Nanoparticle Collisions Research Articles

Enhanced single-nanoparticle collisions for the hydrogen evolution reaction in a confined microchannel

Single nanoparticle (NP) collisions technique has been widely employed in electrocatalysis. However, the short collision duration of single NPs hinders the further improvement in their electrocatalytic performance. Here, to increase the dynamic collision duration of single NPs in the electron tunneling region, enhanced near-wall hindered diffusion is introduced in the stochastic collision process by coupling a Au ultramicroelectrode (UME) with a confined microchannel. In the case of single palladium nanoparticle (Pd NP) collisions for the hydrogen evolution reaction (HER), the hydrodynamic trapping confined in the microchannel effectively permits the activation of the HER on the single Pd NPs. The microchannel-based Au UME is promising in the application of single-NP collisions to energy conversion.

Observation and Analysis of Staircase Response of Single Palladium Nanoparticle Collision on Gold Ultramicroelectrodes.

Collision (or impact) of single palladium nanoparticles (Pd NPs) on gold (Au), copper (Cu), nickel (Ni), and platinum (Pt) ultramicroelectrodes (UMEs) were investigated via electrocatalytic amplification method. Unlike the blip responses of previous Pd NP collision studies, the staircase current response was obtained with the Au UME. The current response, including collision frequency and peak magnitude, was analyzed depending on the material of the UME and the applied potential. Adsorption factors implying the interaction between the Pd NP and the UMEs are suggested based on the experimental results.

Rapid Screening of Bimetallic Electrocatalysts Using Single Nanoparticle Collision Electrochemistry.

The pace of nanomaterial discovery for high-performance electrocatalysts could be accelerated by the development of efficient screening methods. However, conventional electrochemical characterization via drop-casting is inherently inaccurate and time-consuming, as such ensemble measurements are serially performed through nanocatalyst synthesis, morphological characterization, and performance testing. Herein, we propose a rapid electrochemical screening method for bimetallic electrocatalysts that combines nanoparticle (NP) preparation and performance testing at the single NP level, thus avoiding any inhomogeneous averaging contribution. We employed single NP collision electrochemistry to realize in situ electrodeposition of a precisely tunable Pt shell onto individual parent NPs, followed by instantaneous electrocatalytic measurement of the newborn bimetallic core-shell NPs. We demonstrated the utility of this approach by screening bimetallic Au-Pt NPs and Ag-Pt NPs, thereby exhibiting promising electrocatalytic activity at optimal atomic ratios for methanol oxidation and oxygen reduction reactions, respectively. This work provides a new insight for the rapid screening of other bimetallic electrocatalysts.

From ensemble electrochemistry to nanoparticle-impact electrochemistry: Altered reaction process and possible applications

Nanoparticle-impact electrochemistry (NIE) is an electroanalytical method based on the stochastic collisions of individual nanoparticles onto an inert ultramicroelectrode. In this article, we overview different characteristics of NIE-based reactions from their ensemble counterpart, that is, enhanced mass transport, intermittent working mode, and reduced reaction time scale. A particular interest is focused on the survey of the resulting changes in the reaction process regarding enhanced reaction efficiency and rate, altered selectivity, and improved catalyst stability. A summary of the application prospect of NIE is followed, and existing challenges are provided.

Electrochemical Observation and Analysis of Stochastic Single Nanoparticle Collisions on Ultramicroelectrode Using Pt, Ag, Cu, and Ni Nanoparticle

We describe the electrochemical detection of single nanoparticle (NP) collision at an ultramicroelectrode (UME) with various NPs such as Pt, Ag, Cu, and Ni NP. We could observe the single NP collision through the enhanced current by electrocatalytic redox recycling. The overall current transient caused by the NP collision was differed depending on the NP collision system. The peak height and frequency of the current response are proportional to the size and concentration of the NP. The current response is very sensitive to the material and surface state of the measuring electrode. It also changed depending on the applied potential and the reaction mechanism of collided NP. Therefore, the current response was investigated at the various electrode material and surface state of the measuring electrode for better understanding of single NP collision mechanism and NP’s electrocatalytic reaction. For Pt and Ag NPs, the change of current response was mainly investigated with various experimental conditions. For Cu and Ni NPs, the new electrocatalytic reaction such as glucose oxidation and urea oxidation were applied. By observing and analyzing the various current response of the Pt, Ag, Cu, and Ni NP’s collision, the electrocatalytic activity of NP at various circumstance at a single NP level was studied.

(Digital Presentation) Stochastic Impact Electrochemistry in a Lateral-Flow Sensor Architecture

During the recent SARS-CoV-2 pandemic, lateral flow assays (LFAs) have written an indescribable story of success, as they provide means for decentralized, low-cost, and easy-to-use testing. However, LFAs in their most common form support only qualitative results and their sensitivity and limit of detection is significantly limited by the colorimetric readout method. In contrast, single-impact electrochemistry offers the possibility to quantify species beyond picomolar concentrations by recording individual species collisions with a biased microelectrode. Within this work, we investigate the integration of stochastic sensing into a LFA-architecture by combining a wax-patterned microchannel with a microelectrode array in order to detect silver nanoparticles by their oxidative dissolution. Here, we demonstrate the possibility to resolve individual nanoparticle collisions in a paper-based microchannel using a simplified reference-on-chip setup. Furthermore, we simulated a lateral-flow sensor, by flushing previously dried silver nanoparticles towards the electrode array, where the particles are subsequently detected. This proof-of-principle illustrates that single-impact electrochemistry might be a promising technique to extend the capability of LFAs. Especially, the integration of functionalized nanoparticle labels could enable the rapid and on-site detection of very dilute species with exceptional sensitivity.

Electrochemical Detection and Analysis of Various Current Responses of a Single Ag Nanoparticle Collision in an Alkaline Electrolyte Solution.

A single silver (Ag) nanoparticle (NP) collision was observed and analyzed in an alkaline solution using the electrocatalytic amplification (EA) method. Previously, the observation of a single Ag NP collision was only possible through limited methods based on a self-oxidation of Ag NPs or a blocking strategy. However, it is difficult to characterize the electrocatalytic activity of Ag NPs at a single NP level using a method based on the self-oxidation of Ag NPs. When using a blocking strategy, size analysis is difficult owing to the edge effect in the current signal. The fast oxidative dissolution of Ag NPs has been a problem for observing the staircase response of a single Ag NP collision signal using the EA method. In alkaline electrolyte conditions, Ag oxides are stable, and the oxidative dissolution of Ag NPs is sluggish. Therefore, in this study, the enhanced magnitude and frequency of the current response for single Ag NP collisions were obtained using the EA method in an alkaline electrolyte solution. The peak height and frequency of single Ag NP collisions were analyzed and compared with the theoretical estimation.

Bouncing and spinning of amorphous Lennard-Jones nanoparticles under oblique collisions

Collisions of Lennard-Jones nanoparticles (NPs) may be used to study the generic collision behavior of NPs. We study the collision dynamics of amorphous NPs for oblique collisions using molecular dynamics simulation as a function of collision velocity and impact parameter. In order to allow for NP bouncing, the attraction between atoms originating from differing NPs is reduced. For near-central collisions, a finite region of velocities – a ‘bouncing window’ – exists where the 2 NPs bounce from each other. At smaller velocities, energy dissipation and – at larger velocities – also NP deformation do not allow the NPs to surpass the attractive forces such that they stick to each other. Oblique collisions of non-rotating NPs convert angular momentum into NP spin. For low velocities, the NP spin is well described by assuming the NPs to come momentarily to a complete stop at the contact point (‘grip’), such that orbital and spin angular momentum share the pre-collision angular momentum in a ratio of 5:2. The normal coefficient of restitution increases with impact parameter for small velocities, but changes sign for larger velocities where the 2 NPs do not repel but their motion direction persists. The tangential coefficient of restitution is fixed in the ‘grip’ regime to a value of 5/7, but increases towards 1 for high-velocity collisions at not too small impact parameters, where the 2 NPs slide along each other.

Grain‐Boundary‐Rich Noble Metal Nanoparticle Assemblies: Synthesis, Characterization, and Reactivity

AbstractHere, a comprehensive study on the synthesis, characterization, and reactivity of grain‐boundary (GB)‐rich noble metal nanoparticle (NP) assemblies is presented. A facile and scalable synthesis of Pt, Pd, Au, Ag, and Rh NP assemblies is developed, in which NPs are predominantly connected via Σ3 (111) twin GBs, forming a network. Driven by water electrolysis, the random collisions and oriented attachment of colloidal NPs in solution lead to the formation of Σ3 (111) twin boundaries and some highly mismatched GBs. This synthetic method also provides convenient control over the GB density without altering the crystallite size or GB type by varying the NP collision frequency. The structural characterization reveals the presence of localized tensile strain at the GB sites. The ultrahigh activity of GB‐rich Pt NP assembly toward catalytic hydrogen oxidation in air is demonstrated, enabling room‐temperature catalytic hydrogen sensing for the first time. Finally, density functional theory calculations reveal that the strained Σ3(111) twin boundary facilitates oxygen dissociation, drastically enhancing the hydrogen oxidation rate via the dissociative pathway. This reported large‐scale synthesis of the Σ3 (111) twin GB‐rich structures enables the development of a broad range of high‐performance GB‐rich catalysts.

Neutrophil membrane-coated immunomagnetic nanoparticles for efficient isolation and analysis of circulating tumor cells

The isolation and analysis of scarce circulating tumor cells (CTCs) with immunomagnetic nanoparticles (IMNs) have shown promising outcomes in noninvasive cancer diagnosis. However, the IMNs adsorb nonspecific proteins after entering into biofluids and the formed protein coronas cover surface targeting ligands, limiting the detection efficiency of IMNs. In addition, the interaction between surface targeting ligands and white blood cells (WBCs) significantly limits the purity of CTCs isolated by IMNs. Furthermore, the interfacial collision of nanoparticles and cells has negative effects on the viability of isolated CTCs. All of these limitations synthetically restrict the isolation and analysis of rare CTCs for early diagnosis and precision medicine. Here, we proposed that surface functionalization of IMNs with neutrophil membranes can simultaneously reduce nonspecific protein adsorption, enhance the interaction with CTCs, reduce the distraction from WBCs, and improve the viability of isolated CTCs. In spiked blood samples, our neutrophil membrane-coated IMNs (Neu-IMNs) exhibited a superior separation efficiency from 41.36% to 96.82% and an improved purity from 40.25% to 90.68% when compared to bare IMNs. Additionally, we successfully isolated CTCs in 19 out of total 20 blood samples from breast cancer patients using Neu-IMNs and further confirmed the feasibility of the isolated CTCs for downstream cell sequencing. Our work provides a new perspective on engineered IMNs for efficient isolation and analysis of CTCs, paving the way for early noninvasive diagnosis of cancer.

Measurement of thermal conductivity of triple hybrid water based nanofluid containing MWCNT (10%) - Al2O3 (60%) - ZnO (30%) nanoparticles

In this study, the thermal conductivity (TC) of MWCNT (10%)-Al2O3 (60%)-ZnO (30%)/water hybrid nanofluids (HNFs) in different solid volume fractions (SVFs) and temperatures are measured experimentally and then statistically studied. Therefore, the components affecting RTC or Thermal Conductivity Enhancement (TCE) are given special attention. The results show that increasing the SVF and then increasing the number of collisions of nanoparticles (NPs) in all laboratory conditions improves the RTC of the HNFs. The rate of TCE improvement in the best test conditions of this study is reported to be 29.50%. In this research, modeling and optimization of RTC are performed using the response surface methodology (RSM). The maximum agreement of the proposed model with the 4th order with the experimental results has given acceptable validity to the theory section. Another indicator for determining the quality and accuracy of the correlation relationship is −1.05% <MOD < + 1.08%. It is also found that with increasing the SVF, the sensitivity of RTC increases, which in the highest SVF (SVF=1.68%) had the highest sensitivity equal to 1.76%.

Recent Progress of Cellulose-Based Hydrogel Photocatalysts and Their Applications.

With the development of science and technology, photocatalytic technology is of great interest. Nanosized photocatalysts are easy to agglomerate in an aqueous solution, which is unfavorable for recycling. Therefore, hydrogel-based photocatalytic composites were born. Compared with other photocatalytic carriers, hydrogels have a three-dimensional network structure, high water absorption, and a controllable shape. Meanwhile, the high permeability of these composites is an effective way to promote photocatalysis technology by inhibiting nanoparticle photo corrosion, while significantly ensuring the catalytic activity of the photocatalysts. With the growing energy crisis and limited reserves of traditional energy sources such as oil, the attention of researchers was drawn to natural polymers. Like almost all abundant natural polymer compounds in the world, cellulose has the advantages of non-toxicity, degradability, and biocompatibility. It is used as a class of reproducible crude material for the preparation of hydrogel photocatalytic composites. The network structure and high hydroxyl active sites of cellulose-based hydrogels improve the adsorption performance of catalysts and avoid nanoparticle collisions, indirectly enhancing their photocatalytic performance. In this paper, we sum up the current research progress of cellulose-based hydrogels. After briefly discussing the properties and preparation methods of cellulose and its descendant hydrogels, we explore the effects of hydrogels on photocatalytic properties. Next, the cellulose-based hydrogel photocatalytic composites are classified according to the type of catalyst, and the research progress in different fields is reviewed. Finally, the challenges they will face are summarized, and the development trends are prospected.

Potentiometric and SERS Detection of Single Nanoparticle Collision Events on a Surface Functionalized Gold Nanoelectrode

Single-entity electrochemistry is of fundamental importance and shows promise for ultrasensitive biosensing applications. Recently, we have demonstrated that various charged nanoparticles can be detected individually based on the non-redox open-circuit potential (OCP) changes induced by their collision events on a floating carbon nanoelectrode (CNE). Unlike the widely used amperometry approach, the potentiometric method provides the label-free detection of individual nanoscale entities without redox mediators in the solution. However, the CNE lacks specificity for molecular recognition during the collision events because of the limited methods of surface functionalization for carbon surfaces. Herein, we used surface-functionalized gold nanoelectrode (GNE) to overcome this limitation of CNE. The GNE modified with Raman reporter molecule also enabled surface-enhanced Raman spectroscopy (SERS) measurements. By using simultaneous time-resolved OCP and SERS measurements, both the OCP and SERS signals induced by the “hit-n-run” type of gold nanoparticle (GNP) collision events can be better understood. Also, by introducing a zwitterionic molecule, we formed near “stealth” surface and demonstrated that the non-specific adsorptions of GNPs to the surface of GNE have been suppressed, allowing continuous detection of hit-n-run events for over 30 min.

Single-Impact Electrochemistry in Paper-Based Microfluidics.

Microfluidic paper-based analytical devices (μPADs) have experienced an unprecedented story of success. In particular, as of today, most people have likely come into contact with one of their two most famous examples─the pregnancy or the SARS-CoV-2 antigen test. However, their sensing performance is constrained by the optical readout of nanoparticle agglomeration, which typically allows only qualitative measurements. In contrast, single-impact electrochemistry offers the possibility to quantify species concentrations beyond the pM range by resolving collisions of individual species on a microelectrode. Within this work, we investigate the integration of stochastic sensing into a μPAD design by combining a wax-patterned microchannel with a microelectrode array to detect silver nanoparticles (AgNPs) by their oxidative dissolution. In doing so, we demonstrate the possibility to resolve individual nanoparticle collisions in a reference-on-chip configuration. To simulate a lateral flow architecture, we flush previously dried AgNPs along a microchannel toward the electrode array, where we are able to record nanoparticle impacts. Consequently, single-impact electrochemistry poses a promising candidate to extend the limits of lateral flow-based sensors beyond current applications toward a fast and reliable detection of very dilute species on site.

Collision of nanoparticles of covalently bound atoms: Impact of stress-dependent adhesion.

The impact of nanoparticles (NPs) composed of atoms with covalent bonding is investigated numerically and theoretically. We use recent models of covalent bonding of carbon atoms and elaborate a numerical model of amorphous carbon (a-C) NPs, which may be applied for modeling soot particles. We compute the elastic moduli of the a-C material which agree well with the available data. We reveal an interesting phenomenon-stress-dependent adhesion, which refers to stress-enhanced formation of covalent bonds between contacting surfaces. We observe that the effective adhesion coefficient linearly depends on the maximal stress between the surfaces and explain this dependence. We compute the normal restitution coefficient for colliding NPs and explore the dependence of the critical velocity, demarcating bouncing and aggregative collisions, on the NP radius. Using the obtained elastic and stress-dependent adhesive coefficients we develop a theory for the critical velocity. The predictions of the theory agree very well with the simulation results.

Nanocollision mediated electrochemical sensing of host-guest chemistry at a nanoelectrode surface.

Electrochemical (EC) measurements of dynamic nanoparticle collisions on a support electrode provide a powerful approach to study the electrical properties of interfacial molecules self-assembled on the electrode surface. By introducing a special cage-shaped macrocyclic molecule, cucurbit[7]uril (CB7), onto a gold nanoelectrode surface, we show that the dynamic interactions between CB7 and the colliding nanoparticles can be real-time monitored via the appearance of distinct EC current switching signals. When a guest molecule is included in the CB7 cavity, the changed host-guest chemistry can be probed via the amplitude change of the EC current signals. In addition, different guest molecules can be recognized by CB7 on the nanoelectrode surface, giving rise to distinguishable current jump signals for different host-guest systems. Remarkably, two well-defined current states are observed in the EC measurements of the CB7-ferrocene complex, indicating two orientation geometries of ferrocene inside the CB7 cavity can be resolved in this EC sensing platform. This work demonstrates an effective approach for studying the dynamics of host-guest chemistry at the liquid-solid interface and sheds light on a convenient EC sensor for the recognition of target molecules with the aid of CB7.

Experimental investigation and artificial intelligent estimation of thermal conductivity of nanofluids with different nanoparticles shapes

Determining and modelling the effective thermal conductivity of nanofluids is always a concern of investigators. The effect of nanoparticles' shape on the effective thermal conductivity of nanofluids has not been accurately correlated with other influencing factors such as temperature and nanoparticle concentration. The main purpose of this study is to reveal the effects of influencing factors on the effective thermal conductivity of nanofluids by experimental investigation and artificial intelligence (AI). We prepared the TiO2/water nanofluids with four shapes of TiO2 nanoparticles (spherical, ellipsoidal, clubbed, and sheet) and measured the effective thermal conductivities of the samples with nanoparticles concentrations from 0.5 to 4.0 vol% as a function of temperature from 20 to 60 °C. Besides, 389 experimental datasets collected from literature and 80 datasets from our experiment were used to determine the optimum structure of AI-based models. Temperature, concentrations, shape factor, and thermal conductivity of nanoparticles were selected as independent variables, and the relative thermal conductivity of nanofluids was selected as the dependent variable. Six AI-based models were examined, including four artificial neural networks of multi-layer perceptron, cascade feedforward, radial basis function, and generalized regression neural network, adaptive neuro-fuzzy inference systems, and least-squares support vector machines, and the estimating performances were compared. The experimental results showed that increasing temperature and nanoparticles concentrations led to a remarkable improvement in the relative thermal conductivity of nanofluids, attributed to the intensified Brownian motion of nanoparticles with the high temperature and the effective collision of nanoparticles with the high concentrations. Besides, nanoparticles with a large aspect ratio provided the fast pathway with seldom crossing an interparticle boundary or junction point for effective heat transfer in the nanofluids, resulting in higher relative thermal conductivity of nanofluids. Statistical analyses confirmed that the cascade feed-forward neural network with ten hidden neurons and the Levenberg–Marquardt training algorithms was the optimized AI-based model for estimating the relative thermal conductivity of nanofluids. This model estimated allover experimental data by MSE = 0.0039, RMSE = 0.0622, AARD% = 2.66%, and R2 = 0.9908.

Study of the Filtration Performance of Multilayer and Multiscale Fibrous Structures.

As the incidence of small-diameter particles in the air has increased in recent decades, the development of efficient filtration systems is both urgent and necessary. Nanotechnology, more precisely, electrospun nanofibres, has been identified as a potential solution for this issue, since it allows for the production of membranes with high rates of fibres per unit area, increasing the probability of nanoparticle collision and consequent retention. In the present study, the electrospinning technique of polyamide nanofibre production was optimized with the variation of parameters such as polymer concentration, flow rate and needle diameter. The optimized polyamide nanofibres were combined with polypropylene and polyester microfibres to construct a multilayer and multiscale system with an increased filtration efficiency. We observed that the penetration value of the multilayer system with a PA membrane in the composition, produced for 20 min in the electrospinning, is 2.7 times smaller than the penetration value of the system with the absence of micro and nano fibers.

Potentiometric Detection of Single Nanoparticle Collision Events on a Surface Functionalized Gold Nanoelectrode

Electrochemistry single-entity methods are of fundamental importance and show promise for ultrasensitive chemical and biological sensing applications. Recently, we have demonstrated that various nanoparticles can be detected individually based on the open circuit potential (OCP) changes induced by their collision events on a floating carbon nanoelectrode. Unlike the widely used amperometry approach, the potentiometric method provides the label-free detection of individual nanoscale entities without redox mediators in solution. However, the carbon nanoelectrode is chemically inert and limited in surface functionalization. Here, I will present our recent progress of using surface functionalized gold nanoelectrode (GNE) to replace the carbon nanoelectrode for potentiometric single-entity studies. By utilizing the advantage of mixed surface functionalization of GNE with the Raman reporter molecule and polyethylene glycol or zwitterionic molecules, we formed near ‘stealth’ GNE surface and demonstrated that the non-specific adsorptions of nanoparticles to the GNE surface can be minimized, allowing continuous hit-n-run events for over 30 minutes. The surface functionalized GNE also enabled surface enhanced Raman spectroscopy (SERS) measurements. By using simultaneous time-resolved OCP and SERS measurements, both the OCP and SERS signals induced by the hit-n-run type of collision events can be better understood.

Collision, Adhesion, and Oxidation of Single Ag Nanoparticles on a Polysulfide-Modified Microelectrode.

We report the collision, adhesion, and oxidation behavior of single silver nanoparticles (Ag NPs) on a polysulfide-modified gold microelectrode. Despite its remarkable success in volume analysis for smaller Ag NPs, the method of NP-collision electrochemistry has failed to analyze particles greater than 50 nm due to uncontrollable collision behavior and incomplete NP oxidation. Herein, we describe the unique capability of an ultrathin polysulfide layer in controlling the collision behavior of Ag NPs by drastically improving their sticking probability on the electrode. The ultrathin sulfurous layer is formed on gold by sodium thiosulfate electro-oxidation and serves both as an adhesive interface for colliding NPs and as a preconcentrated reactive medium to chemically oxidize Ag to form Ag2S. Rapid particle dissolution is further promoted by the presence of bulk sodium thiosulfate serving as a Lewis base, which drastically improves the solubility of generated Ag2S by a factor of 1013. The combined use of polysulfide and sodium thiosulfate allows us to observe a 25× increase in NP detection frequency, a 3× increase in peak amplitude, and more complete oxidation for larger Ag NPs. By recognizing how volumetric analysis using transmission electron microscopy (TEM) may overestimate quasi-spherical NPs, we believe we can have full NP oxidation for particles up to 100 nm. By focusing on the electrode/solution interface for more effective NP-electrode contact, we expect that the knowledge learned from this study will greatly benefit future NP collision systems for mechanistic studies in single-entity electrochemistry as well as designing ultrasensitive biochemical sensors.