Optically responsive nanoparticle layers for the label-free analysis of biospecific interactions in array formats

A novel nanocomposite surface is prepared by coating surface-adsorbed dielectric colloidal particles with a contiguous layer of gold nanoparticles. The resulting surface shows pronounced optical extinction in reflection with the extinction peaks located in the UV–Vis and NIR region of the electromagnetic spectrum. The peak positions of these maxima change very sensitively with the adsorption of organic molecules onto the surface. For the adsorption of a monolayer of octadecanethiol, we observe a peak shift of 55 nm on average, which is about five times that of established label-free sensing methods based on propagating and localized surface plasmons. In a first proof-of-principle experiment, the interaction of peptides with specific antibodies has been detected without labeling by means of a fiber-optical set-up with microscopic lateral resolution. To avoid crosstalk in high-density arrays, the optically responsive surface areas can be locally separated on a micro- or even nanometer scale. Accordingly, the newly developed optically responsive surfaces are well suited for integration into high-density peptide or DNA arrays as demanded in genomics, proteomics, and biomedical research in general.