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Branched polyethylenimine (BPEI) is a polymer with repeating units composed of amine groups and two carbon spacers. BPEIs contain primary, secondary and tertiary amino groups. Primary amines on the BPEI are used to covalently link BPEI to carboxyl functionalized nanoparticles to generate a robust BPEI surface that is highly positively charged.

A portion of the primary amines are converted to amide bonds to covalently bind the particles to the surface but there remain primary amines (approximately 3 free amines per square nm) that are still available for subsequent binding through EDC/NHS linkage chemistry.


  • Strongly positively charged surface (cationic) with free amines available for subsequent coupling

Representative Source: Polyethylenimine, branched, 25 kDa (Sigma Aldrich, 408727)

Isoelectric Point: ~3.5 (show entire chart) – (show for gold/silver/size)?

Comparison to Alternatives

  • Displaceable: Not displaceable – strongly bound to the particle surface
  • Positively charged (zeta 40+ mV at pH 7.4)
  • Good salt stability: stable in high salt solutions below X mM
  • Toxicity: BPEI has a higher in-vitro toxicity than many of the other surfaces offered at nanoComposix
  • Solvent compatibility: Water, ethanol, chloroform, many other polar solvents


  • Stable in combination with other positively charged particles
  • Layer by layer construction of nanoparticle surfaces
  • Binding to negatively charged substrates or larger particles
  • Color engineering