Optical detection of magnetic resonance by coherent Raman scattering

Transcription

1 Optical detection of magnetic resonance by coherent Raman scattering Applications in biology and solid-state physics Stephen Bingham Department of Physics University of Bath Exeter 24 th October 2008

2 Spectroscopy & Imaging at Bath Optical, microwave and signal processing instrumentation and devices Image and data processing, reconstruction and analysis Spectroscopy and Imaging group Biological and biomedical applications: metallo-enzymes, drug delivery, free radical related (patho)physiology, etc, etc Solid-state physics and nanotechnology applications: opto- and spin-tronic devices, solar cell related devices, carbon nano-tubes, etc

3 Overview Basic principles Metalloprotein applications Semiconductor applications Future directions

4 Coherent versus conventional ODMR Emission (Photoluminescence) Absorption (MCD) Coherent Raman 3> 2> 3> 3> 1> 2> 1> 2> 1> Perfect specificity and selectivity Total intensity unaffected by the presence of other paramagnetic chromophores or relaxation phenomena

5 Coherent Raman detection - MCD detection of microwave frequency spin precession Stokes anti-stokes B 0 S B 1 ω ω0 ω1 ω ω Circularly polarised light Perfect specificity and selectivity (but therefore very small) Total intensity unaffected by the presence of other paramagnetic chromophores or relaxation phenomena Modulation view is valid if the optical broadening is larger than the microwave energy and optical pumping is not significant Assists in the understanding optimal geometry and polarisation

6 Experimental method optical heterodyne detection Laser Polarisation modulator controller PEM Ref. Microwave source S Cavity Power amplifier Absorption Lock-in amplifier Ref. I Lock-in amplifier Quadrature mixer Photodiode Dispersion Q Low noise amplifier Extremely high (near single photon) sensitivity for coherent optical signals Blind to broadband incoherent backgrounds (i.e. luminescence) 1 part in 10 8 absorption modulation detection Allows both amplitude and phase measurements of the optical signal Also in reflection Replaces interferometry S.J.Bingham et al., Rev. Sci. Instrum., (9): p

7 Optical heterodyne receiver

8 Metallobiology applications Crystal structure of nitrous oxide reductase Cu A Cu Z Brown, K., Prudêncio, M., Pereira, A.S., Besson, S., Moura, J.J., Moura, I., Tegoni, M., and Cambillau, C. (2000) Nature Struct. Biol. 7,

9 Reasons to use optically detected electron spin resonance in biology Chemical selectivity deconvolution of ESR and optical spectra correlation of magnetic and optical properties multi-centre enzymes, multiple forms of centres Orientational selectivity symmetry and selection rules assignment of transitions and hence characterisation of electronic structure Not merely a detection method

10 Conventional ODMR - MCD detection of microwave spin heating Microwave absorption changes ground level spin state populations Left circular polarisation Right circular polarisation Azurin 33GHz 1.7K ESR simulation Almost all signal nonresonant Magnetic relaxation dependent Very difficult to interpret and quantify Partial orientational and chemical selectivity Especially difficult in multi-centre proteins Barrett, C. P., J. Peterson, et al., JACS (1986). 108(12):

11 MCD and orientational selectivity M g S ɶ zi g = i µ i ε C S ɶ C Im { } zi = i mx e e my i Oscillating CD as a function of orientation: e z ( ) = 1/2 i mpm m Pm i x e y y e x π π C xx x z 2 2 x y 2 cos cos + sin g 22 4 g g g g ε = Kf( v, ) C yy cos θsin φ cos φ X π + + g g 00 + C g g g g zz 3 2 y z x y g 2 g gz 2 g sin 2 gg θ φ φ θ ɶ cos( ωt) Sɶ sin( ωt) S disp. abs. g 1 sinθdθdφ S.J.Bingham et al., J. Chem. Phys., (10): p

12 Pseudomonas aeruginosa cytochrome c-551 Small and simple Haem redox protein Electron shuttle to nitrogen cycle enzymes Well understood spectroscopically

13 Pseudomonas aeruginosa cytochrome c-551 (a) (b) (c) g-value C xx C yy C zz C MCD C S ɶ = Im{ i m e e m i } zi x y e Only diagonal elements of the C-matrix are observable Spectrum is a linear combination of these three components Magnetic field (T) g i region is absent from C ii spectrum component because the applied magnetic field and the laser beam are perpendicular S.J.Bingham et al., J. Chem. Phys., (10): p

14 A/ Pseudomonas aeruginosa cytochrome c-551 C = Im{ z m e em z } zz x y e g-value nm 1.8 K GHz B 1 = 0.5 G Experiment Simulation C zz >> C xx, C yy All lineshape parameters except MCD anisotropy taken from the X-band ESR spectrum MCD only observable along the g z axis Expected for X-Y polarised transition transition principally within the π manifold Magnetic field (T) S.J.Bingham et al., J. Chem. Phys., (10): p

15 Pa. pantotrophus nitrous oxide reductase N 2 O+2H + N 2 +H 2 O 2e - Cu A Cu Z Cu Z Cu A 2e - N 2 +H 2 O N 2 O+2H + Catalyses the last step of the denitrification (determines environmental nitrogen availability) Nitrous oxide is the third most important greenhouse gas Redox groups: Cu A : dinuclear copper centre as in cytochrome c oxidase (electron transfer) Cu Z : tetranuclear copper centre (catalytic centre)

16 Pa. pantotrophus nitrous oxide reductase Cu A Axial g-values g x and g y are two similar to be resolved at 14 GHz

17 Pa. pantotrophus nitrous oxide reductase Cu A g-value 3 C zz : C perp = -1 : A / nm 1.4 K B 1 = 1 G v = GHz 8 A / nm 750 nm 4 0 C zz : C perp = 1 : C zz : C perp = -1 : A /10-6 g z axis known to be perpendicular to the Cu-S rhombus plane 476 and 514 nm transitions largely charge transfer transitions in this plane A higher d-d character in the 750 nm transition? Magnetic field /Tesla S.J.Bingham et al. Molecular Physics, (15-16): p.2169.

18 Reasons to use optically detected electron spin resonance in solid-state physics Sensitivity better than microwave detection for many semiconductor and magnetic materials thin films Resolution better than other sub-level spectroscopies such as Zeeman, spin-flip Raman & optical hole burning. Chemical/structural/environmental selectivity deconvolution of ESR and optical spectra correlation of magnetic and optical properties defects, impurities, electrons in perturbed environments Orientational selectivity symmetry and selection rules assignment of transitions and hence characterisation of electronic structure

19 ZnSe epitaxial layer 10 5 A Zeeman energy (mev) CRESR Dispersion Absorption Intensity (arb. units) Magnetic field (Tesla) SFRS AS Laser S Raman shift (mev) Excitation Å GHz T = 1.7 K Electron g-factor is Precision: ± Accuracy: ± Comparison of energy scales between CRESR and SFRS (inset) shows the much higher resolution of CRESR. 1 micron epilayer, 10-6 cm 3 sample, spins Bingham, S.J., J.J. Davies, and D. Wolverson, Physical Review B, (15): art. no

20 Dependence of g on excitation energy gyromagnetic ratio g-factor correlated with exciton energy No other technique could reveal this dependence Excitation energy (ev)

21 Mn 2+ ions in CdTe simulation ev CRESR signal 0 0 experiment CRESR signal (arb. units) increasing laser energy Magnetic field (Tesla) Magnetic field / Tesla ev Cd Mn Te Measured in reflection Resonant with an excitonic intermediate state Mn hyperfine observed due to strong exchange between Mn ions and band electrons Smith, L.C., S.J. Bingham, J.J. Davies, and D. Wolverson, Applied Physics Letters, (20): art. no

22 Other applications (so far ) Type 1 Blue copper Pseudomonas aeruginosa Azurin (spin ½) Mono-nuclear iron-sulphur Rubredoxin (high spin ferric) A three- iron sulphur cluster [3Fe 4S] - Azotobacter chroococcum ferredoxin I (spin ½) Inorganic materials and solid-state physics ( Ruby, other II-IV semiconductors) Absence of special magnetic and optical relaxation requirements makes the method widely applicable

23 What s next? More applications New proteins Comparative studies of engineered protein sites Magnetic materials? Electronic structure calculations Transient measurements Distance measurements in proteins from magnetic relaxation studies Solid-state spin dynamics (more sensitive than pulsed laser methods) Higher microwave/mm-wave frequencies Spatially resolved measurements

24 A broader context Different selection rules for non-kramers (integer spin) systems Optical pumping/holeburning Optical excitation of magnetic resonance Detection of nuclear quadrupole resonance Summary A versatile and useful technique!

25 Acknowledgments Bath: Prof. J. John Davies Dr Daniel Wolverson Dr Lowenna Smith Dortmund: Prof. Dieter Suter Dr Birgit Börger-Enkisch Dr Jörg Gutschank Dr Marc-Oliver Schweika Norwich: Dr. Ljiljana Udovicic Prof. Andrew Thomson FRS Dr Tim Rasmussen Dr Myles Cheesman Dr Jaqui Farrar Zürich: Prof. Arthur Schweiger Jörg Forrer Dr Chris Barrett Recent funding: EPSRC Life Sciences Interface programme (Grants GR/M99453 and GR/R38231/01). INTAS and EPSRC Grant No. GR/R38231

26 ESR imaging Oximetry cancer biology, radiotherapy and diabetes research Nitric oxide Cardiovascular (heart attack, stroke) and inflammatory (arthritis) diseases, septic shock, etc Reactive oxygen species (e.g. super-oxide radicals) Degenerative neurological conditions (BSE, Alzheimer's disease), reperfusion injury in organ transplantation, etc Spin labels Drug delivery studies, disease diagnosis (tissue labelling), etc Other spin-trapping methods UV and ionising radiation damage, etc Physical science applications as well

27 When you want to relax