BT505 Biosensor Notes and Current Papers

BT505 - Biosensors

Final Term notes + Current Questions (2021) Lesson # (100-203)

1- DNA Damage:

1. DNA can be damaged by oxidizing agents, alkylating agents and high-energy electromagnetic radiation such as ultraviolet light and X-rays.
2. DNA is damaged due to excessive levels of Reactive Oxygen Species. Normal level of ROS may be necessary for memory and learning.
3. DNA damaged is related to cancer and other diseases.

2- Electrochemical properties of DNA bases

All four bases of DNA can be oxidized and produce their oxidation signals at highly positive potentials on carbon electrodes. The one electron reduction potentials of DNA nucleosides are

1. Guanine 1.29
2. Adenine 1.42
3. Cytosine 1.6
4. Thymine 1.7

3- Drawbacks of Label Free Electrochemical Detection

1. It requires high potential to detect the Guanine oxidation.
2. High background signals.
3. Non-specific adsorption of DNA target containing Guanine bases.

4- Features of Glassy Carbon (Allotropic form of Carbon)

1. High-purity
2. Excellent Stability as high as at 3,000 °C in vacuum
3. Stable at 500 °C in the air
4. Inert against Chemical erosion
5. Impermeability to Gas and Solution
6. Significant Hardness/ Strength
7. Favorable electric conducting property
8. Highly Resistant against Inorganic and Organic salts
9. Nonporous
10. Good Bio-Compatibility

5- Electrochemical Detection HIV target DNA

1. A single-stranded PNA molecule is non-covalently linked the graphene surface with a pyrene linker group.
2. The complementary DNA-strand binds with HIV target DNA.
3. 2D grephene with excellent electronic properties help to detect this hybridization event at a very low noise level.

The changes in oxidation and reduction (with and without hybridization) are bases of the detection. Label-free electrochemical DNA hybridization method is

1. Simple
2. 2. Rapid
3. 3. Highly sensitivity
4. 4. Reproducibility
5. 5. Long-term stable.

6- Floropore and Quencher

1. Fluorophore is attached at one end of one arm and Quencher is attached at the end of other arm.
2. Quenching is a process which decreases the fluorescence intensity of a substance.
3. When the fluorophore and quencher are in close proximity, the quencher absorbs the energy emitted from an excited fluorophore, thereby suppressing its emission.

Designing and principle:

Molecular beacons do not fluoresce in their free form. In the absence of targets, the probe is dark, because the stem places the fluorophore close to the non-fluorescent quencher. Quencher and fluoropore transiently share electrons, eliminating the ability of the fluorophore to fluoresce. Example of Quencher Cl, Acrylamide, NaI.