Micro-SERS of Chromosomes

In addition to DNA and RNA large amounts of associated proteins known as histones, as well as other proteins, are present in the chromosomes. The relatively low cross-section for Raman scattering of chromosomes is the reason for the lack of normal Raman investigations. Recently, the first Raman spectra of intact chromosomes 

All Raman bands measured in DNA fibres or crystals appear in this chromosome Micro-Raman spectrum. In addition, typical vibrations of the protein component were observed (phenylalanine, tyrosine, S—S group and the amide I mode). Recently, Micro-SERS has been applied for the first time to investigate the chromosomes adsorbed at the silver electrode This Micro-SERS spectrum of Chinese hamster metaphase chromosomes shows a number of intense bands. The enhancement factor obtained was estimated to be about 100 for the 790 cm DNA backbone vibration. The most intense bands in this SERS spectrum are located at 730 cm and 1330 cm and can be attributed to the adsorbed adenine base vibration of the DNA. The characteristic protein vibrations in the normal Raman spectrum are missing in the SERS spectrum. 

The peptide backbone vibration (amide 1) and the ring-breathing mode of phenylalanine at 1004 cm are not enhanced in this chromosome. An interpretation of this missing enhancement is that only the DNA has a strong interaction with the surface. The protein contents do not interact directly with the surface. These Micro-SERS investigations have shown that SERS can clarify structural changes of chromosomes in the adsorbed state. 

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