Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Reexamination Certificate
1999-08-03
2001-10-30
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
C250S559400
Reexamination Certificate
active
06310337
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method for detecting optical changes in a test element using a lamp exposure, and the steps of selecting a voltage for the lamp to optimize the exposure level while extending the life of the lamp.
BACKGROUND OF THE INVENTION
It is known to provide feedback circuits in analyzers which alter in real time the output of illuminating devices, depending upon the level of signal detected at the detector. An example of such a system is shown in U.S. Pat. No. 5,491,329, which uses the irradiation on in vivo tissue samples. Such tissue samples of course are not known in advance as to their photoresponse efficiencies. Furthermore, the reason for the feedback circuit in such a system is to allow the proper use of the gain on the photomultiplier tube used in the detector. Such a use is irrelevant to detectors using flash lamps and simple photodiodes.
Yet another example of a real-time adjustment of the exposure device to reflect the system efficiencies of the optics is disclosed in U.S. Pat. No. 5,029,245. In this case, LEDs are modified during sample examination so that the radiation outputted is “regulated in accordance with the intensity data supplied [in real time] by the detector and in such manner that the radiation intensity of that wavelength range, and thus the intensity of the output radiation, is constant,” column 4, lines 10-14.
Other examples of analyzers that adjust a lamp intensity depending upon the sample transmission detected in real time at a detector, but not preselected before exposure, are shown in, e.g.,
Research Disclosure
Publication No. 40001, dated August 1997.
Although real-time adjustments are useful, they have the disadvantage of requiring fairly complex and sensitive optical systems, given the wide range of possible outputs and the lack of a priori control of outputs. Also, real-time adjustments necessitate some delay in the assay while changes are made in response to the reading, compared to the time needed for assays that have predetermined settings selected in advance. Furthermore, those that adjust simply on the basis of an instantaneous result do not provide any adjustment based on known performances of that particular assay as a whole.
Thus, there has been a need for a method of making energy level adjustments to illuminating devices in advance, for testing end-point assays selected from a list having known end-point photoresponse efficiencies, exposed in an optical system having a known system efficiency, without necessitating the complexities required for real-time adjustments.
As used herein, “photoresponse efficiencies” means, efficiencies dictated by the end-point photoresponsiveness of the chemistries used for a particular assay, and more specifically, the photoresponse that is determined from a plot of the photometric end-point density produced by the assay versus concentration of the analyte of that assay. In such plots, the steeper the curve, the more efficient is the photoresponse, and the less intense must be the illuminating device to obtain a satisfactory reading.
SUMMARY OF THE INVENTION
We have discovered a method of adjusting in advance the intensity of the illuminating device, based upon selecting an assay from a pre-selected list having known end-point photoresponse efficiencies and tested in an illuminating system having known system efficiencies that are a function of the center wavelength of exposure. The result is that the illumination intensity is optimal for that assay at that center wavelength, and specifically the power for that intensity is reduced for the more efficient assays and wavelengths, thus reducing the wear on and extending the life of, the illuminating device.
More specifically, there is provided a method of detecting an optical change in a series of test assays producing detectable results at varying efficiencies, the method comprising the steps of:
a) selecting a test assay from the series, the selected assay having a known end-point photoresponse efficiency and a known filter center wavelength;
b) providing a variable-intensity flash lamp illuminator comprising a lamp, a set of multiple filters with pre-selected center wavelengths assigned to particular assays, and a circuit for activating the lamp and comprising a capacitor, a power source, and a variable output voltage converter connected to said source and having its variable voltage output connected across the capacitor, the lamp and the filters providing a known level of system efficiency as a function of the center wavelength of the filter;
c) providing a predetermined relationship of levels of illuminating intensities from the lamp as a function of photoresponse efficiencies of the assays and the system efficiencies, in which the photoresponse efficiencies of the assays are inversely proportional to the lamp intensities and the intensities are proportional to the square of the voltages applied to the lamp;
d) selecting from the relationship a voltage applied to the lamp, and hence an intensity of the lamp, that corresponds to the known photoresponse efficiency of the assay selected in step (a) and its system efficiency based upon the filter center wavelength for the assay; and
e) thereafter exposing the assay to the selected illuminating intensity, so that less intensity is used for assays having either higher photoresponse efficiencies or center wavelengths with a higher system efficiency, than is used for worst-case efficiency assays.
Because the photoresponse efficiencies are calculated in terms of densities, and not relative rates of change, the invention is particularly applicable to end-point assays.
Accordingly, it is an advantageous feature of the invention that voltage levels applied to a flashlamp illuminating device can be reduced in advance based upon known efficiencies of the assay to be illuminated, thereby extending the life of the flashlamp.
It is a related advantageous feature of the invention that the reduction in voltage levels can be based not only upon the known system efficiencies of the illuminating device, but also upon predetermined photoresponse efficiencies of the pre-selected assays.
Other advantageous features will become apparent upon reference to the following Detailed Description, when read in light of the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a schematic circuit diagram of a preferred reading station used in the method of the invention;
FIG. 2
is a plot of relative intensity of the illumination of the station shown in
FIG. 1
, as a function of the center-wavelength of the filter interposed in the path of the illuminating radiation, prior to the use of this invention;
FIG. 3
is a plot of the voltage applied to the firing capacitor of the reading station of
FIG. 1
, when modified in accordance with one aspect of the invention;
FIGS. 4 and 5
are plots of two different photoresponse curves, specifically of reflection density versus concentration on,
FIG. 4
illustrating a maximum photoresponse efficiency example, and
FIG. 5
illustrating a minimum photoresponse efficiency; and
FIG. 6
is a plot of slopes obtained from the calibration curves of particular assays, against their photoresponse efficiency multiplier fractions, which vary from ½ to 1.
REFERENCES:
patent: 4003662 (1977-01-01), Erich et al.
patent: 4117375 (1978-09-01), Bachur et al.
patent: 4643571 (1987-02-01), Feber et al.
patent: 5029245 (1991-07-01), Keranen et al.
patent: 5169601 (1992-12-01), Ohta et al.
patent: 5281540 (1994-01-01), Merkh et al.
patent: 5491329 (1996-02-01), Urakami et al.
patent: 0 115 294 (1984-08-01), None
patent: 0 286 142 (1988-12-01), None
Research Disclosure, Publication No. 40001, Aug. 1997, p. 483-484.
Chiapperi Joseph M.
Josephson Donald M.
MacDonald Stuart G.
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