Quantum dots genosensor for Her2/Neu oncogene - a breast cancer biomarker

Philosophiae Doctor - PhDThe human epidermal growth factor receptor (HER)-family of receptor tyrosine kinases; human epidermal growth factor receptor 1, human epidermal growth factor receptor 2, human epidermal growth factor receptor 3 and human epidermal growth factor receptor 4 (EGFR/HER1, ErbB2/HER2, ErbB3/HER3, and ErbB4/HER4) plays a major role in the pathogenesis of many solid tumours, in approximately 25 - 30% of breast cancers. Breast cancer is the second most common type of cancer and affects around 3000 women annually in South Africa alone. While the benefits of treatment and cancer progress to enhance therapeutic effectiveness for the patient are well documented, it is also important to employ or fabricate methods in which cancer can be screened at an early stage. A number of gene and protein based biomarkers have shown potential in the early screening of cancer. One specific biomarker that is over-expressed in 20 - 30% of human breast cancers is the human epidermal growth factor receptor 2 (Her2/neu). Several methods have been developed for detection of Her2/neu oncogene including immunohistochemistry (IHC), enzyme-linked immunosorbent assay (ELISA), fluorescent in situ hybridisation (FISH) and polymerase chain reaction(PCR). However, these methods are subjected to interference problem. For these reasons an ultrasensitive, cheap and easy to use genosensor has been developed for early detection of the Her2/neu oncogene using electrochemical and spectroscopic methods. Due to their high surface-to-volume ratio, electro-catalytic activity as well as good biocompatibility and novel electron transport properties quantum dots are highly attractive materials for ultra-sensitive detection of biological macromolecules via bio-electronic or bio-optic devices. In this study a quantum dots (QDs)-based genosensor was developed in which Ga2Te3-based quantum dots were synthesised using a novel aqueous solution approach by mixing 3-mercaptopropionic acid (3MPA)-capped gallium metal precursor with reduced tellurium metal. The morphological, compositional and structural characterisation of the QDs was investigated prior to their utilization in DNA sensor construction

Influence of quantum dot surface on electrochemical DNA sensing mechanism

Owing to their high surface‐to‐volume ratio, electrocatalytic activity, biocompatibility and novel electron transport properties, quantum dots (QDs) are highly attractive materials for the ultrasensitive detection of biological macromolecules via bioelectronic devices. In this study, a QD‐based genosensor was developed, in which Ga2Te3‐based QDs were synthesized using an aqueous solution approach by mixing 3‐mercaptosuccinic acid (3MSA)‐capped gallium metal precursor with reduced tellurium metal. The results enabled us to reach an original understanding related to the active material involved in the probe DNA sensing mechanism. The morphological and structural characterization of the QDs was performed prior to their utilization in a DNA sensor construction. High‐resolution TEM (HR‐TEM) and atomic force microscopy (AFM) images confirmed the spherical and crystalline nature of the QDs, whereas X‐ray photoelectron spectroscopy (XPS) and X‐ray diffraction (XRD) analyses were able to confirm the oxidation states and formation of the prepared QDs. UV/Vis was capable of finding the optical band gap energy and the photostability of the QDs. The resultant Ga2Te3 QDs together with metal ions confirmed their use for DNA signal detection through their DNA binding mechanism in the genosensor construction. Genosensing in Cs+ and Li+ ions exhibited high sensitivity (2.74–3.69 μA ng−1 mL) and very low detection limits (0.4 pg mL−1) with a linear dynamic range of 0.1–1 ng mL−1

Cytochrome C biosensor for the determination of trace level arsenic and cyanide compounds

Magister Scientiae - MScIn this work, an electrochemical method based on a cyt c biosensor has been developed, for the detection of selected arsenic and cyanide compounds. Boron Doped Diamond (BDD) electrode was used as a transducer, onto which cyt c was immobilised and used for direct determination of Prussian blue, potassium cyanide and arsenic trioxide by inhibition mechanism. The sensitivity as calculated from cyclic voltammetry (CV) and square wave voltammetry (SWV), for each analyte in phosphate buffer (pH= 7) was found to be (1.087- 4.488 ×10-9 M) and the detection limits ranging from 0.0043- 9.1 μM. These values represent a big improvement over the current Environmental Protection Agency (EPA) and World Health Organisation (WHO) guidelines.South Afric

Nanoscaled Electrocatalytic Optically Modulated ZnO Nanoparticles through Green Process of Punica granatum L. and Their Antibacterial Activities

Most recently, green synthesis of metal oxide nanoparticles has become an interesting subject of the nanoscience and nanotechnology. The use of plant systems has been deemed a green route and a dependable method for nanoparticle biosynthesis, owing to its environmental friendly nature. The present work demonstrates the bioreductive green synthesis of nanosized zinc oxide (ZnO) using peel extracts of pomegranate. Highly crystalline ZnO nanoparticles (ZnO NPs) which are 5 nm in particle size were characterised by HRTEM and XRD. FT-IR spectra confirmed the presence of the biomolecules and formation of plant protein-coated ZnO NPs and also the pure ZnO NPs. Electrochemical investigation revealed the redox properties and the conductivity of the as-prepared ZnO nanoparticles. The optical band gap of ZnO NPs was calculated to be 3.48 eV which indicates that ZnO NPs can be used in metal oxide semiconductor-based devices. Further, the nanomaterials were also found to be good inhibitors of bacterial strains at both low and high concentrations of 5–10 mg mL−1

Electro-Design of Bimetallic PdTe Electrocatalyst for Ethanol Oxidation: Combined Experimental Approach and Ab Initio Density Functional Theory (DFT)—Based Study

An alternative electrosynthesis of PdTe, using the electrochemical atomic layer deposition (E-ALD) method, is reported. The cyclic voltammetry technique was used to analyze Au substrate in copper (Cu2+), and a tellurous (Te4+) solution was used to identify UPDs and set the E-ALD cycle program. Results obtained using atomic force microscopy (AFM) and scanning electron microscopy (SEM) techniques reveal the nanometer-sized flat morphology of the systems, indicating the epitaxial characteristics of Pd and PdTe nanofilms. The effect of the Pd:Te ratio on the crystalline structure, electronic properties, and magnetic properties was investigated using a combination of density functional theory (DFT) and X-ray diffraction techniques. Te-containing electrocatalysts showed improved peak current response and negative onset potential toward ethanol oxidation (5 mA; −0.49 V) than Pd (2.0 mA; −0.3 V). Moreover, DFT ab initio calculation results obtained when the effect of Te content on oxygen adsorption was studied revealed that the d-band center shifted relative to the Fermi level: −1.83 eV, −1.98 eV, and −2.14 eV for Pd, Pd3Te, and Pd3Te2, respectively. The results signify the weakening of the CO-like species and the improvement in the PdTe catalytic activity. Thus, the electronic and geometric effects are the descriptors of Pd3Te2 activity. The results suggest that Pd2Te2 is a potential candidate electrocatalyst that can be used for the fabrication of ethanol fuel cells

A gallium telluride quantum dots bioelectrode system for human epidermal growth factor receptor-2 (Her2/neu) oncogene signalling

Human epidermal growth factor receptor 2 (Her2/neu) is a biomarker that is overexpressed in human breast cancers. A quantum dots (QDs) -based genosensor for Her2/neu oncogene was developed with gallium telluride QDs and amine-terminated probe ssDNA (NH2-5′-AATTCCAGTGGCCATCAA-3′), that is complementary to the DNA sequence of a section of the ERF gene of HER-2/neu (i.e. 5′-GAACATGAAGGACCGGTGGGC-3′). The QDs were highly crystalline, 6 nm (from XRD) in size and had band gap values of 3.3 eV and 3.5 eV calculated from fluorescence emission and UV-visible absorption data, respectively. The sensor sensitivity and limit of detection values were 10.0 μA ng−1 mL−1 and 0.2 pg mL−1 Her2/neu oncogene, respectively

Quantum Dot Nanotoxicity Investigations Using Human Lung Cells and TOXOR Electrochemical Enzyme Assay Methodology

Recent studies have suggested that certain nanomaterials can interfere with optically based cytotoxicity assays resulting in underestimations of nanomaterial toxicity. As a result there has been growing interest in the use of whole cell electrochemical biosensors for nanotoxicity applications. Herein we report application of an electrochemical cytotoxicity assay developed in house (TOXOR) in the evaluation of toxic effects of mercaptosuccinic acid capped cadmium telluride quantum dots (MSA capped CdTe QDs), toward mammalian cells. MSA capped CdTe QDs were synthesized, characterized, and their cytotoxicity toward A549 human lung epithelial cells investigated. The internalization of QDs within cells was scrutinized via confocal microscopy. The cytotoxicity assay is based on the measurement of changes in cellular enzyme acid phosphatase upon 24 h exposure to QDs. Acid phosphatase catalyzes dephosphorylation of 2-naphthyl phosphate to 2-naphthol (determined by chronocoulometry) and is indicative of metabolic activity in cells. The 24 h IC50 (concentration resulting in 50% reduction in acid phosphatase activity) value for MSA capped CdTe QDs was found to be 118 ± 49 μg/mL using the TOXOR assay and was in agreement with the MTT assay (157 ± 31 μg/mL). Potential uses of this electrochemical assay include the screening of nanomaterials, environmental toxins, in addition to applications in the pharmaceutical, food, and health sectors