Single Nanoparticle Level Research Articles

Combining Electrodeposition and Optical Microscopy for Probing Size‐Dependent Single‐Nanoparticle Electrochemistry

AbstractElectrodeposition of nanoparticles (NPs) is a promising route for the preparation of highly electroactive nanostructured electrodes. By taking advantage of progressive electrodeposition, disordered arrays with a wide size distribution of Ag NPs are produced. Combined with surface‐reaction monitoring by using highly sensitive backside absorbing‐layer optical microscopy (BALM), such arrays offer a platform for screening size‐dependent electrochemistry at the single NP level. In particular, this strategy allows rationalizing the electrodeposition dynamics at the single‐NP level (>10 nm), up to the point of quantifying the presence of metal nanoclusters (<2 nm), and probing easier NP oxidation with size decrease, either through electrochemical or galvanic reactions.

Ultrasensitive free bilirubin detection in whole blood via counting quantum dots aggregates at single nanoparticle level

Here we report a versatile strategy for detecting bilirubin by harnessing the cationic polymer polyethylenimine induced aggregation of human serum albumin-modified quantum dots. These aggregates are easily discriminated from the individual QD by single molecule spectral imaging microscopy and correlated to the bilirubin concentration. The proposed method can selectively detect bilirubin with a detection limit as low as 0.6 nM. Remarkably, this method has been successfully applied to the trace detection of free bilirubin in human whole blood and serum samples with satisfactory results.

Plasmoelectric Potential Mapping of a Single Nanoparticle

The plasmoelectric potential effect, based on all-metal nanostructures, is a newly discovered plasmon-induced photoelectric converting mechanism. In this work, we have experimentally demonstrated that gold and silver nanoparticles exhibit opposite plasmoelectric potentials under the same excitation source, depending on their distinct surface plasmon resonance (SPR) frequencies. Three-dimensional mapping of plasmoelectric potentials on gold and silver nanoparticles depicts height-related surface potential information as well as the charge density evolution process down to the single nanoparticle level with Kelvin Probe Force Microscopy (KPFM). Upon employing a statistical method, the quantitative plasmoelectric potential is obtained. Under the power intensity of 5.4 mW/cm2, the maximum value of the plasmoelectric potential reaches −79 mV on the gold nanoparticle and 54 mV on silver nanoparticles. Finally, our work may provide guidance to the understanding of plasmoelectric potential on the single nanoparti...

(Invited) Surface Plasmon-Driven Water Reduction: Nanoparticle Size Matters

Plasmonic-metal/semiconductor heterostructures represent promising photocatalytic constructs for solar-to-fuel energy conversion, but detailed knowledge of the structure-function relationships governing their activity remains elusive. Here, we monitor plasmon-mediated electron transfer (PMET) across Au-TiO2 Schottky junctions at the single-nanoparticle level to clarify the role of metal nanocrystal size in plasmonic photochemistry. Size-dependent photovoltage studies of PMET in Au/TiO2 photoelectrodes reveal that the reduction potential of hot electrons within the TiO2 conduction band is not solely determined by the absolute size of Au nanoparticles, but by the relative size of Au to TiO2. With this new insight, we tailored the physical dimensions of Au/TiO2 photocatalysts to efficiently harvest hot electrons for improved plasmon-driven hydrogen evolution from water. Taken together, these studies elucidate the role of metal nanocrystal size in plasmonic photocatalysis and establish general guidelines for the rational design of plasmonic-metal/semiconductor assemblies that can effectively exploit hot carriers in photochemical reactions.

Yi‐Tao Long

Angewandte Chemie International EditionVolume 57, Issue 45 p. 14682-14682 Author ProfileFree Access Yi-Tao Long First published: 10 July 2018 https://doi.org/10.1002/anie.201806950AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract “My favorite food is tiger prawn. The most important thing I learned from my parents is persistence …” Find out more about Yi-Tao Long in his Author Profile. Yi-Tao Long The author presented on this page has published more than 10 articles in Angewandte Chemie in the last 10 years, most recently: “Single-Nanoparticle Photoelectrochemistry at a Nanoparticulate TiO2-Filmed Ultramicroelectrode”: Y.-Y. Peng, H. Ma, W. Ma, Y.-T. Long, H. Tian, Angew. Chem. Int. Ed. 2018, 57, 3758; Angew. Chem. 2018, 130, 3820. The work of Y.-T. Long has been featured on the inside back cover of Angewandte Chemie: “Electrodeposition of Single-Metal Nanoparticles on Stable Protein 1 Membranes: Application of Plasmonic Sensing by Single Nanoparticles”: L.-X. Qin, Y. Li, D.-W. Li, C. Jing, B.-Q. Chen, W. Ma, A. Heyman, O. Shoseyov, I. Willner, H. Tian, Y.-T. Long, Angew. Chem. Int. Ed. 2012, 51, 140; Angew. Chem. 2012, 124, 144. Date of birth: July 27, 1967 Position: Cheung Kong Professor, School of Chemistry and Molecular Engineering, East China University of Science and Technology E-mail: ytlong@ecust.edu.cn Homepage: http://ytlong.ecust.edu.cn/ ORCID: 0000-0003-2571-7457 Education: 1989 BSc, Shandong University 1996 MSc, Nanjing University 1999 PhD with Professor Hong-Yuan Chen, Nanjing University 1999–2001 Postdoctoral fellow with Professor Michael Grunze, University of Heidelberg 2001 Research associate, École Nationale Supérieure de Chimie de Paris 2001–2005, HSURC Fellow/research associate with Professors Heinz-Bernhard Kraatz and Jeremy S. Lee, University of Saskatchewan 2006 Research associate with Professor Chris Backhouse, University of Alberta 2006–2007 Associate specialist with Professors Luke P. Lee and Gabor Somorjai, University of California, Berkeley Awards: 2016 First Prize, Shanghai Natural Science Award; 2017 Grand Prize, Science and Technology Award, China Association for Instrumental Analysis Research: Electroanalytical chemistry; nanopores; nanoplasmonic sensing; single-molecule analysis Hobbies: Drinking tea, traveling My favorite food is tiger prawn. The most important thing I learned from my parents is persistence. My favorite place on earth is Shanghai. If I were not a scientist, I would be a painter. The most exciting thing about my research is to simplify the sophisticated. The best advice I have ever been given is “God rewards the diligent” (天道酬勤). I celebrate success by drinking a cup of tea. My favorite book (fiction) is The Mysterious Island by Jules Verne. My top three films of all time are The Man with the Golden Gun, Goldfinger, and Goldeneye. The downside of my job is spending too little time with my family. My favorite type of music is Peking opera. The most significant scientific advance of the last 100 years has been elucidating the nature of the chemical bond. My 5 top papers: 1“Self-assembling bacterial pores as components of nanobiosensors for the detection of single peptide molecules”: Y.-T. Long, M.-N. Zhang, Science in China Series B: Chemistry 2009, 52, 731. (Electrochemical nanopore confinement for single-peptide sensing.) 2“Single Gold Nanoparticles as Real-Time Optical Probes for the Detection of NADH-Dependent Intracellular Metabolic Enzymatic Pathways”: L. Zhang, Y. Li, D. Li, C. Jing, X. Chen, M. Lv, Q. Huang, Y.-T. Long, I. Willner, Angew. Chem. Int. Ed. 2011, 50, 6789; Angew. Chem. 2011, 123, 6921. (Established a method based on single plasmonic nanoparticles for single-cell analysis.) 3“Plasmon Resonance Scattering Spectroscopy at the Single-Nanoparticle Level: Real-Time Monitoring of a Click Reaction”: L. Shi, C. Jing, W. Ma, D.-W. Li, J. E. Halls, F. Marken, Y.-T. Long, Angew. Chem. Int. Ed. 2013, 52, 6011; Angew. Chem. 2013, 125, 6127. (Monitoring a click reaction at the single-nanoparticle level.) 4“Nanopore-Based Sequencing and Detection of Nucleic Acids”: Y.-L. Ying, J. Zhang, R. Gao, Y.-T. Long, Angew. Chem. Int. Ed. 2013, 52, 13154; Angew. Chem. 2013, 125, 13392. (Progress in the field of nanopores, including pore-forming materials, sensing mechanisms, advanced instruments, and big data processing methods.) 5“Discrimination of oligonucleotides of different lengths with a wild-type aerolysin nanopore”: C. Cao, Y.-L. Ying, Z.-L. Hu, D.-F. Liao, H. Tian, Y.-T. Long, Nat. Nanotechnol. 2016, 11, 713. (Discovering the unique sensing ability of the aerolysin nanopore.) Volume57, Issue45November 5, 2018Pages 14682-14682 ReferencesRelatedInformation

Single-Nanoparticle Photoelectrochemistry at a Nanoparticulate TiO2 -Filmed Ultramicroelectrode.

An ultrasensitive photoelectrochemical method for achieving real-time detection of single nanoparticle collision events is presented. Using a micrometer-thick nanoparticulate TiO2 -filmed Au ultra-microelectrode (TiO2 @Au UME), a sub-millisecond photocurrent transient was observed for an individual N719-tagged TiO2 (N719@TiO2 ) nanoparticle and is due to the instantaneous collision process. Owing to a trap-limited electron diffusion process as the rate-limiting step, a random three-dimensional diffusion model was developed to simulate electron transport dynamics in TiO2 film. The combination of theoretical simulation and high-resolution photocurrent measurement allow electron-transfer information of a single N719@TiO2 nanoparticle to be quantified at single-molecule accuracy and the electron diffusivity and the electron-collection efficiency of TiO2 @Au UME to be estimated. This method provides a test for studies of photoinduced electron transfer at the single-nanoparticle level.

Electrochemical Dynamics of a Single Platinum Nanoparticle Collision Event for the Hydrogen Evolution Reaction

AbstractChronoamperometry was used to study the dynamics of Pt nanoparticle (NP) collision with an inert ultramicroelectrode via electrocatalytic amplification (ECA) in the hydrogen evolution reaction. ECA and dynamic light scattering (DLS) results reveal that the NP colloid remains stable only at low proton concentrations (1.0 mm) under a helium (He) atmosphere, ensuring that the collision events occur at genuinely single NP level. Amperometry of single NP collisions under a He atmosphere shows that each discrete current profile of the collision event evolves from spike to staircase at more negative potentials, while a staircase response is observed at all of the applied potentials under hydrogen‐containing atmospheres. The particle size distribution estimated from the diffusion‐controlled current in He agrees well with electron microscopy and DLS observations. These results shed light on the interfacial dynamics of the single nanoparticle collision electrochemistry.

Electrochemical Dynamics of a Single Platinum Nanoparticle Collision Event for the Hydrogen Evolution Reaction.

Chronoamperometry was used to study the dynamics of Pt nanoparticle (NP) collision with an inert ultramicroelectrode via electrocatalytic amplification (ECA) in the hydrogen evolution reaction. ECA and dynamic light scattering (DLS) results reveal that the NP colloid remains stable only at low proton concentrations (1.0 mm) under a helium (He) atmosphere, ensuring that the collision events occur at genuinely single NP level. Amperometry of single NP collisions under a He atmosphere shows that each discrete current profile of the collision event evolves from spike to staircase at more negative potentials, while a staircase response is observed at all of the applied potentials under hydrogen-containing atmospheres. The particle size distribution estimated from the diffusion-controlled current in He agrees well with electron microscopy and DLS observations. These results shed light on the interfacial dynamics of the single nanoparticle collision electrochemistry.

Asymmetrical etching of Ag nanoparticles into symmetry-reduced bi-metallic nanocups at the single-nanoparticle level.

Asymmetrical etching of nanoparticles was achieved by employing interface-confined galvanic replacement reactions. Interfacial Ag nanocubes, nanowires and nanospheres were fabricated into symmetry-reduced cubic, trough-like and spherical nanocups, respectively. The formation of nanocups is attributed to in situ local nanomasking and selective etching of interfacial nanoparticles at the single-nanoparticle level.

The self-healing of defects induced by the hydriding phase transformation in palladium nanoparticles

Nanosizing can dramatically alter material properties by enhancing surface thermodynamic contributions, shortening diffusion lengths, and increasing the number of catalytically active sites per unit volume. These mechanisms have been used to explain the improved properties of catalysts, battery materials, plasmonic materials, etc. Here we show that Pd nanoparticles also have the ability to self-heal defects in their crystal structures. Using Bragg coherent diffractive imaging, we image dislocations nucleated deep in a Pd nanoparticle during the forward hydriding phase transformation that heal during the reverse transformation, despite the region surrounding the dislocations remaining in the hydrogen-poor phase. We show that defective Pd nanoparticles exhibit sloped isotherms, indicating that defects act as additional barriers to the phase transformation. Our results resolve the formation and healing of structural defects during phase transformations at the single nanoparticle level and offer an additional perspective as to how and why nanoparticles differ from their bulk counterparts.

Imaging the polymerization of multivalent nanoparticles in solution

Numerous mechanisms have been studied for chemical reactions to provide quantitative predictions on how atoms spatially arrange into molecules. In nanoscale colloidal systems, however, less is known about the physical rules governing their spatial organization, i.e., self-assembly, into functional materials. Here, we monitor real-time self-assembly dynamics at the single nanoparticle level, which reveal marked similarities to foundational principles of polymerization. Specifically, using the prototypical system of gold triangular nanoprisms, we show that colloidal self-assembly is analogous to polymerization in three aspects: ensemble growth statistics following models for step-growth polymerization, with nanoparticles as linkable “monomers”; bond angles determined by directional internanoparticle interactions; and product topology determined by the valency of monomeric units. Liquid-phase transmission electron microscopy imaging and theoretical modeling elucidate the nanometer-scale mechanisms for these polymer-like phenomena in nanoparticle systems. The results establish a quantitative conceptual framework for self-assembly dynamics that can aid in designing future nanoparticle-based materials.

Nanobubbles: An Effective Way to Study Gas-Generating Catalysis on a Single Nanoparticle.

Gas-generating catalysis is important to many energy-related research fields, such as photocatalytic water splitting, water electrolysis, etc. The technique of single-nanoparticle catalysis is an effective way to search for highly active nanocatalysts and elucidate the reaction mechanism. However, gas-generating catalysis remains difficult to investigate at the single-nanoparticle level because product gases, such as H2 and O2, are difficult to detect on an individual nanoparticle. Here, we successfully find that nanobubbles can be used to study the gas-generating catalysis, i.e., H2 generation from formic acid dehydrogenation on a single Pd-Ag nanoplate, with a high time resolution (50 ms) via dark-field microscopy. The research reveals that the nanobubble evolution process includes nucleation time and lifetime. The nucleation rate of nanobubbles is proportional to the catalytic activity of a single nanocatalyst. The relationship between the catalytic activity and the nucleation rate is quantitatively described by a mathematical model, which shows that an onset reaction rate (ronset) exists for the generation of nanobubbles on a single Pd-Ag nanoplate. The research also reveals that a Pd-Ag nanoplate with larger size usually has a higher activity. However, some large-sized ones still have low activities, indicating the size of the Pd-Ag nanoplate is not the only key factor for the activity. Notablely, further research shows that Pd content is the key factor for the activity of single Pd-Ag nanoplates with similar size. The methodology and knowledge acquired from this research are also applicable to other important gas-generating catalysis reactions at the single-nanoparticle level.

Single-Nanoparticle Plasmonic Electro-optic Modulator Based on MoS2 Monolayers.

The manipulation of light in an integrated circuit is crucial for the development of high-speed electro-optic devices. Recently, molybdenum disulfide (MoS2) monolayers generated broad interest for the optoelectronics because of their huge exciton binding energy, tunable optical emission, direct electronic band-gap structure, etc. Miniaturization and multifunctionality of electro-optic devices further require the manipulation of light-matter interaction at the single-nanoparticle level. The strong exciton-plasmon interaction that is generated between the MoS2 monolayers and metallic nanostructures may be a possible solution for compact electro-optic devices at the nanoscale. Here, we demonstrate a nanoplasmonic modulator in the visible spectral region by combining the MoS2 monolayers with a single Au nanodisk. The narrow MoS2 excitons coupled with broad Au plasmons result in a deep Fano resonance, which can be switched on and off by applying different gate voltages on the MoS2 monolayers. A reversible display device that is based on this single-nanoparticle modulator is demonstrated with a heptamer pattern that is actively controlled by the external gates. Our work provides a potential application for electro-optic modulation on the nanoscale and promotes the development of gate-tunable nanoplasmonic devices in the future.

Simultaneous Topography and Reaction Flux Mapping at and around Electrocatalytic Nanoparticles

The characterization of electrocatalytic reactions at individual nanoparticles (NPs) is presently of considerable interest but very challenging. Herein, we demonstrate how simple-to-fabricate nanopipette probes with diameters of approximately 30 nm can be deployed in a scanning ion conductance microscopy (SICM) platform to simultaneously visualize electrochemical reactivity and topography with high spatial resolution at electrochemical interfaces. By employing a self-referencing hopping mode protocol, whereby the probe is brought from bulk solution to the near-surface at each pixel, and with potential-time control applied at the substrate, current measurements at the nanopipette can be made with high precision and resolution (30 nm resolution, 2600 pixels μm-2, <0.3 s pixel-1) to reveal a wealth of information on the substrate physicochemical properties. This methodology has been applied to image the electrocatalytic oxidation of borohydride at ensembles of AuNPs on a carbon fiber support in alkaline media, whereby the depletion of hydroxide ions and release of water during the reaction results in a detectable change in the ionic composition around the NPs. Through the use of finite element method simulations, these observations are validated and analyzed to reveal important information on heterogeneities in ion flux between the top of a NP and the gap at the NP-support contact, diffusional overlap and competition for reactant between neighboring NPs, and differences in NP activity. These studies highlight key issues that influence the behavior of NP assemblies at the single NP level and provide a platform for the use of SICM as an important tool for electrocatalysis studies.

Hybrid dielectric waveguide spectroscopy of individual plasmonic nanoparticles

Plasmonics is a mature scientific discipline which is now entering the realm of practical applications. Recently, significant attention has been devoted to on-chip hybrid devices where plasmonic nanoantennas are integrated in standard Si3N4 photonic waveguides. Light in these systems is usually coupled at the waveguide apexes by using multiple objectives and/or tapered optical fibers, rendering the analysis of spectroscopic signals a complicated task. Here, we show how by using a grating coupler and a low NA objective, quantitative spectroscopic information similar to standard dark-field spectroscopy can be obtained at the single-nanoparticle level. This technology may be useful for enabling single-nanoparticle studies in non-linear excitation regimes and/or in complex experimental environments, thus enriching the toolbox of nanophotonic methods.

Studying the electrochemistry of single nanoparticles with surface plasmon resonance microscopy

Surface plasmon resonance microscopy (SPRM) is an emerging label-free optical microscopic imaging technology. It utilizes the planar surface plasmon resonance effect to visualize the optical mass of individual nano-objects. On the basis of appropriate optical-to-electrochemical conversion models, electrochemical current associated with individual nanoparticles can be quantitatively resolved from SPRM images recorded during electrochemical reactions, allowing for cyclic voltammetry and chronoamperometry analysis at single nanoparticle level. More importantly, the spatial resolution of SPRM further enables us to investigate the structure–activity relationship in a bottom-up manner by correlating the structure (from electron microscopes) and the electrochemical activity (from SPRM) of the very same individuals. In this mini-review, we summarize our recent work on using SPRM to study the electrochemical activities of single nanoparticles, and provide our opinions on the challenges and future research directions in this field.

General Sensitive Detecting Strategy of Ions through Plasmonic Resonance Energy Transfer from Gold Nanoparticles to Rhodamine Spirolactam.

Plasmonic resonance energy transfer (PRET), which occurs between the plasmonic nanoparticles and organic dyes, has significant potential in target sensing chemistry owing to its sensitivity at the single nanoparticle level. In this contribution, by using AuNPs, which has localized surface plasmonic resonance light scattering (LSPR-LS) around 550 nm, as the donor of PRET, a general sensitive detecting strategy of ions were developed. Targets can specifically react with a ring-close structured rhodamine spirolactam, which was prepared from rhodamines in the presence of different primary amine wherein the option of the primary amine is up to the targets, forming ring-open structured rhodamine spirolactam with the strong absorption around 550 nm. This process triggered the PRET from gold nanoparticles (AuNPs) to the ring-open structured rhodamine spirolactam. As a proof of concept, Cu2+ and Hg2+ were detected by using rhodamine B hydrazide and N-(rhodamine B)lactam-ethylenediamine, respectively. With the aid of a dark field microscope, the LSPR-LS of AuNPs gets decreased within 10 min with the addition of Cu2+ or Hg2+. The scattering light spectra get red-shifted during the targets addition due to the quenching dip phenomenon. Further theoretical simulation indicated the PRET process could be aroused by the electric field diminishment of AuNPs via the interaction of rhodamine. This single nanoparticle based detecting strategy could be further applied for other anions, cations, or small organic molecules detection by simply changing the rhodamine spirolactam.

Liquid Cell Electron Microscopy of Nanoparticle Self-Assembly Driven by Solvent Drying.

Drying a colloidal solution of nanoparticles is a versatile method to construct self-assembled structures of nanoparticles. However, mechanistic understanding has mostly relied on empirical knowledge obtained from the final structures of self-assembly as relevant processes during solvent drying are likely kinetic and far from equilibrium. Here, we present in situ TEM studies of nanoparticle self-assembly under various conditions, including the concentrations of the initial solution and the types of nanoparticles and substrates. The capability of tracking trajectories of individual nanoparticles enables us to understand the mechanisms of drying-mediated self-assembly at the single-nanoparticle level. Our results consistently show that a solvent boundary primarily affects nanoparticle motions and the resulting self-assembly processes regardless of different conditions. The solvent boundary drives nanoparticles to form two-dimensional assembly mainly through two pathways, transporting scattered nanoparticles by lateral dragging and flattening aggregated nanoparticles by vertical pressing.

Simultaneous optical and electrochemical recording of single nanoparticle electrochemistry

Single nanoparticle collisions have become popular for studying the electrochemical activity of single nanoparticles by determining the transient current during stochastic collisions with the electrode surface. However, if only the electrochemical current is measured, it remains challenging to identify and characterize the individual particle that is responsible for a specific current peak in a collision event; this hampers the understanding of the structure–activity relationship. Herein, we report simultaneous optical and electrochemical recording of a single nanoparticle collision; the electrochemical signal corresponds with the activity of a single nanoparticle, and the optical signal reveals the size and location of the same nanoparticle. Consequently, the structure (optical signal)–activity (electrochemical signal) relationship can be elucidated at the single nanoparticle level; this has implications for various applications including batteries, electrocatalysts, and electrochemical sensors. In addition, our previous studies have suggested an optical-to-electrochemical conversion model to independently calculate the electron transfer rate of single nanoparticles from the optical signal. The simultaneous optical and electrochemical recording achieved in the present work enables direct and quantitative validation of the optical-to-electrochemical conversion model.

Mussel-Inspired Polydopamine Functionalized Plasmonic Nanocomposites for Single-Particle Catalysis.

Polydopamine functionalized plasmonic nanocomposites with well-distributed catalytically active small gold nanoislands around large gold core were fabricated without using any chemical reductant or surfactant. The optical properties, surface molecular structures, and ensemble catalytic activity of the gold nanocomposites were investigated by time-of-flight secondary ion mass spectrometry and UV-vis spectroscopy, respectively. Moreover, the considerable catalytic activity of the nanocomposites toward 4-nitrophenol reduction was real time monitored by dark-field spectroscopy techniques at the single-nanoparticle level avoiding averaging effects in bulk systems. According to the obtained plasmonic signals from individual nanocomposites, the electron charging and discharging rates for these nanocomposites during the catalytic process were calculated. Our results offer new insights into the design and synthesis of plasmonic nanocomposites for future catalytic applications as well as a further mechanistic understanding of the electron transfer during the catalytic process at the single-nanoparticle level.