QDs for Biomedical Imaging

The first papers devoted to the biological use of quantum dots were published by Dr. A. Paul Alivisatos and Dr. J. Shuming Ni in the same issue of science for 1998. Quantum dots are fragments of a conductor or semiconductor (for example, InGaAs, CdSe or GaInP/InP), whose charge carriers (electrons or holes) are limited in space in all three dimensions. The size of the quantum dot must be so small that the quantum effects are significant. This is achieved if the kinetic energy of the electron is noticeably greater than all other energy scales: first of all, it is greater than the temperature expressed in energy units.

Simply put, a quantum dot is a semiconductor whose electrical characteristics depend on its size and shape. The smaller the crystal size, the greater the distance between the energy levels. When an electron passes to an energy level lower, a photon is emitted. By adjusting the size of the quantum dot, we can change the energy of the emitted photon, which means we can change the color of the light emitted by the quantum dot. The main advantage of a quantum dot is the ability to precisely adjust the wavelength of the emitted light by changing the size.

Quantum dots can be of various shapes and sizes, but most often they are spheres with a diameter of 2-10 nm, and they consist of 103 – 105 atoms. Quantum dots of different sizes can be assembled into gradient multilayer nanofilms.

Quantum dots are special nanocrystals that behave like one single atom. Their properties are so unique that quantum dots are used in various high–tech industries – from cancer diagnostics to the construction of nanoelectronic logic circuits.

Mostly, her research focus on a Micelle Encapsulation.

Microemulsion factors are well-known methods for the synthesis of Q-dots at room temperature. The methods can be classified as normal microemulsions, then there is oil-in-water, or as reverse microemulsions, then there is oil-in-water. In certain cases, other polar solvents, such as alcohol, can be used instead of water. The reverse micelle mechanism is popular for QT synthesis, where

two immiscible liquids (polar water and non-polar long-chain alkane) are mixed and mixed to form an emulsion. Nanometer water droplets dispersed in nalkan solutions can be obtained using surfactantssuch as aerosol OT (AOT), cetyltrimethyl ammonium bromide (CTAB), sodium dodelyl sulfate (SDS) or triton-X. Becausesurfactants end in hydrophilic and hydrophobic groups at opposite ends, numerous continuous droplets, called micelles, are formed in a continuous oil medium. These micelles are thermodynamically stable and can act as “nanoreactors”. Mixing of vigorously stirredmicellar solutions leads to a continuous exchange of reagents due to dynamic collisions. The growth of the resulting QDs is limited by the size of the micelle, which is controlled by the molar ratio of water andsurfactant.

The inverse micelle method was used to prepare quantum dots of the core and core/shell II-VI, such as CDs, CDs: Mn/ZnS, ZnS/CdSe, CdSe/ZnSe, ZnSe and IV-VI KT. Some advantages of this process are the simplicity of controlling the size of QDs by changing the molar ratio of water to the surfactant, a narrow size distribution compared to the sol-gel process and the ease of dispersion of QDs. Some problems include low yield and inclusion of impurities and deficiencies.

Qds uses the motion of conduction band electrons,valence band holes, or excitons. Excitons are pairs of electronsof the conduction band and holes in the valence band, which are defined for asimpler description of the motion of electrons and holes.

Quantum limitation is an effect that occurs on a nanoscalescale, which can be mainly observed in semiconductorswhen their particle size is less than 10 nm. More precisely, this size depends onof the exciton boron radius in this material. Semiconductornanostructures in which such a phenomenon occurs, limited in onedimension, are known as “quantum wells”, limited in two dimensionsare known as “quantum wires” and in three dimensions are called”quantum dots”. The spectacular effect of the mentioned phenomenon canbecome a multicolored glow of quantum dots. When such nanostructuresare irradiated with ultraviolet light at a certain wavelength,radiation is carried out in the visible range. The emission depends onthe size of the nanoparticles. In the first approximation, this can be explainedby an increase in the band gap, that is, by the distance between the orbitalsHOMO-LUMO (the highest occupied molecular orbital is thelowest unoccupied molecular orbital), together with a decreasein particle size. This means that the smallest nanoparticles give a semiconductor.

                                                                        References

Jacak, Lucjan, Pawel. Hawrylak, and Arkadiusz Wójs. Quantum Dots. Berlin;: Springer, 1998. Print.

Fan, Qirui et al. “Effect of Micelle Encapsulation on Toxicity of CdSe/ZnS and Mn-Doped ZnSe Quantum Dots.” Coatings (Basel) 11.8 (2021): 895–. Web.