GB2215838A - Fluorimeters - Google Patents

Abstract

Flash fluorimetric analysis of a specimen expected to produce a first, specific, fluorescent radiation on excitation at a test position 5 is carried out by first performing a "blank" analysis by supporing at said test position a reference fluorophore which produces a second, charateristic, reference radiation on excitation, applying to said test position a pulse of excitation radiation from a source 1, measuring the radiation from the test position with detectors 10 and 12 for the first and second radiations, respectively, determining a "blank" value for the ratio of radiation intensities in the absence of a specimen, and then performing a specimen analysis by supporting at said test position with the reference fluorophore still present, a specimen expected to produce said first specific radiation on excitation, measuring the radiation from the test position with said respective detectors, determining from the detector responses a specimen value for the ratio of radiation intensities in the presence of the specimen, and assessing said "blank" and specimen values to produce a calibrated analysis of the specimen. Filters 9 and 10 pass the first and second radiation respectively to detectors 10 and 12, while a fibre optic 13 ensures that a portion of the reference radiation reaches detector 10 even during the "blank" measurement. <IMAGE>

Description

FLUORIMETERS This invention relates to fluorimeters.

Fluorimeters at present are laboratory instruments of substantial size and use high power light sources such as 150 watt xenon lamp light sources and high voltage photomultiplier tube-detectors. Such instruments while satisfactory are confined to use by skilled operators in laboratory conditions.

It is an object of the invention to provide a fluorimeter which is not constrained to laboratory conditions.

The term fluorimeter, and analogous terms, used herein includes instruments using at least one of fluorescence, phosphorescence and luminescence and the like techniques including a calibration step using a fluorimetric standard, which are similar as will be understood by those skilled in the art.

According to the invention there is provided a method of flash fluorimetric analysis of a specimen expected to produce a first specific, fluorescent radiation on excitation, including in the performance of a "blank" analysis: supporting at a test position a reference fluorophore expected to produce a second, characteristic, reference radiation on excitation, applying to said test position a pulse of excitation radiation, examining the radiation from the test position with a respective detector for the first radiation and a respective detector for the second radiation, determining from the relative response of the detectors a "blank" value for radiation from the test position in the absence of a specimen, and in the similar performance of a specimen analysis:: supporting at said test position in the maintained presence of the reference fluorophore a specimen expected to produce said specific radiation on excitation by incident radiation, examining the radiation from the test position with said respective detectors, determining from the relative response of the detectors a specimen value for radiation from the test position in the presence of a specimen, and assessing said "blank" and specimen values to analyse the specimen with regard to a calibration step.

Advantageously the reference fluorophore is incorporated in the construction of a cuvette to contain a specimen or in another form of specimen support. The cuvette may be of optical construction quality.

The specimen for analysis may be a sample and a reagent to react to be capable of fluorescing to produce said specific radiation.

One of the sample and the reagent may be present during the "blank" analysis the other being added after the "blank" analysis. The reference fluorophore may be included in one of the sample and the reagent.

The method may include limiting the time between the reference and specimen analyses to ensure a stable reference fluorescent radiation.

Conveniently an instrument for fluorimetric analysis of a specimen is battery operated, and includes a control circuit and a flash tube and an optical path from the flash tube via a specimen position to photo detectors, the control circuit being effective to charge and fire the flash tube to provide appropriate radiation through the specimen position to provide in operation radiation including reference fluorescence to the detectors for processing by the control circuit to determine by ratiometric comparison, having regard to a calibration step, the level of specific radiation from a specimen at said specimen position.

According to the invention there is also provided in or for a fluorimeter an optical structure formed in a body of material provided with apertures to receive and hold optical elements in a defined arrangement, the body providing a specimen aperture to receive a specimen and hold the specimen in a specific position, a radiation source aperture to receive a radiation source and hold the source in a specific relation to the aperture, an input radiation path aperture to provide a specific path between the radiation source aperture and the specimen aperture and a detector aperture to define an output radiation path aperture to provide an output radiation path from the specimen aperture to radiation detectors.

The body may be unitary, that is all in one piece. The body may provide a beam splitter aperture in the output radiation path aperture to receive and hold a beam splitter in a specific position in said output path and output radiation component apertures to define output radiation component paths from said beam splitter aperture, together with respective detector apertures in said radiation component paths, whereby the body of material around the apertures maintains a defined arrangement of optical elements with respect to said specimen aperture. The beam splitter may be of the partially-reflective type or of the fibre optic type.

According to the invention there is also provided in or for a fluorimeter a body of material to contain an optical path arrangement, the body being of opaque material and defining apertures therein to receive and hold optical elements in said optical path arrangement, said apertures defined by said body including a specimen aperture to receive, in use, a specimen and hold a specimen in a specific position, a radiation source aperture to receive a radiation source and hold the source in a specific relation to the specimen aperture, an input radiation path aperture to provide a specific radiation path between the radiation source and the specimen aperture, an output radiation path aperture to define a specific output radiation path from the specimen aperture to a radiation detector aperture, whereby the body of material around the apertures maintains a defined arrangement of optical elements with respect to said specimen aperture.

The apertures may have installed therein optical control elements to control at least one of intensity of radiation and frequency range of radiation.

According to the invention there is also provided a fluorimeter optical core structure of unitary thermally conductive opaque material defining apertures for a radiation source, a specimen input radiation path, a specimen for examination and a specimen output radiation path, the body of material around the apertures maintaining said apertures, and optical elements therein, in a defined arrangement around the specimen aperture.

Embodiments of the invention will now be described with reference to the accompanying drawings in which: Figure 1 shows a partial cross-section through the optical portion of a fluorimeter in accordance with the invention, with the optical elements in diagrammatic form, Figure 2 is a block diagram of electronic circuits associated with the fluorimeter of Figure 1, and Figures 3 and 4 show in partial cross-sections the optical portion of further fluorimeters in accordance with the invention.

In diagnostic chemical analysis, potable water supply testing and environmental monitoring there is a growing need for 'on the spot' testing as well as the established centralised laboratory services. In all three of the above analytical domains, fluorimetry is a well-established laboratory technique but no instrumention is available to enable 'on-site' or 'doctor's office' measurements to be made using fluorimetry. As stated above phosphorescence, delayed fluorescence and luminescence measurements are sufficiently similar to fluorescence to be included in the term fluorescence for the present description.

In current fluorimeter design high sensitivity is achieved by using high-power excitation sources (e.g. 150 watt xenon lamps) in conjunction with high voltage photomultiplier tube detectors and specimens are contained within precision quartz cells. This approach is acceptable in laboratory based instruments but inappropriate to battery operated fluorimeters.

A ratiometric dual wavelength fluorimeter and associated assay systems are now described. This fluorimeter measures fluorescence at two wavelengths from the same pulse of high intensity UV-VIS radiation. The construction of both portable battery operated fluorimeters and low cost laboratory fluorimeters is made possible.

A device embodying the invention makes measurements by a ratiometric method using successive pulses of radiation passed through samples and thereafter measured at different wavelengths. Between these successive pulses the reaction of interest is brought about and the successive measurements give information about the reaction. The method has calibration built into it. This simplifies the device making field use possible.

Laboratory use is not precluded, actually being of wider possibility, as such devices would be of lower cost and less demanding of operator skill than present devices.

Figure 1 shows an outline, partly in cross-section, through a fluorimeter in accordance with the invention. In this fluorimeter a suitable framework (not shown in detail) is arranged to support the various elements. The details of construction will be readily apparent to those skilled in the art but significant points will be noted. In one form mentioned below the framework is a block of metal.

A holder 51 for a cuvette 5 which is to contain a sample or other material, positions the cuvette precisely in an optical or other radiation path from a radiation source 1 to a detector assembly including specific radiation detector 10 and reference radiation detector 12. In operation a source of reference fluorescent radiation is provided at the cuvette position, as described below.

Between source 1 and cuvette 5 the radiation path includes apertures 2 and 3 and a quartz window 4. The source 1 is conveniently a high intensity xenon filled flash tube and if required a blocking filter 6 may be provided as shown between apertures 2 and 3, or elsewhere, to prevent decomposition of material in the cuvette by the flash energy. Filter 6 can be arranged to control the intensity and/or wavelength of the radiation reaching the cuvette.

The cuvette 5 may be a precision quartz cell or may be of a disposable design, for example made by injection moulding from acrylic, polystyrene or other optical quality plastics material.

The cuvette and holder should be marked to ensure re-insertion of the cuvette in the same relative position if removed.

Between cuvette 5 and the detector assembly the path includes a quartz window 7 and a beamsplitter 8. Beamsplitter 8 may divide the radiation equally or be weighted (say 80/20) to increase sensitivity in one channel. Energy not deflected by the beamsplitter passes through a narrow band-pass filter 9 for the specific radiation and onto detector 10 for specific radiation.

Energy deflected by the beamsplitter passes through a narrow band-pass filter 11 for the reference radiation and onto reference radiation detector 12 for reference radiation. The filters have appropriate wavelength or frequency response for the expected radiations. If the instrument is for a specific application a dichroic filter could be used to maximise optical efficiency and eliminate the need for separate specific and reference radiation filters. The quartz windows retain liquid spilled from the cuvette within the cuvette holder.

An optical link 13 such as a light pipe is provided between the reference detector 12 and the specific detector 10. This is to ensure that the specific detector always receives a constant part of the reference radiation. The reference radiation is collected from the output side of filter 11 and applied to the detector 10.

The structure of Figure 1 can be made in a very compact form. The outline 53 in one embodiment defines a 40 millimetre square plan view of a 40 millimetre aluminium cube in which the various elements are housed in cavities formed by milling and boring. The cuvette is basically the standard 10 millimetre square (internal dimension) form, typically 12 millimetre square outside. The holder 51 can be a hole of diameter slightly less than the circumcircle of the cuvette plan with grooves reamed to allow the cuvette to enter only in the required position. The flash tube can be of the type used in pocket cameras and is some 35 millimetres long. The beamsplitter is readily obtainable from component suppliers such as Melles-Griot and the filters can be formed by grinding down available elements. The optical link can be a length of fibre optic.

By constructing the device in a solid thermally conductive block mechanical stability is achieved and thermal stability assisted so that portable use is made possible, the solid block forming a strong "core" or "heart" for all the critical components in a shock-resistant arrangement. The core or heart is equally suitable for a laboratory instrument.

The electronic circuits to supply power and to control the fluorimeter will now be described in outline with reference to Figure 2. Suitable components for any particular requirement will be apparent to those skilled in the art but special features will be mentioned.

A main switch has two ganged elements 14A and 14B to switch the device ON and automatically set the ZERO for the device.

Switch element 14A controls the action of a timer 15 which permits a voltage regulator 16 to supply power to the other circuits for a set period from the closing of switch 14A and this thus provides an OFF action at the end of the set period. Switch element 14B when closed enables monostable 17 which is arranged to time a period sufficient for flash tube drive circuit 18 to charge up via regulator 16. The output of monostable 17 is connected directly to the "enable" terminals of a further monostable 30 and via an isolating diode to flash drive circuit 18 and to the "enable" terminal of monostable 20. By the arrangement - described the flash tube 1 is fired and related timing signals are derived from monostables 17, 20 and 30.

Specific detector 10 and reference detector 12 are conveniently photo diodes and are connected to respective operational amplifiers 24 and 25. Gates 22 and 23 are respectively between the outputs of operational amplifiers 24 and 25 and respective storage capacitors 26 and 27. An analogue divider 28 is arranged to receive the voltages on capacitors 26 and 27 and produce an output representing the ratio of these voltages.

To this end monostable 20 is connected to monostable 21 to provide a timing signal for a period during which gates 22 and 23 are open in response to the operation of monostable 17. This period occurs shortly after the flash tube is first fired, by monostable 17, and during it the voltage outputs of operational amplifiers 24 and 25 resulting from radiation incident on the photodiodes are sampled and stored on capacitors 26 and 27 respectively. The optical link 13 (Fig. 1) ensures that the specific detector always receives a constant part of the reference radiation. This has two purposes, to stabilise the behaviour of the detector in the absence of specific radiation and to ensure a consistent reading of specific radiation when it occurs. Monostable 30 is connected to operate gate 31 at the output of divider 28.The output of divider 28 is supplied both to gate 31 and to a first input of a differential operational amplifier 36. The output of gate 31 is connected to a capacitor 32 at one input of a buffer operational amplifier 33. When gate 31 is opened by the operation of monostable 30 the output of the divider 28, representing the ratio of radiation incident on the detectors, is applied to capacitor 32 and by the action of the operational amplifier 33 the value of this output is retained even when gate 31 is again closed by the action of monostable 30. The output of operational amplifier 33 is connected to a second input of differential operational amplifier 36. The output of operational amplifier 36 is applied to a potential divider 40 and the tapped-off portion of the output displayed on indicator 37. The display on indicator 37 represents any difference between the inputs of differential amplifier 36.

Switch 38 when closed enables monostable 39, which times the charging of the flash tube drive circuit 18 and then fires tube 1 in a manner similar to monostable 17. Monostables 20 and 21 respond to monostable 39 as described above for monostable 17 to sample and store the outputs on capacitors 26 and 27. Specific detector 10 and reference detector 12 will have responded to the radiation and the value of the ratio of the specific and reference radiation received is applied by the output of divider 28 only to the "first" input of differential amplifier 36. Any difference between the values of the inputs to differential amplifier 36 is shown on the display indicator.

Timer 15 is effective to limit the time for the operation of switch 38. If switch 38 is not operated soon enough the cycle must be restarted with switch 14A/14B. Some five minutes is a suitable time limit for buffer amplifier 33 to hold the value acquired when the flash tube is first fired.

The operation of the fluorimeter for a typical measurement will be described, after a discussion of the cuvette.

As mentioned above cuvette 5 may be moulded as a disposable component from suitable plastics material. The optical requirements for the moulded cuvette for a fluorimeter according to the invention are not as severe as for disposable cuvettes currently in use. Only two clear faces are required and these will usually be adjacent. It is essential that if the cuvette is removed it is not turned round when it is replaced. Accordingly it should be marked or shaped to guard against this. For example the holder 51 may include a fillet in one corner to co-operate with a chamfered-off cuvette corner.

It is an important feature that a reference fluorophore can be incorporated in the cuvette itself, for example by including the fluorophore in the material from which the cuvette is moulded.

While the inclusion of the fluorophore in the cuvette is a very convenient arrangement other techniques may be used. For example a reference fluorophore may be included in a reagent put in the cuvette.

The significant point is that a stable fluorophore material is present in the fluorimeter optical path. This material provides a dynamic optical "reference" to which all fluorimeter variables, including flash intensity, flash position, and cuvette quality among others, can be normalised.

To operate the fluorimeter using a cuvette including a fluorophore such a cuvette containing pure water is placed in the holder 51 as a "blank" and switch 14A/14B operated. By the automatic action of the circuit a as described above "blank" analysis is first carried out to produce a "zero" value.

Monostable 17 operates to time the charging of the flash tube cicuits and then its output goes 'low' to trigger the flash drive circuit 18 and start the monostable 20, together with monostable 30. The radiation from the flash tube passes through apertures 2 and 3 and quartz window 4 onto the cuvette and reference fluorescence from the cuvette goes to beamsplitter 8. One fraction of the reference fluorescence radiation from the beamsplitter is applied to band-pass filter 11, appropriate to the reference frequency from the fluorophone, for measurement by the detector 12 and simultaneously the other fraction to band-pass filter 9, appropriate to the specific frequency and which therefore blocks the reference frequency radiation from the fluorophore, for measurement by the detector 10.After a delay of a few microseconds set by monostable 20 monostable 21 operates to open gates 22 and 23 for a sampling period of a few milliseconds to store the outputs of the operational amplifiers 24 and 25 on the respective capacitors 26, 27. As mentioned above the band-pass filter 9 obstructs the reference radiation from reaching specific detector 10 but the optical link provides some radiation, as mentioned above. The delay can be chosen with regard to the type of measurement being made. Thus so-called "short-lived" fluorescence is measured in the first 200 microseconds after the flash, while "time-resolved" fluorescence is measured from some 200 microseconds and later, and phosphorescence measured from some 1000 or more microseconds after the flash, as will be understood by those skilled in the art.Suitable controls can be added to circuit to achieve these measurements if required.

The voltages stored on the capacitors are used by the divider 28 to produce an output value representing the ratio of fluorescent radiation detected at the specific and the reference frequencies. When the output of monostable 17 goes low to start monostable 30 monostable 30 opens gate 31 for a short period to apply the output of divider 28 representing the radiation ratio to the capacitor 32. The value representing the radiation ratio with a blank cuvette is thus held on capacitor 32 by operational amplifier 33 and applied to the second input of differential amplifier 36. The output of divider 28 representing the value of the radiation ratio is applied directly to the first input of differential amplifier 36 until capacitors 26, 27 are again charged via gates 22, 23.As the cuvette is a "blank" only reference fluorescence occurs so the inputs to differential amplifier 36 are arranged to balance and a ZERO output is obtained on indicator 37 display. Suitable reset circuits may be needed for indicator 37.

The "blank" in the cuvette is now replaced with the specimen for analysis so that the specimen analysis can be carried out.

Switch 38 is operated and, provided timer 15 has not timed out, the flash tube fires as part of the continued automatic operation of the circuit. The excitation radiation passing into the cuvette now generates at least two fluorescent emissions when analyte is present, that is specimen generated fluorescence and reference generated fluorescence. Some of these emissions will pass through the quartz window 7 and thence into the beamsplitter 8. Fluorescence from the specimen is collected by detectors 10 and 12 and the ratio applied to the "first" input of differential amplifier 36. The optical link again provides some radiation to detector 10.

The value of the ratio for the blank cuvette is already maintained at the second input of differential amplifier 36 so the indicator 37 will display the difference between the value of the ratio for the specimen in the cuvette and the value of the ratio for the "blank" cuvette during the "blank" analysis. By knowledge of the calibration of the instrument the amount of material giving rise to fluorescence in the specimen can be determined.

The scale length of indicator display 37 can be set by potential divider 40.

Timer 15 ensures that the "zero" reading for the blank cuvette is not invalidated by a delay before testing the specimen such that the "zero" is no longer true because of instability in the instrument or the reference fluorophore.

The use of a fluorimetric standard, such as a block doped with a fluorescent material in a known concentration to calibrate the device is well-known in the art and this step is assumed to be carried out when needed, no specific mention being made.

Because the flash is very brief (1 to sums) photo decomposition of the sample is not likely to occur, however a blocking filter, 6, may be incorporated to limit the excitation wavelength to wavelengths lower than the specific and reference emission wavelengths.

A very important feature is that the cuvette includes a fluorescent marker in the thermoplastic material from which it is moulded. Using such a cuvette, a dual wavelength fluorimeter can be standardised (or normaltsed), sychronously with the test, as has been described above.

To make such a cuvette conventional injection moulding tools may be used without modification, it is only necessary to coat the feedstock granules with the reference fluorescent marker.

The marker may be a phenol or indole , fluoresceine, quinine, anthracine, napthalone, ovalene, p-terphenyl, terphenyl-butodiene, rhodamine B, compound 610, or other similar compound. Where the marker is available as a finely divided powder, it may be 'dusted' onto the natural granules, polystrene, polymethylmethacrylate, TPX, or other optical grade thermoplastic. Alternatively the marker may be dissolved in a solvent that is immiscible with the thermoplastic, the granules then washed in the doped solvent and air dried; this leaves each granule coated with a trace of fluorescent marker. The modified feedstock is then used to injection mould cuvettes.

Complete fluorescence homogeneity is not required, and batch to batch variations of 10% are acceptable as the methodology, as mentioned elsewhere, requires that each cuvette be 'zeroed', or at least read relative to a cuvette that has been zeroed. This is standard fluorimetric practice. The absolute amount of fluorophore is not critical, but must be optically stable during the period of analysis (1 to 10 mins), as this reference fluorescence is the level to which all system variables are normalised.

For low volume production a simple mould may be fashioned, and cuvettes cast from acrylic or other polymer, where the monomer has been doped with small amounts of fluorescent marker.

This technique is useful in optimising and testing markers. When the cuvette 5 is a precision silica cell, for example to resist solvents, the reference fluorophore can either be incorporated into one of the test reagents or doped into the silica or borosilicate material. Quinine sulphate is a suitable fluorophore for use in some reagents.

It can be seen that up to the face of the beamsplitter the specific and reference wavelengths share a common optical path, and during the brief period of the excitation flash (1 to Sms) the specific and reference detectors are responding synchronously to the same source radiation. Providing the secondary filters 9 and 11 do not change in any way, nor there be any differential drift between the specific and reference detectors (these are mounted in the same massive heat sink) then the ratio: Fluorescencespecifi,/Fluorescence,,ference will be constant, regardless of variations in subsequent flashes of the excitation source. Thus in fluorimetry the channel in which radiation specific to the test is measured is synchronously normalised (or standardised) to the reference channel.In phosphorimetry the optical layout is identical, but signal acquisition from the specific radiation channel is delayed by a few milliseconds to obtain the phosphorescence measurement. In luminometry there is neither need for high power excitation nor off-axis illumination, but a low power on-axis light emitting diode (LED) could serve as an internal standard for this family of measurements.

The device described above is particularly suitable for battery-powered field use. It can be of compact, robust construction with a self-contained battery. The power consumption is relatively low. Power to charge the tube-firing circuits is needed for only a short time, for the rest of the time only the low power to operate the semiconductor control circuit and indicator 37 is needed.

The device is particularly suitable for use in the protocal devised by the American Society for Testing and Materials.

Referring to Figure 3 this shows in Figure 3a a cross-sectional plan and in Figure 3b a cross-sectional elevation of another fluorimeter optical system mounted in a block of solid material by having the optical elements in bores through the block. In Figure 3b some elements are omitted for clarity. The block, indicated at 353, is conveniently a block 50 mm x 55 mm in plan and 35 mm thick of a readily worked material such as aluminium. In the illustrated arrangement the bores are cut into a solid block but other methods of construction, for example precision die-casting, may be used and the material also chosen for a particular purpose, so long as stability and accuracy are maintained.

As before a holder is formed towards the middle of the block by a bore 351, of basically circular form with reamed grooves, in this case to receive a 16 millimetre square cuvette or other test piece or specimen carrier 305. A further bore 352 is made, parallel to the bore 351, to receive a radiation source 301 (shown diagramatically) which in this case is a xenon flash tube (specifically Maplin type FS77J). This tube is designed to produce flashes at a fast rate typically 60 flashes per minute with an energy input of 0.3 watt seconds per flash. The tube is fitted into bore 352 by insulating bushes (not shown) and provided with suitable electrical connections.

Bores 354, 355 and 356 are provided in a plane which intersects with the bores 351, 352. These bores receive tubes which are fitted with various optical elements and the tubes then securely held in place in the required optical alignment, for example by grub-screws threaded into holes in the block, such as 358, 359. Conveniently the bores are 14 millimetres in diameter.

Considering first the bore 354 this is provided with a filter and collimator assembly in the form of a tube, which is a good sliding fit in the bore, into which at each end is fitted an aperture disc (302, 303) while an ultraviolet pass filter 306 is held inside the tube at the end to be nearest the holder 351.

The aperture disc 302, 303 may have circular apertures or slits or other forms of aperture to provide required collimation and intensity control of light from the radiation source 301. The ultraviolet filter 306 in this embodiment has a pass-band of 300 to 390 nanometres. This filter is of a type used in diagnostic instruments such as that fitted to a TECHNICON (RTM) analyzer, and having a very well-defined pass-band peaking at about 356 nanometres, being reduced to about 10% transmission at 396 and 296 nanometres and having insignificant transmission at 428 and 260 nanometres. The assembly is positioned in bore 354 to be within 0.5 millimetres of a cuvette in holder 351.

Considering now bore 355 and 356. Bore 355 is at right angles to bore 354 and receives radiation emerging from holder region 351. A filter 371 to cut off ultraviolet radiation above 400 nanometres is fitted where bore 355 meets holder 351.

Conveniently this filter is a BALZERS (RTM) UV blocking filter.

A quartz beam splitter 308, to extend into the UV range, is mounted in a tube 360 of 14 millimetre external diameter having a 10 millimetre hole at one end and a 10 millimetre hole in the side, positioned to match bore 356. The beam splitter is positioned in the tube with the reflection output face in the centre of and normal to the axis of the 10 millimetre side hole.

Tube 360 is fitted in bore 355 with the axis of the 10 millimetre side hole aligned with the axis of bore 356.

Two detector assemblies are fitted to block 353, one in each of bores 355, 356. Each detector assembly is a tube to fit the bore and having an Inner diameter to receive a respective photodiode 310, 312 supported by a sleeve. The photodiode is conveniently a Hammamatsu (RTM) type S1226-44BK which has a response range of 320 to 1000 nanometres. The respective interference filter 309, 311 (as described for Figure 1) is fitted in front of each diode, for example on the beam splitter cube faces as shown or on the diode itself, and the detector assemblies are installed in the respective bores to just touch the beam splitter assembly. Electrical connections are provided for the photodiodes.

Figure 4 shows in views 4a and 4b similar to 3a and 3b an optical system using optical fibres to split the radiation from the holder region, instead of a beam splitter. In Figure 4 elements similar to those of Figure 3 are indicated by replacing the initial "3" with a "4" and the above description should be referred to.

The beam splitter, indicated generally at 460, is installed in a bore 457 which is in the plane of bore 454 but at right angles to bore 454 to intersect the holder 451. A filter 471 has the same function as filter 371 (above). The beam splitter is an ordered array of optical fibres all of which have one end exposed to the holder region. The fibres are distributed among two or more subsidiary bundles in a regular way and an individual photodetector and respective filter arranged for each subsidiary bundle of the other ends of the fibres. In one arrangement an ordered rectangular array 6 millimetres by 3 millimetres of 0.25 millimetre diameter fibres has alternate columns (6 millimetre dimension) allocated to each bundle (a 50/50 split).

This produces two bundles 408, 418 each about 4 millimetres in diameter. Suitable ferrules and epoxy based opaque potting compound are placed around the one end and other ends to hold the fibres in the required arrangement. The fibres at the one end and filter 471 are conveniently cemented into a tube 460 which can be fitted and held in bore 457 within 0.5 millimetres. of a cuvette in the holder region. The ferrules at the other ends can be fitted into tubes which hold the respective interference filters and photodetectors (type as above) against the ends of the fibres.

In a further arrangement, not shown, a bore is provided opposite bore 454 (or 354) to receive a detector by which radiation transmitted through the holder region can be examined.

An alternative arrangement for the electronic control and measurement of the radiation source and resulting photodetector signals shown in Figure 2 is to use a microprocessor to control the firing of the flash tube and the processing of the detector signals. While the general procedure set out above still applies better control and performance is possible by the use of techniques to improve signal-to-noise ratio.

As the signals from the detectors can be processed digitally the microprocessor can quickly examine the "ratio" output. If this is not large enough to indicate an acceptable signal-to-noise ratio the flash tube can be fired again (within, for example, 300 milliseconds) and the signals summed on a statistical basis to improve the signal-to-noise ratio. This can continue at a flash rate of, say, 3Hz until an adequate signal has been acquired.

A suitable microprocessor arrangement will be readily apparent to those skilled in the art from the details set out above.

The comparison of radiation intensities removes the effect of flash variation or other lack of optical reproducibility and "normalises' the response of the device. The measurement at two different wavelengths from a single pulse of light is to compensate for optical and electronic drift and noise in the measuring system. Thus one of the wavelengths is a test or active specific wavelength, which is that expected from the specimen to be analysed, whilst the other is a reference wavelength, produced by a fluorophore in the optical path, chosen such that response to this reference fluorescence is not affected by changes in the fluorescence intensity at the specific wavelength. Excitation with small flash tubes provides adequate intensity for silicon p.i.n. photodiodes, which are good detectors but need fairly high illumination levels.Disposable cuvettes, particularly if incorporating a fluorophore, greatly ease the use of the device. To ensure that "drift" of electronic, optical or chemical characteristics is not significant once the device is normalised the specimen must be analysed within a set time.

Clearly devices for bench use can be constructed in the same general form as "field" devices with mains power supplies and other relevant changes but still with the operational advantages described above.

Dual wavelength fluorimetry (DWF) will only give satisfactory performance when the detectors are working optimally. Too little illumination will give poor signal to noise and thus poor reproducibility. Excessive excitation energy will cause saturation and non-linearity.

The use of fibre optic beam-splitters may be extended further. By using a beamsplitter to divide the light from the flash tube to pass through different filters and then a similar fibre optic device to combine the light at the resulting selected frequencies for application to the cuvette and any contents can be excited simultaneously at distinct frequencies for detection in any convenient manner. In this way excitation in the UV range, below 300 nanometres, is possible. Suitable fibre optics and UV enhanced photodetectors can be employed.

In another arrangement of fibre optics one bundle can convey light to a face of the cuvette holder and two other bundles, all three being combined at the cuvette face, convey light away from the same face to respective detectors, as set out above. In particular this arrangement is useful for dry reagent chemistries where the reagent carrier can be inserted into a suitable form of cuvette holder or adaptor and measurement made on one face. Such chemistries are now being offered by, among other, Kodak Ektachem, Miles Laboratories (Ames Division), Boelwinger Mannheim, Fuji Film (all RTM).

In some systems optical measurements are made through a transparent support layer either the support layer or the diffusely reflecting layer (TiO2, BaSO4, etc.) may incorporate the reference fluorophore. In systems where the support is the reflective layer the measurement is made from above and either the diffusely reflecting support or the reagent zone may incorporate the reference fluorophore.

Such techniques avoid the problems associated with the use of liquids in the fluorimeter and it is possible to use "dry" samples. Thus a form of "dip-stick" may be used. A clear plastics substrate has a fluorophore incorporated in it, possibly as described above for the cuvette, and a strip of substrate is coated with a reagent supported in a matrix, as is known in the art. To carry out a test the coated strip has the sample material applied to it in any convenient way, such as dipping or wiping, and is then placed in the holder in the fluorimeter. An adapter or spacing device may be used to ensure that the strip is in the correct position and does not touch the holder, to avoid contamination.

Some general guidance follows on the form of tests to be carried out with the device. The useful analytical range must conform to the optimum performance range of the photodetectors, and ideally, any critical analyte levels (e.g. clinical action levels, or statutary pollution limits) should occur at the peak performance level of the instrument. Methods having high intrinsic sensitivity could be accommodated by reducing the excitation pulse energy or by optically attenuating the radiation reaching the detectors.

The two main types of fluorimetric assay are: 1. Fluorescence increasing with analyte concentration 2. Fluorescence decreasing with analyte concentration (quenching) Quenching methods are well suited to DWF when high accuracy is required at low analyte concentrations. The methods should be tailored so that any critical action levels occur before the test or specific fluorescence is quenched to the point where the performance of the instrument begins to deteriorate. In quenching methods the optical link to apply reference radiation to the specific detector will not be needed.

In assays where high levels of analyte concentration are expected or required fluorescence-increasing methods are preferred. In assays where accuracy at low levels is required but quenching methods are not possible, fluorescence increasing methods can be used by incorporating a fixed amount of analyte in a reagent yielding a small amount of specific radiation during the initialisation stage. This ensures that even at 'zero analyte concentration' the specific detector is still adequately illuminated.

Thus in both quenching and proportionally increasing methods, that ratio FluorescencespeCjfjclFluorescencereference established when the blank is read, (or set to zero), can only subsequently change by a real change in analyte concentration.

Claims (25)

1. A method of flash fluorimetric analysis of a specimen expected to produce a first, specific, fluorescent radiation on excitation at a test position, including in the performance of a "blank" analysis: supporting at said test position a reference fluorophore expected to produce a second, characteristic, reference radiation on excitation, applying to said test position a pulse of excitation radiation, xamining the radiation from the test position with a respective detector for the first radiation and a respective detector for the second radiation, determining from the relative response of the detectors a "blank" value for the ratio of radiation intensities from the test position in the absence of a specimen, and in the similar performance of a specimen analysis:: supporting at said test position in the maintained presence of the reference fluorophore a specimen expected to produce said first specific radiation on excitation by incident radiation, examining the radiation from the test position with said respective detectors, determining from the relative response of the detectors a specimen value for the ratio of radiation intensities from the test position in the presence of a specimen, and assessing said "blank" and specimen values to analyse the specimen with regard to a calibration step.

2. A method according to Claim 1 including providing at said test position a cuvette to support said specimen.

3. A method according to Claim 2 including incorporating in said cuvette the reference fluorophore.

4. A method according to Claim 1 including providing the specimen for analysis as sample and a reagent to react to be capable of fluorescing to produce said specific radiation.

5. A method according to Claim 4 including providing one of said sample and said reagent during the "blank" analysis.

6. A method according to Claim 4 including providing the reference fluorophore in one of the sample and the reagent, adding the other of the sample and the reagent after the "blank" analysis.

7. A method according to Claim 1 including limiting the time between the reference and specimen analyses to ensure a stable reference fluorescent radiation.

8. A method according to Claim 1 including subtracting the "blank" value from the specimen value to analyse the specimen.

9. A method according to Claim 1 for non-quenching fluorimetric analysis including, in the performance of said "blank" analysis, ensuring that some of said first radiation reaches both detectors.

10.Ratiometric dual-wavelength fluorometric analysis.

11.A ratiometric dual-wavelength analyser.

12. A battery operated instrument for fluorimetric analysis of a specimen characterised in that it includes a control circuit and a flash tube and an optical path from the flash tube via a specimen position to photo detectors, the control circuit- being effective to charge and fire the flash tube to provide appropriate radiation through the specimen position to provide in operation radiation including reference fluorescence to the detectors to cause detector outputs for processing by the control circuit to determine by ratiometric comparison, having regard to a calibration step, the level of specific radiation from a specimen at the specimen position.

13. An instrument according to Claim 12 including at the specimen position, in operation, a reference fluorophore.

14. An instrument according to Claim 13 in which the reference fluorophore is in a specimen cuvette.

15. A specimen support incorporating a reference fluorophore for ratiometric fluorimetric analysis.

16. A specimen support according to Claim 15 in the form of a cuvette.

17. A specimen support according to Claim 15 also having at least one reagent in dry chemistry form.

18. In or for a fluorimeter an optical structure formed in a body of material provided with apertures to receive and hold optical elements in a defined arrangement, the body providing a specimen aperture to receive a specimen and hold the specimen in a specific position, a radiation source aperture to receive a radiation source and hold the source in a specific relation to the aperture, an input radiation path aperture to provide a specific path between the radiation source aperture and the specimen aperture and a detector aperture to define an output radiation path aperture to provide an output radiation path from the specimen aperture to radiation detectors.

19. A structure according to Claim 18 in which the body is unitary, that is all in one piece.

20. A structure according to Claim 18 in which the body provides a beam splitter aperture in the output radiation path aperture to receive and hold a beam splitter in a specific position in said output path and output radiation component apertures to define output radiation component paths from said beam splitter aperture, together with respective detector apertures in said radiation component paths, whereby the body of material around the apertures maintains a defined arrangement of optical elements with respect to said specimen aperture.

21. In or for a fluorimeter a body of material containing an optical path arrangement, the body being of opaque material and defining apertures therein to receive and hold optical elements in said optical path arrangement, said apertures defined by said body including a specimen aperture to receive, in use, a specimen and hold a specimen in a specific position, a radiation source aperture holding a radiation source in a specific relation to the specimen aperture, an input radiation path aperture providing a specific radiation path between the radiation source and the specimen aperture, an output radiation path aperture defining a specific output radiation path from the specimen aperture to a radiation detector aperture, whereby the body of material around the apertures maintains a defined arrangement of optical elements with respect to said specimen aperture.

22. A structure according to Claim 21 in which the apertures have therein optical control elements to control at least one of intensity of radiation and frequency range of radiation.

23. A fluorimeter optical core structure of unitary thermally conductive opaque material defining apertures for a radiation source, a specimen input radiation path, a specimen for examination and a specimen output radiation path, the body of material around the apertures maintaining said apertures, and optical elements therein, in a defined arrangement around the specimen aperture.

24. A method of fluorimetric analysis of a specimen substantially as herein described with reference to the accompanying drawings.

25. A fluorimetric analyser substantially as herein described with reference to the accompanying drawings.