The recent development of sensors is in very high demand because of their numerous applications in clinical biochemistry as well as in analytical chemistry and environmental science. This development has gained much interest due to a variety of application in enormous fields. Biosensors offer easily detectable signals with high selectivity and high sensitivity.

Smart Biosensors:

Biosensors are the devices that change biological information into analytically useful signals.In the biosensors, there is a connection of a sensing molecule with a detector system using a transducer. They are most highly selective and sensitive incomparison to other detection and diagnostic methods. The basic principle of biosensors is based on receptor-transducer which could be used for interpreting the biophysical or biochemical property of the medium. These are also perfect for the smart detection of toxicity present in our body in the form of tumors and virus. These can also be used for monitoring the level of glucose in our body.

First, any biological material gets bound with an analyte to form a bound analyte which gives a biological response after that it forms an electronic response (in the form of signal). The electronic response is the last stage which can be measured. We can understand this concept by taking a small example, the analyte and biological material which are the reactants combined together to form a single product which may be related with release of heat, light, electrons or ions. Then by the help of transducer, the product is converted into electric signals which can be measured.                                                                                  

Types of Biosensors

There are enormous types of biosensors based on the sensor devices and the type of biological materials used. A selected few of them are discussed below:

1. Electrochemical Biosensors:

Electrochemical biosensors are the simplest devices. These involve the measurement of electric current, ionic or conductance changes carried out by bio electrodes. Based on this principle, electrochemical sensor is divided into amperometric and potentiometric biosensor.

Amperometric Biosensor: This biosensorinvolvesthe movement of electrons (i.e. determination of electric current) as a result of enzyme-catalyzed redox reactions. Normally, a constant voltage is determined which passes between the electrodes. The enzymatic reaction that is taking place in which the substrate or product can transfer an electron with the electrode surface to be oxidised or reduced.

Blood-glucose Biosensor: The blood-glucose sensor is extensively used all over the world by diabetic patients. It is type of amperometric biosensor. Blood- glucose biosensor looks like a watch pen and has a single use disposable electrode. It can detect the level of glucose within 5 seconds.

2. Piezoelectric Biosensors:

Piezoelectric biosensors are come under the category of mass-based sensors. They are also called acoustic biosensors as they are based on the principle of sound vibrations. In this, the molecules which are to be sensed are joined to a piezoelectric surface in which sound vibrations are set up in the interaction between the analyte and the sensing molecules. Then the vibrations are changed into electric signal. An example of piezoelectric biosensor is nano balance.

3. Optical Biosensors:

Optical biosensors involve the identification of analyte on the basis of adsorption, fluorescenece or scattering of light. These biosensors allow the recognition of multiple analytes by spotting different wavelengths.

Biosensors Applications:

The most important features of biosensors are that they are highly selective, specific, cheapest, most stable as well as small size and naked-eye detection is possible. These all the features make a biosensor most versatile as compared to the traditional methods. They are used in food analysis, heavy metal detection, water treatment, industrial process control and many more. Some of the important applications of biosensors are discussed below:

1. Heavy metal detection:

A variety of metal ions play important role in living systems by occupying the active sites of several enzymes such as Zn²⁺ in carboxypeptidase as well as carbonic anhydrase and Cu²⁺, Zn²⁺, Mn²⁺ in superoxide dismutase. Apart from the enzymatic systems, the role played by Fe²⁺ in the transport of O₂ is also well known. There are a number of cations Fe²⁺, Cr³⁺, Ni²⁺, Hg²⁺ that play detrimental roles as well. Hence the development of selective sensors for the proper identification of metal ions has gained significant attention. Let’s take few examples:

1. The excess of Hg²⁺ causes Minamata diseases and many health problems. It affects vital organs such as the kidney, digestive system, and especially the nervous system.
2. Apart from transport of oxygen, excessive amount of iron in body can effect central nervous system which can cause a number of diseases like Alzheimer’s, Huntington’s, and Parkinson’s diseases and can even lead to cancer. The deficiency of iron in the human body can instigate various problems such as liver and kidney damage, heart diseases, diabetes, and anemia
3. Copper is involved in the synthesis of proteins and enzymes and production of red blood cells. However, the excess of Cu²⁺ can cause severe problems and can damage the cells too.

Therefore, it is clear that identification of the ions is very essential otherwise if not checked properly they can have destructive effects.

2. Food industry

Biosensors are used in food industry for the recognition of microorganisms present in the food items. Microorganisms present in the food can cause a threat to the human health. Hence, biosensors are used to check the quality control of cold drinks, juices, beer, alcohols, water and other drinking items. They also use for simply the measurement of carbohydrates, amino acids, proteins, vitamins, minerals present in different food items.

3. Medical field

With the help of biosensors, today one can know that what is going on inside his/her body by sitting at home only. Biosensors have replaced those old, slow and painful processes of tests and offer a new and frequent process which is much easy to use. Such type of tests can increase the productivity of patient care. For example: Blood-glucose sensor which is broadly used in medical field for the diabetic patient.

Advantages and Disadvantages of Biosensors:

Advantages:

1. Biosensors show a quick response.

2. Highly selective and specific.

3. No complex procedures and complex reagents are involved.

4. Cheaper and more reliable.

5. Reduce the hospitalization fee.

Disadvantages:

1. By introducing the biosensors can reduce the employment and loss of jobs.

2. The design cost of biosensors is high.

Future Scope:

Research work on biosensors is still going on. Researchers are working to produce new biosensors which are more easy to use even for a non-educated person. They are working to produce such biosensors which can detect even most dangerous diseases like HIV, Ebola, rabies etc. Biosensors should also be developed for plants as well.