Protein-Nanoparticle Layer-by-Layer Films as Substrates for Surface-Enhanced Resonance Raman Scattering

摘要

The development of substrates for surface-enhanced spectroscopy that have additional functionality, beyond optical amplification, is now highly desirable. In this work, we report the fabrication, characterization, and utilization as enhancing substrates of layer-by-layer (LbL) films composed of the glycoprotein avidin and metallic Ag nanoparticles. These nanocomposite films demonstrate strong, bio-specific interactions and are employed as chemically selective substrates for surface-enhanced Raman scattering (SERS) and surface-enhanced resonance Raman scattering (SERRS). Fabricated on glass microscope slides, from solutions of avidin and colloidal Ag, they are characterized by UV-visible surface plasmon absorption and atomic force microscopy (AFM) as a function of the number of bilayers deposited. Their average SERRS enhancement is also monitored as a function of architecture, and is found to plateau after the deposition of ca. 8 bilayers. It is also found that they demonstrate excellent enhancement of SERS/SERRS throughout the visible region of the electromagnetic spectrum (442-785 nm). Finally, biotinylated dye molecules are shown to be selectively adsorbed by these films, containing the natural biotin chelator avidin, relative to untagged analogues. This preferential adsorption, facilitated by biotin capture, yields an additional 'concentration enhancement' of ca. 10~2, and improves detection limits by at least 2 orders of magnitude.