A biosensor is a device for the detection of an analyte that combines a biological component with a physicochemical detector component [33].
A biosensor consists of 4 parts (illustrated in Fig 1.10):
The substances (biological material (tissue, micro-organisms, organelles, cell receptors, enzymes, antibodies, nucleic acids, ect.); a biologically derived material or biomimic). The sensitive elements can be created by biological engineering;
The detection (works in a physicochemical way; optical, electrochemical, thermometric, piezoelectric or magnetic);
The transduction: transducer between (associates both components);
The signal conditioning (amplifier) is used to enhance the signal (output) from the initial signal of the detection.
Operation principle of biosensor
As shown in figure 1.10, the specific interactions between the analyte and the biorecognition (biological detection) element produce a physico-chemical change, which is detected by the transducer and measured by peripheral circuits.
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Figure 1.10. The schematic of biosensor (source: http://basicsofbiosensing.blogspot.com/).
The fundamental advantage of biosensors over nearly all other sensor devices is their high selectivity which is benefited the selectivity of this bio-receptor. The amount of electronic signal generated is proportional to the concentration of the analyte,
allowing for both quantitative and qualitative measurements in time.
DNA sensor is a special type of biosensor, which used DNA strands as sensitive biological element, Fig 1.11.
Figure 1.11. General DNA sensor design based on CPs [18].
(source: http:// www.europhysics.com, 2002).
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DNA biosensors are integrated receptor-transducer devices that use DNA as biomolecular recognition element to measure specific binding processes with DNA, usually by electrical, thermal, or optical signal transduction [38].
Figure 1.12. The principle of DNA sensor.
As presented in Fig 1.12, the matching between analyte (DNA target) and recognition layer (DNA probe on surface electrode) provides us a signal transduction of hybridization, which allow us to record electronic read-out.
History of biosensor development 1916
First report on the immobilisation of proteins: adsorption of invertase on activated charcoal
1922 First glass pH electrode
1956 Invention of the oxygen electrode (Clark)
1962 First description of a biosensor: an amperometric enzyme electrode for glucose (Clark)
1969 First potentiometric biosensor: urease immobilised on an ammonia electrode to detect urea
1970 Invention of the Ion-Selective Field-Effect Transistor (ISFET) (Bergveld)
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5/1972 First commercial biosensor: Yellow Springs Instruments glucose biosensor
1975 First microbe-based biosensor; First immunosensor: ovalbumin on a platinum wire; Invention of the pO2 / pCO2 optode
1976 First bedside artificial pancreas (Miles)
1980 First fibre optic pH sensor for in vivo blood gases (Peterson) 1982 First fibre optic-based biosensor for glucose
1983 First surface plasmon resonance (SPR) immunosensor
1984 First mediated amperometric biosensor: ferrocene used with glucose oxidase for the detection of glucose
1987 Launch of the MediSense ExacTech™ blood glucose, Biosensor 1990 Launch of the Pharmacia BIACore SPR-based biosensor system 1992 i-STAT launches hand-held blood analyser
1996 Glucocard launched
1996 Abbott acquires MediSense for $867 million
1998 Launch of LifeScan FastTake blood glucose biosensor
1998 Merger of Roche and Boehringer Mannheim to form, Roche Diagnostics 2001 LifeScan purchases Inverness Medical's glucose testing business for
$1.3 billion
Table 1.4. History of biosensor development (Source: http://nanohub.org).
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Biosensor market
The biosensors market is categorized as a growth market, with the number of applications increasing as each new biosensor is developed.
(http://www.sensorsmag.com).
Figure 1.13. The total biosensors market showing the world revenue forecast for 2009–2016 (source: http://www.sensorsmag.com).
As illustrated in figure 1.13, the global revenue for the biosensor market will continue to exhibit strong growth and will exceed $14 billion mark in the next seven years. The grow rate is estimated up to 11.5% from 2009 to 2016.
Biosensors have been developing and having considerable potential in many applications and commerce.
Introduction to DNA
To design efficient DNA-electrochemical biosensors, it is essential to know the structure and to understand the electrochemical characteristics of DNA molecules.
Deoxyribonucleic acid (DNA) is a nucleic acid which carries genetic instructions for the biological development of all cellular forms of life and many viruses [33]. DNA is sometimes referred to as the molecule of heredity as it is inherited and used to probate traits. During the reproduction, it is replicated and transmitted to offspring.
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DNA composed of 4 bases: adenine (A), thymine (T), cytosine (C) and guanine (G) [23].
Adenin (A) Thymin (T) Guanin (G) Cytosin (C)
Figure 1.14. Four base types of DNA.
DNA consists of two antiparallel polynucleotide chains formed by monomeric nucleotide units. Each nucleotide is formed by three types of chemical components: a phosphate group, a sugar called deoxyribose, and four different nitrogen bases.
Figure 1.15. Hydrogen bonds between the A-T and G-C bases of the two strands of DNA (adopted from reference [18]).
N N NH2
N N9H
N
N1 OH
CH3
HO
N
N OH
H2N
N
N9H
N
N1
NH2
HO
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The phosphate-deoxyribose sugar polymer represents the DNA backbone (Fig 1.15, adopted from Ref [18]). The cellular genetic information is coded by the purine bases, adenine (A) and guanine (G), and the pyrimidine bases, cytosine (C) and thymine (T), as a function of their consecutive order in the chain. The two strands of nucleotides are twisted into a double helix, held together by hydrogen bonds between the A-T and G-C bases of each strand