Aug , 2021, Volume : 2 Article : 13
Biosensors and its importance
Author : R. Prathisha
Cite this article as:
Prathisha, R. (2021) Biosensors and its importance. Food and Scientific Reports. 2 (8) 57-61.
A biosensor is a biological detection system consists of a biological component combined with a transducer to perform measurement of a biochemical quantity. The development of biosensors started with the invention of enzyme electrodes by Leland C. Clark in the year 1962. A typical biosensor includes a bioelement such as an enzyme, antibody, or a cell receptor, and a sensing element or a transducer. These two elements are combined together through a number of methods such as covalent bonding, matrix entrapment, physical adsorption and membrane entrapment. Biosensors are designed in such a way that they are highly specific, independent of physical parameters such as pH and temperature and should be reusable. Fabrication of biosensors, its materials, transducing devices, and immobilization methods requires multidisciplinary research in chemistry, biology, and engineering. The materials used in biosensors are categorized into three groups based on their mechanisms: biocatalytic group comprising enzymes, bioaffinity group including antibodies and nucleic acids, and microbe based containing microorganisms.
Keywords: Biosensors, genotoxicity, flurosence, reporter phage, lectin
Working Principle of Biosensors
Biosensors are operated based on the principle of signal transduction. These components include a bio-recognition element, a biotransducer and an electronic system composed of a display, processor and amplifier. The bio-recognition element, essentially a bioreceptor, is allowed to interact with a specific analyte. The transducer measures this interaction and outputs a signal. The intensity of the signal output is proportional to the concentration of the analyte. The signal is then amplified and processed by the electronic system.
Classification of Biosensors
Biosensors have been classified based upon several perspectives; however, the most commonly used classification relies on two factors:
· the biorecognition element and
· The signal transduction.
Signal transduction perspective Biosensors
It can be categorized based upon methods of signal transduction into four categories:
· thermal sensors,
· optical, and
These are cost effective, portable, highly sensitive, and compatible with modern micro fabrication technologies.
Electrochemical biosensor consists of bio-recognition element which was fixed on the surface of the electrode by physical or chemical method. The biosensors identify the target molecule and capture it onto the electrode surface, owing to the specific recognition function of bio-recognition element with the substance to be tested. As the main body of the signal converter, the electrode can derive the identification signal generated on the surface of the electrode and convert it into an electrical signal, including current, voltage, and resistance, which can be measured and analyzed in order to achieve qualitative or quantitative analysis of the analysis target.
Electrochemical biosensors can be classified into;
· potentiometric and
· conductometric biosensors,
According to the observed data type, such as current, impedance, potential and conductance, respectively
These are characterized by their high detection speed, sensitivity, robustness, and their ability to detect multiple analytes. An example of an optical technique usually employed in biosensors construction is surface plasmon resonance (SPR), which is able to determine the presence of a chemical with no need for labeled molecules. Mass-sensitive biosensors offer various advantages such as real-time operation and monitoring in liquid, vacuum, and air environments.
Micro cantilever biosensors are examples of mass-sensitive biosensors. The main attractive features of micro cantilever biosensors are their lower detection limits compared with classical methods and their miniscule dimensions (less than 10−3 mm2), which means a minute amount of both receptors and analyte is required for the assay.
These have mainly been employed for monitoring of clinical and industrial processes
Biorecognition perspective biosensors
Based on the biological recognition element, biosensors have been classified into
· protein receptor-based,
· DNA biosensors, and
· Whole-cell biosensors.
They are based on the principle of the enzyme-catalyzed alteration of undetectable substrate into electrochemically measureable outcome or vice versa. Many enzyme catalyzed reactions comprise the release or utilization of a measureable outcome (i.e., O2, CO2, and ions), which can be measured using a suitable transducer coupled to an immobilized enzyme. The key analytical enzymes that have been employed in these types of biosensors are oxidoreductases and hydrolases.
Protein receptor-based biosensors
Protein receptor–based biosensors or non catalytic proteins biosensors rely on the ability of cell membrane proteins to act as receptors. These receptors permit the transduction of the binding signal across the membrane either by metabotropic receptors (i.e., enzyme secretion) or by ionotropic receptors.
Immunosensors were established on the fact that antibodies have high affinity towards their respective antigens, i.e. the antibodies specifically bind to pathogens or toxins, or interact with components of the host`s immune system
Immunesensors uses the concept of solid-phase immunoassays, where antigens and antibodies are immobilized on a solid support and antigen– antibody interaction occurs at the solid–liquid interface. Immunosensors involve the substantial sensitivity and selectivity, in addition to the possibility of developing their affinity and selectivity by designing new recombinant antibodies
For example; Alamer et al. developed an immunoassay with sandwich to diagnose pathogenic bacteria in poultry such as Salmonella Typhimurium, Staphylococcus aureus, Salmonella enteritidis, and Campylobacter jejuni. Immobilized lactoferrin on a cotton swab was employed to pick up the bacterial contamination on the surface of the chicken, accompanied by a sandwich immunoassay formulated with a different antibody coupled with colored nano-beads. The form and concentration of the present microorganism defined the color and strength of the cotton swab
The DNA biosensors were devised on the property that single-strand nucleic acid molecule is able to recognize and bind to its complementary strand in a sample. The interaction is due to the formation of stable hydrogen bonds between the two nucleic acid strands
DNA-aptamers-based biosensors have been developed as alternatives to antibodies due to their high stability, specificity, and very low cost. Aptamers are defined as miniscule single stranded DNA (ssDNA) or RNA sequences with approximately 100 nucleotides or less. The unique intramolecular interactions between these nucleotides makes the aptamers fold into a distinctive three-dimensional assembly. DNA-aptamers based biosensors can selectively bind with superior specificity and affinity to a specific bacteria, viruses, proteins, hormones, analyte, and even small molecules and ions. The types of bonds used in this binding are mainly hydrogen bonds and Van der Waals forces. The development of aptamers allowed fabrication of innovative biosensor devices with great stability and specificity, lower cost, and much simpler detection strategies compared with immunosensors.
For example; Alhadrami et al. constructed a DNA-aptamer fluorescence based biosensor for detection of progesterone (P4) using a truncated mechanism. The aptasensor illustrated superior sensitivity for monitoring of progesterone with a detection limit of 100 pg mL−1. The truncated technique used to construct the aptasensor has significantly enhanced the affinity of the DNA-aptamer and thus the overall sensitivity of the fluorescence bioassa
Microbial biosensors, which are based on luminescence reporter genes, have been extensively used for several medical applications. Genetically engineered whole-cell microbial biosensor uses either prokaryotic or eukaryotic cells to report chemicals composition, toxicity, carcinogenicity, and mutagenicity in real time and cost-effective manner.
Whole-cell biosensors reports;
· the presence or absence of chemical under investigation
· Precisely measures the sublethal concentration, which causes toxic or mutagenic effects.
It provides information with high specificity about the bioavailable and bioaccessible fraction of chemicals and/or drugs under investigation. This information is important to determine the maximum amount of analyte concentration that can be absorbed by human gastrointestinal tract and reach to the blood circulation. Hence, they provide more biologically relevant evidence than analytical techniques.
Bioluminescence-based biosensors generally comprise the luxCDABE operon from the donor marine microorganism Vibrio fischeri and the luxAB genes which encode luciferase from V. harveyi. These genes are commonly employed as reporter genes in the construction of several biosensors. Light emission in bioluminescence-based biosensors is generated by a series of reactions encoded by the luxCDABE. The principle of these reactions involves the production of the luciferase enzyme (coded by the luxAB gene), which catalyzes the oxidation of the luciferin substrate (coded by the luxCDE gene) flavin mononucleotide (FMNH2) and fatty acid aldehyde (RCHO) in the presence of O2. Consequently, the aldehyde and the long-chain fatty acid are rejuvenated to FMN and RCOOH, leading to the emission of blue-green light, which can be measured at a wavelength of 490 nm
Different types of Biosensors
Use of Biosensors
Biosensors are generally used for the following
· Monitoring glucose level in diabetes patients
· Food analysis
· Environmental applications
· Protein engineering and drug discovery applications
· Wastewater treatment.
Biosensors used for detection of pathogenic organisms
biosensors are attractive for monitoring and identification of a broad spectrum of pathogenic microorganisms and for clinical diagnostics due to their high sensitivity and specificity. Building-up biosensors for identification of pathogenic microorganisms is based on a biological recognition element (i.e., nucleic acids) connected with an appropriate transducer. Construction of biosensors using the state-of-art nanobiotechnology has several advantages over the conventional methods for detection of pathogenic microorganism. For instance,
· a large number of clinical samples can be screened in a short period of time with a superior sensitivity and small sample volume.
· Several biosensors have been constructed for detection of pathogenic microorganisms using optical, mechanical, chemical, electrochemical, and nuclearv magnetic resonance methods.
optical biosensors (especially colorimetric) are more attractive as they are sensitive, portable, cost effective and rapidly provide high-throughput screening for a large number of clinical samples and can be integrated with microfluidics. The incorporation of optical biosensors with microfluidics allows the fabrication of the lab-on-a-chip system, which offers sample delivery, separation, analysis, and detection all-in-one device with minimum reagent volume and lowest cost. Many optical biosensors for detection of pathogenic microorganisms are now commercially available. Biosensors based on bioluminescence have been extensively employed for identification, detection, and monitoring of several pathogenic microorganisms
For example, Biosensors are used for the detection of pathogens in food. Presence of Escherichia coli in vegetables is a bioindicator of faecal contamination in food. E. coli has been measured by detecting variation in pH caused by ammonia (produced by urease–E. coli antibody conjugate) using potentiometric alternating biosensing systems.
Applications of bioluminescent biosensors for identification and detection of pathogenic microorganisms was initiated by Ulitzur and Kuhn when they constructed the first luciferase reporter phage. The genes encoding luciferase has been infused into the genome of bacteriophage. A bioluminescent phenotype can then be awarded to a previously nonbioluminescent microorganism if that virus infects a host bacterium. Reporter phages are considered as a rapid tool for detection and identification of microbial host cells postphage attack.
The number of detected cells using the reporter phage system is as low as 10 E. coli and enterobacterial cells and 100 S. typhimurium cells. A L5 bacteriophage was constructed by Sarkis et al. to identify Mycobacterium segmantis. L5 was able to measure 100 cells of M. segmantis in few hours postinfection. The same approach was used to monitor and detect different species of Salmonella and Listeria
Listeria monocytogenes is the causative agent of human listeriosis due to ingestion of contaminated food and is one of the most common opportunistic food-born pathogen. L. monocytogenes is detected conventionally by growing on selective media, followed by biochemical identification. Loessner et al. developed the reporter bacteriophage A511::luxAB for identification of various strains of Listeria which was a feasible, rapid, infective, and simple tool for effective and sensitive detection of viable Listeria cells in contaminated food. It can measure the low number of Listeria cells even in the existence of high number of other microorganisms. Further, it can be employed for the quantitative determination of viable Listeria cells on the basis of relative light units (RLUs) reading or by using a microplate luminometer format. The detection limit of this assay is comparable to or better than the results obtained from polymerase chain reaction (PCR) methods or nucleic acid hybridization
Biosensors use for detection of biofilms
The recent advances in biosensors technology have enormously enhanced understanding of biofilm development and formation and have been successfully used to investigate the in vivo manifestation of virulent factors.
For example, the gfp marker gene was employed as a reporter of gtfB expression which encodes glucosyltransferase of Streptococcus mutans during biofilm formation.
Of the DNA-aptamer and thus the overall sensitivity of the fluorescence bioassay
Fluorescent biosensors are imaging agents, for use in cancer and drug discovery. They have enabled insights into the role and regulation of enzymes at cellular level. GFP-based and genetically encoded FRET biosensors play a vital role.
Fluorescent biosensors are small scaffolds onto which one or several fluorescent probes are mounted (enzymatically, chemically or genetically) through a receptor. The receptor identifies a specific analyte or target, thereby transducing a fluorescent signal which can be readily detected and measured.
Fluorescent biosensors are used in drug discovery programmes for the identification of drugs by high throughput, high content screening approaches, for postscreening analysis of hits and optimization of leads. These are considered potent tools for preclinical evaluation and clinical validation of therapeutic potential, biodistribution and pharmacokinetics of candidate drugs. Fluorescent biosensors are effectively employed for early detection of biomarkers in molecular and clinical diagnostics, for monitoring disease progression and response to treatment/therapeutics, for intravital imaging and image guided surgery.
For example; A genetically-encoded FRET biosensor developed for detection of Bcr-Abl kinase activity was used on cancer patient cells to assess Bcr-Abl kinase activity and to establish an interrelation with the disease status in chronic myeloid leukaemia. This probe was further employed to regulate response to therapy, and to observe the onset of drug-resistant cells, permitting prediction for alternative therapeutics
Biosensors used for detection of genotoxicity
Human health can be negatively affected by genotoxic substances. Genotoxic chemicals are widespread, which demand the construction of biosensors to screen a large number of samples for harmful properties such as genotoxicity and carcinogenicity. Biosensors for genotoxicity assessment have shown great consistency with traditional bioassays and are attractive due to their ability to detect the presence of multiple genotoxic compounds with only modest requirements for laboratory equipment and space. Although there is a debate surrounding the predictability of genotoxicity and carcinogenicity by microbial biosensors, a strong correlation has been widely reported between the carcinogenic impact of compounds on microbial biosensors and their genotoxic and tumor-inducing characteristics in mammals. Microbial biosensors are attractive for detection and screening of genotoxic and carcinogenic chemicals in pharmaceutical and medical research due to their simplicity, specificity, and sensitivity
Graphene‑based nanomaterials and antibodies
Graphene-based nanomaterials on antibody biosensors ofer a broad versatility regarding pathogen detection. Recently, several graphene-antibody biosensors with clinical applications have been developed for early detection of diseases
For example; Antibody nanosensors with G were developed to detect E. coli
In bacterial detection, graphene and graphene oxide as sensor platforms give the lowest detection limit (10 times less), compared to reduced graphene oxide. For virus, the modifcation of graphene with gold and silver nanoparticles by covalent attachment of the antibody allows the detection of concentrations as low as picograms per mL (pg/mL) of virus. In the case of detection of cancer cells, the modifcation of graphene oxide by functionalization with magnetic Fe3O4 allows to detection limits in femtograms (fg). An overall comparison among all currently available sensing platforms indicates that the functionalization of graphene or graphene oxide with silver, gold or other metal nanoparticles and the antibody attachment via covalent bond, typically allows the lowest detection limits. Te early detection of these diseases with such sensors can aid in diagnosis, prevention, and management of the disease
Lectin based biosensing
Carbohydrate binding proteins (CBFs, Lectins) as new bioreceptors has being started to play a pivotal role in many biosensing devices due to their exquisite specificity for their cognate carbohydrates.
The microbial lectins may play an essential role in mediating adhesion to surfaces colonized by the microorganism. Many bacteria contain surface-associated lectins that enable these organisms to adhere to surfaces. Most lectins specifically recognize sugar units (e.g., N-acetylneuraminic acid, N-acetylglucosamine, N-acetylgalactosamine, galactose, mannose, or fucose). Stillmark in 1888, as first descriptor of lectins, isolated ricin, an extremely toxic hemagglutinin from seeds of the castor plant (Ricinus communis).
Due to their multifaceted biological properties, lectins were later developed by cell biologists as probes to investigate cell surface structures and functions. Interaction with lectins can be used to obtain independent information about the presence of specific carbohydrates, the configuration of anomeric linkages and the location or position of carbohydrate residues polysaccharide molecules
Advantages of Biosensors
Adavantages of using biosensors include the following:
· Rapid and continuous measurement
· High specificity
· Very less usage of reagents required for calibration
· Fast response time
· Ability to measure non-polar molecules that cannot be estimated by other conventional devices.
Thus biosensors play a vital role in medical and biomedical applications compared to conventional techniques. Biosensors work as a first detection filter for mutagenicity, carcinogenicity, and toxicity of drugs and chemicals of concerns. Biosensors comprise a substantial potential for equipment miniaturization because of their minute size. They are able to detect groups of mutagenic and/or toxic elements rather than single element. This is a remarkable feature when particular compounds of a group have the same toxic and/or mutagenic characteristics. Biosensors can be integrated in microfluidics to establish a lab-on-a-chip platform, which has substantial medical and biomedical applications.
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