Biosensors And Chromotography

Question 1

Biosensors:

Answer 1

Biosensors use a biological molecule (e.g. enzyme) and take a biological or chemical variable that cannot be measured easily. A transducer converts the chemical/biological signals into an electrical signal.
The electrical signal is then processed and used to work out other information.
Biosensors have many applications, e.g. detection of contaminants in water, pathogens/toxins in food, airborne bacteria.
An example is the blood glucose biosensor. This uses the enzyme glucose oxidase to catalyse break down blood glucose. The enzyme is oxidised by the transducer (electrodes) creating an electrical current which is a measure of glucose concentration.

Question 2

Chromatography for:

Answer 2

Used to separate a mixture – biological molecules. Made from two key components:
Stationary phase: The chromatography paper or thin-layer (molecules that can move), made from cellulose or thin-layer chromatography plate made from plastic, covered with silica gel or AlOH.
Mobile phase: The solvent for biological molecules (molecules that can’t move), water for polar molecules, ethanol for non-polar molecules. The mobile phase flows across or over the stationary phase, carrying biological molecules. The longer components spend in the mobile phase, the further they travel

Question 3

How to do chromatography:

Answer 3

Eye protection, draw line in pencil, wait until spots are dry before starting, cover beaker with watch glass/glass plate – to prevent solvent evaporating, in a fume cupboard, measure distances vertically, measure distances before solvent dries so it is visible or mark points and solvent front on with pencil.

Question 4

What happens (chromatography)

Answer 4

As the solvent travels up the paper or plate, the components of the solution mixture travel with it at different speeds.
Rf value (relative distance travelled) = distance of pigment from pencil line / distance form pencil line to solvent front (Rf =distance travelled by pigment / distance travelled by the solvent). In a repeat of the experiment each pigment will have the same Rf value – this allows pigments to be identified.

Question 5

Thin layer chromatography can be used to see colourless molecules:
(Chromatography)

Answer 5

1. UV light – the plates have a chemical which fluoresces under UV light, so everywhere will glow apart
   from where the spots have travelled too.
2. Ninhydrin – Allow the plate to dry and spray with ninhydrin, this binds to the amino acids which are
   visible as purple spots.
3. Iodine – Allow the plate to dry, place in enclosed container with iodine crystals, iodine gas forms
   which binds with the molecules.

Question 6

How does it work:

Answer 6

The speed at which the molecules move up the paper/plate depends on their solubility in the solvent, polarity and size. The exposed -OH groups on the paper/plate make them very polar, allowing hydrogen bond formation with molecules, alongside dipole interactions. A highly polar solute will stick to the surface and move more slowly compared to non-polar solute.
Chromatography is also used to test for illegal drugs in athlete’s urine, analysing drugs for purity of components, and analysis of foods to determine the presence of contaminants.