Quantum Dots: Applications in Biotechnology
Quantum dots are nanoscale semiconductor particles, typically ranging from 2 to 10 nanometres in diameter. At this size, the quantum confinement effect is significant, meaning that the electrons are confined to a finite region of space, leading to distinct energy levels. This results in the electronic band structure being discrete rather than continuous, similar to the behaviour found in atoms. Due to this unique property, quantum dots exhibit fascinating optical and electrical properties, particularly fluorescence, making them extremely valuable in various scientific and industrial applications.
Dr. Matthew Booth explained that quantum dots could be described using the simple model of a particle in a one-dimensional box. In this potential well model, a particle (e.g., an electron) is confined within a region of space where its energy is limited. This is only possible because of the nano-size of the particle, which allows it to exhibit quantised energy states.
This quantum dot has an exciton Bohr radius, above which quantum confinement effects no longer significantly dominate the particle’s behaviour. Crucially, because of the quantum confinement effects, the optical properties of the quantum dot are primarily size-dependent. That is to say, a smaller quantum dot has a larger bandgap, which is the energy gap between the highest occupied and lowest unoccupied energy states. This bandgap determines the wavelength of the light emitted by the dot and, therefore, its colour.
Quantum dots exhibit fluorescence when excited by certain wavelengths of light, typically ultraviolet (UV) light. Because of their nanoscale size and quantum confinement properties, quantum dots are highly photostable. This is in contrast to organic dyes, which degrade under UV exposure. Quantum dots, therefore, can repeatedly emit light at their designated wavelength, making them suitable for many applications where organic dyes would fail.
As to be expected by its title, the seminar discussed many of the medical applications of quantum dots. By using quantum dots, bioimaging techniques are vastly improved. Quantum dots can bind to biomolecules, such as antibodies, and emit fluorescent light that is then detected using fluorescence microscopy. Because of their sustained photostability and high-intensity emission, quantum dots can allow researchers to track a specific biomolecule over extended periods.
Perhaps one of the most exciting areas of research concerns the potential use of quantum dots in the treatment of cancer. Tumours and their antigens can be attached to quantum dots for targeted imaging or treatment, and photodynamic therapy may utilise the photostability of quantum dots to excite photosensitising agents within target cells to more accurately destroy cancerous tissue. Additionally, quantum dots may help solve our current medical records issues by use as an on-body record of an individual’s vaccination history.
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This article gives a detailed overview of Dr Matthew Booth’s seminar on quantum dots. This article covers all the areas in the seminar including relevant examples, theory and applications. It includes relevant quotes from Dr Booth. Well done!