Some bacteria, such as the marine bacterium Vibrio fischeri are bioluminescent. That is, they emit light but the intensity of light emission varies in the presence of some chemicals, and in particular toxins.

The light emission can, therefore, be used as a detectable signal which indicates the presence or absence of the chemical and also represents the concentration of the chemical in the environment, usually an aqueous solution, of the bacterium.

By way of example, such analysis techniques may be used to establish the concentration of toxins in samples of materials such as soil. Thus, a soil sample may be treated with a solvent in order to dissolve the target toxin to produce a test sample. A solution containing the bioluminescent organism is placed in a suitable container or cuvette, the test sample is added to the cuvette, possibly after further dilution of the test sample, so that the bioluminescent response of the organism can be monitored. In order to provide a reference, a control sample may be introduced to the same bioluminescent organism in a different cuvette, the control sample being identical to the test sample, except that it has had no contact with the soil.

The response of the organism, in terms of light emitted, is monitored. The monitoring period begins before the test sample and the control sample are placed in the cuvettes, so that the change in light emission can be detected. If the soil-derived test sample is toxic to the organism, its bioluminescence will be inhibited and this will appear as a difference in response between the organisms in the two cuvettes.

By appropriate calibration, the magnitude of the difference can be used to derive the level of toxicity in the soil-derived sample.

Assaying apparatus, or luminometers, are known for conducting assays based on light emission. For example, US 5837195 discloses a luminometer comprising detector assemblies for detecting emitted light. A guide path is provided for cuvettes, and cuvettes are displaced along the guide path past dispensers for various reagents, past the detector assemblies, and past means for purging the cuvettes after analysis.

This apparatus enables continuous sample analysis, but is a relatively complex and non-portable device which is not suitable for field testing of, for example, soil samples in conjunction with a control sample.

According to the present invention there is provided analysis apparatus comprising a light detector and at least two sample stations for receiving vessels for containing samples for analysis, the apparatus further comprising a mirror which is movable between operative positions in which, respectively, the mirror directs light emitted from samples at the respective sample stations to the light detector.

In this specification, the expression"mirror"is used in a broad sense to denote any device which reflects light, and this embraces devices other than polished or silvered surfaces, such as prisms.

The mirror may be mounted on a support body which is movable, for example in rotation, to move the mirror between the operative positions. The support body is preferably configured and positioned so that, when the mirror is in one of the operative positions to direct light from one of the sample stations to the light detector, the support body shields the other sample station, or one of the other sample stations, from the light detector. For this purpose, the support may be part-cylindrical, for example semi-cylindrical.

While apparatus in accordance with the present invention may have three or more sample stations, a preferred embodiment of the apparatus comprises two of the sample stations. Thus, one of the sample stations is used for a test sample and the other is used for a control sample. In the preferred embodiment, the mirror may be disposed between the two stations, and rotatable through 90° between the operative positions.

The mirror is preferably motor driven, and may be moved between the operative conditions in response to a computerised control system of the apparatus. The motor may be a stepping motor or may comprise a two position rotary solenoid.

The apparatus may comprise a carrier, for example in the form of a base plate, on which other components of

the apparatus, such as the light detector, the mirror, and components associated with the sample stations are mounted. The base plate may be provided with legs for supporting the apparatus on a suitable surface, so that the base plate is in a generally horizontal orientation. In this case, the mirror and the sample stations may be provided on the upper surface of the base plate, with the motor, if provided for the mirror, secured beneath the base plate.

The light detector may be mounted at or adjacent one edge of the base plate.

The present invention also provides a method of conducting analysis of two samples by detecting light emission from the samples, the method comprising alternately directing light from the samples to a light detector by means of a mirror which is movable between two operative positions.

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:- Figure 1 is a perspective view of analysis apparatus; Figure 2 is a perspective view of the apparatus as viewed in a direction opposite that of Figure 1; and Figure 3 is a plan view of the apparatus.

The apparatus shown in the Figures comprises a base plate 2 supported on legs 4. A light detector unit 6,

comprising a photo multiplier tube (PMT) is secured to the base plate 2 by a bracket 8. The bracket 8 has a window (not shown) for admitting light to the PMT of the unit 6 in operation of the apparatus. This window is disposed generally in the position indicated at W in Figure 3.

The base plate 2 supports two sample stations 10 and 12. Each sample station is configured to receive a respective cuvette 14 of square horizontal cross- section. The cuvettes 14 are made from transparent material such as glass or clear plastics. The cuvettes 14 are supported at the sample stations 10 and 12 on support blocks 22 disposed between respective side plates 16,18. Spacers 20 extend between the side plates 16,18. The units comprising the support blocks 22, the side plates 16 and 18 and the spacers 20 are secured to the base plate 2. The units are provided with Peltier heat pumps 23 which are secured to the support blocks 22, to maintain a desired temperature in the cuvettes 14. As can be appreciated from Figures 1 and 2, the side plates 18 have central apertures 24 which expose part of the adjacent face of the respective cuvette 14.

A support body 26 is situated between the sample stations 10 and 12, in the gap between the side plates 18. The support body is approximately semi-cylindrical with an upwardly extending longitudinal axis, assuming the base plate 2 is horizontal. The diametral face of the support body 26 carries a plane mirror 28. An electric stepping motor or a motor in the form of a two-position solenoid 30 is supported beneath the plate 2. Its output shaft (not shown) extends through an

opening in the base plate 2 and carries the support body 26.

The two operative positions of the stepping motor or of the solenoid 30 correspond to two operative positions of the support body 26 and the mirror 28. These positions are established accurately by means of an adjustable stop mechanism 31. One of these positions is shown in the Figures. To move to the other operative position, the support body 26 is rotated through 90° anticlockwise from the position shown in Figure 3. It will be appreciated from Figure 3 that light emitted from the cuvette 14 in the sample station 12 will pass through the window 24 and be reflected by the mirror 28 to the window W of the PMT in the light detector 6. In the other operative position, the mirror is positioned so that light emitted from the cuvette 14 at the sample station 10 will be directed by the mirror 28 to the window W.

As shown in Figure 3, upright ribs 32 are provided on the side plates 14, these ribs abutting, or lying close to, the circular periphery of the support body 26. It will be appreciated that, in the operative position shown in Figure 3, the support body 26 abuts the ribs 32, so blocking the emission of light from the cuvette 14 in the sample station 10. Similarly, in the other operative position, cooperation between the support body 26 and the ribs 32 at the sample station 12 will block the emission of light from the cuvette 14 in the sample station 12.

Circuit boards 34 are secured to the side plates 16.

These circuit boards carry lights in the form of light-

emitting diodes (LEDs) 36, of which the terminal pins 38 are visible in the Figures. The LEDs 36 are associated with means for measuring the turbidity of the liquid in the cuvettes 14.

The apparatus described may be used in an assay technique as described in our British Patent Application No (attorney's ref: HL83941), the disclosure of which is incorporated herein by reference. Consequently, details of the technique will not be described in detail in this specification, except as is necessary for understanding the present invention.

The apparatus may, for example, be used to test a soil sample for toxicity. The soil sample is treated so as to dissolve the toxins of interest, or to separate them from the soil particles. To achieve this, the soil sample is placed in a water-miscible solvent. The solvent, containing the toxin, may then be diluted and further ingredients may be added if required. The resulting solution constitutes a test sample.

A control sample is prepared using the same solvent, diluent and other ingredients in the same proportions as the test sample, except that the solvent had not been in contact with the soil sample and therefore does not contain the toxin.

A liquid containing a bioluminescent organism, for example Vibrio fischeri is introduced into each of the cuvettes 14. Such bacteria may be supplied and stored as freeze-dried or lyophilised cells, and can be reconstituted by adding a reconstitution solution of 2%

aqueous sodium chloride or phosphate buffer and allowing incubation at a temperature within a range of about 15°C to about 25°C. At this temperature, Vibrio fischeri will bioluminesce.

The cuvettes 14 are placed in the stations 10 and 12 and maintained at a desired constant temperature, for example 15°C by means of the Peltier heat pumps 23.

The apparatus is then activated and the support body 26, with the mirror 28, switches between its two operative positions at regular intervals. These intervals may be of any practicable duration, but for most purposes they will be intervals in the range 0.1 to 10 seconds, and usually towards the upper part (ie 5 to 10 seconds) of this range. Thus, the light detector 6 receives, through the window W, light alternately from each of the cuvettes 14 in stations 10 and 12.

Since the organisms and their carrier solutions in the cuvettes 14 are substantially identical, the signals received (ie the intensity of light emitted by the light detector 6) should be approximately the same in both operative positions of the mirror 28.

When the signals from the bioluminescent organisms have stabilised, for example after approximately 5 to 7 minutes, the test sample prepared as described above is introduced into one of the cuvettes 14, for example that at the sample station 10, and the control sample is introduced to the other cuvette 14, for example that at the sample station 12. The presence of toxins in the test sample will inhibit the bioluminescence of the organism, and the reduced light output will be detected

by the light detector 6 when the mirror 28 is in the operative position.

Although the control sample contains no toxin, the increased dilution of the organism in the respective cuvette 14 and the effect of the chemicals in the control sample may also cause a reduction in bioluminescence. However, depending on the concentration and toxicity of the toxin in the test sample, the inhibition of bioluminescence will be different as between the test and control samples.

The apparatus is preferably linked to a computer which controls the operation of the apparatus, for example the movement of the mirror 28, and gathers data from the light detector 6 and processes that data to provide a useful output. By appropriate calibration, the computer may be programmed to output a reading representing the concentration of the toxin in the original soil sample.

If turbidity is detected in the samples, by means of the circuitry including the LEDs 36, appropriate steps are taken to compensate for the reduced light emission resulting from the turbidity.

The apparatus may include a GPS (Global Positioning System) module to enable the location of the apparatus, and consequently of the soil sample under analysis, to be automatically recorded. A GSM module (Global System for Mobile Communication) may also be included in the apparatus to enable remote downloading of data.

It will be appreciated that, since both the test sample and the control sample are prepared at substantially the same time and are analysed together by means of the movement of the mirror 28 between its operative positions, a single analysis sequence can, in a relatively short time'provide a useful output in a relatively simple manner. The apparatus is compact, compared with laboratory apparatus provided with automated conveying, dispensing and purging means, and can also be constructed in a relatively robust manner.

The apparatus as disclosed is thus suitable. for rapid analysis of soil and other samples in the field.

Although the present invention has been described with reference to bioluminescent organisms, it will be appreciated that the principles underlying the present invention can be applied to analysis techniques which rely on other forms of light generation, such as biofluorescence or chemical light generation.