Chapter 2 - Water

Question 1

What is a biosensor?

Answer 1

An analytical device that uses a biological molecule to detect the presence of a specific chemical molecule (analyte)

Question 2

What can a biosensor be used for?

Answer 2

Determining the presence and/or concentration of the analyte

Question 3

What happens if the analyte is present?

Answer 3

A colour change or electrical change occurs

Question 4

What are the 4 main components of a biosensor?

Answer 4

BTrAP
1. Bioreceptor - Molecular recognition
A protein e.g. enzyme or antibody or single strand of DNA (ssDNA) is immobilised to a surface. It will interact with or bind to the analyte.
2. Transduction
The transducer reacts with the analyte to cause a change in itself, e.g. change in pH. It then converts the chemical change into an electrical current (signal) —- it has produced a response.
3. Amplifier
It increases the strength of the signal. The size is proportional to the concentration of the analyte
4. Processor - display
Processor converts the electrical signal into a visible reading or measurement e.g. a particular colour or numerical reading. This can be qualitative or quantitative.

Question 5

How do clinistrips work?

Answer 5

Clinistix or Diastix used to detect presence and quantity of glucose in urine
1. Dip test strip into urine
2. Glucose oxidase is immobilised and attached to the test strip
3. Active site of glucose oxidase is complementary to glucose
4. A 2nd enzyme, peroxidase is immobilised on the test pad
5. Glucose oxidase catalyses the reaction between glucose and oxygen
6. This produces gluconolactone and hydrogen peroxide
7. Peroxidase breaks down the hydrogen peroxide to hydrogen and oxygen
8. Water converts gluconolactone to gluconic acid
9. Oxygen oxidises a chromogen on the test pad
10. Intensity of colour change on the pad reflects quantity of glucose present in urine
11. Compare colours on test strip to colour chart after specified period of time
12. Results are a QUALITATIVE estimate on the concentration of glucose

Question 6

What are the colour changes in Diastix?

Answer 6

Light blue = negative (normal levels)
Dark brown = abnormally raised levels

Question 7

What are the colour changes in Clinistix?

Answer 7

Light pink = negative (normal levels)
Dark pink = abnormally raised levels

Question 8

How do you use a glucometer to measure the concentration of glucose?

Answer 8

1. Sterile lancet used to pierce the skin on a warm finger pad
2. Single drop of blood is smeared on test strip
3. Test strip placed in portable meter
4. Test strip impregnated with glucose dehydrogenase
5. Glucose converted into gluconolactone
6. Gluconolactone converted to gluconic acid, causing the pH to decrease
7. This chemical signal is converted to an electrical current by the electrode (transducer) on the test strip
8. Size of the current is dependent on glucose concentration
9. QUANTITATIVE result is shown on screen within 25-30 seconds