DE102020110192A1 - Method and device for the luminescence-based measurement of an analyte, independent of the source of interference - Google Patents

Abstract

The invention relates to a method for the luminescence-based measurement of the concentration of an analyte in a fluid, comprising the application of excitation light (10) from a light source (1) to a fluorophore (4) which is in contact with the fluid and which contains a fluorescent material sensitive to the analyte ), by means of a light detector (2), detection of luminescent light (20), which the fluorophore (4) in response to the excitation with the excitation light (10) of the light source (1) and, if necessary, of stray light (30) from stray light sources (5 , 6) emits, and, by means of a controller (3), measuring a response delay (Δ, ΔT), and determining the concentration of the analyte from the measured response delay (Δ, ΔT), using a sequence of individual pulses as the excitation light (10) is, whereby a time interval (T1, T2, T3) of successive individual pulses is chosen randomly or quasi-randomly. The invention further relates to a device for luminescence-based measurement of the analyte concentration according to this method.

Description

The present invention relates to a method and a device for the luminescence-based optical measurement of the concentration of an analyte, in particular oxygen, in a fluid, in particular a gas mixture, with one in contact with the fluid that is sensitive to the analyte, i.e. its fluorescence properties in the presence of the analyte changing, fluorophore is acted upon by excitation light from a light source, which detects luminescent light emitted by means of a light detector in response to the excitation light as well as light from possibly existing interference sources and a delay, in particular a response time delay or a phase shift, is measured by a controller and the concentration of the analyte is determined from this .

The problem of a quick and reliable measurement of the concentration of an analyte in a fluid arises in various areas of science, technology and medicine. For example, when determining the oxygen content in the air we breathe, in the blood or in the exhaust air of an internal combustion engine. In the case of bioreactors, too, monitoring of the supply and / or exhaust air is very important in order to be able to follow and regulate the process or growth parameters and the material balance as precisely as possible.

Luminescence and fluorescence are essentially used synonymously in the following, even if luminescence is actually a broad generic term which, in addition to the fluorescence falling under the more restricted term photoluminescence, also includes other effects with spontaneous photon emission by an excited medium, in which the excitation is not by photons but took place in other ways, for example mechanically (mechanoluminescence), chemically (chemiluminescence) or electrically (electroluminescence).

Luminescence or fluorescence-based gas sensors, such as oxygen sensors, use sensitive fluorescent materials for the respective analyte, i.e. the gas to be detected, in order to measure the analyte concentration of a fluid to be examined, i.e. a gas mixture or a liquid. A fluorescent material emits luminescent light of a second, usually higher (ie lower-energy) wavelength through spontaneous emission of photons after its molecules have been excited by excitation light of a first wavelength or a first wavelength range. This spontaneous emission takes place with a certain delay, which corresponds to the lifetime of the excited states occupied by the excitation light. Both the intensity and the delay of the spontaneous emission, i.e. of the luminescent light, can depend on environmental parameters.

In the case of an oxygen-sensitive fluorescent material, for example, the intensity and delay are dependent on the oxygen content of the material. Oxygen can diffuse into the material from the environment or, conversely, diffuse out of the material into the environment. Intensity and delay can therefore be a measure of the oxygen content in the vicinity of the material.

A determination of the analyte concentration from the delay is much more accurate compared to a determination from the intensity, since the intensity of the luminescent light is caused by several uncontrolled, temporally variable factors, such as the transparency of the fluid in the wavelength ranges involved and possibly a container that houses the fluid or the supply voltage and the aging of the excitation light source.

In addition to oxygen, the luminescence-based measurement is also suitable for determining the concentration of other monatomic gases such as nitrogen (N2) and hydrogen (H2).

Response or delay-based measurement methods according to the state of the art provide for a periodic control of the excitation light source so that it emits a light pulse of a certain duration with periodic intensity variation. A simple, sinusoidal excitation light pulse is often used. The control voltage or also part of the excitation light is compared with detected luminescent light in a comparator of a controller and a phase shift is determined from this, which is a measure of the response delay and thus the analyte concentration sought. Such a method is for example in the publication WO 2004/070367 A1 presented.

In the case of luminescence-based measurements, however, it cannot always be avoided that, in addition to the actual excitation light from the light source, interfering light also reaches the fluorescent material that is sensitive to the analyte. This stray light can come from natural light sources such as the sun or artificial light sources such as room lighting. This interfering light falsifies the detected luminescence light signal both in the case of an intensity measurement, which is already susceptible for other reasons, and in the case of a response time or phase shift measurement.

The published international application WO 2014/095506 A1 describes an optical measuring device with an excitation light source for emitting a periodic excitation signal a first clock frequency and a detector for detecting an optical response signal, wherein a controller filters the response signal with a second clock frequency, which is an even multiple of the first clock frequency. In this way, electronic interference, which act on the light source via supply lines, or interference caused by parasitic effects such as capacitances between the supply lines, is filtered out because these flow in with opposite signs for the two half-periods of the second clock signal and are thus eliminated if they are during a period remain roughly constant over time. In this way, electronic interference on the excitation light source of a luminescence-based measuring device can be avoided, but the negative influence of interference light sources is not eliminated.

The publication font WO 2005/033746 A2 describes a device for measuring the phase shift of luminescent light, in which interfering influences on the measured phase shift, which are caused by the components of the device themselves, are reduced by using a second light source with an emission spectrum in the range of the fluorescent material to calibrate the system immanent, not phase shift caused by the fluorescence is provided. Even this procedure does not help to eliminate the adverse effects of interfering light.

In the absence of an effective method for reducing or avoiding the negative effects of stray light, efforts are made in the prior art to avoid stray light as far as possible. However, this cannot always be fully achieved, for example when a fluid is to be monitored in a transparent container and this container is in an artificially or naturally illuminated laboratory room.

The influence of interfering light with constant intensity on the short time scales of interest, such as that emitted by natural sources of interference such as the sun, can basically be controlled by a high-pass filter, which filters out the DC voltage component of the detected luminescence signal, or a noise measurement, i.e. a measurement without excitation light , eliminate. Artificial light sources whose light contains periodic modulation are therefore essentially problematic. In the case of a light source fed by the power grid, this can be, for example, the frequency of the AC mains voltage, for example 50 Hz in Germany. In addition, many use artificial light sources, such as the fluorescent tubes that are particularly widespread in the commercial sector or even more modern LED light sources, ballasts, which impress modulations in the kilohertz range on the emitted light. Unlike the mains frequency, the modulation frequencies occurring in the ballasts are not uniform, but differ from light source to light source.

As long as the modulation frequency of the stray light is known, its influence can in principle be taken into account and reduced or eliminated. One possible strategy would therefore be to determine the modulation frequencies of all artificial light sources present at the location of a luminescence-based analyte measurement and to take them into account when evaluating the detected luminescence signal, for example by filtering the signal in the corresponding areas and of course choosing a frequency of the periodic excitation light that differs from differs from all sources.

However, this procedure is very complex and would have to be repeated before each measurement or at least after each replacement of a light source, since the modulation frequencies that occur could have changed.

The object of the present invention is therefore to develop a method and a device which allows a reliable and largely interference source-independent luminescence-based determination of the concentration of an analyte in a fluid.

This object is achieved by a method according to one of claims 1-7 and a device according to one of claims 8-10.

According to the method according to the invention for luminescence-based measurement of the concentration of an analyte in a fluid, a fluorophore in contact with the fluid, which contains a fluorescent material sensitive to the analyte, is exposed to excitation light from a light source, and then by means of a light detector, luminescence light which the fluorophore in response to the excitation with the excitation light from the light source and possibly interfering light from interfering light sources, it is detected, a response delay is measured by means of a controller and the concentration of the analyte is determined therefrom, a sequence of individual pulses being used as the excitation light, with a time interval of successive individual pulses is chosen randomly or quasi-randomly.

The device according to the invention for luminescence-based analyte concentration measurement comprises a light source which can emit excitation light in a first wavelength range, a fluorophore which contains a fluorescent material that is sensitive to the analyte and is arranged so that the fluorescent material in is in direct contact with the fluid and can be exposed to the excitation light emitted by the light source, the fluorophore then emitting luminescent light in a second wavelength range in response to the excitation light and, if necessary, interference light from interference sources, the intensity of the luminescence light being dependent on an intensity of the excitation light and the oxygen content of the fluid, and a response delay of the luminescent light is dependent on the content of the analyte in the fluid but is essentially independent of the intensity of the excitation light, a light detector which can detect at least light within the second wavelength range and a detected one Outputs an analog detector signal representing light intensity, in particular proportional thereto, and a control which controls the light source and, from the signal of the light detector, an ana representing the concentration of the analyte in the fluid derives loges or digital measurement signal, the control deriving the concentration of the analyte from a delay, in particular a response time delay or a phase shift of the luminescent light, the control being prepared to emit excitation light by means of the light source in the form of a sequence of short individual light pulses, with a temporal Distance of successive individual pulses is chosen randomly or quasi-randomly.

With the method according to the invention and the device according to the invention, absolute analyte concentrations can be determined directly. If a relative proportion is also to be determined, a desired value characterizing the total fluid, such as its total pressure or total density (mass density or molar density, etc.), would have to be determined in a manner known per se by additional, simultaneous measurements, and this determined the value here Relative to the absolute value characterizing the analyte concentration, if necessary after previous unit conversion.

The main innovation compared to the known luminescence-based measurement methods and devices is that instead of a sinusoidal or otherwise periodic excitation light pulse, a sequence of individual pulses is used, with the individual light pulses having a random or quasi-random time interval from one another.

In this way, they differ fundamentally from that produced by light, which the fluorescent material emits as a result of the excitation by interfering light sources. This is either periodic itself, for example in the case of artificial light, which has modulations, i.e. intensity variations with the excitation voltage frequency used, or indeed aperiodic, such as sunlight, but in a different way than the excitation light. As mentioned above, modulations in the excitation voltage can result from the use of a supply voltage with a certain frequency, e.g. 50 Hz mains voltage, or a ballast to generate the supply voltage of the light source, such as fluorescent tubes or LED lamps.

It is essential in the method according to the invention that the time intervals between the individual pulses are chosen randomly or quasi-randomly, but are known when evaluating the detected luminescent light. In this way, when evaluating the detected luminescent light, such intensity changes which are due to the excitation light pulses can be distinguished from those which are due to the interfering light.

For example, the detected signal can be evaluated at the times or time windows corresponding to the pulse intervals. Periodic or non-periodic interfering signals with a different random pattern than the one selected are thereby eliminated. The probability that an aperiodic source of interference causes an interference signal rectified to the excitation signal for several consecutive of the randomly selected measurement times tends to approach zero with the number of measurement times.

The time intervals can be chosen genuinely randomly, for example by means of a quantum random generator. However, this is not absolutely necessary in order to achieve the goal set here, the elimination of interfering light influences, and pulse intervals / measurement times selected quasi-randomly are completely sufficient. Numbers are called quasi-random, which are calculated with the help of a more or less complex formula, i.e. determined deterministically and are therefore actually not random, but have certain properties of real random numbers, such as consistency with a certain probability distribution.

The measuring method according to the invention suppresses or even completely eliminates the influence of interfering light on the luminescence-based concentration measurement in a surprisingly simple but effective manner. In the case of the use of quasi-randomly selected time intervals, the method according to the invention can also be retrofitted in existing measuring devices, provided that they include a programmable, for example microcontroller-controlled, control and their excitation light source is capable of emitting individual pulses with variably changeable pulse intervals. All that is necessary for this is a software change that controls the activation of the excitation light source in single-pulse mode from the controller provides predetermined times, the control times being selected according to a more or less complex quasi-random formula.

Advantageous further developments of the present invention, which can be implemented individually or in combination, provided that they are not obviously mutually exclusive, will be briefly presented below.

In order to facilitate the assignment of a detected luminescence light pulse to a specific excitation light pulse, the time interval between successive individual pulses is preferably selected to be greater, as is the response time delay of the received luminescence light.

In particular, the individual pulse spacing, that is to say the time spacing between adjacent individual pulses of the excitation light, is selected between a minimum pulse spacing and a maximum pulse spacing. The minimum pulse interval is preferably between 0.1 and 1 ms, particularly preferably 0.5 ms, and the maximum pulse interval between 1 and 10 ms, particularly preferably 2 ms. Within the interval between the minimum and maximum pulse spacing, the pulse spacings are preferably evenly distributed or are selected such that shorter time intervals are preferred.

The pulse intervals can be selected by a random generator, for example integrated into the control of the device according to the invention, which can generate either real random numbers or also quasi-random numbers.

This random generator can be a separate hardware module which is integrated into the controller or at least has a data connection with it. Alternatively, this random number generator is a software module and part of control software for the measuring device according to the invention.

wobei i eine laufende Nummer des Einzelpulses, s ein einmalig oder auch periodisch neugewählter Startwert, und p und q (große) Primzahlen sind. Diese Formel liefert gleichverteilte quasizufällige Pulsabstände aus dem Interval zwischen 0 und q-1, sofern nur ganzzahlige Werte eingesetzt werden, bzw. dem Intervall [0, q) sofern für Ti und s auch rationale Werte zugelassen sind. Sofern gewünscht ist, dass die Pulsabstände T_i dzwischen eine minimalen Abstand T_min und einem maximalen Abstand Tmax liegen, müsste der nach obiger Formel ermittelte Wert noch nach folgender Formel korrigiert werden: $${\text{T'}}_{\text{i}}={\text{T}}_{\text{min}}+\left({\text{T}}_{\text{max}}-{\text{T}}_{\text{min}}\right)/{\text{q}}^{\ast }{\text{T}}_{\text{i}}\text{.}$$

The determination of the pulse intervals between adjacent individual pulses can be carried out in embodiments of the method according to the invention and the device according to the invention using the formula $${\text{T}}_{\text{i}}={\text{p}}^{\ast }\left({\text{T}}_{\text{i-1}}+\text{s}\right)\text{Mod q}$$

where i is a running number of the single pulse, s is a one-time or periodically newly selected start value, and p and q are (large) prime numbers. This formula provides uniformly distributed, quasi-random pulse intervals from the interval between 0 and q-1, if only integer values are used, or the interval [0, q) if rational values are also permitted for Ti and s. If it is desired that the pulse intervals T _i d lie between a minimum distance T _min and a maximum distance Tmax, the value determined using the above formula would have to be corrected using the following formula: $${\text{T '}}_{\text{i}}={\text{T}}_{\text{min}}+\left({\text{T}}_{\text{Max}}-{\text{T}}_{\text{min}}\right)/{\text{q}}^{\ast }{\text{T}}_{\text{i}}\text{.}$$

However, the invention is not restricted to a specific quasi-random number. Other formulas known to the person skilled in the art or devised in the future can be used just as well.

The pulse shape, that is to say the shape of the envelope of the intensity curve of the individual pulses, is basically arbitrary within the scope of the invention, as long as a clear temporal resolution is guaranteed in the detector. For example, each pulse can also have several intensity maxima, the response delay between corresponding maxima, e.g. between the first maximum of the excitation pulse and the first maximum of the response pulse, being measured. However, preference is given to using individual pulses with a rectangular, sawtooth-shaped, Lorenz-shaped or Gaussian-shaped intensity curve, since these allow a sharp temporal resolution of the intensity maximum or the rising pulse edge and thus a more precise determination of the response time delay of the luminescent light.

For preferred embodiments of the method according to the invention, it is proposed to emit short excitation light pulses with a duration between 0.1 and 10 microseconds, in particular about 0.3-0.5, particularly preferably 0.4 microseconds. Any light source which can be controlled with the desired repetition rate and which emits light in a wavelength range in which the fluorescent material is sensitive can be used as the excitation light source. However, a laser diode is preferably used as the excitation light source.

Further details, advantages and features of the present invention emerge from the exemplary embodiments explained in more detail below with reference to the figures. These are only intended to illustrate the invention and in no way limit its generality.

• 1: in zwei Teilfiguren eine schematische Darstellung eines mit periodischen Anregungspulsen arbeitenden Messverfahrens gemäß dem Stand der Technik.
• 2: in zwei Teilfiguren, eine schematische Darstellung des Erfindungsgemäßen Messverfahrens, welches zufällig oder quasi-zufällig verzögerter Einzelpulse verwendet.

Show it:

• 1 : In two sub-figures, a schematic representation of a measurement method according to the prior art that works with periodic excitation pulses.
• 2 : in two sub-figures, a schematic representation of the measuring method according to the invention, which uses randomly or quasi-randomly delayed individual pulses.

In 1 a known measuring method is shown schematically.

An excitation light source 1 is controlled by a controller 3 controlled in such a way that it emits a periodic, here sinusoidal, excitation light pulse 10 emits which on a fluorescent, for the analyte to be measured sensitive material containing fluorophore 4th meets and this to emit luminescent light 20th , 20 ' stimulates. The intensity and response delay of the luminescent light are dependent on the concentration of the analyte sought. By a light detector 2 becomes the luminescent light 20th , 20 ' detected and the signal from the detector 2 evaluated by the control.

In the absence of interfering light sources, the luminescence response of the fluorophore is also periodic and in its shape with the excitation light pulse 10 matching light pulse 20 ' . When evaluating the signal from the detector 2 can control 3 the phase shift Δ ' determine which is a measure of the analyte concentration sought.

In addition to the excitation light 10 becomes the fluorophore 4th but also from stray light 50 a natural source of interfering light 5 and stray light 60 an artificial source of interfering light 6th met. The luminescent light emitted without interfering light 20 ' therefore differs significantly from the actual luminescent light, also with regard to the phase position measured here 20th showing the fluorophore under the influence of the sum of excitation light 10 , and natural and artificial stray light 50 , 60 sends out. The one from the controller 3 determined phase shift Δ therefore deviates from the correct phase shift that would result without interfering light Δ ' from, as shown in the partial figure B schematically. In addition, due to the influence of interfering light, there is no longer a fixed phase position, as is also indicated in part B. The measured value Δ changes over time in an unpredictable way.

These disadvantages of luminescence-based analyte concentration measurements according to the prior art are advantageously avoided by the method according to the invention and the device according to the invention.

The mode of operation of the invention is shown in the two sub-figures of 2 which which the 1 are ajar, illustrated schematically. The basic structure of the device, with an excitation light source 1 which through a controller 3 is controlled, and a light detector 2 to detect the luminescent light emitted by the fluorophore 20th respectively. 20 ' and its evaluation by the controller 3 , is similar to the one in Figure 1 illustrated structure of known devices. The characteristic difference of the solution according to the invention lies in the control of the light source 1 . Instead of a periodic excitation light pulse, this consists of the light source 1 emitted excitation light 10 from a sequence of individual pulses, here rectangular pulses, which are not periodic, but at random or quasi-random time intervals T1 , T2 , T3 , ... are sent out.

Through this, the control 3 when evaluating the signal from the light detector 2 as known available random or quasi-random pulse intervals T1 , T2 , T3 can control 3 on the excitation light 10 decreasing intensity changes in the actually received luminescent light 20th differ from those that affect the influence of natural stray light 50 the interfering light source 5 or artificial stray light 60 the interfering light source 6th go back. For this purpose, the controller can use the known ones for controlling the light source 1 Take into account the pulse intervals used and the luminescent light 20th only at times predetermined by these pulse intervals or within time windows predetermined by these intervals, within which the luminescence response of the fluorophore to a specific, comparatively short, individual excitation pulse is to be expected.

The method according to the invention ensures that the actual influence of the interfering light 50 , 60 containing luminescent light determined response time delay ΔT essentially that of an ideal luminescent light 20 ' , which is the fluorophore 4th without stray light 50 , 60 would send out, determined undisturbed response time delay ΔT ' is equivalent to. For the sake of clarity, this is the ideal luminescent light 20 ' in both sub-figures A and B shown as negative rectangular pulses, whereas the actual luminescent light 20th , which is intended to illustrate the influence of interfering light, as essentially positive rectangular pulses superimposed with natural interfering light 50 incidental or constant and from artificial stray light 60 originating periodic variatons is shown. The method according to the invention and the device implementing it thus solve, in a surprisingly simple manner, the set object of enabling an interfering light-dependent luminescence-based analyte concentration measurement.

In order to determine the quasi-random pulse intervals, the control includes 3 a random generator 31 which can be implemented as a separate hardware module or simply in the form of a software module as part of the control software.

Here is the pulse length of the square-wave pulses shown and the pulse intervals T1 , T2 , T3 adjacent pulses not to scale. In preferred embodiments, the pulse length compared to the pulse intervals is significantly shorter than it appears here. Likewise, it cannot be seen in the figure that, in preferred embodiments, the pulse intervals are selected within an interval between a minimum and a maximum pulse interval. The minimum pulse spacing is preferably selected to be higher than the expected response delay ΔT of fluorophore. This ensures that the response to a pulse has always arrived before the next pulse is sent out. In principle, a measurement would also be possible with overlapping pulses, but the described preferred choice facilitates the assignment of the luminescence response to the individual excitation pulses.

List of reference symbols

1

Excitation light source

10

Excitation light

2

Light detector

20th

Luminescent light under the influence of interfering light

20 '

Luminescent light without the influence of interfering light

3

steering

31

Random generator

4th

Fluorophore

5

natural source of interfering light

50

by 5 stray light emitted

6th

artificial interfering light source

60

by 6 stray light emitted

Δ

Phase shift determined with stray light

Δ '

phase shift determined without interfering light

ΔT

Response delay determined with interference light

ΔT '

Response delay determined without interfering light

T1, T2, T3

Pulse intervals

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• WO 2004/070367 A1 [0008]
• WO 2014/095506 A1 [0010]
• WO 2005/033746 A2 [0011]

Claims (10)

A method for luminescence-based measurement of the concentration of an analyte in a fluid, comprising • applying excitation light (10) from a light source (1) to a fluorophore (4) which is in contact with the fluid and which contains a fluorescent material sensitive to the analyte a light detector (2), detection of luminescent light (20, 20 '), which the fluorophore (4) in response to the excitation with the excitation light (10) and, if necessary, of interfering light (50, 60) emitted by interfering light sources (5, 6) ), emits, and • by means of a controller (3), measuring a delay such as a response time delay (ΔT) or a phase shift (Δ), and determining the concentration of the analyte from the measured delay (Δ, ΔT), characterized in that a sequence of individual pulses is used as the excitation light (10), a time interval (T1, T2, T3) between successive individual pulses being selected randomly or quasi-randomly. Procedure according to Claim 1 , characterized in that the time interval (T1, T2, T3) of successive individual pulses is selected in an interval between a minimum pulse interval and a maximum pulse interval. Procedure according to Claim 2 , characterized in that the time interval (T1, T2, T3) in the interval • is chosen to be uniformly distributed, or, • shorter intervals are preferably chosen. Procedure according to Claim 2 or 3 , characterized in that the minimum pulse interval between 0.1 and 1 ms, in particular 0.5 ms, and / or the maximum pulse interval between 1 ms and 10 ms, in particular 2 ms, is selected. Method according to one of the preceding claims, characterized in that the time interval between successive individual pulses is selected by means of a random generator (31). Method according to one of the preceding claims, characterized in that the time interval between successive individual pulses is quasi-randomly using the formula $${\text{T}}_{\text{i}}={\text{p}}^{\ast }\left({\text{T}}_{\text{i-1}}+\text{s}\right)\text{Mod q}$$

where i is a running number of the individual pulse, s is a start value, and p and q are prime numbers. Method according to one of the preceding claims, characterized in that the individual pulses generated by the light source (1) • a rectangular, sawtooth-shaped, Lorenz-shaped or Gaussian-shaped intensity curve, and / or • a pulse duration of between 0.1 and 10 microseconds, in particular 0.4 Microseconds. Device for luminescence-based measurement of the concentration of an analyte in a fluid, comprising - a light source (1) which can emit excitation light (10) in a first wavelength range, - a fluorophore (4) which contains a fluorescent material sensitive to the analyte and so on is arranged so that the fluorescent material is in direct contact with the fluid and can be exposed to the excitation light emitted by the light source (1), the fluorophore (4) thereupon as a response to the excitation light (10) and possibly interfering light (50) , 60) emits luminescent light (20, 20 ') from interference sources (5, 6) in a second wavelength range, where ◯ an intensity of the luminescent light (20, 20') depends on an intensity of the excitation light (10) and the oxygen content of the fluid , and ◯ a delay such as a response time delay (ΔT) or a phase shift (Δ) of the luminescent light depends on the content de s analytes in the fluid, however, are essentially independent of the intensity of the excitation light (10), - a light detector (2) which can detect at least light within the second wavelength range and which outputs an analog detector signal that represents a detected light intensity, in particular that is proportional to it, and - a controller (3) which controls the light source (1), from the signal of the light detector (2) determines the delay (Δ, ΔT) of the luminescent light (20, 20 ') and from this determines the concentration of the analyte in the fluid representing analog or digital measurement signal, characterized in that the controller (3) is prepared to emit excitation light (10) in the form of a sequence of individual light pulses by means of the light source (1), a time interval (T1, T2, T3) of successive individual pulses is chosen randomly or quasi-randomly. Device according to Claim 8 , characterized in that the controller (3) comprises a random generator (31) for determining the time interval between successive individual pulses. Device according to Claim 9 , characterized in that the random generator (31) quasi-random pulse intervals using the formula $${\text{T}}_{\text{i}}={\text{p}}^{\ast }\left({\text{T}}_{\text{i-1}}+\text{s}\right)\text{Mod q}$$

where i is a running number of the single pulse, s is a start value, and p and q are prime numbers.

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