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A Review on Fluorescence Measuring Systems

Science&Tech


In recent years, new and less expensive commercial instruments for measuring fast fluorescence induction OJIP traces have emerged. Most of new commercially available systems provide new great advantages, as extended memory and energy supply units, Bluetooth communications, faster data transfer USB 2.0 ports, improved leaf clips, lighter and smaller dimensions, programmable scripts and user defined sampling protocols.

Unfortunately, besdie great new features and developments in fluorescence instruments, they also present some drawbacks and limitations on the side of measured signals, offsets, amplification gain, excitation light quality and intensity, signal and time resolution.

This editorial section intends to provide a compared review on the advantages and technical shortcomings of current commercially available fluorescence systems for measuring fast chlorophyll fluorescence signals. We aim to help researchers to do the best use of their fluorometers by helping them to take advantage of their capabilities and overcome troubles related to instrument drawbacks. On a monthly basis, we present a short review on fluorometer instruments.

September 2009
The PEA(TM) (Plant Efficiency Analyser)
Our veredict: 5/6

A shutterless and LED-based instrument for direct (continuous excitation) chlorophyll fluorescence measurements, the PEA or plant efficiency analyser, was developed and marketed in 1992 by the UK based Hansatech Instruments Ltd company. This instrument has an initial time resolution of 10 s , effectively starting at 50 s. The 10 s is used during the first 2 ms, then it switches to 100 s, 1 ms and 1 s acqusition rates at different acquisition times).

The PEA was the first commercially available instrument that allowed recording the whole fluorescence transient between 50 s and 250 s at ultrafast time resolution (10 s for the first 2 ms), and at high light intensity (4000 mol photons m-2 s-1).

Fast measurements of the fluorescence transient have been widely used before the introduction of the PEA fluorometer, but the quality of these measurements was hampered by a 1-4 ms full opening delay of the mechanical shutters that were used. Consequently, the Fo-intensity was overestimated.

Morin (in 1964) and Delosme (in 1967) had made measurements of the fluorescence transient at high time resolution. These authors were able to speed up the opening time of their shutter by shooting at it with a gun. Later on, Neubauer and Schreiber published in 1987 a tandem study in which they were also able to resolve the complete kinetics of the fluorescence transient. The time resolution of their study was only 800 s, but the use of a PAM-technique (pulse amplitude modulated fluorescence measurements) allowed them to determine their Fo-level independently.





Comparing the measurements of Neubauer and Schreiber on the one hand and those of Strasser and Govindjee (1992) on the other hand allows an appreciation of the importance of another innovation to be found in the PEA. The different time base at different data acquisition intervals put more emphasis on the initial and intermediate fluorescence induction steps. This PEA feature had a major impact on the way researchers working with fluorescence transients look at their data, especially when fluorescence traces are presented in a logarithmic time scale plot.

The PEA instrument measures nearly 1200 fluorescence points during the first second, thus enabling to observe a rich fluorescence induction phenomenology along the first second of induction rise. Equipped with a built in LCD screen menu, it has some basic data file manipulations, adjustable gain, offset and other useful settings.

Drawbacks:

  • Portable but still heavy.
  • Low battery life.
  • Low memory (max 78 full data traces are stored).
  • Ancient COM serial port (RS-232) for transferring stored data to a computer.
  • Dark adapting leafclips do not completely protect the measuring head from incoming external light.
  • Requires dark adaption of samples previous measuring.


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