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Phase-Modulation Fluorometer Using a Dynode-Voltage Burst-Modulated Photomultiplier Tube

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We propose a new scheme for a phase-modulation fluorometer (PMF) in which a photomultiplier tube (PMT) is used as a photo detector whose gain is modulated sinusoidally with a burst signal of period T and duty ratio 0.5. The carrier wave of the burst modulation signal is synchronized with an incident fluorescence signal. In order to modulate the gain of the PMT, one of the dynodes in the PMT was deeply biased and the burst signal was superimposed. Because the fluorescence signal is converted to a direct current (dc) signal by the PMT internal modulation, we can make the value of the load resistance of the PMT relatively large under the condition τ ≤ T/2, where τ is a time constant of a low-pass filter attached to the output of the PMT. The proposed scheme brings about advantages in sensitivity and noise immunity in detecting weak fluorescence in comparison with those of the conventional PMF. The combined technique of the burst modulation of the gain of the PMT and the alternating current (ac) signal detection alleviates the influence of the background light.


Document Type: Research Article

DOI: http://dx.doi.org/10.1366/0003702054615151

Affiliations: 1: Department of Mechanical Engineering, The University of Tokushima, 2-1 Minami-Jyosanjimacho, Tokushima 770-8506 Japan 2: Division of Bioengineering, Graduate School of Engineering Science, Osaka University, Machikaneyama, Toyonaka, Osaka 560-8531 Japan

Publication date: August 1, 2005

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