© 2006 OSA/LACSEA 2006
TuE7
Laser Induced Breakdown Spectroscopy ~Application to Tissue Analysis~ Hongbo Zheng1, Fang Yu Yueh1, Shane Burgess2 and Jagdish P Singh1 1
Diagnostic Instrumentation and Analysis Laboratory Mississippi State University 205 Research Boulevard Starkville, MS 39759-7704 Telephone: 662-325-7375 Email:
[email protected] 2
Department of Basic Sciences College of Veterinary Medicine Mississippi State University Abstract: Laser-induced breakdown spectroscopy (LIBS) is applied to characterize animal tissue samples. Samples include brain, kidney, liver, lung, muscle and spleen tissues. LIBS intensity ratios of certain trace elements are used for the sample identification. Concentration ratios from inductively coupled plasma emission spectroscopy (ICPES) of those tissues are obtained for comparison. 1. Introduction Laser-induced breakdown spectroscopy (LIBS) is a diagnostic technique based on laser technology for elemental analysis[1-2]. In LIBS, a pulsed laser beam is focused at the sample to produce a plasma. The plasma atomizes and excites the atomic elements in the sample. The atomic emission from the plasma is then collected with a collimating lens and sent to the spectrometer for analysis. The intensity of the atomic emission lines from the LIBS spectra is used for analysis of the atomic elements. LIBS is a simple and fast method of elemental analysis. In general, solid, liquid or gaseous materials can be analyzed and no or very little sample preparation is required[2]. LIBS can be applied directly from a sample in situ and at remote distance (stand-off detection), and also in vivo analysis of living organism samples is possible. Although, the LIBS technique has been applied in biological investigation in the past [3,4,5], yet literature about LIBS on bio-matrix materials is sparse. This is understandable due to some reasons. First, the hardness of the biological tissue samples is less than metals or other solid materials texturally. The laser ablation process destroys the sample surface much more rapidly and results in weaker focusing, thus creating poor reproductively of signal. Secondly, biological samples are more inhomogeneous in most cases. And inhomogeneity brings poor reproductively of results. Finally, molecular species are important in biology, which are normally beyond the capabilities of LIBS. However, LIBS provides rapid, non-destructive tissue analysis. LIBS analysis results are also compared with those from inductively coupled plasma emission spectroscopy (ICPES).
© 2006 OSA/LACSEA 2006
TuE7
2. Experiment Laser-induced plasmas are generated by a frequency-doubled Nd:YAG laser (Continuum Surelite III, repetition rate 10 HZ, pulse width 5 ns, wavelength 532 nm). An ultraviolet (UV) fused-silica lens is used to focus the laser beam directly on the sample. The sample is placed on a small cooling unit which is placed in a plastic box and cooled down to -20 0 C by a circulation bath and translating back and forth. The same lens is used to collect emission light from the plasma. Two UV-grade quartz lenses are used to couple the LIBS signal to an optical fiber. And the optical fiber is coupled to a UV-visible Echelle spectrometer(LLA Instruments, GmbH, ESA3000 EV/I, Berlin, Germany). The spectra of the plasma emission are detected by an element intensified charge-coupled device(ICCD). A high-voltage fast-pulse generator is used to operate the detector. Data acquisition and analysis are performed using a personal computer and will be presented in the paper. 3. Results The intensity ratio of the major element with Ca393.367nm is analyzed and the results are shown in the figure below. The analyte lines selected for this calculation are the lines that give a better relative standard deviation.From the differences of the intensity ratio among the ten samples for the analyte lines we are able to distinguish one sample from the others. Results from ICPES will be used to compare those from LIBS.
Sample vs Intensity Ratio 0.35
0.3
Intensity Ratios
0.25
Mg285.213/Ca393.367
0.2
Al396152/Ca393.367 Fe430.79/Ca393.367 Na589.592/Ca393.367 0.15
K404.414/Ca393.367
0.1
0.05
0 m1
m2
m3
m4
m5
m6
Samples
m7
m8
m9
m10
© 2006 OSA/LACSEA 2006
TuE7 References 1. L. J. Radziemski, D. A. Cremers(Ed.), “Spectrochemical analysis using plasma excitation,” in: Laser Induced Plasmas and Applications, Marcel Dekker, NewYork, NY, ch.7, pp 295-325 (1989). 2. F. Y. Yueh, J .P. Singh and H. Zhang, Laser-induced breakdown spectroscopy: Elemental analysis. Encyclopedia of Analytical Chemistry, John Wiley & Sons, Ltd. Vol. 3 2065-2087 (2000). 3. Q. Sun, M. Tran, B. Smith, and J. D. Winefordner, “In-situ evaluation of barrier-cream performance on human skin using laser-induced breakdown spectroscopy,” Contact Dermatitis 43, 259-263 (2000). 4. M. Corsi, G. Cristoforetti, M. Hidalgo, S. Legnaioli, V. Palleschi, A. Salvetti, E. Tognoni, and C. Vallebona, “Application of laser-induced breakdown spectroscopy technique to hair mineral analysis,” Appl. Opt. 42, 6133-6137 (2003). 5. A. Kumar, F. Y. Yueh, J. P. Singh and S. Burgess, “Characterization of malignant tissue cells by laser-induced breakdown spectroscopy,” Appl. Opt. 43, 5399-5403 (2004).
