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electronics and biological cell.

Discussion in 'Electronic Basics' started by BPO, Oct 8, 2004.

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  1. BPO

    BPO Guest

    Hi everybody,

    I'm a biologist and I would like to try to culture some cells on a
    Gold (or other biocompatible metal) rod/needle. I would like to try
    some basic electronics measurements, as capacitance, conductance,
    etc... and try to relate them to cell growth.

    As I'm really bad in electronics, I come up with several basic
    questions for you.

    1)How can I measure the capacitance of a metal needle ?
    2) What sort of instrument (cheap one)do I need ? I expect changes in
    the 0.1 pF range.
    3) Could I measure these electrical properties by accessing only one
    end of the metal needle ?

    Thx.
     
  2. In relation to what? You need to define another body and seek the
    capacitance between these two bodies.
    Between your needle and the planet earth, for example.
    Hardly cheap. Such small capacitances are difficult to measure, because
    the capacitances of bodies around it will interfere.

    One of the common ways to measure small capacitances is to involve it in
    an oscillator, so the frequency of the oscillator depends on the
    capacitance.
    Yes. A piece of metal is to the electrical current like water is to
    sound. You can explore a water body with the help of sound, measure
    echoes and timings and determine the size of the water body, its length,
    etc..

    In a similar way can we explore a piece of metal through measuring
    reflected waves, capacitance, etc.., even though we only have access to
    one end of the metal body.

    When measuring small capacitances remember that two inch-long pieces of
    isolated wire tightly twisted together have a capacitance of something
    like 7pF. It is a trick often used to create a small capacitor out of
    wires. I hope you understand that an instrument measuring sub-pF
    capacitances would have a giant problem with its own terminals, unless
    they were placed at least a meter apart. And the connecting leads will
    have even bigger problems as their capacitance will be dependent on their
    position.
     
  3. Ban

    Ban Guest

    I have the L/C Meter IIB by "Almost All Digital Electronics" which is
    sold(as a kit) for a little more than 100 bucks, which has a resolution of
    0.01pF. You can position the probes in the right way and then zero the
    display. When I move my hand from 20cm to 2 cm closer to the probes, the
    capacitance increases about 0.03pF. Amazingly accurate(1%) and sensitive.
    when you cross the probes the capacitance increases about 0.95pF. I think it
    comes from Australia?
     
  4. I found the schematics for this L/Cmeter at:

    http://www.aade.com/lcm2binst/LC2Binst.htm

    If the 311 is used as an oscillator here, the display component
    has to work as a frequency counter.
     
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