**3. Biosensors**

A biosensor is an analytical device consisting of immobilized biological material in direct contact with a compatible transducer that will convert the biochemical signal into a measurable electrical signal. Biomolecules are responsible for specific recognition of the analyte, while the physicochemical converter provides electrical output signal that is amplified by electronic component [14]. Biosensors find application in various areas, from agriculture, food quality control, medicine, army, and control of various processes in the environment. Biosensors can provide quick information about the site of pollution, which is necessary for environmental control and monitoring. In addition, the advantage of biosensors over other analytical methods is their mobility that allows researchers to measure the in situ pollutant concentration and the ability to measure the concentration of pollutants in situ without additional sample preparation. Also, in addition to the determination of specific compounds, they can provide information on their biological effect (e.g., toxicity of a compound).

Due to exceptional performances, including high specificity and sensitivity, rapid response, low cost, relatively small size, and simple operation, biosensors have become an important tool for detecting chemical and biological components and their monitoring for clinical, nutritional, and ecological needs [15].

### **3.1 General characteristics of biosensors**

Biosensors are analytical sensory devices that combine physical and chemical sensing techniques [16, 17]. Their performance is based on direct contact of two elements: biological and physicochemical, whose tight bond is achieved by physical or chemical methods of immobilization. Biological element serves as a receptor (bioreceptor), i.e., for the recognition of particular analyte from the medium of interest, based on the interaction of analyte and bioreceptor. Physicochemical transducer converts the response that occurs as a result of analyte-bioreceptor interaction on their interface into a measurable signal which can be processed and displayed in the form of readable values. For proper biosensor operation, the biological compound has to be immobilized in the vicinity of the transducer, and immobilization can be done either by physical entrapment or chemical attachment. Only small amounts of bioreceptor molecules are required, and they will be repeatedly used for measurements [18].

The displayed values are in correlation with the detected analyte-bioreceptor interactions, i.e., the concentration of a specific analyte or group of analytes in the analyzed sample [4, 16, 17]. General working principle of biosensors is illustrated in **Figure 1**.

Although widely used, conventional analytical techniques require sophisticated instruments and highly trained personnel to conduct operational procedures and

**145**

**Figure 2.**

*Biosensors for Determination of Heavy Metals in Waters DOI: http://dx.doi.org/10.5772/intechopen.84139*

**3.2 Classification and types of biosensors**

*3.2.1 Classification by type of transducer*

*3.2.1.1 Electrochemical biosensors*

present in the sample solution.

tions are poor reproducibility and stability [27].

*Schematic illustration of the common classification of biosensors.*

biosensors can be further classified into subclasses (**Figure 2**).

piezoelectric, and thermal biosensors may be distinguished.

sample preparation, which makes them expensive and time-consuming [19, 20], thus not enabling determination of a large number of samples in a short time [21]. The main advantages of biosensors in relation to conventional analytical techniques are possibility of miniaturization and portability of device, reduced requirements for laboratory skills, reduced sample volume and pretreatment [1, 22], assessment of all possible types of analytes, inorganic or organic [23, 24], and possibility of performing single measurements or continuous real-time monitoring of analytes [1, 25]. Biosensors allow estimation of biological effects, e.g., toxicity of specific chemicals, because they can be used to detect their bioavailable concentrations [26].

Biosensors can be divided into classes according to different approaches, among which the two are commonly used—type of biorecognition element (biocomponent, bioreceptor) and type of transduction system in biosensor. Each class of

Based on the principle used in transduction systems, electrochemical, optical,

The first proposed and commercialized biosensors were electrochemical biosensors, which is why they are most commonly reported. The basic principle of this class of biosensors is that the interaction between the biomolecule (bioreceptor) and the target analyte results in a chemical reaction that produces or consumes ions or electrons and in turn changes the electrical properties of the analyte solution, such as electrical current or potential. Transducer detects these changes by producing an electrochemical signal which is correlated with the amount of analyte

Advantages of electrochemical biosensors include minimal requirements for sample preparation and sensitivity at small sample volumes. It is also possible to perform sample analysis directly, which enables automation. Drawbacks of detec-

**Figure 1.** *Schematic illustration of a biosensor general working principle.*

### *Biosensors for Determination of Heavy Metals in Waters DOI: http://dx.doi.org/10.5772/intechopen.84139*

*Biosensors for Environmental Monitoring*

A biosensor is an analytical device consisting of immobilized biological material in direct contact with a compatible transducer that will convert the biochemical signal into a measurable electrical signal. Biomolecules are responsible for specific recognition of the analyte, while the physicochemical converter provides electrical output signal that is amplified by electronic component [14]. Biosensors find application in various areas, from agriculture, food quality control, medicine, army, and control of various processes in the environment. Biosensors can provide quick information about the site of pollution, which is necessary for environmental control and monitoring. In addition, the advantage of biosensors over other analytical methods is their mobility that allows researchers to measure the in situ pollutant concentration and the ability to measure the concentration of pollutants in situ without additional sample preparation. Also, in addition to the determination of specific compounds, they can provide information on their biological effect (e.g.,

Due to exceptional performances, including high specificity and sensitivity, rapid response, low cost, relatively small size, and simple operation, biosensors have become an important tool for detecting chemical and biological components

Biosensors are analytical sensory devices that combine physical and chemical sensing techniques [16, 17]. Their performance is based on direct contact of two elements: biological and physicochemical, whose tight bond is achieved by physical or chemical methods of immobilization. Biological element serves as a receptor (bioreceptor), i.e., for the recognition of particular analyte from the medium of interest, based on the interaction of analyte and bioreceptor. Physicochemical transducer converts the response that occurs as a result of analyte-bioreceptor interaction on their interface into a measurable signal which can be processed and displayed in the form of readable values. For proper biosensor operation, the biological compound has to be immobilized in the vicinity of the transducer, and immobilization can be done either by physical entrapment or chemical attachment. Only small amounts of bioreceptor molecules are required, and they will be

The displayed values are in correlation with the detected analyte-bioreceptor interactions, i.e., the concentration of a specific analyte or group of analytes in the analyzed sample [4, 16, 17]. General working principle of biosensors is illustrated in

Although widely used, conventional analytical techniques require sophisticated instruments and highly trained personnel to conduct operational procedures and

and their monitoring for clinical, nutritional, and ecological needs [15].

**3. Biosensors**

toxicity of a compound).

**3.1 General characteristics of biosensors**

repeatedly used for measurements [18].

*Schematic illustration of a biosensor general working principle.*

**144**

**Figure 1.**

**Figure 1**.

sample preparation, which makes them expensive and time-consuming [19, 20], thus not enabling determination of a large number of samples in a short time [21].

The main advantages of biosensors in relation to conventional analytical techniques are possibility of miniaturization and portability of device, reduced requirements for laboratory skills, reduced sample volume and pretreatment [1, 22], assessment of all possible types of analytes, inorganic or organic [23, 24], and possibility of performing single measurements or continuous real-time monitoring of analytes [1, 25]. Biosensors allow estimation of biological effects, e.g., toxicity of specific chemicals, because they can be used to detect their bioavailable concentrations [26].

## **3.2 Classification and types of biosensors**

Biosensors can be divided into classes according to different approaches, among which the two are commonly used—type of biorecognition element (biocomponent, bioreceptor) and type of transduction system in biosensor. Each class of biosensors can be further classified into subclasses (**Figure 2**).
