Biosensors- Concepts, Principles , and Applications

Key Concepts

• Concept of biosensors

• General features of biosensors

• Principle of biosensor

• Different types of biosensors

• Applications of biosensor

Introduction:

History of biosensors:  

M. Cremer established that the concentration of an acid in a liquid is proportional to the electric potential that occurs between segments of the fluid positioned on opposite sides of a glass membrane. 

•  However, Sren Peder Lauritz Srensen was the first to introduce the notion of pH (hydrogen ion concentration) in 1909, and Hughes’ invention of the glass pH electrode enables researchers to measure the concentration of [H+] in any given substance. 
•  Griffin and Nelson were the first to show that the enzyme invertase could be immobilized on aluminum hydroxide and charcoal between 1909 and 1922.  
• In 1956, Leland C. Clark, Jr created the first ‘real’ biosensor for oxygen detection. He is renowned as the “Father of Biosensors,” and the oxygen electrode he invented retains his name—the “Clark electrode.” 
• In 1962, Clark created the first biosensor device, an amperometric enzyme electrode that measures the amount of glucose specifically in blood. 

• Yellow spring instruments eventually created the first commercial biosensor in 1975. The first immunosensor, ovalbumin or egg protein on a platinum wire, and the microbe biosensor paved the way for modern detection in 1975 In the realm of biosensors, considerable progress has been made since the development of the i-STAT sensor.  

The discipline has evolved into a multidisciplinary research area that connects basic science concepts (physics, chemistry, and biology) with micro/nanotechnology, electronics, and clinical medical foundations. 

A biosensor is a measurement instrument that contains an immobilized biological material (enzyme, antibody, nucleic acid, hormone, organelle, or complete cell) that can interact with an analyte and produce physical, chemical, or electrical signals. 

Biosensors are used to analyze diverse chemicals quantitatively by turning their biological effects into measurable signals.   

Immobilized enzymes are found in the vast majority of biosensors. Apart from the stability of the enzyme, the performance of biosensors is mostly determined by the specificity and sensitivity of the biological reaction. Biosensors is a device that uses signals proportional to the concentration of an analyte in a reaction to assess biological or chemical responses. 

Analyte: An analyte is a substance whose concentration must be determined (for example, glucose, urea, a medicine, or a pesticide). 

A substance of interest that must be discovered is called as analyte.  

In a biosensor that is designed to detect glucose, so here, glucose is an ‘analyte.’ 

Types of analytes: 

Many people believe that blood is the only body fluid that may be utilized for biosensing, but this isn’t the case. Saliva, perspiration, urine, tears, and breath, in addition to blood, can be utilized to identify a variety of biomarkers. 

Let’s check out some examples: 

• Biosensors based on blood are used to detect blood components such as glucose. In comparison to invasive blood-based biosensors, saliva-based biosensors are steadily gaining acceptance for glucose measurement. These can also be used to measure levels of lactate and cortisol, among other substances. 
• Sweat-based biosensors can detect levels of chemicals like glucose, lactate, ascorbic acid, and uric acid. 
• Urine-based biosensors can detect levels of compounds like glucose, lactate, ascorbic acid, and uric acid. 
• Tears can be used to estimate glucose, alcohol, and some vitamins, whereas police departments commonly utilize breath-based biosensors to detect residues of alcohol. 

Bioreceptor: 

A bioreceptor is a molecule that recognizes the analyte specifically. Bioreceptors include enzymes, cells, aptamers, deoxyribonucleic acid (DNA), and antibodies.  

Bio-recognition is the process of signal creation (in the form of light, heat, pH, charge, or mass shift, etc.) when a bioreceptor interacts with an analyte. 

Transducer: 

A transducer is a component that transforms one form of energy into another.  The transducer’s job in a biosensor is to turn a bio-recognition event into a quantifiable signal. 

Signalization is the name for energy conversion process. The number of analytes–bioreceptor interactions is usually proportionate to the amount of optical or electrical signals produced by most transducers. 

Electronics and display: 

This is the section of a biosensor that processes and prepares the transduced signal for display. It is made up of complicated electronic circuitry that performs signal conditioning functions such as amplification and digital signal conversion.  

The display device of the biosensor then quantifies the processed signals. 

A user interpretation system, such as a computer’s liquid crystal display or a direct printer, generates numbers or curves that are understandable to the user.  

Display is often made up of a combination of hardware and software that delivers user-friendly biosensor results. Depending on the end user’s needs, the output signal on the display can be numeric, visual, tabular, or a picture. 

In short two features of biosensors: 

Biosensors have two distinctive components: 

Biological components: enzyme, cell, DNA, etc. 

Physical components: Electronics, transducer, amplifier, etc. 

The biological component recognizes the analyte and interacts with it to create a physical change (a signal) that the transducer can detect.  

In practice, the biological material is adsorbed correctly on the transducer, and the resulting biosensors can be used repeatedly for a long time. 

Working principle of biosensor: 

Conventional approaches are used to immobilize the desired biological material (typically a specific enzyme) (physical or membrane entrapment, non- covalent or covalent binding). 

The transducer is in direct touch with the immobilized biological material. 

 The analyte attaches to the biological substance, forming a bound analyte, which generates the measurable electrical response. The analyte may be transformed to a product that involves the release of heat, gas (oxygen), electrons, or hydrogen ions in some cases. 

The product-related changes can be converted into electrical impulses that can be amplified and measured by the transducer. 

Explanation:

Types of biosensors: 

There are many types of biosensors depending on the sensor devices and the type of biological materials used. 

Electrochemical biosensors are simple devices that use bio electrodes to measure electric current, ionic, and conductance changes. 

The electrochemical biosensor works by using an enzymatic catalytic reaction to consume or create electrons. Redox enzymes are a type of enzyme that does just that. 

This biosensor’s substrate usually has three electrodes: a counter, a reference, and a working type.   

Types of electrochemical biosensor: 

• Electrochemical biosensors: 
• Amperometric biosensor 
• Potentiometric biosensor 

• Conduct metric biosensor 

Amperometric biosensor: 

The movement of electrons (i.e., the determination of electric current) as a result of enzyme-catalyzed redox reactions is the basis for these biosensors. 

 A constant voltage can be determined when a constant voltage is passed between the electrodes. 

This causes a change in current flow, which may be measured. The current is proportional to the concentration of the substrate.  

The simplest type of amperometric biosensor is the Clark oxygen electrode, which measures O2 decrease. 

 A notable example is the measurement of glucose using glucose oxidase. 

Biosensor for blood glucose: 

It is a good example of amperometric biosensors, which are frequently used by diabetes patients around the world. The blood-glucose biosensor resembles a watch pen and contains a single-use disposable electrode containing glucose oxidase and a ferrocene derivative (composed of an Ag/AgCI reference electrode and a carbon working electrode) (as a mediator). The electrodes are wrapped in a hydrophilic mesh gauze to ensure that a blood drop spreads evenly. The disposable test strips, which are packed in aluminium foil, have a six-month shelf life. 

The development of an amperometric biosensor for determining the freshness of fish has been completed. Ionosine and hypoxanthine concentration in relation to the other nucleotides reveals the freshness of the fish—how long it has been dead and preserved. 

Potentiometric biosensor: 

Ion-selective electrodes are used in these biosensors to determine changes in ionic concentrations.  

Because many enzymatic activities involve the release or absorption of hydrogen ions, the pH electrode is the most often used ion-selective electrode. Ammonia-selective and CO2-selective electrodes are two more significant electrodes. 

Conduct metric biosensor: 

Changes in ionic species occur as a result of numerous processes in biological systems. 

The electrical conductivity of these ionic species can be tested. The urea biosensor with immobilized urease is a nice example of a direct metric biosensor. 

Urease catalyzes the following reaction. 

The above-mentioned reaction is linked to a significant change in ionic concentration, which can be utilized to monitor urea levels. 

In reality, urea biosensors have a long history of application in dialysis and kidney surgery. 

Thermometric biosensor: 

The creation of heat is linked to a number of biological reactions, and thermometric biosensors are based on this.  

Thermal biosensors or calorimetric biosensors are the terms used to describe them. 

It is made up of a heat-insulated box with a heat exchanger (aluminum cylinder).  

In a tiny enzyme packed bed reactor, the reaction takes place. The substrate is transformed to a product and heat is created as it enters the bed.  

Thermistors measure the temperature differential between the substrate and the product. Thermal biosensors can detect even the tiniest changes in temperature. 

Thermometric biosensors are used to calculate serum cholesterol levels. When the enzyme cholesterol oxidase oxidizes cholesterol, heat is produced, which can be measured.  

These biosensors can also estimate glucose (enzyme-glucose oxidase), urea (enzyme-urease), uric acid (enzyme-uricase), and penicillin G (enzyme-P lactamase). 

Optical biosensor: 

The optical biosensor is a device that works on the principle of optical measurement.  

Fiber optics and optoelectronic transducers are used.  

The word optrode is a combination of the words optical and electrode.  

Antibodies and enzymes, as well as transducing elements, are primarily used in these sensors. 

Optical biosensors provide non-electrical remote detection of materials in a safe manner. 

Piezoelectric biosensor: 

Piezoelectric biosensors are sometimes known as acoustic biosensors since they work on the principle of acoustics (sound vibrations).  

These biosensors are made up of piezoelectric crystals. Positive and negative-charged crystals have distinct vibrational frequencies. The adsorption of specific molecules on the crystal surface changes the resonance frequencies, which can be detected using electronic instruments.  

These crystals can also hold enzymes with gaseous substrates or inhibitors. 

Piezoelectric Biosensors’ Limitations: 

The application of these biosensors to determine compounds in solution is quite difficult. 

This is because crystals in viscous liquids may entirely stop oscillating. 

Whole cell biosensors: 

Whole cell biosensors are especially effective for reactions that require multiple steps or cofactors.  Live or dead microbial cells may be used in these biosensors. 

One of the most recent molecular techniques utilized in environmental monitoring is whole-cell microbial biosensors.  

A reporter gene, such as lux, gfp, or lacZ, is fused to a responsive promoter to create these biosensors. 

The biosensors rely on gene expression analysis, which is commonly accomplished by forming transcriptional fusions between a target promoter and a reporter gene. 

Microbial cell biosensors have the following advantages: 

Microbial cells are less expensive and have longer half-lives. In addition, compared to isolated enzymes, they are less susceptible to changes in pH and temperature. 

Biosensors made from microbial cells have a number of drawbacks. In general, catalysis takes longer in entire cells. Furthermore, as compared to enzymes, the specificity and sensitivity of whole cell biosensors may be lower. 

Immuno biosensors: 

Immuno-biosensors, also known as immunochemical biosensors, work on the basis of immunological specificity, with measurement (mainly) using amperometric or potentiometric biosensors. 

There are several possible configurations for immuno-biosensors and some of them are depicted in image. 

1. Antibody that has been immobilized and can attach to antigen directly. 

2. An immobilized antigen that attaches to an antibody, which can then bind to a second antigen that is free. 

3. An antibody bound to immobilized antigen which can be partially released by competing with free antigen 

4. In a competition, an immobilized antibody binds free antigen and enzyme labelled antigen. 

Piezoelectric devices can be used for biosensors A, B, and C. 

The enzyme-based immuno-biosensors are the most widely utilized in figure D. Thermometric or amperometric devices are used in these biosensors.  

The relative quantities of labelled and unlabeled antigens affect the activity of enzymes bound to immuno-biosensors.  

The enzyme activity can be used to determine the concentration of the unlabeled antigen. 

Applications of biosensors: 

• Biosensors provide the following advantages over lab-based equipment: 
• Size is small. 
• Cost-effective 

• Quick outcomes 
• Very simple to use 
• In the food industry: 
• Biosensors have been widely employed in the food sector for quality assurance and control.  
• Applications in the agricultural field, such as crop cultivation and food processing, are among them.  

• Quality control is still an important aspect of food manufacturing since it ensures that healthy food has a long shelf life and conforms with standards. 
• To identify specific substances in foods, biosensors have been developed.  
• These devices detect chemicals or biological agents that can taint food or identify the presence of undesired items.  
• Furthermore, biosensors for monitoring and estimating cross-contamination of surfaces and food products have been created. 
• Environment: 

• Chemical agents, organic pollutants, potentially poisonous substances, and infections that may represent a health threat have all been detected using biosensors in environmental monitoring.  
• Pollutants are detected using biosensors that measure color, light, fluorescence, or electric current. 
• Medical science: 
• Biosensor applications are fast expanding in the field of medical science.  
• Cancer diagnosis and monitoring, cardiovascular disease monitoring, and diabetes control are just a few of the applications that have profited from the development of biosensors.  

• Biosensors can be used in medicine to monitor diabetic blood glucose levels, identify infections, and diagnose and track cancer growth.  
• Early identification of cancer and effective therapy delivery could be aided by the use of developing biosensor technology. 
• Biosensors can detect the presence of a tumor, whether benign or cancerous, by measuring the amounts of particular proteins expressed and/or secreted by tumor cells. 
• They can also tell if treatment is effective in lowering or removing cancerous cells. 
• Cardiovascular disorders, which are the leading cause of death, are still regarded as one of the world’s most serious problems, with approximately one million individuals suffering from them.  

• The capacity to diagnose such diseases sooner could lead to fewer incidences of fatality.  
• Immunoaffinity column assays, fluorometric assays, and enzyme-linked immunosorbent assays are some of the sensing techniques employed here. 
• However, the approaches described above are time demanding and require well-trained and skilled staff.  
• As a result, biosensors are being utilized to detect cardiac indicators and provide early diagnosis.  
• Biosensors have been shown to have significant advantages over traditional diagnosis assays since they are based on electrical measurements and also use biochemical molecular recognition elements to achieve desired selectivity with a specific biomarker of interest.

Summary

• In 1956, Leland C. Clark, Jr created the first ‘real’ biosensor for oxygen detection. He is renowned as the “Father of Biosensors,” and the oxygen electrode he invented retains his name—the “Clark electrode.”

• A biosensor is a measurement instrument that contains an immobilized biological material (enzyme, antibody, nucleic acid, hormone, organelle, or complete cell) that can interact with an analyte and produce physical, chemical, or electrical signals.

• An analyte is a substance whose concentration must be determined (for example, glucose, urea, a medicine, or a pesticide).

• A bioreceptor is a molecule that recognizes the analyte specifically. Enzymes, cells, aptamers, deoxyribonucleic acid (DNA), and antibodies are examples of bioreceptors.

• Transducer is a component that transforms one form of energy into another.

• Electronics processes and prepares the transduced signal for display.

• Working principle of biosensor: The analyte attaches to the biological substance, forming a bound analyte, which generates the measurable electrical response.

• Electrochemical biosensors are simple devices that use bio electrodes to measure electric current ionic, and conductance changes.

• The creation of heat is linked to a number of biological reactions, and thermometric biosensors are based on this. It is also termed as calorimetric biosensor.

• The optical biosensor is a device that works on the principle of optical measurement

• Piezoelectric biosensors are sometimes known as acoustic biosensors since they work on the principle of acoustics (sound vibrations).

• Whole cell biosensors are especially effective for reactions that require multiple steps or cofactors. Live or dead microbial cells may be used in these biosensors.

• Immuno-biosensors, also known as immunochemical biosensors, work on the basis of immunological specificity, with measurement (mainly) using amperometric or potentiometric biosensors.

• These sensors have been popular in recent years, and they can be used in a variety of fields. Such as routine medical examinations, measuring metabolites, sickness examination etc.