Atomic force microscopy and rotated-grating-coupled surface plasmon resonance spectroscopy is performed on biosensing layers produced by a bottom-up method. Glass substrates were evaporated by silver and gold layers and poly-carbonate films were spin-coated onto this bimetal layer. Sub-micrometer linear structures were generated by two-beam interference lithography using the fourth harmonic of a Nd:YAG laser. It is shown by tapping-mode AFM that the highly adhesive valleys of the periodic structures can be covered by a thin layer of small peptide molecules. Due to the very tight binding between biotin and avidin, the biotinylated portion of the peptide pre-cover ensures attachment of the same amount of unlabeled, nano- and colloidal gold-particle labeled Streptavidin from solvents. The effect of different biomolecules on the surface plasmon resonance is investigated in a modified Kretschmann arrangement allowing polar and azimuthal scans, collecting information regarding changes in minima and FWHM of the rotated-grating-coupling caused secondary resonance peaks. It is shown that the presence of 10 nm diameter colloidal gold particles results in enhancement of the angle-shift to FWHM-broadening ratio compared to the normalized sensitivity experienced in case of unlabeled streptavidin attachment. This result cannot be predicted theoretically by Transfer Matrix Method calculations. Numerical simulations proved that the plasmon excitation occurring with higher efficiency in colloid particles at the optimal azimuthal orientation causes field confinement around the bio-molecules to be detected. Utilization of colloidal metal labeling particles in biosensing applications based on rotated-grating-coupled SPR phenomenon is proposed, due to the demonstrated enhanced sensitivity.
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics
- Electrical and Electronic Engineering