Nanotechnology: quantum dots with impermeable shells, powerful tools for nanoengineering discovery!
The unique optical properties of quantum dots make them attractive tools for many applications, from tip display to medical imaging. However, the physical, chemical or biological properties of quantum dots must be suitable for specific applications of quantum dots. Unfortunately, quantum dots prepared by chemical methods using copper-based click-through reactions destroy the luminescence ability of quantum dots. However, Russian scientists have shown that zinc oxide (ZnO) quantum dots, prepared by a new method, which have been modified by the click-reaction of copper ions, completely retain their ability to emit light.
“The click-through reaction catalyzed by copper cations has long attracted chemists' attention to quantum dots. However, the experimental results are disappointing: after modification, the luminescence is very poor and is not suitable for use. We are the first to show that organometallic precursors can form quantum dots while retaining their valuable optical properties after copper catalyzed click-through reactions.” Professor Janusz Lewinski (IPC PAS,FC WUT) said.
Quantum dots are crystal structures of several nanometers. As semiconductor materials, they have various interesting characteristics of typical quantum objects, including strictly limited energy absorption and emission radiation. Because atoms interact with light in similar ways, quantum dots are often called artificial atoms. In some ways, however, quantum dots are more common than atoms. The optical properties of each point actually depend on the size and type of the material they form. This means that quantum dots can be precisely designed for specific applications.
In order to adapt them to specific applications, quantum dots must be customized according to their physical and chemical properties. For this purpose, chemical molecules with suitable properties are attached to their surfaces. Due to the simplicity, effectiveness and speed of the process, a particularly convenient method is click response. Unfortunately, the copper ion click-through reaction causes the quantum dots to almost completely quench their luminescence.
“Failure is usually caused by insufficient quantum dot mass, which is determined by the synthesis method. At present, ZnO sites are mainly produced from inorganic precursors by sol-gel method. Quantum dots produced in this way are coated with heterogeneous and possibly are leaky shells of various chemical molecules. During the click-through reaction, the copper ion is directly in contact with the surface of the quantum dot and the luminescence of the quenching point becomes completely useless.“ Dr Agnieszka explained, the first author of an article in the Grala (IPC PAS), Journal of Chemical Communications.
For years, Professor Lewinski's team has been developing alternatives to producing high-quality ZnO quantum dots. The proposed method provides quantum dots derived from organic zinc precursors. The composition of nanoparticles can be programmed at the precursor preparation stage, which allows for precise control of the properties of the organic-inorganic interface.
Quantum dots have many applications in various industrial processes and are used as nanopharmaceuticals in biology and medicine in which they are combined with bioactive molecules. Nanoscale objects functionalized in this way are used to mark individual cells and the entire tissue. The unique properties of quantum dots can also be used for long-term monitoring of labeled objects. However, commonly used quantum dots contain toxic heavy metals, including cadmium. In addition, they have come together in the solution, which supports their shell's lack of tension. At the same time, the ZnO sites produced by Professor Lewinski are nontoxic, and do not aggregate and bind to many compounds, so they are more suitable for medical diagnosis and imaging of cells and tissues.