Quantum dots (QDs), popularly used as QLED displays in TVs, are now playing a crucial role in the development and transformation of the medical field. QDs are now being used in advanced and intelligent applications like bio-imaging, drug delivery, sensing, and therapy
Nanotechnology, the branch of science and engineering that deals with the world of nanometer-sized particles, is rapidly growing due to its potential to solve some of the most pressing problems in the world like hunger and serious diseases such as cancer.
An important topic of research in nanotechnology, quantum dots (QDs) that find their popular use as QLED displays to light up TVs have a much wider scope beyond that. QDs are nanoscale crystals made of pure metal or semiconductor alloys with special optic and electronic properties compared to larger particles due to quantum mechanics.
Characteristics of these particles include good photostability, high brightness, high quantum yield, narrow and symmetrical emission, broad excitation, and so on. These advantages make them suitable for advanced and intelligent applications like bio-imaging, drug delivery, sensing, and therapy. This is especially beneficial for diseases hard to diagnose or treat.
When ultraviolet rays hit these dots, they can emit light of different colours based on their size. QDs have tunable optical properties, which make them useful as fluorescent dyes for deep-tissue imaging typically used in animal models since most conventional organic dyes are not capable of near-infrared (NIR) emissions. Visible light, with a wavelength range of about 400-700nm, is unsuitable for transmission through biological tissues but QDs can make use of the NIR optical window. This is done by controlling the size of the QDs.
Development of theranostics platforms for simultaneous sensing, imaging and therapy is also increasing. In theranostics, specific targeted therapy is delivered to a patient based on specific targeted diagnostic images and tests. QDs can behave as nano-carriers for drug delivery or fluorescent labels for a theranostic approach in therapy. Fluorescent labelling and detection involve binding fluorescent dyes to biomolecules so as to visualise them through fluorescence imaging, such as lymph nodes in a pig. Theranostics helps in detecting target biomolecules like tumour cells for early diagnosis of cancer, tracking progress of tumour elimination, and localised treatment to specific sites.
Last year, researchers headed by a team at the Massachusetts Institute of Technology (MIT) created a microneedle platform using QDs, which can deliver vaccines as well as invisibly encode vaccination history directly in the skin for recordkeeping at the same time. The NIR emission detection was made possible by a specially equipped smartphone.
They can also work as optical indicators for the development of biosensors. For instance, Project BioSensing, a collaboration among Germany’s Fraunhofer institutes (ISC and IME) and Leiden University’s Institute of Physics in the Netherlands, is aimed at developing advanced biosensors using quantum technology.
QDs also find other application areas such as solar cells, lasers, photovoltaic devices, computing, and so on. One such example is a new type of solar panel created by scientists at the National Research Nuclear University MEPhI, Russia based on hybrid material consisting of QDs and photosensitive protein. According to a report from Regal Intelligence, the global QDs market is expected to grow to US$ 10,423.13 million by the end of 2025 at a CAGR of 22.06 per cent.
Although there are numerous chemical and physical methods available to synthesise QDs, biosynthetic methods enhance the biocompatibility and biostability of their structure through the utilisation of biomolecules such as proteins, enzymes, and nucleic acids for formation. Other ways include modifying the surface of available QDs and using artificial cellular structures. In these types of processes, no toxic products are generated and the QDs obtained are suitable for biological and biomedical applications. This is important as toxic elements like cadmium, mercury, lead, and more can leak causing cell death and inflammation.
Several challenges in this realm still remain to be solved including environmental impact, toxicity, manufacturing costs, among others. This restricts their use to animal research. The issue is that biosynthesised QDs have a lower quantum yield and lesser uniformity in their size as compared to those sythesised through other methods. More research needs to be done in relation to the mechanisms and protocols for the scalability of high-quality, non-toxic QD production. In addition, the biosensors must have higher sensitivity to improve the reliability and efficiency of disease diagnosis in real-time.