Real-time characterization of polyelectrolyte multilayers
with MP-SPR

Application Note #111

polyelectrolyte measurement


"Monitoring of PEMs Layer-by-Layer Assembly"
SPR-spectra of gold sensor slide in buffer (black) and with increasing number of PE-layers (blue).

Polyelectrolyte multilayers (PEMs) are soft nanoscale films that are built by layer-by-layer (LbL) assembly in solution on a substrate. Materials such as nanoparticles, carbon nanotubes, light-, pH- or temperature-active polymers are used to develop functional materials and coatings.

MP-SPR instrument is used to monitor the multilayer assembly in situ with full angular spectra. Such measurement enables collection of biochemical (molecular kinetics), physical (thickness, refractive index), electrochemical information about the layer formation in a single experiment. In this experiment SPR Navi™ was used to determine molecular kinetics and layer thickness at a single wavelength.

Poly(ethyleneimine) (PEI), poly(styrenesulfonate) sodium salt (PSS) and poly(diallydimethylammoniumchloride) (PDADMAC) were used in NaCl solution. The layer formation process was monitored in situ in angular scan mode. Since measurements were performed at a single wavelength, a refractive index was used based on literature. With MP-SPR it´s also possible to determine both refractive index and thickness of deposited layer, see two wavelengths measurement from AN128. The PEM growth is exponential, which is confirmed also by ellipsometry. The layer thickness is determined with MP-SPR for each layer.

Note: MP-SPR works also with materials of complex refractive index, like metallic nanoparticles.

Recommended instrument for this application:

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Further reading

  • If you are interested in polyelectrolytes, see also AN#128 about thickness
    and refractive index of polyelectrolytes and AN#159 about polymer swelling in vapors.

  • Do you want to find out how to calculate thickness out of MP-SPR measurements? Click here.

  • Do you want to see MP-SPR instruments range? Click here.

  • Here are a few publications you can have a look at.


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