The Effects of Laser Energy , Repetition of Pulse Laser , Wavelength , and Temperature on Silver NanoParticles

To study the effects of temperature, wavelength, laser energy, and repetition of pulsed laser on the silver nanoparticles. The laser induced photoacoustic technique has been used to study photoacoustic properties of silver nanoparticles. The study found a direct correlation between the wavelength and the concentration of the photoacoustic signal. Moreover, an indirect correlation was predicted between the temperature and concentration of the photoacoustic signals. The laser energy was found out to be 355 nm at a constant repetition rate of 2 Hz and the repetition rate of 2 Hz was also selected for the entire measurements. The photoacoustic properties of silver nanoparticles were significantly affected by wavelength, temperature, repetition of pulsed laser, and input energy as predicted by the data collected from the study.


Introduction
The silver nanoparticles exhibit unique properties when they are prepared with different methods and techniques due to which they are of great importance.The silver nanoparticles have been used in various applications such as photosensitive components, surface-enhanced Raman spectroscopy and catalysts.The surface effect of metal nanoparticles is responsible for exhibiting unique properties since most of the atoms in metal are surface atoms (Solangi et al., 2015).The photoacoustic effect is used to study the physical properties of silver nanoparticles.Alexander Graham Bell, during his search for the discovery of wireless communication, discovered the photoacoustic effect (Rahman et al., 2016).The photoacoustic spectroscopy, which is used to analyze the physical properties of silver nanoparticles, can be classified as photothermal technique.The spectroscopy uses the incident light beam to change the thermal state of the sample.The changes in the thermal state can result in the change in temperature, density, or any other measurable properties of the sample.Thus, the pressure wave produced in the sample can be detected with the help of optical methods, sensitive microphone or piezoelectric devices.The techniques utilized for the detection of these changes are called photoacoustic techniques (Sandler, 2017).
The silver nanoparticles are extensively used in good deal of applications including; biomedical application sensors, nanocomposite fabrications, antibacterial applications, and computing.The nanostructured particles are subjected to various factors, which affect the use of silver nanoparticles in various applications.Shape and size of the nanoparticles are the most important aspects, which greatly influence the properties of nanoparticles.Moreover, the fabrication process also imposes significant influence on the properties of the nanoparticles.Thus, by varying the size and shape of the nanoparticles and by altering the processes for the fabrication of silver nanoparticles, the applications of silver nanoparticles were altered.
The study evaluates the size-dependent properties of the silver nanoparticles and also identifies the optical and electronic properties of the AuNPs.The study also develops strategies to understand and control the collective properties of nanoparticles.Furthermore, the effects of ablation parameters and mechanisms were also studied to control the shape and size of the nanoparticles.Kim, Park & Lim (2015) conducted a study in which the characterization, preparation and utilization of the starch nanoparticles was being discussed.Starch is the most well-known biopolymer and exhibit unique physical property.The starch nanoparticles are being extensively utilized in cosmetics, foods, medicines and several other composites.Furthermore, the starch nanoparticles can be used as drugs and bio-functional ingredients.The most up-to-date information regarding the starch nanoparticles were also included in the overview as well as the physiochemical characterization and preparation processes.Thus, nanoparticles are extremely useful in various applications including its extensive use in medicines and food preservation.Austin et al (2014) also conducted a study in which the use of gold and silver particles was discussed relating to their optical, photothermal and facile surface chemical properties.The study showed that gold and silver particles are heavily used in the biomedical field due to their extensively small size, which makes them capable of penetrating the cellular membranes.The extremely small size of these particles enables them to interact with the biomolecules and causes changes in their chemical and physical properties.The particles are commonly prepared by using the colloidal synthesis technique.Thus, the study concluded that the use of Au and Ag in biomedical field is extremely useful for drug delivery and therapeutic applications.Moreover, Li and Chen (2015) also conducted a study to evaluate the use of Ag nanoparticles for photoacoustic imaging.

Methodology
The laser induced photoacoustic technique has been used for the study of the photoacoustic properties of silver nanoparticles in dispersions.The study evaluates the use of several devices being used in the study and also discusses the optical effect of photoacoustic signal.The preparation and the optical properties of silver nanoparticles are also discussed in this study.

Materials
The materials used are sodium borohydride and silver nitrate.Triple distilled water was also used for the preparation of aqueous solution with the help of ultrapure purification system.

Synthesis of Nanoparticles
For the production of silver nanoparticles, sodium borohydride is used in an excess amount for the reduction of ionic silver and for the stability of the AuNPs being formed in the process.The initial concentration of sodium borohydride was taken to be [NaBH 4 ]/[AgNO 3 ] = 2, i.e. the amount of sodium borohydride must be twice of silver nitrate.The variation of sodium borohydride from 2.0 mM resulted in the breakdown of the product; whereas, the silver nitrate was kept to be 1.0mM.

Experimental Setup
The study was conducted to evaluate the photoacoustic properties of the silver nanoparticles in dispersion as well as the repetition of laser pulses, wavelength, size, temperature, and effects of laser energy on the silver nanoparticles were also discussed in the study.The experimental setup being used in the study included: YAG laser with the pump energy of 23 J, Output energy of 532 nm, pulse energy of 532 nm, beam divergence of 1 mrad, polarization of 532 nm, and delay of output relative to pump pulse of 154 micro seconds, the third harmonic generator was also used with the laser; a titanium doped sapphire laser was also used to study the correlation between the wavelength and the photoacoustic signal; UV visible spectrophotometer; a holographic grating; deuterium and halogen lamps as radiative sources; a luminescence spectrometer; xenon flash tube as excitation source; mirror, plane mirror, toroidal mirror and spherical mirrors are also being used in the setup.Excitation and emission monochromators are also used in the experiment.Furthermore, Photodiode Amplifier, two channel digital real-time oscilloscope, intensified charge coupled device, Microtrac S3500 Tri-laser particle size analyzer, transmission electron microscopy, and x-ray diffraction were also used in the experimental setup.Rhodamine 6G dye was used for testing of the calibration of the experimental setup.

Photoacoustic
Nine samples were created with varying concentrations and different parameters were investigated.The samples were created with following concentrations: between th laser sourc choice.

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The effect PA signals  .The study conducted an optical transmission analysis in which the surface plasmon absorption bands of the silver nanoparticles were demonstrated and showed that it increased with increase in the pulse energies.The thermal analysis conducted in the study showed similar results at the microscopic level for both ps and ns pulses to a temperature distribution which was similar for both.The absorption length was found out to be decreasing with the increase in temperature and the results for ns and ps suggested a very short absorption length at the surface absorption.
The combination of laser therapy with metal nanoparticles in cancer treatment originates from epithelial tissues (Fekrazad et al., 2016).Cancer treatment with the help of laser and nanoparticles has gained enormous attention in the past few decades.The combined use of nanoparticle and laser was investigated in the study for the death of cancerous cells.The type of laser which was used in different investigations NIR which had a wavelength spectrum of 785nm up to 1046nm; whereas, 808nm wavelength was used more rapidly and frequently than others.Another wavelength which was investigated and was found in the visible spectra was 420nm and up to 690nm.However, there are few disadvantages of using combined therapy due to difficulty in finding identical particles and high cost of this therapy.Moreover, combined therapy requires high and advanced technology which is difficult to achieve.
Another study conducted by Simandoux et al. (2015) investigated the thermal-based nonlinear photoacoustic generation to differentiate between the different types of absorbing particles.The study focused on the photoacoustic generation from the solutions of gold nanospheres and dye molecules with the help of high frequency ultrasound transducer.At an equilibrium temperature, the photoacoustic emission of the gold nanospheres was observed at a certain low influence for an equilibrium temperature of around 4°C.At this temperature, the photoacoustic effect appeared to vanish in water; thus, suggesting a non-linear emission from the nanosphere solution.Moreover, the photoacoustic amplitude was also studied, which was chosen as a function of equilibrium temperature from 2°C to 20°C.At the whole temperature range, the photoacoustic amplitude was found to be consistent from the gold nanospheres; however, the photoacoustic amplitude was found to vanish at 4°C.The results of the study suggested that with respect to the high frequency photoacoustic imaging, the difference can be calculated between the nanoparticles and molecular absorber based on nanoscale temperature rises.
The following study aimed at analyzing the effects of laser energy, repetition of pulse laser, wavelength, and temperature on silver nanoparticles.The study utilized nine samples of varying concentrations and different parameters to evaluate their effects.The results of wavelength on the silver nanoparticles suggested a direct relation between the two parameters.The results of the effects of laser energy on the silver nanoparticles showed that the laser input energy was of the wavelength of 355 nm at a constant repetition rate 2 Hz.Moreover, effects of repetition of pulse laser was also investigated in which the repetition rate of 2 Hz was selected for the entire measurements due to the occurrence of best PA signals at this specific value.In the end, the effect of temperature was also studied on the silver nanoparticles.The results suggested that the temperature affected the particles in the solution of silver nanoparticles.Moreover, an indirect relationship was predicted between the PA signal and the temperature.The following study have several implications; such as, the study will prove to be beneficial to reduce the errors associated with the photoacoustic signal analysis due to the wavelength and temperature.The study will help the physicists to improve the thermal photoacoustic measurement and imaging quality.
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