1. UV Plasmonics
F. Mahdavi, X. Jiao, M. Diwekar, S.
Attavar, and Steve Blair
Electrical and Computer Engineering
University of Utah
Photonics Research Group

2. Why UV?
Label-free biomolecule detection via native fluorescence
• aromatic amino acids
• DNA
• excitation 220nm to 280nm
• emission 320nm to 370nm
UV resonant Raman interactions
• ~105 more efficient than non-resonant Raman
Photochemical reactions
• photodissociation/ionization
• photo-crosslinking
• disulphide bonds free thiol
• aryl azides, diazirine rings, and anthraquinones
• photo-isomerization
Ray K, Chowdhury MH, Lakowicz JR (2007) Aluminum nanostructured films as substrates for enhanced fluorescence
in the ultraviolet-blue spectral region. Analytical Chemistry 79:6480– 6487
Chowdhury MH, Ray K, Gray SK, Pond J, Lakowicz JR (2009) Aluminum nanoparticles as substrates for metal-
enhanced fluorescence in the ultraviolet for the label-free detection of biomolecules. Anal Chem 81:1397–1403
Taguchi A, Hayazawa N, Furusawa K, Ishitobia H, Kawata S (2010) Deep-UV tip-enhanced Raman scattering. J.
Raman Spectroscopy 40:1324-1330
Photonics Research Group

3. What are the challenges?
Materials
• high plasma frequency (> 7eV): Al, Ag, Au
• damping, interband transitions: Ag, Au
• surface modification schemes (Al, oxide)
Absorption spectroscopy
• low absorption cross-sections
(220nm – 280nm)
Fluorescence spectroscopy
• low quantum yields
• “brightness”
~100x lower than organic dye labels
Ray K, Chowdhury MH, Lakowicz JR (2007) Aluminum nanostructured films as substrates for enhanced fluorescence
in the ultraviolet-blue spectral region. Analytical Chemistry 79:6480– 6487
Chowdhury MH, Ray K, Gray SK, Pond J, Lakowicz JR (2009) Aluminum nanoparticles as substrates for metal-
enhanced fluorescence in the ultraviolet for the label-free detection of biomolecules. Anal Chem 81:1397–1403
Taguchi A, Hayazawa N, Furusawa K, Ishitobia H, Kawata S (2010) Deep-UV tip-enhanced Raman scattering. J.
Raman Spectroscopy 40:1324-1330
Photonics Research Group

4. Materials
• Figure of merit – β’/β’’ for SPP @ metal – air interface
• Al has best response into the UV
Ray K, Chowdhury MH, Lakowicz JR (2007) Aluminum nanostructured films as substrates for enhanced fluorescence
in the ultraviolet-blue spectral region. Analytical Chemistry 79:6480– 6487
Aslan K, Previte MJR, Zhang Y, Geddes CD (2008) Surface plasmon coupled fluorescence in the ultraviolet and visible
spectral regions using zinc thin films. Analytical Chemistry 80:7304– 7312
Photonics Research Group

5. Materials
• Figure of merit – ε’/ε’’ for sphere LSP @ metal – air interface
• Al has best response into the UV
• Zn has also been used in some studies
Ray K, Chowdhury MH, Lakowicz JR (2007) Aluminum nanostructured films as substrates for enhanced fluorescence
in the ultraviolet-blue spectral region. Analytical Chemistry 79:6480– 6487
Aslan K, Previte MJR, Zhang Y, Geddes CD (2008) Surface plasmon coupled fluorescence in the ultraviolet and visible
spectral regions using zinc thin films. Analytical Chemistry 80:7304– 7312
Photonics Research Group

6. UV Plasmonic Structures
bow-tie antenna
Data and image courtesy of Dr. Reuven Gordon, U. Victoria
(dual polarization) bullseye
Photonics Research Group

7. UV Plasmonic Structures
Data and image courtesy of Dr. Reuven Gordon, U. Victoria
Photonics Research Group

8. UV Plasmonic Structures
Data and image courtesy of Dr. Reuven Gordon, U. Victoria
Photonics Research Group

9. UV Enhancement - aperture
Al Au
Ag
50nm aperture diameter, 100nm thickness
F. Mahdavi and S. Blair, “Nanoaperture fluorescence enhancement in the ultraviolet,” Plasmonics 5, 169-174 (2010)
Photonics Research Group

10. Fluorescence Enhancement
fluorescence emission κ = collection efficiency
k rad
φ= = quantum efficiency
krad + k nrad
σI e krad ,knrad = radiative, non - radiative rates
CRM = κφ σ = absorption cross - section
1+ Ie /Ie
Ie = excitation intensity
ktot
Is = = saturation intensity
σ (1+ kisc /kd )
€
there are two limits in excitation
CRM I → κφσIe
e <<I sat €
CRM I → κφσIs ≈ κk rad
e >>I sat
a “universal” emission enhancement factor can be defined κkrad
measured fluorescence signal
€  
T
F ( t ) = ∫ CRM ( r )C ( r ,t ) dr 3 F= ∫ F(t)dt
0
where C(r,t) is the concentration and T the integration time
S. Blair and J. Wenger, “Enhancing fluorescence with sub-wavelength metallic apertures,” in Metal Enhanced
Fluorescence, ed. by Chris Geddes (2008)
Photonics Research Group
€

11. UV Enhancement - nanoaperture
Tryptophan – native quantum efficiency ~ 13%
F. Mahdavi and S. Blair, “Nanoaperture fluorescence enhancement in the ultraviolet,” Plasmonics 5, 169-174 (2010)
Photonics Research Group

12. UV Enhancement - nanoaperture
Tryptophan – native quantum efficiency ~ 13%
F. Mahdavi and S. Blair, “Nanoaperture fluorescence enhancement in the ultraviolet,” Plasmonics 5, 169-174 (2010)
Photonics Research Group

13. UV Enhancement
F. Mahdavi and S. Blair, “Nanoaperture fluorescence enhancement in the ultraviolet,” Plasmonics 5, 169-174 (2010)
Photonics Research Group

14. UV Enhancement
F. Mahdavi and S. Blair, “Nanoaperture fluorescence enhancement in the ultraviolet,” Plasmonics 5, 169-174 (2010)
Photonics Research Group

15. Controlling Photochemical Reactions
light-directed capture molecule attachment
• ATFB – photoactivated cross-linker
• forms aryl nitrene under UV (365nm)
• highly reactive – insertion into C-H or N-H bonds
• attach biotinylated probe
S. Attaver, M. Diwekar and S. Blair, “Photoactivated capture molecule immobilization in plasmonic nanoapertures in
the ultraviolst,” to appear Lab on a Chip (2011)
Photonics Research Group

16. Large Area Plasmonic Substrates
Working with Utah company – MOXTEK
• adapt existing manufacturing process for wire-grid polarizers
• process currently developed for Al
• must develop new passivation methods
Produce 1” x 3” microarray substrates
• can work with off the shelf instruments
• e.g. spotters, hybridization systems, scanners
Photonics Research Group

17. Passivating Aluminum Substrates
Need chemistry to prevent silanization of aluminum oxide layer
Phosphonic and carboxylic acids
• attach to many metal oxides
• can prevent attachment to SiO2
After treatment, can directly silanize
S. Attavar, M. Diwekar, M. R. Linford, M. Davis, and S. Blair “Passivation of aluminum with alkyl phosphonic acids
for biochip applications,” submitted to Applied Surface Science (2010)
Photonics Research Group

18. Passivating Aluminum Substrates
molecule O(cta)D(ecyl)PA D(ecly)PA B(utyl)PA none
contact ang
Al film 116 103 83 ~10
Al array 114 97 ~25
SIMS
images
passivation
450:1 200:1 N/A
ratio
Al + Silane
Al + DPA
Array + DPA
Photonics Research Group

19. Passivating Aluminum Substrates
molecule O(cta)D(ecyl)PA D(ecly)PA B(utyl)PA none
contact ang
Al film 116 103 83 ~10
Al array 114 97 ~25
SIMS
images
passivation
450:1 200:1 N/A
ratio
PO2- SiCO2H3
PO3-
Photonics Research Group

20. Controlling Photochemical Reactions
light-directed capture molecule attachment
• ATFB – photoactivated cross-linker
• forms aryl nitrene under UV (365nm)
• highly reactive – insertion into C-H or N-H bonds
• attach biotinylated probe
S. Attaver, M. Diwekar and S. Blair, “Photoactivated capture molecule immobilization in plasmonic nanoapertures in
the ultraviolst,” to appear Lab on a Chip (2011)
Photonics Research Group

21. Enhanced Photochemical Reaction Rate
550nm/200nm
650nm/250nm
500nm/200nm
• 3.2x intensity enhancement @ 365nm
S. Attaver, M. Diwekar and S. Blair, “Photoactivated capture molecule immobilization in plasmonic nanoapertures in
the ultraviolst,” to appear Lab on a Chip (2011)
Photonics Research Group

22. UV Enhancement
550nm/200nm 650nm/250nm 500nm/200nm
S. Attaver, M. Diwekar and S. Blair, “Photoactivated capture molecule immobilization in plasmonic nanoapertures in
the ultraviolst,” to appear Lab on a Chip (2011)
Photonics Research Group

23. Enhanced Red Fluorescence
S. Attaver, M. Diwekar and S. Blair, “Photoactivated capture molecule immobilization in plasmonic nanoapertures in
the ultraviolst,” to appear Lab on a Chip (2011)
Photonics Research Group

24. Enhanced Red Fluorescence
8.2x
6.1x
3.3x
S. Attaver, M. Diwekar and S. Blair, “Photoactivated capture molecule immobilization in plasmonic nanoapertures in
the ultraviolst,” to appear Lab on a Chip (2011)
Photonics Research Group

25. Outlook
Building blocks in place
• materials (e.g. Al)
• antenna designs
• nanofabrication
• surface modification
Possible applications
• label-free real-time binding arrays
• biomolecule analysis
• nanolithography
Question
• can we develop better materials?
Photonics Research Group