1. Immobilization Of Biomolecules On Biosensors
LECTURE OF SUBJECT :
Dr. sharafaldin Al-musawi
College of Biotecholgy
LECTURE: 3
SUBJECT: Biosensors & Biochips
LEVEL: 4
Immobilization Of Biomolecules On Biosensors

2. Quartz Crystal Microbalance (QCM)
The quartz crystal microbalance (QCM) is an extremely sensitive mass sensor, capable of measuring mass changes in the nanogram range.

3. Quartz Crystal Microbalance (QCM)
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.

4. 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.

5. The main applications of QCMs
 The main applications of QCMs are the Determination the adsorption properties of biomaterials and functional surfaces, for proteins, lipids, polymers, (MOFs), cells and bacteria.

6. The main applications of QCMs

7. Affinity Interactions used in QCM

8. Measuring principle
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.

9. Measuring principle
The deposition of a thin film increases the oscillation and the resonant frequency decreases. This dependence is described by the Sauerbrey equation:

10. Immobilization Molecules may be immobilized either passively through:
Hydrophobic
Ionic interactions
Covalently by attachment to activated surface groups.

11. Immobilization
Hydrophobic Immobilization

12. Immobilization
Ionic interactions

13. Immobilization
Noncovalent surfaces are effective for many applications; however, passive adsorption of receptors fails in many cases.

14. Immobilization
Covalent immobilization is often necessary for binding of molecules that:
Do not adsorb,
Adsorb very weakly
Adsorb with improper orientation

15. Immobilization
Covalent immobilization may result in reduced nonspecific adsorption, and greater stability.

16. Immobilization
The immobilization process should occur selectively in the presence of common functional groups, including amines, thiols, carboxylic acids, and alcohols.

17. Immobilization 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.

18. Immobilization
1) unhindered binding. 2) inaccessible binding site. 3) hindered binding site when adjacent site is occupied. 4) restricted access binding site.