ICPMS has made considerable headway while a challenge remains to differentiate single cell from doublets during the analysis. One burgeoning solution is to encapsulate single cell into droplets on the platform of the microfluidic chip. However, the manufacture of the droplet-based microfluidic chip requires sophisticated fabrication and limits its potential application. In this paper, we presented an off-the-shelf three-dimensional (3D) microfluidic device by assembling commercially available parts without any proficient manufacturing process. Uniform monodisperse microdroplet was generated from the 3D microfluidic device with a size variation of 1.5%, and the innner diameter of the 3D microfluidic device was the same as the nebulizer (150 μm). The proposed 3D microfluidic device-time-resolved ICPMS system was applied to detect silver in single AgNPs (51 nm), and the result is in good agreement with conventional acid digestion method, demonstrating the accuracy of the method. Silver uptake behaviors in HepG2 cells were then studied by incubating with Ag+ or AgNPs under biocompatible conditions. The results revealed that the cell-to-cell variability in terms of the diversity of cells incubated with AgNPs was wider than those cells incubated with Ag+ from the aspect of the content distribution of silver at the single-cell level.

Enhancing solar cell efficiency with plasmonic behavior of double metal nanoparticle system

The use of special arrangement of silver nanoparticle (Ag Np) arrays is presented in order to enhance light trapping capability of the thin film solar cells due to their ability to couple incident sunlight into localized modes. The spatial distribution of the nanoparticles in the matrix and their relative position are the important factors governing the performance of the device. Double nanoparticle system (DNS) over the silicon substrate, which is not a commonly studied system, is explored and the performance (absorption enhancement) was compared with periodically arranged single Ag Nps system. Finite difference time domain (FDTD) simulation has been performed to investigate the effect of silver nanoparticle array patterning on the absorption of solar radiation. The presence of DNS was found responsible for increased coupling of photons into plasmonic modes, and consequently increased absorption of photons into the substrate over a broad range of the solar spectrum.

Single Ag Nanoparticle Electro-oxidation: Potential-Dependent Current Traces and Potential-Independent Electron Transfer Kinetic.

Potential-dependent current traces were first observed for the same sized nanoparticles (NPs) during the dynamic electro-oxidation process of single AgNPs. In this work, we demonstrated that the motion trajectories of NPs, coupled with electrochemical kinetics parameters, qualitatively predicted from the series of the experimentally observed current traces obtained single AgNPs collision behaviors. Based on the Poisson-Boltzmann equation for a general electrochemical reaction, a rate constant of Ag oxidation could be further estimated to be 1 × 10-6 mol·cm-2·s-1 for electron transfer between AgNPs and the Au electrode by comparing the experimental results. Our method provided a meaningful attempt to test electron transfer kinetics and motion behaviors of single NPs using the high-resolution electrochemical signal.

Oxygen Reduction Activity and Reversible Deactivation of Single Silver Nanoparticles during Particle Adsorption Events

AbstractThe activity towards the oxygen reduction reaction (ORR) of single silver nanoparticles (AgNP) was quantified by using AgNP impacts on dual‐bore carbon nanoelectrodes in highly alkaline media. We found suitable conditions for the particles to adhere sufficiently stably for detailed electrochemical characterization of a single particle. The special electrode design opens the possibility to dose gaseous oxygen to the nanoparticle under study. Deactivation of the catalytic activity of the AgNP upon excessive exposure to oxygen as well as the recovery of catalytic activity under reducing conditions is presumably attributed to hydrogen evolution at the applied low potentials. The proposed approach allows mechanistic parameters for the ORR to be extracted at a single AgNP in highly alkaline media in the absence of any binder materials and under exclusion of averaging ensemble effects.

Structural Change of a Single Ag Nanoparticle Observed by Dark‐field Microspectroscopy

Silver nanoparticles (AgNPs) have been widely used as photocatalysts and nanosensors. Observation of the spectroscopy of a single AgNP greatly helps us understand the catalytic characteristics and morphology change of the AgNP during reactions. In the present study, AgNPs physically adsorbed on indium tin oxide (ITO) conductive glass were electrochemically reduced and oxidized, and the plasmonic resonance Rayleigh scattering (PRRS) spectrum of an individual AgNP was observed under a dark-field microscopy (DFM) equipped with a spectrometer. The electrochemical oxidization of the AgNP under constant potential caused a redshift of the PRRS peak for 30±5 nm. However, electrochemical reduction of the AgNP could not make the PRRS peak completely shift back to the initial position. In situ AFM and SEM characterization confirmed that very small Ag fragments (<10 nm) formed around the AgNP core during electrochemical oxidization. Results showed that dark-field microspectroscopy could be used as a sensitive tool for estimating the morphology/structural changes of nanoparticles that can hardly be observed through the cyclic voltammograms of multiple AgNPs.