Bio Sensors and Lab on a chip Flashcards
Define biosensor
A sensor that integrates a biological element with a physico-chemical transducer to produce an electronic signal proportional to a single analyte which is then conveyed to a detector
What do you need to consider when building a biosensor
- The analyte
- The sample handling
- Detection/recognition
- Signal- how do tou
What is the analyte
What you want the biosensor to detect
What do we mean by the sample handling of a biosensor
How it is going to deliver the analyte to the sensitive region
What do we mean by the detection/recognition of a biosensor
How does the biosensor specifically recognise the analyte
What is the signal?
This needs to be a specific signal from a specific binding
If there is non specific binding and interface. False recognition can distort the result leading to false positives and negatives
What are the essential characteristics of a biosensor ?
Linearity- The sensor should have a linear response to the concentration of the substrate
Sensitivity - This is the value of the electrode response per substrate concentration
Selectivity - The chemical interface must be minimised for obtaining the correct result
Response time - This is the time necessary for having 95% of the response - want this to be short
When was the first modern biosensor made?
1962 by prof leland clark
What are the two most common biosensors ?
Pregnancy tests
Glucose tests
What does a pregnancy test test for ?
Human chorionic gonadotrophin (hCG)
This is an enzyme which increases in concentration post conception and during foetal growth and is detected in the urine
What chemical reaction occurs on a pregnancy test?
Monoclonal antibodies which only bind to this enzyme have been developed
- They work because the anti-alpha-hCG binds to the alpha domain and the anti-beta-hCG binds to the beta domain on the hCG
The Fc end of the enzyme is bound to activate dye in the catch region
The process by which it studies these enzymes is ELISA (enzyme linked immunosorbent assay)
What physical interaction occurs in a pregnancy test
The test uses a hydrophillic wicking strip
The enzyme labelled reporter antibodies bind to the hCG and travel to the catcher region where antibodies are covalently bound.
the hCG binds to the catcher region and the colour is generated by the enzymatic activation of dye.
What are glucose tests used for
Used by diabetics as frequent glucose monitoring has been shown to mean significantly fewer diabetes related complications to their health as tighter control on blood sugar levels
What hormones are responsible for blood sugar levels and where are they produced
The pancreas produces insulin and glucagon
1st Generation glucose measuring device
measures directly H2O2 and depends on O2 and H2O2 levels
2nd Generation glucose measuring device
This is a mediated biosensor - It uses ferrocene independent from oxygen pressure –> This means it has lower redox potential
3rd Generation glucose measuring device
Mediatorless- looks at direct electron transfer
Early examples of glucose detection
One of the earliest diagnostic methods involved a uroscopy where sugar is present when it shouldn’t be.
Define microfluidics
Devices that control liquids constrained at volumes in the micro litre range- exploiting the flow behaviour in this length scale
Why do we use microfluidics in biosensing
Microfluidics are used because you can use smaller sample volumes with high concentrations of analyte - this makes it easier to detect at low compound concentrations
What materials are biosensors made out of
Often made from glass and perspex which under goes eplication with silicone to form PDMA- This is easily made into moulds of patterned surfaces
Properties of microfluidics
- Experiences laminar flow - there is no mixing of fluids or diffusion so need to manually mix
- Fast thermal relaxation (estimating the time required for heat to conduct away from a directly-heated tissue region)
- Surface tension is one of the main forces acting on the fluid
What two ways can we mix fluids in a biosensor. What do these overcome
T junction fluidic mixers
Chaotic mixers
These overcome the laminar flow nature of the fluid and enable us to mix fluids
Give some examples of lab on a chip devices
Biochemical assays
Chemical applications
Biological application
