**2.2 Bioreceptor/biorecognition**

A bioreceptor is a molecule that identifies the analyte in a specific manner. A small number of examples include cells, DNA, enzymes, aptamers, and antibodies. The best bioreceptors, which are used in the formation of electrochemical DNA biosensors for the purpose of food-borne detection of illnesses, are aptamers or single-stranded nucleic acids. The bioreceptor and the target react to one another on the electrode surface. DNA is a biosensor. Two different types of DNA exist: aptamer DNA, which

*Biosensor elements/steps.*

#### *Biosensing Basics DOI: http://dx.doi.org/10.5772/intechopen.113771*

is synthetic DNA produced intentionally *in vitro* using a known base sequence, and naturally occurring recognition element DNA. "Genosensors" are biosensors that use naturally occurring DNA as a bioreceptor. Such sensors typically target the DNA of infections. By pairing complementary bases, DNA probes immobilized on electrode surfaces can identify and hybridize with targets' DNA. Aptamers made of tiny molecules, entire cells, and high-molecular-weight substances can also recognize and capture targets. Aptasensors are biosensors that use aptamers as bioreceptors. We credit the strong affinity between the target and the single-stranded DNA (ssDNA) or aptamer for the high selectivity of electrochemical DNA biosensors.

Biorecognition is the procedure of signal development following the association of the bioreceptor with an analyte. For instance, the conversion of heat, pH, light, charge, etc. A biorecognition element's main objective is to give a biosensor analyte specificity. Biorecognition components fall into a number of categories, including both naturally occurring and artificial substances. Antibodies and enzymes are examples of naturally occurring biorecognition elements. These biologically derived constructions make use of physiological interactions that have evolved over time. To serve as an example of each category, prominent biorecognition components from each will be succinctly outlined. There are several distinct types of recognition structures that make up each class of biorecognition element [2–5].

## *2.2.1 Antibody*

Antibody biorecognition elements are affinity based, and the binding event is monitored using colorimetric or piezometric transduction methods. Covalent bonding between antibodies and a sensor surface immobilizes them, generating a brush-like array [6].

#### *2.2.2 Enzymes*

The target bioanalyte is captured and catalyzed by enzymes, which act as biocatalytic biosensors to produce a quantifiable end product. Since they are frequently embedded inside surface structures, there are very brief diffusion paths between the transducer and the biorecognition element. Since enzymes frequently reside in surface structures, there are little barriers to diffusion between the biorecognition component and the transducer [6].

### *2.2.3 Nucleic acid*

In order to obtain bioanalyte selectivity, the complementary DNA-binding motif is being used by nucleic acid biosensors (genosensors). Locked nucleic acids (LNAs) and peptide nucleic acids (PNAs) in the usage of nucleic acid recognition elements are recently known to take part in developments. The 3<sup>0</sup> -endo conformation of the ribose is locked by LNA, which decreases conformational flexibility and enhances binding to the target of corresponding nucleic acid. A repeating aminoethyl-glycine unit connected by a peptide makes up the synthetic oligonucleotide known as PNA. Overall, because their utilization is best suited for biosensor applications that target nucleic acids, nucleic acid biorecognition elements have a very narrow range of applications [6].

### *2.2.4 Aptamer*

The SELEX (Systemic Evolution of Ligands by Exponential Enrichment) method is useful for obtaining single-stranded oligonucleotides named aptamers that are shaped. SELEX is an iterative procedure for significant binding affinities, which lies between the target analyte and oligonucleotide sequences in a collection of randomly produced oligonucleotide sequences. The majority of aptamers are 100 base pairs in length, keeping both ends with consistent primer binding regions and a randomly chosen base pair binding region in the middle [6].
