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Figure 5. Covalent linkage of enzyme over the support (a) with spacer and (b) without spacer.

Figure 5 Covalent linkage of enzyme over the support (a) with spacer and (b) without spacer.

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Technological innovations for the development of self-monitoring systems for health factors are inspirable. Cardiovascular diseases (CVD) have been the major cause in the human mortality rate in recent years. In the present context, development of various cholesterol biosensors as a reliable and self-examining instinct solution for evaluating the biochemical levels in the human body is a contemporary aspiration. In this review, utilization of different polymers, biopolymers and its nanocomposites for biosensor applications have been discussed. Also, factors affecting the performance of cholesterol biosensors are included for a simple and cost-effective biosensors to the global market.
Technological innovations for the development of self-monitoring systems for health factors are inspirable. Cardiovascular diseases (CVD) have been the major cause in the human mortality rate in recent years. In the present context, development of various cholesterol biosensors as a reliable and self-examining instinct solution for evaluating the biochemical levels in the human body is a contemporary aspiration. In this review, utilization of different polymers, biopolymers and its nanocomposites for biosensor applications have been discussed. Also, factors affecting the performance of cholesterol biosensors are included for a simple and cost-effective biosensors to the global market.
Figure 1. Structure of (a) cholesterol, (b) triglyceride and (c) lipoprotein.) fats and the cells utilize them for the production of adenosine triphosphate (ATP). The unused fragment of dietary intakes with fat is conveyed to the fat cells and keeps as triglycerides. The fat is removed and sent to cells when energy is required. their density. CM has the highest density among lipo- proteins and they distribute cholesterol and triglycerides from intestine to liver and other tissues. From intestine and liver, VLDL provides triglycerides to the muscle and adipose tissue. LDL binds with cholesterol from the liver and it is transported into the cells. Because of its low- density large number of LDL can accumulate in blood vessels. Excess LDL in blood vessels escalate the level of cholesterol and it ends in diseases such as atherosclerosis by stimulating the formation of plaques. HDL is said to be a ‘good cholesterol’ since it picks up excess cholestero while moving through the blood vessels and brings it back to the liver.
Figure 1. Structure of (a) cholesterol, (b) triglyceride and (c) lipoprotein.) fats and the cells utilize them for the production of adenosine triphosphate (ATP). The unused fragment of dietary intakes with fat is conveyed to the fat cells and keeps as triglycerides. The fat is removed and sent to cells when energy is required. their density. CM has the highest density among lipo- proteins and they distribute cholesterol and triglycerides from intestine to liver and other tissues. From intestine and liver, VLDL provides triglycerides to the muscle and adipose tissue. LDL binds with cholesterol from the liver and it is transported into the cells. Because of its low- density large number of LDL can accumulate in blood vessels. Excess LDL in blood vessels escalate the level of cholesterol and it ends in diseases such as atherosclerosis by stimulating the formation of plaques. HDL is said to be a ‘good cholesterol’ since it picks up excess cholestero while moving through the blood vessels and brings it back to the liver.
Table 1. Types of lipoproteins and their desirable limits""" and forms glycerol-3-phosphate.''*! Glycerol-3-phos- phate oxidase (GPO) catalyzes the oxidation of gly- cerol-3-phosphate to dihydroxyl acetone phosphate and as a result of oxidation, H,O, is formed. Splitting of H,O, under high potential will release electrons that can penetrate through the transducer as reported by Pundiret et al.!'®! The biochemical reaction on the electrode surface is illustrated in Scheme 3. 2. Biosensor: concepts and instrumentation
Table 1. Types of lipoproteins and their desirable limits""" and forms glycerol-3-phosphate.''*! Glycerol-3-phos- phate oxidase (GPO) catalyzes the oxidation of gly- cerol-3-phosphate to dihydroxyl acetone phosphate and as a result of oxidation, H,O, is formed. Splitting of H,O, under high potential will release electrons that can penetrate through the transducer as reported by Pundiret et al.!'®! The biochemical reaction on the electrode surface is illustrated in Scheme 3. 2. Biosensor: concepts and instrumentation
Table 2. Characteristics of various cholesterol biosensors.
Table 2. Characteristics of various cholesterol biosensors.
Figure 2. Components of biosensor.
Figure 2. Components of biosensor.
Figure 3. Bioreceptors in biosensors.
Figure 3. Bioreceptors in biosensors.
Scheme 3. The Catalytic chemical reaction of triglyceride with an enzyme such as lipases, glycerol kinase, and glycerol-3-phosphat oxidase.
Scheme 3. The Catalytic chemical reaction of triglyceride with an enzyme such as lipases, glycerol kinase, and glycerol-3-phosphat oxidase.
Figure 4. Microcapsule synthesis and enzyme loading.'°*! 3.1.1.2. Solgel method. The solgel method has been popular among the immobilization methods since it does not concern about the functionalities of the enzymes. In this method, the enzyme is entrapped physically which ensures the integrity without any directional changes in the enzyme. Another advantage of t his method is that the enzyme is secured enough since the suitable size of pores is formed for incorpor- ating enzymes.!°°! However, production of alcohol dur- ing creates a harmful effect on the enzymatic activity. The app. hydrolysis and condensation of alkoxide precursors [61,62] solgel method is long established in biosensor ications.'°*4! By incorporating metal particles within the solgel matrix via doping the diffusion rate, Adsorption is the simplest technique for the immobili- zation of enzymes, and enzyme denaturation is mini- mal in this process. Attachment of enzyme is achieved by weak van der Waals forces and _ electrostatic interactions.'”'! Using physical adsorption technique stability of ~3 months has been reported with the ChOx enzyme immobilized over polypyrrole/dodecyl- benzenesulphonate (PPy/DBS) films.!77!
Figure 4. Microcapsule synthesis and enzyme loading.'°*! 3.1.1.2. Solgel method. The solgel method has been popular among the immobilization methods since it does not concern about the functionalities of the enzymes. In this method, the enzyme is entrapped physically which ensures the integrity without any directional changes in the enzyme. Another advantage of t his method is that the enzyme is secured enough since the suitable size of pores is formed for incorpor- ating enzymes.!°°! However, production of alcohol dur- ing creates a harmful effect on the enzymatic activity. The app. hydrolysis and condensation of alkoxide precursors [61,62] solgel method is long established in biosensor ications.'°*4! By incorporating metal particles within the solgel matrix via doping the diffusion rate, Adsorption is the simplest technique for the immobili- zation of enzymes, and enzyme denaturation is mini- mal in this process. Attachment of enzyme is achieved by weak van der Waals forces and _ electrostatic interactions.'”'! Using physical adsorption technique stability of ~3 months has been reported with the ChOx enzyme immobilized over polypyrrole/dodecyl- benzenesulphonate (PPy/DBS) films.!77!
Figure 6. Techniques used in the fabrication of electrodes (a) drop casting, (b) electrochemical polymerization, (c) doctor blade method, (d) spin coating, (e) dip coating and (f) screen printing.
Figure 6. Techniques used in the fabrication of electrodes (a) drop casting, (b) electrochemical polymerization, (c) doctor blade method, (d) spin coating, (e) dip coating and (f) screen printing.
Figure 7. Arrangements in a screen printed electrode.
Figure 7. Arrangements in a screen printed electrode.
Figure 8. Biosensor based on conducting polymer.
Figure 8. Biosensor based on conducting polymer.
Figure 9. Mediated reaction between enzyme and electrode.?°”!
Figure 9. Mediated reaction between enzyme and electrode.?°”!
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