THE SHORT-RANGE COMPONENT OF SERS : RESULTS OF BIOPOLYMERS

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THE SHORT-RANGE COMPONENT OF SERS : RESULTS OF BIOPOLYMERS

E. Koglin, J. Séquaris

To cite this version:

E. Koglin, J. Séquaris. THE SHORT-RANGE COMPONENT OF SERS : RESULTS OF BIOPOLYMERS. Journal de Physique Colloques, 1983, 44 (C10), pp.C10-487-C10-490.

�10.1051/jphyscol:19831098�. �jpa-00223556�

JOURNAL DE PHYSIQUE

Colloque C10, supplCment au n012, Tome 44, dbcembre 1983 page Cl0-487

THE SHORT-RANGE COMPONENT O F SERS : R E S U L T S OF B I O P O L Y M E R S

E . Koglin and J . M . Sgquaris

Chemistry Department, I n s t i t u t e o f Applied Physical Chemistry, Nuclear Research Center (KFA), J u e l i c h , F.R.G.

RQsum6. - La composante B c o u r t e p o r t 6 e de l a d i f f u s i o n Raman e x a l t g e de s u r f a c e ISERSl e s t Q t u d i 6 e 2 l ' a i d e desbiopolyrn8res,DNA e t poly-A. Les deux rnolQcules forment une double h e l i c e [diarnktre d ' e n v i r o n 20 X I . Les chaines sont d i s p o s g e s avec l ' a r m a t u r e sucre-phosphate a 1 1 e x t 6 s i e u r e t l e s bases nucleiques f a c e au c e n t r e . Sur une s u r f a c e d l A r g e n t chargbe positivement ( c o l l o i d e s , Q l e c t r o d e l , ces biomol6cules s o n t p r i n c i p a l e - ment adsorbees par l ' i n t e r m e d i a i r e de l ' a r m a t u r e sucre-phosphate chargee nggativement. Les bases nuclgiques, s i t u Q e s au c e n t r e de l ' h g l i c e , ne p r g s e n t e n t aucun s i g n a l Raman. Cependant, aprks l a d e s t a b i l i s a t i o n de l a s t r u c t u r e en double h e l i c e , l e s bases nuclgiques i n t e r a g i s s e n t d i r e c - tement avec l a s u r f a c e e t donnent des signaux Raman i m p o r t a n t s . Ces ob- s e r v a t i o n s i n d i q u e n t que l ' i m p o r t a n t e a m p l i f i c a t i o n c o n s t a t g e pour DNA e t poly-A s u r des c o l l o i d e s e t des g l e c t r o d e s d'Argent e s t due B un m6- canisme B c o u r t e p o r t g e , s u r d e s d i s t a n c e s 5 l a s u r f a c e i n f e r i e u r e s 2 5

W.

A b s t r a c t . - The short-range component of s u r f a c e enhanced Raman s c a t - t e r i n g (sERS) i s i n v e s t i g a t e d u s i n g t h e biopolymers, DNA and poly-A.

Both molecules form a double s t r a n d e d h e l i x (diameter about 20 % ) . The c h a i n s a r e a r r a n g e d with t h e sugar-phosphate backbone on t h e o u t - s i d e and t h e n u c l e i c b a s e s f a c i n g t h e c e n t e r . A t a p o s i t i v e l y charged s i l v e r s u r f a c e ( c o l l o i d s , e l e c t r o d e ) t h e s e biomolecules a r e adsorbed mainly t r o u g h t h e n e g a t i v e l y charged sugar-phosphate backbone. Nucleic b a s e s , l o c a t e d i n t h e c e n t e r o f t h e h e l i x do n o t e x h i b i t any Rarnan s i g - n a l s . However a f t e r t h e d e s t a b i l i z a t i o n of t h e double h e l i c a l s t r u c t u r e t h e n u c l e i c b a s e s i n t e r a c t d i r e c t l y with t h e s u r f a c e and show s t r o n g SERS s i g n a l s . These experimental o b s e r v a t i o n s i n d i c a t e t h a t t h e s t r o n g enhancement f o r DNA and p l y - A on s i l v e r c o l l o i d s and e l e c t r o - d e s i s caused by a s h o r t range mechanism f o r d i s t a n c e s s m a l l e r t h a n 5

8

There are both short-range and long-range enhancements contributing to the total surface enhanced Raman scattering (SERS) intensity ( 1 , 2 ) . It was our goal to exploit the natural geometry of the biomolecules deoxyribonucleic acid (DNA) and polyriboadenylic acid (poly-A) to clarify the range of the short-range component of the enhancement.

These biomolecules consist of a double stranded helix with a weak scat- terer (sugar-phosphate-group) on the outside of the molecules and strong Raman scatterers (nucleic bases) located in the center of the helix. The distance of the center of DNA, measured from the phosphate group, is about 10

2.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19831098

C 10-488 JOURNAL DE PHYSIQUE

these building stones of DNA and poly-A exhibit strong SERS (3,4).

Prominent SERS bands for the nucleic acid bases are the ring-breathing modes at 648 cm-I (electr.), 653 cm-' (coll.) in guanine, 728 cm-I

(electr.)

,

,

(coll.) in thymine and 798 cm-I (electr.), 797 cm-I (coll.) in cytosine.

These specific Raman frequencies are usually found in the normal solu- tion Raman scattering (NSRS) of DNA. However, in the case of the SERS spectrum of DNA adsorbed at a high positively charged silver electrode, Fig. 1 bands appear predominantly at 245 cm-I and 81 8 cm-I which can be respectively assigned to a silver-phosphate group vibration and to the backbone vibration of the polymeric-deoxyribose-phosphate chain.

SERS spectrum of natcve DNA

Fig. 1

SERS-spectrum of CT-DNA

.

0.1 M KC1

+

w

1

- c j a 2 z 225 ug DNA/ml; pH 8.0;

electrode potential vs sat. /

Ag/Ag C1 electrode = -0.1 V, laser power at the cell 100 mW.

The presence of these Raman bands indicate a preferential interaction of the nucleic residues lying outside the helical structure. The nuc- leic bases, located in the center of the helix exhibit no signals or very weak SERS signals. Thus, these experimental results show that the Raman enhancement is limited ts the sugar phosphate residues at 5

2

maximum distance from the electrode surface.

It is interesting now to compare these SERS results from the intact double helical structure of native DNA and the SERS spectra ofr-irra- diated DNA. It is well known that ionizing radiation causes different damages in DNA. These damages in modified nucleic acid residues, consist of strand breaks which induce the labilization of the helical structure.

I

10OGyllOkrndl

1OGyllkra

natlve DNA c xnwm OGy *rod)

1325 1175875 725

Roman shift lcrn-'ll

high dorc

R-

lmv dcse dginojhtion

-

w-

DNA

P P Fig. 2

SERS spectra of na- tive and

8

+

l f 3 M Na2HP04; 300 / ug DNA/ml; pH 8.0;

irradiated with

8 -

rays from a 6 0 ~ o - source, Siemens.

Other experimental conditions as in Fig.1

Fig. 2 shows the SERS spectra of the intact and 3-irradiated DNA in the spectral range of the ring modes of the bases. The most striking features are the new pronounced lines at 734 cm-I and 1334 cm-I. These characteristic bands can be assigned to the adsorbed adenine base vi- brations. It follows that the nucleic base adenine becomes more acces- sible to the electrode surface. Thus, this result confirms that the short-range interactions play an important role in the enhancement fac- tor of the Raman scattering.

In view of these results obtained with a rough silver electrode sur- face, we also investigated the Raman scattering from biomolecules ad- sorbed on dispersed silver particles of the silver colloids. Using the results of the strong interaction of the adenine base with the colloidal silver surface (4) we turned our attention to a polynucleotide based solely on the adenine-monophosphate: that is the polyriboadenylic acid, poly A. This biomolecule forms a double stranded helix at acid pH. The strands are also arranged with the sugar-phosphate backbone on the outside and the adenine base facing the center. The SERS spectrum of this polynucleotide and its building stones (adenine, adenosine-5'- phosphate and ribose-5'-phosphate) adsorbed at silver colloids are shown in Fig. 3. The most characteristic vibrations of the poly-A spectrum

(cf. Fig. 3) are located at 606, 796 and 1282 cm-I

For the interpretation of these bands it is necessary to assign pre- cise frequencies of the SERS bands of the building stones. Adenine and adenine 5'-monophosphate exhibit the characteristic ring breathing modes at 726 cm-I and 721 cm-I. Prominent SERS bands for the ribose

5'-phosphate are at 600 c d and 1282 cm-I. Comparing these results, we can thus conclude that in the case of poly-A we only observe the

C10-490 JOURNAL DE PHYSIQUE

SERS signals of the ribose-phosphate groups lying outside of the he- lical strands. The appearance of a band at 796 cm-' in the SERS spec- trum of poly-A corresponding to the stretching of the ribose-phosphate backbone confirms that the ribose-phosphate group is preferentially ad- sorbed. The adenine molecule located at a distance of about 5

8

the phosphate group does not give any SERS signals.

7 2 6 d

Fig.3

SERS spectra of poly-A and its building stones, adenine, adeno- sine 5'-monophosphate and ribose 5-phosphate. Freshly prepared sil- ver colloids, pH 4.5; 4.10 -4 M adenine, 5'-AMP or ribose 5-phos- phate added; poly-A concentration 1.6 mg/ml; Laser excitation line:

h =

(The drawing of poly-A shows the adenine base /black

/

1

. .

.

..

1200 900 Sm

1

Roman sh~ft km-1)

In summary we have presented surface enhanced Raman spectra from bio- molecules adsorbed at silver surfaces (electrodes and colloids) and discussed the influence of the short-range component in SERS. The ob- servations show that an enhancement for the helical biomolecules is only detected at distances ranging up to 5

8 .

Acknowledgement

We thank H.H. Lewinsky for the measurements of I(-irradiated DNA and Dr. P. Valenta for helpful discussion. We are indebted to Prof. Dr.

H.W. Nurnberg for his interest in this work.

References

1. A-Otto, Light scattering in Solids, Vol. IV, eds., M-Condano and G. Guntherodt, Springer 1983

2. R.K.Chang and T.E.Furtak, eds., Surface enhanced Raman scattering (Plenum Press, New York, 1982)

3. E-Koglin, J.-M.Sequaris and P.Valenta, J. Mol. Struct. 79, 185 (1982) 4. E-Koglin, J.-M. Sgquaris and P-Valenta in: Surface-Studies with

Lasers, Springer Series in Chemical Physics (Springer Berlin, Hei- delberg, New York 1983) eds., F.R.Aussenegg, A-Leitner, M.E.Lippitsch 5. S.C.Erfurth and W.L.Peticolas, Biopolymers 14, 247 (1975)