Electrochemical Detection of Single Microbeads Manipulated by Optical Tweezers in the Vicinity of Ultramicroelectrodes

Abstract

Latex micrometric beads are manipulated by optical tweezers in the vicinity of an ultramicroelectrode (UME). They are optically trapped in solution and approached the electrode surface. After the electrochemical measurement, they are optically removed from the surface. The residence time of the particle on the electrode is thus controlled by the optical tweezers. The detection is based on diffusional hindrance by the insulating objects which alters the fluxes of the redox Ru(NH 3 ) 6 3+ species toward the UME and thus its mass-transfer limited current. We have optically deposited successively 1, 2, and 3 beads of 3-μm radius on the UME surface, and we have recorded the variations of the current depending on their landing locations that were optically controlled. Finally we decreased the current by partially blocking the electroactive surface with a six-bead assembly. The variation of the steady-state current and the approach curves allow for the indirect electrochemical localization of the bead in the vicinity of the UME, not only when the bead is in contact but also when it is levitated at distances lower than the UME radius. These experiments show that single particles or more complex structures may be manipulated in situ in a contactless mode near the UME surface. From comparison with simulations, the electrochemical detection affords an indirect localization of the object in the UME environment. The developed approach offers a potential application for interrogating the electrochemical activity of single cells and nanoparticles.

Individual Detection and Characterization of Non‐Electrocatalytic, Redox‐Inactive Particles in Solution by using Electrochemistry

“…In contrast to electrocatalytic amplification, in these methods the detection of the particles is based on the hindrance of an ongoing electrode reaction (A‐to‐B in Scheme ) and hence the less of electrochemical signal. Since Lemay's seminal work, the rationale and fundamentals have been well‐established via combined electrochemical and optical monitoring of insulating microbeads of different materials ,,.…”

“…In contrast to electrocatalytic amplification, in these methods the detection of the particles is based on the hindrance of an ongoing electrode reaction (A‐to‐B in Scheme ) and hence the less of electrochemical signal. Since Lemay's seminal work, the rationale and fundamentals have been well‐established via combined electrochemical and optical monitoring of insulating microbeads of different materials ,,. It was demonstrated that the electrochemical events observed were associated with particles landing on the UME active area (blocking a portion of the electrode surface) or close to it (perturbing the mass transfer field,,).…”

“…Since Lemay's seminal work, [32] the rationale and fundamentals have been wellestablished via combined electrochemical and optical monitoring of insulating microbeads of different materials. [16,32,47] It was demonstrated that the electrochemical events observed were associated with particles landing on the UME active area 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 (blocking a portion of the electrode surface) or close to it (perturbing the mass transfer field [16,17,23] ).…”

Optical Nanoimpacts of Dielectric and Metallic Nanoparticles on Gold Surface by Reflectance Microscopy: Adsorption or Bouncing?

“…Adsorption of NPs is also an important issue in the electrochemistry of individual NPs. Different authors [47][48][49][50] demonstrated that when large dielectric insulating spheres (from 150 nm to µm) collide with an UME, they irreversibly adsorb onto it. This adsorption sufficiently blocks the mass transfer of a redox probe toward the UME so that each individual adsorption event can be monitored electrochemically from a step-like transient (decrease) in UME current.…”

Review Article: Flow battery systems with solid electroactive materials

“…In the first case, inert and electrically insulating particles partially block electrochemical reactions on the surface of the electrochemically active electrode upon collision, creating transient current changes by reducing the active area of the electrode (and in some cases, the adsorption was permanent). [159][160][161] In the second scenario, electrocatalytic particles are suspended in the electrolyte and only facilitate electrochemical reactions when a sufficient potential driving force is available, which is only provided when Brownian motion causes the particles to collide with the electrode surface resulting in a collision-dependent current response. 162,163 For this electrocatalytic system, research has been performed to specifically understand the impact of surface chemistry, 164,165 electrode size, 165 electrode material, and mass transfer effects.…”