Biosensors Flashcards
What is a biosensor?
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.
What is considered when building a biosensor?
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)
How can a biosensor be a specidifc signal?
needs to be from a specific binding
What is the effect of non specific binding and interference o
can distort results FALSE POSITIVE – FALSE NEGATIVE
What are the essential basic characteristics of a biosensor?
1) linearity
2) sensitivity
3) selectivity
4) response time
Why is linearity important in biosensors?
The sensor should have a linear response to the concentration of the substrate (analyte).
Why is sensitivity important in biosensors?
Value of the electrode response per substrate concentration
Why is selectivity important in biosensors?
Chemicals Interference must be minimised for obtaining the correct result
Why is response time important in biosensors?
Time necessary for having 95% of the response, should be short
What are the most common biosensor?
glucose
pregnancy test
What is diabetes?
a disease in which the body can no longer regulate the level of glucose in blood due to the failure to produce enough insulin
What are the complications associated with diabetes?
• 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
What is the cause of diabetes?
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)
What is Diabetes Control and Complications Trials?
- 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
What was the first generation glucose sensing?
Measures directly H2O2 and depends on O2/H2O2
What was the second generation of glucose sensors?
mediated biosensor: uses ferrocene independent from oxygen pressure, lower redox potential
What was the third generation of glucose sensors?
mediatorless, direct electron transfer
What is early glucose sensing?
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
How do pregnancy tests work?
- 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.
What are microfluids?
devices that and control of liquids constrained to volumes near the μL range, exploiting flow behavior in this length scale.
What are the advantages of microfluids in biosensing?
Small sample volumes – high concentrations of analyte – easier to detect low concentration compounds
What is the common method to produce a microfluid?
Microfluidics can be made from glass or perspex Simple production is eplication with silicone (PDMS) Easily makes moulds of patterned surface
What are the properties of microfluid?
• 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
How can mixing of two fluids be achieved?
2 routes
- T-junction fluidic mixer
- chaotic mixers
