Gamma Radiation Synthesis and Characterization of Silver and Gold Nanoparticles in Polymer Matrices

Nanoparticles are referred to nanostructure materials having dimensions in the range of 1 − 100 nm and typically contain few hundred to few thousand atoms. They may compose of single or more elements to form zero-dimensional nanomaterials such as metal nanoparticles, semiconductor quantum dots, colloids, and clusters. Nanoparticles exhibit unusual optical, electronic, magnetic and chemical properties dissimilar to the properties of their molecular and bulk materials due to their quantized nature and large surface area-to-volume ratios. Noble metal nanoparticles such as silver (Ag) and gold (Au) nanoparticles embedded in polymer matrices present high catalytic activity, remarkable optical effects such as light absorption, surface enhanced Raman scattering (SERS), and extraordinary optoelectronic and electronic properties useful for biosensors and electronic devices. The shape, size,and nanoparticle distribution density of metal nanoparticles and the ambient conditions are crucial parameters to understand the physics and chemistry phenomena of matter at nanometer scales. The potential technological applications depend on our capability to control these parameters during synthesis. Of various reduction methods including chemical, photochemical, electrochemical, and sonochemical techniques, the radiation-induced production method offers clean, harmless, controllable size, highly pure and stable nanoparticles, and free from reducing agents or impurities. In this works, colloidal Ag and Au nanoparticles were synthesized using gamma-radiation method by reducing silver ions of silver nitrate (AgNO3 concentration between 3.7 ×10-4 and 21.0 × 10-4 M) and gold ions of tetrachloroauratehydrate (HAuCl4 concentration between 1.0 × 10-4 and 7.5 × 10-4 M) stabilized by 4.7% poly(vinyl alcohol) (PVA) and 5.6% poly(vinyl pyrolidone) (PVP). All the samples at different concentrations of silver and gold salts were irradiated with doses of 10, 20, 30, 40, 50, 60, 70 kGy using a 60Co γ-rays radiation source. Upon gamma irradiation, free electrons, hydrated electrons, and free radicals that are produced able to produce the Ag+ and Au3+ ions into Ag0 and Au0 atoms prior to an aggregation to form (Ag0)n and (Au0)n nanoparticles respectively. The formation of Ag and Au nanoparticles have been observed by the change in color of the colloidal samples from colorless to golden yellow for Ag nanoparticles and to red for Au nanoparticles. The presence of Ag and Au metals were confirmed by the Energy Dispersive X-ray Spectroscopy (EDX) elemental analysis. The size of Ag and Au nanoparticles were determined at 90% cumulative distribution of the Photon Cross Correlation Spectroscopy (PCCS) and confirmed by the Transmission Electron Microscopy (TEM). The average diameter of colloidal Ag and Au nanoparticles decreases with increasing dose and increases with increasing starting salts concentration. The minimum diameters achieved were at 12 and 2 nm respectively for Ag and Au nanoparticles in PVP obtained from the lowest salts concentration and the highest radiation dose at 70 kGy. This radiation-induced nucleation event has been described as a dose-dependent process and the kinetics of nucleation of Ag and Au nanoparticles stabilized in PVA and PVP have been quantitatively studied. At high doses, where the nucleation event is more than the total metal ions, the radiation synthesis produced smaller sizes of nanoparticles following aggregation. On the other hand, at low doses were the nucleation event is less than the total metal ions, the radiation synthesis produced larger sizes of nanoparticles. The shape of Ag and Au nanoparticles were spherical in shape as determined by TEM method. The optical properties of Ag and Au nanoparticles were measured by means of UV-Visible absorption spectrophotometer. The presence of Ag and Au nanoparticles was revealed at the absorption peaks between 400 and 425 nm for Ag nanoparticles and between 500 and 550 nm for Au nanoparticles depending on the salts concentration and radiation dose. The maximum absorbance of the colloidal Ag and Au nanoparticles increases with increasing radiation dose, indicating an increase of the nanoparticle distribution density of Ag and Au nanoparticles at higher doses. Exceptional for radiation-induced synthesis, the absorption peaks shifted to lower wavelengths or blue-shift with increasing radiation dose indicating the diameter of Ag and Au nanoparticles decreases with increasing dose. Consequently, this gave a confinement effect on the conduction band of Ag and Au nanoparticles, which increases with the decrease of nanoparticle diameter. The fundamental characteristics of Ag and Au nanoparticles have been explained in terms of the quantum mechanical description for metal nanoparticles deviating from the more established concept of the surface Plasmon resonance derived from the classical electrodynamics theory

Influence of dose on particle size of colloidal silver nanoparticles synthesized by gamma radiation.

Colloidal silver nanoparticles were synthesized by γ-irradiation-induced reduction method of an aqueous solution containing silver nitrate as a precursor in various concentrations between 7.40×10−4 and 1.84×10−3 M, polyvinyl pyrrolidone for capping colloidal nanoparticles, isopropanol as radical scavenger of hydroxyl radicals and deionised water as a solvent. The irradiations were carried out in a 60Co γ source chamber at doses up to 70 kGy. The optical absorption spectra were measured using UV–vis spectrophotometer and used to study the particle distribution and electronic structure of silver nanoparticles. As the radiation dose increases from 10 to 70 kGy, the absorption intensity increases with increasing dose. The absorption peak λmax blue shifted from 410 to 403 nm correspond to the increase of absorption conduction electron energy from 3.02 to 3.08 eV, indicating the particle size decreases with increasing dose. The particle size was determined by photon cross correlation spectroscopy and the results showed that the particle diameter decreases exponentially with the increase of dose. The transmission electron microscopy images were taken at doses of 20 and 60 kGy and the results confirmed that as the dose increases the diameter of colloidal silver nanoparticle decreases and the particle distribution increases

Microwave irradiation effects on hydrothermal and polyol synthesis of ZnS nanoparticles

Cubic structure of spherical ZnS nanoparticles with relatively small size and narrow size distribution were synthesized via microwave-hydrothermal (M-H) and microwave-polyol (M-P) methods from zinc acetate and thioacetamide as starting materials. Distilled water and ethylene glycol were used as solvents for the M-H and M-P method respectively. To monitor the effect of microwave irradiation, the reactions were carried out in different irradiation time from 5 to 40 min. An increase in irradiation time increases the reaction yield and the average particle size, which subsequently decreases the optical band gap. ZnS nanoparticles synthesized by M-H method have narrower size distribution between 3 and 7 nm, while those synthesized by M-P method were between 2 and 9 nm. Moreover, the formation of hierarchical nanoballs ZnS were observed in the M-H method after 25 min irradiation time. Because of lower dielectric constant, higher dielectric loss, and higher boiling point of ethylene glycol compared to water, in the M-P method the heating rate and final temperature are higher than in M-H method, leading to the decomposition of thiocetamide, promoting higher rate of nucleation. ZnS nanocrystals synthesized with the polyol method have a higher degree of crystallinity compare with those synthesized using the hydrothermal method

Distribution of heavy metals in surface sediments from the South China Sea ecosystem, Malaysia

The concentrations of arsenic, cadmium, chromium, copper, mercury, nickel, lead and zinc in surface sediments collected from the east coast of peninsular Malaysia, along the South China Sea, were measured by two methods instrumental neutron activation analysis and inductively coupled plasma mass spectroscopy. The obtained results were use to determine the areal distribution of the metals of in the east coast of peninsular Malaysia and potential sources of these metals to this environment. The geochemical data propose that most of the metals found in the east coast of peninsular Malaysia constitute a redistribution of territorial materials within the ecosystem. Then, the metal concentrations can be considered to be present at natural background levels in surface sediments

Dependence of thermal diffusivity on particle size in Au nano-fluid

In this paper we report the measurement of thermal diffusivity of gold nanofluid prepared by γ-radiation with various particle sizes ranging from 7.0 nm to 18.7 nm. The thermal lens technique is used to measure thermal diffusivity of gold nano-fluid. In this technique a diode laser (wavelength 514 nm, power 80 mW) and He-Ne laser were used as the excitation source and probe beam respectively. Experimental results showed that thermal diffusivity values of nanofluid increase when the particle size increase

Global, regional, and national incidence and mortality for HIV, tuberculosis, and malaria during 1990–2013: a systematic analysis for the Global Burden of Disease Study 2013

BACKGROUND: The Millennium Declaration in 2000 brought special global attention to HIV, tuberculosis, and malaria through the formulation of Millennium Development Goal (MDG) 6. The Global Burden of Disease 2013 study provides a consistent and comprehensive approach to disease estimation for between 1990 and 2013, and an opportunity to assess whether accelerated progress has occured since the Millennium Declaration. METHODS: To estimate incidence and mortality for HIV, we used the UNAIDS Spectrum model appropriately modified based on a systematic review of available studies of mortality with and without antiretroviral therapy (ART). For concentrated epidemics, we calibrated Spectrum models to fit vital registration data corrected for misclassification of HIV deaths. In generalised epidemics, we minimised a loss function to select epidemic curves most consistent with prevalence data and demographic data for all-cause mortality. We analysed counterfactual scenarios for HIV to assess years of life saved through prevention of mother-to-child transmission (PMTCT) and ART. For tuberculosis, we analysed vital registration and verbal autopsy data to estimate mortality using cause of death ensemble modelling. We analysed data for corrected case-notifications, expert opinions on the case-detection rate, prevalence surveys, and estimated cause-specific mortality using Bayesian meta-regression to generate consistent trends in all parameters. We analysed malaria mortality and incidence using an updated cause of death database, a systematic analysis of verbal autopsy validation studies for malaria, and recent studies (2010-13) of incidence, drug resistance, and coverage of insecticide-treated bednets. FINDINGS: Globally in 2013, there were 1·8 million new HIV infections (95% uncertainty interval 1·7 million to 2·1 million), 29·2 million prevalent HIV cases (28·1 to 31·7), and 1·3 million HIV deaths (1·3 to 1·5). At the peak of the epidemic in 2005, HIV caused 1·7 million deaths (1·6 million to 1·9 million). Concentrated epidemics in Latin America and eastern Europe are substantially smaller than previously estimated. Through interventions including PMTCT and ART, 19·1 million life-years (16·6 million to 21·5 million) have been saved, 70·3% (65·4 to 76·1) in developing countries. From 2000 to 2011, the ratio of development assistance for health for HIV to years of life saved through intervention was US$4498 in developing countries. Including in HIV-positive individuals, all-form tuberculosis incidence was 7·5 million (7·4 million to 7·7 million), prevalence was 11·9 million (11·6 million to 12·2 million), and number of deaths was 1·4 million (1·3 million to 1·5 million) in 2013. In the same year and in only individuals who were HIV-negative, all-form tuberculosis incidence was 7·1 million (6·9 million to 7·3 million), prevalence was 11·2 million (10·8 million to 11·6 million), and number of deaths was 1·3 million (1·2 million to 1·4 million). Annualised rates of change (ARC) for incidence, prevalence, and death became negative after 2000. Tuberculosis in HIV-negative individuals disproportionately occurs in men and boys (versus women and girls); 64·0% of cases (63·6 to 64·3) and 64·7% of deaths (60·8 to 70·3). Globally, malaria cases and deaths grew rapidly from 1990 reaching a peak of 232 million cases (143 million to 387 million) in 2003 and 1·2 million deaths (1·1 million to 1·4 million) in 2004. Since 2004, child deaths from malaria in sub-Saharan Africa have decreased by 31·5% (15·7 to 44·1). Outside of Africa, malaria mortality has been steadily decreasing since 1990. INTERPRETATION: Our estimates of the number of people living with HIV are 18·7% smaller than UNAIDS's estimates in 2012. The number of people living with malaria is larger than estimated by WHO. The number of people living with HIV, tuberculosis, or malaria have all decreased since 2000. At the global level, upward trends for malaria and HIV deaths have been reversed and declines in tuberculosis deaths have accelerated. 101 countries (74 of which are developing) still have increasing HIV incidence. Substantial progress since the Millennium Declaration is an encouraging sign of the effect of global action. FUNDING: Bill & Melinda Gates Foundation

Measuring routine childhood vaccination coverage in 204 countries and territories, 1980-2019 : a systematic analysis for the Global Burden of Disease Study 2020, Release 1

Background Measuring routine childhood vaccination is crucial to inform global vaccine policies and programme implementation, and to track progress towards targets set by the Global Vaccine Action Plan (GVAP) and Immunization Agenda 2030. Robust estimates of routine vaccine coverage are needed to identify past successes and persistent vulnerabilities. Drawing from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2020, Release 1, we did a systematic analysis of global, regional, and national vaccine coverage trends using a statistical framework, by vaccine and over time. Methods For this analysis we collated 55 326 country-specific, cohort-specific, year-specific, vaccine-specific, and dosespecific observations of routine childhood vaccination coverage between 1980 and 2019. Using spatiotemporal Gaussian process regression, we produced location-specific and year-specific estimates of 11 routine childhood vaccine coverage indicators for 204 countries and territories from 1980 to 2019, adjusting for biases in countryreported data and reflecting reported stockouts and supply disruptions. We analysed global and regional trends in coverage and numbers of zero-dose children (defined as those who never received a diphtheria-tetanus-pertussis [DTP] vaccine dose), progress towards GVAP targets, and the relationship between vaccine coverage and sociodemographic development. Findings By 2019, global coverage of third-dose DTP (DTP3; 81.6% [95% uncertainty interval 80.4-82 .7]) more than doubled from levels estimated in 1980 (39.9% [37.5-42.1]), as did global coverage of the first-dose measles-containing vaccine (MCV1; from 38.5% [35.4-41.3] in 1980 to 83.6% [82.3-84.8] in 2019). Third- dose polio vaccine (Pol3) coverage also increased, from 42.6% (41.4-44.1) in 1980 to 79.8% (78.4-81.1) in 2019, and global coverage of newer vaccines increased rapidly between 2000 and 2019. The global number of zero-dose children fell by nearly 75% between 1980 and 2019, from 56.8 million (52.6-60. 9) to 14.5 million (13.4-15.9). However, over the past decade, global vaccine coverage broadly plateaued; 94 countries and territories recorded decreasing DTP3 coverage since 2010. Only 11 countries and territories were estimated to have reached the national GVAP target of at least 90% coverage for all assessed vaccines in 2019. Interpretation After achieving large gains in childhood vaccine coverage worldwide, in much of the world this progress was stalled or reversed from 2010 to 2019. These findings underscore the importance of revisiting routine immunisation strategies and programmatic approaches, recentring service delivery around equity and underserved populations. Strengthening vaccine data and monitoring systems is crucial to these pursuits, now and through to 2030, to ensure that all children have access to, and can benefit from, lifesaving vaccines. Copyright (C) 2021 The Author(s). Published by Elsevier Ltd.Peer reviewe

Global, regional, and national incidence, prevalence, and years lived with disability for 328 diseases and injuries for 195 countries, 1990–2016: a systematic analysis for the Global Burden of Disease Study 2016

As mortality rates decline, life expectancy increases, and populations age, non-fatal outcomes of diseases and injuries are becoming a larger component of the global burden of disease. The Global Burden of Diseases, Injuries, and Risk Factors Study 2016 (GBD 2016) provides a comprehensive assessment of prevalence, incidence, and years lived with disability (YLDs) for 328 causes in 195 countries and territories from 1990 to 2016