Particle analysis

Abstract

A particle characterization apparatus (100, 200) is disclosed, comprising a sample cell (106, 206) for holding a sample (104, 204) including particles suspended in a diluent, a light source (101, 201) configured to irradiate the sample (104, 204) with a light beam (108, 208) thereby generating scattered light from an interaction of the light beam (108, 208) with the particles, a light detector (103, 203) configured to detect the scattered light and output scattering data representative of a diffusion coefficient of the particles in the diluent, a processor (105, 205) configured to determine a characteristic of the particles from the scattering data, and a temperature sensor (107, 207) in thermally conductive contact with a wall (116, 216) of the sample cell (106, 206) and at a distance of less than 5 mm from the sample (104, 204). The processor (105, 205) is configured to determine a characteristic of the particle using the output of the temperature sensor (107, 207), the characteristic of the particle determined by the processor (105, 205) being responsive to the output from the temperature sensor (107, 207).

Description

[Technical field]

[0001] The present invention relates to a method of optical particle analysis and to an instrument for optical particle analysis. [Background technology]

[0002] The present invention relates to an apparatus and method for performing nanoparticle tracking analysis (NTA), and more generally to any method of optical particle analysis that is sensitive to particle temperature.

[0003] Nanoparticle Tracking Analysis is a relatively recently developed method for visualizing and analyzing nanoparticles directly and in real time in liquids (see, for example, International Publication No. WO 2003 / 093801). NTA uses a light source (e.g., a laser) to illuminate particles suspended in a dispersion and an optical detector to detect the light scattered from the particles. Even when the particles are too small to be directly imaged, the light scattered from the particles can be easily detected, for example by a camera positioned to detect the scattered light.

[0004] The scattering from each particle can be tracked and the Brownian motion of the nanoparticles analyzed. Particle size can be inferred from their motion. The brightness of the scattering from the particles allows heterogeneous mixtures of particles to be separated. NTA can also be used to estimate particle concentration and / or particle size distribution. The particle size distribution profile obtained by NTA is directly a number distribution / frequency distribution.

[0005] NTA is already a technical term accepted by those skilled in the art. There are over 900 scientific papers and presentations that refer to data collected using NTA. The term is also used by, for example, the American Society for Testing and Materials International (ASTM International), the U.S. Environmental Protection Agency (EPA), the U.S. Food and Drug Administration (FDA), and the National Institutes of Health (NIH).

[0006] The sizing of individual nanoparticles by NTA is based on an analysis of the Brownian motion exhibited by micron and submicron particles suspended in a liquid when illuminated by an appropriate light source (e.g., a laser). The light scattered by these particles is detected by a microscopical arrangement, where a portion of the light is scattered by the particles which is imaged by a video camera.

[0007] The average distance traveled by any particle in a known time interval (e.g., the inverse of the camera's frame rate, typically 30 frames per second) is related to the particle size through the Stokes-Einstein equation, where the temperature and viscosity of the surrounding liquid are known quantities. The Stokes-Einstein equation is:

[0008]

number

[0009] where D is the diffusion coefficient of the particle in the dispersion and k B is the Boltzmann constant, T is the absolute temperature, η is the kinematic viscosity of the dispersant, and r is the hydrodynamic radius of the particle.

[0010] In nanotracking analysis, the Stokes-Einstein relation can be rewritten as follows:

[0011]

number

[0012] Here, 〈x,y〉 2 is the mean squared displacement between successive frames, and t s is the frame time.

[0013] Because Brownian motion is virtually independent of particle mass, particle density, and particle optical properties, NTA (like the related technology dynamic light scattering (DLS)) is an absolute technique and has the advantage of being independent of these particle properties and does not require calibration when used. Because it examines particles individually (and simultaneously) within a suspension, it can produce high-resolution particle size distribution profiles.

[0014] Dynamic light scattering (DLS), also known as photon correlation spectroscopy (PCS), is another technique that detects the motion of Brownian particles to determine their properties. In DLS, a light source is used to illuminate a sample containing particles suspended in a dilute liquid. The light scattered by the particles is detected. The intensity of the scattered light varies with time due to the Brownian motion of the illuminated particles. The autocorrelation function can be determined from the time history of the scattered intensity. If the scattering vector (usually denoted q) is known, the diffusion coefficient D can be determined from the autocorrelation function. For example, for a dilute solution of monodisperse nanoparticles, the normalized autocorrelation function g (1) (t) has been shown to be related to the scattering vector q and the diffusion coefficient according to the following equation:

[0015]

number

[0016] The diffusion coefficient can be related to particle size via the Stokes-Einstein relation:

[0017] Techniques that rely on the characterization of Brownian particle motion to determine particle properties via the Stokes-Einstein relation are temperature sensitive. Typically, NTA and DLS instruments contain a temperature control system that ensures that the sample has a specific and known temperature so that temperature does not introduce errors into the particle characterization.

[0018] Although considerable progress has been made in improving the accuracy of temperature control, there is still room for improvement. It is desirable to minimize temperature-related errors in particle characterization. Summary of the Invention

[0019] According to a first aspect, there is provided a particle characterization apparatus. The particle characteristic evaluation device comprises: a sample cell for holding a sample including particles suspended in a diluent; a light source configured to illuminate the sample with a light beam to generate scattered light from interactions between the light beam and the particles; a photodetector configured to detect the scattered light and output scattering data; a processor configured to determine a characteristic of the particle from the scattering data; a temperature sensor in thermally conductive contact with the wall of the sample cell and less than 5 mm from the sample; Including, The processor is configured to determine a characteristic of the particle using the output of the temperature sensor, the characteristic of the particle determined by the processor being responsive to the output from the temperature sensor.

[0020] The temperature sensor may be positioned less than 3 mm from the sample.

[0021] The scattering data may represent the diffusion coefficient of the particles in a dilute solution. The scattering data may include a time history of the scattering intensity or a series of images in which individual particles can be tracked.

[0022] The sample cell includes an optical component defining a wall of the sample cell, and the temperature sensor is disposed within a recess or through-hole defined in the optical component.

[0023] The particle characterization device may further include a thermally conductive potting compound disposed within the recess or through-hole and in contact with the temperature sensor and the optical component.

[0024] The holes may be formed by ultrasonic drilling.

[0025] The optical component may include a surface including a metal coated region. The metal coated region may be configured to reflect scattered light. The surface may include an uncoated region. The light beam may be configured to exit the optical component through the uncoated region and be incident on the sample. An exit location where the light beam exits the optical component through the uncoated region may be within 5 mm of the metal coated region.

[0026] The optics may be configured to refract the light beam so that it is at an angle of 10 degrees or less relative to the surface, or 5 degrees or less (eg, an angle parallel to the surface).

[0027] The optical components include an optical prism configured to refract the light beam into the sample.

[0028] The optical prism may include a first surface (angled surface) where the light beam enters the prism. The wall may include a second surface (inner surface) in contact with the sample. The optical prism may be configured to refract the light beam to the sample such that at the sample the light beam is at an angle of less than 20 degrees relative to the second surface (inner surface). The first surface may be at an angle between 10 and 80 degrees (or between 50 and 70 degrees) relative to the inner surface.

[0029] The second surface (inner surface) may be any surface previously described (ie, a surface that includes uncoated areas, metal coated areas, etc.).

[0030] The photodetector is configured to receive the scattered light along a detection optical path. The photodetector may include any suitable lens and detector arrangement. The photodetector may be positioned in the far field (also called the far field) normal or at a high angle to the plane of the surface (e.g., the second surface (inner surface) and / or the metal coated region of the surface).

[0031] The scattering region is defined by the intersection of the detection light path and the illumination light beam. The temperature sensor may be less than 20 mm from the scattering region. The temperature sensor may be less than 15 mm from the scattering region. The temperature sensor may be at least 5 mm (or at least 10 mm) from the scattering region. The temperature sensor may be located at an offset of at least 5 mm (or at least 10 mm) from the detection light path.

[0032] The walls of the sample cell may be transparent.

[0033] The walls of the sample cell may include or be constructed from silicate glass (eg, BK7 or other borosilicate crown glass).

[0034] The walls of the sample cell may be constructed of a material that has a refractive index, n, of at least 1.5 at a wavelength of 500 nm.

[0035] The particle characterization device may be configured to perform nanoparticle tracking analysis (NTA) or dynamic light scattering (DLS).

[0036] The particle characterization apparatus may further include an ambient temperature sensor, the ambient temperature sensor may be at least 10 mm away from the sample cell and configured to measure the ambient temperature in the region of the sample cell.

[0037] The processor may be configured to receive the air temperature and determine a sample temperature as a function of both the output of the temperature sensor and the ambient temperature.

[0038] The apparatus may include a temperature regulator operable to control a temperature of the sample. The apparatus may be operable in an ambient temperature compensation mode in which the temperature regulator is used to match the temperature of the sample to a temperature measured by an ambient temperature sensor.

[0039] According to a second aspect, an apparatus is provided. The device comprises: an optical component having a surface; a temperature sensor conductively coupled to the surface and positioned within 5 mm of the surface; Includes.

[0040] The temperature sensor may be positioned within 3 mm of the surface.

[0041] The optical component can be used in a particle characterization device. The particle characteristic evaluation device comprises: a light source configured to illuminate a sample with a light beam through a transparent optical element, the sample including particles suspended in a diluent and in contact with the transparent optical element; a photodetector configured to detect scattered light due to interaction of the light beam with the particles and output scattering data representative of a diffusion coefficient of the particles in the diluent; a processor configured to determine a characteristic of the particle from the scattering data; Includes.

[0042] The optical component may be a prism. The prism may have a first surface. The surface (within 5 mm of the temperature sensor) may be a second surface.

[0043] The second surface may include a metal coated region. The metal coated region may be optically opaque. The surface may include an uncoated region. The light beam may be configured to exit the optical component through the uncoated region and be incident on the sample. An exit location at which the light beam exits the optical component through the uncoated region may be within 5 mm of the metal coated region.

[0044] The optics may be configured to refract the light beam so that it is at an angle of 10 degrees or less with respect to the surface, or 5 degrees or less (eg, an angle parallel to the surface).

[0045] The second surface may be flat and configured to form an inner surface of the sample cell.

[0046] The optical component may further include a recess or a through-hole, and the temperature sensor may be disposed within the recess or through-hole.

[0047] The optical component may further include a thermally conductive potting compound disposed within the recess or through hole to improve thermal contact from the second surface to the temperature sensor.

[0048] The holes may be formed by ultrasonic drilling.

[0049] The optical component may be configured to refract a light beam entering the prism perpendicular to the first surface such that the light beam exiting the second surface into the water is at an angle of 10 degrees or less with respect to the second surface.

[0050] The second surface may be at an angle between 10 and 80 degrees (or between 50 and 70 degrees) relative to the first surface.

[0051] The optical components may include silicate glass (eg, BK7 or other borosilicate crown glasses).

[0052] The optical component may be constructed of a material that has a refractive index, n, of at least 1.5 at a wavelength of 500 nm.

[0053] The optical component may be used as a wall of a sample cell in the device according to the first aspect.

[0054] According to a third aspect, there is provided a method for particle characterization. Particle characterization methods include: illuminating a sample containing particles suspended in a diluent with a light beam to generate scattered light due to interaction of the light beam with the particles; detecting the scattered light with a photodetector to generate scattering data; processing the scattering data to determine a characteristic of the particle from the scattering data; measuring the temperature of the sample using a temperature sensor in thermally conductive contact with a wall of a sample cell containing the sample, the temperature sensor being less than 5 mm from the sample; Including, Processing the scattering data includes determining a characteristic of the particle using the output of the temperature sensor, the determined characteristic of the particle being responsive to the output from the temperature sensor.

[0055] The method may further include receiving a measurement of the ambient air temperature and determining a sample temperature as a function of both the output of the temperature sensor and the ambient temperature.

[0056] The scatter data may include a video of the scattered light.

[0057] The scattering data may represent the diffusion coefficient of the particles in a dilute solution.

[0058] The method may further include using a temperature regulator operable to match the temperature of the sample to the ambient air temperature.

[0059] According to a fourth aspect, there is provided a method for optical detection and / or analysis of sub-micron particulates. The method is: (i) illuminating an optical component with a focused light beam, the optical component having a portion of one surface coated with a film comprising an optically opaque metal and another portion of the surface uncoated, such that the surface has a coated portion and an adjacent uncoated portion, the focused light beam being incident on the optical component at a location on the uncoated portion of the coated surface, the location of incidence being adjacent to or within 5 mm of and not coincident with the coated portion of the metal film on the surface, the focused light beam being incident on the optical component such that at least a portion of the light beam propagates above and parallel to or at an angle of less than 5 degrees to the surface of the metal film; (ii) placing a sample containing a submicron sized particle or population of particles on a surface of the substrate such that the particle falls within an area illuminated by a light beam propagating over the metal film; (iii) detecting optical radiation scattered individually or emitted from the particles as a result of their interaction with the light beam by suitable lenses and detectors positioned in the far field, normal or at a high angle to the plane of the metal film; Includes.

[0060] The optical component further includes a temperature sensor, the temperature sensor being in thermally conductive contact with a wall of the sample cell and less than 5 mm from the sample.

[0061] According to a fifth aspect, there is provided an apparatus for carrying out the method of the fourth aspect. The apparatus includes a substrate, an illumination means, and a detector. A portion of one surface of the substrate is coated with a film comprising an optically opaque metal, and another portion of the surface is uncoated, such that the surface has a coated portion and an adjacent uncoated portion. The illumination means illuminates the surface with a focused light beam. The illumination means includes a source of light illumination. The light beam is incident on the substrate at a location on the uncoated portion of the coated surface. The incident location is adjacent to the coated portion of the metal film on the surface, or is within 5 mm of the coated portion of the metal film and does not coincide with the coated portion. The light beam propagates over the surface of the metal film and is either parallel to the surface of the metal film or at an angle of less than 5 degrees to the surface of the metal film. The detector is positioned in the far field and detects optical radiation scattered by or emitted from the particles as a result of their interaction with the light beam.

[0062] Features of each embodiment (including optional features) can be combined with features of any other embodiment. Features mentioned in the first, second or fifth embodiment can also be used in the method according to the third embodiment. Features mentioned in the first or second embodiment (including optional features) can also be used in the method according to the fourth embodiment.

[0063] Embodiments will now be described, by way of example only, with reference to the drawings in which: [Brief description of the drawings]

[0064] [Figure 1] FIG. 1 shows an embodiment in which the device is a nanoparticle tracking assay device and the temperature sensor is provided in a through hole in the prism. [Diagram 2] FIG. 1 illustrates an embodiment in which the device is a nanoparticle tracking assay device and the temperature sensor includes a thin film sensor in contact with the sample. [Diagram 3] FIG. 1 shows an embodiment in which the apparatus is a dynamic light scattering evaluation apparatus and the temperature sensor is provided in a recess in the sample cell. [Figure 4] FIG. 1 shows an embodiment in which the apparatus is a dynamic light scattering evaluation apparatus and the temperature sensor is provided on a heat spreader that contacts the base of the sample cell. [Diagram 5] Graph showing the accuracy achievable in some examples DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0065] 1, an NTA apparatus 100 according to one embodiment is shown generally at 100. The apparatus 100 includes a light source 101, a sample cell 106, a light detection system 102, and a processor 105.

[0066] A light source 101 generates a light beam 108, which is refracted into the sample 104 by a prism 110 that forms part of the sample cell 106. The light beam 108 generates scattered light by interacting with particles in the sample 104. The scattered light from the particles is detected by a light detection system 102, which is typically a conventional microscope with an imaging camera. A light detector 103 of the light detection system 102 is shown diagrammatically (not to scale) in FIG. 1.

[0067] The particle is tracked in each successive frame imaged by the optical detection system 102, and the diffusion coefficient of the particle is determined by the processor 105 as described in the Background of the Invention. The prism 110 includes a through hole or recess in which the temperature sensor 107 is positioned in close proximity to the sample 104. Because the prism 110 is in direct contact with the sample and the thermal conductivity of the prism is relatively high (e.g., high enough to minimize temperature gradients and subsequent temperature differences between the temperature sensor 107 and the sample 104), the temperature sensor 107 provides a relatively accurate measurement of the temperature of the sample 104.

[0068] For each particle tracked, the processor 105 estimates a diffusion coefficient. From the diffusion coefficient, the hydrodynamic radius of the particle can be determined using the Stokes-Einstein relation (either on an individual particle basis or on an average or population basis). The Stokes-Einstein relation requires that the temperature of the sample is known. The temperature sensor 107 provides a relatively accurate measurement for the sample temperature, which the processor 105 uses to determine a relatively accurate estimate for the particle size. The processor 105 may also be configured to count the number of particles to provide an estimate of the particle concentration. The processor 105 may, for example, determine a particle size distribution based on the concentration of each particle size.

[0069] In typical prior art NTA instruments, the temperature used in the Stokes-Einstein relation is typically measured off-sample. Due to concerns about sample contamination, as well as challenges with small sample volumes, the sensor is typically not in contact with the sample. In typical prior art NTA instruments, the temperature of the sample is inferred from the ambient temperature or from a temperature sensor on or near the temperature controller (e.g., a thermoelectric temperature controller). These methods of determining the temperature of the sample are typically subject to error.

[0070] In prior art systems that do not use prisms, it is typically difficult to get the temperature sensor closer than 1 or 2 cm from the sample. In such situations, there are typically multiple materials and interfaces between the temperature sensor and the sample, making it difficult to correct for temperature offsets due to heat flow and introducing potential variations between different devices. In contrast, the temperature sensor in this embodiment is placed very close to the sample, with a single material between the temperature sensor and the sample. The thermal mass of the region of the prism between the temperature sensor and the sample is low enough that there is little thermal lag, and the thermal conductivity of the prism material is typically high enough that the steady-state offset in temperature is relatively low.

[0071] The use of a prism as part of the sample cell 106 allows for the formation of a narrow beam for light scattering and also allows for the use of an embedded sensor to measure the temperature of the sample 104 with high accuracy from a location close to the sample 104.

[0072] An additional advantage of using the prism 110 to refract the light directly onto the liquid sample 104 is that the light is thereby directed onto the sample as a thin sheet. The intersection of the imaging area of ​​the light detection system with the illuminating light beam in the sample defines the scattering area of ​​the particles that is detected. The narrow light beam allows for a compact design and the use of microfluidics to introduce the sample into the sample cell, conserving sample volume.

[0073] The light source 101 may be a laser (e.g., a laser with a visible wavelength, or a wavelength in the range of 380 nm to 700 nm). A light beam 108 enters the prism 110 on a first surface 111. The light beam 108 may be perpendicular to the first surface 111. The light beam 108 exits the second (top) surface 112 of the prism 110 and is refracted (due to the difference in refractive index between the prism and the diluent containing the sample). If the light were perpendicular to the first surface 111, the angle between the first surface 111 and the second surface 112 may be selected such that the light beam exits the second surface at a very shallow angle, typically less than 5 degrees. As a result, the light beam either grazes the second surface or is substantially parallel to the second surface. The diluent may be assumed to be, for example, water, and an appropriate angle between the first surface 111 and the second surface 112 (assuming the light beam is incident perpendicularly to the first surface) may be selected based on the refractive index of the prism. Prism 110 may have a refractive index of at least 1.4, or at least 1.5. Prism 110 may include a silicate glass, such as BK7.

[0074] The holes or recesses in the prism 110 may be formed using any suitable technique. For example, the holes or recesses may be laser machined or ultrasonically drilled. Applicants have discovered that ultrasonic drilling of the holes is a particularly suitable approach because it does not cause damage to the portion of the prism 110 through which the light beam 108 passes.

[0075] In this embodiment, the temperature sensor 107 is approximately 3 mm from the second surface 112 of the prism 110, and therefore approximately 3 mm from the sample 104. Any holes or recesses in the prism 110 can cause microcracks and defects that can scatter light. Therefore, it is desirable for the temperature sensor 107 to be located far enough away from the light detection system 102 and the field of view of the illuminating light beam 108 to be unaffected by optical noise (due to scattering of the illuminating light beam or scattering of scattered light from particles). The temperature sensor should also be close enough to the scattering region that the temperature measured by the temperature sensor 107 represents the temperature of the sample in the scattering region.

[0076] In this example, the temperature sensor 107 is positioned within 15 mm of the scattering region defined by the intersection of the detection path (in this case the field of view of the microscope) and the illuminating light beam. The temperature sensor 107 is also positioned at least 10 mm off-center of the axis of the detection path 109. Similarly, the temperature sensor 107 is positioned at least 10 mm away from the illuminating light beam 108.

[0077] The temperature sensor 107 may be any suitable device. For example, a pre-calibrated thermistor (e.g., a negative coefficient thermistor) may be used. Such sensors are readily available, accurate, small, and low cost.

[0078] The top surface of the prism 110 includes a metallic coating region that reflects scattered light and a non-metallic coating region through which the illuminating light beam 108 exits the prism 110 and enters the sample 104. The illuminating light beam 108 exits the prism 110 at a location close to the metallic coating region, for example, within 5 mm or within 2 mm of the metallic coating region. The illuminating light beam 108 is refracted by the sample to illuminate an area of ​​the sample directly above the metallic coating region with a beam that is substantially parallel to the metallic coating region on the top surface 112. The metallic coating region reflects the scattering back to the light detection system 102, improving the ease of detecting scattering from the particle.

[0079] The illumination light beam 108 may be shaped by at least one light shaping optic 121 disposed between the light source 101 and the prism 110. Although the light shaping optic 121 is shown diagrammatically in FIG. 1 as a lens element, the light shaping optic 121 may include a combination of refractive optical elements and mirrors to shape and direct the light beam 108 from the light source 101 to the sample cell 106.

[0080] The illumination light beam 108 in the sample 104 may form a sheet of light adjacent to the metal coated area of ​​the top surface 112. The light beam 108 may be linearly polarized, collimated, symmetric, and thin.

[0081] The light detection system 102 is shown diagrammatically in FIG. 1 as including a light detection lens 123 and a light detector 103. As previously discussed, a typical light detection system suitable for NTA may include a substantially standard microscope having an imaging camera. For example, a long working distance objective lens can be used with a conventional microscopic optical train and imaging sensor (e.g., CCD, CMOS, etc.).

[0082] The sample cell 106 includes a cover sheet 113 through which light scattered from the particles reaches the light detection system 102. The cover sheet may include glass (e.g., silicate or borosilicate glass). Together with the prism 110 and the cover sheet 113, they define the sample cell 106 that holds the sample 104. The sample cell 106 may include part of a flow cell and has an inlet 114 and an outlet 115. The cover sheet 113 may be held by a plastic element that defines further flow paths that communicate the sample with the inlet 114 and the outlet 115.

[0083] The prism 110 is attached to a temperature regulator 120, which controls the temperature of the sample 104 (e.g., in response to a control signal from the processor 105). The temperature regulator 120 includes a heat sink 117, a thermoelectric element 118, and a thermal spreader 119. The thermoelectric element 118 is operable to heat or cool using the thermoelectric effect. The heat sink 117 blocks heat generated by the Peltier element 118, and the thermal spreader 119 ensures that heat flow to and from the thermoelectric element 118 is uniformly applied to the prism 110. The thermal spreader 119 may include aluminum or any other material with high thermal conductivity. Thermal paste (also called thermal grease) may be applied between the components of the temperature regulator 120 and between the temperature regulator 120 and the prism 110.

[0084] An ambient temperature sensor 128 is provided to measure the ambient temperature in the area of ​​the sample cell 106 .

[0085] In some circumstances, the desired temperature of the sample 104 may differ from the ambient temperature above the sample cell 106. In such circumstances, a temperature gradient may exist between the sample 104 and the temperature sensor 107 because the temperature regulator 120 may cause heat flow between the sample and the thermoelectric device 118 to maintain the desired temperature regardless of the ambient temperature. The greater the temperature difference between the sample and the surrounding air, the greater the temperature gradient tends to be. This temperature gradient may cause an error between the temperature reported by the temperature sensor 107 and the temperature of the sample 104. To correct the error, the ambient temperature sensor 128 may be positioned to measure the ambient air temperature in the area of ​​the sample cell 106. The ambient temperature may be used by the processor 105 to correct the error to the apparent sample temperature measured by the temperature sensor 107. For example, the processor 105 may correct the error using a look-up table or using a mathematical function that models the correction. Additionally or alternatively, the ambient temperature may be used to set the temperature of the sample to match the temperature of the ambient air to minimize heat flow.

[0086] The instrument 100 may be operable in two modes: (i) an ambient temperature compensation mode; and (ii) a temperature control mode. In the ambient temperature compensation mode, the temperature regulator 120 is set to maintain the temperature of the sample 104 at the same temperature as that measured by the ambient temperature sensor 128. This minimizes any heat flow between the sample 104 and the ambient environment, and therefore any temperature gradients that would cause an error between the temperature measured by the temperature sensor 107 and the true temperature of the sample 104. In the temperature control mode, the temperature regulator 120 may be used to set any desired temperature for the sample 104, and the processor may correct for temperature errors as described above.

[0087] Table 1 below shows the calculated error in particle size resulting from sample temperature error when measuring 100 nm latex particles.

[0088] [Table 1]

[0089] The effect of temperature error is greater at lower temperatures because the temperature error dominates at lower temperatures. Compared to the typical design goal of <6% for a filling system, the particle size error for a large temperature error can be significant.

[0090] Figure 5 shows a graph illustrating the accuracy achievable in some embodiments. To obtain these results, a calibrated precision sensor was placed in contact with a sample and the error in the temperature measured by the temperature sensor 107 was recorded. The temperature error is well controlled, with a temperature offset (between the sample temperature and the ambient temperature) of roughly 0.3°C, ranging from -10°C to 50°C.

[0091] Figure 2 shows an alternative embodiment, which is similar to Figure 1, except that in Figure 2, the temperature sensor 107 is a thin film sensor and is disposed on a second surface of the prism 110 in contact with the sample 104. All features disclosed with respect to Figure 1 are also applicable to Figure 2, except as they relate to the specifications of the temperature sensor 107.

[0092] The thin film temperature sensor 107 may include, for example, a platinum layer patterned into a resistor to form a platinum resistance thermometer. A chemically inert, thin (<5 pm) passivation layer (e.g., silicon nitride, silicon oxide, etc.) may be placed over the platinum resistance thermometer to reduce interaction with the sample.

[0093] This arrangement allows for more accurate measurements than the arrangement shown in Figure 1 because the temperature sensor 107 is in contact with the sample 104. However, creating a thin film sensor on a prism can be more complicated and expensive than using a readily available calibrated temperature sensor.

[0094] The invention is particularly suitable for NTA instruments, but is also applicable to DLS instruments. Figure 3 shows a schematic of a DLS apparatus 200 including a light source 201, a light detector 203, a sample cell 206, a processor 205 and a temperature sensor 207.

[0095] The light source 201, which may include a laser or light emitting diode, illuminates the sample 204 in the sample cell 206 with an illumination light beam 208 via a focusing lens 222 (which can be moved to select a specific location within the sample cell). An illumination optical fiber 233 and a fiber coupling lens 223 (e.g., a graded refractive index lens, GRIN lens) can be positioned between the light source and the focusing lens 222. The sample 204 includes particles suspended in a diluent, and the illumination light beam 208 generates scattered light by interacting with the particles of the sample. The backscattered light is detected by the photodetector 203 via a detection optical path 209, which reaches the photodetector 203 via the focusing lens 222, the coupling lens 223, and the detection optical fiber 233.

[0096] More complex detection arrangements for DLS are also possible (eg, Multi-Angle Dynamic Light Scattering (MADLS) uses multiple detection paths at different angles).

[0097] Alternatively, the photodetector 201 may be a photon-counting detector such as an avalanche photodiode. As previously described in the Background, the output from the detector 201 may be processed by the processor 205 to determine particle characteristics such as intensity-weighted particle average size (Zaverage), polydispersity, and / or particle size distribution. Such processing may include determining an autocorrelation function from the time history of the scattered intensity, determining a diffusion coefficient from the autocorrelation function, and determining particle size using the Stokes-Einstein relation (which requires the temperature of the sample as input).

[0098] Considering the effect of temperature on measurements obtained by DLS, the device may include a temperature control arrangement for controlling the sample temperature. The problems with temperature measurement already described with reference to NTA also exist in DLS. In the field of DLS temperature compensation, similar to those described with reference to NTA, the temperature sensor is typically placed at a relatively large distance from the sample, making accurate sample temperature measurement difficult.

[0099] The temperature sensor 207 in the device of FIG. 3 is placed in a recess or through-hole in the base wall 216 of the sample cell 206 at a distance of less than 3 mm from the sample. This approach is similar to that applied in FIG. 2. By using a thermally conductive potting material between the temperature sensor 207 and the sample cell 206, good thermal contact between the temperature sensor 207 and the sample cell 206 can be ensured. The sample cell 206 comprises a modified standard cuvette (e.g., a cuvette with a cross section of 1 cm×1 cm). The temperature sensor 207 may comprise a connection in the wall of the sample cell 206, which connects with a contact in the sample cell holder. The contact in the sample cell holder may be in communication with the processor 205. Inserting the sample cell 206 into the sample cell holder may result in the temperature sensor 207 being automatically connected to the processor 205.

[0100] In some embodiments, the temperature sensor 207 may not be located in a recess defined in the base wall 216 of the sample cell 206. Instead, the temperature sensor 207 may be glued to the base wall 206 with a thermally conductive epoxy. If the sample cell 206 is placed in a sample cell holder, a surface mount type device may be used and pogo pins may be used to make contact with fixed contacts on the temperature sensor.

[0101] An ambient temperature sensor 228 can be provided to measure the ambient temperature proximate the sample cell 206 as described with reference to Figure 1. The processor 205 may perform the same correction techniques (temperature correction and ambient correction modes) as described with reference to the NTA. The DLS device may also include a temperature regulator (e.g., a thermoelectric temperature regulator) not shown in Figure 3, which may operate in a similar manner as described with reference to Figure 1.

[0102] FIG. 4 shows an alternative DLS apparatus 200 similar to that shown in FIG. 3, except for the temperature sensing arrangement. In FIG. 4, instead of the temperature sensor 207 being embedded or affixed to the base wall 216 of the sample cell 206, the temperature sensor 207 is embedded in a heat spreader that is placed in thermal contact with the base wall 216 of the sample cell 206 when the sample cell 206 is placed in the sample cell holder. An actuator 230 or elastic element (e.g., a spring) can be positioned to urge the sample cell 206 towards the heat spreader to make good thermal contact. In this way, the sample cell 206 can remain a simple cuvette with relatively thin walls, and the temperature sensor 207 can be placed in close proximity to the sample 204 (e.g., closer than 3 mm or 5 mm from the sample 204). The temperature sensor 207 may have a low thermal conduction path to the sample 204 through the heat spreader material (e.g., 1.5 mm aluminum) and the base wall of the sample cell (which may be constructed of glass and be up to 1 mm thick).

[0103] While specific examples have been described, it will be understood that these examples are not limiting and that the scope of the invention should be determined by reference to the appended claims.

Claims

1. 1. A particle characterization apparatus comprising: a sample cell for holding a sample including particles suspended in a diluent; a light source configured to illuminate the sample with a light beam to generate scattered light from an interaction of the light beam with the particles; a photodetector configured to detect the scattered light and output scattering data representative of a diffusion coefficient of the particles in the diluent; a processor configured to determine a characteristic of the particle from the scattering data; a temperature sensor in thermally conductive contact with a wall of the sample cell and less than 5 mm from the sample; Including, the processor is configured to determine a characteristic of the particle using an output of the temperature sensor, the characteristic of the particle determined by the processor being responsive to the output from the temperature sensor. Particle characterization equipment.

2. the sample cell includes an optical component defining a wall of the sample cell, the temperature sensor being disposed within a recess or through-hole defined in the optical component.

10. The particle characterization apparatus of claim 1.

3. a thermally conductive potting compound disposed within the recess or through hole and in contact with the temperature sensor and the optical component.

3. The particle characterization apparatus of claim 2.

4. the optical component includes an optical prism configured to refract the light beam into the sample; 4. An apparatus for characterizing particles according to claim 2 or 3.

5. the wall includes an inner surface in contact with the sample; (ii) the optical prism includes a first surface where the light beam enters the prism and a second surface in contact with the sample, the first surface being at an angle between 10 degrees and 80 degrees with respect to the second surface; and / or (i) the optical prism is configurable to refract the light beam into the sample such that the light beam within the sample is at an angle of less than 10 degrees with respect to the second surface; 5. An apparatus for characterizing particles according to claim 4.

6. the light detector is configured to receive scattered light along a detection path, a scattering region defined by an intersection of the detection path and the illumination light beam, and the temperature sensor is less than 20 mm from the scattering region, and optionally at least 5 mm from the scattering region. The particle characteristic evaluation apparatus according to any one of claims 1 to 5.

7. the light detector is configured to receive scattered light along a detection path, and the temperature sensor is positioned at an offset of at least 5 mm from the detection path. The particle characteristic evaluation apparatus according to any one of claims 1 to 6.

8. the wall of the sample cell comprises or is composed of silicate glass; The particle characteristic evaluation apparatus according to any one of claims 1 to 7.

9. the walls of the sample cell are constructed of a transparent material having a refractive index n of at least 1.5 at a wavelength of 500 nm; The particle characteristic evaluation apparatus according to any one of claims 1 to 8.

10. configured to perform nanoparticle tracking analysis (NTA) or dynamic light scattering (DLS); The particle characteristic evaluation apparatus according to any one of claims 1 to 9.

11. and an ambient temperature sensor at least 10 mm away from the sample cell and configured to measure an ambient temperature in the region of the sample cell. A particle characteristic evaluation apparatus according to any one of claims 1 to 10.

12. (i) the processor is configured to receive an air temperature and determine a sample temperature as a function of both an output of the temperature sensor and the ambient temperature; and / or (ii) the apparatus includes a temperature regulator operable to control a temperature of the sample, the apparatus being operable in an ambient temperature compensation mode, in which the temperature regulator is used to match a temperature of the sample to a temperature measured by the ambient temperature sensor; 12. An apparatus for particle characterization according to claim 11.

13. an optical component having a surface; a temperature sensor conductively coupled to the surface and positioned within 5 mm of the surface; Including, Device.

14. illuminating a sample containing particles suspended in a diluent with a light beam to generate scattered light by interaction of the light beam with the particles; detecting the scattered light with a photodetector to generate scattering data representative of a diffusion coefficient of the particles in the diluent; processing the scattering data to determine a characteristic of the particle from the scattering data; and measuring the temperature of the sample using a temperature sensor in thermally conductive contact with a wall of a sample cell containing the sample, the temperature sensor being less than 5 mm from the sample; Including, and processing the scattering data includes determining a characteristic of the particle using an output of the temperature sensor, the determined characteristic of the particle being responsive to an output from the temperature sensor. Particle characterization methods.

15. (i) receiving a measurement of an ambient air temperature and determining a sample temperature as a function of both an output of the temperature sensor and the ambient temperature; and / or (ii) using a temperature regulator operable to match the temperature of the sample to the ambient air temperature; Further comprising: The method of claim 14.

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