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The Strobe Technique

The Strobe Technique

PTI pioneered the strobe technique. The company has a patent on the instrumentation related to this
technique. PTI is the only company that offers this technique for the measurement of fluorescence
lifetimes. We have placed over 100 systems into service. The technique is not new, there are publications
using it. It is an excepted and proven technique.

The major advantages of this technique are low cost, excellent performance and ease of use. No other
technique offers these benefits for the measurement of lifetimes.

The major difference between the TCSPC and the Strobe techniques is in the detection. The same
nanosecond lamp is used to generate the same excitation pulse. But now, the detector (which is a specially-
configured PMT) is only active for a very short period of time after the excitation pulse is released. The
detector records the intensity of the fluorescence at the moment is it active.

The window of time during which the PMT is active is controlled by a delay gate generator. The standard
delay gate generator used with our existing systems steps the delay in 100 picosecond increments. The
delay increases with each pulse (in other words, it sweeps the delay). In this manner a decay curve is
produced. Here is a graphic representation of the Strobe technique:





























The three steps illustrated above are repeated. With each cycle, the delay gate generator increases the delay
by a multiple of 100 picoseconds and the data is collected again.



Time (at 2 nanoseconds)










This is how the data looks after the first pulse.


Time (at 2.1 nanoseconds)









The second pulse is measured at 2.1 nanoseconds.












After ten pulses, the data begins to resemble a decay curve.











When all of the data is collected, the computer fits it to a model decay curve.


F
or increased accuracy, the entire sweep can be repeated, and the individual intensities averaged. This is
helpful when the overall signal is low. However, as you can see, a full decay curve is attainable after just
one sweep. Compare this with TCSPC: for every 100 pulses, you get only up to three useful statistical
points to build up a decay curve. As shown below, the contrast is striking.













STROBE after 100 pulses




TCSPC after 100 pulses



The Strobe technique is much faster than the TCSPC technique for generating the decay curve. This is
particularly important in the life science area. Whereas the chemist can take hours or days to measure an
inert chemical very accurately, the life scientists cell samples are long dead. In fact, this is one of the
reasons why the Phase technique has survived, even though is inferior and complicated there were simply
no other alternatives for life scientists.

The Strobe technique has an additional feature, which allows measurement of a single lifetime almost
instantaneously (10 to 15 seconds).























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Denmark: PhotoMed GmbH, Sondre Alle, DK-4600 Koge Phone: +45 56 66 33 86 Fax: +45 56 66 33 81

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