**6.5 Silicon biosensor**

Silicon photonic integrated circuit (PIC) technology is a promising method for producing photonic biosensors. It can be produced efficiently and volumetrically using complementary metal-oxide-semiconductor (CMOS) foundry techniques. The high refractive index difference between silicon and surrounding media allows for the fabrication of multiple sensors on a single chip, creating small, miniature sensor devices. Silicon photonics offer superior transducers for continuous and quantitative label-free biosensing, responding quickly to affinities between analyte and receptor molecules [42–46].

Because of their short response times and ability to solve the deficiency in sensitivity of flow-over porous silicon (Psi)-based biosensors, porous silicon membranes (PSiMs) are prospective biosensors. Also, they do not need any action to get the analyte on to the transducer and keep it there. In this study, we recapitulate the potential of these platforms for detection and emphasize their application to the detection of bacteria. Standard microfabrication methods and electrochemical etching were used to create PSiMs. A large number of samples could be manufactured in one try, and the entire manufacturing process took less than a week. The sensors were not functionalized since endolysins were used to provide specificity [47–53].

#### **6.6 Fluorescent biosensor**

Fluorescence-based biosensors are used in various applications, including medical diagnostics, pharmaceutical administration, drug discovery, environmental monitoring, and food safety. Techniques for detecting various analytes include fluorescence intensity, anisotropy, decay time, energy transfer, quenching efficacy, and quantum yield. These sensors consider various variables to ensure accurate and reliable detection of various analytes.

Many compounds spontaneously fluoresce or seem luminous in one condition but nonfluorescent in another. By using this characteristic, a relatively straightforward fluorescence biosensor can be created; for instance, nicotinamide adenine dinucleotide + hydrogen (NADH) is fluorescent, whereas nicotinamide adenine dinucleotide (NAD+) is not. Therefore, fluorescence-based detection is a viable option for all enzymatic processes reliant on NAD/NADH. Analytical chemists frequently employ this method to identify and measure diverse analytes. The format employed here is direct fluorescence. Many proteins and other macromolecules, including nucleic acids, NADH, green fluorescent proteins, and flavin nucleotides, have inherent fluorescence capabilities. However, these molecules' fluorescent characteristics, such as their emission intensity or polarization, alter when these proteins bind to ligands or these ligands bind to these proteins [53–58].

#### **6.7 Microbial fuel-based biosensor**

Microbial fuel-based biosensors monitor environmental toxicity and biochemical oxygen demand by converting organic substrates into electrical energy. These biosensors use bioelectrochemical devices to control microbial respiration, but are limited by low-power density and high production and operating expenses. Technological advancements are aiming to increase performance and save costs, enabling selfpowered microbial biosensors.

Another use for microbial biosensors is the detection of heavy metals and pesticides, where eukaryotic bacteria have an advantage over prokaryotic cells. By creating whole-cell biosensors, it is helpful for the selective and sensitive detection of pesticide and heavy metal toxicity. In a way that is applicable to higher animals, higher eukaryotic bacteria can likewise be more susceptible to a number of toxic substances. The fact that microbial biosensors may be used for everything from energy production to environmental monitoring is noteworthy. Innovative techniques will enable the development of novel biosensors with selectivity and high sensitivity, from modified prokaryotes to eukaryotes of microbial origin [59–61].

#### **6.8 Magnetic biosensor**

Recent research supports efforts in magnetic sensors for biomedicine applications, detecting nanoparticles. Examples of extremely effective scientific and clinical techniques include the use of nanoparticles with magnetic properties in the treatment of hyperthermia, guided medication administration, and the usage of magnetic particles as magnetic resonance imaging (MRI) contrast agents. Because of their exceptional benefits, magnetic biosensors have garnered more attention than other types of biosensors. For instance, magnetic biosensors have four advantages over fluorescentbased techniques.

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

First, magnetic probes may be employed for long-term labeling tests because they are more stable over time in culture. Magnetic nanotags are not influenced by their reliability over time like fluorescent tags are since they are chemical compounds, as opposed to fluorescent tags. Such a feature may be used for long-term labeling tests while fabricating tissues and organs. Second, unlike fluorescently tagged samples, magnetic materials do not produce background noise effects. In biological samples, background fluorescence is a frequent occurrence that results from the tissue's natural characteristics. Third, applying regulated magnetic fields to the outside surface offers a method for monitoring and controlling the biological environment from a distance. Finally, magnetic assays have been found to have greater sensitivity than fluorescence tests. Compared to fluorescent-based methods, the great sensitivity permits detection at much lower protein concentrations [62].
