Detection of carcinogenic metals in kidney stones using ultraviolet laser-induced breakdown spectroscopy Ahmed Asaad I. Khalil,1,2 Mohammed A. Gondal,3,* Mohamed Shemis,3 and Irfan S. Khan4 1

Department of Laser Sciences and Interactions, National Institute of Laser Enhanced Sciences (NILES), Cairo University, Giza 12613, Egypt

2

Physics Department, Faculty of Science for Girls, University of Dammam 31441, Saudi Arabia

3

Laser Research Group, Physics Department, King Fahd University of Petroleum and Minerals, Box 5047, Dhahran 31261, Saudi Arabia 4

King Fahd Specialist Hospital, Dammam 31444, Saudi Arabia *Corresponding author: [email protected]

Received 15 January 2015; revised 30 January 2015; accepted 30 January 2015; posted 2 February 2015 (Doc. ID 232604); published 10 March 2015

The UV single-pulsed (SP) laser-induced breakdown spectroscopy (LIBS) system was developed to detect the carcinogenic metals in human kidney stones extracted through the surgical operation. A neodymium yttrium aluminium garnet laser operating at 266 nm wavelength and 20 Hz repetition rate along with a spectrometer interfaced with an intensified CCD (ICCD) was applied for spectral analysis of kidney stones. The ICCD camera shutter was synchronized with the laser-trigger pulse and the effect of laser energy and delay time on LIBS signal intensity was investigated. The experimental parameters were optimized to obtain the LIBS plasma in local thermodynamic equilibrium. Laser energy was varied from 25 to 50 mJ in order to enhance the LIBS signal intensity and attain the best signal to noise ratio. The parametric dependence studies were important to improve the limit of detection of trace amounts of toxic elements present inside stones. The carcinogenic metals detected in kidney stones were chromium, cadmium, lead, zinc, phosphate, and vanadium. The results achieved from LIBS system were also compared with the inductively coupled plasma–mass spectrometry analysis and the concentration detected with both techniques was in very good agreement. The plasma parameters (electron temperature and density) for SP–LIBS system were also studied and their dependence on incident laser energy and delay time was investigated as well. © 2015 Optical Society of America OCIS codes: (300.6365) Spectroscopy, laser induced breakdown; (140.3440) Laser-induced breakdown. http://dx.doi.org/10.1364/AO.54.002123

1. Introduction

Development of new devices and instrumentation to study the biomaterials is highly interesting for biochemists and the medicine community. Many 1559-128X/15/082123-09$15.00/0 © 2015 Optical Society of America

analytical techniques such as single–pulse (SP) laser-induced breakdown spectroscopy (LIBS), atomic absorption spectroscopy (AAS), inductively coupled plasma (ICP)–atomic emission spectroscopy (AES) [1], laser ablation (LA)-ICP-mass spectroscopy (MS), optical emission spectrometry (OES), infrared spectroscopy (IR) [2], and X-ray fluorescence (XRF) [3] have been applied for elemental analysis of 10 March 2015 / Vol. 54, No. 8 / APPLIED OPTICS

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bio-materials. All of these techniques are based on the emission of electromagnetic radiations generated after de-excitation of ions, atoms, and molecules in these samples. However, there are certain disadvantages of wet chemical analysis which consume large amount of samples and chemicals. There is a major difficulty in calibration of an LA–ICP–MS/OES) system, where matrix effect and the transfer of the dry aerosol are formed in the ICP analysis by the buffer gas [4,5]. Many solutions have been suggested to overcome this problem by using the LA–ICP system [6]. The SP–LIBS technique is a well-known analytical technique that is remote, in situ, rapid, and with no or minimum sample preparation [7]. Pasquini et al. [8] discussed the basics of SP–LIBS technique. In addition, calibration-free SP–LIBS spectra was discussed by Tognoni et al. [9], which was established on the basis of recording of the line intensities, electron temperature, electron number density, and Boltzmann population distribution of excited levels. Recently, SP–LIBS has been applied for fast elemental analysis of pollutants present in the aerosol, solid, and liquid samples [10–13]. The analysis and detection of trace amounts of heavy and toxic metals in kidney stones is highly significant as their presence can affect the human health. In our case, SP–LIBS technique was applied for detection and quantification of toxic elements present in the kidney stones to solve the urolithiasis prevalence problems. The location of kidney stones in human body may be in the ureteral, kidney/renal, or bladder regions. The patient could be treated by drugs after removal of kidney stones by surgery or shock wave lithotripsy and then the stones could be analyzed to know the trace metal presence [14,15]. Recently SP–LIBS technique has been applied in different biomedical disciplines, clinical analysis, and is more suitable to the other conventional techniques [16]. The main advantages of SP–LIBS technique are no sample preparation, very little amount (micrograms) of sample requirement, excellent for online analysis, and it is a rapid and real-time analytical technique. The kidney stone contains about 55% calcium oxalate (CaC2 O4 · H2 O) and sometimes it is called calcium oxalate stones and other types contain about 15–25% uric acid (C5 H4 N4 O3 ) or magnesium ammonium phosphate cysteine stones contain (MgNH4 PO4·6 H2 O); (C6 H12 N2 O4 S2 ) [17]. The concentration of elements (Zn, Ca, Cr, P, Cd, and Pb) in renal calculus have been determined so far by various techniques [18,19]. SP–LIBS technique is much superior technique as compared with the other techniques such as LA– ICP–MS, XRF, ICP–AES, and AAS to study the kidney stones. By optimizing the SP–LIBS detection system, the electron number density (N e ) and excitation temperature (T e ) could be measured which are essential parameters in understanding the physical and chemical processes such as ionization, excitation, and chemical reactions in these complex spectroscopic sources [20]. The T e and N e are 2124

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dependent on laser parameters, target material, and ambient conditions. The plasma produced by laser is assumed to be in local thermodynamic equilibrium (LTE) where T e controls the population distribution in the excited state (upper energy level) through the Boltzmann equation and the ionization equilibrium through the Saha equation, respectively [21]. To detect and quantify elements using spectral line intensities in LIBS, the laser-induced plasma should be optically thin and in LTE. The plasma formed by a pulsed laser ablation which is transient process, LTE is achieved if the electron–atom and electron–ion collision processes are extremely rapid and dominate the radiative processes [22]. In this work, we applied the SP–LIBS technique using intense laser pulses having UV wavelength to ablate the kidney stone sample and to generate plasma spark which emits characteristic electromagnetic waves that helps to identify the plasma species and also to calculate the concentrations of different substances present inside the kidney stones. The accumulation of certain toxic elements by kidneys result harmful disease and disorder of kidneys. The data generated through this work could shed light regarding the factors responsible for the formation of these stones in the human body. A highresolution spectrometer and a high-sensitivity intensified CCD (ICCD) camera were installed to analyze the collected plasma emission. In addition in our setup, we investigated the temporal behavior of T e and N e for plasma produced under atmospheric conditions through laser ablation of kidney stone samples to understand the behavior of this plasma. This information is important to design models for plasma processes to calculate the energy transport in plasma which is related to the temporal behavior and to enhance the sensitivity of SP–LIBS system. This work is significant to create awareness for better human health. 2. Experimental Setup A. Sample Preparation

Three kidney stones of different dimensions were surgically picked up from the patients at King Fahd Specialist Hospital, in Dammam, Kingdom of Saudi Arabia. Stones No. 1–3 were extracted from male patients 24, 35, and 50 years old, respectively, and are depicted in Fig. 1. These samples were carefully cleaned with deionized water to remove the blood clots, contaminants, and uric acid, and then kept after drying in sealed tubes for LIBS investigations. We used a special knife to cut the stones into halves and irradiate them by focusing the laser beam on various locations of kidney stones, starting from the center to the shell and ending on stone surface. Small amounts from each previous location in stones were carefully extracted to be analyzed by an ICP– MS system. The calibration curves between the analyte concentration in the kidney stone matrix and its SP–LIBS signal lines intensity were carefully

Stone #1

Stone #2

Stone #3 Fig. 1. Pictorial view of the Stones No. 1–3 samples which were extracted from male patients 24, 35, and 50 years old, respectively.

plotted for estimation of the limit of detection of our LIBS system. In this work, the 5; 000 μg∕mL solution of Ca, Zn, Mg, Na, Cr, Cd, Pb, and Cu was used to prepare standard samples of known concentrations in double-distilled water. The standard solutions were having concentrations varying from 50 to 5,000 ppm for Ca, Zn, Mg, Na, Cr, and Cu by weight. These solutions with known concentration were utilized, and the wet paste was dried in the oven at 350 K during 1 day for preparation of standard samples to draw the calibration curves. B.

SP–LIBS System

A Q-switched neodymium yttrium aluminium garnet (Nd:YAG) laser source (Spectra Physics, Model GCR100) of 266 nm wavelength was employed with 50 mJ maximum laser energy, 8 ns pulse width, and 20 Hz repetition rate. The more details of our LIBS system are described in [10]. The laser radiations were focused onto a certain location on the kidney stone to produce the plasma plume, using an optical quartz convex lens of small focal length (f  20 mm). The test sample was fixed on a holder which was moved by using computer-controlled xy–translator to minimize the development of any crust on the stone sample and to avoid the drop in LIBS signal intensity. The light emitted by the plasma plume was collected by a miniature lens fixed inside the head of multimode silica fiber optic. This fiber optic was located

at a suitable distance relative to the laser generated plasma plume. The plasma emission was collected at 45° angle as an optimum angle relative to the stone. The plasma emission was transmitted through fiber optics to a high-resolution spectrometer (Andor SR 500 i-A, grating with groove density  1200 line∕mm), which was interfaced to a synchronized ICCD (Synch. ICCD camera, Model Andor-50SI) with laser pulses for sensitive detection. Programmable software built in the spectrometer was utilized to record the optical emission spectrum, analyze the data from the chip, and electronically control the laser pulse delay (the time between the laser pulse and the opening of camera shutter  200 ns) and the gate width (the shutter opening time). Such parameters like 100 μm slit width, 40 μs gate width, 10 numbers of accumulations, and 5 s exposure times were optimized to achieve the best signal to noise ratio. A calibrated energy meter (Ophir Model 300) was applied to measure the laser energy/pulse in order to study the LIBS spectral intensity versus the laser fluence. 3. Results and Discussion A. Optical Spectroscopy

For the characterization of the laser-producedplasma, we measured the spectral lines under different laser fluencies by scanning the spectrometer in the 200–900 nm region and after optimization of 10 March 2015 / Vol. 54, No. 8 / APPLIED OPTICS

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4000 3000 2000

Cr I 410.95 nm

5000

1000

Cr I 428.9 nm

6000 Ca II 369.4 nm Ca II 370.6 nm

LIBS signal (a.u.)

7000

Ca I 422 nm

Ca II 393.36 nm

(a) 8000

Ca II 396 nm

all parameters like focusing of incident laser beam, optimum collection of plasma emission, gate width, and delay time. After achieving the optimal experimental conditions, the SP–LIBS spectra were recorded. Figs. 2(a)–2(c) depicts different chemical elements present in the kidney stone sample in the 360–440, 620–700, and 720–800 nm wavelength regions. The identification of the atomic transition lines was carried out using the NIST spectral database [23]. As clear from Figs. 2(a)–2(c), the carcinogenic metals such as chromium (Cr), lead (Pb), and cadmium (Cd) were detected along with trace metals like calcium (Ca), phosphorus (P), zinc (Zn), nickel (Ni), and vanadium (V). The spectral marker lines of these elements were used for the calibration and quantifications of these elements. This identified spectrum is due to emission of the neutral or singly ionized transitions of calcium, chromium, potassium (K), zinc, phosphorus, lead, cadmium, and vanadium.

370

380

390

400

410

420

430

440

Ca I 644.9 nm

200

Cd II 672.58 nm

300

Pb II 666.02 nm

400

P I 649.6 nm

Cd II 635.47 nm

500

V I 624.5 nm

LIBS signal (a.u.)

600

Ca III 642.5 nm

Wavelength (nm)

(b) 700

B. Optimization of LIBS Parameters for High-Sensitivity Detection

Generally, in an LIBS spectrum, the atomic lines and broadened ionic lines emissions are superimposed on the continuum. The continuum is due to elastic collisions of the ionic particles with negative electrons and plasma blackbody radiation [24]. Therefore we have to optimize the delay time between the laser trigger pulse and acquisition of the SP–LIBS spectrum to avoid the continuum emission and for reduction of the background noise and enhancing the LIBS emission line intensity. In our work, the SP–LIBS spectral line intensities of 422 nm [Ca(I)] were recorded at various delay times (10–1000 ns) as depicted in Fig. 3. The SP–LIBS intensity increases until the maximum value is reached at 500 ns delay time and subsequently drops. Therefore the optimum delay time was selected to be 500 ns. The optimized delay time basically depends on the transition probability and the lifetime of the upper level of the analytical spectral line [24]. Hence each element has certain temporal evolution behavior of LIBS signal intensity. C. Effect of Incident Laser Fluence on LIBS Signal Intensity

0 360

The presence of Ca and P atomic lines in the spectra proves our prediction of the existence of calcium and phosphate as one of the constituents in the kidney stones as mentioned previously in the Introduction.

The dependence of SP–LIBS signal intensity of neutral Ca spectral line (422 nm) on the laser fluence (J∕cm2 ) at a fixed 500 ns delay time was studied and is depicted in Fig. 4. It can be seen that the SP–LIBS intensity increases almost linearly with the rise in incident laser fluence. This is due to the increase in the amount of ablated material from the sample and also the rise in the plasma temperature. At higher laser fluence, more than 24 J∕cm2 , the SP–LIBS emission intensity attains saturation.

100

6000

0

300 200 100

700

4000 3000 2000 1000 0

0 720

740

760

780

800

Wavelength, nm

Fig. 2. SP–LIBS spectra showing different chemical elements present in the kidney stone sample in the 360–440, 620–700, and 720–800 nm wavelength regions. 2126

5000

Intensity (a. u.)

400

Pb I 722.8 nm

500

680

K I 766.9 nm

600

Zn II 758.89 nm

700

660 Wavelength (nm) Zn II 747.87 nm

800

640

Ca I 732.6 nm

(c) Intensity, arbitrary unit

620

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0

100

200

300

400

500

600

700

800

Delay time (ns) Fig. 3. LIBS signal intensity dependence on delay time between the laser excitation and the shutter opening of the ICCD detection system.

16000

2

5000

4000

3000

2000

ln (Iλ/Ag )

Electron Temperature (K)

Intensity (arb. units)

0

14000

12000

-2 -4 -6 0

10

20

30

40

50

E (eV)

10000 Stone # 1

8000

Stone # 2

1000

Stone # 3

6000 14

16

18

20

22

24

0

26

1

2

By knowing the plasma parameters such as T e and N e , one could determine whether a LTE assumption is valid or not by applying McWhriter criterion [23]. In order to calibrate our SP–LIBS spectrometer, the laser-induced plasma should be optically thin. If the distribution of free electrons in the plasma is Maxwellian, then the created plasma will be in LTE regime. The electron velocity distribution (EVD) of comparatively low-temperature dense plasma (N e > 1016 cm−3 , kT < 5.5 eV) is roughly considered as a Maxwellian [25,26]. In addition the excitation, collision, and de-excitation processes should govern the plasma conditions. In this work, we used the Boltzmann plot and Stark broadening to determine the T e and N e , respectively. In this context, the populations of the upper excited levels pursue a Boltzmann distribution, and their relative emissivity (εjk ) might be defined as [27]

6

(1)

where λjk , εjk , gj , and Ajk are the wavelength, relative emissivity, the statistical weight. and the transition probability, for the excited state, respectively; Ej is the upper state energy; T e is the excitation temperature; h and k are the Planck and Boltzmann constants, respectively; QT is the partition function; and NT is the ion number density. All these parameters of Ca lines are listed in Table 1 as reported in NIST atomic spectra database [23]. The T e for the

17

10

5000

Intensity (arb. units)

Electron Excitation Temperature Measurement

    λjk εjk Ej NT ; −  ln Ajk gj kT exc QT

5

three kidney stones was estimated from the slope λ ε of the line drawn by plotting lnAjkjk gjkj  against the energy of the upper state (Ej ) [from Eq. (1)]. The inset in Fig. 5 depicts the typical Boltzmann plots for three different kidney stones using Ca(I) spectral line on which data were properly matched with the leastsquares fit approximation and T e of 12; 500  450 K was calculated from the slope of the plotted curve. The regression was lying between 0.976 and 0.985 for three different kidney stones indicating that the selected lines are sensitive to plasma temperature. Figure 5 depicts the temporal evolution of the T e at different delays of the plasma generated by 266 nm laser irradiation at ambient air conditions. As clear from Fig. 5, the plasma temperature is higher initially and decreases rapidly with the delay time. A peak in the excitation temperature can be noticed at the early times. The excitation temperature varies from 15,200 to 6000 K in the delay time

-3

This saturation may result from the plasma shielding [24]. Inverse Bremsstrahlung is the most prominent mechanism that could be responsible for absorption of high laser fluence (24 J∕cm2 ) by free electrons in the plasma. At lower values of plasma temperature; the absorption of laser radiations by plasma increases and leads to less ablated stone material and hence reduces the density of the ionic species [24].

ln

4

Fig. 5. Temporal evolution of plasma temperature (T e ) for three different kidney stones. Inset, Boltzmann plot to estimate the plasma temperature of the kidney stone plasma.

Electron Density (cm )

Fig. 4. LIBS signal intensity dependence on incident laser fluence imparted on the sample surface.

D.

3

Delay time (μs)

Laser Fluence (J/cm2 )

16

Ca I 422 nm Lorentz Profile

4000 3000 2000 1000 0 422

10

424

426

428

430

Wavelength (nm)

Stone # 1 Stone # 2 Stone # 3

0

2

4

6

8

10

Delay time (μs) Fig. 6. Temporal evolution of electron density (N e ) for three different kidney stones. Inset, Stark broadening profile of the atomic transition line of Ca(I) at 422 nm used to estimate the electron density. Solid points represent the experimental data and the smooth curves are the Lorenzian fits. 10 March 2015 / Vol. 54, No. 8 / APPLIED OPTICS

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2.00

1.25

Center

1.00

Shell

0.75

Surface

Cr (428.9)/Ca (732.6)

Cd (672.58)/Ca (732.6)

1.50

1.75 Center

1.50

Shell

Surface

1.25

Stone # 3

Stone # 3 1.00

0.50 0

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Delay time ( μs)

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1.4 Center

0.75 Shell

Surface

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Stone # 2

Cr (428.9)/Ca (732.6)

Cd (672.58)/Ca (732.6)

4

Delay time ( μs)

1.00

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Shell

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Stone # 2

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Delay time ( μs)

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Stone # 1 0.50 Center

Shell

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Cr (428.9)/Ca (732.6)

Cd (672.58)/Ca (732.6)

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0.75 Shell Surface

0.50

Surface

0.25

0.00 0

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4

0

6

Delay time ( μs)

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Delay time ( μs)

Fig. 7. LIBS signal intensity ratio for atomic lines of Cd(II) 672.58 nm/Ca(I) 732.6 nm and Cr(I) 428.9 nm/Ca(I) 732.6 nm ratios versus the delay time at the surface, shell, and center of the three different stones samples.

(0–10 μs) range for the third stone, and from 13,800 to 6150 K for the second stone, and from 13,000 to 8000 K for the first stone. E.

Electron Density Measurements

The N e can be estimated from [28,29]     Ne N e 1∕4  3.5A Δλ1∕2 A  2ω 1016 1016     3 −1∕3 Ne × x 1 − ND ω ; 4 1016

(2)

where A is the ion-broadening parameter, ω is the theoretical Stark width parameter for neutral atoms, and N D is the sum of particles in a Debye sphere. 2128

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Terms A and ω have weak dependence on temperature [30]. Hence the second part of Eq. (2) can be neglected and Eq. (2) leads to   Ne ; (3) ΔλFWHM A  2ω 1016 where ΔλFWHM (nm) is the full-width at halfmaximum (FWHM) observed for neutral Zn, Ca, K, Cr, P, Pb, and Cd lines. The recorded line shapes were fitted correctly by deducting the instrumental width as follows Δλtrue  Δλobserved − Δλinstrument ;

(4)

where Δλtrue , Δλobserved , and Δλinstrument are the true spectral line width, the observed spectral line width

Zn II 747.87 nm

500

y= 0.039 + 0.023 x

400

Slope = 0.023

600

SP-LIBS signal (a.u.)

SP-LIBS signal (a.u.)

600

2

R = 0.991

300 200 100 0

Ca I 644.9 nm

500

y = 0.045 + 0.067 x

400

Slope = 0.067

300

R = 0.980

2

200 100 0

0

200

400

600

800

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1000

1600

Cr I 428.9 nm

1400

y= 0.098 + 0.0014 x

1200

Slope = 0.0014

1000

R = 0.986

2

800 600 400 200 0 0

1000

2000

3000

4000

450 400 350 300 250 200 150 100 50 0

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1000

2

R = 0.967

Slope = 0.209 2

R = 0.994

100 50

200

400

600

800

1000

Phosphorus concentration (ppm)

SP-LIBS signal (a.u.)

SP-LIBS signal (a.u.)

800

Slope = 0.0087

120

y= 2.27+0.209 x

150

600

P I 649.6 nm

0

Cd II 672.58 nm

200

400

y = 0.0507 + 0.0087 x

Chromium concentration (ppm) 250

200

Calcium concentration (ppm)

SP-LIBS signal (a.u.)

SP-LIBS signal (a.u.)

Zinc concentration (ppm)

Pb II 666.02 nm

100

y= 0.032+0.115 x Slope = 0.115

80

2

R = 0.982

60 40 20 0

0 0

200

400

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800

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0

200

400

600

800

1000

Lead concentration (ppm)

Cadmium concentration (ppm)

Fig. 8. Calibration curves for the detection of zinc, calcium, chromium, phosphorus, cadmium, and lead using ionic and atomic transition lines at 747.87 nm [Zn(II)], 644.9 nm [Ca(I)], 428.9 nm [Cr(I)], 649.6 nm [P(I)], 672.58 nm [Cd(II)], and 666.02 nm [Pb(I)], respectively, as the marker lines.

of Ca I (422 nm) and the instrumental spectral line width, respectively. The corresponding relative error is approximately 10%. The spectral line width of Ca I (422 nm) was numerically fitted by a Lorentzian profile as shown in the inset of Fig. 6. Figure 6 depicts the temporal trend of the N e for the plasma generated by 266 nm laser. The electron density is high during the initial stages of the plasma and then decreases rapidly. Therefore, the N e ranges from 6.8 × 1016 to 3.2 × 1015 cm−3 in the delay time (0–10 μs range) for the third stone, and from 3 × 1016 to 2.5 × 1015 cm−3 for the second stone, and from 1.9 × 1016 to 2.3 × 1015 cm−3 for the first stone in the same delay time range for the plasma generated by the UV laser. It is worth mentioning that the values of N e for third stone are higher than those obtained for the first and second stone. The error bars lead to the standard deviation for 10 LIBS signals accumulated during the recording of each spectrum. The T e and N e trend observed in this work is in good agreement with the

trend noticed in [30,31]. Figure 7 depicts the LIBS signal intensity ratio for atomic lines Cd(II) 672.58 nm/Ca(I) 732.6 nm and Cr(I) 428.9 nm/Ca (I) 732.6 nm ratios versus the delay time at the surface, shell, and center of the three different stones. The experimental results depict that the LIBS signal intensity of atomic lines ratios Cd(II)/Ca(I) and Cr(I)/ Ca(I) at longer delay time from 3 to 10 μs for three different stones has approximately similar trend. The measured intensity ratios were found within the optical thin limit with acceptable error bars as a function of delay time. It was observed that the error bars of the intensity ratio are reduced by increasing the number of laser pulses, and the best ratio was achieved at accumulation of 30 laser pulses as depicted in Fig. 7. F.

Determination of Toxic Elements Concentration

Figure 8 depicts the calibration curves and the intensities of the atomic transition lines of 747.87 nm [Zn 10 March 2015 / Vol. 54, No. 8 / APPLIED OPTICS

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Table 1.

List of Elements Detected in Kidney Stones Collected from Local Saudi Hospital and Comparison of LIBS with a Standard Conventional Technique (i.e., ICP)

Host of Toxic Materials Sample 1 2 3

Kidney Stones First stone Second stone Third stone

Calcium (ppm)

Zinc (ppm)

Chromium (ppm)

Lead (ppm)

LIBS

ICP

LIBS

ICP

LIBS

ICP

LIBS

ICP

LIBS

ICP

5625 11,250 6000

5776 11,450 6068

3.003 6.789 2.874

3.340 7.378 3.013

0.009 0.018 0.015

0.012 0.297 0.028

0.0368 0.489 0.314

0.429 0.531 0.386

0.051 0.179 0.082

0.067 0.292 0.099

(II)], 644.9 nm [Ca(I)], 428.9 nm [Cr(I)], 649.6 nm [P (I)], 672.58 nm [Cd(II)], and 666.02 nm [Pb(I)] were used as a marker wavelengths. The concentrations measured in three kidney stone samples after drawing the calibration curve were in the 10–19 ppm range. It is worth mentioning that these values are higher than the permissible safe limits specified by the International Environmental Agency [32–34]. In addition, the measured concentrations by our SP—LIBS system were counter verified by using a standard method such as ICP spectrometry. Our LIBS results are in good agreement with the results obtained using ICP–MS technique. Therefore the SP–LIBS system could be applied for in situ rapid analysis of carcinogenic traces in kidney stones to know the reason of its accumulation in the kidney. The recorded LIBS spectra in this work were wellidentified to the line wavelengths of 747.87 nm [Zn (II)], 644.9 nm [Ca(I)], 428.9 nm [Cr(I)], 649.6 nm [P(I)], 672.58 nm [Cd(II)], and 666.02 nm [Pb(I)] using NIST data base [23]. Emission intensities corresponding to the lines 428.9, 747.87, 644.9, and 649.6 nm for each stone were registered and a straight line calibration curve was established by drawing the emission intensity in arbitrary units versus zinc, calcium, chromium, phosphorus, cadmium, and lead concentration in part per million which are depicted in Fig. 8. The recorded concentrations for each sample were compared with the results obtained with ICP–MS and are presented in Table 1. The recorded values obtained by each technique (LIBS and ICP–MS), indicated clearly that concentration of each [Zn(II)], [Ca(I)], [Cr(I)], [P(I)], [Cd (II)], and [Pb(I)] present in the kidney stones is above the acceptable permissible limit of 1 ppm [32]. 4. Conclusions

A study of the kidney stones using self-developed LIBS spectrometer and Nd:YAG laser pulses at 266 nm was carried out. The dependence of LIBS signal intensity on incident laser energy, delay time, and other plasma parameters was investigated. Our LIBS spectrometer was tested to measure the trace amounts of toxic metals present in human kidney stones extracted via surgical operation. The atomic marker lines were identified by using the NIST database. Our optimized SP–LIBS system with very low limit of detection was able to detect trace amounts of Zn, Ca, Cr, P, Cd, and Pb concentration in 10–19 ppm range. The LIBS signal intensities relating to the atomic transition lines of 747.87 nm [Zn(II)], 644.9 nm [Ca(I)], 428.9 nm [Cr(I)], 2130

Cadmium (ppm)

APPLIED OPTICS / Vol. 54, No. 8 / 10 March 2015

649.6 nm [P(I)], 672.58 nm [Cd(II)], and 666.02 nm [Pb(I)] were used to determine the carcinogenic metal concentrations in the kidney stones. The detected concentrations using SP–LIBS of the kidney stones were verified using ICP–MS spectroscopy standard method and both the data (LIBS and ICP) were in good agreement. This work obviously elucidates that SP–LIBS can be utilized very easily for the rapid analysis of kidney stones for detection of carcinogenic metals. The data measured by each technique (LIBS and ICP–MS) clearly indicate that the concentration of each element like Zn(II), Ca (I), Cr(I), P(I), Cd(II), and Pb(I) present in kidney stones is above the acceptable safe permissible limit set by international regulatory bodies like the U.S. Environmental Protection Agency (EPA), U.S. Food and Drug Administration (FDA), and so on. This work was supported under Project No. 2014101 by the Deanship of Scientific Research (DSR), University of Dammam (UOD), Saudi Arabia. The support provided by the Physics Department of King Fahd University of Petroleum and Minerals (KFUPM), Dhahran, is also acknowledged. References 1. V. K. Singh, A. K. Rai, P. K. Rai, and P. K. Jindal, “Cross-sectional study of kidney stones by laser-induced breakdown spectroscopy,” Lasers Med. Sci. 24, 749–759 (2009). 2. E. Takasaki, “An observation on the analysis of urinary calculi by infrared spectroscopy,” Calcified Tissue Research 7, 232–240 (1971). 3. M. Volmer, J. C. M. De Vries, and H. M. J. Goldschmidt, “Infrared analysis of urinary calculi by a single reflection accessory and a neural network interpretation algorithm,” Clin. Chem. 47, 1287–1296 (2001). 4. R. Thomas, Practical Guide to ICP–MS (Marcel Dekker, 2004). 5. M. Hola, V. Konecna, P. Mikuska, J. Kaiser, and V. Kanicky, “Influence of physical properties and chemical composition of sample on formation of aerosol particles generated by nanosecond laser ablation at 213 nm,” Spectrochem. Acta B 65, 51–60 (2010). 6. R. E. Russo, X. Mao, H. Liu, J. Gonzalez, and S. S. Mao, “Laser ablation in analytical chemistry: a review,” Talanta 57, 425–451 (2002). 7. D. A. Cremers, F. Y. Yueh, J. P. Singh, and H. Zhang, Laser Induced Breakdown Spectroscopy, Elemental Analysis (Wiley, 2000). 8. C. Pasquini, J. Cortez, L. M. C. Silava, and F. B. Gonzaga, “Laser induced breakdown spectroscopy,” J. Braz. Chem. Soc. 18, 463–512 (2007). 9. E. Tognoni, G. Cristoforetti, S. Legnaioli, and V. Palleschi, “Calibration-free laser-induced breakdown spectroscopy: state of the art,” Spectrochem. Acta B 65, 1–14 (2010). 10. A. A. I. Khalil, M. A. Gondal, and M. Dastageer, “Detection of trace elements in non-degradable organic spent clay waste using optimized dual-pulsed laser induced breakdown spectrometer,” Appl. Opt. 53, 1709–1717 (2014).

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10 March 2015 / Vol. 54, No. 8 / APPLIED OPTICS

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Detection of carcinogenic metals in kidney stones using ultraviolet laser-induced breakdown spectroscopy.

The UV single-pulsed (SP) laser-induced breakdown spectroscopy (LIBS) system was developed to detect the carcinogenic metals in human kidney stones ex...
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