Radiant energy – Luminophor irradiation – With ultraviolet source
Patent
1985-09-18
1987-08-11
Howell, Janice A.
Radiant energy
Luminophor irradiation
With ultraviolet source
356318, G01N 2164
Patent
active
046863710
DESCRIPTION:
BRIEF SUMMARY
This invention relates to apparatus for measuring fluorescence decay characteristics (referred to hereinafter simply as `fluorescence characteristics`) of materials.
Apparatus for measuring fluorescence characteristics of a material is already known and comprises a light source (either narrow band or monochromatic), and hereinafter referred to as an excitation light source, capable of emitting a train of light pulses which are directed onto the material (or sample) under test to excite that sample into a fluorescent state. When the sample fluorescences it emits energy in the form of single photons and the known apparatus comprises photon detection and measuring systems, the latter functioning according to the well-known photoncorrelation technique using synchronisation pulses derived from the excitation light source, whereby fluorescence decays and decay times for the sample (and associated properties such as anisotropy decay) are evaluated.
In practise typical excitation light sources are flashlamps (with associated waveband filters) and lasers both of which suffer from long-term time-dependent changes in their optical pulse profile and it is therefore necessary to measure the excitation pulse profile applied to each sample. In the known apparatus this is undertaken either immediately before or immediately after irradiation of the sample by substituting at the sample station a reflective device or scatterer so that the reflected excitation is directed into the detection and measuring systems. In consequence certain long-term time-dependent changes in the characteristics of the detection and measuring systems are accounted for in addition to long-term excitation pulse profile changes.
The known apparatus suffers from a number of disavantages and it is an object of the present invention to obviate or mitigate these disadvantages. For example, the known apparatus measures the excitation pulse profile before or after sample irradiation and therefore relies upon constancy of excitation pulse profile both during sample irradiation and in continuity with measurement of the excitation pulse profile. In fact known excitation light sources have pulse profiles which tend to vary from pulse to pulse in addition to long-term pulse profile variation. Furthermore, substitution of the sample and reflective device at the sample station requires interchangeability which in fact is not universally practical because certain samples fluoresce under environmental conditions which render the reflective device difficult to substitute. Additionally, fluorescence usually occurs at a spectral wavelength different from (being larger than) that of the excitation and the detection and measuring systems usually have differing characteristics at these two wavelengths so that the assessment of changes in the detection and measuring systems by directing the excitation light through these systems is inherently inaccurate.
According to the present invention there is provided apparatus for measuring fluorescence characteristics of a material sample, said apparatus comprising
a sample station for receiving a material sample the fluorescence characteristics of which are to be measured,
a fluorescence photon-event receiving means coupled to said sample station to receive single photon events arising therefrom,
an excitation light source capable of emitting a train of excitation light pulses towards said sample station so as to irradiate a sample therein,
excitation pulse profile determining means sensitive to said train of excitation light pulses and having sufficient attenuation to provide an output event count rate compatible with the fluorescence photon event count rate,
detecting means coupled to receive the output of said receiving means and the output of said determining means,
synchronisation means operable by said excitation light source to generate a train of synchronisation pulses,
measuring means coupled to the output of said detecting means and to the output of said synchronisation means and operable according to the photon correlat
REFERENCES:
Birch et al., "Differential Pulse Fluorometry Using Photomultipliers", Journal of Physics E: Sci. Intr., vol. 17, No. 5, May 1984, pp. 417-418.
Birch et al., "A Single Photon Counting Fluorescence Decay Time Spectrometer", Jour. of Physics E: Sci. Inst., vol. 10, No. 10, Oct. 1977, pp. 1044-1049.
Rayner et al., "Correction of Instrumental Time Response Variation with Wavelength in Fluorescence Lifetime Determination", Rev. of Sci. Inst., vol. 48, No. 8, Aug. 1977, pp. 1050-1054.
Wijnandts van Resandt et al., "Double Beam Fluorescence Lifetime Spectrometer with Subnanosecond Resolution", Rev. of Sci. Instr., vol. 53, No. 9, Sep. 1982, pp. 1392-1397.
Birch David J. S.
Imhof Robert E.
Howell Janice A.
University of Strathclyde
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