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Volume 18, Issue 3, Pages 433-440

Single molecule Raman detection of enkephalin on silver colloidal particles

Katrin Kneipp,1,2,3,4 Harald Kneipp,2,4 Salim Abdali,1 Rolf W. Berg,5 and Henrik Bohr1

1Quantum Protein Center, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
2Department of Physics, Technical University Berlin, 10234 Berlin, Germany
3Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
4Wellman Center for Photomedicine, Harvard Medical School, Boston, MA 02114, USA
5Department of Chemistry, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark

Copyright © 2004 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Enkephalin, an endogeneous substance in the human brain showing morphine‒like biological functions, has been detected at the single molecule level based on the surface‒enhanced Raman signal of the ring breathing mode of phenylalanine, which is one building block of the molecule. For enhancing the Raman signal the enkephalin molecules have been attached to silver colloidal cluster structures. The experiments demonstrate that the SERS signal of the strongly enhanced ring breathing vibration of phenylalanine at 1000 cm−1 can be used as “intrinsic marker” for detecting a single enkephalin molecule without using a specific label molecule. The reported result suggests the use of the phenylalanine 1000 cm−1 SERS line as spectroscopic signature for monitoring single proteins containing this amino acid as a building block.