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Spectrometer | Photomultiplier tube | Fluorometer | Spectrophotofluorometer
image of molecule The Spectro-Photo-Fluorometer
 

 

The purpose of a photomultiplier tube (PMT) is to measure very weak light.

 

 

Photomultiplier tube
The purpose of a photomultiplier tube (PMT) is to measure very weak light. The tube multiplies the effect of the light that strikes it and converts photons of light into electrical signals so that the light can be precisely measured.

Each photon (bit of light) strikes a photocathode, ejecting an electron. The electrons are accelerated toward a secondary electrode called a dynode, which is held at a more positive potential so that each electron gains enough energy to eject several electrons from the dynode. This is the electron "multiplier." By using a series of dynodes, the PMT creates a cascading effect-the system creates 100,000-10,000,000 electrons for each photon hitting the first cathode. The amplified signal can be collected and measured at the end.



Fluorometer
A fluorometer measures the intensity of fluorescing molecules in a sample of blood or body tissue. Individual molecules are too small to be seen. However, when hit with ultraviolet light, these same materials can be seen with a fluorometer, because now the substances fluoresce, or glow. Scientists can use the fluorescent properties to see things that are otherwise too small to be visible.

The fluorometer measures the amount of fluorescent radiation produced by a sample when the sample is exposed to monochromatic light. Light focuses in on the cuvette. In early fluorometers, fluorescent light entered the vacuum phototube through the secondary filter at right angles to the exciting light. The photocurrent is recorded by an electric amplifier connected to a galvanometer, which detects and measures a small electric current by movements of a magnetic needle of coil in a magnetic field.

 

A fluorometer measures the intensity of fluorescing molecules in a sample of blood or body tissue.

 

Diagram of the Coleman Photofluorometer

The Coleman filter fluorometer measures the total fluorescence emitted by all materials in a sample

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