Observing Single Nanoparticle Collisions at an Ultramicroelectrode by Electrocatalytic Amplification

Abstract

Detection of single gold (Au) nanoparticle (NP) collisions on a carbon-fiber (C-fiber) ultramicroelectrode (UME) was carried out successfully using the electrocatalytic amplification method. The C-fiber UME shows a low and quite stable background current for the hydrazine oxidation over a wide potential range. The electrocatalytic current transient generated by Au NP collision on the C-fiber UME was also detected simultaneously without any pretreatment of the UME or deformation of the Au NP. The magnitude and frequency of the transient current from Au NP collisions agree well with the calculated values based on the size and concentration of the Au NP.

Electrochemical detection of a single cytomegalovirus at an ultramicroelectrode and its antibody anchoring

“…Second, the frequency of collision can be calculated theoretically by assuming a diffusionlimited flux of particles to the electrode surface and experimentally by counting the number of collision events over time. The frequency of collision based on diffusion (28), f D, theoretical , is given by f D,theoretical = 4DCr e N A , [1] where N A is Avogadro's number, r e is the radius of the electrode, C is the concentration of colloid in solution, and D is the diffusion coefficient of the particular particle. The concentrations of the MCMV and MHV-68 (a virus used for negative control in gaining specificity with the primary antibody) were determined using nanoparticle tracking analysis (NTA), which tracks individual particles and determines a size distribution based on the diffusion coefficient using the random walk model.…”

“…By observing the collisions of small particles, there is the possibility that information can be deduced that is not available in ensemble measurements. The electrochemical study of single collision events has been applied to a wide range of hard nanoparticles (NPs), which include metal, metal oxide, and organic NPs [platinum (1), silver (2), gold (3), nickel (4), copper (5), iridium oxide (6), cerium oxide (7), titanium oxide (8), silicon oxide (9), indigo (10), polystyrene (11), and relatively large aggregates of fullerene (12)]. Recently, collisions of soft particles have been investigated, such as toluene droplets (13) and liposomes (14).…”

“…The interested reader can consult the references for a discussion on each of the techniques used to observe stochastic events electrochemically: blocking (9, 13), electrocatalytic amplification (1), open circuit potential (16), droplet blocking/reactor (13,14), and ECL (15,17,18). The simplest and most reproducible method of observing collisions is a technique termed blocking, which is so named because particles, which are brought to the electrode by a diffusion-limited flux and/or electrophoretic migration, irreversibly adsorb (1) to the electrode surface, blocking the flux of redox active species.…”

Visualizing Zeptomole (Electro)Catalysis at Single Nanoparticles within an Ensemble

“…1,[5][6][7][8][9][10][11][12][13] However, as the vast majority of investigations have employed a large number of particles in a catalytic ensemble, the information obtained is limited due to unavoidable variations in NP size, shape and local environment. 14 Efforts to circumvent this limitation have been made by shifting to single particle measurements, [15][16][17][18][19][20] but such studies are rather challenging. 21 In general, single particle experiments fall into one of two categories.…”

“…First, a single NP can be deposited on an electrode with a small surface area, either through electrodeposition 15,16 or through collision of a colloidal NP in solution with the electrode. 17 Valuable insights can be obtained, but such studies preclude an understanding of ensemble behavior and are limited in the range of electrode supports and environments that can be investigated. Second, attempts have been made to study NP ensembles at a single particle level by scanning probe techniques, such as scanning tunneling microscopy 19 and scanning electrochemical microscopy.…”