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Biomedical Optics Express

Biomedical Optics Express

  • Editor: Joseph A. Izatt
  • Vol. 1, Iss. 5 — Dec. 1, 2010
  • pp: 1401–1407
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Detection of nanoscale structural changes in bone using random lasers

Qinghai Song, Zhengbin Xu, Seung Ho Choi, Xuanhao Sun, Shumin Xiao, Ozan Akkus, and Young L. Kim  »View Author Affiliations


Biomedical Optics Express, Vol. 1, Issue 5, pp. 1401-1407 (2010)
http://dx.doi.org/10.1364/BOE.1.001401


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Abstract

We demonstrate that the unique characteristics of random lasing in bone can be used to assess nanoscale structural alterations as a mechanical or structural biosensor, given that bone is a partially disordered biological nanostructure. In this proof-of-concept study, we conduct photoluminescence experiments on cortical bone specimens that are loaded in tension under mechanical testing. The ultra-high sensitivity, the large detection area, and the simple detection scheme of random lasers allow us to detect prefailure damage in bone at very small strains before any microscale damage occurs. Random laser-based biosensors could potentially open a new possibility for highly sensitive detection of nanoscale structural and mechanical alterations prior to overt microscale changes in hard tissue and biomaterials.

© 2010 OSA

1. Introduction

2. Materials and methods

2.1. Bone specimen preparations

2.2. Photoluminescence experiments

In optical lasing measurements, to optically pump the specimen, we used a tunable pulsed laser (optical parametric amplifier pumped with a Ti:sapphire regenerative amplifier). The pump laser wavelength was at ~690 nm, which is the absorption peak of Rhodamine 800. The pulse width was 100 fs and the repetition rate was 1 KHz. The pumping beam was focused normally onto the specimen through a cylindrical lens to form a narrow strip of ~150 μm × 5 mm along the notch direction as shown in Fig. 2
Fig. 2 Photoluminescence experiment setup. A narrow strip of the Ti:sapphire laser illumination is normally focused onto the surface of bone tissue along the transverse orientation.
. The pumping strip was along the transverse orientation of the bone structure to maximize light confinement for random lasing. When the pumping strip was along the longitudinal orientation, random lasing action was hardly observed at the sample pumping power, supporting the idea that the partially disordered bone structure in the transverse orientation is primarily responsible for light confinement. The emission light was collected with an acquisition time of 1 second from the side using a fiber bundle through a lens and coupled to a spectrometer with the resolution of ~0.2 nm. The pumping illumination was blocked by a 20-nm bandpass filter centered at 720 nm. The specimen was covered with a microscope slide. Kimwipes were connected to an ethanol reservoir below the specimen to keep the specimen wet and to avoid the aggregation of the laser dye.

2.3. Mechanical testing

2.4. Numerical simulation

3. Results

3.1. Confirmation of coherent random lasing action

We first confirmed coherent random lasing action from the bone specimen infiltrated with the laser dye before applying any loading. Figure 4(a)
Fig. 4 (a) Representative emission spectrum measured from the side of the bone specimen infiltrated with Rhodamine 800 before loading. The pump intensity was kept at 80 mW. (b) The output emission intensity as a function of pumping power. A clear laser threshold can be seen at ~45 mW.
shows a typical random laser emission spectrum at the pumping power of 80 mW. The discrete and randomly distributed peaks in the emission spectrum are clearly observed, although the detailed spectral features are masked by the spectral resolution of the spectrometer (~0.2 nm). In Fig. 4(b), we plot the emission intensity as a function of the pumping power. A clear laser threshold behavior at ~45 mW confirmed the lasing action in the bone specimen.

3.2. Spectral changes in random lasing emission during peak loading

We further examined emission spectral changes at the notch area before loading, under peak loading, and after removal of the loading, while keeping the same experiment conditions and the same pumping power at 80 mW. In Fig. 5
Fig. 5 Lasing emission spectra recorded before loading (black solid line), under peak loading (red solid line), and after removal of loading (blue solid line). A clear shift of ~0.55 nm in all of the emission peaks can be observed under the peak loading (i.e. 2.0 lbs). After removal of the loading, the laser peaks restored to the original peak positions. The vertical gray lines are plotted to clearly visualize the wavelength shift. The spectra are shifted vertically for the clear visualization of each emission spectrum in the vertical axis.
, representative spectra are normalized and vertically shifted for the clear visualization of each emission spectrum. Before the loading, the discrete laser peaks (the black curve in Fig. 5) can be observed. Under the peak loading (i.e. 2.0 lbs), the random laser emission peaks (the red curve) is clearly shifted to the left by ~0.55 nm. After removal of the loading, most of them (the blue curve) return to the original spectrum. This experimental result strongly indicates that a structural alteration (i.e. compression along the transverse orientation) occurred in the pumping area during the peaking loading and this alteration disappeared after removal of the loading.

3.3. Lasing emission spectral changes induced from nanoscale structural alterations

We numerically studied that the possible structural alteration under our experimental conditions can induce spectral changes in the random lasing emission. The primarily responsible structural alteration in our experiments would be the thinning of the mineralized collagen fibrils. In this numerical study, the thickness of each collagen fibril layer was reduced by 0.2% of the original value of each collagen layer. Figure 6(a)
Fig. 6 (a) Representative eigenvalues of the system. The blue circles are the eigenvalues of the original structure, while the red circles are the eigenvalues after reducing the thickness of each collagen fibril layers by 0.2%. (b1) Electric field intensity distribution at κ = 8.992 - 1.060*10−2*i [1/μm] (the blue solid dot in (a)) (b2) Electric field intensity distribution at κ = 8.993 - 1.060*10−2*i [1/μm] (the red solid dot in (a)).
shows the representative eigenvalues before and after the thinning of the collagen fibril layer. We arbitrarily selected one of the high Q eigenvalues and visualized the electric field. Figure 6(b1) and (b2) show the electric fields before and after the structural change, respectively. In this case, the eigenvalue changed from κ = 8.992 – 1.060*10−2*i [1/μm] (the blue solid dot) to κ = 8.993 - 1.060*10−2*i [1/μm] (the red solid dot), resulting in a spectral shift of ~0.08 nm. While the spatial distributions of both the electric fields are relatively preserved covering the large area, the overall intensity increases after the thinning of the collagen fibril layers. Although other internal structural changes may contribute to the spectral change in the random laser emission, this simulation result supports the idea that the spectral properties of the random laser emission can be highly sensitive to nanoscale structural alterations.

4. Discussion

4.1. Possible origins of the random laser spectral alteration

A displacement of the while specimen might induce the spectral change in the random laser emission during the loading. However, this was highly unlikely to occur under our experimental conditions, because the loading stage maintained the observation region fixed during the loading. In addition, as shown in Fig. 5, the emission spectra contain the periodic patterns over the wavelength, possibly due to the boundary effect of the thin specimen. However, the emission spectrum under the peak loading possessed the same number of the laser emission peaks and the similar spacing among the laser emission peaks, while the overall spectral shape was slightly shifted to the shorter wavelength. This means that most of the lasing modes remained within the pumping area, given that lasing modes are formed only if the field distribution overlaps with the gain region [19

19. K. L. van der Molen, R. W. Tjerkstra, A. P. Mosk, and A. Lagendijk, “Spatial extent of random laser modes,” Phys. Rev. Lett. 98(14), 143901 (2007). [CrossRef] [PubMed]

,20

20. H. E. Türeci, L. Ge, S. Rotter, and A. D. Stone, “Strong interactions in multimode random lasers,” Science 320(5876), 643–646 (2008). [CrossRef] [PubMed]

]. Collectively, our results strongly support that the idea that the spectral shift in the lasing emission under the peak loading was caused by subtle structural alterations at the extremely small strain.

4.2. Drawbacks of our current study

The dehydration of the bone specimen may have changed the mechanical properties of the cortical bone specimen in our photoluminescence experiments, because the solvent of Rhodamine 800 was ethanol. However, we intended to demonstrate the sensitivity of coherent random lasing to nanoscale structural alterations as a proof-of-concept study. Thus, this issue would not be critical in our current study. In our numerical study, the thinning of the collagen fibrils may account for one of several possible nanoscale deformation mechanisms that can occur in our experimental conditions. For example, shear deformation of the interfibrillar matrix [17

17. H. S. Gupta, W. Wagermaier, G. A. Zickler, D. Raz-Ben Aroush, S. S. Funari, P. Roschger, H. D. Wagner, and P. Fratzl, “Nanoscale deformation mechanisms in bone,” Nano Lett. 5(10), 2108–2111 (2005). [CrossRef] [PubMed]

] or debonding of mineral crystals from the neighboring collagen fibrils [16

16. X. H. Sun, J. Hoon Jeon, J. Blendell, and O. Akkus, “Visualization of a phantom post-yield deformation process in cortical bone,” J. Biomech. 43(10), 1989–1996 (2010). [CrossRef] [PubMed]

] can induce spectral changes in the random laser emission. Another drawback of our current study is the lack of quantitative comparison with other convention techniques at such a small strain level for bone (e.g. electron microscopy, atomic force microscopy, or x-ray diffraction). In other words, the exact structural origin in the nanoscale deformation during this level of peak loading has not been determined by a conventional nanoscale measurement. We note that x-ray diffraction methods are typically used to study relatively higher strains compared with our study. With fairly simple sample preparation, our random laser-based method allows the detection of extremely small strains and deformation.

5. Conclusion

We demonstrated that random lasers can be used as a mechanical or structural sensor to detect nanoscale deformation and prefailure damage in bone, and that the simple numerical study supports such feasibility. Although conventional nanoscale measurements such as electron microscopy, x-ray diffraction, and atomic force microscopy are highly valuable tools to study nanoscale mechanical and structural characteristics of hard tissue and biomaterials, they have limitations and restrictions in specific experimental situations. In this respect, our results from this pilot study suggest that random laser-based methods could potentially find their own unique applications.

Acknowledgments

This project was supported in part by grants from Purdue Research Foundation and NIH1R03CA153982. We thank Umut Atakan Gurkan for the SEM image of the bone specimen.

References and links

1.

H. Cao, “Review on latest developments in random lasers with coherent feedback,” J.Phys. A Math. Gen. 38(49), 10497–10535 (2005). [CrossRef]

2.

D. S. Wiersma, “The physics and applications of random lasers,” Nat. Phys. 4(5), 359–367 (2008). [CrossRef]

3.

P. Pradhan and N. Kumar, “Localization of light in coherently amplifying random media,” Phys. Rev. B Condens. Matter 50(13), 9644–9647 (1994). [CrossRef] [PubMed]

4.

H. Cao, Y. G. Zhao, S. T. Ho, E. W. Seelig, Q. H. Wang, and R. P. H. Chang, “Random laser action in semiconductor powder,” Phys. Rev. Lett. 82(11), 2278–2281 (1999). [CrossRef]

5.

R. C. Polson, A. Chipouline, and Z. V. Vardeny, “Random lasing in pi-conjugated films and infiltrated opals,” Adv. Mater. 13(10), 760–764 (2001). [CrossRef]

6.

R. C. Polson and Z. V. Vardeny, “Random lasing in human tissues,” Appl. Phys. Lett. 85(7), 1289–1291 (2004). [CrossRef]

7.

A. Tulek, R. C. Polson, and Z. V. Vardeny, “Naturally occurring resonators in random lasing of pi-conjugated polymer films,” Nat. Phys. 6(4), 303–310 (2010). [CrossRef]

8.

X. Wu, W. Fang, A. Yamilov, A. A. Chabanov, A. A. Asatryan, L. C. Botten, and H. Cao, “Random lasing in weakly scattering systems,” Phys. Rev. A 74(5), 053812 (2006). [CrossRef]

9.

C. Vanneste, P. Sebbah, and H. Cao, “Lasing with resonant feedback in weakly scattering random systems,” Phys. Rev. Lett. 98(14), 143902 (2007). [CrossRef] [PubMed]

10.

S. Mujumdar, M. Ricci, R. Torre, and D. S. Wiersma, “Amplified extended modes in random lasers,” Phys. Rev. Lett. 93(5), 053903 (2004). [CrossRef] [PubMed]

11.

S. Mujumdar, V. Turck, R. Torre, and D. S. Wiersma, “Chaotic behavior of a random laser with static disorder,” Phys. Rev. A 76(3), 033807 (2007). [CrossRef]

12.

R. C. Polson and Z. V. Vardeny, “Organic random lasers in the weak-scattering regime,” Phys. Rev. B 71(4), 045205 (2005). [CrossRef]

13.

Q. Song, S. Xiao, Z. Xu, J. Liu, X. Sun, V. Drachev, V. M. Shalaev, O. Akkus, and Y. L. Kim, “Random lasing in bone tissue,” Opt. Lett. 35(9), 1425–1427 (2010). [CrossRef] [PubMed]

14.

R. O. Ritchie, M. J. Buehler, and P. Hansma, “Plasticity and toughness in bone,” Phys. Today 62(6), 41–47 (2009). [CrossRef]

15.

Q. Song, S. Xiao, Z. Xu, V. M. Shalaev, and Y. L. Kim, “Random laser spectroscopy for nanoscale perturbation sensing,” Opt. Lett. 35(15), 2624–2626 (2010). [CrossRef] [PubMed]

16.

X. H. Sun, J. Hoon Jeon, J. Blendell, and O. Akkus, “Visualization of a phantom post-yield deformation process in cortical bone,” J. Biomech. 43(10), 1989–1996 (2010). [CrossRef] [PubMed]

17.

H. S. Gupta, W. Wagermaier, G. A. Zickler, D. Raz-Ben Aroush, S. S. Funari, P. Roschger, H. D. Wagner, and P. Fratzl, “Nanoscale deformation mechanisms in bone,” Nano Lett. 5(10), 2108–2111 (2005). [CrossRef] [PubMed]

18.

O. Akkus, “Elastic deformation of mineralized collagen fibrils: an equivalent inclusion based composite model,” J. Biomech. Eng. 127(3), 383–390 (2005). [CrossRef] [PubMed]

19.

K. L. van der Molen, R. W. Tjerkstra, A. P. Mosk, and A. Lagendijk, “Spatial extent of random laser modes,” Phys. Rev. Lett. 98(14), 143901 (2007). [CrossRef] [PubMed]

20.

H. E. Türeci, L. Ge, S. Rotter, and A. D. Stone, “Strong interactions in multimode random lasers,” Science 320(5876), 643–646 (2008). [CrossRef] [PubMed]

OCIS Codes
(140.2050) Lasers and laser optics : Dye lasers
(140.4780) Lasers and laser optics : Optical resonators
(170.3660) Medical optics and biotechnology : Light propagation in tissues
(280.1415) Remote sensing and sensors : Biological sensing and sensors

ToC Category:
Biosensors and Molecular Diagnostics

History
Original Manuscript: October 5, 2010
Revised Manuscript: November 9, 2010
Manuscript Accepted: November 9, 2010
Published: November 11, 2010

Citation
Qinghai Song, Zhengbin Xu, Seung Ho Choi, Xuanhao Sun, Shumin Xiao, Ozan Akkus, and Young L. Kim, "Detection of nanoscale structural changes in bone using random lasers," Biomed. Opt. Express 1, 1401-1407 (2010)
http://www.opticsinfobase.org/boe/abstract.cfm?URI=boe-1-5-1401


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References

  1. H. Cao, “Review on latest developments in random lasers with coherent feedback,” J.Phys. A Math. Gen. 38(49), 10497–10535 (2005). [CrossRef]
  2. D. S. Wiersma, “The physics and applications of random lasers,” Nat. Phys. 4(5), 359–367 (2008). [CrossRef]
  3. P. Pradhan and N. Kumar, “Localization of light in coherently amplifying random media,” Phys. Rev. B Condens. Matter 50(13), 9644–9647 (1994). [CrossRef] [PubMed]
  4. H. Cao, Y. G. Zhao, S. T. Ho, E. W. Seelig, Q. H. Wang, and R. P. H. Chang, “Random laser action in semiconductor powder,” Phys. Rev. Lett. 82(11), 2278–2281 (1999). [CrossRef]
  5. R. C. Polson, A. Chipouline, and Z. V. Vardeny, “Random lasing in pi-conjugated films and infiltrated opals,” Adv. Mater. 13(10), 760–764 (2001). [CrossRef]
  6. R. C. Polson and Z. V. Vardeny, “Random lasing in human tissues,” Appl. Phys. Lett. 85(7), 1289–1291 (2004). [CrossRef]
  7. A. Tulek, R. C. Polson, and Z. V. Vardeny, “Naturally occurring resonators in random lasing of pi-conjugated polymer films,” Nat. Phys. 6(4), 303–310 (2010). [CrossRef]
  8. X. Wu, W. Fang, A. Yamilov, A. A. Chabanov, A. A. Asatryan, L. C. Botten, and H. Cao, “Random lasing in weakly scattering systems,” Phys. Rev. A 74(5), 053812 (2006). [CrossRef]
  9. C. Vanneste, P. Sebbah, and H. Cao, “Lasing with resonant feedback in weakly scattering random systems,” Phys. Rev. Lett. 98(14), 143902 (2007). [CrossRef] [PubMed]
  10. S. Mujumdar, M. Ricci, R. Torre, and D. S. Wiersma, “Amplified extended modes in random lasers,” Phys. Rev. Lett. 93(5), 053903 (2004). [CrossRef] [PubMed]
  11. S. Mujumdar, V. Turck, R. Torre, and D. S. Wiersma, “Chaotic behavior of a random laser with static disorder,” Phys. Rev. A 76(3), 033807 (2007). [CrossRef]
  12. R. C. Polson and Z. V. Vardeny, “Organic random lasers in the weak-scattering regime,” Phys. Rev. B 71(4), 045205 (2005). [CrossRef]
  13. Q. Song, S. Xiao, Z. Xu, J. Liu, X. Sun, V. Drachev, V. M. Shalaev, O. Akkus, and Y. L. Kim, “Random lasing in bone tissue,” Opt. Lett. 35(9), 1425–1427 (2010). [CrossRef] [PubMed]
  14. R. O. Ritchie, M. J. Buehler, and P. Hansma, “Plasticity and toughness in bone,” Phys. Today 62(6), 41–47 (2009). [CrossRef]
  15. Q. Song, S. Xiao, Z. Xu, V. M. Shalaev, and Y. L. Kim, “Random laser spectroscopy for nanoscale perturbation sensing,” Opt. Lett. 35(15), 2624–2626 (2010). [CrossRef] [PubMed]
  16. X. H. Sun, J. Hoon Jeon, J. Blendell, and O. Akkus, “Visualization of a phantom post-yield deformation process in cortical bone,” J. Biomech. 43(10), 1989–1996 (2010). [CrossRef] [PubMed]
  17. H. S. Gupta, W. Wagermaier, G. A. Zickler, D. Raz-Ben Aroush, S. S. Funari, P. Roschger, H. D. Wagner, and P. Fratzl, “Nanoscale deformation mechanisms in bone,” Nano Lett. 5(10), 2108–2111 (2005). [CrossRef] [PubMed]
  18. O. Akkus, “Elastic deformation of mineralized collagen fibrils: an equivalent inclusion based composite model,” J. Biomech. Eng. 127(3), 383–390 (2005). [CrossRef] [PubMed]
  19. K. L. van der Molen, R. W. Tjerkstra, A. P. Mosk, and A. Lagendijk, “Spatial extent of random laser modes,” Phys. Rev. Lett. 98(14), 143901 (2007). [CrossRef] [PubMed]
  20. H. E. Türeci, L. Ge, S. Rotter, and A. D. Stone, “Strong interactions in multimode random lasers,” Science 320(5876), 643–646 (2008). [CrossRef] [PubMed]

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