Biosensors

Question 1

What is a biosensor?

Answer 1

A sensor that integrates a biological element with a physicochemical transducer to produce an electronic signal proportional to a single analyte which is then conveyed to a detector.

Question 2

What is considered when building a biosensor?

Answer 2

The Analyte (What do you want to detect) Sample handling (How to deliver the analyte to the sensitive region?) Detection/Recognition (How do you specifically recognize the analyte?) Signal (How do you know there was a detection)

Question 3

How can a biosensor be a specidifc signal?

Answer 3

needs to be from a specific binding

Question 4

What is the effect of non specific binding and interference o

Answer 4

can distort results FALSE POSITIVE – FALSE NEGATIVE

Question 5

What are the essential basic characteristics of a biosensor?

Answer 5

1) linearity
2) sensitivity
3) selectivity
4) response time

Question 6

Why is linearity important in biosensors?

Answer 6

The sensor should have a linear response to the concentration of the substrate (analyte).

Question 7

Why is sensitivity important in biosensors?

Answer 7

Value of the electrode response per substrate concentration

Question 8

Why is selectivity important in biosensors?

Answer 8

Chemicals Interference must be minimised for obtaining the correct result

Question 9

Why is response time important in biosensors?

Answer 9

Time necessary for having 95% of the response, should be short

Question 10

What are the most common biosensor?

Answer 10

glucose

pregnancy test

Question 11

What is diabetes?

Answer 11

a disease in which the body can no longer regulate the level of glucose in blood due to the failure to produce enough insulin

Question 12

What are the complications associated with diabetes?

Answer 12

• 2-4 fold increase in incident of heart disease • Over 40% all new cases of serious kidney disease • Over 60% of all non-traumatic limb amputations • Major cause of adult blindness, erectile dysfunction in man, etc, etc, et

Question 13

What is the cause of diabetes?

Answer 13

Insulin and glucagon (produced by pancreas) are the hormones responsible People with diabetes mellitus are either unable to produce insulin (type 1, autoimmune disorder), or unable to produce it in sufficient amounts cells don’t react to it (type 2, correlated with obesity)

Question 14

What is Diabetes Control and Complications Trials?

Answer 14

• The study spanned a period of 10 years (1983-1993) and involved 1441 type I diabetics • Two groups: (1) standard regime insulin shots and glucose measurements and (2) frequent glucose monitoring and [often] more frequent insulin injections
• Bottom line: Over time group (2) had significantly fewer diabetes-related complications
• Computer simulations: People in group (2) will have an additional 5 years of life, 8 years of sight, 6 years free of kidney disease and 6 years free of amputations Hence, regular monitoring is a critical part of effective health care system for diabetics, ~$6-7 bn pa business

Question 15

What was the first generation glucose sensing?

Answer 15

Measures directly H2O2 and depends on O2/H2O2

Question 16

What was the second generation of glucose sensors?

Answer 16

mediated biosensor: uses ferrocene independent from oxygen pressure, lower redox potential

Question 17

What was the third generation of glucose sensors?

Answer 17

mediatorless, direct electron transfer

Question 18

What is early glucose sensing?

Answer 18

Sugars are not normally present in the urine of healthy people Uroscopy – an examination of urine by colour, consistency, smell and taste, was one of the earliest methods of diagnostics
XIX century: Moore’s potash test boiling urine with potash (K2CO3) led to the development of dark coloration in the presence of glucose
Unreliable, especially for the detection of small amounts of glucose, since most urine darkens on boiling with potash

Question 19

How do pregnancy tests work?

Answer 19

• Commercial pregnancy test kits are remarkably sensitive – detect down to nM (10-9) or lower concentrations of human chorionic gonadotrophin (hCG).
• Human chorionic gonadotrophin is an enzyme which increases in concentration post-conception, during foetal growth.
• Detected in urine
• Monoclonal antibodies which only bind this enzyme have been developed: anti--hCG, binds to  domain and anti--hCG binds to  domain on hCG.

Question 20

What are microfluids?

Answer 20

devices that and control of liquids constrained to volumes near the μL range, exploiting flow behavior in this length scale.

Question 21

What are the advantages of microfluids in biosensing?

Answer 21

Small sample volumes – high concentrations of analyte – easier to detect low concentration compounds

Question 22

What is the common method to produce a microfluid?

Answer 22

Microfluidics can be made from glass or perspex Simple production is eplication with silicone (PDMS) Easily makes moulds of patterned surface

Question 23

What are the properties of microfluid?

Answer 23

• Behavior of liquids in the micro domain differs greatly from macroscopic fluids
– Surface tension / capillary action (surface vs. bulk effects)
– Laminar flow (no mixing of liquids) / Diffusion
– Fast thermal relaxation

Question 24

How can mixing of two fluids be achieved?

Answer 24

2 routes

• T-junction fluidic mixer
• chaotic mixers

Question 25

What can ‘lab-on-a-chip’ devices do?

Answer 25

1) Biochemical assays: real-time PCR, immunoassay, dielectrophoresis for detecting cancer cells and bacteria, etc.
2) Chemical application: separating molecules from mixtures, chemical reactors, chemical detections. etc.
3) Biological application: cell coculture, biosensor, drug screening, single-cell analysis, etc.

Question 26

What are microfluid diagnostic methods?

Answer 26

1) Portable Point-of-Care (POC) Medical Diagnostic Systems

- The chips should be inexpensive, accurate, reliable and suited to the medical conditions in developing countries

Question 27

What is a human on a chip device?

Answer 27

Human body = complex environment Drugs get transformed in body
• Break down by gut
• Oxidation in liver
• Storage in fat (concentration can reach lethal level)

Question 28

What are the more sophisticated tissue models currently developed?

Answer 28

• Co-culture of different cells
• Place cells in “biomimetic environment”
• Include mechanical cues in the tissue environment to make it more ”biomimetic”

Question 29

What is a liver on a chip device?

Answer 29

a highly porous membrane to mimic the endothelial barrier Back fill device with hepatocytes

Question 30

What can a liver on a chip device be used for?

Answer 30

Lung alveolar-capillary barrier:
During inhalation in the living lung, contraction of the diaphragm causes a reduction in intrapleural pressure (Pip), leading to distension of the alveoli and physical stretching of the alveolar-capillary interface.

Question 31

What is the function of a liver?

Answer 31

The liver receives blood flow from the hepatic artery and the portal vein, which carries xenobiotics such as ingested drugs from the small intestine to be metabolized by liver hepatocytes.
Low pressure blood flow travels from branches of the hepatic arteries and hepatic portal vein through the liver sinusoids and drains out via the central vein.
The hepatocytes reside in thin cords and form extensive cell-cell contacts. The sinusoid space is bordered by a sheet of endothelial cells which lack a basement membrane (highly permeable).