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2 pm: Meeting with Anna about Biosensors

  • Discussion on biosensors with Christin, Farah, Jonny (and Vincent)
  • Duration of meeting: 1:15 h

Summary of the meeting

  • Quick overview of of all the available electrodes that were available to us
  • Brief mention of the different immobilization techniques
  • Recommendations
  • Areas that need to be researched before any decisions can be made
1) Membrane Electrode
  • Advantages
    • Very specific, very accurate, few interferences from other molecules (an exception being silver molecules)
  • Disadvantages
    • Difficult to miniaturize, high resistance (lots of electrical noise, easy to distort, hard to immobilize enzyme on them
2) Oxide Electrode
  • Advantages
    • Easy to miniaturize and regenerate, easy to immobilize enzymes
  • Disadvantages
    • Not widely used, lots of interfering substances, smallish range (pH 3-9)
3) Glass Electrode
  • Large range(pH 1-13)
4) Membrane electrode II
  • More robust, low resistance, large pH range
  • Low selectivity
5) Transistors
  • Easy to miniaturize
  • Not well characterized for analytical chemistry
6) Optical Sensors
  • Require very specific dyes to be applied

Immobilization techniques


Not very robust, hard to reproduce, moderate enzyme activity


More robust, easier to reproduce, better enzymatic activity


The main problem that we have, is that the values we expect are in the nanomolar range. However, the sensors mentioned above generally only have a sensitivity in the millimolar and perhaps micromolar range. This does not mean we definitely won't pick up any results - but the probability of successful results is lessened significantly.

The make-up of the medium is vitally important. This is firstly because more buffer in the medium results in a reduction in the sensor sensitivity. Secondly the medium may contain other molecules that the enzymes are able to break down - and we do not want these to saturate the enzyme on the sensor.

We have two different media that we can use - LB medium and M9 minimal medium The LB medium has no buffer, however will have a significant amount of interference. The M9 medium does have buffer, but is unlikely to have any interference.

We want the enzyme that will be used to be as specific as possible to reduce interference. Therefore it would be ideal if we could get hold of a lactonase. However it seems that we may have to settle for using an esterase as lactonases are not freely available.

Further Work

It needs to be decided whether or not we are going to continue to pursue this. If so, then we need to get hold of a suitable enzyme and decide on the make-up of our buffer.

Look into other commercially available pH sensors