WO2025191266A1

WO2025191266A1 - Water sensor

Info

Publication number: WO2025191266A1
Application number: PCT/GB2025/050505
Authority: WO
Inventors: Robert Stevens; Kieran KHAMIS
Original assignee: Proteus Instruments Ltd
Current assignee: Proteus Instruments Ltd
Priority date: 2024-03-12
Filing date: 2025-03-12
Publication date: 2025-09-18
Anticipated expiration: 2026-09-12
Also published as: GB202503673D0; GB202403582D0

Abstract

A sensor arrangement (10a) for water measurements comprises a sensing volume (14) for a liquid sample, an optical emitter arrangement (20a, 20b), and a detection arrangement (25), arranged relative to the sensing volume (14) such that optical radiation is detectable by the detection arrangement from at least two different angles, for instance orthogonally to each other, relative to the optical emitter arrangement (20a, 20b). Two emitters may be arranged at two different angles relative to one detector, or two detectors may be arranged at two different angles relative to one emitter. The detection arrangement (25) comprises a spectrometer to acquire measurements from different wavelengths, to allow recording of spectra for the different angles. The arrangement allows spectra to be obtained as a function of different emitter wavelengths and/or as a function of measurement angle.

Description

Water sensor

Field of the Invention

The present invention relates to a water quality sensor of the type permitting practically continuous or real-time monitoring of water bodies. More specifically, the invention relates to sensor arrangement configured for obtaining multiple parameters for simultaneous or practically simultaneous measurements of multiple analytes in flowing or standing water bodies.

Background

Several tests are known to determine the quality of a body of water based on markers or other suitable analytes, such as biological oxygen demand (BOD) or others. Such procedures determine the water quality via a bioassay and/or by a surrogate measure in the form of presence and/or quantity of specific analytes. A drawback of such procedures is that they can often take several days before results are obtained, reducing the value of such procedures when quick response times are of interest.

Great British Patent Publication GB2553218 by the present applicant discloses a sensor design for measuring Biochemical Oxygen Demand (BOD) using an optical interrogation array to determine fluorescent properties in a water sample. It would be desirable to use methods for several analytes and surrogate indicators. However, the scaling of such systems can become uneconomical, particularly once measurements are required in short intervals, or practically continuously, and of multiple analytes including analytes at relatively low concentration levels and/or varying concentration levels.

The present invention seeks to ameliorate at least some of the issues outlined above.

Summary of the Invention

In accordance with a first aspect of the invention, there is provided a sensor arrangement for water measurements, the arrangement comprising a sensing volume for a liquid sample, an optical emitter arrangement, and a detection arrangement, arranged relative to the sensing volume such that optical radiation is detectable by the detection arrangement from at least two different angles relative to the optical emitters, wherein the detection arrangement comprises a spectrometer to acquire measurements from different wavelengths, to allow recording of spectra for each one of the at least two different angles.

The sensing volume is understood to be a region in the form of a passage or holding cell into or through which liquid-to-be-interrogated is passed, the liquid being, typically, water. The sensing volume may be probed by optical radiation (light) emitted by the optical emitter arrangement. The detection arrangement is provided to capture light emitted from the sensing volume, e.g. transmitted, scattered, and/or fluorescence.

A spectrometer will be understood as a sensor for measuring different wavelengths of light simultaneously. The spectrometer allows, therefore, emission of light out of, or through, the sensing volume to be obtained, such as transmitted light and/or fluorescence. For instance, the spectrometer may obtain measurements in a wavelength region covering at least the range from 200 nm to 1 ,000 nm, and may be separated into bins defining a spectral resolution of no less than 5 nm, 4 nm, 3 nm, 2 nm, 1.5 nm, or 1 nm. It will be appreciated that a spectrometer will also acquire measurements from wavelength regions that do not create a signal. For instance, the spectrum may comprise baseline values, such as “0” or “NaN”, that are also recorded as part of the measurements.

The spectrometer allows the system to generate spectrograms, i.e. a series of successive spectra, although spectrograms are not necessarily used in all embodiments. Spectrograms may show a timedependent wavelength response for a given excitation wavelength or region. For instance, a first spectrum soon after excitation may show spectra indicative of transmission, or absorption, respectively. A second spectrum obtained later than the first spectrum may show spectra indicative of slower response behaviour, such as fluorescence. The spectra may differ for different angles, for instance due to different scattering behaviour.

Without wishing to be bound by theory, it is believed that the use of a spectrometer makes the sensor arrangement more robust to a shift in wavelength responses, where such as shift may be observed depending on complexity of the sample to be measured and the number and type of analytes. Furthermore, it is believed that the shift may itself be indicative of certain analytes. E.g., being able to record spectra, the sensor arrangement may enable a determination of a magnitude of a shift, in dependence on excitation wavelength from optical emitters and/or in dependence on the angle from which the measurements are acquired.

As will be appreciated, the method may involve averaging a number of successive spectra to generate an average spectrum, and or a sliding average of successive spectra to provide an average spectrogram.

To enable the optical radiation to be detected from at least two different angles, the present disclosure suggests two approaches. In one approach, the emitter arrangement is configured to emit into the sensing volume from different angles, e.g., orthogonally, relative to a common detector. This may be achieved by using two emitters, or by using an arrangement comprising an emitter coupling into two light guides that are arranged to emit into the sensing volume from different angles.

In another approach, the detector arrangement is configured to detect incoming light from different angles, e.g., orthogonally to each other relative to the sensing volume, to detect optical radiation from a common emitter. This may be achieved by using two detectors, or by using an arrangement comprising a detector coupled with two light guides that are arranged to capture light from the sensing volume from different angles.

In some embodiments, the optical emitter arrangement comprises a first optical emitter and a second optical emitter, each configured to emit optical radiation into the sensing volume, wherein the first optical emitter is arranged to emit into the sensing volume from a different angle than the second optical emitter, relatively to the detection arrangement.

A single detector may, in that case, be used for measurements using the first optical emitter and for measurements using the second optical emitter.

An optical emitter, herein, is an optical source module capable of emitting different wavelengths. The optical emitter may be controllable to emit different wavelengths sequentially. For instance, an optical emitter may be a multi-LED chip comprising one or more single-wavelength LEDs and a broadband source.

The optical emitter arrangement may be provided by a single light source and a light guide arrangement with shutter control and/or repositionable control, to alter the angle at which light is emitted into the sensing volume, the light-emitting ends of the light guide arrangement providing the first and second optical emitter.

The use of two separate optical emitters, such as multi-LED chips is believed to increase the robustness of the system, by reducing the need for movable parts and for shutter arrangements.

In many embodiments, the two optical emitters are offset perpendicularly, or orthogonally, to each other. For instance, one of the optical emitters may be opposite the detection arrangement, and the other of the optical emitters may be perpendicular (orthogonal) to the detection arrangement. This achieves that light captured by the detection arrangement may be indicative of transmission behaviour, using the opposite optical emitter, and/or scattering and/or fluorescent behaviour, using the perpendicularly positioned optical emitter. It will be appreciated that the optical emitters may be operated sequentially to reduce interference between measurements. In this manner, a single spectrometer unit or module may be used for measurements from multiple (e.g., two) different optical emitters, arranged such that the detector arrangement captures light interrogating the sensing volume from different directions.

In some embodiments, the detection arrangement comprises a first detection arm and a second detection arm, each configured to detect optical radiation from the sensing volume, wherein the first and second detection arms are offset to capture radiation at different angles from the sensing volume. In embodiments using multiple detection arms, a single optical emitter module may be used, whose emissions are to be detected via the first detection arm and the second detection arm. The single optical emitter module may comprise a broadband source, and one or more single-wavelength LEDs.

To this end, the detection arms are located and/oriented at different positions or angles, respectively, e.g. such that they point to a common sensing volume from different angles.

The suggestion underlying the embodiment is to arrange at least two detectors, or two arms of a common detector, such that they capture light at different angles from the sensing volume. To this end, a single spectrometer unit or module may be operatively coupled with multiple detection arms that may be offset angularly and/or spatially, such that they are oriented to capture light emitted from the sensing volume in different directions therefrom. Alternatively, each detector or detection arm, respectively, may comprise, or may be operatively coupled with, a separate spectrometer.

In some embodiments, at least one detection arm is located opposite at least one optical emitter, relative to the sensing volume, to enable a transmission measurement indicative of absorbance in the sensing volume.

Being positioned opposite the, or one of the, optical emitters, the detection arm is for practical purposes in a direct light path of the optical emitter, respectively, the detection arm is positioned such that the light reaching the detection arm has travelled at least a full length, or at least a full width, of the sensing volume.

In some embodiments, at least one detection arm and at least one optical emitter are located laterally of each other, relative to the sensing volume, to enable an emission measurement indicative of fluorescence emissions and/or turbidity in the sensing volume.

Being laterally of an optical emitter, a detection arm may be positioned to capture light in a direction other than a straight optical path between emitter and opposite detection arm, e.g. light that has been scattered, which may be indicative of turbidity, and/or emitted by fluorescence. The lateral position may be an orientation that is orthogonal to the orientation of the detector.

In many embodiments, the water sensing arrangement comprises at least one optical emitter opposite at least one detection arm, and at least one of another optical emitter and another detection arm orthogonally to the optical path between the at least one optical emitter and the at least one detection arm.

In some embodiments, the arrangement comprises two detection arms for one optical emitter, one detection arm opposite the optical emitter, the other orthogonal to the optical emitter. In some embodiments, the arrangement comprises two optical emitters for one detection arm, one optical emitter opposite the detection arm, the other orthogonal to the detection arm.

In some embodiments, the, or each, optical emitter comprises at least one broadband source.

A broadband source will be understood as an optical source emitting light from a range of wavelengths covering several 100 nm, in practice at least 400 nm or at least 500 nm, and most or practically all of the visible spectrum. For instance, a broadband source may emit in a region including a range from 500 nm to 1000 nm, i.e. including a range of visible light and near infrared light. The arrangement may include multiple broadband emitting elements, e.g. a source capable of emitting from 350 nm to 900 nm, and a source capable of emitting from 500 nm to 1000 nm. As will be appreciated, the light emitted from the broadband source may excite several analytes simultaneously. The wavelength regions provided herein are exemplary and other wavelength regions may be used.

In some embodiments, the broadband source is controllable such that different wavelength regions of the broadband source can be operated to emit while blocking other wavelength regions of the broadband source, thereby allowing the arrangement to operate at least some wavelength regions of a broadband source to interrogate the sensing volume sequentially.

In some embodiments, the, or each, optical emitter comprises a plurality of individually activatable emitters, such as LEDs, operable to enable the optical emitter to emit at least two different wavelengths or wavelength regions.

The plurality of optical emitters may be provided by a multi-LED chip. As will be appreciated, LEDs may be emitting at a nominal wavelength, e.g. 255 nm. Depending on the type of LED, the nominal wavelength may comprise a certain bandwidth, e.g. ±5 nm. It will be appreciated that such a LED emitting at e.g. 255 nm ±5 nm is for the purposes of this disclosure emitting in the same wavelength region.

The two wavelengths may be spaced apart in the electromagnetic spectrum. E.g., an LED emitting at 250 nm is considered to emit at a different wavelength, or wavelength region, than an LED emitting at 280 nm. As the wavelength regions of the different LEDs do not usually overlap, the wavelength regions may be considered discrete wavelength regions from different spectral regions or from different spectral bands.

The emitters are individually activatable, e.g. under the coordination of a controller, to allow one or more of the emitters to be activated independently of the activity status of the others of the plurality of emitters.

Alternatively, or in addition, the plurality of emitters is provided by a broadband LED. The array of optical emitters may comprise a combination of one or more broadband emitters and one or more narrow (single) wavelength emitters. The broadband emitter is understood to emit a plurality of wavelengths simultaneously. In that case, the arrangement may comprise actuatable filters to selectively pass or block wavelength regions.

In some embodiments, the arrangement is controllable such that optical emitters of the plurality can be activated independently of one or more other optical emitters of the plurality, thereby allowing the arrangement to operate at least some of the optical emitters sequentially.

During the development of the invention, it was observed that interrogation of a sample using broadband sources, or using wavelengths covering a relatively wide spectrum, may result in distorted measurements, believed to result from light scattering between measurements. To provide an illustration of the problem, a fluorescent measurement may be carried out using a UV light emitter emitting at around 260-300 nm, for the purpose of measuring ensuing fluorescence at 295-405 nm. A contemporaneous measurement using another light emitter, for instance a broadband source, emitting within the range of 295-405 nm will create scattering in a similar or same wavelength region, overlapping with the expected fluorescence-excited radiation, thereby affecting the measurement intended to be correlated with the UV light emitter’s nominal wavelength region.

Underlying the development of embodiments of the invention was an appreciation that such effects can be mitigated by sequential flashing of the light emitters. The emitters may be operated such that a first emitter or preceding emitter is deactivated, such that the system is “dark”, before a second emitter or subsequent emitter is activated, and so on. In this context, “dark” refers to a configuration in which no optical emitter of the optical array is active to emit into the sensing volume. In practice, dark periods or pauses between emitter activity may be relatively short. Using an example of a first measurement using a first excitation source, having a first emission angle and/or wavelength, or fluorescence therefrom, and a second measurement using a second excitation source, having a second emission angle and/or wavelength, it will be appreciated, that pauses between first and second measurement need to be only long enough to avoid interference. The duration of the pause may depend on the wavelength and type of emission, such as fluorescence. In some embodiments, the sequential activation is a sequential activation of light sources of the same multi-LED optical emitter. In some embodiments, the sequential activation is a sequential activation of light sources from two or more multi-LED optical emitters.

Likewise, the emitters may be operated to accommodate a minimum data acquisition time, as may be determined by the spectrometer. In that case, the emitters may be operated such that a first emitter or preceding emitter remains deactivated at least until the minimum data acquisition time has elapsed. The data acquisition time is not necessarily long, and may be in the region of seconds per wavelength, which may have to be repeated for different wavelength regions and/or for measurements from different angles. In test devices, the process of flashing through an array of, e.g., six or eight different wavelength LEDs may take less than 60 seconds. In this manner, the arrangement can use narrow wavelength and/or single wavelength emitters for specific wavelength measurements, and, in the same setup, broadband emitters in a measurement sequence, without the broadband emitters interfering with specific wavelength measurements.

The arrangement may be controllable to use optical emitters in a non-consecutive order, e.g. to use a higher wavelength emitter, followed by a lower wavelength emitter, followed by a higher wavelength emitter. Using illustrative values, a 250 nm emitter may be followed by a 650 nm emitter, followed by a 380 nm emitter, and so forth. A non-consecutive sequence is believed to further reduce the likelihood of interference between measurements.

Likewise, the arrangement may be controllable to use optical emitters simultaneously, if there is practically no interference expected, or practically not measurable, for two simultaneous wavelengths. This may be the case, for instance, when combining emission wavelengths selected from a spectral region between 250 nm and 450 nm, and another wavelength from a sufficiently remote spectral region, e.g. 850 nm.

In some embodiments, the arrangement is controllable such that optical emitters of the plurality can be activated independently of one or more other optical emitters of the plurality, thereby allowing the arrangement to drive different optical emitters for different durations of time and/or to drive different optical emitters at different power levels.

In this manner, the emissions of emitters with different strength power levels may be balanced and/or adjusted according to expected analyte concentration levels.

In some embodiments, the arrangement is configured to obtain measurements from the first detection arm and from the second detection arm sequentially.

For instance, the first and second detection arms may comprise a shutter mechanism allowing each arm to be individually blocked, such that measurements are obtained from the respective arm that is not blocked. By coordinating the shutter operation with the flashing of optical emitters, it will be appreciated that the measurements from the first detection arm and the second detection arm can be obtained sequentially.

In some embodiments, the arrangement is configured to carry out measurements using the first optical emitter and the second optical emitter sequentially.

For instance, the first and second optical emitters may be individual actuated, for instance in the form of a multi-LED chip. As another example, each of the first and second optical emitters may comprise an arrangement of LEDs and a broadband source. Alternatively, or in addition, each optical emitter may comprise a filter to define wavelengths to be utilised for optical interrogation, and/or to block wavelengths to be omitted for optical interrogation. For instance, an optical emitter, or both optical emitters, respectively, may comprise a broadband source operable to emit one of several selectable wavelength regions. In some embodiments, the different wavelength regions may be activated sequentially in the manner of individually actuatable LEDs.

Alternatively, or in addition, the, or each, optical emitter may comprise a single optical emitter module comprising LEDs and/or a broadband source, configured to emit light via two source arms, such as light pipes. In such embodiments, each light source arm may comprise a shutter to selectively block either or both of the first source arm and the second source arm. Each of the first and second source arms may comprise a free emission end, the two emission ends arranged to guide light towards the sensing volume at different angles, whereas the shutter can be used to block the arms selectively to direct light via one of the different angles, or another of the different angles.

In some embodiments, the arrangement comprises a single spectrometer module to measure light obtained from each detection arm of the detection arrangement.

Preferably, the one or more optical emitters and the one or more detection arms, as the case may be, are arranged to obtain measurements from the same sensing volume, such as a common channel providing a passage or holding volume for a liquid. In embodiments, the arrangement may comprise two or more separate channels to form a sensing volume, e.g. one channel providing a passage for a liquid for absorbance measurements, and another channel providing another passage for a liquid for fluorescence measurements. The channels may be supplied from a common inlet region of the device, the supply from the inlet region splitting to supply separate sensing volumes.

In embodiments with multiple detection arms, these may comprise light guides or pipes to feed optical signals to a common spectrometer module. In this manner, a single spectrometer may be used to read and analyse signals from light captured contemporaneously at different angles from the sensing volume, to thereby allow it to measure absorbance (transmission) and fluorescence.

In some embodiments, the arrangement comprises a light-guiding arrangement to direct light from two or more different optical emitter elements of an optical emitter to a common interrogation area of the sensing volume.

Each optical emitter arrangement may comprise an individual light-guiding arrangement.

When increasing the number of independent light sources, even in the case of relatively small footprint LEDs that may be provided in the form of a spatially distributed array, e.g. on a “single chip”, or one or more printed circuit boards, it was a concern by the applicant that slight differences in emission angle may affect the comparability of results. By joining light paths from different emitter elements of an optical emitter, so that they impinge on or in the same volume, originating from a single emission outlet or window, such disadvantages can be mitigated. In addition, it was found that the use of light-guiding arrangements allows the sensing volume for sample interrogation to be reduced in size.

In some embodiments, the light-guiding arrangement is provided by a collimator.

Alternatively, or in addition, the light-guiding arrangements may comprise mirrors, beam reflectors, fused silica windows, and/or shutter mechanisms. As will be appreciated, the type and design of the light guides may depend on whether or not the part is exposed to the fluid or contained in a fluid-tight chamber. Likewise, the type and design of the light guides may depend on the wavelength range of the optical emitter, available space within the device housing, and other configurations. Several suitable light guide mechanisms will be known to a skilled person.

In some embodiments, the arrangement comprises a focusing arrangement for each detection arm of the detector arrangement.

A focusing arrangement may be provided to one or each of the detection arms to assist with the gathering of light into the detection arm. For instance, the focusing arrangement may comprise a plano-convex lens, spherical or aspherical lenses, a mirror arrangement, and/or a combination of lenses. The focusing arrangement may comprise a flat lens provided for waterproofing.

In some embodiments, the sensing volume is provided in the form of an open channel.

The expression “open”, in relation to a channel, refers herein to a non-closed periphery between an inlet region and an outlet region. The channel may be open along its passage length, shaped in the form of a notch, comprised of a re-entrant profile along all or at least part of its elongate extension. The open profile reduces the likelihood of particles becoming entrapped. It will be appreciated that a channel may comprise, viewed in cross-section, two lateral walls and a base. It will be appreciated that the walls may be parallel to each other, although the invention is not necessarily so limited, and the channel may have a trapezoidal cross-section along its elongate extension.

In such a geometry, one of the optical emitters may be located on one of the lateral walls, one of the detection arms on the other of the lateral walls opposite the optical emitters, and another one of the optical emitter or the detection arm may be on the base, e.g. laterally of the optical emitters. In other words, for a device installed vertically, usually in the shape generally of an elongate rod comprising at a distal end thereof a lateral recess providing a sensing volume. The sidewalls of the lateral recess, and therefore the optical emitter and/or absorption arms, may be on a lateral channel wall facing in a direction distally (away or outward from the device) or proximally (inward towards the device), respectively.

The provision of an open channel allows particles carried in the liquid to enter and pass through the sensing volume. In this context, an open channel configuration may have to tolerate liquid ingress laterally between the inlet and outlet of the channel. However, it was observed that for many natural samples, an open channel avoids a risk of a channel becoming blocked as may be the case with closed periphery channels, while permitting an unfiltered sample to be measured. Nevertheless, some measurement protocols may comprise a filtering step, to filter particles from the fluid, prior to an optical measurement. For instance, the device may be provided with a mesh, with a mesh size selected such that it blocks entry of small animals, plant material, and/or other debris, while permitting passage of smaller particles.

The open channel facilitates cleaning by providing ready access for cleaning mechanisms such as a wiper, brush, or gas, such as pressurised gas. One or more of the optical emitters may comprise a high-powered UV light source enabling UV inactivation of impurities or biological substances. This facilitates regular cleaning of optical surfaces to mitigate against deposition of particles.

In some embodiments, the arrangement comprises a cleaning mechanism for the sensing volume and/or surfaces defining walls thereof.

The cleaning mechanism may be provided by a wiper or brush, operating mechanically to clear windows and surfaces of optical components exposed to the sensing chamber. The cleaning mechanism may comprise a jet or other suitable device to flush the sensing volume, with liquid and/or gas, and/or UV light.

The sensor arrangement may comprise a configuration allowing it to prevent operation of the cleaning mechanism during operation of the optical emitters and the first and/or second detection arms. The sensor arrangement may comprise a configuration allowing it to delay operation of the optical emitters and the first and/or second detection arms for a predetermined settling period after operation of the cleaning mechanism.

In some embodiments, the cleaning arrangement comprises at least one of a gas-based cleaning arrangement, a mechanical wiper arrangement, and/or a UV-based arrangement, wherein, optionally, the UV based arrangement is provided by one or more of emitters of the optical emitter arrangement.

In some embodiments, the arrangement is configured to obtain both absorbance and fluorescence measurements, and to use measurement values from one or both of the absorbance and fluorescence measurements as an input for a calibration of measurements.

The arrangement may be configured to use the same flashing sequence for measurements using a detector arm opposite an emitter arrangement, and for measurements using a detector arm laterally of an emitter arrangement. Measurements from different measurement angles may enable comparison and/or calibration as a function of measurement angle, by referencing a measurement made at one of the different angles against a measurement made at another one of the different angles. As will be appreciated, the absorbance and fluorescence measurements may be obtained sequentially. The absorbance and fluorescence measurements may be measured as a function of wavelength and/or broadband spectrum, or LED number, respectively. E.g., for an LED array of six different wavelengths, the device may capture a data set, for instance in the form of a data matrix, corresponding to six data pairs, each data pair comprising an absorbance value and a fluorescence value.

In addition to fluorescence and absorbance, the arrangement may obtain scattering values as a function of wavelength, and/or as a function of angular orientation of the detection arm(s) relative to the emitter(s). E.g., a while the illustrative embodiment is described with two detection arms, opposite and at a perpendicular (90°) position relative to the optical emitter, in some embodiments the device may comprise an array of detection arms e.g. at 45° (e.g. for forward scattering) and/or 135° and/or at around 180°, close to the emitter (e.g. for backscattering), or other suitable angles, to allow measurements to be obtained as a function of angular detector position. For instance, a device may comprise two optical emitter arrangements, positioned perpendicularly to each other, and two detector arrangements, positioned at an angle of 45 degrees to each other, to enable measurements at 180° and 90° using the first detector arrangement, and at 45° and 135° using the second detector arrangement. In that case, each measurement may be obtained using the same spectrometer. In this manner, the sensor arrangement may be operated to obtain turbidity measurements, e.g. using infrared wavelengths and scattering at a 90° sensor orientation or other suitable angular sensor orientation towards the sensing volume. Alternatively, a design may comprise three or more optical emitter arrangements, for instance at 0°, 45°, 90°, (and other angles, respectively) for one detector arrangement, or an optical emitter arrangement for three detector arrangements, for instance at 90°, 135°, and 180° (and other angles, respectively).

In some embodiments, the arrangement is provided in the form of a modular component for use with a sensor device.

The sensor device may be a multi-sensor probe, such as a modular multi-sensor probe.

In some embodiments, the arrangement is provided as part of a self-contained analysis device.

The device may be a handheld device.

It will be appreciated that different correction algorithms may be applied for different target analytes. Likewise, while some testing may be interested in a quantitative result, some other tests may require a qualitative result. As such, the type of correction algorithm may depend on the accuracy that is required of a specific measurement.

Description of the Figures

Exemplary embodiments of the invention will now be described with reference to the Figures, in which: Figure 1 is a schematic illustration of an embodiment;

Figure 2 is a schematic illustration of another embodiment; and

Figure 3 is a flow chart showing exemplary steps of a method of using an embodiment.

Description

Figure 1 shows a water sensor device 10 comprising a probe housing 12 comprising an integrally formed channel to provide a sensing volume 14. The sensing volume 14 is defined by a recess in the form of an open channel, providing a water passage to be submerged in a water body to be tested, such as a river, tank, or other test area. The recess may have a volume of around 1 cm width (wall- to-wall distance) x 1 cm depth x 2 cm length (open end-to-end distance), although other dimensions may be used.

A side wall of the sensing volume 14 is provided with an array of light emitters 20, constituting part of an interrogation arm, here in the form of a plurality of LEDs arranged to emit optical radiation for probing the sensing volume 14. For simplicity, the expression “light” may be used herein to refer to photons from the electromagnetic spectrum in the wavelength region from 200 nm to around 1000 nm, of suitably low attenuation in water so as to be usable for optical measurements. Individual ones of the plurality of LEDs may emit at a narrow region within the wavelength region of around 200 nm to 1000 nm, e.g. at 255, 275, 375, 450, 545, and 850 nm. As will be appreciated, not all of the exemplary wavelengths are necessarily used in each embodiment, and/or other wavelengths or combinations of wavelengths may be used depending on the type of analyte to be detected. One or more of the LEDs may be a broadband LED source. By broadband LED source, it will be understood that the source emits over a wide spectrum simultaneously, such as a range of at least 100 nm, 200 nm, 300 nm, 400nm, 500 nm, or 600 nm. In some embodiments, the wavelength range has a minimum wavelength no higherthan 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, 210 nm, 220 nm, 230 nm, 240 nm, or no higher than 250 nm. In some embodiments, the wavelength range has a maximum wavelength of at least 550 nm, 600 nm, 800 nm, 1000 nm, or at least 1200 nm. The emission range of the broadband LED may include wavelength regions attenuated in water.

The housing 12 comprises a first detection arm 22, arranged such that its end, the first light-capturing end 22a, is located opposite the light emitters 20, on an opposite wall of the sensing volume 14, and thereby arranged to capture light passing through a liquid in the sensing volume 14 for absorbance measurements. As will be appreciated, light captured in the first detection arm has travelled through the full length of the sensing volume 14.

Furthermore, the housing comprises a second detection arm 24, comprising a second light-capturing end 24a located generally perpendicularly to the emission path of the light emitters 20, and thereby arranged to capture light emitted laterally from the sensing volume, including fluorescence and scattered light, for fluorescence and scatter measurements. The second light-capturing end 24a may be offset around 90° from the first light capturing end 22a.

The light emitters 20 of the interrogation arm are provided in the form of an array of LEDs. Individual LEDs of the array may be spaced apart from each other, albeit by a small distance, e.g. distributed on a common printed circuit board, or chip. The device 10 comprises a collimator element 21 or condenser constituting a light guide to allow light emitted from the LEDs to impinge via a common interrogation arm in the same interrogation volume within the sensing volume 14. In this manner, the sensing volume 14 may be made smallerthan would otherwise be the case. Likewise, the arrangement allows LEDs to be spaced apart further than would otherwise by the case. This enables the use, potentially, of larger components and allows components for the array to be sourced from a wider range of suppliers. Depending on the type and power of the LEDs, the wider spacing may assist with cooling.

The first light-capturing end 22a comprises a first optical window 26, and the second light-capturing end 24a comprises a second optical window 28. The first and second optical windows 26, 28 may be flat fused silica windows, for instance. The light-capturing ends 22a and 24a each comprise a lightdirecting arrangement to direct light from the sensing volume 14 towards and into the respective detection arms 22, 24.

In this example, the first light-capturing end 22a is designed for transmission measurements and may comprise a collimating lens, plano-convex lens or other suitable component. The second lightcapturing end 24a is designed for fluorescent and scattering measurements. It may comprise a collimating lens, plano-convex lens or other suitable component for light capture into the second detection arm 24. In order to facilitate integration of a right-angle in the light guide, the second lightcapturing end 24a may comprise a 90° collimator and a 45° reflecting mirror, to guide emitted fluorescent light into the second detection arm 24. It will be appreciated that the illustrated arrangement is exemplary and that other light-capturing arrangements may be used. Likewise, the position and orientation of the open side of sensing volume 14, and the position of the light emitters 20 and the light capturing ends 22a, 24a may be rearranged, e.g. such that the emitters emit sideways, or in a distal direction pointing away from the device.

Herein, the detection arms 22 and 24 are constituted by portions of two detection branches 32 and 34, here in the form of a light guide such as an optical fibre, joining into a common detection arm 36 to direct light signals to a spectrometer module 30.

Figure 2 shows another water sensor device 10a, which is a variant of the water sensor device 10. Several components of the water sensor devices 10 and 10a are equivalent, and may even be identical components, and are identified by identical numerals, the description of which is not repeated. In the device 10a, the sensing volume 14 is provided with two interrogation arms 23a, 23b, the first interrogation arm 23a comprising a first optical emitter 20a, the second interrogation arm 23b comprising a second optical emitter 20b. The optical emitters 20a, 20b may each correspond to the optical emitter 20, i.e. each be constructed like the optical emitter 20, and are oriented to emit light into the sensing volume from different angles, here perpendicularly to each other.

The device 10a comprises, here, a single detection arm 32a, comprising a light-capturing end 25 which may comprise an optical window 26a. The light-capturing end 25 may correspond to one of the components 26, 28, described with reference to Figure 1 .

The first interrogation arm 23a is positioned opposite the light-capturing end 25, on opposite ends of the sensing volume 14. The second interrogation arm 23b is positioned laterally, orthogonally to the light-capturing end 25.

The spectrometer module 30 is designed in a manner allowing it to measure light, specifically the spectra emitted from e.g. fluorescent radiation or transmitted radiation collected by the detection arms 22 and 24, or 32a, respectively. The same spectrometer module 30 may be used to measure light captured from two detection arms 22 and 24. To this end, the spectrometer module may comprise one or more detection elements such as photodiodes, complementary metal oxide semiconductor (CMOS) sensor, and/or charge-coupled device (CCD) sensor, or other suitable sensors, sensitive to wavelengths or wavelength regions of interest from the electromagnetic spectrum. The spectrometer module 30 may be provided as a spectrometer to measure a spectrum in the region of UV, visible, and near infrared light, e.g. from around 200 to 1000 nm. Suitable spectrometer designs with appropriate resolution and acquisition speeds will be known to a skilled person. Due to the use of one or more detection arms arranged to capture light at different emission angles, the spectrometer module 30 is capable of capturing transmitted, scattered and fluorescence-emitted light simultaneously. The spectrometer is capable of measuring wavelength dependent light from a broadband source, while also providing sufficient resolution to measure single-wavelength, or narrow-wavelength, signals from an LED.

For the purpose of the present disclosure, it is assumed that standard optical emitters, light guides and spectrometers, specifically a wide range of LEDs and optical fibre designs, suitable for optical measurements in the region of around 200 to around 1000 nm, are known to a skilled person, and will not be described in detail herein. Likewise, it will be appreciated that the optical components are affixed in a waterproof manner so as to allow the device, or at least a probing end thereof, to be submersible in a body of water, and to permit passage of a liquid such as water through the sensing volume. Several technical designs that are suitable as waterproof optical windows will be known to a skilled person and are not described in detail herein.

The arrangement may be provided with shutter mechanisms, e.g. shutter mechanisms that are individually actuatable - in the example of Figure 1 - for each of the first and second detection arms 22 and 24, to allow the light capture into either or both of the detection arms to be blocked upon demand. In some embodiments, the shutter mechanisms are integrated in a subassembly, such as the first light-capturing end 22a and the second light-capturing end 24a. However, the integration with a sub-assembly at the light-capturing end is not a requirement of all embodiments. For instance, the two detection branches 32, 34 may each comprise a shutter component. A shutter mechanism may be omitted in a design using a single detection arm, such as the device 10a illustrated in Figure 2. In a shutter-free design, interference between measurements may be avoided by sequential, nonoverlapping actuation of the emitters of first interrogation arm 23a and emitters of the second interrogation arm 23b. A shutter-free design using two optical emitters, constituted by two interrogation arms 23a, 23b, reduces the number of moving parts in the device.

The spectrometer unit 30 is operatively connected with a processing system 40 for data transfer of measured data, control signals, and other data. In this example, the processing system 40 comprises a driver board for the spectrometer 30 and the light emitters 20, or 20a and 20b, respectively. The processing system 40 may comprise a processor and machine-readable instructions to control the operation of the emitters 20, or 20a and 20b, respectively, and the spectrometer unit 30. Furthermore, the processing system 40 may control the display of a user interface and operation of a data transfer module, allowing the system to export data. In embodiments comprising a cleaning mechanism and/or shutters (if incorporated), the processing system 40 may control operation of the cleaning mechanism and/or shutters, respectively, e.g. in pre-determined intervals coordinated with optical measurements and/or to avoid interference with optical measurements.

The device 10 or 10a comprises, further, a power source or connection to a power supply. The power supply may be provided by an external source or in the form of an internal source such as a battery. Power and/or data connection may be provided via a connector 18, although the device 10, 10a may comprise different individual connectors for power and data, if desired, or may comprise a wireless interface to permit charging and/or data transmission without reliance on a physical connector.

The device 10, 10a further comprises, or comprises a connection to, a temperature sensor 42, pressure sensor 44, and relative humidity sensor 46, to obtain sensor data indicative of environmental conditions in which the device is operating. As will be appreciated, temperature, pressure and relative humidity data may be used to calibrate measurements and/or monitor characteristics of the device 10, 10a.

The light emitters 20, or 20a and 20b, respectively, are provided in the form of an array of LEDs. The LEDs are operable to emit at different wavelengths, and may include UV, visible light, and may also include regions beyond the visible spectrum, including near IR regions, provided the wavelengths are not attenuated by water, and/or not attenuated by the main matrix or liquid-to-be-interrogated, to an extent that makes the wavelengths unsuitable for the measurement. E.g., the light emitters may comprise LEDs emitting at several different wavelengths, e.g. five or six different wavelengths. For instance, the LEDs may emit at 235, 275, 350, 450, and 850 nm, and/or at 255, 275, 375, 450, 545, and 850 nm. In addition, or as an alternative, the light emitters 20, or 20a and 20b, may comprise a broadband emitter. It will be appreciated that the exact wavelength or wavelength region may depend on the type of LED used, and on the type of analytes to be measured. In embodiments, the light emitters comprise both a broadband LED to provide a broadband source, and one or more single (or narrow) wavelength LEDs.

In this manner, the device may be operated to emit specific, narrow/single wavelength emitters for fluorescence measurements, and broadband emitters for absorbance measurements. In combination with a collimator element 21 , 21 a, or 21 b, respectively as described above, it can be achieved that light from different source locations is directed into the same probing volume. In prototype embodiments, it was found that a sensing device using the above-mentioned example of five wavelengths (235, 275, 350, 450, and 850 nm) or six wavelengths (255, 275, 375, 450, 545, and 850 nm) for interrogation, and measuring transmission and fluorescence properties as a pair, each at the different wavelengths sequentially, allows the levels of several analytes, including nitrate, tryptophan-like fluorescence (TLF), fluorescent dissolved organic matter (fDOM), turbidity, chlorophyll, phycocyanin, phosphate, and ammonium to be measured in one measurement cycle. It is believed that using suitable wavelength combinations, the device is able to measure BOD, COD, TOC, DOC, Total Coliforms, E. coli, faecal coliforms, enterococci, as well as certain organic compounds or contamination measurements, such as Oil-in-water, blue-green algae, polycyclic aromatic hydrocarbons (PAH), benzene, optical brightening agents (OBA), Chlorophyll a and b, turbidity, and others.

To provide an illustrative example, tryptophan concentrations may be measured using the following equation: where TLF is a tryptophan concentration (ppb), T is a temperature (°C) value and mes and ref represent measured TLF and reference TLF, respectively, and rho (p) is a correction factor to account for temperature-dependent influences on signal strength. Likewise, correction factors may take into account concentration-depending influences. A calibration curve may use coefficients to correct for other interferences. For instance, for turbidity measurements, regression coefficients are known for different sediment compositions, such as silt, clay, etc.

As will be appreciated, the example provided above is only one of many models and different analytical models may be used for different analytes.

A full measurement cycle, i.e. a measurement cycle using multiple or all LEDs, may be completed in no more than 60 seconds per analyte, and in some configurations in no more than 30 seconds. As will be appreciated, measurement cycles may also take longer, particularly for large numbers of analytes. The analytes listed herein are examples and other analytes may be detected using a different combination of LEDs emitting at different wavelengths, including fewer and more different wavelengths, and different measurement durations. The individual light emitters of an array are able to cover a wide range of wavelengths from the electromagnetic spectrum, similar to a broadband region, however interrogating at specific wavelengths or wavelength regions defined by the controller operating the LEDs. The processing system 40 may individually drive each one of the LEDs of the light emitter array to operate them to emit optical radiation independently of other LEDs. In this manner, the device 10, 10a can, with the use of individual single-wavelength or narrow-band emitters, achieve a multi-wavelength interrogation, while minimising interference or crosstalk from other wavelengths. Likewise, the device 10, 10a is capable of broadband measurements if that is desired, e.g., for absorbance measurements.

Furthermore, as will be appreciated, the processing system 40 may drive each one of the LEDs with different voltage and/or for a different duration of time. The voltage and duration may be selected to balance variations in output power between different LEDs. Likewise, the voltage and duration may be selected according to expected analyte concentrations. For instance, an LED at 450 nm or broadband LED may be used to probe an analyte by absorbance measurement, and may require a relatively higher-powered emission, whereas an LED at 280 nm may be used to prove an analyte expected to emit fluorescence, and may require a relatively lower-powered emission for sufficiently strong excitation.

As will be appreciated, these are only examples and may be modified depending on the type of liquid to be tested, and/or depending on the type of analytes and/or expected concentration ranges to be detected. For instance, a lower-power LED parameter may be used when a relatively higher load of analytes or organisms is expected, whereas a higher-power LED parameter may be used when a relatively lower load of analytes or organisms is expected.

In use, the device 10 may be calibrated against known reference samples, including clean water, and including reference samples comprising a known quantity or concentration of a target analyte. The calibration may be carried out in a dark environment or measurement chamber. Depending on analyte, reference or calibration curves may use two or more calibration points. It was found that calibration may be carried out with reference samples comprising multiple analytes, thereby reducing overall calibration time for multiple samples. A benefit of the device 10, 10a is that it allows samples to be directly taken after optical measurement for analysis by an external reference method. While external reference methods may take considerably longer, sometimes in the region of days, this provides a further mechanism for confirming the accuracy of, and/or degree of correlation between, different measurement protocols.

The capture, storage and analysis of data may be carried out entirely within the device 10, 10a, e.g. by the processing system 40. In such a configuration, the device 10, 10a may be providing as an output a numerical value or table, e.g. as an output to a printer, display, or via a data interface to a handheld device. For instance, and output module may be provided in the form of a software application providing an interface for communication with the device 10, 10a and to display and store output data from the device 10, 10a. The handheld device may be a portable computer, tablet or mobile phone. Likewise, the portable device may be a wearable device or other suitable device. The output may be provided in a form that is interpretable by a human user and/or in a form in which it is interpretable by a processing system such as an autonomous monitoring station. The output may be provided in raw data form, and/or in processed data form, and may be transferred to a remote server for analysis and/or storage. It will be appreciated that the exact manner in which the output is transmitted for interpretation by a user or processing system is not necessarily a requirement of each embodiment of the invention.

As will be appreciated, the data acquired via the spectrometer module 30 and/or the temperature sensor 42, pressure sensor 44, and relative humidity sensor 46, may be recorded together in a data set or data matrix. The data may be analysed using a machine learning model, trained by an algorithm.

Figure 3 shows a method 50 to illustrate an exemplary use scenario or measurement protocol for use of a sensor arrangement such as the device 10 or 10a. In step 52, a sensor arrangement is provided in the form of a self-contained, portable device such as the device 10 or 10a illustrated in Figure 1. The device 10, 10a comprises a sensing volume 14 in the form of a notch or other open passage suitable for providing a passage for a liquid to be tested.

In an optional step 54, the device is calibrated using known reference liquids as calibration samples. Known reference liquids may comprise clean water of a predetermined degree of purity, e.g. reverseosmosis water or de-ionised water. Likewise, reference liquids may comprise one or more target analytes of known concentrations or suitable standard solutions. Similarly, reference liquids may comprise substances known to interfere with target analytes and/or known to be likely to confuse measurements. In this manner, such reference liquids may enable the fine-tuning of measurement parameters to ensure any such ‘undesired’ analytes can be readily discerned from target analytes.

As will be appreciated, depending on the type of sample to be measured, and/or concentrations to be expected, step 54 may not be carried out in all circumstances. For instance, it may be appropriate to calibrate a probe on demand, and/or in monthly or quarterly intervals.

In step 56, the probing end of the device 10, 10a is submerged in liquid to be tested, or an arrangement is provided to allow the liquid to be tested to flow through the sensing volume 14 of the device 10, 10a. The device 10, 10a may be installed using a suitable mount or carrier. The device 10, 10a may be a sensing module to be used with a sensor device, such as a multi-sensor device. As will be appreciated, in some scenarios the entire device 10, 10a may be submerged in a body of water, whereas in other scenarios only its probing end may be submerged. The device 10, 10a may be of a water-proof design tolerating complete submersion so as to be operable in changing water levels.

In step 58, the device 10, 10a is operated to emit optical radiation into the sensing volume. The device 10, 10a is understood to operate as set out above, by operating individual LEDs sequentially to “flash” through different wavelengths, and, alternatively or in addition, to use a broadband source as one of the optical emitters. In this manner, the device 10, 10a probes the volume at several individual wavelengths across the electromagnetic spectrum, in the region from around 200 nm to 1000 nm, as well as a broadband source.

In step 60, the detector arm or arms of the device 10, 10a are used to pass transmitted, scattered and/or fluorescence-emitted light to a spectrometer, such as a common spectrometer module 60, to allow the emissions to be recorded sequentially and using the same detector module.

In an optional step 62, some or all of the data obtained at different measurement angles are used to calibrate respective others of the data. For instance, fluorescence and/or scattering measurements may be calibrated relative to contemporaneous transmission (or absorbance) measurement, and vice versa. As will be appreciated, in this manner, data can be calibrated as a function of wavelength. However, the invention is not necessarily so limited. In some embodiments, absorbance or fluorescence data obtained at one wavelength may be calibrated with reference to absorbance or fluorescence data obtained at one or more other wavelengths. For instance, absorbance measurements obtained using a broadband source may be used to correct fluorescence measurements obtained using a UV source.

An appreciation underlying the embodiments of the invention was that fluorescence and/or absorbance data may be affected by the presence of components that may be exhibiting a different optical behaviour than an analyte of interest. In this manner, data representative of the different optical behaviour can be used to calibrate, or use for error-correction, data relating to an analyte of interest.

In step 64, the data obtained via steps 58 to 60, or via steps 58 to 62, are used to make a determination about the presence or absence, and/or the concentration, respectively, of one or more analytes of interest.

In optional step 66, the device 10, 10a provides an output indicative of the determination made in step 64. The output may be a numerical value. In some embodiments, the output may be provided in the form of a risk level, e.g. “high”, “low”, “safe”, or a colour code such as “green” or “red”, or the like.

The device 10 or 10a may allow a protocol such as the method 50 to be carried out repeatedly, and for practical purposes continuously, over prolonged periods of time. The method 50 may be repeated in pre-determined intervals, e.g. to obtain a measurement every fifteen minutes, hourly, or other appropriate intervals.

The device 10, 10a may be provided in the form of a module for a multi-sensor probe. For instance, the connector 18 may permit the device 10, 10a to be attached to a socket, or to one of several sockets, of a probe. In the case of a multi-sensor probe, some of the processing functionality, and/or some of the sensor functionality, such as that of the temperature sensor 42, the pressure sensor 44, and/or the humidity sensor 46, may be provided by other components or other modules of the multi-sensor probe. Alternatively, or in addition, a module constituting the device 10, 10a may comprise such sensors, integrated with the module. In that case, the device 10, 10a may optionally comprise a data sharing configuration, allowing the device 10, 10a to provide readings from such sensors, such as a temperature sensor 42, pressure sensor 44, or humidity sensor 46, of the device 10, 10a, respectively, to be made available for processing by other sensor modules of the multi-sensor probe.

Water sensors such as the water sensing arrangement described herein are understood to comprise a light shield, or to be part of an assembly providing a light shield, the light shield protecting the sensing volume from external, ambient light. As such, embodiments in the form of a stand-alone device, such as a handheld device, are understood to comprise a light shield. However, as will be appreciated, embodiments provided in the form of a module for use with sensing device may not necessarily comprise an integral light shield, in the understanding that a light shield is provided as part of a device housing. For instance, a module may be designed such that it can be fitted within a light-shielded region of a sensor device. Consequently, it will be appreciated that measurements using a device according to the invention are typically intended to be carried out while the sensing volume is shielded from external light.

Whilst the principle of the invention has been illustrated using exemplary embodiments, it will be understood that the invention is not limited to exemplary embodiments and that the invention may be embodied by other variants defined within the scope of the appended claims.

Claims

CLAIMS:

1 . A sensor arrangement for water measurements, the arrangement comprising a sensing volume for a liquid sample, an optical emitter arrangement, and a detection arrangement, arranged relative to the sensing volume such that optical radiation is detectable by the detection arrangement from at least two different angles relative to the optical emitter arrangement, wherein the detection arrangement comprises a spectrometer to acquire measurements from different wavelengths, to allow recording of spectra for each one of the at least two different angles.

2. The arrangement according to claim 1 , wherein the optical emitter arrangement comprises a first optical emitter and a second optical emitter, each configured to emit optical radiation into the sensing volume, wherein the first optical emitter is arranged to emit into the sensing volume from a different angle than the second optical emitter, relatively to the detection arrangement.

3. The arrangement according to claim 1 or 2, wherein the detection arrangement comprises a first detection arm and a second detection arm, each configured to detect optical radiation from the sensing volume, wherein the first and second detection arms are offset to capture radiation at different angles from the sensing volume.

4. The arrangement according to any one of the preceding claims, wherein at least one detection arm is located opposite at least one optical emitter, relative to the sensing volume, to enable a transmission measurement indicative of absorbance in the sensing volume.

5. The arrangement according to any one of the preceding claims, wherein at least one detection arm and at least one optical emitter are located laterally of each other, relative to the sensing volume, to enable an emission measurement indicative of fluorescence emissions and/or turbidity in the sensing volume.

6. The arrangement according to any one of the preceding claims, comprising two detection arms for one optical emitter, one detection arm opposite the optical emitter, the other orthogonal to the optical emitter.

7. The arrangement according to any one of claims 1 to 5, comprising two optical emitters for one detection arm, one optical emitter opposite the detection arm, the other orthogonal to the detection arm.

8. The arrangement according to any one of the preceding claims, wherein the, or each, optical emitter comprises at least one broadband source.

9. The arrangement according to claim 8, controllable such that different wavelength regions of the broadband source can be operated to emit while blocking other wavelength regions of the broadband source, thereby allowing the arrangement to operate at least some wavelength regions of a broadband source to interrogate the sensing volume sequentially.

10. The arrangement according to any one of the preceding claims, wherein the, or each, optical emitter comprises a plurality of individually activatable emitters, operable to enable the optical emitter to emit at least two different wavelengths or wavelength regions.

11 . The arrangement according to claim 10, controllable such that optical emitters of the plurality can be activated independently of one or more other optical emitters of the plurality, thereby allowing the arrangement to operate at least some of the optical emitters sequentially.

12. The arrangement according to claim 10 or 11 , controllable such that optical emitters of the plurality can be activated independently of one or more other optical emitters of the plurality, thereby allowing the arrangement to drive different optical emitters for different durations of time and/or to drive different optical emitters at different power levels.

13. The arrangement according to any one of the preceding claims, when depending from claim 3, configured to obtain measurements from the first detection arm and from the second detection arm sequentially.

14. The arrangement according to any one of the preceding claims, when depending from claim 2, configured to carry out measurements using the first optical emitter and the second optical emitter sequentially.

15. The arrangement according to any one of the preceding claims, comprising a single spectrometer module to measure light obtained from each detection arm of the detection arrangement.

16. The arrangement according to any one of the preceding claims, comprising a light-guiding arrangement to direct light from two or more different optical emitter elements of an optical emitter to a common interrogation area of the sensing volume.

17. The arrangement according to claim 16, wherein the light-guiding arrangement is provided by a collimator.

18. The arrangement according to any one of the preceding claims, comprising a focusing arrangement for each detection arm of the detector arrangement.

19. The arrangement according to any one of the preceding claims, wherein the sensing volume is provided in the form of an open channel.

20. The arrangement according to any one of the preceding claims, comprising a cleaning mechanism for the sensing volume and/or surfaces defining walls thereof.

21 . The arrangement according to claim 20, wherein the cleaning arrangement comprises at least one of a gas-based cleaning arrangement, a mechanical wiper arrangement, and/or a UV-based arrangement, wherein, optionally, the UV based arrangement is provided by one or more of emitters of the optical emitter arrangement.

22. The arrangement according to any one of the preceding claims, configured to obtain, using the first and second detectors, both absorbance and fluorescence measurements, and to use measurement values from one or both of the absorbance and fluorescence measurements as an input for a calibration of measurements.

23. The arrangement according to any one of the preceding claims, provided in the form of a modular component for use with a sensor device.

24. The arrangement according to any one of the preceding claims, provided as part of a self- contained analysis device.