Immobilization of-biomolecules-on-biosensors
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Transcript of Immobilization of-biomolecules-on-biosensors
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Immobilization Of Biomolecules On
Biosensors
LECTURE OF SUBJECT :
Dr. sharafaldin Al-musawi
College of Biotecholgy
LECTURE: 3SUBJECT: Biosensors & Biochips
LEVEL: 4
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The quartz crystal microbalance (QCM) is an extremely sensitive mass sensor, capable of measuring mass changes in the nanogram range.
Quartz Crystal Microbalance (QCM)
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QCM’s are piezoelectric devices fabricated of a thin plate of quartz, with gold, platinum (Pt) or silver (Ag) electrodes affixed to each side of the plate.
Quartz Crystal Microbalance (QCM)
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Oscillator: is an electronic circuit that produces a periodic, oscillating electronic signal, often a sine wave or a square wave.Oscillators convert direct current (DC) to an alternating current (AC) signal.
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The main applications of QCMs are the
Determination the adsorption properties of
biomaterials and functional surfaces, for
proteins, lipids, polymers, (MOFs), cells and
bacteria.
The main applications of QCMs
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The main applications of QCMs
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Affinity Interactions used in QCM
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A spontaneous excitation of the sensor with an AC voltage is used to oscillate the quartz disc with a frequency that is dependent on the total oscillating mass.
Measuring principle
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The deposition of a thin film increases the oscillation and the resonant frequency decreases. This dependence is described by the Sauerbrey equation:
Measuring principle
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Molecules may be immobilized either passively through:
Hydrophobic
Ionic interactions
Covalently by attachment to activated surface groups.
Immobilization
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Hydrophobic Immobilization
Immobilization
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Ionic interactions
Immobilization
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Noncovalent surfaces are effective for many applications; however, passive adsorption of receptors fails in many cases.
Immobilization
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Covalent immobilization is often necessary for binding of molecules that:
• Do not adsorb, • Adsorb very weakly• Adsorb with improper orientation
Immobilization
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Covalent immobilization may result in reduced nonspecific adsorption, and greater stability.
Immobilization
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The immobilization process should occur selectively in the presence of common functional groups, including amines, thiols, carboxylic acids, and alcohols.
Immobilization
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Surface density of the ligand should be optimized.
Low density surface coverage will yield a correspondingly low frequency.
High surface densities may result steric interference between the covalently immobilized receptor molecules, impending access to the target molecules.
Immobilization
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1) unhindered binding. 2) inaccessible binding site. 3) hindered binding site when adjacent site is occupied. 4) restricted access binding site.
Immobilization