Immobilization Of Biomolecules On

Biosensors

LECTURE OF SUBJECT :

Dr. sharafaldin Al-musawi

College of Biotecholgy

LECTURE: 3SUBJECT: Biosensors & Biochips

LEVEL: 4

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

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.

Quartz Crystal Microbalance (QCM)

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.

 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

The main applications of QCMs

Affinity Interactions used in QCM

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

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

Measuring principle

Molecules may be immobilized either passively through:

Hydrophobic

Ionic interactions

Covalently by attachment to activated surface groups.

Immobilization

Hydrophobic Immobilization

Immobilization

Ionic interactions

Immobilization

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

Immobilization

Covalent immobilization is often necessary for binding of molecules that:

• Do not adsorb, • Adsorb very weakly• Adsorb with improper orientation

Immobilization

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

Immobilization

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

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.

Immobilization

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

Immobilization