Week 11

Question 1

what is a biosensor?

Answer 1

It is a device that transforms chemical information into an analytically useful signal

Question 2

give some applications of sensors

Answer 2

• pathogen discovery
• soil quality monitoring
• drug discovery
• toxin detection
• water monitoring
• point of care (ex diabetes)
  …

Question 3

3 main types of sensors, what do all of them need to be connected to?

Answer 3

1) physical: distance, mass, T, pressure, …

2) chemical: chemical/physical sensing element

3) biosensors: biological sensing element

Connected to a transducer to have a visible response

Question 4

4 types of transducers

Answer 4

• electrochemical (measures potential)
• optical
• piezo electric
• thermal

Question 5

what can a sensor detect?

Answer 5

chemical sensors and biosensors detect ANALYTES

Question 6

5 methods for immobilization of analyte

Answer 6

1) adsorption onto surface
2) microencapsulation between membranes
3) entrapment (in gel, polymer, …)
4) covalent attachment with transducer
5) cross-linking with transducer

Question 7

7 performance factors, which is the most important?

Answer 7

most important = selectivity (discriminate between substances)

• sensitivity: sub-millimolar
• accuracy: better than 5%
• nature of solution
• response time (longer with biosensors)
• recovery time (before analysing next sample, not more than a few minutes)
• working lifetime: often several months

Question 8

three types of sensing elements

Answer 8

1) ionic (both sensors)
2) molecular (both sensors)
3) biological (biosensor)

Question 9

explain ion-selective electrodes

Answer 9

based on principle of electromagnetic field (emf) of a concentration cell.

potentiometric device in which the change in emf is proportional to the log of analyte concentration.

Membrane separating analyte from reference solution

Question 10

what is meant by “interference” ?

Answer 10

the small response of a sensor to unwanted ions -> measured by the selectivity coeff

Question 11

two ways to modify electrodes to gain selectivity

Answer 11

1) modify themselves

2) coat with polymers
- conducting
- ion exchange
- redox

Question 12

enzyme biosensor: michaelis-menten law, pros and cons

Answer 12

• law relates the initial reaction rate, the max reaction rate, and initial substate concentration, through K_M (substrate-binding affinity)

+:
- catalytically active
- fairly fast acting
- one of the most known biological component

-:
- expensive
- loses activity when immobilized on transducer
- lose activity after short period of time

Question 13

pros and cons of organism biosensors

Answer 13

+:
- cheaper
- less sensitive to inhibition by solutes
- more tolerant to pH and T (longer lifetime)

-:
- longer response time
- longer recovery time
- many enzymes and less selectivity

Question 14

antibody sensors pros and cons

Answer 14

+:
- high selectivity
- ultra sensitive
- bind very powerful

-:
- not catalytical
- not fast in detection
- incubation time
- expensive

Question 15

pros and cons of sensors with nucleic acid

Answer 15

+:
- high selectivity
- ultra sensitive
- bind very powerful
- point of care

-:
- not fast in detection
- incubation time

Question 16

three electrochemical processes useful for electrochemical transducers

Answer 16

1) potentiometry: measure cell potential at zero current, using an indicator and a reference electrode

2) voltammerry: potential is applied between cell electrodes and cell current is measured

3) conductometry: conductance of cell is measured

Question 17

2 types of electrodes

Answer 17

1) working electrode (that measures)

2) reference electrode to which other electrodes may be referred

Question 18

conductivity varies according to : (3 things)

Answer 18

• charge of ion
• mobility of ion
• degree of dissociation of ion

Question 19

advantages of optical sensors in a clinical setting?

Answer 19

• can be detected under the skin
• can be inserted
• stable
• doesn’t need electronics