APMDA O'Hare Biosensors 1&2

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What are the ideal characteristics of Reference electrodes
- Potential should remains constant even if small amounts of current
- Potential should be reproduceable
- Electrode should be easy to assemble
- Components should ideally be non-toxic
What are the three types of electrodes? Give examples
- Glass electrodes eg pH
- Crystalline solid membranes like LaF3
- Supported liquid ion exchange membranes
Why is it important to have an excess of supporting electrolyte in a typical voltammetry
- 1. It increases conductivity by increasing the number of charge carriers.
- This reduces voltage error from the resistance between the working electrode and the reference electrode.
- 2. The debeye length is suppressed with increased shielding
blah blah. See the biosensors problem sheet answers for more
What is the typical experimental set-up for amperometry and voltammetry
- Working electrode: Pt, Au, carbon
- Reference electrode: Ag/AgCl, SCE
- Counter(auxiliary electrode): to provide current path.
Electrolyte solution
- Instrumenation: A potentiostat that maintains the potential between working and reference electrode.
- Also need a i-V converter to measure the current between the working and counter electrode.
What is the need for electrolyte solution in setup for amperommetry and voltammetry
- 1.Ensures majority charge carriers are not analyte.
- Only modes of transport are diffusion and convection
- 2. Populates double layer with inert ions to minimise effect of electrode reaction
- 3. Lowers resistance.
What goes wrong when applying electrochemical devices to measure molecules?
- Interference: Ascorbic acid for example is oxidisable at most electrodes at potentials where many interesting target analytes are oxidised.
- Adsorption: Big molecules can block diffusion and can deactivate catalytic sites
- Injury: Exposes cell contents a, rupturing capillaries. Causes inflammation.
- Occlusion: Sensor occupies space where nutritional supply arrived at the tissue is being measured
- Electrode failure: Integrity of the metal insulator seal is problematic.
- Osmotic swelling or mechanical failure is common
- Noise:Eg mains and tiny currents from high impedance sources. Is patient earthed?
What are the three ways of stabilising nernst layer?
- Forced convection: The rotating disc electrode
- Membrane: prevent convective flow
- Microelectrode: Make electrode small. make use of convergent diffusion. Memorise that weid quater circle diagram.
How do you get potential control?
- Potential control
- Selective membranes: learn diagram
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Author

keesukim

339906

Card Set

APMDA O'Hare Biosensors 1&2

Description

Biosensors 1 part of APMDA

Updated

2018-04-30T22:53:26Z

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