1. Tip-enhanced Raman spectroscopy of single RNA strands
Elena Bailo and Volker Deckert
ISAS – Institute for Analytical Sciences
Dortmund, Germany
Poltersdorf,

2. Motivation Direct and label-free sequencing of single DNA strand
Characterization of the structure and dynamic of cell walls
U. Neugebauer et al. ChemPhysChem 2007, 8, 124.
C. Budich et al. J. Microsc. 2007, (accepted)

3. TERS setup AFM Bottom illumination configuration
Coarse xy sample stage
Coarse xy AFM-positioning IF
Laser NF
Piezo xy sample stage
Spectrometer & CDD
Piezo z-focusing
A. Rasmussen, V. Deckert, J. Raman Spectrosc. 2006, 37, 311.

4. TERS tips preparation Si AFM tip Ag Thermal source Diameter ~20 nm
Low Rate ~ 0.05 nm/s

5. Tip and laser alignment
High NA objective enable to
Tip and laser alignment
Direct reflected image X PD

6. Sample: Synthetic RNA homopolymer on mica
Topographical Image

7. Single RNA strand
AFM image
Profile

8. TERS experiment 15s,1mW, @ 530 nm
E. Bailo and V. Deckert, Angew. Chem. Int. Ed., 2007, accepted.

9. Band assignment

10. Enhancement factor 50 Fold 104 C Laser spot  ~ 1 µm
Signal-to-noise ratio 200:1
~ 3000 bases x
Ag Tip
Radius ~ 20 nm C
50 Fold
104
~ 60 bases
Enhancement factor at least

11. Spectral fluctuations
Ag Particle

12. Band fluctuations: adenine-silver complexes
SERS
TERS
Adenine
Predicted Raman spectra:
Vibrational frequencies
and
Raman intensities
change for each isomer
Ad-N1
Ad-N3
Ad-N7
Ad-N10
H. Watanabe et al., Phys. Rev. B 2004, 69,

13. Band identification TERS on poly(cytosine) Raman on cytosine
Vibrational modes
801
803
1045
1097
1106
1166
1146
1248
1245
1279
1273
1380
1379
1453
1458
1488
1490
1549
1531
1602
1606
J. Florian et al. J. Phys. Chem. 1996, 100, 5578.

14. TERS and DNA sequencing
Ag particle

15. Summary and Outlook Single RNA strands detection Next step
Approx. 60 nucleobases
SNR ~ 200
Next step
Natural DNA or RNA sequencing

16. Acknowledgement Volker Deckert Christian Budich, Marc Richter
H. Herzog, E. Pulvermacher, B. Gosciniak

17. Tip shape
TIP
Sample