**2.2 Quantum dots**

magnesium, sodium, calcium, potassium, ferric, aluminum, barium and zinc ions. In the experimental stage, polymer and electrolyte concentrations, pH, temperature

This method is based on a salt interaction such as a polymer, organic solvent, and magnesium chloride hexahydrate or magnesium acetate tetrahydrate. An emulsification mechanism is performed. Salting out method is based on increasing hydrophobic effect as a result of electronic repulsion of dissolved anions with highdensity loads. This resulting hydrophobic effect increases the uniformity of the water-soluble intermediate phase structure, reduces entropy and causes agglomeration of the solvent. This is because the presence of high-charge salts in the system decreases entropy by increasing the regularity between similar surfaces, this result

≈ Rb+ ≈ Ca2+ ≈ Co2+ ≈ Mg2+ ≈ Fe2+ ≈ Zn2+ ≈ Cs+ ≈ Mn2+ ≈ Al3+ > NH4<sup>+</sup> > H<sup>+</sup>

In this method, gelation is formed using calcium chloride and sodium alginate. A suitable mixture of these two compounds results in gelling. Poly-L-lysine is added to the resulting solution as a polymer and a polyelectrolyte mixture is formed by mixing. Subsequently, nanospheres are synthesized by centrifugation [8].

This method is based on the principle of emulsifying the active substance in the polymer and an organic solvent and removing the solvent by reducing the temperature and pressure. In this method, polyvinylchloride or gelatin may be used as the

It is one of the most widely used methods for the synthesis of nanoparticles. The solvent displacement is based on the displacement of a semi-polar solvent with the polymer interface. In this method, the organic phase containing the active substance and the polymer structure in the aqueous phase is self-emulsified. The polymer and active ingredient are dissolved in an organic solvent such as watermiscible ethanol, methanol or acetone. The organic phase is injected into the aqueous phase containing the active ingredient. The nanospheres are synthesized by precipitating the polymer in which the organic phase is dispersed in the aqueous

This method is particularly preferred for obtaining nanospheres from natural polymers. The active substance is added to the polymer and solvent, and crosslinking is performed. Crosslinking agents must be added to effect crosslinking. The suspension is lyophilized by centrifugation, and the nanospheres are synthesized [9]. The most common and advantageous method used in the synthesis of nanospheres is the solvent displacement method. This method will provide great advantages especially in controlled drug release systems. Nanospheres synthesized

<sup>2</sup> ≈ CO3

and the cations: Na<sup>+</sup> > K<sup>+</sup> > Li<sup>+</sup> ≈ Ba2+

<sup>2</sup> > ClO3

.

≈

and biomolecule concentrations are important parameters to be considered.

is also desirable. Anions reducing water solubility; OH ≈ SO4

> Br ≈ I > NO3

*Smart Nanosystems for Biomedicine, Optoelectronics and Catalysis*

*2.1.3 Salting out*

Cl ≈ OAc ≈ IO3

*2.1.4 Controlled gelification*

*2.1.5 Solvent evaporation*

emulsifying agent.

phase.

**116**

*2.1.6 Solvent displacement*

*2.1.7 Desolvation technique*

Quantum mechanics is the starting point of nanotechnology. These nano-sized semiconductor crystals are called quantum dots. Quantum dots are giant atomic structures that contain thousands of atoms. When substances are nano-sized, they


#### **Table 1.**

*Some examples of nanospheres, according to the literature.*

**Figure 4.** *The cancer treatment with gold nanospheres.*

act according to quantum laws. The most preferred quantum points due to their semiconductivity, optical, and electrical properties are CdSe, InAs, CdS, GaN, InGeAS, CdTe, PbS, PbSe, ZnS. The controllable size of the quantum dots leads to outstanding optical and electrical properties, as the size of the quantum dots changes, the wavelength and color of their radiation changes. Quantum points are revealed by the stimulation of electrons [18, 19].

*2.2.2 Colloidal synthesis*

**Figure 6.**

*regrowth.*

**Figure 7.**

**119**

*2.2.3 Electrochemical coupling*

nents: precursors, organic surfactants, and solvents.

*The Components of Functional Nanosystems and Nanostructures*

*DOI: http://dx.doi.org/10.5772/intechopen.92027*

face, the nanostructures spontaneously form on the metal.

Colloidal synthesis is a practical synthesis technique where quantum dots can be synthesized easily under laboratory conditions. They consist of three main compo-

*Quantum dots fabrication process. (a) After AFM oxidation. (b) After removing oxide dots. (c) After MBE*

Electrochemical coupling is a technique in which quantum dots can form spontaneously regularly. As a result of the ionic reaction at the electrolyte-metal inter-

In the field of medicine, positron emission tomography and single-photon emission computed tomography are used in nuclear imaging systems, especially in the diagnosis of cancer diseases. Quantum dots can also be used in many engineering branches such as more efficient solar panels, bio-agents used for diagnostic purposes in medicine, low-energy lasers, LED lights of the desired color, low-energy, and more-lit bulbs, low-energy plasma televisions and displays. **Figure 7** shows the visualization of the quantum dots under UV light to detect different tumor cells by the addition of bioagents. Biological applications of quantum dots are examples of DNA protein sensors, sugar sensors, immunoassays, live cell imaging, bio-sensing, in vitro imaging, biological imaging, single molecule tracking, in vivo and animal

*Visualization of the quantum dots under UV light to detect different tumor cells by the addition of bioagents [19].*

Quantum dots can be synthesized using methods such as plasma synthesis, viral coupling, bulk production, colloidal synthesis, fabrication, electrochemical coupling, and massive metal-free production. The parameters such as dimensions of quantum points, amount of solvent, amount of solution, amount of semiconductor metal, pH, and temperature are significant in the synthesis stage. **Figure 5** shows the wavelengths of quantum dots.
