Surface plasmon resonance detection of metal ions: layer-by-layer assembly of polyelectrolyte sensing layers on a multichannel chip

A single-chip multichannel surface plasmon resonance sensor (SPR) has been used to detect metal ions in aqueous solutions. The equipment was designed around a commercial light-emitting diode and a CCD camera and incorporated no moving parts. The sensing materials were based on molecular architectures of polyelectrolyte films, deposited by the layer-by-layer self-assembly technique. Two bilayer architectures, poly(ethyleneimine) (PEI)/poly(ethylenealt-maleic acid) and PEI/poly(styrenesulfonate), were shown to produce different responses to solutions containing copper, nickel, and iron. The SPR equipment was able to measure concentrations of these metals down to levels of at least 2×10^-5 M.