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Tannic acid offers an intermediate surface stability option when compared to the other non-covalently-bound surfaces of citrate and PVP, all of which associate with the particle surface by Van der Waals attraction. The tannic acid molecule is a naturally-occurring polyphenol that is a component of oak bark and leaves often used as a dye or stain. Tannic acid (~1.7 kDa, depending on source) is a polyphenol that associates with the particle surface more strongly than citrate (192 Da), but is smaller and more displaceable than PVP (40 kDa). Tannic acid is a common reagent in the fabrication of gold and silver nanoparticles and tannic acid or tannic acid/citrate surfaces are a common stability and surface coating for many colloidal solutions.

Advantages

  • Intermediately displaceable surface for stabilizing particles in aqueous solutions. Molecules with thiols or amine will displace tannic acid from the surface.
  • Useful in situations where the surface needs to be exchanged but a more stable surface than citrate is needed during the initial formulation.
  • Only a moderate difference between the hydrodynamic and TEM measured diameter is observed.
  • Negatively charged zeta potential with an isoelectric point of ~X

Representative Source: tannic acid (Sigma Aldrich XXX, XXX)

Molecular Weight: (1700 g/mol; 1700 Da; 1.7 kDa?)

Comparison to Alternatives

  • Displaceable: Tannic acid is less displaceable than citrate or carbonate but more displaceable than PVP
  • Negatively charged
  • Salt stability: moderately stable in low concentration salt solutions (above X mM)
  • Toxicity: Very low
  • Solvent compatibility: Water, weak buffers
  • Applications

    • SERS
    • Lateral Flow
    • Color engineering