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MEDICAL PHYSICS IN <strong>THE</strong> BALTIC STATES 7 (2009) Proceedings of International Conference “Medical Physics 2009” 8 - 10 October 2009, Kaunas, Lithuania INVESTIGATIONS <strong>OF</strong> SILVER NANOPARTICLES FOR UV PERSONAL DOSIMETERS Judita PUIŠO* , **, Asta Guobienė* , ***, Igoris PROSYČEVAS** *Department of Physics, Kaunas University of Technology, Studentų g. 50, LT - 51368, Kaunas, Lithuania ** Institute of Physical Electronics, Kaunas University of Technology Savanorių pr. 271, LT-50131, Kaunas, Lithuania *** International Studies Centre, Kaunas University of Technology, Mickevičiaus g. 37, LT - 44244, Kaunas, Lithuania Abstract People are exposed to natural or artificial UV radiation in different ways; unintentionally or intentionally, as at their workplace or on their spare time. The effects of UV on health can be harmful – as in its effect on skin cancer rates, or beneficial – as in the case of its effect on vitamin D status. A personal dosimetry is necessary in order to quantify the amount of individual UV exposure. Silver nanocomposites layers as possible personal UV dosimeters were investigated. Silver nanocomposites layers were fabricated using spin coating and UV irradiation on glass substrate. Ag/PVP nanocomposites were investigated by UV-VIS and AFM. Keywords: Silver, nanoparticles, PVP, UV irradiation, UV-VIS, AFM 1. Introduction People are exposed to natural or artificial UV radiation in different ways; unintentionally or intentionally, at their workplace on their spare time. UV radiation contributes to the aging of the skin and, in different ways, to the generation of skin cancers [1-5]. Primarily because of behavioral changes resulting in higher UVexposure of the skin to UV the incidence rates of skin cancer have increased dramatically in many industrialized countries with a larger Caucasian population. Currently, for example, the annual incidence rate for basalioma and squamous cell carcinoma in Germany is about 70 per 100,000 population (it was 15 in 1970) and for melanoma 14 per 100,000 citizens (3 in 1970). The corresponding data for melanoma currently is 19 cases per 100,000 citizens in USA. The risk for melanoma in the USA was about six times lower in 1960s. Part of the increase in incidences of skin cancers certainly can be ascribed to a longer life expectancy and also to a higher skin cancer awareness amongst physicians and consequently an increased diagnosis rate. Besides these factors, UV-exposure as a result of both UV radiation levels and behavior plays an important role [2]. Solar UV-A (320 to 400 nm) and the higher-energy and the shorter wavelength UV-B (290 to 320 nm) penetrate the Earth’s atmosphere, and chronic exposures have been linked to melanoma, the most fatal form of skin cancer. UV-C (100 to 290 nm) has the highest energy but is blocked by the ozone layer [3]. 39 However, UV-C exposures are possible from artificial sources, including germicidal lamps, arc welding equipment, and mercury arc lamps in older tanning beds [1]. There is widespread public interest in the relationships between UV radiation and health. The effects of UV on health can be harmful – as in its effect on skin cancer rates, or beneficial – as in the case of its effect on vitamin D status. In the past, researchers have attempted to determine these relationships as functions of ambient UV radiation. However, the UV doses that humans are typically received are less than 5% of that available UV [1, 2]. A personal dosimetry is necessary to quantify the amount of individual UV exposure. In practical use dosimeters are based on polysulphone and on polyphenylene oxide (PPO), polymers undergoing changes in its optical properties upon irradiation with UV [4-5]. Other systems determine the UV dose by quantifying damage induced in Bacillus subtilis spores upon UV exposure [3]. In our days silver nanostructures hold great interest due to their unique properties and potential application in nanoelectronics, magnetic, biosensors, data storage, catalysis, surface enhanced Raman scattering and excellent antibacterial properties. Silver nanostructures are particularly interesting due to their size- and shape – dependent plasmonic properties. Plasmonic properties of silver nanoparticles are very sensitive to UV and gamma irradiation and structural changes [6-10]. The results of UV effect on morphology and plasmonic properties of silver nanocomposites are presented. Silver/PVP nanocomposites layers are
J. Puiso et al. / Medical Physics in the Baltic States 7 (2009) 39 - 42 presented there also. The possible formation mechanism of Ag nanostructures the effect of molar ratio of PVP to silver nitrate, UV exposure time are discussed based on experimental results obtained by UV-VIS, AFM and FTIR. 2. Experimental Silver nitrate (AgNO3 analytical reagent) and poly(N)- vinyl pyrrolidone (PVP) (average MW=10 000) and sodium dodecyl sulfate (SDS) (MW=288.38) were obtained from Sigma Aldrich. Deionised water was prepared with a Milipore water purification system. In a typical experiment 250 mg of AgNO3 were added to 4 ml of aqua’s PVP (30 wt%) solution. Ag-PVP films were produced on the pre-treated glass substrates from the colloidal silver solution in PVP by spin coating. The glass substrates were pretreated for 10 min sonically in acetone and were dried in air stream. Ag/PVP films were spin-coated with “DYNAPERT PRECIMA” centrifuge. The spin speed was above 1800 rpm and spinning time was 30 s. UV source (Hibridas Exposure Unit MA4, power 1200 W, wavelength 300-400 nm, and exposure time from 1 to min.) were used for UV irradiation. The Ag/PVP layers were aged in the “black box” for 3 months. Samples were placed on the table as a patient and irradiated by UV source under atmospheric pressure and ambient temperature. The formation of silver nanoparticles in PVP solution and thin Ag/PVP films were confirmed by recording absorbance by UV- VIS (UV/VIS/NIR AvaSpec-2048) spectrometers. The morphology properties of the silver polymer nanocomposites (Ag/PVP) were investigated by atomic force microscope NT- 206 (AFM). V type noncontact silicon cantilever NSC11/15 silicon probe (constant force 3 N/m, resonant frequency 65 Hz) was used for AFM measurements. Image processing and analysis of the scanning probe microscopy data were performed with a program “Surface View version 2.0”. 3. Results and discussion Absorbance spectra of Ag/PVP thin films after UV irradiation on glass and 3 months ageing is presented in Fig.1. Absorbance, a.u. 2,0 1,8 1,6 1,4 1,2 1,0 0,8 0,6 0,4 0,2 0,0 b a c 350 400 450 500 550 600 Wavelenght, nm Fig. 1. Absorbance spectra of Ag/PVP films after primary UV irradiation and aging: a) 1 min, b) 20 min, and c) 180 s 40 The surface plasmon (SPR) peak in UV-VIS spectra at 415-419 nm, indicated plamonic properties of silver nanoparticles. According [6-9] we produce spherical silver nanoparticles with 20 nm size in polymer [7-9]. Using Chumanov’s calculations [10] we find that size of silver nanoparticles is about 40 nm. According “Mieplot” calculations results, the size of spherical silver nanoparticles is 30-35 nm. The intensity of SPR peak dependences (position, halfwidth and cording adsorbance) on UV exposure time, irradiation induces the redshift of SPR peak from 415 nm to 420 nm, increasing half-width of peak. UV irradiations induce silver nanoparticles aggregation. Absorbance of Ag/PVP layers after the secondary UV irradiation is presented in Fig 2. Absorbance, a.u. Absorbance, a.u. Absorbance, a.u. 2,0 1,5 1,0 0,5 0,0 2,0 1,5 1,0 0,5 0,0 2,0 1,8 1,6 1,4 1,2 1,0 0,8 0,6 0,4 0,2 0,0 1+4 min 1 min 1+2 min 400 600 Wavelength, nm a) 2 min 2+2 min 2+4 min 350 400 450 500 550 600 Wavelength, nm b) 3+2 min 3+4 min 3 min 400 600 Wavelength, nm c) Fig. 2. Absorbance spectra of Ag/PVP films after secondary UV irradiation a) 1 min, b) 20 min, and c) 180 s
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