In situ study of self-assembled nanocomposite films by spectral SPR sensor

Spectral surface plasmon resonance (SPR) sensor with a time-resolved charge-coupled device (CCD) detector is a powerful analytical tool for label-free detection of biomolecular interaction at the liquid/solid interface and for in situ study of molecular adsorption behavior. In this work, the layer-by-layer self-assembly processes for three nanocomposite films were monitored in real time using a broadband spectral SPR sensor with a large dynamic range. Kinetics studies suggest that cytochrome c (Cyt c) and deoxy ribonucleic acid (DNA) adsorptions obey the Langmuir-isotherm theory, while gold nanoparticle (GNP) adsorption follows the Diffusion-controlled model. Using poly(sodium 4-styrenesulfonate) (PSS) and poly(dimethyldiallylammonium chloride) (PDDA) as the positively charged agents, three kinds of multilayer films such as the PSS/Cyt c, GNP/Cyt c and PDDA/DNA binary nanocomposites were fabricated on the SPR chips by the electrostatic attraction based on self-assemble. The SPR response in terms of ΔλR was measured to linear increase with increasing the number of layers for a six-bilayer PSS/Cyt c nanocomposite film, indicating that every PSS/Cyt c layer has equal mass coverage. In contrast, the nonlinear dependences of ΔλR on the number of bilayers were observed for the GNP/Cyt c and PDDA/DNA nanocomposite multilayer films.