IR-Laser Welding and Ablation of Biotissue Stained with Metal Nanoparticles
aa r X i v : . [ phy s i c s . b i o - ph ] S e p IR-Laser Welding and Ablation of Biotissue Stainedwith Metal Nanoparticles
A. A. Lalayan, S. S. Israelyan
Centre of Strong Fields Physics, Yerevan State University, 1 A. Manukian, Yerevan0025, ArmeniaE-mail: [email protected]
Abstract.
In the present work we have studied the possibility of laser weldingand ablation of biological tissue by the using of spherical metal nanoparticles (NPs)and infrared laser irradiation which spectrally located far from plasmon resonances.YAG:Nd laser with 1064 nm wavelength, 8ns pulse duration, and operating intransverse electromagnetic modes TEM was used for the synthesis of metal NPs.The Au,Ti Ni and Cu as well as Au-Ag and Au-Cu hybrid metal NPs were formed inthe liquid medium. Effectiveness of laser ablation in the case of the biotissue samplethat stained with the metal NPs was approximately on 4-5 times larger than for thenative sample. Also the scheme of a laser point welding for the deep-located biotissuelayer selectively stained by the metal NPs has been demonstrated.PACS numbers: 79.20.Eb, 81.20.Vj, 78.67.Bf Keywords : nanoparticles, biotissue, laser, ablation, welding
R-Laser Welding and Ablation of Biotissue Stained with Metal Nanoparticles
1. Introduction
Nanoparticles (NPs) are homogeneous and composite materials with size in a rangeof 1-100 nm which exhibit some unexpected optical, electromagnetic, chemical andmechanical properties not inherent to bulk materials and atomic-molecular structuresdue to quantum confined nature of their energy levels and surface area to volume ratio.The unique properties of NPs depend on their size, morphology, composition, uniformity,and agglomeration. These extraordinary qualities make superior the application of NPsin nanophotonics, biomedicine, environment science, engineering etc [1]-[5]. Especially,in medical applications the NPs are able to pass through biological filters inside oforganism by that deliver drugs. Also, nanomaterials are used for protein detection,fluorescent biological labels, tumor destruction, tissue engineering etc. Various physicaland chemical processes are currently widely used for the production of NPs, neverthelesswe focus on the laser synthesis of colloidal spherical NPs by the laser ablation inliquid media [6]-[9]. This method favorably differs from other methods in its simplicity,efficiency, and it does not harm the environment. Also, by this method we can obtainnanoparticles of different sizes varying in the wide range and strongly depending on thedetails of experimental setup. In work the [6] we have reported on laser synthesis of GaAsand CdSe semiconductor NPs with picosecond Nd:YAG laser. The considerable blueshift of the photoluminescence was observed when picosecond laser beam with transverseelectromagnetic modes TEM structure has been used. Particle sizes was estimated (2-3 nm) from the spectral data and the bandwidth of the luminescence spectra of about 40nm reveals a narrow size distribution of the produced quantum dots which was achievedwithout any size selection methods. Such ultra fine sizes of NPs are excellently meetwith the requirements for medical applications. In recent years the use of nanoparticlesin biomedicine for the early detection, accurate diagnosis and treatment of cancer isextensively studied. Particularly, the possibilities for cancer photothermal therapy dueto tissue heating by using metal NPs have been successfully demonstrated [10, 11, 12].This method is based on localized surface plasmon resonance (LSPR), when nanoscalelocalization and amplification of electromagnetic fields occur in the vicinity of metalnanoparticles [13]. The locally amplified optical fields generate localized thermal energydue to the rapid conversion of photon energy into heat via electron–electron scatteringand electron–phonon coupling [14] in the wavelengths of the plasmon resonance [15]-[18].The plasmon resonances for gold and silver nanospheres are in the green-blue range ofthe visible spectrum, which can be red-shifted into the near infrared if nanoparticlesshape is modified to nanorods or nanoshels. This is more practical as biological tissuesare relatively transparent to near infrared light. However the strong tuning to plasmonresonance wavelength is required in medical applications of photoheating that in mostcases is not provided by commercial medical laser devises. R-Laser Welding and Ablation of Biotissue Stained with Metal Nanoparticles Figure 1.
Picture of chicken skin tissue sample stained with the metal NPs.
2. Experimental results
For syntheses of metal NPs in the considered experiment, the YAG:Nd laser with1064nm wavelength, 8 ps pulse duration, repetition rate of 10Hz and operating intransverse electromagnetic modes TEM was used. The same scheme of laser synthesisdescribed in the work [6] has been used. The laser beam was focused on the surfaceof a bulk metal target allocated in the glass cuvette with distilled water. Expositionof the laser irradiation was two hours. The Au, Ti, Ni and Cu, as well as Au-Ag andAu-Cu hybrid spherical metal NPs were formed in the liquid medium. Laser weldingand ablation of biotissue stained with the metal nanoparticles has been studied onsamples of chicken skin. Figure (1) shows typical photographical picture (taken byan optical microscope) of tissue stained with the metal NPs. In the present workwe have studied the possibility of tissue heating by using infrared laser irradiationat 1064 nm wavelengths. This wavelength is located far from plasmon resonances ofknown spherical metal NPs. Particularly, silver and gold nanoparticles exhibit strongplasmon resonance at wavelengths 405 nm and 520 nm correspondingly. The absorptionproperties of colloidal solutions of Ag, Au and Cu nanoparticles that were synthesizedby method of laser ablation in a liquid has been measured (see Figure (2)). Obtaineddata are consistent with the previous publications on plasmon resonances of widelyused Ag, Au spherical NPs with the sizes of about 50 nm. As we can see in Figure(2), the plasmon resonance of Cu nanoparticles in comparison with other consideredmetal NPs is located in the red range of the optical spectrum, however, its value israther smaller. The continuous wave YAG:Nd laser with an output beam of 3mmdiameter and power up to 4W was used for the biotissue welding and ablation. Twoareas of sample’s surface - unstained and stained with metal nanoparticles were ablatedat the same dose of the laser irradiation. Figure (3) shows the picture of skin surfaceafter ablation procedure. The surface of the area which has been exposed to laser R-Laser Welding and Ablation of Biotissue Stained with Metal Nanoparticles nm a b s o r b a n c e / a u AuAu-AgAu-CuCu
Figure 2.
Absorbance spectra of Au, Cu, Au-Ag and Au-Cu nanoparticles.
Figure 3.
Images of sample’s surface after laser ablation procedure. The left side ofthe picture represents non-colored area of the sample and the right side – the samplecolored with silver (Ag) nanoparticles. ablation in the case of the tissue sample that colored with silver NPs is approximatelyon 4-5 times larger than that for the sample with non-colored area. Furthermore, thesame result was obtained in case of several other metal nanoparticles with differentwavelength of plasmon resonances, as well as with Ni and Ti nanoparticles which doesnot exhibit any plasmon resonance properties. Thus, we observe significant differencein photodamage for biotissue samples which are unstained or stained with the metalnanoparticles. Such difference in absorption of infrared radiation may be explained bythe presence of the metal nanoparticles clusters in the tissue samples. Indeed, as wecan see in the Figure (1), the coloration of biotissue is highly nonhomogeneous and onecan observe the number of cluster centers colored in intense black. In the book [19]there are given experimental and numerical analysis of optical characteristics of fractalaggregates of nanoparticles. As it is shown, the absorption spectra for clusters with
R-Laser Welding and Ablation of Biotissue Stained with Metal Nanoparticles skin samplesnanoparticleslaser beam Figure 4.
Scheme of laser point welding of two skin samples colored with the silvernanoparticles. large amount of nanoparticles (500-10000) are shifted toward infrared range. This resultdemonstrates that the application of metal NPs in laser surgical procedures will lead tosignificant reduction of an irradiation dose even in cases when plasmonic resonance isabsent or the wavelength of laser radiation is far from it. Furthermore the application ofnanoparticles in laser surgery allows effectively use IR laser light that penetrates deeplyin the tissue and absorbed poorly by the native tissue itself. However, this radiation maybe absorbed strongly by the nanoparticles aggregates. This advantage can be used fordevelopment of the schemes of laser welding for deep-located biotissue areas selectivelycolored by the metal NPs. For example, we performed the point welding of two chickenskin samples with thickness of 2 mm each (see Figure (4)). The surfaces of the sampleswere colored with the silver nanoparticles. The laser radiation penetrates through thefirst sample from the noncolored side without production of the visible damages oftissue and reaches the contacting area of samples that contain nanoparticles. In thiscase we observe the strong absorption of light in the area of biotissue colored with thenanoparticles and, subsequently, the local heating of the tissue. In the result, the localspot welding of two layers of the skin tissue was realized. Note that in case of theusing of radiations of 405 nm or 520 nm wavelengths which are in the range of Agand Au plasmon resonances, we would have strong absorbance by the tissue of 2 mmthickness, which will lead to the photodamage of the superficial layers. Furthermore,the application of Ag nanoparticles that exhibit strong microbicidal effect may lead tosignificant improvement of the postsurgical healing of the patients. It is also importantas tissue photoheating could cause inflammatory process due to local antimicrobialimmune resistance reduction, and this negative effect could be also minimized.
R-Laser Welding and Ablation of Biotissue Stained with Metal Nanoparticles
3. Acknowledgments
We would like to thank Prof. H. K. Avetissian for valuable discussions. This work wassupported by State Committee of Science of RA.
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