Heavy Metal Nanoparticles Research Articles

Nanoparticles: balancing benefits, ecological risks, and remediation approaches

Nanoparticles are the simplest form of structure, having sizes ranging from 1 to 100 nm and can provide considerably high surface areas through rational design. Their size, shape and structure are responsible for their high reactivity and strength. In the last few decades, nanoparticles have been widely used in many dosage forms due to their excellent solubility, less size and better penetrability. They have attained prominence in various technological advancements because their properties can be tuned as desired via precisely controlling the size, shape, synthesis conditions, and appropriate functionalization. Due to these unique properties, Nanoparticles have acquired a substantial global market in various commercial and domestic applications, including catalysis, imaging, medical applications, sports equipment, sensors, energy-based research, and environmental applications. Due to the increased growth of the production of nanoparticles and their industrial applications, issues relating to toxicity are inevitable. Several reports are available on the benefits of these nanomaterials in various sectors, but relatively more minor literature is available on their effect on the environment and human health. Several heavy metal nanoparticles are reported to be so rigid and stable that their degradation is not readily achievable, leading to much environmental toxicity. This review discusses a brief history, various applications and the possible fate of the Nanoparticles after use. In particular, we describe how Nanoparticles affect the environment, natural resources, natural micro-flora and humankind. It also describes several techniques currently being used to remove nanoparticles.

Heavy Metal Nanoparticle Detection in Human and Formula Milk.

Breast milk is the natural source of nutrition for infants, but while it supports their health, it can also be a potential source of toxic inorganic particulate matter, and this applies to both breast milk and industrially produced milk. The aim of the present study was to evaluate the presence of nanoparticles in both breast milk and formula milk samples. We collected and analyzed, via a new electron scanning microscopic procedure, 19 samples of breast milk from Italian women and 19 formula milk samples produced by different companies. Organic-inorganic agglomerates were detected in 58% of formula and in 63% of breast milk samples, respectively. In addition, a significantly (p < 0.05) greater size of nanoparticles was observed in formula milk samples. The results, showing the presence of inorganic nanosized particles in breast and artificial milk, may lead to future studies aimed at investigating possible nanosized contamination of milk and identifying early prevention strategies for women and animals involved in the food chain.

Fe3O4/Au@SiO2 nanocomposites with recyclable and wide spectral photo-thermal conversion for a direct absorption solar collector

The Fe3O4-based photothermal materials have been widely applied for the recycling of heavy metal nanoparticles to avoid secondary pollution in the utilization of solar energy owing to excellent magnetic properties. However, the narrow absorption band of Fe3O4 or metal nanoparticles limits their capacity for solar energy harvesting. In this paper, a recyclable and wide spectral photo-thermal conversion system (Fe3O4/Au@SiO2) based on Fe3O4 nanospheres and SiO2-modified Au nanorods (NRs) is prepared. Owing to the strong coupling effect between Fe3O4 and different Au NRs, the wide and strong absorption band from 400 nm to 1100 nm is obtained. Under the influence of magnetic field, the temperature change of nanofluids (NFs) at different positions can be controlled. When the concentration is 0.0467 vol%, the solar energy absorption fraction reaches 96.50 %. Besides, the photothermal performance of Fe3O4/Au@SiO2 NFs at different flow rates is investigated and the results show that temperature rise decreases as increasing flow rate. Finally, a water evaporator device based Fe3O4/Au@SiO2 NFs is developed. The maximum water evaporation rate of 2.6 kg m−2 h−1 can be reached and the movement of evaporator on water can be operated using magnetic field, showing great photothermal conversion performance and recovery potential in practical applications.

Enhanced TiO2-Based Photocatalytic Volatile Organic Compound Decomposition Combined with Ultrasonic Atomization in the Co-Presence of Carbon Black and Heavy Metal Nanoparticles.

Volatile organic compounds (VOCs) are representative indoor air pollutants that negatively affect the human body owing to their toxicity. One of the most promising methods for VOC removal is photocatalytic degradation using TiO2. In this study, the addition of carbon black (CB) and heavy metal nanoparticles (NPs) was investigated to improve the efficiency of a TiO2-based photocatalytic VOC decomposition system combined with ultrasonic atomization and ultraviolet irradiation, as described previously. The addition of CB and Ag NPs significantly improved the degradation efficiency. A comparison with other heavy metal nanoparticles and their respective roles are discussed.

Antibacterial, antibiofilm and larvicidal activity of silver nanoparticles synthesized from spider silk protein

Green synthesis of silver nanoparticles has gained attention due to its simple process of synthesis and varied applications. Scientists have tried its synthesis from a wide range of materials, but there is lack of reports that can use the metabolites of insects. Here in this study, we have used the spider silk protein which is considered as complete waste collected from household and field sources and processed to synthesize silver nanoparticles which were subsequently analyzed using different analytical tools like SEM, TEM, FTIR, and XRD. The spider silk protein-mediated synthesized nanoparticle (SP-AgNPs) showed a sharp peak at 420 nm when analyzed spectrophotometrically giving an indication of successful synthesis of AgNP. The synthesized nanoparticle ranges from 10 to 40 nm and were of varied shapes. The synthesized SP-AgNPs showed remarkable antibacterial activity. The MIC values against B. subtilis and E. coli were recorded 45 and 40 μg/mL respectively. Further to know the mechanisms of antibacterial activity protein leakage and conductivity measurement were conducted. The synthesized nanoparticle also showed excellent antibiofilm activity with inhibition percentages of 74 % and 68 % for E. coli and B. subtilis respectively at MIC concentration of the treatment. Finally, the synthesized nanoparticles was applied as mosquito larvicidal agent against Culex sp. and the difference between LC50 and LD90 value was recorded as statistically significant (p < 0.0267) during 24 h of incubation. Therefore, it can be said that spider-web could be an excellent biological reducing and capping agent for heavy metal nanoparticle synthesis that can minimize the ailments caused by mosquitoes and pathogenic microorganisms.

Integrating Chlorophyll a Fluorescence and Enzymatic Profiling to Reveal the Wheat Responses to Nano-ZnO Stress.

It has been shown that increased concentrations of zinc oxide nanoparticles (nano-ZnO) in the soil are harmful to plant growth. However, the sensitivity of different wheat cultivars to nano-ZnO stress is still unclear. To detect the physiological response process of wheat varieties with different tolerance to nano-ZnO stress, four wheat cultivars (viz., cv. TS1, ZM18, JM22, and LM6) with different responses to nano-ZnO stress were selected, depending on previous nano-ZnO stress trials with 120 wheat cultivars in China. The results found that nano-ZnO exposure reduced chlorophyll concentrations and photosynthetic electron transport efficiency, along with the depressed carbohydrate metabolism enzyme activities, and limited plant growth. Meanwhile, the genotypic variation in photosynthetic carbon assimilation under nano-ZnO stress was found in wheat plants. Wheat cv. JM22 and LM6 possessed relatively lower Zn concentrations and higher leaf nitrogen per area, less reductions in their net photosynthetic rate, a maximum quantum yield of the PS II (Fv/Fm), electron transport flux per cross-section (ETo/CSm), trapped energy flux per cross-section (TRo/CSm), and total soluble sugar and sucrose concentrations under nano-ZnO stress, showing a better tolerance to nano-ZnO stress than wheat cv. TS1 and ZM18. In addition, the chlorophyll a fluorescence parameters Fv/Fm, ETo/CSm, and TRo/CSm could be used to rapidly screen wheat varieties resistant to nano-ZnO stress. The results here provide a new approach for solving the issues of crop yield decline in regions polluted by heavy metal nanoparticles and promoting the sustainable utilization of farmland with heavy metal pollution.

Single-step detection of toxic airborne metallic nanoparticles using Goos–Hänchen effect in photonic Bragg grating structures

A real-time photonic crystal sensor is suggested for the detection of airborne heavy metal nanoparticles (HMNPs). The sensor consists of a sandwiched sampling cell between two stacks of alternating TiO2 and Si-Ge layers, forming the core of the device. The sensor’s performance is based on monitoring changes in both the intensity and phase of a probe beam as it propagates through the core. By analyzing the fluctuations in intensity, central frequency, and full width at half maximum (FWHM) of the resonant mode within the transmittance spectrum bandgap, or by monitoring the phase changes at the angle of maximum transmittance that may result in a remarkable Goos–Hänchen (GH) shift in transmittance, the sensor can identify the pollutant nanoparticles. Tuning the thicknesses of the slabs and the number of unit cells in the photonic crystal can dynamically shift the resonant mode and bandgap edges, allowing for easy adjustment of the sensor’s responsivity. Furthermore, the optical response of the sensor can be tuned through external parameters such as the incident angle of the probe light or an externally applied electric field. Additionally, the sensor exhibits sensitivity not only to changes in the extent of the sample but also to the shape of the present HMNPs. These characteristics make the proposed configuration cost-effective, user-friendly, and suitable for HMNPs detection without the need for complex sample preparation, data analyses or additional tools/accessories.

Toward Visualizing Genomic DNA Using Electron Microscopy via DNA Metallization

Electron microscopy‐based DNA imaging is a powerful tool that provides a high resolution for observing genomic structures involved in biochemical processes. The first method, heavy metal shadow casting, was developed in 1948. Uranyl acetate has been widely used for DNA electron microscopic imaging since the 1960s. However, for this method, scientists must deal with government regulations for the safety and disposal. Additionally, sample preparation is often complicated and time‐consuming. Recently, nanoparticles and nanowires have emerged as a new way of imaging DNA molecules under both transmission and scanning electron microscopes. However, as this technology is still in its early stages, there is room for further development. In this review, heavy metal staining, nanoparticle staining, and nanowire growth for DNA visualization are introduced. The applications of shadow casting and uranyl acetate staining in the visualization of DNA structures and protein–DNA complexes are discussed. Then, nanomaterial‐based DNA staining methods are covered, including electrostatic interactions, DNA chain modification, reducing‐group‐modified DNA ligands and DNA–peptide/protein interactions. This review provides up‐to‐date information on different DNA staining approaches and their applications in DNA studies. Ultimately, it offers a new direction for genome analysis through DNA visualization.

High-performance MTJ-based sensors for monitoring of atmospheric pollution

Solid and liquid particles in the atmosphere, referred to as airborne particulate matter (PM), have been rising significantly over the past two decades. Exposure to PM carries significant health risks such as lungs damage, heart disease, cancer, and death. PM2.5 is a subgroup of PM particles that are smaller than 2.5 µm and is a major concern as it is more harmful to health and more difficult to detect. One problematic component of PM2.5 is magnetite nanoparticles (&amp;lt;200 nm), which are readily absorbed into the bloodstream through the respiratory system. Eventually, magnetite nanoparticles deposit inside the brain causing neurodegenerative diseases such as Alzheimer’s or cancerous tumors by inducing oxidative stress. Additionally, Magnetite nanoparticles are often surrounded by heavy metal nanoparticles such as Cadmium and lead which are a great concern to the environment and health. Traditional PM detection methods such as laser scattering are bulky, expensive, and incapable of detecting particles smaller than 200 nm such as magnetite nanoparticles. Therefore, developing a low-cost highly sensitive sensor for monitoring magnetite nanoparticles is vital. Tunneling Magneto-Resistance (TMR) sensors are an attractive option due to their low-cost and high sensitivity toward magnetic nanoparticle detection. Moreover, developing a cheap, portable, and precise remote monitoring technique will allow for the creation of high spatial resolution highly sensitive monitoring networks for magnetic PM2.5. This work focuses on developing, modeling, and simulation of low-cost highly sensitive TMR sensor based on Magnetic Tunnel Junction (MTJ) that can detect and count magnetite nanoparticles.

Recent Advances in Reactive Oxygen Species (ROS)-Responsive Polyfunctional Nanosystems 3.0 for the Treatment of Osteoarthritis.

Osteoarthritis (OA) is an inflammatory and degenerative joint disease with severe effects on individuals, society, and the economy that affects millions of elderly people around the world. To date, there are no effective treatments for OA; however, there are some treatments that slow or prevent its progression. Polyfunctional nanosystems have many advantages, such as controlled release, targeted therapy and high loading rate, and have been widely used in OA treatment. Previous mechanistic studies have revealed that inflammation and ROS are interrelated, and a large number of studies have demonstrated that ROS play an important role in different types of OA development. In this review article, we summarize third-generation ROS-sensitive nanomaterials that scavenge excessive ROS from chondrocytes and osteoclasts in vivo. We only focus on polymer-based nanoparticles (NPs) and do not review the effects of drug-loaded or heavy metal NPs. Mounting evidence suggests that polyfunctional nanosystems will be a promising therapeutic strategy in OA therapy due to their unique characteristics of being sensitive to changes in the internal environment.

Genetically Engineered Organisms: Possibilities and Challenges of Heavy Metal Removal and Nanoparticle Synthesis

Heavy metal removal using genetically engineered organisms (GEOs) offer more cost and energy-efficient, safer, greener, and environmentally-friendly opportunities as opposed to conventional strategies requiring hazardous or toxic chemicals, complex processes, and high pressure/temperature. Additionally, GEOs exhibited superior potentials for biosynthesis of nanoparticles with significant capabilities in bioreduction of heavy metal ions that get accumulated as nanocrystals of various shapes/dimensions. In this context, GEO-aided nanoparticle assembly and the related reaction conditions should be optimized. Such strategies encompassing biosynthesized nanoparticle conforming to the green chemistry precepts help minimize the deployment of toxic precursors and capitalize on the safety and sustainability of the ensuing nanoparticle. Different GEOs with improved uptake and appropriation of heavy metal ions potentials have been examined for bioreduction and biorecovery appliances, but effective implementation to industrial-scale practices is nearly absent. In this perspective, the recent developments in heavy metal removal and nanoparticle biosynthesis using GEOs are deliberated, focusing on important challenges and future directions.

A brief review of C-Dots preparation using top-down and bottom-up approaches.

This review paper aimed to reveal several methods that have been used in the preparation of carbon dots (C-Dots). C-Dots were principal to be studied because they have luminous properties that can be used in photocatalyst processes, heavy metal sensors, glowing paints, and nanoparticles for biomedical applications such as bio-tagging. The methods that have been developed were also varied using the two principal approaches, i.e., top-down and bottom-up. Here, we tried to reveal the arc-discharge, laser ablation techniques for top-down approaches, while simple heating methods (simple hydrothermal methods), and microwave for bottom-up. Furthermore, the microwave method was excellent because of the vibration process which caused the carbon chains to undergo rearrangement so that the result was not much reducing the water content in the solution.

Exploring the Role of Heavy Metals and Their Derivatives on the Pathophysiology of COVID-19.

Many aspects of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its disease, COVID-19, have been studied to determine its properties, transmission mechanisms, and pathology. These efforts are aimed at identifying potential approaches to control or treat the disease. Early treatment of novel SARS-CoV-2 infection to minimize symptom progression has minimal evidence; however, many researchers and firms are working on vaccines, and only a few vaccines exist. COVID-19 is affected by several heavy metals and their nanoparticles. We investigated the effects of heavy metals and heavy metal nanoparticles on SARS-CoV-2 and their roles in COVID-19 pathogenesis. AgNPs, AuNPs, gold-silver hybrid NPs, copper nanoparticles, zinc oxide, vanadium, gallium, bismuth, titanium, palladium, silver grafted graphene oxide, and some quantum dots were tested to see if they could minimize the severity or duration of symptoms in patients with SARS-CoV-2 infection when compared to standard therapy.

Distribution of Heavy Metals and Their Corresponding Nanoparticles in Different Treatment Unit Processes in the Sewage Treatment Plant

Total heavy metal concentration, heavy metal nanoparticle concentration, particle size, and the removal effect of different treatment unit processes on heavy metals and heavy metal nanoparticles were analyzed in this study. Inductively coupled plasma mass spectrometry (ICP-MS) and single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) were applied in nine treatment units performing continuous wastewater treatment processes in the Chengdu Shuangliu International Airport sewage treatment plant. Results showed that different treatment unit processes had different effects on the removal of different total heavy metal elements, with the effects on Fe being the most significant; Fe was mainly removed in the secondary sedimentation tank at a rate of 98.53%. The removal effects of different heavy metal nanoparticles varied in different treatment unit processes, with the effects of Ni, Pd, and Fe being the most significant. Heavy metal nanoparticles removal varied by treatment unit processes (aeration grit tank, secondary sedimentation tank, and high-efficiency sedimentation tank). The particle size distribution of heavy metal nanoparticles in different treatment unit processes was 23.28-147.83 nm, and different treatment unit processes did not have a significant impact on the particle size of each heavy metal nanoparticle. In addition, pH exhibited a significant negative correlation with Fe and Fe nanoparticles. Excluding Fe and Fe nanoparticles, other heavy metals and their nanoparticles were not significantly related; thus, different processing unit processes exhibited different removal mechanisms for heavy metals and their corresponding nanoparticles.

Isolation and characterization of halophilic bacteria with the ability of heavy metal bioremediation and nanoparticle synthesis from Khara salt lake in Iran

Increasing environmental pollutants such as heavy metals have become one of the most severe health dangers because of rapid industrialization. Exposure to lead and nickel heavy toxic metals can lead to hazardous diseases affecting most of the organs in humans. Bioremediation is a process that uses the ability of microorganisms or plants to detoxify environmental contaminants at lower costs than physicochemical techniques. This study isolated halophilic bacteria from Khara salt lake in Iran and screened their ability to resist lead and nickel. After screening stages, three selected strains including Bacillus sp. A21, Oceanobacillus sp. A22 and Salinicoccus A43 were identified by16S rDNA sequencing and the related sequences were submitted to GeneBank with accession IDs MN588312, MN588313, and MN 588,314, respectively. These strains resist 7.2 mM, 4.1 mM, and 6.7 mM lead and 3.6 mM, 3.7 mM, and 4.1 mM nickel, respectively. Investigation of growth pattern and evaluation of bioremediation ability by atomic absorption spectroscopy revealed that Bacillus sp. A21 could decrease lead and nickel in culture medium up to 97.5% and 76%, respectively. Oceanobacillus sp. A22 showed higher lead bioremediation rate (98.8%) and lower nickel-bioremediation rate (73.5%). Salinicoccus sp. A43 showed the least bioremediation ability (92% lead and 71.7% nickel). The ability of selected strains to synthesize lead and nickel nanoparticles was evaluated using UV/Vis spectrophotometry and Energy-Dispersive X-ray Spectroscopy (EDX). Particle dimensions were measured using Scanning Electron Microscopy (SEM). Bacillus sp. A21 and Oceanobacillus sp. A22 strains were able to synthesize lead nanoparticles; however, Salinicoccus sp. A43 could synthesize both lead and nickel nanoparticles.

One-Pot Detection of Heavy Metals and Biosynthesis of Fluorescent Nanoparticles from Metals in Groundwater Samples

Heavy metals like Pb2+ and Hg2+ are well known for their toxicity and harmful health impacts. The present study was designed to carry out on-site detection of heavy metals like Pb2+ and Hg2+ in the water samples passed through the egg shell powder column. Egg shells are washed and powdered, preheated at 110 °C for activation, and used as stationary phase in the column. Two metal solutions of varying concentrations (1 μg·L−1, 10 μg·L−1, 100 μg·L−1, and 1000 μg·L−1) were prepared in different buffers of basic pH (8–11) and then passed through the column, and plain buffer solutions were used as control. The column eluent was observed under a trans-illuminator for fluorescence and checked for absorbance in a UV-visible spectrophotometer from 200 to 600 nm. The presence of fluorescence and UV absorption indicated the presence of heavy metals in the sample. Proteins present in the egg shell, on reacting with metal ions, formed stable nanoparticles due to reduction and capping. The biosynthesized nanoparticles from egg shell proteins were confirmed by SEM analysis, where Pb2+ and Hg2+ nanoparticles were formed. The study was repeated for the detection of heavy metals present in groundwater samples, which was confirmed from fluorescence, UV-visible spectrum, EDAX, and FESEM where heavy metal nanoparticles of size range 12–23 nm were formed. Therefore, this method could be a good alternative for the detection of heavy metals at low concentrations in environmental samples and is feasible for on-site detection.

High-Energy and High-Rate X-Ray Measurements Using HfO₂ Nanoparticle-Loaded Plastic Scintillator

The detection efficiency of a plastic scintillator (PLS) can be enhanced by loading with heavy metal nanoparticles to measure high-energy X-rays at a high count rate exceeding $10^{{7}}\,\,\text{s}^{{-1}}$ using a fast scintillation detector. We successfully polymerized up to 60 wt% HfO2 nanoparticle-loaded PLSs (Hf-PLSs) by mixing with polystyrene and 2-(4-tert-butylphenyl)-5-(4-biphenyl)-1,3,4-oxadiazole as a fluorophore. Loading 40 wt% HfO2 maintained a light yield of 79% of a commercially available 5 wt% lead-loaded PLS (EJ-256) with a much higher high- ${Z}$ loading. We tested the 40 wt% Hf-PLS (8 mm in diameter, 3 mm in thickness) mounted on a photomultiplier tube using a synchrotron X-ray beam at beamline BL-14A of the photon factory (PF) ring. The detection efficiency of the X-ray detector reached 44.3 ± 0.2% at 50.0 keV. Counting rates of up to $2.76\times 10^{{7}}\,\,\text{s}^{{-1}}$ were recorded at input photon rates of up to $3.74\times 10^{{8}}\,\,\text{s}^{{-1}}$ in the multibunch mode of the PF ring. The pulse height and time spectra were observed using the 40 wt% Hf-PLS at 67.4 keV for application to synchrotron radiation nuclear resonant scattering on 61Ni. The detection efficiency was 49.2 ± 0.2% at 67.4 keV, 7.2 times greater than that of EJ-256. A time resolution (full-width at half-maximum) of 0.32 ± 0.06 ns was obtained in the time spectrum but with a time resolution of 0.46 ns at best using EJ-256. The Hf-PLS is promising for applications in counting and timing measurements within the high-energy X-ray regions.

Recent Advances in the Application of Functionalized Lignin in Value-Added Polymeric Materials.

The quest for converting lignin into high-value products has been continuously pursued in the past few decades. In its native form, lignin is a group of heterogeneous polymers comprised of phenylpropanoids. The major commercial lignin streams, including Kraft lignin, lignosulfonates, soda lignin and organosolv lignin, are produced from industrial processes including the paper and pulping industry and emerging lignocellulosic biorefineries. Although lignin has been viewed as a low-cost and renewable feedstock to replace petroleum-based materials, its utilization in polymeric materials has been suppressed due to the low reactivity and inherent physicochemical properties of lignin. Hence, various lignin modification strategies have been developed to overcome these problems. Herein, we review recent progress made in the utilization of functionalized lignins in commodity polymers including thermoset resins, blends/composites, grafted functionalized copolymers and carbon fiber precursors. In the synthesis of thermoset resins such as polyurethane, phenol-formaldehyde and epoxy, they are covalently incorporated into the polymer matrix, and the discussion is focused on chemical modifications improving the reactivity of technical lignins. In blends/composites, functionalization of technical lignins is based upon tuning the intermolecular forces between polymer components. In addition, grafted functional polymers have expanded the utilization of lignin-based copolymers to biomedical materials and value-added additives. Different modification approaches have also been applied to facilitate the application of lignin as carbon fiber precursors, heavy metal adsorbents and nanoparticles. These emerging fields will create new opportunities in cost-effectively integrating the lignin valorization into lignocellulosic biorefineries.

Bacteria in Heavy Metal Remediation and Nanoparticle Biosynthesis

Biosynthesis of nanomaterials using natural and biological materials as reducing, stabilizing and capping agents is an important field of biomaterial science, nanoscience and nanobiotechnology. Rel...

Study of Radiation Dose Enhancement to Capillary Endothelial Cells Due to the Presence of Heavy Metal Nanoparticles in Two Cell and Tumor Scales by Monte Carlo Method

Introduction: Recently, the use of various sensitizers has been used to increase photon-induced doses in brachytherapy. One of these cases is the addition of heavy metal nanoparticles such as gold in the target area, which increases the production of ionizing electrons by increasing the possibility of photoelectric effects, and increases the efficacy of the treatment. In this study, the target of the irradiation was the endothelial cell in the wall of blood capillaries located inside the tumor, which, if destroyed, would result in abnormal blood cell counts and tumor cell death. Methods: The effect of using nanoparticles of gold, silver, bismuth and copper has been evaluated by calculating the dose increase ratio using Geant4 tool that was based on Monte Carlo method. These calculations were performed on two microscopic (cellular) and macroscopic (tumor dimensions) scale and the effects of different concentrations of these nanoparticles were compared. Also, the dose increase ratio has been evaluated to determine the most appropriate photon energy range. Results: As the concentration of nanoparticles increases, the dose enhancement factor increased in photon energy. In addition, for energies less than 70 keV, with increasing energy, dose enhancement factor increased and for energies above 80 keV, this quantity decreased with increasing energy. Conclusion: In terms of dose, gold is the best option, and in terms of the dose enhancement factor, silver and bismuth are better alternative among the four elements studied. Also, the most suitable photon energy range is 70 keV to 80 keV.