Ultra-sensitive vibrational spectroscopy of protein monolayers with plasmonic nanoantenna arrays.

Journal Article (Journal Article)

Infrared absorption spectroscopy enabling direct access to vibrational fingerprints of the molecular structure is a powerful method for functional studies of bio-molecules. Although the intrinsic absorption cross-sections of IR active modes of proteins are nearly 10 orders of magnitude larger than the corresponding Raman cross-sections, they are still small compared to that of fluorescence-label based methods. Here, we developed a new tool based on collective excitation of plasmonic nanoantenna arrays and demonstrated direct detection of vibrational signatures of single protein monolayers. We first tailored the geometry of individual nanoantennas to form resonant structures that match the molecular vibrational modes. The tailored nanoantennas are then arranged in such a way that their in-phase dipolar coupling leads to a collective excitation of the ensemble with strongly enhanced near fields. The combined collective and individual plasmonic responses of the antenna array play a critical role in attaining signal enhancement factors of 10(4)-10(5). We achieved measurement of the vibrational spectra of proteins at zeptomole levels for the entire array, corresponding to only 145 molecules per antenna. The near-field nature of the plasmonic enhancement of the absorption signals is demonstrated with progressive loading of the nanoantennas with varying protein film thicknesses. Finally, an advanced model based on nonequilibrium Green's function formalism is introduced, which explains the observed Fano-type absorption line-shapes and tuning of the absorption strengths with the antenna resonance.

Full Text

Duke Authors

Cited Authors

  • Adato, R; Yanik, AA; Amsden, JJ; Kaplan, DL; Omenetto, FG; Hong, MK; Erramilli, S; Altug, H

Published Date

  • November 2009

Published In

Volume / Issue

  • 106 / 46

Start / End Page

  • 19227 - 19232

PubMed ID

  • 19880744

Pubmed Central ID

  • PMC2770897

Electronic International Standard Serial Number (EISSN)

  • 1091-6490

International Standard Serial Number (ISSN)

  • 0027-8424

Digital Object Identifier (DOI)

  • 10.1073/pnas.0907459106


  • eng