Libs application

1. LIBS: Laser Induced Breakdown Spectroscopy
Over view
LIBS is an analytical method by which one can determine
(qualitatively and quantitatively) the elemental composition
of solid, liquid or gas samples.
LIBS
 focused laser pulses
 vaporize, atomize and excite the
sample
 plasma emission
 collect, disperse and analyze light
 atomic spectral lines determine the
elemental composition
Emission of continuum light during early stage (<
200 ~ 300 nsec) of plasma cooling process.

2. Born immediately after the invention of the laser in the early 1960's,
LIBS has developed in lock-step with the laser, gaining wider popularity
in the early 1980's.
A Brief History of LIBS
Research in the late 1960's and 1970's included significant work on
plasmas generated via laser. Much of this work was published in Russian
literature by authors such as Afana'ev, Krokhin, Raizer, Biberman
Norman, and Buravlev [24]. Seminal work by Cremers and Radziemsk
began in the early 1980's at Los Alamos National Laboratory with time
resolved Measurements .At this time the term "`LIBS"' was also coined
and its popularity began to grow rapidly.

3. Laser Induced Breakdown Spectroscopy (LIBS) is a rapid
chemical analysis technology that uses a short laser pulse to
create a micro-plasma on the sample surface. This analytical
technique offers many compelling advantages compared to other
elemental analysis techniques. These include:
A sample preparation-free measurement experience
Extremely fast measurement time, usually a few seconds, for a
single spot analysis
Broad elemental coverage, including lighter elements, such as H,
Be, Li, C, N, O, Na, and Mg
Versatile sampling protocols that include fast raster of the sample
surface and depth profiling
Thin-sample analysis without the worry of the substrate
interference

4. LIBS Fundamentals
A short laser pulse is focused on to the surface of a sample to create the plasma. A laser
with a good Gaussian profile allows focusing to a near diffraction-limited spot. The tighter
the focus, the less laser energy is required to produce the laser-induced breakdown.
Typically energies of only tens of millijoules are required.
The plasma is emitted into >2Π steradians, so a fast f/1 lens will collect more light.
Sometimes a blocking filter is used to remove any scatter from the incident laser - however,
since the incident laser light and the signal are well resolved temporally, a filter is rarely
required. An Intensified CCD (ICCD) detector attached to a spectrograph analyzes the
collected plasma light.

5. For LIBS, Echelle spectrographs are typically used.For analysis of a wide range of
samples, a system based on an echelle spectrograph offers a combination of high
resolution and wide wavelength coverage.It is also possible to relay the laser light to the
sample and collect the signal by fiber optics. The gating requirements of LIBS are not
very demanding. Gate times and delays of several microseconds are typical, so a slow
gate ICCD is suitable. The system can usually be operated in internal trigger mode, with
the controller board triggering the laser and the delay generator. The intensity of the
plasma emission is usually high enough to allow good spectra to be recorded in single
scan mode.A typical experimental configuration is shown below.
Typical LIBS Configuration

6. LIBS Techniques
LIBS spectroscopy can be produced from a variety of lasers
but typically excimers or pulsed Nd:Yag lasers are used.The
high intensity laser pulse interacting with the sample produces
a plasma plume that evolves with time from the point of
impact of the incident laser pulse. The laser pulse usually lasts
for 5 to 20ns.The emission from the plasma plume is collected
and analyzed by the detection system.

8. Typically the emission is collected at some distance from the
sample to reduce the significance of self-absorption effects or
surface effects.The plasma created breaks down all the sample's
chemical bonds and ionizes many of the constituent elements.The
spectral emission occurs as a result of the subsequent relaxation of
the constituent excited species.The spectrum that is observed in
the first 100ns is dominated by continuous, intense, white-light
radiation; consequently no discrete lines can be observed. The
plasma plume expands with time and the excited species relax
further.After around 1µs from the incident laser pulse, discrete
spectral lines originating from various ionic species start to
become visible.

9. Emission of continuum light during
early stage (< 200 ~ 300 nsec) of
plasma cooling process.

10. Emitted light collection by a set of
optical lens and optical fiber.

11. Applications of LIBS
LIBS is a useful method for determining the elemental composition of
various solids, liquidsand gases.In the LIBS technique, a high power
laser pulse is focusedon to a sample to create a plasma or laser
spark.Emission from the atoms and ions in the plasma is collected by a
lens or fiber optics and analyzed by a spectrograph and gated
detector.The atomic spectral lines can be used to determine the elemental
composition or theelemental concentrations in the sample.The analysis is
similar tothat performed by an ICP (Inductively Coupled Plasma)
analyzer.The great appeal of LIBS is that little or no sample preparation
is required to obtain useful results and the technique is readily portable to
the field.

12. Methods that have commonly been used for such analyses
include inductively-coupled plasma atomic emission
spectroscopy (ICP-AES), graphite furnace atomic
absorption spectroscopy (AAS), proton-induced X-ray
emission (PIXE), neutron activation analysis (NAA), X-ray
fluorescence (XRF), scanning electron microscopy (SEM)
with energy dispersive X-ray fluorescence microanalysis,
and laser ablation inductively-coupled plasma mass
spectrometry (LA-ICP-MS) [30–34].

13. How does LIBS compare with other analytical methods?
 Different types of samples
 Little sample preparation
 No (chemical) waste
Micro-LIBS
 Portability
 Rapid
This is not to say that there are no
complications in LIBS.
Of course, there are!

14. What is LIBS used for?
(applications, from the literature)
Environmental monitoring to measure soil contamination
(Zolotovitskaya et al., 1997)
Detect toxic metals (Yamamoto et al., 1996; Buckley et al.,
2000)
Study the chemical compositions in liquids (Yueh et al., 2002;
Samek et al., 2000)
Study the chemical compositions in polymers (Sattmann et al.,
1998)
In forensics and military applications (Kincade, 2003)
Biomedical studies of bones and teeth
Art restoration (or conservation), by analyzing pigments and/or
precious and ancient metals (Anzano et al., 2002)

15. LIBS for coin compositional determination
Experimental set-up
Nd-YAG
3rd harmonic
prism
dichroic
mirror
personal
computer
monochromator
mirror
collecting lens
Rotating
sample
holder
sample
PDA
Movie

16. LIBS for coin compositional determination
Experimental Results
1. PDA Calibration
2. Apply LIBS to coins
a. Check repeatability
b. Look for coin signatures
c. Reliability (same results
in different regions!!)
d. NDT

17. LIBS for coin compositional determination
10% iron in KBr (calibration pellet)
Fe I 4045.8 4000
Fe I 4063.6 1500
Fe I 4071.7 1200
Fe I 4143.9 800
Br II 4223.9 1000
Fe I 4260.5 800
Fe I 4271.8 1200
Fe I 4282.4 1200
Fe I 4307.9 1200
Fe I 4325.8 1500
Br I 4365.1 2000
Br II 4365.6 1000
Fe I 4375.9 800
Fe I 4383.5 3000
Fe I 4404.8 1200
Br I 4425.1 1500
http://physics.nist.gov/cgi-bin/AtData/lines_form
Data: 4000-4400 Å

18. 0
5000
10000
15000
20000
25000
4000 4050 4100 4150 4200 4250
Wavelength (A)
Intensity
(A.U.)
LIBS spectra for (solid) one side of a 25 Fils Bahrain
coin and (dashed) the other side of the same coin.
Notice how the spectra are almost identical!!

19. Display of LIBS spectra and their subsequent analysis by the
instrument software for both qualitative and quantitative elemental
analysiss

20. 0
5000
10000
15000
20000
25000
30000
35000
40000
4000 4100 4200 4300 4400
Wavelength (A)
Intensity
(A.U.)
LIBS spectra for (solid) a 10-Hallalah Saudi coin, (dashed) 20 cent
Euro coin and (dotted) a game token, in the 4000-4425 Å region.
There are
similarities
between the
three
spectra; for
example, all
have Fe
peaks (e.g.,
@ 4228 Å.
The game token has more iron and
nickel than the other (real) currencies.
The game
token does
not contain
copper
(e.g. @
4180, 4275
& 4377 Å).
The real
currencies
do contain
copper!!
The Euro coin does not have
the 4201 & 4401Å Ni peaks.

21. LIBS spectra for (solid) a 10-Hallalah Saudi coin, (dashed) 20 cent
Euro coin and (dotted) a game token, in the 5250-5550 Å region.
Common
iron peaks
(e.g. 5270
Å).
The game
token does
not contain
copper. The
real
currencies do
contain
copper!! (e.g.
5293 Å).
The Euro
coin does not
have the Ni
peaks. (e.g.
5475 Å).
The results are
consistent with
that of the 4000-
4400 Å region.
It is difficult to distinguish between Saudi and Bahrani coins.
They probably have very similar elemental composition.
0
5000
10000
15000
20000
25000
30000
35000
40000
5250 5300 5350 5400 5450 5500 5550
Wavelength (A)
Intensity
(A.U.)

22. LIBS for coin compositional determination
Conclusions
 LIBS spectra are repeatable.
 LIBS gives consistent/ reliable results in different regions.
 Coins have iron.
 Game token has no copper.
 20 cent Euro coin is nickel-free.
 We can distinguish between “different” currencies using LIBS.
 The spectra of the Saudi 10-Hallalah and the Bahrain 25 Fils
are very similar.
 At the macroscopic level, LIBS procedure can be NDT.

23. Good general references on LIBS
Also, check Applied Optics vol 42 (30), Oct. 2003 (theme issue)

24. 1. LIBS is a very useful technique for the elemental
analysis of material.
2. LIBS can be used for fast, precise, on-line, non-
destructive testing of coins.
3. LIBS can be beneficial for the identification of currency
and also for quality control in coins production.
4. LIBS applies to different types of material and is
conducive to interdisciplinary research, a concept very
beneficial for academic research in Saudi Arabia.
Concluding Remarks

25. the biomedical applications of LIBS can be
classified into two broad categories according to the ultimate goal of
the analysis.
These two categories are: (1) the use of LIBS as an elemental assay
and (2) the use of LIBS for the classification of an unknown target. In
the first category, the practitioner may use the LIBS elemental
spectrum to measure or quantify the concentration or change in
concentration of a specific element or elements present in a biomedical
specimen to diagnose, monitor, or predict a disease state. An example
of this is the use of the intensity of a specific calcium emission line to
discriminate healthy from carious dental tissue

26. In the second category, the LIBS elemental spectrum is used as a unique
‘‘signature’’ or ‘‘fingerprint’’ to rapidly classify the biomedical specimen
(perhaps using a precompiled library of reference specimens) to
diagnose, monitor, or predict a disease state. In this category of
applications, the absolute concentrations or quantities of specific
elements are unimportant for the diagnosis and are typically not
measured. An example of this is the use of LIBS spectra to discriminate
pathogenic from non-pathogenic bacteria (described in detail in Sect.
17.5.2 below). This concept of the two categories which utilize the LIBS
spectrum indifferent ways is shown in Fig. 17.1.

28. Analysis of Hard/Calcified Tissues
Calcified Tissues
Important diagnostic information can be obtained
from calcified tissues via the LIBS technique.
Assays of the observed elemental concentrations
can provide information about the tissue’s age, the
environmental conditions of its growth (perhaps
related to the patient’s geographic location), the
dietary influences of the person from which the
sample was obtained, and the accumulation of
potentially toxic elements [15].

30. Sample matrix
Morphology
Power [energy per pulse & pulse width] dependence
Atmosphere type and pressure
Shot to shot energy fluctuation
Depends on photon energy [esp. plasma absorption]
Complications in Using LIBS

31. Using nanosecond 1,064 nm laser pulses on a variety of removed and
cross-sectioned dental tissues, they were able to show that by using LIBS
to quantify and monitor changes in the concentrations of major elements
(such as Ca and Mg) and minor elements (such as Ag, Al, Ca, Cr, Hg, K,
Mg, Mn, Na, Ni, P, Sn, Ti, and Zn) at the level of a few tens of parts per
million in real-time, clinically relevant information can be obtained and
utilized as a feedback diagnostic by the dental practitioner. Particular
experimental emphasis was placed on two components of the tooth tissue
which made excellent LIBS targets: the surface enamel of the tooth,
which is the hardest substance in the body (composed
95%hydroxyapatite , 4 % water, and 1 % organic matter) and the dentine
which lies under the enamel (composed of 70 % hydroxyapatite, 20 %
organic matter, and 10 % water [

33. 0.00E+00
5.00E+03
1.00E+04
1.50E+04
2.00E+04
2.50E+04
3.00E+04
3.50E+04
200 250 300 350 400 450 500 550 600 650 700
Wavelength (nm)
Intensity
contemporer
y
new
kingdom
Ca
Pb
Mg
Mg
C
Fe Fe
Ca
Ca
Ca
Na
Na
Sr
Al
Mo
Ca
Ca Ca
Cu
Ca
Ca
Ca
Ca
Ca

34. 0.00E+00
5.00E+03
1.00E+04
1.50E+04
2.00E+04
2.50E+04
3.00E+04
3.50E+04
390 391 392 393 394 395 396 397 398 399 400
Wavelength (nm)
Intensity
contempo
rery
new
kingdom
Ca
Ca

35. 0.00E+00
5.00E+03
1.00E+04
1.50E+04
2.00E+04
2.50E+04
3.00E+04
3.50E+04
406 406.5 407 407.5 408 408.5 409 409.5 410
Wavelength (nm)
Intensity
recent
middl
e
Sr

36. From their results, that it is possible to establish a link
between elements detected in toothpastes, tooth fillings, and
other restorative compounds with those present in m the
tooth and also to relate the spatial distribution of such
elements to their migration and accumulation in the tooth due
to exposure to those dental materials.

37. In 2008 Thareja et al. using a 355 nm nanosecond LIBS system also
observed spectral changes consistent with the presence of caries tissue
[22]. They measured a dramatic variation in the relative concentrations
of Ca, Sr, and Na in carious tooth tissue relative to healthy tissue. This
variation was the result of calcium bound to the hydroxyapatite being
washed out of the caries tissues and being replaced by other elements.
The conclusion reached by these groups is that LIBS has the potential to
become a useful tool for in vivo/in vitro caries identification during a
drilling or cleaning process with a spatial resolution on the order of
100–200 lm and a depth resolution of approximately 10 lm[21].

38. In 2011 Singh and Rai reached the same conclusion and also
observed a decrease in the concentration of titanium (a
common additive to toothpaste in the form of TiO and a
common element in dental implant material) and an increase in
the concentration of Cu (absorbed during normal eating,
drinking, and breathing) in caries-affected tissues relative to
healthy dental tissue [23

39. Abdel-Salam et al. have shown that not only can the elemental
composition of a tooth be measured, but that enamel surface hardness
can be determined .By monitoring the ratio of CaII/CaI and MgII/MgI,
they were able to quantify elemental differences and thus classify
specimens of human tooth enamel obtained from two dynasties of
ancient Egyptians and from two populations of modern man.
As well, these authors investigated the dependence of the classification
on the use of a single-pulse or double-pulse LIBS technique and also on
the use of nanosecond versus picosecond laser pulse durations. In a
related study, Alvira et al. demonstrated that LIBS analysis of trace
elements in teeth can be an effective tool for use in anthropology and
paleontology by measuring strontium and magnesium
levels in dentin and enamel in tooth samples from Neolithic, middle age,
and modern Homo sapiens teeth .

40. Stones and Calculi
A calculus is a stone (a concretion of material, usually mineral
salts) that forms in an organ or duct of the body. The most
common stones are gallstones, urinary bladder stones, and
kidney stones [27]. Upon removal from the body, an elemental
analysis of a stone’s composition is often a first step in a
diagnosis of patient pathology [28]. It has even been suggested
that the analysis of urinary calculi can be helpful in providing
complementary information on human exposure to mercury.

41. Singh et al. demonstrated that the LIBS spectrum from 200 to 900 nm
obtained with nanosecond 532 nm pulses on surgically removed
gallstones could be used to classify the stones as cholesterol stones,
black pigment stones, or mixed stones [27, 28]. As well, they performed
a quantitative analysis of trace metal elements with results in agreement
with inductively coupled plasma atomic emission spectroscopy (ICP-
AES) measurements and recorded single-shot LIBS spectra from
different points on the cross section to study the variation of constituents
from the center to the surface. This is shown in Fig. 17.3. In a similar
study they measured the in situ elemental spatial distribution of kidney
stones and made a quantitative estimation of the concentrations of Cu,
Mg, Zn, and Sr in different
parts of the stones [37].

42. A spatial analysis of cholesterol stones was also
performed, demonstrating that the light elements, such as
hydrogen, carbon, and oxygen (which can be difficult for
other techniques such as XRF to detect), could be easily
detected by LIBS in these stones. They concluded that Cu
and Mg play important roles in the nucleation and
formation of the stones on the basis of their distribution
from the center to the surface. In a related study, these
authors used the atomic spectral lines and the observed
molecular bands (such as CN and C )to characterize the
different layers seen in the gallstones [38]

43. Fingernails
Hosseinimakarem et al. used 1,064 nm nanosecond pulses to obtain
LIBS spectra from removed cleaned nails [45]. The elements detected
in the emission spectra were Al, C, Ca, Fe, H, K, Mg, N, Na, O, Si, Sr,
and Ti, as well as CN molecular emission. Using a discriminate
function analysis (DFA), the authors were able to discriminate among
specimens from different genders and age groups. It was noted that the
number of samples in the study and their distribution was not sufficient
to generate a truly statistically significant analysis. Intriguingly, it was
observed that there was an agreement between elevated levels of
potassium and sodium in the fingernails (as determined by the LIBS
spectrum) and hyperthyroidism and high blood pressure as indicated by
self-reporting and also as measured in blood test results. This is
intriguing because a potassium deficiency is one of the symptoms of
hyperthyroidism and a high level of an element in the hair or innails
may indicate a depletion of that element in the body [45].

44. Analysis of Soft Tissues
Compared to the calcified tissues discussed in section two,
performing LIBS on soft tissues can involve significant
difficulties, not the least of which are a paucity of sample,
difficulty in obtaining well-defined representative tissue
cross-sections, the varying effect of tissue hydration
(depending on whether the tissue has been preserved or
not), and sample heterogeneity (in both the lateral and
depth dimension). Despite this, significant work has been
performed on a variety of soft tissues. In this section, the
studies of these tissues are organized into the categories of
organs, malignancies, and skin/hair.

45. Cancerous/Malignant Tissues
While the previous studies focused on the ability to identify or
discriminate presumably healthy tissues, a considerable amount of
work has been done to differentiate healthy tissues from
malignant or cancerous tissue. In the first such study, Kumar et al.
utilized a nanosecond 532 nm LIBS system to acquire spectra to
distinguish normal and malignant tumor cells in histological
sections of a canine hemangiosarcoma [55]. They observed that
the concentration of trace elements like Ca, Na, and Mg were
higher and the concentration of Cu was lower in malignant cells
relative to the normal cells. These results were confirmed with
inductively coupled plasma emission spectroscopy (ICPES).

46. In 2010 El–Hussein et al. investigated the use of LIBS for the
identification/ characterization of colorectal cancer and breast
cancer. By detecting a significant increase in the abundance of
calcium and magnesium in malignant tissues relative to the healthy
tissues, discrimination was observed in 41 specimens of breast
cancers of grade 2 and 3 (with various conditions of metastasis) and
32 specimens of colorectal cancers of grade 2 and 3 [59]. This is
shown in Fig. 17.5. These experiments were performed with a 532
nm nanosecond Nd:YAG system under vacuum (10 Torr) in a
specially designed vacuum chamber. In addition, the specimens
were frozen down to -196 C. An increase in both calcium and
magnesium was observed in atomic absorption spectrometry (AAS)
measurements of uterine cancer tissues, where a significant increase
in Ca concentration and an insignificant increase in Mg
concentration was observed when compared to nonneoplastic
uterine tissues. A significant increase in Mg and the Mg/Ca ratio was
reported in uterine myoma, confirming the observations of El-
Hussein et al. [60

47. Hair/Skin
In 2000 Sun et al. investigated the use of nanosecond LIBS with 1,064
nm laser light to analyze the concentration of trace elements in human
skin, specifically zinc in the stratum corneum [61]. As commented by
them (and references therein) trace elements in the skin, such as the
metals Mg, Zn, Ca, and Fe, play important roles in skin cell biology,
relating rates of cell turnover and cell metabolism, for example.
Concentrations of these trace metals are therefore biomarkers for overall
skin health. By applying zinc in solution prior to the removal of skin
specimens, they were able to efficiently track the absorption of the metal
as a function of depth through the skin to a depth of approximately 12–
18 lm. By testing the skin specimens on glass slides, they were able to
measure concentrations effectively to 0.3 ng/cm with a calibration curve
exhibiting good linearity up to 1,000 ng/cm
2
.

49. Analysis of Biomedical Specimens
Blood
To investigate this possibility, Melikechi et al. performed
preliminary tests on specimens of whole blood to determine the
resulting LIBS emission spectrum. Spectra in the region 200–970
nm were obtained from solid frozen mouse blood tested in a helium
environment with a nanosecond 1,064 nm LIBS system [63]. The
authors observed that nearly 90 % of the peaks below 300 nm were
due to carbon and iron alone, most likely due to iron’s large
number of UV emission lines and its important role in hemoglobin.
They also observed lines of Ca, Mg, Na, O, K, N, and H. No
attempt was made to quantify the concentrations of these elements
in the blood samples.

50. Analysis of Microorganisms Causing Human Disease
Significant research effort has been expended in the area of LIBS-
based pathogen identification. Pathogens are a loosely defined
group of microorganisms that can infect a human host including
bacteria, viruses, amoebae, and fungi. Because of their ubiquity
and their impact on human health, there is a wellrecognized need
for new diagnostic technologies that can rapidly identify
pathogenic bacteria without an a priori knowledge of nucleic acid
sequences (required for polymerase chain reaction (PCR)
techniques) or antibodies against known bacterial antigens (which
fluorescence immuno-assay techniques require). Numerous
research efforts have been initiated worldwide to investigate if the
speed and lack of sample preparation that a LIBS-based analysis
offers can fill this role.

51. Laser-Guided Surgery
One last medical application of LIBS remains to be covered, and
that is the use of the visible wavelength emission spectrum
produced during ablation as a real-time monitor of surgical
progress. Much as it has been suggested in Sect. 17.2.3 that the
differences in the LIBS spectrum from caries and healthy dental
tissue can provide a dentist with a way of monitoring tooth
drilling progress, it is believed that a similar optical feedback can
be used to guide the surgeon utilizing a laser scalpel or a
cardiologist performing laser angioplasty.