Metal Nanoparticle Synthesis & Plasmon Resonance

Nanoparticle Synthesis

Reducing agent concentration 1.0×

Temperature 25 °C

Particles nucleated

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Mean size

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Au³⁺ remaining

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λ_SPR peak

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How it works

Adding a reducing agent to a solution of Au³⁺ ions triggers the LaMer mechanism: ion concentration rises past a critical supersaturation threshold, fires a short burst of nucleation, then relaxes as remaining ions diffuse onto the existing nuclei and grow them — no new nuclei form once the burst ends, so the final particle count is fixed early.

dC/dt = -k(T)·C·R
nucleate when C > C_crit(R)
growth ∝ (C - C_eq) · surface area

Reducing agent concentration — higher R spikes the supersaturation faster, triggering a shorter, sharper nucleation burst → more, smaller final particles.
Temperature — raises the reduction rate constant k(T) (Arrhenius), speeding both nucleation and growth.
SPR color — small gold particles (~10–20 nm) resonate near 520 nm and scatter red/pink; as particles coarsen toward 50–100 nm the plasmon band red-shifts toward 600+ nm, turning the sol blue/purple.

Real-world relevance: this is the physical basis of the classic Turkevich citrate-reduction synthesis of gold colloids, and the same size-dependent plasmon shift underlies gold-nanoparticle biosensors and lateral-flow assay strips.

Phase: Waiting

Absorption spectrum (visible)

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