Abstract

Protein analysis is playing an important role in various biomedical applications. Performing such analysis at the molecular level is critical for further advancements in diagnostics. New instruments for measuring protein primary and secondary structures are in great demand for synthesis, purification, and recognition of proteins. Human insulin (humulin) and its artificial substitute humalog used for people with diabetes, are among particularly important proteins. There is a tiny difference in structures of these two proteins: the humalog structure can be obtained from humulin by interchanging lysine and proline amino acids at the B28 and B29 positions. These two proteins have the same mass, but because of the small structural difference, rather different properties, including their medical activity. Raman spectroscopy is known to have a high sensitivity in detecting bond structures of molecules, and thus it can be a powerful means for detection even smallest differences. Furthermore, surface-enhanced Raman scattering (SERS), providing a dramatic increase for Raman signals, makes possible analysis even at very minute protein quantities. In our experiments, we demonstrated that SERS substrates based on semicontinuous silver films [1] can be successfully used as highly sensitive substrates for distinguishing Humalog and Humulin at the sub-monolayer density, 80 fmol/mm².

© 2003 Optical Society of America