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Carbonate terminated nanoparticles have a surface that is the closest to “bare” of all of our particles. Similar to citrate, carbonate molecules provide a negatively zeta potential across a wide range of pH. However, instead of three carboxylic acid groups like citrate (MW 189), carbonate has only a single carboxyl group and has a lower molecular weight (MW of CO32– is 60.0). The smaller size and reduced effective charge of the molecule makes it easier to displace resulting in higher surface loadings of physisorbed protein. The higher loading of proteins possible makes particle with this surface ideal as a starting material for bioconjugation applications such as lateral flow where a robust, dense antibody layer increases assay sensitivity.


  • Highly displaceable surface groups for performing ligand exchange with proteins or other ligands. Molecules with thiols or amine will strongly associate with gold or silver surfaces, readily displacing carbonate.
  • Carbonate has a minor effect on hydrodynamic diameter with the TEM measured diameter very close to the hydrodynamic diameter as measured with DLS.
  • Negatively charged Zeta potential with an isoelectric point of ~X

Representative Source: Potassium carbonate (Sigma Aldrich P5833)

Molecular Weight: K2CO3 (138.2), CO3 (60.0)

Comparison to Alternatives

  • Displaceable: Carbonate is more displaceable than citrate and tannic acid stabilized particles; closest to “bare” surface of all of our particles
  • Negatively charged
  • Salt Stability: destabilized in salt concentrations above X mM
  • Toxicity: Very low
  • Solvent compatibility: Water, low osmolarity buffers


  • SERS
  • Lateral Flow
  • Color engineering