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Nanotechnology Research

This research involves the synthesis of nanomaterials such as single walled carbon nanotubes, quantum dots and magnetic fluids for use in medical applications (in combination with dyes such as metallophthalocyanines) and for the development of sensors.

Single-walled carbon nanotubes (SWCNT) are defined as quasi-one-dimensional (1-D) quantum structures. The ability of SWCNT to absorb light in the near-infrared (NIR) region and initiate cell death via a photothermal or photohyperthermia (PHT) effect is of particular interest. Death of cancerous tissue is initiated, since such tissue is sensitive to heat, while normal cells are less affected. PHT is also known to improve the effectiveness of other cancer therapies such as chemotherapy, radiotherapy and photodynamic therapy (PDT).

Quantum dots (QDs) are defined as 0-dimensional semiconductor materials. Recently, QDs have found focus as a new generation of photosensitizers in photodynamic therapy. QDs are capable of transferring energy to ground state molecular oxygen to generate cytotoxic singlet oxygen and thus enhance the efficacy of PDT. The singlet oxygen-generating capabilities of QDs are limited, therefore conjugation of QDs and other nanoparticles such as gold, silver and platinum to a mediating PDT photosensitizer, e.g. a metallophthalocyanine, facilitates the probability of increased PDT efficiency through energy transfer (ET).

Hyperthermia (HPT) is a type of treatment in which body tissue is exposed to high temperatures to damage and kill cancer cells or to make cancer cells more sensitive to the effects of radiation and certain anti-cancer drugs. Hyperthermia (HPT) is, very simply, the application of concentrated therapeutic heat to treat cancer. Malignant cells are more sensitive to heat than normal cells and the raising of temperature is a way to selectively destroy cancer cells. Nanoparticles of magnetic fluids (iron oxide) are used for HPT.

Development of electrochemival sensors based on self-assembled monolayers, carbon nanotubes and electospun fibres

The development of electrodes modified with metallophthalocyanines at nano-scale for detection of substances that are
important in the environmental, medical and biological sector, is of importance. In order to construct materials with optimum properties, the study of phthalocyanine molecules organized as supramolecular structures such as thin films (by polymerization) and self assembled monolayers (SAMs) will be undertaken. The fabrication of carbon nanotubes (CNT) and their use in improving the electrode behaviour will be explored. As stated above the phthalocyanine molecules (in the presence and absence of CNTs) have a diverse range of applications - hence we
have been using SAMs and electropolymerized phthalocyanines as sensors for a range of molecules, including environmentally important molecules such as thiols and pesticides.

Electrospinning is a method to produce nanofibres on conductive surfaces by forcing solutions containing polymers to travel from the tip of a capillary to a collecting target by applying a high voltage (few kV) between capillary tip and collecting target. On its way, the jet of solution starts to split (known as spraying) due to solvent evaporation, and results in the deposition of nanofibres on the collecting target. The advantage of this way of deposition is that the ratio of active surface/geometrical surface is much bigger than for common deposition methods. The formed fibres will be used for the detection of medically important molecules such as NO detection for air filtration.

Photodynamic Therapy

Photodynamic therapy (PDT) is an exciting new approach to cancer diagnosis and treatment, using a combination of oxygen, laser light and a photosensitizer. PDT may be thought of as specialized form of chemotherapy in which the drug (the photosenstitizer) is harmless by itself, but gets activated in the presence of molecular oxygen on exposure to light. It is thus a localized form of treatment which does not have the side effects of chemotherapy. Current evidence suggests that PDT has the potential to be widely applicable to a wide range of human cancers. Porphyrin photonsitizers have been tested for use in many cancers such as lung and bladder. However, many of the drugs based on porphyrins have limitations, such as localization in healthy tissue and irreproducible synthesis. Also, porphyrin photosensitizers are absorbed in the UV region where tissue penetration by light is minimal. The synthesis of new drugs that are absorbed in the visible and near IR regions will allow for the treatment of thicker tumours. Thus the aim is to study metallophthalocyanines and related molecules as photosensitizers for PDT.

Recent advances in the treatment of tumours are towards the synthesis of bi-functional agents that allow the combined action of PDT and hyperthermia. This is expected to result in tumour damaging based on both heat dissipation (HPT) and light photosensitization (PDT). HPT increases the cellular uptake of oxygen, since the heating up of the cell causes dilation which allows free flow of oxygenated blood to the cells. This is essential for PDT, where ground state oxygen is needed to produce cytotoxic derivatives of oxygen. uptake of phthalocyanines in tumours may help localize the magnetic particles (used for HPT) in tumours, if the two (phthalocyanines and magnetic particles) are connected together. Magnetic particles produce heat through various kinds of energy losses during application of an external AC magnetic field. If magnetic particles can be accumulated only in the tumour tissue, cancer specific heating is available.

MPc-PDT agents will also be combined with quantum dots (QDs), which are nanoparticles of for example CdSe that absorb and then re-emit light, hence can be used in locating cancers. The combination of PDT, HPT and QDs allows for an efficient cancer treatment involving photosensitization (PDT), heat treatment (HPT) and imaging QDs.

The project involves (i) the synthesis of novel phthalocyanine molecules for PDT, (ii) the study of their photochemical and photophysical properties using state-of-art laser flash photolysis equipment and (iii) the study of the behaviour of the selected drugs on cancer The preferential cells. The novel phthalocyanine materials will then be combined with nanoparticles of magnetic fluids (iron oxide) for use in combination PDT-HPT. The novel phthalocyanine materials will also be combined with surface fuctionalised quantum dots (e.g. CdSe).

The photophysical and photochemical properties of MPc combined with QDs or HPT agents will be studied. The complexes will then be studied in cells in collaboration with Prof Chen (China).

Enzyme-like Catalysts

Cytochrome-P450s are a class of biological enzymes with an iron porphyrin active site which catalyzes the addition of oxygen to a substrate. The most important representation of this class of reactions is the insertion reaction:

R-H + 1/2 O2 -----> R- OH

Such reactions are imperative for the elimination of harmful hydrophobic compounds such as steroid precursors and pesticides. This reaction is of great interest to many industries, in particular the petroleum industry, which produces thousands of tons of alkanes per annum. These industries have a limited usage for alkanes and they are therefore compounds of low value. Thus, companies like Sasol are interested in the partial oxidation of alkanes , which will produce fine chemicals of high value such as alcohols, ketones and aldehydes.

Intensive research has been undertaken during the past few decades using synthetic iron porphyrins as models of the Cytochrome-P450 enzymes. A large amount of success has been achieved using porphyrins with good turnover rates, yields and selectivity on an industrial scale. Phthalocyanines have the same chemical behaviour as the naturally occurring porphyrins, with an added advantage of stability and ease of production. We plan to study the effects of different peripheral substituents and central metals in phthalocyanines on the activity of these catalysts.

Pollution Control

Phenol derivatives such as chlorinated phenols are well-known pollutants. They are spread through the environment due to their discharge from industrial plants or factories and because of their use as pesticides. The European Economic Community (EEC) and USA have included phenols and substituted-phenols among the priority pollutants. One of the methods for purification of water is photochemical destruction of pollutants using UV light. However, photodegradation products for some of the chlorinated phenols are more toxic than the parent compounds. Photosensitized oxidation has been suggested as a possible solution to this problem. We explore the use of phthalocyanines as photosensitizers in the transformation of chlorinated phenols and other pollutants.

Analysis of low concentrations of the pollutants in water is desirable. Electrochemical methods are superior to spectroscopic methods because of (i) low cost of the equipment (ii) portability and (iii) high sensitivity. We plan to improve the stability and sensitivity of the electrodes for analysis and degradation of phenolic and other pollutants by modifying them with phthalocyanine catalysts.

Development of non-linear optical material

Safety: development of protecting agents

Phthalocyanines (Pcs) display both second- and third-order nonlinear optical (NLO) properties such as second harmonic generation (SGH), third harmonic generation (THG) and optical limiting (OL). These molecules can thus be used for protection of optical elements (e.g. eyes) against damage by exposure to sudden high intensity light. OL is a nonlinear effect consisting of a decrease in the transmittance of NLO material (such as Pc) under high-intensity illumination. Thus the transmission of the optical limiter (Pc) is high at normal intensities and low for intense beams.

Phthalocyanines containing In and Ge central metals exhibit good NLO properties. These phthalocyanines are being synthesized in our laboratory and characterized.

It has been reported that NLO properties of phthalocyanines are enhanced by fabrication of nanoparticles from phthalocyanines. Pc nanoparticles are readily synthesized using methods which includes microwave irradiation. The nanoparticles thus formed have to be characterized using AFM, since again the size and morphology are important.

Last Modified: Thu, 02 May 2013 12:59:55 SAST