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    • 专利摘要:
    Device for measuring nanoparticles (1) in a liquid (2), comprising a light source (3), a channel (4) for receiving the liquid (2), the channel (4) being at least partially separated from the light source (3). permeable to light and having a channel height (5), the apparatus further comprising an optical assembly (6) and a two-dimensional detector (17) for receiving a series of images generated by the optical assembly (6), the light source (3), the channel (4) and the optical assembly (6) are in a dark field arrangement to transmit light emitted by the light source (3) and scattered at the nanoparticles (1) through the optical assembly (6) to the detector (17 ), wherein positions of diffraction patterns of the nanoparticles (1) scattered light (21) on the detector (17) can be determined. In order to enable the determination of long trajectories (26, 27) of the nanoparticles (1), the channel height (5) and the optical structure (6) are designed such that the depth of field DOF of the optical structure (6) is at least 10%, preferably at least 30% of the channel height (5).
    公开号:AT515416A4
    申请号:T50221/2014
    申请日:2014-03-26
    公开日:2015-09-15
    发明作者:Christoph Dipl Ing Haiden；Martin Dipl Ing Dr Jech；Michael Dipl Ing Dr Techn Vellekoop；Thomas Dr Wopelka
    申请人:Ac2T Res Gmbh；
    IPC主号:
    专利说明:

    DEVICE FOR MEASURING NANOPARTICLES AND METHOD FOR DETERMINING THE DIAMETERS OF NANOPARTICLES IN ONE
    LIQUID
    FIELD OF THE INVENTION
    The present invention relates to a device for measuring nanoparticles in a liquid, comprising a light source, a channel for receiving the liquid, wherein the channel is at least partially transparent to light emitted by the light source and having a channel height, the device further comprising a optical structure and a two-dimensional detector for receiving a series of images generated by the optical structure, wherein the light source, the channel and the optical structure are in a dark field arrangement to light, which is emitted by the light source and scattered on the nanoparticles, through the optical Recording structure with the detector, wherein positions of diffraction patterns of the scattered at the nanoparticles light can be determined on the detector.
    The present invention also relates to a method for determining the diameters of nanoparticles in a liquid.
    Finally, the invention relates to the use of the device according to the invention.
    STATE OF THE ART
    To determine the size of particles suspended in liquids, it is known to measure their Brownian motion. In this case, particle trajectories are used to determine the trajectories of the particles, for example, in that the particles are imaged magnified directly with a microscope and a series of images or a video of the two-dimensional image generated by the microscope is recorded. In this way, however, only particles larger than the wavelength of light used can be measured.
    For smaller particles, such as nanoparticles, especially nanoparticles, whose diameters range from 10 nm to 200 nm, a dark field array can be used. Here, only light emitted by a light source and scattered on the nanoparticles is captured and magnified by the microscope. That instead of the direct images of the particles, only their diffraction images are magnified with the microscope. Because the particle size is much smaller than the wavelength of light used, the diffraction pattern of each nanoparticle consists of its point spread function (sometimes referred to as a point spreading function), which appears essentially as diffraction slices (also referred to as Airy slices). The trajectory of each particle corresponds to the trace of the moving center of gravity of the associated diffraction disk.
    Thus, for each trajectory, the mean displacement square can be calculated as a function of the time interval (also referred to as "time lag") of two considered nanoparticle positions or images. By fitting a straight line one obtains the diffusion coefficient for the diffusion of the respective nanoparticle in two dimensions. Knowledge of the viscosity of the liquid allows the calculation of a diameter of the nanoparticle using the Stokes-Einstein equation. This is its hydrodynamic diameter, which can generally be slightly larger than the diameter of the free nanoparticle, since the nanoparticle in the liquid is e.g. may be surrounded by a solvation shell.
    The problem with the above-described method is that the length of the receivable trajectories is greatly limited in practice, since the diffusion of the nanoparticles is actually not limited to two dimensions, but also takes place in a third dimension. As a result, each nanoparticle stays only a limited amount of time in that region of the liquid that is focused in the microscope. If the respective nanoparticle leaves this area, its scattered image appears blurred and washed out and finally blurs in the background, so that a position determination or a determination of the center of gravity of the diffraction pattern of the nanoparticle is impossible. That The diffraction pattern of the respective nanoparticle is typically sufficiently recognizable for evaluation in a maximum of several ten successive images for an evaluation. Correspondingly short is the associated evaluable trajectory, which can be used for the calculation of the mean displacement square, which in turn has a negative effect on the error of the determined diameter of the nanoparticle.
    OBJECT OF THE INVENTION
    It is therefore an object of the present invention to provide a device and a method which avoid the above-mentioned disadvantage and allow the determination of long trajectories in order to be able to determine the diameter of nanoparticles in liquids with particular accuracy.
    PRESENTATION OF THE INVENTION
    In order to solve the stated problem of determining the diameter of nanoparticles, in particular in the range from 10 nm to 200 nm, in a liquid, the liquid is measured in a channel with a certain channel height. The channel is transparent to at least light emitted from a light source. The light is scattered at the nanoparticles, and only the scattered light is recorded by means of an optical structure and a downstream two-dimensional detector whose sensitive surface can be divided into pixels and which can be embodied in particular as an image sensor. The optical structure can be a system comprising mirrors, lenses (in particular comprising a lens), filters, etc. In particular, the optical structure can be realized by a microscope. That the optical assembly or microscope generally produces an enlarged image containing the diffraction patterns of the nanoparticles, each diffraction image being essentially a diffraction disk. By contrast, light which comes directly from the light source or is reflected speculatively does not get into the optical structure or into the microscope and accordingly is not detected at the detector or image sensor. In other words, there is a dark field arrangement of the light source, the channel or the liquid in the channel and the optical structure.
    In order to be able to follow position changes or trajectories of the nanoparticles, it is important that the position of each diffraction image or diffraction disk in the recorded image can be clearly determined, for example by determining its outline and / or its center of gravity. For this purpose, the magnification of the optical structure and the pixel density of the detector must be coordinated so that a clear determination of the position of each diffraction image is meaningfully possible.
    In practice, if the center of gravity of each diffraction image is to be determined, it will be sufficient if each diffraction disk appears so large on the detector that it is imaged at least at 2 * 2 pixels. That the pixels of the detector are arranged along two directions, in the following x and y, and thus cover an area, whereby the diffraction disks are enlarged so large by the optical structure or the pixels are so small that two pixels in the x-direction and two pixels in the y-direction are at least partially covered by the respective diffraction disc. The position of the center of gravity of each diffraction disc is then determinable with an accuracy of less than one pixel, correspondingly each center of gravity can be assigned an x and a y coordinate. In the event that the pixels of the detector are so small that no magnification is needed, the optical structure can dispense with magnifying elements and e.g. essentially consist of a hole through which the scattered light enters the detector.
    In order to determine trajectories of the nanoparticles, a series of images are taken and the positions of the diffraction patterns / diffraction slices of the nanoparticles in each image are determined so that a position can be assigned to each diffraction image in each image. The idea underlying the invention is to match the depth of field DOF of the optical structure and the channel height to one another such that a sufficiently sharp image takes place over the entire channel height. Accordingly, the scattering pattern of a nanoparticle always appears sufficiently sharp, even if the nanoparticle diffuses in the direction of the channel height or moves in the direction of the channel height. That the diffraction image / diffraction disk or its position is always determinable for the nanoparticle in the series of images, as long as the nanoparticle does not move laterally out of the field of view, i. until either no more light is scattered on this nanoparticle or the light scattered on this nanoparticle no longer enters the optical structure.
    In elaborate test series it could be determined that a sufficient depth of field DOF is given, if this amounts to at least 10% of the channel height. In this case, although there may be a slight blurring of the diffraction patterns of the nanoparticles, the positions of the diffraction images, in particular their focal points, can still be determined. Preferably, the depth of field DOF should be at least 30% of the channel height. In this case, the diffraction images remain practically completely sharp and the determination of the positions of the diffraction images, in particular their focal points, is possible very precisely.
    Therefore, in a device for measuring nanoparticles in a liquid, comprising a light source, a channel for receiving the liquid, the channel being permeable, at least in sections, to light emitted by the light source and having a channel height, the device further comprising an optical assembly and a two-dimensional detector for taking a series of images generated by the optical structure, wherein the light source, the channel and the optical structure are in a dark field arrangement to transmit light emitted from the light source and scattered on the nanoparticles through the optical structure According to the invention, the channel height and the optical structure are designed such that the depth of field DOF of the optical structure is at least 10%, preferably at least 30% of the optical depth Kan alhöhe.
    The depth of field DOF of the optical structure can be influenced, in particular in the case of a microscope, by a suitable choice of an objective of the microscope, the depth of field in particular having the numerical aperture NA having the following formula
    with λ the wavelength of the light used. That By decreasing the numerical aperture, the depth of field DOF can be increased. However, as described above, it should be noted that the magnification always remains so great that the positions, preferably the centroids, of the diffraction patterns of the nanoparticles can be determined sufficiently well at the detector.
    Accordingly, in a method for determining the diameters of nanoparticles in a liquid, it is provided according to the invention that the method comprises the following steps: taking a series of images by means of a device according to the invention; - Determining the positions of the diffraction images of the nanoparticles in the images; Determination of the trajectories of the nanoparticles according to the positions of the associated diffraction images in the images; Determination of diffusion coefficients D of the nanoparticles from their trajectories; Calculation of the diameter d of each nanoparticle (1) by means of the Stokes-Einstein equation
    with kB of the Boltzmann constant, T the temperature in Kelvin and η the viscosity of the liquid.
    A common method for determining the diffusion coefficient for a nanoparticle is the
    Calculation of the mean displacement square MSD (x) as a function of the time interval x between the observed images for the trajectory of the nanoparticle. That in the series of images, two successive images have a temporal distance of Et. For example, if the image sensor of a camera whose take-up rate is 25 frames per second is used as the detector, then Et = 0.04 s. The time interval between two viewed images must then be an integer multiple n of this value, i.
    Conveniently, therefore, MSD (n) is calculated:
    with Xi / yi of the x / y coordinate of the center of gravity in the i-th image.
    MSD (n = 1) then corresponds to MSD
    Etc.
    Then, adaptation of a function occurs in an initial region of MSD (x), preferably at least three of the first ten points of MSD (x), more preferably the second, third, fourth and fifth points of MSD (x). In the simplest case, in the presence of undisturbed diffusion, the function to be fitted is a straight line, the slope of the line corresponding to 2 * dim * D, with dim of the dimensionality and D the diffusion coefficient.
    Other functions are e.g. necessary in the presence of anomalous diffusion, such as when an interaction of the nanoparticles with their environment affects the diffusion of the nanoparticles. This can be modeled for example by an exponent CC with
    where α < 1 describes sub-diffusion, while CC > 1 describes super-diffusion.
    Another example of a deviation of MSD (x) from a straight line is when the normal diffusion is superposed by a velocity v flow. In this case, the relationship changes
    As said, very long trajectories can be determined in this way, with which the precision in the calculation of the size of the nanoparticles can be increased. In particular, only very long trajectories can be deliberately taken into account in the evaluation in order to deliberately keep the resulting error in the calculated diameters of the nanoparticles small. The length of the trajectories does not necessarily mean the absolute time duration over which the trajectories extend, but the number of support points or nanoparticle positions of the trajectories. That For example, a trajectory resulting from determining the centroid of the diffractive slice of a nanoparticle in 567 consecutive images of a series of images is 567 images or (nanoparticle) positions long - with 566 steps. The absolute time length of the trajectory results from the multiplication of the number of steps with Et. Therefore, it is provided in a preferred embodiment of the method according to the invention that for determining the diffusion coefficient D trajectories having a length of at least 200 positions, preferably of at least 500 positions, more preferably of at least 1000 positions are used, wherein for determining the diffusion coefficient D preferably only Trajectories with a length of at least 200 positions, preferably of at least 500 positions, more preferably of at least 1000 positions are used. It is understood that the
    Total number of images in the recorded series can be significantly larger than the length of the trajectories used.
    The thus achievable high precision in the calculation of the diameter of the nanoparticles also makes it possible to determine a distribution of the diameter and also close to each other lying maxima in the distribution - also known as peaks - dissolve with sufficient accuracy. Consequently, e.g. in a histogram of the frequency distribution of the determined diameter of the nanoparticles resulting maxima clearly distinguishable from each other and determinable. The latter can be done by adapting a suitable function to the respective peak of the frequency distribution. Compared to existing methods, the measurement of polydispersed nanoparticles can be decisively improved within one measurement. Accordingly, it is provided in a preferred embodiment of the method according to the invention that a distribution of the calculated diameter d is determined.
    The above-described evaluation, in particular the determination of the trajectories, is ideally carried out automatically, which is why it is provided in a preferred embodiment of the device according to the invention that a computer is provided to automatically determine trajectories of the nanoparticles from the series of images. For nanoparticles with a diameter of 10 nm to 200 nm, the channel heights can be chosen correspondingly small in order to achieve a sufficiently large depth of field at a sufficiently large magnification and at the same time still exclude strong interactions with channel walls. Therefore, it is provided in a preferred embodiment of the device according to the invention that the channel height is less than or equal to 30 pm, preferably less than or equal to 20 pm, more preferably less than or equal to 10 pm. Accordingly, the minimum depth of field DOF for these embodiments is 3 pm, 2 pm and 1 pm, respectively. The use of such low channel heights also has the advantage that liquids which are generally non-transparent, e.g. Motor oil, can still be irradiated.
    For a channel having a channel height of 10 pm, as an optical structure, e.g. a microscope with a lens with numerical aperture NA = 0.45 are used, whereby at a wavelength λ = 532 nm a sufficient depth of field DOF of about 1.3 pm results. Even more accurate results are achieved with the same channel height and light of the same wavelength, for example with a microscope with a lens with numerical aperture NA = 0.3, the depth of field DOF is about 3 pm.
    If the channel height in relation to the size of the nanoparticles becomes so small that an interaction of the nanoparticles with the channel walls is compulsory, the device according to the invention as well as the method according to the invention can in principle still be used. In the evaluation, an excessively large diameter for the nanoparticle diameter is then generally obtained, which, however, can be corrected by multiplication with a suitable correction factor.
    In order to realize a particularly simple construction, it is provided in a preferred embodiment of the device according to the invention that the light source is arranged on the same side of the channel as the optical structure.
    It should be noted that it is also conceivable to simultaneously use at least one further optical structure and a further detector. The further optical structure and the further detector can be arranged on the other side of the channel, i. the optical structure and the detector opposite.
    For optimum intensity, best results are achieved when the light hits the channel at a relatively steep angle to minimize channel reflections. On the other hand, the existing or available distance between the channel and the optical structure must be taken into account. Decisive here is that the angle is selected so that no light can pass directly or by specular reflection in the optical structure, but only by scattering at the nanoparticles. Good results have been found in practice, when the light emitted by the light source with an optical axis of the optical structure at an angle of at least 60 °, preferably at least 70 ° includes. The optical axis is preferably normal to a surface of the channel.
    In order to realize a very simple construction, it is provided in a preferred embodiment of the device according to the invention that at least one laser is provided as the light source. The use of lasers also allows a very precise choice of the wavelength of light. Several different lasers also make it possible to provide light of different wavelengths.
    Since high light intensities are necessary for the detection of nanoparticles, stability problems with laser sources with 100 mW or more can occasionally occur. When lasers are used, e.g. due to the finite roughness of the walls of the channel, speckle patterns in the scattered light, which are an undesirable background signal for the diffraction patterns of the nanoparticles. When these speckle patterns change while taking a series of images, it is difficult to distinguish the diffraction patterns of the nanoparticles from the changing background. Changing
    Speckle patterns may be e.g. caused by minor instabilities of the laser light source. Light-emitting diodes, in particular so-called high-power LEDs, can sometimes work more stably at very high intensities. In addition, when using light-emitting diodes which fundamentally do not emit coherent light, in principle no speckle patterns occur, which has an advantageous effect with regard to the background of the diffraction patterns of the nanoparticles. It is therefore provided in a preferred embodiment of the device according to the invention that at least one light-emitting diode is provided as the light source. Light emitting diodes also offer the possibility to select certain wavelengths relatively precisely, although this is not as precise as possible with lasers. Different wavelengths can in turn be realized with several different light-emitting diodes. Alternatively or additionally, it would also be possible to use light-emitting diodes which emit substantially white light.
    The use of different wavelengths of light in principle allows spectroscopic measurements. For example, by measuring the scattering intensity of the nanoparticles at several wavelengths and already determined diameter of the nanoparticles, a comparison with the theoretical scattering behavior of nanoparticles can be carried out and their material concluded, provided that a limited number of possible materials is present. For each particle, its diameter is determined individually from the Brownian motion. When evaluating the spectroscopic information, it is thus possible to take into account the scattering behavior that results for exactly this particle due to its size. Accordingly, statements about the material of the particle under consideration can be made. Therefore, it is provided in a preferred embodiment of the device according to the invention that the light source emits light of multiple wavelengths.
    One way to use it is to use the different wavelengths pulsed so that each image is captured at a particular wavelength. For example, For example, at three different wavelengths, an image of the first wavelength, the next image of the second wavelength, and the subsequent image of the third wavelength may be successively taken, and the first wavelength may be restarted, etc. After completion of the series of images For each nanoparticle, three trajectories can be determined, each trajectory being extracted only from images each having one of the three wavelengths.
    In order to realize the device according to the invention with minimal dimensions, it is provided in a preferred embodiment of the device according to the invention that the channel is formed in a microfluidic chip. Accordingly, the microfluidic chip must be at least partially transparent to the light emitted by the light source.
    The use of microfluidic components or a microfluidic chip offers an excellent possibility of integration and miniaturization of the entire system. This is i.a. with regard to an installation of a device according to the invention in a motor interesting.
    In this case, a detector or image sensor with optical system or microscope for a single fixed magnification serve to detect the scattered light. Accordingly, it is provided in a preferred embodiment of the device according to the invention that the optical structure and the detector are integrated in a structural unit. In particular, this structural unit can be made small and portable together with a microfluidic chip, which can also be designed as a disposable chip, as well as with a light source and associated electronics for the evaluation.
    The use of microfluidic chips also allows them to be implemented as disposable elements, i. the microfluidic chip is replaced by a new one after a measurement. Alternatively and / or additionally, it is possible to transport the liquid out of the channel after a measurement and to bring new liquid into the channel. Therefore, it is provided in a preferred embodiment of the device according to the invention that means are provided to convey the liquid in and out of the channel. A particularly simple means would be e.g. a syringe, but of course a pump would be a suitable means to pump liquid out of the channel and pump it into the channel. Thus, it would be e.g. conceivable to integrate the device according to the invention in an engine and regularly to determine the wear particles in the engine oil or its diameter automatically, for example, by pumping motor oil into the channel after each operation of the engine and a measurement is performed.
    Similarly, to improve statistics, it may be desirable to perform multiple measurements with different fluid samples. Accordingly, it is provided in a preferred embodiment of the inventive method that after taking the series of images at least once the liquid is removed from the channel, new liquid is introduced into the channel and another series of images is taken.
    In particular, if the channel is formed in a microfluidic chip, a " vertical " Arrangement easily realized to observe specific sedimentation effects. Here, the channel height as well as the optical axis is oriented horizontally. That sedimentation, which occurs due to gravity, is normal to the direction of observation. In addition to the targeted observation of the sedimentation of nanoparticles and the determination of their diameters, larger, heavier particles, which in principle can influence the measurement of smaller particles or clog the channel, can be deposited in advance by sedimentation in such an arrangement.
    Similarly, it is possible to generate an additional force acting on the nanoparticles, which is preferably normal to the viewing direction, and thus to characterize or deposit nanoparticles on the basis of the respective additional property. Therefore, it is provided in a preferred embodiment of the device according to the invention that the device is designed such that a force with a directional component, which is normal to an optical axis of the optical structure, acts on the nanoparticles.
    In the case of sedimentation, the acting force is gravity. In addition, in particular electrical or magnetic forces can be imparted to the nanoparticles. Therefore, it is provided in a particularly preferred embodiment of the device according to the invention that means for generating an electric and / or magnetic field are provided to generate an additional force acting on the nanoparticles force with a directional component normal to the optical axis of the optical Construction stands. Suitable means would be, for example, electrodes or capacitor plates for application of an electric field or coils, e.g. Helmholtz coils, for applying a magnetic field.
    Alternatively or additionally, other physical parameters that can be impressed are also conceivable, for example a flow caused by an osmotic pressure or a velocity profile generated elsewhere.
    The viscosity of the liquid is highly relevant to the above-described calculation of the size of the nanoparticles from their Brownian motion. It is therefore provided in a preferred embodiment of the device according to the invention that a viscosity sensor for measuring the viscosity of the liquid is provided. In particular, if the channel is formed in a microfluidic chip, a variety of miniaturized viscosity sensors can be integrated. Thus, for example, known viscosity sensors based on channel networks or oscillating microstructures are available. Of course, the viscosity sensor can also be formed separately from the microfluidic chip which contains the channel.
    The viscosity of the liquid is significantly influenced by the temperature. In order to be able to influence the viscosity of the liquid, it is provided in a preferred embodiment of the device according to the invention that a heating element and / or a cooling element are provided in order to bring the channel to a desired temperature. Examples would be a heating resistor, e.g. in the form of a plate or a heating wire, as a heating element and / or a Peltier element as a cooling element. It is understood that a temperature sensor is also provided if it is not already integrated in the heating element / cooling element.
    Also, the heating element and / or cooling element can - as well as any existing pumps - are small and compact, so that a device that has these components at least partially, can also be made small, compact and portable.
    As already described, the invention provides for the use of a device according to the invention for determining the size and / or size distribution of particles, preferably wear particles, in a liquid lubricant, in particular in engine oil. The lubricants may be lubricants of a variety of machines, i. not necessarily lubricants for engines. For example, these may be lubricants for the lubrication of bearings. In particular, metallic nanoparticles are measured here.
    With the device according to the invention or the method according to the invention, however, it is generally possible to investigate nanoparticles which have a different refractive index than the carrier medium or the liquid. That not only metallic wear particles but also other inorganic and organic nanoparticles can be measured and their diameters determined. This allows u.a. interesting applications in pharmacy. For example, the purity of preparations or liquid medicines can be examined. Accordingly, the invention provides the use of a device according to the invention for determining the size and / or size distribution of foreign particles in a liquid drug.
    In particular with regard to the use of the device according to the invention for measuring wear particles in lubricants, it is important to take into account that in addition to the wear particles present as nanoparticles, larger wear particles - e.g. in the sub-micrometer range or micrometer range - may be present in the lubricant. If the channel heights are too low, these larger wear particles can block the channel. In order to avoid clogging of the channel, it is therefore provided in a preferred embodiment of the device according to the invention that the channel height is at least 1 pm, preferably at least 3 pm, more preferably at least 5 pm. It is understood that in a particularly preferred embodiment, not only the channel height, but generally a clear cross-section of the channel is greater than / equal to the channel height, to effectively prevent clogging.
    To determine the diameter of the nanoparticles according to the invention, the viscosity of the liquid must be known in principle. In this case, liquids can be examined in a very wide viscosity range by means of the device according to the invention, preferably in a range of 0.1 mPa s to 1000 mPa s. Conversely, it is of course also possible to deduce the viscosity of the liquid with known size of the nanoparticles. Therefore, according to the invention, the use of a device according to the invention for determining the viscosity of a liquid in which nanoparticles of known size are provided is provided.
    BRIEF DESCRIPTION OF THE FIGURES
    The invention will now be explained in more detail with reference to exemplary embodiments. The drawings are exemplary and are intended to illustrate the inventive idea, but in no way restrict it or even reproduce it.
    Showing:
    Fig. 1 is a schematic sketch of the structure of a device according to the invention
    FIG. 2 shows a detail of a sectional view of a channel of the device from FIG. 1. FIG
    Fig. 3 is a schematic sketch of the structure of another
    Embodiment of the device according to the invention, which is suitable for observing sedimentation effects
    Fig. 4 is a schematic detail view of the liquid in
    3 shows a channel of the device of FIG. 3, illustrating trajectories of a larger, heavier and a smaller, lighter nanoparticle under the influence of gravity and a direction of flow
    Fig. 5 is a schematic sketch of a detail of the structure of another embodiment of the device according to the invention, which is suitable for observing the diffusion of nanoparticles under additional influence of an electric field
    Fig. 6 is a schematic sketch of a detail of the structure of another embodiment of the device according to the invention, which is suitable for observing the diffusion of nanoparticles under additional influence of a magnetic field
    Fig. 7 is a schematic sketch of a detail of the structure of another embodiment of the device according to the invention with a heating element, a cooling element and with a viscosity sensor
    WAYS FOR CARRYING OUT THE INVENTION
    Fig. 1 in conjunction with Fig. 2 shows an embodiment of the device according to the invention for measuring nanoparticles 1 in a liquid 2, e.g. Water or oil, wherein the liquid 2 is located in a channel 4. In the embodiment shown, the channel 4 is formed in a microfluidic chip 9, which in turn is arranged on a microscope stage 19 of a microscope 6, which forms an optical structure. The microscope 6, the channel 4 and a light source 3 are in a dark field arrangement. That light 20 emitted from the light source 3 and incident on the liquid 2 is scattered on the nanoparticles 1, and only scattered light 21 enters the microscope 6. In particular, light does not enter the microscope 6 directly from the light source 3, nor does light that is reflected at the channel 4 or microfluidic chip 9.
    As the light source 3, a laser is used in the illustrated embodiment, for example, with a wavelength λ = 532 nm. The light source 3 is arranged to the channel 4 and the microfluidic chip 9 and the microscope 6, that the emitted light at such an angle on the channel 4 or the microfluidic chip 9 is incident that no light can pass directly or by (specular) reflection in the microscope 6, but only by scattering on the nanoparticles 1. The channel 4 and the microfluidic chip 9 is this is at least partially transparent to the light. In the embodiment shown, this arrangement is achieved by an angle 8 between the incident light 20 and an optical axis 7 of the microscope 6 is between 60 ° and 70 °, wherein the optical axis 7 substantially normal to the channel 4 and the microfluidics Chip 9 stands.
    The nanoparticles 1 are generally smaller - at least not significantly larger - than the wavelength λ, so that with the microscope 6, the diffraction images of those nanoparticles 1 are captured and enlarged, at which the incident light 20 is scattered. Each of these diffraction patterns consists of the associated point spread function (sometimes also referred to as point spread function), which essentially appears as diffraction slices (also referred to as Airy slices). Preferably, the investigated nanoparticles 1 have a diameter d in the range between 10 nm and 200 nm, so that each nanoparticle 1 is an im
    Essentially equal-sized diffraction disc produced.
    By means of a two-dimensional image sensor 17, which represents a two-dimensional detector and in the embodiment shown is part of a camera 16, the image magnified by the microscope 6 is taken or a series of such images is taken. Such a series typically consists of at least 1000 images, with an equal time interval of, for example, 40 ms between each image. The magnification of the microscope 6 and the pixel density of the image sensor 17 are coordinated so that the determination of the center of gravity of each diffraction disk is meaningfully possible by each diffraction disk appears so large on the image sensor 17 that it is at least 2 * 2 pixels imaged. For this purpose, for example, a lens with 10x magnification and a numerical aperture NA = 0.3 is used, in combination with a by a factor of 1.25 to 2.5 magnifying adapter and an image sensor 17 with 1920 * 1080 pixels. At 2.5 times magnification of the adapter, in the illustrated embodiment, the area imaged on the image sensor 17 is 774 pm * 435 pm, i. 2.48 pixels per pm. Accordingly, the diffraction disks whose diameter in the focus several pm large, sufficiently resolved in order to determine their center of gravity.
    Two-dimensional trajectories of the nanoparticles 1 then result from the positions of the respective diffraction disk, i. in the present case from the coordinates of the center of gravity of the respective diffraction disk, as a function of the steps or the successive images of the recorded series. In order that the diffraction disk of each nanoparticle 1 in each image of the series is imaged so sharply that the determination of the center of gravity is easily possible, the channel 4 has a limited channel height 5, which is shown in FIG
    Embodiment 10 pm. The depth of field DOF resulting from the wavelength λ and the numerical aperture is DOF
    that is about 30% of the channel height 5. D.h. the channel height 5 and the depth of field DOF are coordinated so that the diffraction disc of each nanoparticle 1 is always displayed sufficiently sharp - regardless of where the respective nanoparticles 1 relative to the channel height 5 is located. Accordingly, the recordable trajectories are virtually arbitrarily long, since the nanoparticles 1 or their diffraction disks can not essentially move out of focus during the acquisition of the series of images. At e.g. 1000 recorded images, so also trajectories can be recorded for the nanoparticles 1, which contain 1000 positions. That the length of trajectories picked up by the device according to the invention may be at least two orders of magnitude greater than the length of trajectories that can be accommodated by devices known from the prior art.
    Experiments have shown that sufficiently sharp images of the diffraction disks can be achieved as long as the depth of field DOF is at least 10% of the channel height 5. Accordingly, experiments with a lens with 50x magnification, a numerical aperture NA = 0.45 and a resulting depth of field DOF of about 1.3 pm still provided useful results.
    To determine the diameter d of the nanoparticles 1, the mean displacement square MSD (x) for each trajectory is calculated by means of a computer 18, where X is the time interval of two images viewed. Then a line in the initial range of MSD (x) is adjusted. The slope of the fitted straight line corresponds to 4 * D, where D is the diffusion coefficient of the considered nanoparticle 1 for its diffusion in the two considered dimensions. The diameter d of the respective nanoparticle 1 results from the Stokes-Einstein equation:
    with kB the Boltzmann constant, T the temperature in Kelvin and η the viscosity of the liquid 2. Since with the device according to the invention practically any length trajectories can be recorded, e.g. with a length of 1000 images, the determination of the diameter d of the individual nanoparticles 1 with an unprecedented accuracy.
    This in turn makes it possible to determine a size distribution of the diameter d very precisely. As shown schematically in FIG. 1, the size distribution can be represented as a histogram of the frequency distribution of d (frequency # versus diameter d). Maxima (also called peaks) can be adjusted by means of a suitable function, even if these maxima are relatively close together. Thus, in particular size distributions of polydispersed nanoparticles 1 can be accurately determined. The distribution shown in Figure 1 shows the result of such measurement with 1000 images (or trajectories of that length), with the maxima for diameters d of 115 nm and 170 nm being determined, i. the peak resolution is approximately 1: 1.5 in the case shown.
    FIG. 3 shows a further embodiment of the device according to the invention, wherein the microfluidic chip 9 with the channel 4 in this case "vertical". is arranged. That compared to the embodiment of Fig. 1, the structure is rotated substantially 90 ° and the observation direction and the optical axis 7 and the channel height 5 are arranged horizontally. Since the channel 4 has normal dimensions to the channel height 5, ie in the embodiment of FIG. 3 in a vertical plane, substantially larger dimensions than the channel height 5, the sedimentation of nanoparticles 1 can be observed. That The random Brownian motion of the nanoparticles 1 is superimposed by a directed movement corresponding to the direction 23 of gravity. Sedimentation is stronger for larger, heavier nanoparticles 24 than for smaller, lighter nanoparticles 25.
    The latter is illustrated in Fig. 4, which shows a schematic detail view of the liquid in the channel 4 of the apparatus of Fig. 3. Since gravity in relation to the Brownian motion has a stronger effect on the larger, heavier nanoparticle 24 than on the smaller, lighter nanoparticle 25, the trajectory 26 of the larger, heavier nanoparticle 24 has a strong downward orientation. In contrast, the trajectory 27 of the smaller, lighter particle 25 has no such orientation.
    In the exemplary embodiment of FIGS. 3 and 4, the random Brownian movement of the nanoparticles 1, 24, 25 is also superimposed by a further directed movement. This results from the fact that the liquid 2 does not rest in the channel 4, but moves along a flow direction 22. This is achieved by continuously conveying liquid 2 through the channel 4 by means of a syringe 15. Accordingly, in FIG. 4 both the trajectory 26 of the larger, heavier nanoparticle 24 and the trajectory 27 of the smaller, lighter nanoparticle 25 have an orientation along the direction of flow 22.
    The fact that at the same time the sedimentation has a stronger effect on the larger, heavier nanoparticles 24 than on the smaller, lighter nanoparticles 25 can be exploited to separate the larger, heavier nanoparticles 24 from the smaller, lighter nanoparticles 25. For this purpose, an upper microfluidic connection 28 and a lower microfluidic connection 29 are arranged vertically at one end of the channel 4. Through the upper microfluidic port 28, essentially only liquid 2 with smaller, lighter nanoparticles 25 passes through the lower microfluidic port 29, especially liquid 2 with sunken larger, heavier nanoparticles 24 passes. Accordingly, have containers in which the liquid 2 from the upper microfluidic Port 28 and from the lower microfluidic port 29 is passed, each liquid 2 with predominantly smaller, lighter nanoparticles 25 or predominantly larger, heavier nanoparticles 24 on.
    It should be noted that both the preferential direction caused by the sedimentation in the movement or in the trajectories of the nanoparticles 1 and the preferential direction caused by the flow direction 22 in the movement or in the trajectories of the nanoparticles 1 can be taken into account by known methods, to infer the pure Brownian movement. That the determination of the diameter d of the nanoparticles 1 is also possible in the case of superimposed sedimentation and / or superimposed flow direction 22 -more generally even in the presence of an overlaid drift velocity.
    Instead of a permanent, continuous change of the liquid 2 in the channel 4, the syringe 15 can also be used to gradually replace the liquid 2 in the channel 4, preferably after completion of a measurement and before the start of a new measurement. In this way, the statistics of the determined size distribution of the nanoparticles 1 can be improved. In addition, the occurrence of superimposed drift rates is avoided.
    In addition to gravity, additional additional forces can be specifically imparted to the nanoparticles 1 in order to investigate corresponding properties of the nanoparticles 1. Thus, FIG. 5 schematically shows a detail of a construction of an embodiment variant of the device according to the invention for measuring nanoparticles 1 under the additional influence of an electric field. To generate such an electric field, electrodes 10 are provided, which are arranged on two opposite end regions of the channel 4 and to which an electrical voltage is applied. In this way, for example, in the case of charged nanoparticles 1, a drift velocity of the nanoparticles 1 superimposed on the diffusion can be generated. In this way, e.g. a distinction between charged and uncharged nanoparticles 1 possible.
    Analogous to the embodiment of FIG. 5, FIG. 6 shows a further embodiment of the device according to the invention for measuring nanoparticles 1 under the additional influence of a magnetic field. To generate such a magnetic field, a coil 11 is provided, wherein magnetic field lines are indicated by dashed lines. In this way, for example magnetic nanoparticles 1, a diffusion-superimposed specific drift behavior can be impressed, whereas non-magnetic nanoparticles 1 move purely diffusively, so that a distinction between magnetic and non-magnetic nanoparticles 1 is possible.
    In principle, the result for the obtained diameter d of the nanoparticles 1 is decisively influenced by the viscosity η of the liquid 2. Therefore, in a further embodiment of the device according to the invention, a viscosity sensor 14 is provided, as schematically illustrated in FIG. Such viscosity sensors 14 are known per se and are based on channel networks or oscillating
    Microstructures. In the embodiment of FIG. 7, both the channel 4 and the viscosity sensor 14 are formed as microfluidic elements, which are connected to one another via a line, so that liquid 2 can be measured from the channel 4 with the viscosity sensor 14.
    In addition to the precise knowledge of the viscosity η of the liquid 2, it may be desirable to specifically influence the viscosity η in order to increase or decrease the speed of diffusion of the nanoparticles 1 and to better match the image refresh rate of the series of images. Accordingly, the microfluidic chip 9 in FIG. 7 also has a heating wire 12. Moreover, the microfluidic chip 9 is arranged on a Peltier element 13. Thus, the channel 4 and thus also the liquid 2 can be brought to the desired temperature by heating or cooling. Alternatively, the Peltier element 13 could not only be used for cooling, but also by reversing for heating, so that the use of the heating wire 12 could also be dispensed with.
    REFERENCE LIST 1 nanoparticles 2 liquid 3 light source 4 channel 5 channel height 6 microscope 7 optical axis of the microscope 8 angle 9 microfluidic chip 10 electrodes 11 coils 12 heating wire 13 Peltier element 14 viscosity sensor 15 syringe 16 camera 17 image sensor 18 computer 19 microscope stage 20 incident light 21 Scattered light 22 Flow direction 23 Direction of gravity 24 Large, heavy particle 25 Small, lightweight particle 26 Trajectory of the large, heavy particle 27 Trajectory of the small, light particle 28 Upper microfluidic port 29 Lower microfluidic port DOF Depth of field λ Wavelength X Time interval dim Dimensionality D Diffusion coefficient d Diameter of a nanoparticle kB Boltzmann constant T Temperature η Viscosity of the liquid
    权利要求:
    Claims (22)
    [1]
    1. A device for measuring nanoparticles (1) in a liquid (2), comprising a light source (3), a channel (4) for receiving the liquid (2), the channel (4) at least in sections from the light source (3) is transparent and has a channel height (5), the apparatus further comprising an optical assembly (6) and a two-dimensional detector (17) for receiving a series of images generated by the optical assembly (6), the light source ( 3), the channel (4) and the optical assembly (6) are in a dark field arrangement to transmit light emitted by the light source (3) and scattered on the nanoparticles (1) through the optical assembly (6) Detector (17), wherein positions of diffraction patterns of the nanoparticles (1) scattered light (21) on the detector (17) can be determined, characterized in that the channel height (5) and the optical structure (6) are designed that the sharpness The DOF of the optical structure (6) is at least 10%, preferably at least 30% of the channel height (5).
    [2]
    2. Apparatus according to claim 1, characterized in that the channel height (5) is less than or equal to 30 pm, preferably less than or equal to 20 pm, more preferably less than or equal to 10 pm.
    [3]
    3. Device according to one of claims 1 to 2, characterized in that the channel height (5) is at least 1 pm, preferably at least 3 pm, more preferably at least 5 pm
    [4]
    4. Device according to one of claims 1 to 3, characterized in that the light source (3) on the same side of the channel (4) is arranged as the optical structure (6).
    [5]
    5. Device according to one of claims 1 to 4, characterized in that as the light source (3) at least one laser is provided.
    [6]
    6. Device according to one of claims 1 to 5, characterized in that at least one light-emitting diode is provided as the light source (3).
    [7]
    7. Device according to one of claims 1 to 6, characterized in that the channel (4) is formed in a microfluidic chip (9).
    [8]
    8. Device according to one of claims 1 to 7, characterized in that the light source (3) emits light of several wavelengths (λ).
    [9]
    9. Device according to one of claims 1 to 8, characterized in that a computer (18) is provided to automatically determine from the series of images trajectories (26, 27) of the nanoparticles (1).
    [10]
    10. Device according to one of claims 1 to 9, characterized in that the device is designed such that a force with a directional component which is normal to an optical axis (7) of the optical structure (6), on the nanoparticles (1 ) acts.
    [11]
    11. The device according to claim 10, characterized in that means (10, 11) are provided for generating an electric and / or magnetic field to generate an additional force acting on the nanoparticles (1) force with a directional component, the normal the optical axis (7) of the optical assembly (6) is.
    [12]
    12. Device according to one of claims 1 to 11, characterized in that a heating element (12) and / or a cooling element (13) are provided to bring the channel (4) to a desired temperature.
    [13]
    13. Device according to one of claims 1 to 12, characterized in that a viscosity sensor (14) for measuring the viscosity of the liquid (2) is provided.
    [14]
    14. Device according to one of claims 1 to 13, characterized in that means (15) are provided to convey the liquid (2) in and out of the channel (4).
    [15]
    15. Device according to one of claims 1 to 14, characterized in that the optical structure (6) and the detector (17) are integrated in a structural unit.
    [16]
    Method for determining the diameters of nanoparticles (1) in a liquid (2), characterized in that the method comprises the following steps: - taking a series of images by means of a device according to one of claims 1 to 15; - Determining the positions of the diffraction images of the nanoparticles (1) in the images; - determining the trajectories (26, 27) of the nanoparticles (1) according to the positions of the associated diffraction patterns in the images; Determination of diffusion coefficients D of the nanoparticles (1) from their trajectories (26, 27); Calculation of the diameter d of the nanoparticles (1) by means of the Stokes-Einstein equation D = kB * T / (3 * d * π * η), with kB the Boltzmann constant, T the temperature in Kelvin and η the viscosity of the Liquid (2).
    [17]
    17. The method according to claim 16, characterized in that after taking the series of images at least once the liquid (2) from the channel (4) is removed, new liquid (2) is introduced into the channel (4) and another Series of pictures is taken.
    [18]
    18. The method according to any one of claims 16 to 17, characterized in that for determining the diffusion coefficient D trajectories (26, 27) are used with a length of at least 200 positions, preferably of at least 500 positions, more preferably of at least 1000 positions, wherein For determining the diffusion coefficients D, preferably only trajectories (26, 27) with a length of at least 200 positions, preferably of at least 500 positions, particularly preferably of at least 1000 positions, are used.
    [19]
    19. The method according to any one of claims 16 to 18, characterized in that a distribution of the calculated diameter d is determined.
    [20]
    20. Use of a device according to one of claims 1 to 15 for determining the size and / or size distribution of particles (1), preferably wear particles in a liquid lubricant (2), in particular in engine oil.
    [21]
    21. Use of a device according to one of claims 1 to 15 for determining the size and / or size distribution of foreign particles (1) in a liquid drug (2).
    [22]
    22. Use of a device according to one of claims 1 to 15 for determining the viscosity of a liquid (2) in which nanoparticles (1) of known size are located.
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    同族专利:
    公开号 | 公开日
    WO2015143467A1|2015-10-01|
    AT515416B1|2015-09-15|
    引用文献:
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    EP2647977A1|2012-04-03|2013-10-09|ETH Zurich|Method and apparatus for measuring charge and size of single objects in a fluid|EP3384273B1|2015-12-02|2021-04-28|Nanolyze AB|A method for determining a hydrodynamic size of an object|
    法律状态:
    2020-11-15| MM01| Lapse because of not paying annual fees|Effective date: 20200326 |
    优先权:
    申请号 | 申请日 | 专利标题
    ATA50221/2014A|AT515416B1|2014-03-26|2014-03-26|Device for measuring nanoparticles and method for determining the diameter of nanoparticles in a liquid|ATA50221/2014A| AT515416B1|2014-03-26|2014-03-26|Device for measuring nanoparticles and method for determining the diameter of nanoparticles in a liquid|
    PCT/AT2015/050072| WO2015143467A1|2014-03-26|2015-03-20|Apparatus for measuring nanoparticles and method for determining the diameter of nanoparticles in a liquid|
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