**2. Electrochemical biosensors**

Over time, the need for more precise technologies was necessary, making biosensors excellent alternative platforms, as they contain standards based on several points, such as high selectivity and sensitivity for detecting the specific analyte, even in small quantities. The fast response time, along with the reproducibility, linearity, and stability it offers, provides confidence in the measured value during the trial, thereby guaranteeing the superiority of this platform [14].

As in other platforms, biosensors have several classifications defined by how the biorecognition of the analyte occurs during the reaction. For example, enzymes are commonly used in various tests due to their catalytic properties, accelerating general biological processes. The principle of this type of biosensor is based on analyte metabolization processes, the transformation of the analyte into measurable by-products, inhibition of reactions, and the alteration of the initial enzymatic characteristics [15–17].

Currently, nanoparticles have been routinely used in electrochemical tests due to their ease of use and amplification of signals during the trial. Besides, nanoparticles have different behavior from sensors based on enzymes, with various advantages: immobilizing biomolecules, electrochemical catalysis, increasing electron transfer, and acting as reactants in solution [18, 19].

Most biosensors use platforms based on electrochemical transducers due to their low cost, ease of use, and portability. Reactions are easily measured through techniques such as current measurement (amperometry), charge accumulation (potentiometry), impedance differences (amperometry), or the union between conductive properties between the electrodes (conductometry) [20, 21].

One of the areas with great attention focused on the development of biosensors is related to the miniaturization of the architectures present in electrochemical platforms. This approach not only reduces noise but also enables the utilization of this platform in multiplexed assays, with the ability to detect multiple analytes [22].

*Electro Sensors Based on Quantum Dots and Their Applications in Diagnostic Medicine DOI: http://dx.doi.org/10.5772/intechopen.111920*

**Figure 1.** *A schematic of a biosensor with electrochemical transducer.*

The selection of electrodes in electrochemical immunoassays brings several advantages related to their construction methods, such as the use of only one reaction substrate and the reduced size, allowing the use of smaller amounts of reagent (**Figure 1**). Furthermore, in addition to the potential for mass production, the utilization of biosensors based on quantum dots offers advantages such as reduced cost compared to conventional electrodes. Thses biosensors also provide the option of single-use, eliminating the need for cleaning processes that can negatively affect reproducibility and stability [23–25].
