LOW NOISE RECORDING
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Chapter 5
Even if one uses electrically superior glasses, low noise will not be obtained unless the
outer surface of the glass is coated with a hydrophobic substance, such as Dow Corning
Sylgard #184. This substance prevents the bathing solution from creeping up the outer wall
of the pipette glass. This is important since a thin film of solution on the outer surface of
the glass produces a distributed resistance that interacts with the glass capacitance to
produce a noise source that rises with frequency. Since it becomes the dominant noise
source, it must be eliminated. While many other hydrophobic substances have been used,
none, to the best of our knowledge, produces as low noise as does Sylgard #184. Sylgard
also decreases the capacitance of the pipette wall and so reduces the lossiness of the wall as
well. It has been shown experimentally that Sylgard will improve the noise of any glass but
it will not turn a poor electrical glass into a good one. Low-loss glasses coated with
Sylgard give significantly less noise than poor glasses coated with Sylgard. Obviously, the
closer to the tip that the Sylgard can be painted the lower the noise.
Sylgard can be obtained from:
Dow Corning
2200 Salzburg, Midland, Michigan 48611, USA, (517) 496-6000
K.R. Anderson
2800 Bowers Avenue, Santa Clara, CA 95051, USA, (800)538-8712
UTSU SHOJI
Tokyo, Japan, 03-3663-5581
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