*2.2.1 Fabrication*

This method involves two different approaches, bottom-up and top-down. In the top-down method, small particles are formed by lithography. **Figure 6** shows quantum dots fabrication process.

**Figure 5.** *The wavelengths of quantum dots [18].*

*The Components of Functional Nanosystems and Nanostructures DOI: http://dx.doi.org/10.5772/intechopen.92027*

#### **Figure 6.**

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

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

This method involves two different approaches, bottom-up and top-down. In the top-down method, small particles are formed by lithography. **Figure 6** shows

revealed by the stimulation of electrons [18, 19].

*Smart Nanosystems for Biomedicine, Optoelectronics and Catalysis*

the wavelengths of quantum dots.

*The cancer treatment with gold nanospheres.*

quantum dots fabrication process.

*The wavelengths of quantum dots [18].*

*2.2.1 Fabrication*

**Figure 5.**

**118**

**Figure 4.**

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

## *2.2.2 Colloidal synthesis*

Colloidal synthesis is a practical synthesis technique where quantum dots can be synthesized easily under laboratory conditions. They consist of three main components: precursors, organic surfactants, and solvents.

#### *2.2.3 Electrochemical coupling*

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

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

#### **Figure 7.** *Visualization of the quantum dots under UV light to detect different tumor cells by the addition of bioagents [19].*

imaging. UV-vis and photoluminescence spectroscopy are generally used for characterization of quantum dots. Thanks to these methods, it is possible to perform fast, undamaged and contactless characterization. The use of photomodulated reflectance spectroscopy, an experimental method, offers a wide range of critical point advantages. The optical properties of quantum dots can be controlled by the dimensions of the dots. The size of the quantum dots can be characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and dynamic light scattering (DLS). Optical activity properties and particle sizes of quantum dots can be measured by photoluminescence excitation and Raman scattering spectroscopy. Atomic force microscopy (AFM), scanning tunneling microscopy (STM) and transmission electron microscopy (TEM) analysis methods are used to display the particle sizes. However, the best analysis results are obtained with AFM and TEM analysis methods.

biomolecules, develop polymorphism analysis, cancer, rapid diagnostic testing,

Biochips provide great convenience in early and accurate diagnosis of diseases by reducing the detection time of protein sequences to less than 15 min and reducing the analysis time of nucleic acid sequences to less than 2 h. Especially in the food industry, DNA amplification of the genes of the target pathogen allows for rapid and accurate identification of pathogens. Biopharmaceuticals are also needed to identify mutations related to rifampin resistance in mycobacteria (RIF). Biochips are intended to be used to create a giant database for the narration of living and occurring events in the world soon. Biochips that can predict the health history of a person who is injured, sick or exposed to an accident, and that can give information about the food microbiota and nutritional values at every stage of food safety technologies from food production to consumption, and that can make diagnosis of diseases such as blood pressure and high blood sugar will be synthesized in the

Nanosensors are a combination of chemical, biological, and surgical sciences used to deliver nanoparticles to the world macroscopically. Nanosystems such as porous silicon, nanoparticles, nanoprobes, nanowires, nanotubes are widely used in

**Purpose of usage Nanosensors References**

For improved dialysis treatment microfuidic DNA-based potassium

Anticancer drug SPR nanosensor [27] Detection of mercury ions Multimodal nanosensor [28] Detection of serum albumin Copolymer nanosensor [29] Detection of cysteine Colorimetric nanosensor [30] Detection of cadmium ions Quantum dots based-fluorescence

Emerging strategies AuNP-based ICTS nanosensor [32] Detection of curcumin Carbon-based chem nanosensor [33]

Black phosphorene nanosensor (FRET)-based nanosensor

nanosensors

nanosensörler

Fluorescent nanosensors [24]

MgCO2O4 nanosensor [26]

[22, 23]

[25]

[31]

the design of nanosensors. Examples of nanoparticles used in the design of nanosystems are MNPs magnetic nanoparticles, AuNPs gold nanoparticles, upconversion nanoparticles, QDs quantum dots, SWNTs single-wall carbon nanotubes, MWNTs multiwall carbon nanotubes, nano barcode technology and electronic nose [21]. These devices are tiny devices that can detect and respond to physical stimuli such as biological and chemical substances, displacement, motion, force, mass, acoustic, thermal and electromagnetic. In the literature studies, many

nanosensors were synthesized for different purposes (**Table 2**).

Detection of ochratoxin for real-time display of arsenic (As3+) dynamics in living cells

Near-infrared imaging of serotonin release from

Development of ethanol and acetone gas sensing

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

identifying, biowarfare agents [20].

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

*The Components of Functional Nanosystems and Nanostructures*

nearest future.

**3.2 Nanosensors**

cells

**Table 2.**

**121**

performance
