currently , nanoparticles ( nps ) are used in several scientific applications , but among these silver nanoparticles ( ag - nps ) are predominant .
this is because of several characteristic features of this type of metal np.13 antimicrobials and nanocomposite fabrication are some of the highly useful applications , among others , of applications that were attributed to ag - np.4,5 in the fabrication of nps , it is very important to control particle size , shape , and morphology .
laser ablation in liquid media is a simple and clean method for synthesis of nps.69 in this technique , there is no need to use any chemical reagents ( such as nabh4 ) in the fabrication process or any purification techniques to characterize the produced nps .
for example , nps using fatty acids ( oleic and lauric acid ) and vegetable oils as stabilizers have been synthesized.1012 it was found that these materials consist of amphiphilic molecules with polar carboxylic groups which are able to adsorb nps , and their nonpolar long carbon chain prevents nps agglomeration through steric repulsion . castor oil is a vegetable oil obtained by cold pressing the seeds and subsequent clarification of the oil by heat .
it has high viscosity , high polarity , and very low vapor pressure and optical activity in comparison with other oils .
castor oil is classified as a safe and effective stimulant laxative by the us food and drug administration ( fda ) .
it is a triglyceride containing fatty acid chains , 90% of which are ricinoleic acid .
oleic and linoleic acids are the other significant components.12 with the above characteristics , it is expected that castor oil can be used as a good stabilizer in nps fabrication . in this study
, we report fabrication of ag - nps in castor oil . to the best of our knowledge ,
fabrication of ag - nps in castor oil using laser ablation has not been reported previously .
for the fabrication of ag - nps , a silver plate was ablated by laser in castor oil for 10 min .
as shown schematically in figure 1 , the plate with high purity ( > 99.99% ) was located 5 mm behind a glass cell wall filled with 10 ml of castor oil .
a nanosecond - pulsed q - switched nd : yag laser ( brilliant ; lambda photometrics ltd , hertfordshire , uk ) with 10-hz repetition rate , 5-ns pulse duration , and 360 mj / pulse energy at its original wavelength ( 1064 nm ) was applied .
a lens with focal length of 250 mm was used to focus the laser pulses onto the silver plate . during plate ablation ,
an atomic absorption spectrometer ( aas - s series ; thermo scientific , san jose , ca ) was used to measure concentration of ag - nps in castor oil .
the obtained concentration of ag - nps in castor oil was 0.13 mg / l . due to the high viscosity of castor oil
the prepared sample was characterized using a uv - vis double beam photospectrometer ( shimadzu , columbia , sc ) , a transmission electron microscope ( tem , hitachi h-7100 ; hitachi , tokyo , japan ) , and a fourier transform - infrared ( ft - ir ) spectrometer ( 1650 ; perkin elmer , waltham , ma ) .
figure 2a indicates the absorption spectrum of the castor oil immediately after laser ablation of the silver plate inside it .
the appearance of the maximum absorption peak around 400 nm confirms that the solution contained ag - nps , and that this peak originated from the oscillation of collection of free conduction electrons of ag - nps , which is called surface plasmon resonance .
the ultraviolet - visible spectrum of the ag - nps in castor oil was measured after a period of 2 months in order to check the ability of castor oil as a stabilizer . as shown in figure 2b
, the spectrum does not show any significant change in comparison with the spectrum of the freshly prepared sample ; however , there is a small reduction in absorption .
this showed that the ag - nps produced in castor oil using the laser ablation technique were stable and did not agglomerate during storage of the sample at room temperature for quite a long period of time .
the slight decrease in absorption intensity was possibly due to the sedimentation of larger particles .
the spherical shape nps can be very appropriately used for drug loading and for most biological applications such as antibacterial properties.13 figure 3 shows an approximate 5.06 nm average diameter for freshly prepared ag - nps obtained from two areas .
nps are formed via nucleation , transition , and crystal growth of materials such as silver atoms , clusters , and droplets that were emitted from the silver plate upon laser ablation.14 castor oil can adsorb the produced ag - nps and long - chain hydrophobic moieties protect them through a steric stabilization mechanism .
ft - ir spectroscopy of castor oil and castor oil containing ag - nps ( figure 5 ) shows absorption bands at 3448 , 2923 , 2857 , 1739 , and 1160 cm related to the vibrational - stretching mode of o  h ( intermolecular hydrogen bond ) , c  h ( sp ) , c  h ( sp ) , co , and c  o , respectively .
in addition , the appearance of the absorption band at 3780 cm can be attributed to nonhydrogen - bonded o 
we believe that the existence of ag - nps prevents intermolecular hydrogen bonding , and therefore , the vibrational stretching modes of free o  h appear at a higher wave number.15
ag - nps have been successfully prepared in castor oil by laser ablation from a silver plate . the results obtained showed that the produced ag - nps were well dispersed and also stable for quite a long period of time .
this ability of castor oil to prevent agglomeration of ag - nps is due to the presence of long - chain hydrophobic moieties .
 silver nanoparticles were fabricated by ablation of a pure silver plate immersed in castor oil . 
 a nd : yag - pulsed q - switch laser with 1064-nm wavelength and 10-hz frequency was used to ablate the plate for 10 minutes . 
 the sample was characterized by ultraviolet - visible , atomic absorption , fourier transform - infrared spectroscopies , and transmission electron microscopy . 
 the results of the fabricated sample showed that the nanoparticles in castor oil were about 5-nm in diameter , well dispersed , and showed stability for a long period of time . 