Nano-Impact Electrochemistry: Single Nanoparticle Collision Spikes

Nano-Impact Cell

Blocking — stick & shrink

Particle radius 45 nm

Particle concentration 40

Electrode radius 5 µm

Instantaneous I

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Impact count

Mean spike |I|

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Baseline I_ss

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How it works

A microelectrode held at a fixed potential sits in a dilute suspension of freely diffusing nanoparticles. Each time Brownian motion carries one particle onto the electrode surface, a single discrete current transient fires — a "nano-impact" — riding on top of (or replacing) the smooth steady-state background current. Three regimes, all used in real single-entity electrochemistry:

Blocking — an inert particle physically adsorbs and permanently masks a patch of electrode area. Each impact drops the baseline current by a fixed step, building a descending staircase as more particles stick.
Catalytic amplification — a catalytically active particle briefly boosts the local reaction rate while it's in contact, producing a fast current spike, then desorbs and keeps diffusing. Spike height scales with the particle's surface area (~r²).
Direct oxidation — the whole particle is electrolyzed on contact. Faraday's law ties the total charge under the spike to the particle's volume (Q ∝ r³), so bigger particles fire bigger, shorter transients before being consumed.

I_ss ∝ r_electrode          (disc microelectrode, steady state)
blocking:  ΔI_step ∝ -(r_particle / r_electrode)²
direct ox: Q_spike ∝ r_particle³   (Faraday's law)

Real-world relevance: nano-impact experiments let electrochemists size, count and characterise individual nanoparticles — or even single catalytic sites — one collision at a time, well below what bulk voltammetry can resolve.

● Free nanoparticle

● Microelectrode

Current vs. time (chronoamperogram)

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