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Exploring socialities on Black Twitter: an ethnographic study of everyday concerns of South African users in 2018 and 2019

  • Authors: Adebayo, Binwe
  • Date: 2020
  • Subjects: Twitter (Firm) , Social media South Africa , Social media and society South Africa , Black people and mass media South Africa , Language and the Internet South Africa , Mass media and culture South Africa , Race in mass media , Ethnicity in mass media , Mass media and minorities South Africa , Mass media Social aspects South Africa , Sex differences in mass media , Social media Political aspects South Africa , South Africa Social conditions , Finance In mass media , Intersectionality (Sociology) South Africa , ‎Black Twitter
  • Language: English
  • Type: text , Thesis , Masters , MA
  • Identifier: http://hdl.handle.net/10962/140575 , vital:37900
  • Description: In this thesis, I examine the phenomenon of Black Twitter, as it exists in South Africa. Drawing on its socio-cultural and linguistic elements, I analyse the kinds of socialities which are constituted on the platform. In the study, I do this by focusing on the key issues which drive the space by evaluating the key everyday concerns as expressed by its users. As such, the overarching lens focuses on three elements: Firstly, the idea of socialities and the way in which they manifest in online spaces; a focus on the everyday as an important site for social inquiry; and lastly the issue of ‘blackness’, in terms of the way it is used and understood in the South African Black Twitter context. Historically, the Black Twitter space has been linked almost exclusively to its broad base of African American users, who are significant both in terms of their numbers, and their impact on online social culture. However, in this study I engage with the ways in which Black Twitter has been adopted, co-opted and used by young South Africans. As a bona fide ‘member’ of South African Black Twitter, my approach to the study was cyberethnographic. Drawing on my access to the space, my knowledge of many of its members and dynamics, I engaged in participant observation as my primary methodology. My discussion focuses on three areas of everyday concerns, namely: gender and sexuality; race and politics; finances and the economy. These three areas emerge both as prominent sites of discussion, but also give the best insight into the ways in which young South Africans are grappling with these issues. My analysis focuses on how everyday concerns are handled on the platform, and I focus on the deployment of solidarity, formal language, platform-based language and the invocation of blackness. I argue in my conclusion that while the structure of the broad Black Twitter space reflects a leaning towards a digital public sphere, that the process and construction of Black Twitter’s ideas and content are approached via an incomplete, fluid convivial approach.
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  • Date Issued: 2020

Information communication and technology in Port Elizabeth secondary schools : exploring the digital divide

  • Authors: Adebisi, Adeolu Abiodun
  • Date: 2008
  • Subjects: Information technology -- Study and teaching (Secondary) -- South Africa , Educational technology -- South Africa , Information technology -- South Africa , Computer-assisted instruction -- South Africa , Educational innovations
  • Language: English
  • Type: Thesis , Masters , MTech
  • Identifier: vital:9770 , http://hdl.handle.net/10948/914 , Information technology -- Study and teaching (Secondary) -- South Africa , Educational technology -- South Africa , Information technology -- South Africa , Computer-assisted instruction -- South Africa , Educational innovations
  • Description: The primary goal of the research is to investigate the extent of ICT adoption in secondary schools within the larger Port Elizabeth area. In order to demonstrate the current status, two geographical areas within that area namely privileged and less privileged areas will be selected and surveyed. The main objective of this research study is to survey the access to ICT services by learners and teachers living and working in less privileged communities compared with that of learners and teachers in the more privileged communities of Port Elizabeth. At present all the schools in these communities are funded by the same provincial government, but the extent of the digital divide is not known. This research will investigate the factors that lead to the inequalities in the access to ICT among secondary school learners and teachers. This research has the following sub goals and objectives: 1. To identify the factors that impact on the status of access to ICT services; 2. To determine which socio-economic factors contribute to the status of access to ICT services in the specific areas; 3. To determine the status of access to ICT services in specific communities within the larger Port Elizabeth area; 4. To determine whether the level of access differs between secondary schools and the homes of teachers and learners in the identified areas.
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  • Date Issued: 2008

Acute and sub-chronic antihypertensive properties of Taraxacum officinale leaf (TOL) and root (TOR)

  • Authors: Adebola O. Oyedeji2
  • Date: 2019
  • Language: English
  • Type: Journal
  • Identifier: http://hdl.handle.net/11260/5091 , vital:44344
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A multi-stakeholder approach to productivity improvement in the South African construction industry

  • Authors: Adebowale, Oluseyi Julius
  • Date: 2018
  • Subjects: Labor productivity , Construction industry -- Labor productivity Construction industry -- South Africa Construction industry -- Management
  • Language: English
  • Type: Thesis , Doctoral , DPhil
  • Identifier: http://hdl.handle.net/10948/19597 , vital:28902
  • Description: As poor productivity in construction continues to constitute a setback to projects’ success in different countries of the world, the situation in South African construction is no exception. Poor productivity on construction projects and its detrimental impact on project objectives have continually resonated for decades. As a result, several strategies, interventions, and measures that aimed at improving productivity in the construction sector have been proposed. Nevertheless, the phenomenon importunately creates a major challenge on construction projects, and by extension, the construction industry especially in developing countries. Even when construction management literature acknowledged the commonalities in productivity influences, the practice of addressing construction productivity influences as separate entities has gained much relevance over the years. Taking into perspective, the multidisciplinary and complexity inherent in construction, a systemic approach to addressing construction productivity influences is fast becoming essential. This study addressed productivity-influencing factors by considering factors that are related to rework, shortage of construction resources, constructability, political, socio-economic, working environment, welfare conditions, disputes, planning and training. Consequently, the interdependencies of the most significant productivity-influencing factors in South African construction was developed in the form of a qualitative model. The study adopts the underlying assumptions of the quantitative approach, but also accepts some qualitative data. With regards to the subject of enquiry, the paradigm of the research is positivism which consists of realists’ ontological prescriptions and objectivists’ epistemological prescriptions. Site engineers, site managers, and site supervisors working for cidb registered contractors in four South African provinces constitute the sample stratum. Statistical Package for the Social Sciences (SPSS) version 24 was used to analyse the data gathered from these project participants; both descriptive and inferential statistics were used. Descriptive statistics was used to summarise and describe the data obtained, while inferential statistics in the form of analysis of variance, T-test, and Tukey post hoc test were adopted. The study reported the most significant factors which negatively influence productivity on South African construction projects as inadequate workers’ skills, defective workmanship, the practice of awarding contracts to lowest bidders, political activities resulting in industrial action, inadequate contractors’ experience in project planning, payment delays by contractors, and corruption. Furthermore, it was found that contractors largely share similar perceptions regarding the factors that constrain productivity growth in South African construction. The approximate level of labour, material, and plant productivity on South African construction projects is 50.4%, 72.9%, and 62.0% respectively, while the approximate multifactor productivity was estimated as 61.8%. The study concluded that productivity has a considerable relationship with time and cost and a less potent relationship with quality. Based on the research findings, contractors’, consultants’, clients’ and government qualitative intervention models were proposed while recommendations towards improving South African construction productivity were made. The study recommended the reinvention of the apprentice training system to develop skills in construction, the involvement of stakeholders in improving workers’ skills, improved collaboration between the construction industry and higher institutions of learning regarding curricula development, adequate supervision of construction activities to mitigate the propagation of rework on construction projects, character in leadership, and integrity of project stakeholders.
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  • Date Issued: 2018

Enhancing the role of the Kaizen suggestion tool in South African lean automotive companies of the Eastern Cape

  • Authors: Adedeji, Adeyemi Charles
  • Date: 2011
  • Subjects: Lean manufacturing , Manufacturing processes , Production management -- Mathematical models
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: vital:8644 , http://hdl.handle.net/10948/d1008157 , Lean manufacturing , Manufacturing processes , Production management -- Mathematical models
  • Description: The Toyota manufacturing system, aptly referred to as Lean manufacturing, has received a reasonable appreciation and awareness over the past decade in South African industry. This production phenomenon constitutes an organizational culture that encourages world-class production success through the liberation of factory resources, while employees are empowered and encouraged to contribute ideas for the improvement of processes and products. However, despite lean awareness and the crucial role of employee participation in the suggestion of ideas in world-class organizations, the performance level of lean manufacturing in South African industry is largely devoid of the Kaizen suggestion tool, particularly in the automotive companies of the Eastern Cape. The aim of this research was to proffer appropriate recommendations, improved awareness, understanding and practice for the improvement of the Kaizen suggestion principle in the automotive companies of the Eastern Cape. The research primarily focused on the ‘management/employees’ paradigm within the organisational context. The methodology employed in the study included a thorough review of the relevant literature and a questionnaire, which was developed and administered to both the management and employees of the thirty automotive components suppliers in Eastern Cape. The target companies constituted the units of analyses and therefore provided the opportunity for a detailed investigation of the links between management and employees as well as a submission of ideas for operational and organisational processes as established in the literature review. Epistemologically, the research is objectivist and paradigmically, positivist. However, some qualitative aspects of the data were relevant to the study and, therefore, were used in a complementary manner. The case approach utilized mixed methods by applying a range of data collection techniques and evidence from multiple sources while the sampling technique was sequential, involving both purposive and stratified random sampling. The study reveals the apparent lack of a systematic mechanism for the practice and administration of the Kaizen suggestion tools in most Eastern Cape automotive companies. This demerit is found to have negatively affected maximum employee participation and involvement in organizational decision making within the Province. The study has established a basic level of awareness and understanding among employees / employers relations that the Kaizen suggestion scheme is a vital tool for delivering strategic objectives in the management of decision making and organizational growth. The study strongly advocates the inclusion of employee suggestion systems as part of the organizational process.
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  • Date Issued: 2011

An exploration of leadership practices: a case study in a public high school in Nigeria

  • Authors: Adediji, John Oluwole
  • Date: 2013
  • Subjects: Educational leadership -- Nigeria -- Case studies Teacher participation in administration -- Nigeria -- Case studies School management and organization -- Nigeria -- Case studies Education, Secondary -- Nigeria
  • Language: English
  • Type: Thesis , Masters , MEd
  • Identifier: vital:1405 , http://hdl.handle.net/10962/d1001955
  • Description: The management of Nigeria high schools are noted for administrative practices in the management of their schools; hence the term administration is commonly used in their daily operations. This fact on ‘administration’ was emphasised by the Nigerian government in the National Policy on Education (Nigeria, 1981, p. 21). Therefor as a researcher from Nigeria, my rationale for embarking on this research study was to find out to what extent a public high school in Nigeria was still operating in a hierarchical, individualistic, authoritarian style of leadership or whether it has started embracing contemporary approaches such as distributed leadership. The main goal of this study was to explore leadership practices in the case study school with the main focus on how different people relate to each other in the various leadership practices of the school, such as staff and briefing meetings of the school. In addition, my research questions aimed at exploring the respondents’ perceptions of leadership and factors enabling or constraining the distribution of leadership in the school. The study is located within the interpretive paradigm. As a researcher in a wheelchair studying in South Africa I needed to find alternative ways of accessing the research site and gathering data. I was able to use electronic communication for the collection of my data. I used four different tools of data collection methods namely document analysis, observation, questionnaire and stimulated recall interviews. Findings from the study indicated that there was limited evidence of contemporary leadership approaches in the case study school. The school was still operating traditional leadership, while school activities were dominated by a hierarchical chain of command. What emerged from the leadership practices of the school could be termed authorised distributed leadership which was under the command of the school principal. Data also indicated that there were some forms of restricted teacher leadership in the management and administration of the school. In addition, findings revealed that the case study school was very good at the management and administrative functions. The school was very effective and efficient in the controlling and management of both human and material resources. Lastly, findings from the case study school indicated some enabling factors to the distribution of leadership in the case study school which include a culture of respect and cordial relations among the SMT and the teachers, Prominent among constraining factors to the distribution of leadership in the case study school were: cultural orientation of the people where the case school was located, exclusionary religious practices by the principal of the school and the inhibiting role played by the Ministry of Education. Finally, based on these findings, recommendations were made both for practice and for future research.
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  • Date Issued: 2013

On-site evaluation of smoking, alcohol consumption and physical inactivity among commercial taxi drivers in Buffalo City Metropolitan Municipality, South Africa

  • Authors: Adedokun, Aanuoluwa Odunayo , Ter Goon, Daniel , Owolabi, Eyitayo Omolara , Adeniyi, Oladele Vincent , Ajayi, Anthony Idowu
  • Date: 2019
  • Subjects: Alcohol use , Substance use , Commercial drivers
  • Language: English
  • Type: article , text
  • Identifier: http://hdl.handle.net/11260/5086 , vital:44345 , https://doi.org/10.5539/gjhs.v11n2p110
  • Description: Commercial drivers have been identified as eliciting behaviours that promote non- communicable diseases and road traffic accidents. The aim of the study is to determine the prevalence and pattern of alcohol use, smoking and physical inactivity among commercial taxi drivers in Buffalo City Metropolitan Municipality, South Africa. A cross-sectional study was conducted among 403 commercial drivers using the face-to-face interviews method. The WHO STEPwise questionnaire was used to obtain the demographic data, self-reported rate of alcohol consumption, tobacco use and physical inactivity. The participants’ mean age was 43.3 ± 12.5 years. About 30% of the participants were daily smokers, 37% consumed alcohol regularly and only 18% were physically active, whilst 82% were physically inactive. The prevalence of alcohol use, smoking and physical inactivity is high among commercial drivers in East London. Workplace health education on the health effects of these lifestyles’ risky behaviours on individuals and the general public should be given to the drivers.
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  • Date Issued: 2019

Screening for cardiometabolic risk factors among commercial drivers in Buffalo City Metropolitan Municipality, Eastern Cape, South Africa

  • Authors: Adedokun, Aanuoluwa Odunayo
  • Date: 2018
  • Subjects: Diabetes -- South Africa -- Eastern Cape Obesity -- South Africa -- Eastern Cape Commercial vehicles
  • Language: English
  • Type: Thesis , Masters , Nursing Science
  • Identifier: http://hdl.handle.net/10353/10431 , vital:35463
  • Description: Cardio-metabolic risk factors are the aggregates of conditions that increase the susceptibility of developing cardio-metabolic diseases such as cardiovascular diseases (CVD) and diabetes. This includes insulin resistance, obesity, hyperglyceamia, dyslipoproteinemia, hyperinsulinemia and hypertension. This condition are worsen by smoking and physical inactivity as they mostlyare not easily detected. This was a cross-sectional survey of 403 commercial taxi drivers at ten different taxi ranks in BCMM. The study utilized a convenient sampling technique for the participants of the study. The WHO STEPwise approach was used for data collection. The WHO STEPwise questionnaire was used for a face-to-face interview. Socio-demographic (sex, age, marital status, driving experience, income) and behavioural characteristics (smoking, alcohol consumption, consumption of sweet drinks, physical activity, and dietary intake) of participants were obtained. Also, objective reports concerning anthropometric measurements (weight, height, waist and hip circumference), blood pressure and biochemical measurement that is the blood glucose measurement. All anthropometric measurements were taken following a standard procedure using a Lufkin nonextensible flexible anthropometric tape (W606PM), Rosscraft, Canada and a SECA weighing scale and stadiometer (Hamburg, Germany). Blood pressure was checked also in accordance with standard protocols using a Medic+ Digital Blood Pressure Monitor Model 1219 (Hamburg, Germany). A validated ACCU-CHEK glucose monitoring apparatus (Mannheim, Germany) wasused for blood glucose measurement. Overweight and obesity was defined as a body mass index (BMI) of 25.0 kg/m2 –29.9 kg/m2 and≥ 30 kg/m2, respectively. Pre-hypertension was defined according JNC-8 criteria a systolic blood pressure of 120- 139 mmHg and diastolic of BP 80-89 mmHg while hypertension was defined as an average of two systolic BP ≥140mmHg and/or diastolic BP of ≥90mmHg or a history of hypertension or anti hypertensive medication use. Diabetes status was determined using the fasting blood glucose (FBG) test and defined as a FBG ≥ 7.0mmol/L or self-reports of history or current diabetes medication use (treatment), while pre-diabetes was defined as a FBG of 5.6-6.9mmol/L. Awareness of diabetes was defined as self-reported history of diabetes among the people with diabetes. Metabolic syndrome status was determined according to the National agreement among makers of abdominal obesity. Statistical Package for Social Sciences (SPSS) was used for data analysis. The mean age of the participants was 43.3 (SD12.5) years. The prevalence of overweight and obesity was 34.0 percent and 38.0 percent, respectively. Age, marital status, period of driving, not-smoking, hypertension and diabetes were significantly associated with obesity. In logistic regression analysis, after adjusting for confounding factors, only age (OR 1.6, CI 1.0-2.7), hypertension (OR 3.6, CI 2.3-5.7) and non-smoking (OR 2.0, CI 1.3-3.1) were the independent and significant determinants of obesity. The prevalence rates of abdominal obesity by waist circumference (WC), waist-hip-ratio (WHR), waist-to-height ratio (WHtR) and neck circumference (NC) were 61.5 percent, 67.5 percent, 80.1 percent and 65.3 percent, respectively. A strong correlations exists between WHR and WC (>0.64); and WHtR and WC (>0.62). There exists a good agreement between WC and WHR. Also, a moderate agreement exists between WC and WHtR, WC and NC, WHR and WHtR, and WHtR and NC. The prevalence of above normal body composition for participants with hypertension was 71.0 percent, 65.9 percent, 63.2 percent and 66.5 percent by WC, WHR, WHtR and NC, respectively. For diabetes, the prevalence was 20.6 percent, 19.4 percent, 17.0 percent and 18.6 percent by WC, WHR, WHtR and NC, respectively. Waist circumference was a stronger predictor of hypertension and diabetics, with odds ratio of 3.7 (95 percent CI: 2.3-6.1 and 3.1 (95 percent CI: 1.6-6.0), compared to NC, with odds ratio of 1.7 (95 percent CI: 1.1-2.8). The prevalence of pre-hypertension was 33.7 percent and hypertension was 57.0 percent. Age, marital status, level of education, period of driving, obesity, alcohol, sweet drinks consumption and diabetes were significantly associated with hypertension. After adjusting for confounders, age >35 years (P=0.004), obesity and alcohol use (P<0.001), period of driving >5years (p=0.028) and diabetes (P=0.003) were significant predictors of hypertension. Prevalence of pre-diabetes and diabetes was 17 percent and 16 percent, respectively. Of those who were diabetic (n=63), the majority were aware of their diabetes status (n=43) and were on treatment (n=30). Age, marital status, level of education, period of driving, obesity, sweet drinks consumption, physical activities and hypertension were significantly associated with diabetes. Only age >35 (AOR= 3.6, CI 1.2-11.1), ever married (AOR= 3.3, CI 1.5-7.0) and hypertension (AOR= 3.4, CI 1.7-6.8) were the independent predictors of diabetes after adjusting for confounders. The prevalence of metabolic syndrome was 22 percent. Age, marital status, level of education, physical inactivity and period of driving were significantly associated with metabolic syndrome. After adjusting for confounders, only age above 35 years (Adjusted Odd Ratio [AOR] =3.8, CI=1.4- 9.5), ever married (AOR=3.0, CI=1.6-5.3) and period of driving above five years (AOR= 2.4, CI=1.2-4.7) were the significant and independent predictors of metabolic syndrome. About 30 percent of the participants were daily smokers, 37 percent consume alcohol regularly and only 18 percent were physically active, while 82 percent were physically inactive. In conclusion, there was a high prevalence of obesity, hypertension and diabetes among the commercial drivers in this setting, which is associated with unhealthy lifestyles (smoking, excessive alcohol consumption, physical inactivity). Interventions aimed at promoting cardiovascular health of commercial drivers such as health education and workplace screening, should prioritize weight reduction, healthy eating and physical activity in this population.
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  • Date Issued: 2018

Assessment of national small and medium scale policy as a driver of local economic development : a case study of Ife Central Local government, Nigeria

  • Authors: Adefemi, Adebayo Oluwaseun
  • Date: 2017
  • Subjects: Economic policy Economic development -- Nigeria
  • Language: English
  • Type: Thesis , Masters , M.Admin
  • Identifier: http://hdl.handle.net/10353/12711 , vital:39301
  • Description: This study, assessment of national small and medium scale policy as a driver of local economic development: a case study of Ife Central Local Government, Nigeria, was undertaken to find out if the National SME policy in Nigeria has performed its critical role of driving the local economic and if not, why, and also to identify measures to solve the problems that are hindering the implementation of the National SMEs policy. This study will therefore investigate the contributions of the Small and Medium Enterprises sub-sector of the Nigerian economy, its problems and prospects and also examine the National SME policy and the importance of the policy. The objective of this study is to explore the implementation of National SME policy as a driver of local economic development, analyse the challenges that are associated with implementing the National SME policy in Ife Central Local Government and make recommendations regarding the implementation of SME policy in Nigeria. A total of 5 MP’s were randomly selected from a cross section of 7 MP’s that represent Ife Central Local Government. Interviews was used to determine how the National SME policy is been implemented in there constituency and if they are facing any challenges as to the implementing the policy and how are they solving the problems that are associated with the policy. The major findings of this study include the following: the National SME policy is an important policy which if well implemented would help the development of SMEs and also have great impact on the local economic development. Among the problems associated with the policy according to the MP’s are financial problems, illiteracy level of people in their constituency, Land segmentation problem, marketing problems. This study therefore recommended that government should strengthen financial laws that mandates financial institutions to give low interest rate loans to SMEs with little or no collateral. The government should accelerated development and upgrade of rural roads and rail network and other infrastructural facilities and review taxies in favour of local manufacturers especially the SMEs.
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  • Date Issued: 2017

Evaluation of the incidence of enteric viruses, Vibrio species and Escherichia coli pathotypes in effluents of two wastewater treatment plants located in Keiskammahoek and Stutterheim in the Eastern Cape Province of South Africa

  • Authors: Adefisoye, Martins Ajibade
  • Date: 2016
  • Subjects: Escherichia coli -- South Africa -- Eastern Cape Water -- Purification -- South Africa -- Eastern Cape Effluent quality -- South Africa -- Eastern Cape
  • Language: English
  • Type: Thesis , Doctoral , DPhil
  • Identifier: http://hdl.handle.net/10353/3165 , vital:28328
  • Description: South Africa is currently experiencing water shortage crisis, a challenge that has been attributed not only to the scarcity of freshwater, but also to fast degrading water quality. Factors such as rapid urbanisation, population and economic growth, climate change as well as poor operational and maintenance of many of the exisiting water/wastewater treatment facilities have been acknowledged as important contributors to degrading water quality in the country. Untreated or inadequately treated discharged wastewater effluents constitute point source pollution to many freshwater environments in South Africa. Hence, it becomes imperative to evaluate wastewater discharges in other to protect the scarce freshwater resource, the environment and public health. Over a twelve-month sampling period (September 2012 to August 2013), we assessed the bacteriological, virological and physicochemical qualities of the discharged final effluents of two wastewater treatment facilities in the Eastern Cape Province of South Africa. For the physicochemical assessment, a total of 144 final effluent samples were collected from both the final effluent tanks (FE) and the discharge points (DP) of the treatment facilities. Physicochemical parameters including pH, temperature, turbidity, total dissolved solids (TDS), dissolved oxygen (DO), electrical conductivity (EC) and free chlorine concentration were determined on site while biological oxygen demand (BOD), nitrate (NO3-), nitrite (NO2-), phosphate (PO4-) and chemical oxygen demand (COD) were determined in the laboratory. The bacteriological analysis of the samples was done using standard membrane filtration (MF) technique. Bacterial group assessed included: faecal indicator bacteria (faecal coliforms and E. coli) and Vibrio species, while the antibiotic susceptibility profiles of selected E. coli and Vibrio species isolates against some selected antibiotics commonly used in human therapy and veterinary medicine were determind using the standard agar-disc diffusion method. The occurrence and concentrations of human enteric viruses including: human adenovirus (HAdV), hepatitis A virus (HAV) and rotavirus (RoV) in the samples were determined by TaqMan-based real-time polymerase chain reaction (qPCR) following concentration by adsorption-elution method. The physicochemical characteristics of the samples ranged as follows: pH (6.5 – 7.6), TDS (95 – 171 mg/L), EC (134 – 267 μS/cm), temperature (12 – 27 °C), turbidity (1.5 – 65.7 mg/L), free chlorine (0.08 – 0.72 mg/L), DO (2.06 – 9.81 mg/L), BOD (0.13 – 9.81 mg/L), NO3- (0 – 21.5 mg/L), NO2- (0 – 0.72 mg/L), PO4- (0 – 18.3 mg/L) and COD (27 – 680 mg/L). Some of the characteristic such as pH, TDS, EC, temperature, nitrite and DO (on most instances) complied with recommended guidelines. Other characteristics, however, including turbidity, BOD, nitrate, phosphate and COD fell short of the recommended guidelines. All the 48 samples analysed for bacteriological qualities tested positive for the presence of the bacterial groups with significant (P≤0.05) seasonal variation in their densities. Faecal coliforms were detected in counts ranging from 1 CFU/100ml to 2.7 × 104 CFU/100ml. Presumptive E. coli counts ranged generally between 1 CFU/100ml – 1.4 × 105 CFU/100ml while counts of presumptive Vibrio species ranged between 4 CFU/100ml – 1.4 × 104 CFU/100ml. Molecular identification of the presumptive isolates by polymerase chain reactions PCR gave positive reaction rates of 76.2 percent (381/500) and 69.8 percent (279/400) for E.coli and Vibrio species respectively. The antibiotic susceptibility profiling of 205 PCR-confirmed Vibiro isolates against 18 commomly used antibiotics showed resistance frequencies ranging from 0.5 percent (imipenem) to 96.1 percent (penicillin G) at recommended breakpoint concentrations. Eighty-one percent (166/205) of the Vibrio isolates showed multidrug resistance (resistance to 3 or more antibiotics) with the most common multiple antibiotic resistance phenotype (MARP) being AP-T-TM-SMX-PG-NI-PB, occurring in 8 isolates.
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  • Date Issued: 2016

Anti-diabetic and phytochemical analysis of sutherlandia frutescens extracts

  • Authors: Adefuye, Ogheneochuko Janet
  • Date: 2016
  • Subjects: Medicinal plants -- Africa , Traditional medicine -- Africa , Herbs -- Therapeutic use -- Africa
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: http://hdl.handle.net/10948/3549 , vital:20441
  • Description: In Africa, the importance of medicinal plants in folklore medicine and their contribution to primary healthcare is well recognized. Across the continent, local herbal mixtures still provide the only therapeutic option for about 80% of the population. The vast floral diversity and the intrinsic ethnobotanical knowledge has been the backbone of localized traditional herbal medical practices. In Africa, an estimated 5400 of the 60000 described plant taxa possess over 16300 therapeutic uses. Similarly, with a therapeutic flora comprising of approximately 650 species, herbal medical practitioners in South Africa, make use of a plethora of plants to treat different human diseases and infections. Over the years, studies have identified numerous plant species with potential against chronic metabolic diseases including type 2 diabetes mellitus (T2DM). Globally, the incidence and prevalence of T2DM have reached epidemic proportions affecting people of all ages, nationalities and ethnicity. Considered the fourth leading cause of deaths by disease, T2DM is a global health crisis with an estimated diagnosis and mortality frequency of 1 every 5 seconds and 1 every 7 seconds respectively. Though the exact pathophysiology of T2DM is not entirely understood, initial peripheral insulin resistance in adipose tissue, liver, and skeletal muscle with subsequent pancreatic β-cell dysfunction resulting from an attempt to compensate for insulin resistance is a common feature of the disease. The current approach to treating T2DM is the use of oral antidiabetic agents (OAAs), insulin, and incretin-based drugs in an attempt to achieve glycaemic control and maintain glucose homeostasis. However, conventional anti-T2DM drugs have been shown to have limited efficacies and serious adverse effects. Hence, the need for newer, more efficacious and safer anti-T2DM agents. Sutherlandia frutescens subsp. microphylla is a flowering shrub of the pea family (Fabaceae/Leguminaceae) found mainly in the Western Cape and Karoo regions of Southern Africa. Concoctions of various parts of the plant are used in the management of different ailments including T2DM. However, despite extensive biological and pharmacological studies, few analyses exist of the chemical constituents of S. frutescens and no Triple Time of Flight Liquid Chromatography with Mass Spectrometry (Triple TOF LC/MS/MS) analysis has been performed. The initial aim of this study was to investigate the phytochemical profile of hot aqueous, cold aqueous, 80% ethanolic, 100% ethanolic, 80% methanolic and 100% methanolic extracts of a single source S. frutescens plant material using colorimetric and spectrophotometric analysis. The hot aqueous extractant was found to be the best extractant for S. frutescens, yielding 1.99 g of crude extract from 16 g fresh powdered plant material. This data suggests that application of heat and water as the extractant (hot aqueous) could play a vital role in extraction of bioactive compounds from S. frutescens and also justifies the traditional use of a tea infusion of S. frutescens. Colorimetric analysis revealed the presence of flavonoids, flavonols, tannins, and phenols in all extracts with varying intensity. The organic extracts 100% methanol, 80% and 100% ethanol exhibited high color intensity (+++) for flavonoids and flavonols respectively, while all the extracts exhibited a moderate color intensity (++) for tannins and phenols. Spectrophotometric analysis of S. frutescens extracts revealed that all the organic extracts contained a significantly higher concentration (in mg/g of extract) of flavonols and tannins when compared to the aqueous extracts. All extracts contained approximately equal levels of phenols. These data confirm the presence of all four groups of bioactive phytocompounds in the S. frutescens extracts used in this study, and also confirm that different solvent extractants possess the capability to differentially extract specific groups of phytocompounds. in individual extracts. Further comparison of these compounds with online databases of anti-diabetic phytocompounds led to the preliminary identification of 10 possible anti-diabetic compounds; α-Pinene, Limonene, Sabinene, Carvone, Myricetin, Rutin, Stigmasterol, Emodin, Sarpagine and Hypoglycin B in crude and solid phase extraction (SPE) fractions of S. frutesecens. Furthermore, using two hepatic cell lines (Chang and HepG2) as an in-vtro model system, the anti-T2DM properties of crude aqueous and organic extracts of S. frutescents was investigated and compared. Both aqueous and organic extracts of S. frutescens were found to decrease gluconeogenesis, increase glucose uptake and decrease lipid accumulation (Triacylglycerol, Diacylglycerol, and Monoacylglycerol) in Chang and HepG2 hepatic cell cultures made insulin resistant (IR) following exposure to high concentration of insulin and fructose. Using real-time quantitative reverse transcriptase polymerase chain reaction (qRT-PCR), the aqueous and organic extracts of S. frutescens were confirmed to regulate the expression of Vesicle-associated membrane protein 3 (VAMP3), Mitogen-activated protein kinase 8 (MAPK8), and Insulin receptor substrate 1 (IRS1) in insulin resistant hepatic cells. IR-mediated downregulation of VAMP3, MAPK8, and IRS1 mRNA in IR HepG2 hepatic cell cultures was reversed in the presence of aqueous and organic extracts of S. frutescens. The hot aqueous extract displayed the highest activity in all the assays, while all the organic extracts displayed similar potency. In conclusion, this study reports that aqueous and organic extracts of S. frutescens possess numerous anti-diabetic compounds that can be further investigated for the development of new, more efficacious and less toxic anti-diabetic agents. The presence of multiple compounds in a single extract does suggest a synergistic or combinatorial therapeutic effect. These findings support the burgeoning body of in-vivo and in-vitro literature evidence on the anti-diabetic properties of S. frutescens and its use in folklore medicine.
  • Full Text:
  • Date Issued: 2016

Cultivation, nutritional and pharmacological evaluation of Celosia argentea (L) Kuntze: an endangered wild vegetable in the Eastern Cape Province of South Africa

  • Authors: Adegbaju, Oluwafunmilayo Dorcas
  • Date: 2019-09
  • Subjects: Celosia , Edible greens
  • Language: English
  • Type: Doctoral theses , text
  • Identifier: http://hdl.handle.net/10353/19806 , vital:43250
  • Description: Green leafy vegetables are important in human nutrition, but their cultivation is limited to a few staple ones. These vegetables possess high nutritious and therapeutic properties that could help in achieving nutritional security and alleviating the burden of some diseases. A typical example is Celosia argentea, which in South Africa, is little known and grossly under-utilized despite its numerous nutritional and pharmacological values. The present study investigated the cultivation, nutritional and pharmacological potentials of C. argentea at three stages of maturity of two trials. Evaluation of cultivation in the greenhouse towards possible domestication of C. argentea included seed viability test, seed germination under varying temperatures (5, 10, 15, 20 25 30, 35, 40°C), light conditions (continuous light, continuous darkness, alternating light and dark (12h light/12 dark photoperiod) and sowing depths (0, 1, 2, 3, 4 and 5cm). The nutritional evaluation assessed the proximal, mineral, vitamins and antinutrient content of the plant; while pharmacological potentials of C. argentea were evaluated by investigating the ultramorphology, phytochemical content, anti-oxidant, antimicrobial, toxicity and cell-based anti-inflammatory properties of the plant at different stages of growth. Germination experiment revealed that optimum seed germination requirements for C. argentea were 25°C, alternating light and dark regime and a sowing depth of 1cm. Microrphological assessment of C. argentea revealed that the leaves were amphistomatic; with the abaxial surface having higher stomata density. Characteristic, distinguishing protuberances were observed at the polar ends of the stomata on the adaxial surface of the plant epidermis, and the major elements on the foliar epidermis were beryllium, carbon, oxygen and potassium; while pigmentation and colouration, showing localization of bioactive compounds were mostly at the site where trichomes were abundant. Growth parameters and yield potential (plant height, stem girth, leaf area, number of leaves, number of branches, number of days to flowering, number of flowers as well as dry and fresh weight) of C. argentea showed that for agricultural practices on the field, increase in growth parameters should be expected around 4-5 weeks after transplanting while higher yield should be expected around 7-9 weeks after transplanting. The results encouraged cultivation during summer or late spring for best farm management. Proximal, mineral, vitamins and anti-nutrients content of C. argentea at three different maturity stages of two trials were performed using AOAC, ALASA and inductively coupled plasma-optical emission spectrometer techniques. Results revealed that the pre-flowering stage of growth had the highest ash (28.15± 0.10 percent) and crude protein (25.80 ± 0.20 percent) contents. While post-flowering stage had the highest carbohydrate (28.51± 0.20 percent and 36.16± 0.22 percent), crude fibre (33.41± 0.87 percent) and energy (435.28± 27.6 percent) with low fat and moisture (8.43± 0.15 percent and 6.35±0.09 percent) contents respectively; while no marked demarcation in most mineral contents in all the growth stages was observed. Zinc was highest at the flowering stage of growth, while vitamin contents decreased as the plant approached maturation. Antinutrients content of the plant was not dependent on growth stage. Total phenols, flavonoids and proanthocyanidin content of C. argentea were evaluated colourimetrically, while the antioxidant potency of the aqueous, acetone and methanolic extracts was measured using 2,2 diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), Ferric reducing antioxidant power (FRAP) and total antioxidant capacity (TAC) models. All the solvent extracts of the flowering stage had the highest total phenolic (80.75±4.21GAE/g), flavonoids (946.19±7.87QE/mg) and proanthocyanidin contents (100.90±1.29 CE/g); with the acetone extracts showing significantly higher phytochemical content. The flowering stage exhibited the best radical inhibitory activity, with the methanol extract having the highest scavenging power for ABTS and DPPH radicals, while acetone extract showed the highest inhibition against FRAP and highest total antioxidant capacity. The antimicrobial potential of the aqueous acetone and methanolic extracts of C. argentea evaluated using agar dilution method against six bacteria (Klebsiella pneumonia, Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus, Bacillus subtilis and Bacillus cereus) and four fungal strains (Candida glabarata, Candida albicans and Penicillium aurantiogriseum and Penicillium chrysogenum) showed that Streptococcus pyrogenes and P. aeruginosa were susceptible to the methanol extracts of all the growing phases of both trials at 10 mg/mL; while Klebsiella pneumoniae was susceptible at 10 mg/mL to only the methanol post-flowering extracts of both trials. C. albicans and P. aurantiogriseum were highly susceptible to all the extracts. Possible toxicity evaluated using brine shrimp lethality assay and calculation of LC50 against brine shrimp nauplii revealed that C. argentea was not toxic at any stage of maturity at all concentrations evaluated. Anti-inflammatory activities and cytotoxicity of C. argentea extracts evaluated using RAW 264.7 macrophages and 3T3-L1 cell lines revealed that the acetone extract of the flowering stage had moderate anti-inflammatory activity with no significant toxicity against activated macrophages. Findings from this study indicate that C. argentea is a safe functional leafy vegetable of high nutritional and pharmacological importance which can easily be cultivated and domesticated in South Africa. This could significantly alleviate the burden of micronutrient deficiencies among pre-school children in rural communities. , Thesis (PhD) (Botany) -- University of Fort Hare, 2019
  • Full Text:
  • Date Issued: 2019-09

In vitro evaluation of antimicrobial and antioxidant activities of olea europaea subsp. africana and euryops brevipapposus used by Cala community folkloric medicine for the management of infections associated with chronic non-communicable diseases

  • Authors: Adegborioye, Abiodun
  • Date: 2016
  • Subjects: Antioxidants Medicinal plants Traditional medicine -- South Africa -- Eastern Cape
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10353/4869 , vital:28624
  • Description: Chronic non-communicable diseses are a global public health challenge that continuously threatens the development and health of humans. Risk factors such as unbalanced diet-the high consumption of processed food or food from animal origin are responsible for NCDs. NCDs result in weakened immune system, making the host susceptible to opportunistic infections. Thus, the NCDs burden is most times chronic and multiple with the illness and suffering of the affected person numerous. The lack of cure for NCDs, the high cost of drugs, their high side-effects, and the emergence of multiple drug resistance has given rise to the investigation of other sources for therapeutic cure such as medicinal plants. The ethanol, n-hexane and ethyl acetate extracts of Olea europaea were analysed for their antioxidant and antimicrobial activities. The essential oil was also analysed for their chemical constituents. The n-hexane extracts of O. europaea exhibited no inhibition against all of the microorganisms tested, while the ethyl acetate and ethanol extracts exhibited inhibition, with minimum inhibitory concentration values between 0.625 mg/ml to 1.25 mg/ml. The ethanol leaf and ethyl acetate stem extracts exhibited significant activity in the inhibition of 2, 2-azinobis-(3-ethylbenzothiazolin - 6-sulfonic acid diammonium salt (ABTS) free radical, the n-hexane leaf extract had the overall significant lipid peroxidation inhibition activity, while in the inhibition of 2, 2- diphenyl-1-picrylhydrazyl radical (DPPH), the ethanol and ethyl acetate leaf extracts had strong activity. Nonanal, phytol, α-Pinene, α-Phellandrene, spatulenol and farnesol were some of chemical components identified after the GC-MS analysis of O. europaea oil. In the final part of the dissertation, Euryops brevipapposus essential oil was assessed for the antioxidant activities using free radical scavenging assays. In addition to this, the antimicrobial activities were assessed and the chemical composition was analysed using GC-MS. The essential oil demonstrated significant antioxidant activity against 2, 2-diphenyl-2-picryl-hydrazyl free radical (DPPH), 2, 2′-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) and lipid peroxides with IC50 value of 0.0000000671 mg/ml, 1.05 mg/ml, and 1.170 mg/ml respectively. The essential oil also showed significant activity against all microorganisms tested with minimum inhibitory concentration (MIC) values between 0.055 mg/ml to 0.5 mg/ml. α-pinene, α- Phellandrene, germacrene D, β-pinene, trans- β.-Ocimene, bicyclogermacrene and β -Phellandrene were some of the chemical compounds identified in E. brevipapposus oil. The study has shown that E. brevipapposus and O. europaea are abundant in phytochemical compounds which were thought to be the root cause for the activities demonstrated. Therefore, these therapeutic properties observed validate and elucidate the traditional usage of the both plants in the treatment /management of diseases.
  • Full Text:
  • Date Issued: 2016

Commensal bacteria belonging to the Staphylococcus Acinetobacter and Stenotrophomonas genera as reservoirs of antibiotic resistance determinants in the environment of Nkonkobe Municipality, Eastern Cape Province , South Africa

  • Authors: Adegoke, Anthony Ayodeji
  • Date: 2012
  • Subjects: Acinetobacter infections Drug resistance in microorganisms Staphylococcal infections Bacterial diseases
  • Language: English
  • Type: Thesis , Doctoral , Degree
  • Identifier: http://hdl.handle.net/10353/6539 , vital:30551
  • Description: A study to assess the potentials of some commensal bacteria that belong to Staphylococcus, Acinetobacter and Stenotrophomonas genera as reservoirs of antibiotic resistance determinants in the environment of Nkonkobe Municipality of the Eastern Cape Province, South Africa, was carried out using standard microbiological and molecular techniques. A total of 120 Staphylococcus isolates which consisted of Staphylococcus haemolyticus (30%), Staphylococcus aureus (23.3%) from pig; Staphylococcus capitis (15%) from goat; Staphylococcus heamolyticus (5%) and Staphylococcus xylosus (15%) from cattle and other Staphylococci (11%) from dead chicken and pigs were isolated. About 23.3% of these isolates were coagulase positive and 76.7% were coagulase negative. This difference in prevalence along coagulase production divide was statistically significant (p < 0.05). Eighty-six Acinetobacter species (Acinetobacter baumannii/calcoaceticus and Acinetobacter haemolyticus) were also isolated from Alice and Fort Beaufort towns samples, while 125 Stenotrophomonas maltophilia isolates were from grass root rhizosphere (96%) and soil butternut root rhizosphere (4%). Between 75-100% of the Staphylococccus species were resistant to Penicillin G, tetracycline, sulphamethaxole and nalidixic acid; about 38 % were methicillin resistant, consisting of 12.6% methicillin resistant Staphylococcus aureus (MRSA) from pig and a total of 12% vancomycin resistant were observed. Also, 12% of the isolates were erythromycin resistant while 40.2 % were resistant to the third generation cephalosporin, ceftazidime. The antibiotic resistance genes vanA, VanB, eryA, eryB, eryC were not detected in all the phenotypically resistant Staphylococccus species, but mec A gene and mph genes were detected. In the Acinetobacter species, a wide range of 30-100% resistance to penicillin G, ceftriazone, nitrofurantoin, erythromycin, and augmentin was observed. Polymerase chain reaction (PCR) revealed the presence of Tet(B) and Tet(39) genes in these species, while Tet (A), Tet(M) and Tet(H) were absent. Also, 9.3% of the Acinetobacter species showed phenotypic production of extended spectrum beta lactamases (ESBLs) while 3.5% were positive for the presence of blaCTX-M-1 genes. The Stenotrophomonas maltophilia isolates showed varying resistance to meropenem (8.9%), cefuroxime (95.6 %), ampicillin-sulbactam (53.9%), ceftazidime (10.7%), cefepime (29.3 %), minocycline (2.2%), kanamycin (56.9%), ofloxacin (2.9%), levofloxacin (1.3%), moxifloxacin (2.8%), ciprofloxacin (24.3%), gatifloxacin (1.3%), polymyxin B (2.9 %), cotrimoxazole (26.1%), trimethoprim (98.6%), aztreonam(58%) and Polymyxin B (2.9 %). The isolates exhibited significant susceptibility to the fluoroquinolones (74.3-94.7 %), polymycin (97.1%) and meropenem (88.1%). Only sul3 genes were the only sulphonamide resistance gene detected among the trimethoprim-sulphamethoxazole resistant isolates. The observed multiple antibiotic resistance indeces (MARI) of >2 for Staphylococcus species, Acinetobacter species and Stenotrophomonas maltophilia suggest that they have arisen from high-risk sources where antibiotics are in constant arbitrary use resulting in high selective pressure. The presence of tetracycline resistance genes in Acinetobacter species justifies the observed phenotypic resistance to oxytetracycline and intermediate resistance to minocycline. High phenotypic resistance and the presence of some resistance genes in Staphylococcus species is a possible threat to public health and suggests animals to be important reservoirs of antibiotic resistance determinants in the environment. Indiscriminate use of antibiotics induces this kind of antibiotic resistance and should be discouraged. Personal hygiene is encouraged as it reduces the load of Acinetobacter species contacted from the environment that may be difficult to control. Commensal Stenotrophomonas maltophilia are as important as their clinical counterparts due to their roles in opportunistic infection, antibiotic resistance and their associated genes, especially sul gene. Personal hygiene is hereby advocated especially when in contact with soil, plants and plants’ rhizospheric soil
  • Full Text:
  • Date Issued: 2012

Fluorescence “turn on” probe for bromide ion using nanoconjugates of glutathione-capped CdTe@ ZnS quantum dots with nickel tetraamino-phthalocyanine

  • Authors: Adegoke, Oluwasesan , Nyokong, Tebello
  • Date: 2013
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/190479 , vital:44998 , xlink:href="https://doi.org/10.1016/j.jphotochem.2013.05.013"
  • Description: In this paper, three differently sized glutathione (GSH)-capped CdTe@ZnS quantum dots (QDs) have been successfully conjugated to nickel tetraamino-phthalocyanine (NiTAPc) to form different QDs-NiTAPc nanocomplexes. Several techniques such as TEM, FT-IR, time-resolved fluorescence measurement and electronic spectroscopy were employed to characterize the nanocomplex. Bromide ion was chosen as a model anion to test the efficacy of the nanoprobe. The fluorescence of the nanoconjugate was “turned off” upon binding but was progressively “turned on” upon interaction with varying concentrations of bromide ion. Experimental results showed that the quantum size effect of nanocrystal QD determined the overall sensitivity and selectivity of the nanoprobe and followed the order QD563-NiTAPc > QD605-NiTAPc > QD621-NiTAPc. The mechanism of reaction is proposed.
  • Full Text:
  • Date Issued: 2013

Structural and optical properties of alloyed quaternary CdSeTeS core and CdSeTeS/ZnS core–shell quantum dots

  • Authors: Adegoke, Oluwasesan , Nyokong, Tebello , Forbes, Patricia B C
  • Date: 2015
  • Language: English
  • Type: Article
  • Identifier: vital:7244 , http://hdl.handle.net/10962/d1020248
  • Description: Synthesis of fluorescent alloyed quantum dots (QDs) with unique optical properties suitable for a wide array of chemical, physical and biological applications is of research interest. In this work, highly luminescent and photostable alloyed quaternary CdSeTeS core QDs of two different sizes were fabricated via the organometallic hot-injection synthetic route. Characterization of the nanocrystals were performed using TEM, XRD, UV/vis and fluorescence spectrophotometric techniques. We have demonstrated in this work that the well fabricated alloyed quaternary CdSeTeS core QDs possess unique optical properties that are advantageous over conventional core/shell systems. Formation of the CdSeTeS/ZnS core/shell with the desired optical properties comes with a number of challenges, hence the advantages of the quaternary alloyed core over the core/shell QDs are (i) avoidance of the challenging process of determining the proper shell thickness which can provide the desired optical properties in the core/shell system and (ii) avoidance of the lattice-induced mismatch between the core and the shell material which can either lead to incomplete exciton confinement or dislocation at the core/shell interface. , Original publication is available at http://dx.doi.org/10.1016/j.jallcom.2015.05.083
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  • Date Issued: 2015

A comparative study on the sensitive detection of hydroxyl radical using thiol-capped CdTe and CdTe/ZnS quantum dots

  • Authors: Adegoke, Oluwasesan , Nyokong, Tebello
  • Date: 2012
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/242778 , vital:51077 , xlink:href="https://doi.org/10.1007/s10895-012-1089-2"
  • Description: Four types of water-soluble luminescent quantum dots (QDs) whose surface was functionlaized with thioglycolic acid (TGA), 3-mercaptopropionic acid (MPA), or glutathione (GSH), were investigated for the sensitive and selective detection of hydroxyl radical (●OH) in aqueous media. It was found that the type of capping agent and QD influenced the sensitivity of the probe. The order of sensitivity of the probe was: GSH-CdTe@ZnS > MPA-CdTe@ZnS > TGA-CdTe > MPA-CdTe QDs. Under the optimum conditions, a limit of detection as low as 8.5 × 10-8 M was obtained using GSH-CdTe@ZnS. The effects of foreign reactive oxygen species and the Fenton reactants and products as possible interferences on the proposed probe were negligible for CdTe@ZnS QDs. Besides, experimental results indicated that CdTe@ZnS QDs were more attractive for the selective recognition of ●OH than CdTe QDs. The mechanistic reaction pathway between the QDs and ●OH is proposed.
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  • Date Issued: 2012

Optical properties of water-soluble L-cysteine-capped alloyed CdSeS quantum dot passivated with ZnSeTe and ZnSeTe/ZnS shells

  • Authors: Adegoke, Oluwasesan , Nyokong, Tebello , Forbes, Patricia B C
  • Date: 2015
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/193609 , vital:45352 , xlink:href="https://doi.org/10.1016/j.optmat.2015.05.024"
  • Description: Alloyed quantum dots (QDs) passivated with shell materials have valuable optical characteristics suitable for a wide array of applications. In this work, alloyed ternary CdSeS QDs passivated with ZnSeTe and ZnSeTe/ZnS shells have been synthesized via a hot-injection method and a ligand exchange reaction employing L-cysteine as a thiol ligand has been used to obtain these water-soluble nanocrystals for the first time. The photoluminescence (PL) quantum yield (QY) of alloyed L-cysteine-capped CdSeS was 71.2% but decreased significantly to 5.2% upon passivation with a ZnSeTe shell. The red shift in PL emission of the CdSeS/ZnSeTe QDs was attributed to be strain-induced whilst a lattice-induced process likely created defect states in the core/shell interface hence contributing to the decline in the PL QY. Nonetheless, the fluorescence stability of CdSeS/ZnSeTe QDs in aqueous solution was unperturbed. Further passivation with a ZnS shell (CdSeS/ZnSeTe/ZnS) improved the PL QY to a value of 58.7% and thus indicates that the defect state in the QDs core/shell/shell structure was reduced. PL lifetime exciton measurements indicated that the rates of decay of the QDs influenced their photophysical properties.
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  • Date Issued: 2015

Probing the sensitive and selective luminescent detection of peroxynitrite using thiol-capped CdTe and CdTe@ ZnS quantum dots

  • Authors: Adegoke, Oluwasesan , Nyokong, Tebello
  • Date: 2013
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/193757 , vital:45393 , xlink:href="https://doi.org/10.1016/j.jlumin.2012.08.002"
  • Description: CdTe and CdTe@ZnS quantum dots (QDs) capped with 3-mercaptopropionic acid (MPA), thioglycolic acid (TGA), or glutathione (GSH) have been employed for the first time as luminescent probes for the sensitive and selective detection of peroxynitrite (ONOO−) in aqueous solution. The sensitivity of the proposed probe followed the order: MPA–TGA–CdTe@ZnS>GSH–TGA–CdTe@ZnS>MPA–CdTe QDs. The varying degree of quenching is elucidated based on the QD–thiolate bond of CdTe@ZnS being more sensitive to oxidation from ONOO− than CdTe. The selectivity of the probe in the presence of co-existing species followed the order: GSH–TGA–CdTe@ZnS>MPA–TGA–CdTe@ZnS>MPA–CdTe QDs. QDs capped with MPA showed less selectivity for ONOO− than GSH. The best limit of detection (LOD) of 12.6 nM was obtained for MPA–TGA–CdTe@ZnS QDs. Time-resolved fluorescence measurements indicated that the interaction between ONOO− and the QDs is static in nature.
  • Full Text:
  • Date Issued: 2013

Fluorescence properties of alloyed ZnSeS quantum dots overcoated with ZnTe and ZnTe/ZnS shells

  • Authors: Adegoke, Oluwasesan , Mashazi, Philani N , Nyokong, Tebello , Forbes, Patricia B C
  • Date: 2016
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/240754 , vital:50868 , xlink:href="https://doi.org/10.1016/j.optmat.2016.02.024"
  • Description: Fluorescent alloyed ternary ZnSeS quantum dots (QDs) have been synthesized via the pyrolysis of organometallic precursors. The effects of passivation of ZnTe and ZnTe/ZnS shells on the optical properties of the ternary alloyed ZnSeS core have been studied. A ligand exchange reaction using L-cysteine as a capping ligand was used to obtain water-soluble nanocrystals. The nanocrystals were each characterized by UV/vis absorption and fluorescence spectroscopy, transmission electron microscopy, X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS). The photoluminescence (PL) quantum yield (QY) of alloyed ZnSeS QDs was 14% and this value increased to 27% when ZnTe was overcoated around the surface but further coating with a ZnS shell decreased the PL QY slightly to 24%. This implies that ZnTe shell suppressed non-radiative recombination exciton states in the alloyed core while further layering with a ZnS shell offered no further improvement in suppressing the defect states. XPS analysis confirmed the presence of the first shell layering but showed a weakened intensity signal of S (2p) and Se (3d) for the ZnSeS/ZnTe/ZnS QDs. Our work demonstrates for the first time that shell passivation of alloyed Zn-based QDs can offer improved optical properties. We hope the optical information presented in this work will be useful in the selection of alloyed Zn-based QDs appropriate for the intended application.
  • Full Text:
  • Date Issued: 2016
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