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Addressing Colloidal Stability for Unambiguous Electroanalysis of Single Nanoparticle Impacts
Donald A Robinson1, Aditya M Kondajji1, Alma D Castañeda1
1Department of Chemistry, Center for Nano- and Molecular Science, and Center for Electrochemistry, University of Texas at Austin , Austin, Texas 78712, United States.
The Journal of Physical Chemistry Letters
|June 17, 2016
Summary
Colloidal instability in nanoparticle (NP) solutions can be mitigated by controlling ionic strength. Lowering ionic strength improves nanoparticle stability and enables accurate electrochemical detection of single NP collisions.
Area of Science:
- Electrochemistry
- Nanotechnology
- Physical Chemistry
Background:
- Electrochemical detection of nanoparticle (NP) collisions with ultramicroelectrodes (UMEs) is a powerful technique.
- Colloidal instability can interfere with accurate NP detection and analysis.
- Citrate-stabilized platinum NPs are commonly used in electrochemical studies.
Purpose of the Study:
- To address the problem of colloidal instability affecting electrochemically detected NP collisions.
- To investigate the influence of ionic strength on the stability of Pt NPs in solution.
- To optimize conditions for reliable single NP impact electroanalysis.
Main Methods:
- Nanoparticle tracking analysis (NTA) for monitoring aggregation and diffusion.
- Electrocatalytic amplification at a mercury (Hg) UME for detecting NP collisions.
- Varying ionic strength of hydrazine/phosphate buffers to assess colloidal stability.
Main Results:
- Rapid aggregation of Pt NPs occurred at ionic strengths above 70 mM.
- Colloidal stability significantly improved with decreased ionic strength.
- At low ionic strength, most signals corresponded to single NP impacts, validated by NTA.
- NP diffusion coefficients from NTA and electroanalysis agreed for stable colloids.
Conclusions:
- Ionic strength is a critical factor in the colloidal stability of Pt NPs.
- Charge screening of NP double-layer interactions is affected by cation concentration.
- Optimized low ionic strength conditions allow for accurate single NP collision detection and analysis.
- The study confirms a unity sticking probability for Pt NPs on Hg UMEs and validates diffusive flux models.
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