Surface plasmon resonance sensing of liquids using polyelectrolyte thin films

We report on the use of polyelectrolyte molecular films, assembled on a gold substrate by the layer-by-layer (LbL) electrostatic deposition technique, to monitor small quantities of positively and negatively charged ions in solution. The detection system is based on surface plasmon resonance (SPR), the optical configuration consisting of a light emitting diode as a photon source and a CCD camera as the detector. Reflectivity changes in real time have been used to follow the adsorption steps during the deposition of the multilayer film. The sensing behaviour of the organic film is shown to depend of the architecture of molecular assembly. Concentrations of copper ions of less than one part per million could be detected by the compact SPR equipment.