Patent Description:
Embodiments of the present invention relate in general to systems and methods for sensing and characterizing small particles, and in particular to techniques for detecting and evaluating blood cells suspended in a liquid medium having an electrical impedance per unit volume which differs from that of the cells.

A seminal method for sensing particles suspended in a liquid medium is described in <CIT>. Over the past several decades, a broad variety of devices based on the Coulter principle described therein have been proposed, including highly automated hematology implementations.

Although such developments provide clinically useful devices for analyzing biological samples of an individual, still further improvements are desirable. For example, there is a continuing need for accurate and cost effective ways to analyze particles, and in particular blood cells of a biological sample obtained from a human individual. Embodiments of the present invention provide solutions for at least some of these outstanding needs. <CIT> discloses a method and apparatus for sensing and characterizing particles. <CIT> discloses an electrode assembly for resistive pulse spectroscopy. <CIT> discloses a particle analyzing apparatus having a flow cell with an elongated or tube-like aperture.

In accordance with embodiments of the present invention there is provided systems and methods for sensing and characterizing particles by the Coulter principle. Particle evaluation systems is embodied in devices having a two-terminal configuration where both excitation and sensing functions are provided by or faciliated by conduit walls of an aperture. In some instances, the operation of devices may involve the use of low current densities which leads to little or no electrolysis (and corresponding gas bubble generation) which may otherwise interfere with detection and sizing of particles going through a composite conduit. For example, operation of the device may avoid or lessen the production of high field gradients near the join of an entry field amending unit and an insulative center of a field amending sandwich.

Exemplary particle evaluation systems include a volumeter assembly through which a liquid suspension of particles to be sensed and characterized can be made to pass, and a liquid containment system that holds a particle suspension which is passed through a conduit of the volumeter assembly. The volumeter assembly can be constructed such that the electrical resistivity of a wall defining the volumeter conduit varies in an axisymmetric manner along the conduit length (i.e., in a direction parallel to the flow of suspension through the conduit). In some instances, the conduit provides a central region of high electrical resistivity which is smoothly contiguous on its opposing boundaries to distal regions of substantially lesser electrical resistivity. Such distal regions can also be referred to as field amending units. The peripheral field amending units and intervening central substrate can provide a hydrodynamically smooth conduit containing wall.

The evaluation systems and methods disclosed herein are well suited for use in analyzing any of a variety of particles, including blood cells such as white blood cells, red blood cells, platelets, and other components of blood or biological samples. In some instances, particle evaluation systems can be implemented as or part of hematology systems for use in clinical, laboratory, or other biomedical settings. In some instances, particle evaluation systems can be implemented for industrial particle analysis applications.

Particle evaluation systems includes electronic circuitry in operative association with the field amending units. Such circuitry is configured to produce electrical excitation current through the volumeter conduit and also to monitor the amplitude of the electrical current through the volumeter conduit to sense the characteristics of particles passing through said conduit. In some instances, the central region of high electrical resistivity can be provided by a sapphire substrate, and the electronic circuity associated with the distal regions can be formed by integrated-circuit techniques. In some cases, particle evaluation systems can be constructed without including certain features used in known systems, such as hydrodynamically focused flow and sweep flow. In many cases, particle evaluation systems as disclosed herein allow for reduced coincidence volumes.

Particle evaluation systems according to embodiments of the present invention can also provide simplified apparatus construction features and reduced building costs. Further, such systems can be provided in convenient forms for a broad range of particle sensing and characterizing applications. For example, minimal AC or DC versions packaged as remote transducers may be useful in many process applications, where they can be adapted to detect particles in the normal fluid flow. Further, DC versions may be adapted into instruments serving solute-analytic functions, thereby providing a particle detection, sizing, or characterization function as well. In some instances, a small hand-held, battery-powered version (e.g. a dipstick Coulter counter) may be useful in marine biology. A similar version may be useful in environmental studies at remote sites, and the like. In some instances, such an instrument may include a rubber bulb, a plastic bellows, or other fluid control means, to draw or express a set volume of sample suspension through the volumeter conduit of the particle evaluation system. In some instances, a micro-pipette having highly adjustable volume-aspiration mechanism can be used to draw or express a set volume of sample suspension through the volumeter conduit of the particle evaluation system.

The particles to be characterized are suspended in a liquid medium having an electrical impedance per unit volume which differs from that of the particles. The particles pass substantially one at a time through an electrically excited field-amending volumeter conduit while changes in electrical current through the conduit are monitored using the field amending units.

All features of the described systems are applicable to the described methods mutatis mutandis, and vice versa.

In one aspect, embodiments of the present invention encompass a system for evaluating particles of a biological sample obtained from an individual according to claim <NUM>. The method is set out in claim <NUM> and the dependent claims define preferred implementations of the invention.

The above described and many other features and attendant advantages of embodiments of the present invention will become apparent and further understood by reference to the following detailed description when considered in conjunction with the accompanying drawings.

Embodiments of the present invention encompass systems and methods for sensing and characterizing particles. In some instances, particle evaluation systems can be provided as handheld devices which operate upon the Coulter principle.

Turning now to the drawings, <FIG> depicts aspects of an exemplary particle evaluation system <NUM> according to embodiments of the present invention. The system <NUM> can be used for evaluating particles of a biological sample obtained from an individual. As shown here, the system <NUM> includes a dual-compartment dielectric vessel <NUM> containing a wall <NUM> of dielectric material separating compartments <NUM> and <NUM>, each of which contains a particle-suspending liquid medium M (e.g., isotonic saline solution). System <NUM> also includes a volumeter assembly <NUM> having a volumeter conduit C that is adapted to receive a particle-containing fluid suspension therethrough. The volumeter assembly <NUM> may be coupled with or integral to wall <NUM>. A small through-hole transpiercing volumeter assembly <NUM> provides a volumeter conduit C which constitutes an operative electrical and fluidic connection between compartments <NUM> and <NUM>. Hence, a first chamber or compartment <NUM> can contain a fluid suspension or a portion thereof, and can be in fluid communication with a first orifice (e.g. an opening in assembly <NUM> facing toward chamber <NUM>). Similarly, a second chamber or compartment <NUM> can contain a fluid suspension or a portion thereof, and can be in fluid communication with a second orifice (e.g. an opening in assembly <NUM> facing toward chamber <NUM>).

In operation, an electrical source <NUM> electrically connected with field amending units <NUM>, <NUM> establishes an electrical flow through conduit C. For example, where the electrical source is a current source, the source <NUM> establishes a current flow through conduit C. In some instances, particles (P) can be introduced into compartment <NUM> via inlet port <NUM>, and a vacuum applied to port <NUM> can operate to establish or facilitate a flow of suspended particles (P) from compartment <NUM> through conduit C and into compartment <NUM>. In addition to or as an alternative to the inlet and vacuum port fluid control features shown here, embodiments of the present invention encompass the incorporation of any of a variety of other fluid-control means for facilitating passage of suspended particles (P) through the conduit. Often, operation of a particle evaluation system may involve coordinating the function of a fluid-control means with characteristics of the conduit.

Conduit C may operate to constrict both the electric and hydrodynamic fields so established in vessel <NUM>, so that wall <NUM> of conduit C surrounds and defines the flows of particle suspension and electric current between compartments <NUM> and <NUM>. As discussed elsewhere herein, the conduit can provide a wall of hydrodynamic smoothness, having contiguity at the junction of the first and second peripheral conduit walls (e.g. associated with field amending units <NUM>, <NUM>) with the central conduit wall (e.g. of a central substrate disposed between the field amending units). The conduit defines an axial conduit wall length having a central region of higher electrical resistivity (e.g. corresponding to the central substrate) disposed between a first distal region (e.g. corresponding to field amending unit <NUM>) of lower electrical resistivity and a second distal region (e.g. corresponding to field amending unit <NUM>) of lower electrical resistivity. According to the example not forming the present invention, the central region of the conduit wall length can be provided by a layer of material having high electrical resistivity, and the first and second distal regions of the conduit wall length can be provided by a first layer of material having a lower electrical resistivity and a second layer of material having a lower electrical resistivity, respectively.

Exemplary methods for evaluating particles of a biological sample obtained from an individual may include transmitting a fluid suspension containing the particles (P) through a volumeter assembly conduit (C). The conduit defines an axial conduit wall length having a central region of higher electrical resistivity disposed between a first distal region (e.g. corresponding to field amending unit <NUM>) of lower electrical resistivity and a second distal region (e.g. corresponding to field amending unit <NUM>) of lower electrical resistivity. Methods also include providing an electrical excitation current to the first and second distal regions with a current source and sensing circuit module (e.g. electrical source <NUM> in combination with sensing circuit <NUM>) in electrical connectivity with the first and second distal regions, so as to establish a particle-sensitive zone within the conduit (e.g. zone Z as shown in <FIG>). Further, methods include detecting current changes occasioned by the particles (P) of the biological sample passing through the particle-sensitive zone with the current source and sensing circuit module via the first and second distal regions.

In some instances, electrical source <NUM> is a constant-current source such that the current it supplies is substantially independent of changes in impedance between field amending units <NUM> and <NUM>. In some instances, electrical source <NUM> is a voltage source having a high internal impedance. In some instances, a sensing circuit <NUM> can be in operative association with field amending units <NUM>, <NUM>, and can function to detect impedance changes within the conduit C occasioned by particles passing therethrough. Hence, a current source (e.g. source <NUM>) and sensing circuit (e.g. source <NUM>), optionally in combination as a module, can be in electrical connectivity with first and second distal regions of the volumeter assembly, such that the current source and sensing circuit module is configured to provide an electrical excitation current to the first and second distal regions (e.g. corresponding to field amending units <NUM>, <NUM>) to establish a particle-sensitive zone within the conduit, and the current source and sensing circuit module can be configured to detect current changes occasioned by particles of the biological sample passing through the particle-sensitive zone. As shown here, circuitry <NUM>, <NUM>, <NUM>, and <NUM> can be electrically associated with field amending units. These circuitry components can operate to sense, monitor, process current pulsations in conduit current as occasioned by the more or less individual passage of particles through conduit C, and display evaluation results. For example, the circuitry can include a sensing circuit component <NUM> such as an AC-coupled sensing circuit, a counter and processing circuitry component <NUM>, a sizing circuitry component <NUM>, and a display or recording component <NUM>. The display or recording component <NUM> can operate to display or record particle count and characteristic data. In some instances, electrical source <NUM> is configured to provide a DC current. In some instances, electrical source <NUM> is configured to provide an AC current. In some instances, electrical source <NUM> is configured to provide a combination of AC and DC currents. According to certain embodiments, electrical source <NUM> includes an AC-coupled sensing circuit that has a low input impedance compared to the conduit impedance. With current excitation, it may be desirable to use low-input impedance in a preamp.

Hence, a particle evaluation system provides an exemplary means for detecting, counting, or otherwise analyzing particles whereby a fluid containing such particles is passed through a constricted path within a conduit, and the presence or absence of a particle within the constriction or conduit gives rise to a detectable change in the electrical characteristics of the constricted fluid path. Relatedly, a particle evaluation system provides an exemplary means for detecting, counting, or otherwise analyzing particles whereby a constricted current path is established within a fluid suspension containing particles, and the presence or absence of a particles disposed in the constricted current path can produce detectable changes in the circuit carrying the current.

As discussed elsewhere herein, due at least in part to certain properties of the conduit C, the evaluation apparatus <NUM> may provide accurate particle characterization results, without using fluidic subsystems such as hydrodynamic flow focusing or sweep flow.

According to some embodiments, a direct current (DC) can be provided through the conduit, and resistive Coulter volume (V) signals can be acquired via the field amending units positioned outside the opposite ends of the volumeter conduit. According to some embodiments, an excitation current including at least one alternating current (AC) can be provided through the conduit, thereby permitting determination of not only the resistive but also reactive components of the conduit current resulting from its modulation by passage of a particle body. When such currents include one having a frequency in the radio-frequency (RF) range (e.g., <NUM>), the respective components permit estimation of the volume (V) and electrical conductivity (C) of a formed body, and the ratio of the reactive to resistive components can said to be the "opacity" of the particle body.

<FIG> depicts aspects of a volumeter assembly <NUM> according to an example useful for understanding the disclosure. As discussed elsewhere herein, a volumeter assembly can be part of a particle evaluation system such as that shown in <FIG>. For example, the volumeter assembly may be disposed between compartments that contain a particle-suspending liquid medium, such that a volumeter conduit C provides an operative electrical and fluidic connection between the compartments. As depicted in <FIG>, field amending units <NUM>, <NUM> can be in operative electrical connectivity with an electrical source and sensing circuit module <NUM>, for example via respective conductive connections <NUM>, <NUM>. The electrical source can include a current source or a voltage source. According to the configuration shown here, the field amending units <NUM>, <NUM> can operate as electrodes for providing electrical excitation to the aperture or conduit C, and can also operate to perform a pulse pickup function when a particle transits the composite volumeter conduit C (e.g. through field amending unit <NUM>, substrate <NUM>, and field amending unit <NUM>).

In some examples useful for understanding the disclosure, the volumeter assembly <NUM> can be constructed as a flow cell of the type described in <CIT> or <CIT>. Such flow cells can be made from an optically transparent material such as fused quartz, synthetic silica, sapphire, or beryllia, and can be used in devices which combine the Coulter principle with optical sensing modalities. Other suitable materials for use in construction of the volumeter assembly are discussed elsewhere herein. Exemplary flow cell embodiments include the devices of <CIT><CIT>, and <CIT>. In some instances, evaluation systems as disclosed herein may include fluidic subsystems providing hydrodynamically focused flow. In some instances, particle evaluation systems may not include fluidic subsystems providing hydrodynamically focused flow. In some instances, particle evaluation systems as disclosed herein may include fluidic subsystems providing sweep flow. In some instances, particle evaluation systems may not include fluidic subsystems providing sweep flow. In some instances, particle evaluation systems as disclosed herein may include fluidic subsystems providing hydrodynamically focused flow and sweep flow. <CIT> discusses hydrodynamically focused flow and sweep flow techniques which could be used in conjunction with particle evaluation techniques disclosed herein.

According to certain examples useful for understanding the disclosure, a volumeter conduit C can have a constant circular cross-section, of a diameter D in the <NUM> to <NUM> range. As shown here, volumeter assembly <NUM> includes a first field amending unit or collar <NUM> and a second field amending unit or collar <NUM>. The field amending units <NUM>, <NUM> also include interior passages or apertures of diameter D, and are adapted into conical cups <NUM> and <NUM> in the dielectric flow cell <NUM>. The thicknesses of collars <NUM> and <NUM> combine with the length L of functional conduit <NUM> to form the hydrodynamically smooth conduit C.

In some instances, collars <NUM>, <NUM>, can be made of a platinum alloy or other appropriate material. According to some embodiments, the field amending units or collars <NUM>, <NUM> can be inset into flow cell <NUM> so that the outer collar surfaces are smoothly continuous with the conical cups <NUM> or <NUM>. Elements <NUM> and <NUM> can be joined with flow cell <NUM> using any appropriate method, e.g., use of metal-loaded epoxies or frits, or extensions <NUM> and <NUM> which may provide or be part of electrically conductive paths <NUM> and <NUM> to respective collars <NUM> and <NUM>. In other implementations, holes formed through element <NUM> (and located out of any desired optical path) may be used to provide access for electrically conductive path <NUM> or <NUM> to respective field-amending collars <NUM> or <NUM>. In some cases, a compatible conductive epoxy may be used to both establish and protect the electrical junction. For example, the conductive paths <NUM> and <NUM> to respective elements <NUM> and <NUM> can be coated with epoxy or insulating elements <NUM> and <NUM>. Accordingly, the conductive paths can be protected from any degrading influence of a suspending medium or other deleterious factors. As shown here, conductive connections <NUM>, <NUM> can also be in operative electrical connectivity with a current source and sensing circuit module <NUM>.

In some examples useful for understanding the disclosure, volumeter assemblies may provide conduits of prismatic cross section, for example such as those as discussed in <CIT>, by incorporating appropriate collars of minimal thickness at least approximating the diagonal of the particular conduit cross section and providing operative electrical connections thereto. In some instances, conduits of square cross section may be implemented in particle evaluation systems. Hydrodynamically focused flow may be used with field-amending volumeter conduits, e.g., to stabilize suspension flow through the sensitive zone. As discussed elsewhere herein, a particle evaluation system may operate without using hydrodynamically focused flow. In some cases, the length L, the entry shape of collar <NUM>, or other parameters of the volumeter conduit may be selected so that acceptable performance can be achieved without use of hydrodynamically focused flow.

As discussed elsewhere herein, the conduit C can provide a wall of hydrodynamic smoothness, having contiguity at the junction of the first and second peripheral conduit walls (e.g. associated with field amending units <NUM>, <NUM>) with the central conduit wall (e.g. of a central substrate <NUM> disposed between the field amending units. The conduit C can operate to receive suspended particles therethrough, and can define a central wall region (e.g. provided by substrate <NUM>) disposed between a first peripheral wall region (e.g. provided by field amending unit <NUM>) and a second peripheral wall region (e.g. provided by field amending unit <NUM>). The central wall region typically has an electrical impedance greater than electrical impedances of the first and second peripheral wall regions. In operation, the electrical source provides electrical excitation to the first and second peripheral regions, and the sensing circuit, which is also coupled with the first and second peripheral regions, detects impedance changes within the conduit occasioned by particles passing therethrough.

<FIG> shows aspects of a volumeter assembly <NUM>, according to embodiments of the present invention. Here, a conduit C is provided by a substrate <NUM> and field amending units <NUM>, <NUM>. As shown here, the field amending units <NUM>, <NUM>, can operate to establish internal e-field equipotentials <NUM> associated with the interior of the conduit, and external e-field equipotentials <NUM> associated with the exterior of the conduit. In some instances, the substrate <NUM> is made of sapphire, although other materials may be used for fabrication of the substrate as discussed elsewhere herein. The volumeter assembly may also include electrodes or conductive connections <NUM>, <NUM> in operative association or electrical connectivity with field amending units <NUM>, <NUM>, respectively. The conductive connections <NUM>, <NUM> or other electrical circuitry associated therewith can be produced using integrated circuit techniques. In some cases, conductive connections can be placed on the substrate using techniques such as those described in <CIT>.

As shown here, the field amending units <NUM>, <NUM> can be in operative electrical connectivity with an electrical source <NUM> and sensing circuit <NUM>. In some embodiments, the electrical source and sensing circuit can be provided as separate modules. In some embodiments, the electrical source and sensing circuit can be combined in a single module. In some embodiments, the electrical source and sensing circuit can be electronically coupled with the field amending units via respective conductive connections <NUM>, <NUM>. The electrical source may include a current source or a voltage source. As shown here, the conduit C can provide a wall of hydrodynamic smoothness, having contiguity at the junction of the first and second peripheral conduit walls (e.g. associated with field amending units <NUM>, <NUM>) with the central conduit wall (e.g. of a central substrate <NUM> disposed between the field amending units). The conduit C can operate to receive suspended particles therethrough, and can define a central wall region (e.g. provided by substrate <NUM>) disposed between a first peripheral wall region (e.g. provided by field amending unit <NUM>) and a second peripheral wall region (e.g. provided by field amending unit <NUM>). The central wall region typically has an electrical impedance greater than electrical impedances of the first and second peripheral wall regions. In operation, the electrical source provides electrical excitation to the first and second peripheral regions, and the sensing circuit, which is also coupled with the first and second peripheral regions, detects impedance changes within the conduit occasioned by particles passing therethrough. Based on this design, it is possible to operate the device using low current or power. Operation of the device may also avoid or reduce the generation of high field gradients near an interface between a peripheral conductive field amending unit and the central insulative substrate, which in turn can eliminate or reduce the generation of gas bubbles due to electrolysis caused by current densities, and hence can improve the detection or sizing of particles passing through the conduit (e.g. without undue interference from such gas bubbles). In some instances, an external field caused by a field amending unit (e.g. in the absence of inhibition provided by an external excitation) is sufficiently weak that it does not unduly affect performance of the device.

According to some embodiments, an external field can originate from potentials applied to the field-amending elements and/or from external electrodes remote from them. If both fields are present, as in the case of a four-terminal potential-sensing configuration, the external field can be the result of superposition of the two, but with lessening impact the further from the conduit. In some cases, external fields caused by remote excitation electrodes can be distributed differently due to the conductive field amending units on a conduit substrate.

According to some embodiments, equipotentials are only part of an orthogonal network originating at right angles to insulative surfaces and more or less parallel to conductive ones, and another part of the network (not shown in <FIG>) may include the current trajectories which intersect the equipotentials at right angles.

According to certain embodiments, the substrate or separating layer <NUM> of volumeter assembly <NUM> includes a solid material of resistivity substantially greater than that of the suspending medium M in which the particles to be characterized are suspended. As shown here, the substrate <NUM> can include an inner aperture of diameter D that is smoothly contiguous and unitary with inner apertures of respective axially-distal layers or elements <NUM> and <NUM>. The distal layers or field amending elements <NUM>, <NUM> can include uninsulated solid material of resistivity substantially less than that of suspending medium M.

In some cases, conduit C provides a continuous wall <NUM> defining a right cylindrical conduit of circular cross-section through volumeter assembly <NUM>. For example, wall <NUM> can be a bore-wall and the conduit cross-section is constant along the axis. In some cases, prismatic or non-constant conduit cross-sections may be used. As shown here, conduit C includes an entry orifice or edge <NUM> and an exit orifice or edge <NUM>. As discussed elsewhere herein, by delivering electrical excitation to field amending units that are at the conduit, it is possible to operate a particle evaluation system using less power than what might otherwise be needed when delivering electrical excitation to electrodes disposed at a remote distance from the conduit. The use of lower current to the excited field amended units, for example, can also result in a reduced amount of electrolytic bubble formation at the edges <NUM>, <NUM>.

Conduit C can be defined by a continuous, hydrodynamically smooth wall <NUM> collectively including sequential wall portions through elements <NUM>, <NUM>, and <NUM>, such that contiguous complementary surfaces of elements <NUM> and <NUM> form hydrodynamically smooth delimiting boundary <NUM>, and those of <NUM> and <NUM> form hydrodynamically smooth delimiting boundary <NUM>, respectively, between the portions of conduit C bounded by the respective elements <NUM>, <NUM>, and <NUM>.

Accordingly, wall portions of conduit C can thus be circumferentially bounded by an uninsulated solid material composing the respective elements and smoothly contiguous at delimiting boundaries <NUM> and <NUM>, respectively, to a congruent adjacent wall portion. Consequently, the characteristic electrical resistivity of defining wall <NUM> can be caused to be substantially axisymmetric, and in some embodiments can be made to have significant axial gradients at delimiting boundaries <NUM> and <NUM> along the length of any longitudinal section of conduit C. The characterizing axial variation in axisymmetric resistivities may originate in the characteristics of the solid materials selected for the make-up of volumeter assembly <NUM>, although geometries of individual elements may be caused to augment certain properties of conduit C. Volumeter assemblies incorporating the characteristic axial variation in axisymmetric resistivity of wall <NUM> may be embodied by a variety of techniques in a broad range of designs, geometries, and materials.

In some instances, the field amending distal elements <NUM> and <NUM> assume individual potentials over their surfaces which directly superimpose independent equipotentials in the vicinity of conduit C. For example, the field amending units <NUM>, <NUM> can operate to establish e-field equipotentials, both inside and outside of the conduit, which depend on the potential between the field amending units, such that both parts of the e-field scale with the potential. In some instances, the distribution of a resultant hydrodynamic through-field depends at least in part on D and the cumulative length (L'+L<NUM> + L<NUM>) of conduit C, where L<NUM> and L<NUM> are the dimensions along wall <NUM> of elements <NUM> and <NUM>, respectively, and L' is the dimension along wall <NUM> of element <NUM>.

It is understood that certain features of <FIG> are intended to provide an illustrative example, and that certain features may vary in practice. For example, the equipotentials coming off the edges of element <NUM> may become concentric to the conduit axis, i.e., parallel to the conduit surfaces of <NUM> and <NUM>, so that not all originate at the outer edge of those two elements. Relatedly, the equipotentials may be extended continuously outward from the edges of <NUM> into the space outside <NUM> and <NUM>, with only the weakest equipotentials seeming to originate at the orifices of the conduit portions.

The e-field distribution is typically determined by the shape of the field-amending elements <NUM> and <NUM> and the potential difference between them. It is noted that where a voltage source is used, such a source can make the sensed particle pulse sensitive to both electrolyte conductivity and its resistivity change with ambient temperature. As discussed elsewhere herein, the e-field equipotentials, both inside and outside the conduit, typically depend on the potential between the field-amending elements <NUM> and <NUM>, that is, both parts of the e-field scale with the potential.

In the two-terminal embodiment depicted in <FIG>, there is no e-field imposed by remote electrodes. Rather, this drawing indicates that potential can be independently applied to the field-amending elements. As discussed elsewhere herein, particles are typically characterized according to the internal conduit fields <NUM>. The equipotentials <NUM> external to the field amending unit outer surfaces typically have relatively low potentials, and thus these external fields may be so minimal as to provide little or no contribution to the particle characterization process. During operation, the external e-fields of the field amending units can operate to lengthen an initial and a final near-baseline phase of a sigmoidal rise and fall of particle pulses (e.g. when considering detected current as a function of particle position, as the particle transits the conduit). Typically, these leading and trailing pulse edges are below threshold levels and can be mitigated by DC-restoration methods. For homogeneous surrounding electrolyte in the absence of other applied e-fields, the e-field equipotentials established by field-amending elements <NUM> and <NUM> can be almost totally determined by their geometry and potential and so can be nearly independent of whether driven by a current or voltage source. In some instances, the bulging external equipotentials <NUM> due to the field amending units can have voltages at single digit percentages of the voltage applied, and such low voltages can be below typical sensing levels, and can cause a slowly rising and falling initial and final pulse phases, respectively.

According to certain embodiments, due to their immersion in the particle-suspending liquid medium surrounding volumeter assembly <NUM> and filling conduit C, field amending distal elements <NUM> and <NUM> of volumeter assembly <NUM> may assume individual potentials over their surfaces which impose new field distributions in the axisymmetric electric field established by current through the conduit. For axial lengths L<NUM> or L<NUM> of elements <NUM> or <NUM> greater than approximately the conduit diameter D, the resultant electric field external to conduit C is substantially homogeneous.

As shown here, internal ambit fields or equipotential field regions <NUM> can operate to provide a particle sensitive zone Z that is within volumeter conduit C. The distribution of the resultant electric field making up sensitive zone Z may depend at least in part on conduit diameter D at boundaries <NUM> (e.g. within conduit and defined between field amending unit <NUM> and substrate <NUM>) and <NUM> (e.g. within conduit and defined between substrate <NUM> and field amending unit <NUM>) and axial length L' of conduit portion <NUM>, while the semielliptical equipotentials corresponding to a desired detectability threshold may operate to at least in part determine the effective spatial extent of ambit fields <NUM>.

According to certain embodiments, conduit C provides an axial variation in axisymmetric wall resistivity. Further, in certain embodiments, conduit C is fluidically continuous and hydrodynamically smooth throughout its length. In some cases, element <NUM> has an electrical resistivity substantially greater than that of the particle-suspending medium M and is can be made from a dielectric such as ruby, sapphire, alumina, beryllia, synthetic quartz, or other material suited to a given application. In some cases, element <NUM> may be made from a lossy dielectric such as a conductive glass, a conductive ceramic, or a type of conductive polymer or plastic, the resistivity of which is effectively greater than that of the suspending medium but less than that of the aforementioned dielectrics. In some cases, elements <NUM> and <NUM> have resistivities substantially less than that of the suspending medium M. In some cases, elements <NUM> and <NUM> can be made from metals or alloys from the platinum group or conductive ceramics such as certain titanium, tungsten, or silicon carbides. Some applications may benefit from use of metals such as gold, silver, titanium tantalum, tungsten, or their various alloys. Still other applications may benefit from use of nickel, copper, or their alloys, either as a metal or as a cermet comprising one of these metals infiltrated into the microstructure of a ceramic such as alumina. Yet other applications may benefit from use of glassy carbon. Elements <NUM> and <NUM> need not be of the same material, and some applications of the volumeter assembly may benefit from a judicious mismatch in one or more material properties. In some cases, the materials may be homogeneous. In some cases, the materials may be inhomogeneous. In some cases, elements <NUM> or <NUM> may be formed from one material and coated or plated with another material in order to provide combinations of material properties. In some cases, high-resistivity element <NUM> is formed of alumina of appropriate grain size and purity, and elements <NUM> and <NUM> are made of an appropriate cermet (e.g., alumina infiltrated with nickel or other metal appropriate to the intended application) or one of the conductive ceramics (e.g., titanium carbide). Complementary elements <NUM>, <NUM>, and <NUM> may be molded (e.g., by injection processes), sintered, finished to form if desired, and joined (e.g., by appropriate brazing methods or through use of appropriate metal-filled adhesives) prior to transpiercing and finishing volumeter assembly <NUM> to the desired conduit diameter D' and lengths L<NUM> and L<NUM>.

In some embodiments, elements <NUM> and <NUM> of volumeter assembly <NUM> may be either preformed of one of the metallic conductors and appropriately affixed into concavities in element <NUM> or formed in place therein, e.g., through use of an appropriate metallic-filled adhesive or paint. For example, discs of <NUM> thickness may be prepared from a convenient rod of <NUM>% purity alumina having grain size in the range between <NUM> and <NUM>, and centered spherical concavities approximately <NUM> deep by <NUM> in segment diameter at the surface of the disc are prepared on each side of the discs. In some embodiments, concavities in element <NUM> may be either filled with gold-filled adhesive and cured, or given repeated coats of a platinum-filled paint such as used in forming electrodes on glass and fired, according to the appropriate protocol to form a slightly protruding conductive deposit in each concavity. Each disc may then be lapped flat on each surface to form elements <NUM> and <NUM>, transpierced through the center of the disc, and the through-holes finished to form hydrodynamically smooth circular conduit C. In some embodiments, element <NUM> of a volumeter conduit may include a lossy ceramic. In some embodiments, a volumeter assembly <NUM> may be constructed from a single material, by using suitable doping methods to induce an appropriate resistivity profile. At the site intended for forming the through-hole defining field-amending conduit C, the electrical resistivity of an appropriate solid substrate may be made to effectively vary through the thickness thereof, e.g., to define a central delimited region of high electrical resistivity (approximately equal in thickness to the intended conduit diameter) which is contiguously bounded by distal regions of substantially lesser electrical resistivity (approximately equal in thickness to one to three times the intended conduit diameter). For example, suitable semiconductor impurity doping methods may be used to create regions <NUM> and <NUM> of substantially lesser resistivity which intersect the surfaces on opposite sides of an intrinsic semiconductor (e.g., silicon) substrate <NUM> to form exposed regions of diameter approximately five times the conduit diameter. The exposed surfaces of regions <NUM> and <NUM> may be electrically uninsulated, and all exposed surfaces of volumeter assembly <NUM> may be made to be compatible with the liquid medium used to suspend the particles.

According to some embodiments, the field amending units <NUM>, <NUM> and the respective conductive connections <NUM>, <NUM> may be constructed of the same material. In some instances, a combined field amending unit and conductive connection (e.g. elements <NUM> and <NUM>) can be provided as a single unitary structure. As discussed elsewhere herein, the field amending units can operate to shape the ambit fields of the conduit or aperture. Relatedly, currents between electrodes or conductive connections near the field amending units can also affect the ambit fields (e.g. fields <NUM> and <NUM>).

As shown here, where the field amending units are configured to function as aperture excitation electrodes, the allowable aperture excitation current can be significantly reduced. Because low aperture excitation currents can be effectively employed, exemplary particle evaluation volumeter assemblies (e.g. two terminal configurations) are well suited for use in producing a Coulter Counter on a chip, with or without actual single-chip implementation of the aperture and electronics. For example, the power requirements involved with effectively exciting such volumeter conduits can be significantly reduced compared with other known aperture based sensing systems. By incorporating the use of lower excitation currents, it is possible to implement particle evaluation systems with more integrated components and smaller hybrid components.

In a four-terminal configuration, the shape of the electrode or conductive connection may have a more significant effect where the electrode or conductive connection is positioned more closely to the conduit or aperture. Depending on any impedance operatively connected to the conductive connections <NUM>, <NUM>, the contact between the conductive connections <NUM>, <NUM> and the corresponding field amending units <NUM>, <NUM> may affect the surface potentials of the field amending units. Hence, in some embodiments, the field amending units and conductive connections may be free of connections to any other external circuitry, other than that associated with the current source and sensing circuit.

<FIG> illustrates aspects of a volumeter assembly <NUM> of a particle evaluation system, according to an example useful for understanding the disclosure. Volumeter assembly includes a substrate <NUM>, and first and second field amending units <NUM>, <NUM>. As shown here, the first field amending unit <NUM> is operatively connected with a first electrode or conductive connection <NUM>, and the second field amending unit <NUM> is operatively connected with a second electrode or conductive connection <NUM>. Conductive connections <NUM>, <NUM> are in electrical connectivity with other circuitry, such that the field amending units <NUM>, <NUM> can operate to facilitate the sensing of electrical fluctuations within conduit C or circuitry associated with the field amending units.

During a particle evaluation process or method, where electrical excitation is provided at the conduit via the field amending units <NUM>, <NUM>, a particle transiting through conduit C can operate to raise change the resistivity within the confines of the substrate wall <NUM>. For example, the particle may increase the resistance inside of the conduit. Accordingly, where a current source is used, excitation current provided by a field amending unit which would otherwise pass through the conduit in the absence of such a particle or increased resistivity consequently may be diverted either back into the excitation source (e.g. electrical source <NUM>) or into the sensing circuitry (e.g. circuit <NUM>) depending on the relative impedance of the excitation source and sensing circuit. For example, with a low-impedance sensing circuit, the current can be diverted into such a sensing circuit and sensed therein as a current pulse. Where the excitation source <NUM> is a voltage source, a particle transiting through conduit C can operate to produce a voltage pulse. Hence, in some instances evaluation of a particle may involve sensing pulsations in current, and in some instances evaluation of a particle may involve sensing pulsations in voltage.

In this sense, the volumeter assembly facilitates a two-terminal current sensing Coulter approach for analyzing particles. For example, as shown here, the field amending units <NUM>, <NUM> is in operative electrical connectivity with a current source and sensing circuit module, for example via respective conductive connections <NUM>, <NUM>. Relatedly, the volumeter assembly facilitates a two-terminal potential sensing Coulter approach for analyzing particles. For example, as shown here, the field amending units <NUM>, <NUM> is in operative electrical connectivity with a voltage source and sensing circuit module, for example via respective conductive connections <NUM>, <NUM>. Such configurations can allow the volumeter assembly to operate in the absence or minimized presence of a hydrodynamically focused flow for guiding particles through the conduit. These constructions can also allow such volumeter assemblies to operate in the absence or minimized presence of a sweep flow for moving particles once they have passed through the conduit. In an example not forming part of the present invention, the field amending conductive collars at the conduit inlet and outlet orifices can operate to contain the orifice electric fields therewithin, and thus the coincidence volume of the conduit can be reduced.

The conduit C can provide a wall of hydrodynamic smoothness, having contiguity at the junction of the first and second peripheral conduit walls (e.g. associated with field amending units <NUM>, <NUM>) with the central conduit wall (e.g. of central substrate <NUM> disposed between the field amending units). The conduit C can operate to receive suspended particles therethrough, and can define a central wall region (e.g. provided by substrate <NUM>) disposed between a first peripheral wall region (e.g. provided by field amending unit <NUM>) and a second peripheral wall region (e.g. provided by field amending unit <NUM>). The central wall region typically has an electrical impedance greater than electrical impedances of the first and second peripheral wall regions. In operation, the electrical source provides electrical excitation to the first and second peripheral regions, and the sensing circuit, which is also coupled with the first and second peripheral regions, detects impedance changes within the conduit occasioned by particles passing therethrough.

As depicted in <FIG>, the field amending units <NUM>, <NUM> are contiguous with the respective conductive leads <NUM>, <NUM>. Conduit C is defined by a substrate wall <NUM>, and coaxially aligned congruent wall portions <NUM> and <NUM> of the field amending units <NUM>, <NUM>, respectively. The uninsulated elements <NUM>, <NUM> may be operatively connected with respective electrodes or conductive connections <NUM>, <NUM> by an appropriate conductive bond <NUM>, such as a conductive epoxy or a low-temperature solder. Hence, conduit C can be defined by a continuous, hydrodynamically smooth wall that collectively includes sequential wall portions <NUM>, <NUM>, and <NUM>, through elements <NUM>, <NUM>, and <NUM> of the volumeter assembly <NUM>. The contiguous complementary surfaces of elements <NUM> and <NUM> form a hydrodynamically smooth delimiting boundary <NUM>, and the contiguous complementary surfaces of elements <NUM> and <NUM> form a hydrodynamically smooth delimiting boundary <NUM>, respectively, between the portions of conduit C bounded by the respective elements <NUM>, <NUM>, and <NUM>. Thus, the individual wall portions (<NUM>, <NUM>, and <NUM>) of conduit C are circumferentially bounded by the uninsulated solid material composing the respective elements (<NUM>, <NUM>, and <NUM>) and smoothly contiguous at boundaries <NUM> and <NUM>, respectively, to a congruent adjacent wall portion.

According to certain embodiments, the electrical resistivity of element <NUM> is substantially greater, and the electrical resistivity of elements <NUM>, <NUM> less, than that of the liquid in which the particles to be characterized are suspended. Consequently, the characteristic electrical resistivity of the composite wall defining conduit C can be substantially axisymmetric, and can have significant axial gradients at delimiting boundaries <NUM> and <NUM> along the length of any longitudinal section of conduit C. The characterizing axial variation in axisymmetric resistivities may substantially originate in the characteristics of the solid materials selected for the make-up of the volumeter assembly. In certain embodiments, the geometries of individual elements (e.g. <NUM>, <NUM>, and <NUM>) may operate to augment certain properties of the conduit C. Volumeter assemblies incorporating the characteristic axial variation in axisymmetric resistivity of the wall may be embodied by a variety of techniques in a broad range of designs, geometries, and materials.

In an example not forming part of the present invention, element <NUM> can be made of semiconductor-grade sapphire (e.g. of the type used in silicon-on-sapphire integrated-circuit technology) polished to thickness <NUM>. Such sapphire substrates may be available in standard thicknesses of <NUM> and <NUM>, for example. Elements <NUM> and <NUM> may be provided as uninsulated collars formed of an electrically conductive material (e.g., a platinum alloy or titanium carbide), and fixed to element <NUM> so that the respective congruent through-holes defining walls <NUM>, <NUM>, or <NUM> in the three elements <NUM>, <NUM>, and <NUM> align to form a fluidically continuous and hydrodynamically smooth wall.

As shown here, within individual device regions on such substrates, there may be provided a recess <NUM> into a first surface (the lower surface shown in <FIG>), of depth and diameter appropriate to the diameter D and length <NUM> of the conduit C provided therein. According to some embodiments, the recess <NUM> can operate to locate element <NUM> in its approximate position. In some instances, recess <NUM> may be etched as part of a circuit-fabrication process whereby integrated circuitry <NUM> is formed, although recess <NUM> may be formed by other means. The formation of integrated circuitry <NUM> on substrate <NUM> may be made by other processes as well. An exemplary integrated-circuit technique may involve using sequential photolithographic projections through patterned masks, followed by development and processing of the prepared surface area. According to some embodiments, an epitaxial silicon layer can be formed in a desired pattern on a surface of substrate <NUM>, and integrated circuitry <NUM> can be formed therein, according to integrated-circuit techniques. In some instances, circuitry <NUM> may include a low-noise amplifier circuit, to allow coupling of the low-level current pulsations occasioned by particles transiting conduit C to be relayed to remote signalprocessing circuitry. In some instances, circuitry <NUM> may include other types of circuits, such as those that may otherwise be provided as printed circuit cards in a cabineted apparatus. Interconnects between such sub-circuits, as well as conductive paths used for input/output and power connections, can also be provided. These may be formed by converting epitaxial intrinsic silicon to a more conductive form in the desired pattern, for example, or by conversion to polysilicon (e.g. electrode or conductive lead <NUM>), by doping with donor impurities, or by application of metalization layers in the desired pattern.

In some embodiments, a conductive guard layer <NUM> can be formed over the completed integrated circuit and conductive paths, and insulated from them. For some applications it may be desirable to protect the entire second surface (the upper surface shown in <FIG>), except for the terminations of the output and power paths and electrode <NUM>, by a layer of inert dielectric such as silicon dioxide. Electrode or conductive lead <NUM> can then be formed by metalizing a desired pattern on the first surface of the substrate. The individual device chips can then be separated in a dicing operation and tested for electrical function. The outer dimensions may be chosen for handling convenience. According to some embodiments, individual devices in the range of <NUM> to <NUM> may be used. Where a round device chip is desired, the chips may be separated by etching methods, for example.

In some instances, an undersized through-hole can be formed by photo ablation in each device chip at the desired location of conduit C, and field-amending elements <NUM> and <NUM> (having undersized respective openings <NUM> or <NUM>) can be aligned and positioned over each rough conduit, e.g., with an alignment wire as described in <CIT>, and appropriately attached to the respective surfaces of <NUM>. The undersized conduit C can then be finished to a desired diameter D by polishing according to Coulter wafer processing techniques. Operative electrical connections between field-amending elements <NUM> and <NUM> and respective conductive leads <NUM> and <NUM>, and between appropriate external connectives and the terminations of the output and power paths, can be formed using various techniques, such as with a conductive epoxy paint or epoxy or a low-temperature solder. In certain embodiments, electrical connections can be protected from corrosion by a layer of insulative material. With some materials it may be desirable to mount disc preforms of <NUM> and <NUM>, photo ablate the rough conduit through the conjoined assembly, and then polish the conduit to the desired diameter D. This process sequence may involve attaching field amending preforms to substrate <NUM> prior to separating the device chips and can avoid the step of aligning elements <NUM> and <NUM> over the rough conduit openings to the required degree. With other materials, the disc preforms may be provided an undersized opening, attached to substrate <NUM>, conduit C enlarged and cleared by photo ablation, and then finished by polishing to the final diameter D. The device chips may then be tested for electrical function and provided practical furniture, such as electrical connections and a mount and protective means suited to the intended application. The completed devices may then be functionally tested, calibrated, and provided the appropriate identification means. Depending on intended application, many forms of the apparatus are possible.

<FIG> illustrates aspects of a particle evaluation system <NUM>, according to another example useful for understanding the disclosure. As shown here, the system includes a tubular ceramic element <NUM>, which may be housed under slight compressive strain in a metal tubular sleeve <NUM> and containing an internal flow channel in fluid communication with conduit C. In some instances, a particle evaluation system may include an appropriate electrical connector operatively connected to a volumeter assembly <NUM> and appropriate pipe fittings, so as to be substantially continuous with a process line to be monitored. Such a particle detection device may have wide applicability. For example, inserted into a process line having appropriate flow volumes (such as a pressure line in a hydraulic system) and driven by the appropriate electrical source (e.g. AC current), the device can be used for the detection and Coulter sizing of metallic wear particles accumulating within the process system. For example, embodiments of the device can be used to remotely sense wear-particles in a hydraulic system. In some instances, the process system may be industrial or vehicular, such particle evaluation systems as disclosed herein can be used to analyze any of a variety of industrial particles.

In some embodiments, a particle evaluation system may include the tubular ceramic element <NUM>, but not the metal tubular sleeve <NUM>. Such configurations may be well suited for situations where particle evaluation system <NUM> can be provided an external Faraday shield by a portion of the process being monitored. In some instances, a form without the metal tubular sleeve may be broadly applicable, for example to add particle-sensing capability to low-pressure instrumentation for solute analysis. In some embodiments, the tubular sleeve <NUM> may be provided on the inside of the tubular ceramic element <NUM>, instead of on the outside as depicted in <FIG>.

In some embodiments, the particle evaluation system can be used to provide enhanced volumetric accuracy. In some embodiments, the particle evaluation system <NUM> may include remote signal conditioning circuitry such as that which is described in <CIT>. In some cases, circuitry may include an impedance matching amplifier. In some cases, a particle evaluation system may include a baseline restorer or additional circuitry. As shown here, an excitation current source and sensing circuitry <NUM> can be operatively connected with field amending units <NUM>, <NUM>, optionally via respective conductive leads <NUM>, <NUM>. In a four-terminal configuration, a pair of excitation electrodes can be positioned remotely from the field amending units and operatively connected with an excitation current source, as describe in <CIT>.

In some embodiments, tubular sleeve <NUM> can serve as a common (ground) lead from field amending unit <NUM> and conductive lead <NUM> to circuitry <NUM>. As noted above, the metal tubular sleeve <NUM> may be disposed interior to the tubular element <NUM>, and the tubular element <NUM> can be fabricated of glass instead of ceramic. In such configurations, the metal tubular sleeve <NUM> can served both as a Faraday shield and as connection to field amending unit <NUM> and/or conductive lead <NUM>. The conduit C can provide a wall of hydrodynamic smoothness, having contiguity at the junction of the first and second peripheral conduit walls (e.g. associated with field amending units <NUM>, <NUM>) with the central conduit wall (e.g. of a central substrate disposed between the field amending units. The conduit C can operate to receive suspended particles therethrough, and can define a central wall region (e.g. provided by substrate <NUM>) disposed between a first peripheral wall region (e.g. provided by field amending unit <NUM>) and a second peripheral wall region (e.g. provided by field amending unit <NUM>). The central wall region typically has an electrical impedance greater than electrical impedances of the first and second peripheral wall regions. In operation, the electrical source provides electrical excitation to the first and second peripheral regions, and the sensing circuit, which is also coupled with the first and second peripheral regions, detects impedance changes within the conduit occasioned by particles passing therethrough.

<FIG> illustrates aspects of a particle evaluation system <NUM>, according to a further example useful for understanding the disclosure. As shown here, the system includes a tubular ceramic element <NUM>, which may be housed under slight compressive strain in a metal tubular sleeve <NUM> and containing an internal flow channel adapted to conduit C. In some instances, a particle evaluation system may include an appropriate electrical connector operatively connected to a volumeter assembly. Such a particle detection device may have wide applicability.

In some embodiments, a particle evaluation system may include the tubular ceramic element <NUM>, but not the metal tubular sleeve <NUM>. In some instances, a form without the metal tubular sleeve may be broadly applicable, for example to add particle-sensing capability to low-pressure instrumentation for solute analysis. In some embodiments, the particle evaluation system can be used to provide enhanced volumetric accuracy. In some embodiments, the particle evaluation system <NUM> may include remote signal conditioning circuitry such as that which is described in <CIT>. In some cases, circuitry may include an impedance matching amplifier. In some cases, a particle evaluation system may include a baseline restorer or additional circuitry. The conduit C can provide a wall of hydrodynamic smoothness, having contiguity at the junction of the first and second peripheral conduit walls (e.g. associated with field amending units <NUM>, <NUM>) with the central conduit wall (e.g. of a central substrate disposed between the field amending units. The conduit C can operate to receive suspended particles therethrough, and can define a central wall region (e.g. provided by substrate <NUM>) disposed between a first peripheral wall region (e.g. provided by field amending unit <NUM>) and a second peripheral wall region (e.g. provided by field amending unit <NUM>). The central wall region typically has an electrical impedance greater than electrical impedances of the first and second peripheral wall regions. In operation, the electrical source provides electrical excitation to the first and second peripheral regions, and the sensing circuit, which is also coupled with the first and second peripheral regions, detects impedance changes within the conduit occasioned by particles passing therethrough.

According to some embodiments, a conductive tube can be connected to a field amending unit of the conduit, which can also serve as a flow restrictor to control flow rate. In some instances, sample volume can be monitored by an insulated electrode or glass capillary fitted with level sensors. For example, an exemplary particle evaluation system may include a <NUM>/<NUM>" glass tubing about <NUM>" long. One end of the tubing can be coupled with a two-terminal field-amending/electrode set including a <NUM>-micra Coulter wafer, and an opposing end of the tubing can be coupled with a rubber bulb (e.g. similar to the type used to fill and empty laboratory pipettes). One field-amending element can face outward at the end of the tubing, while the other field amending unit can be sealed inside the tubing, for example where the electrode set is epoxied onto the tubing. The electrode set can be connected with small insulated hook-up wires to electrode leads of a Coulter Counter or similar apparatus. AC signal coupling can be used to separate signals of microvolt level from volt-level excitation voltages across the conduit C. A particle evaluation system may also include a level electrode, which may be provided as a third length of small hook-up wire running down the inside of a stainless steel tubing (e.g. grade or type <NUM>), with the wire from the internal field-amending element serving as a common connection for the outside electrode lead and the level detection wire. Exemplary particle evaluation systems can provide clearly visible pulses (e.g. from a suspension of <NUM>-micra latex particles). It is also observed that pulses may occur as the suspension is expelled from the tube. Further, it is demonstrated that the excitation current is significantly less that with a standard <NUM>-micra Coulter aperture to avoid microbubble generation, requiring higher amplifier gain. What is more, it is shown that fewer "M" pulses and almost no recirculator pulses occurred, this with a smaller coincidence volume. Exemplary particle evaluation systems may also include a mechanism for aspirating analyte, such that operation of the mechanism is matched to flow characteristics of the volumeter conduit.

According to some embodiments, fluid control means <NUM> may include features of an automatic micropipette, or other devices for performing volume aspiration. In some instances, fluid control means <NUM> may include features of a hand held micropipette mechanism.

In some instances, the stainless steel <NUM> tube mentioned above can be acid-passivated to reduce electrochemical interactions with the suspension. According to some embodiments, for example where provided as a disposable part of a hand-held Coulter Counter type device, it is possible to use well-passivated <NUM> stainless steel tubing for the metal tube and have it coated (for example with glass, or with a polymer cross-linked in situ after application) on the outside to insulate the tube from analyte and then conductively seal such a tube to conductive lead <NUM> and/or field amending unit <NUM>. In some cases, analogous treatments may be applied to the inside of the stainless steel <NUM> tube, including a similar seal to conductive lead <NUM> and/or field amending unit <NUM>, and using a separate (but protected) connection to conductive lead <NUM> and/or field amending unit <NUM>. For the level detection electrode, it is possible to use another length of smaller tubing, insulated on the outside in the first approach, and inserted to the desired level in the structural tube.

According to some embodiments, particle evaluation systems may operate with reduced noise levels and improved pulse acquisition, despite any higher transimpedance amplification that may be used due to a desire to limit current density between the at-aperture field-amending/electrode elements.

According to some embodiments, a volumeter assembly as disclosed herein can be incorporated into a hand-held instrument containing an integrated or hybrid form of a complete Coulter counter. In some cases, such an instrument may be exclusive of fluidics and glassware. In some cases, such an instrument may include a rubber bulb, a plastic bellows, or some other fluid control means, to draw or express a set volume of sample suspension through the conduit (e.g. conduit C of <FIG>, <FIG>, <FIG>, <FIG>, or <FIG>). A fluid control means may also be provided in the form of a micropipette mechanism, as discussed elsewhere herein. In some cases, a fluid control means such as a rubber bulb can draw or express a volume of sample suspension through the conduit, for example via a conductive tube-electrode connected to a field-amending element of the conduit. Such a conductive tube-electrode may also serve as a flow restrictor to control flow rate. In some instances, a sample volume can be monitored, for example by an insulated electrode set an appropriate distance up the conductive tube or through use of a glass capillary fitted with level sensors.

In some instances, one or more user-selectable thresholds can be provided, and displayed on a liquid-crystal display. In some cases, a handheld instrument can be dipped into a particle suspension of an appropriate concentration, and such a dipstick Coulter device can be used to accurately count particles in a variety of remote-sampling situations. Although <FIG> depicts a conductive tube <NUM> disposed exterior to an insulative tube <NUM>, as discussed elsewhere herein it is understood that examples useful for understanding the disclosure also encompass configurations where the conductive tube is instead disposed interior to the insulative tube. In exemplary embodiments, a combined construct that includes field-amending units, conductive leads or electrodes, and a tube structure (e.g. a sample tube) can be provided as a disposable device.

As mentioned elsewhere herein, where the field amending units are configured to function as aperture excitation electrodes, the allowable aperture excitation current is significantly reduced. Because low aperture excitation currents can be effectively employed, exemplary particle evaluation volumeter assemblies (e.g. two terminal configurations) are well suited for use in producing hand held particle evaluation devices that operate based on the Coulter principle. In many cases, the power requirements involved with effectively exciting such volumeter conduits can be significantly reduced compared with other known aperture based sensing systems. By incorporating the use of lower excitation currents, it is possible to implement particle evaluation systems with more integrated components and smaller hybrid components.

According to certain embodiments, a multi-channel pulse-height analyzer can be provided in an integrated or hybrid form and included in a handheld device. Using a device having tubular ceramic element as discussed with reference to <FIG>, optionally including a metal tubular sleeve, it is possible to provide a handheld device where the volumeter assembly is present as a two-terminal construct (e.g. <FIG>), or as a four-terminal construct, such as that which is described in <CIT>. In a two-terminal configuration, an excitation current source and sensing circuitry <NUM> can be operatively connected with the field amending units <NUM>, <NUM>, optionally via respective conductive leads <NUM>, <NUM> that are coupled with an intermediate substrate <NUM>. In a four-terminal configuration, a pair of excitation electrodes can be positioned remotely from the field amending units and operatively connected with an excitation current source, as described in <CIT>. Consequently, a similar device chip may be adapted to a variety of applications. In some forms, it may be desirable to use two-wire methods to couple excitation in to, and pulses out from, the device chip. Such a configuration can permit an operative connection to be made between the respective remote electrodes and the field-amending elements, whereby a functional four-terminal measurement could be made with an apparent two-terminal device.

As discussed elsewhere herein, with the implementation of exemplary two-terminal configurations, the use of hydrodynamically focused flow into and sweep flow behind the conduit can be minimized or eliminated. Use of the field amending units can also allow elimination of the bulk and expense of associated with other known counters. According to some embodiments, the use of a vacuum source to help pull a sample through a composite volumeter conduit can also allow the conduit to control sample throughflow.

In some instances, a particle evaluation system such as that shown in <FIG> can be provided as a minimal AC version and packaged as a remote transducer. Such embodiments can be configured to detect particles in a fluid flow. In some instances, a particle evaluation system such as that shown in <FIG> can be provided as a DC version. Exemplary particle evaluation systems can be configured to provide solute-analytic functions, thereby providing a particle detection, sizing, or characterization function as well. In some instances, a small hand-held, battery-powered version (e.g. a dipstick Coulter counter) can be used for marine biology applications. Similarly, exemplary systems can be used in environmental studies at remote sites, and the like. As shown here, such instruments may include a rubber bulb, a plastic bellows, a micropipette assembly, or other fluid control means, to draw or express a set volume of sample suspension through the conduit, for example via a conductive tube-electrode connected to a field amending element of the conduit, which in some instances can also serve as a flow restrictor to control flow rate. Exemplary particle evaluation systems can be configured for sensing and characterizing small particles, and in particular to techniques for detecting and evaluating blood cells or ceramic powders. Often, the particles may be suspended in a liquid medium having an impedance contrast or electrical impedance per unit volume which differs from that of the particles. In many instances, the systems and methods disclosed herein are well suited for use in sensing and characterizing such particles by the Coulter principle.

Each of the calculations or operations described herein may be performed using a computer or other processor having hardware, software, and/or firmware. The various method steps may be performed by modules, and the modules may comprise any of a wide variety of digital and/or analog data processing hardware and/or software arranged to perform the method steps described herein. The modules optionally comprising data processing hardware adapted to perform one or more of these steps by having appropriate machine programming code associated therewith, the modules for two or more steps (or portions of two or more steps) being integrated into a single processor board or separated into different processor boards in any of a wide variety of integrated and/or distributed processing architectures. These methods and systems will often employ a tangible media embodying machine-readable code with instructions for performing the method steps described above. Suitable tangible media may comprise a memory (including a volatile memory and/or a non-volatile memory), a storage media (such as a magnetic recording on a floppy disk, a hard disk, a tape, or the like; on an optical memory such as a CD, a CD-R/W, a CD-ROM, a DVD, or the like; or any other digital or analog storage media), or the like.

Different arrangements of the components depicted in the drawings or described above, as well as components and steps not shown or described are possible. Similarly, some features and sub-combinations are useful and may be employed without reference to other features and sub-combinations. Embodiments of the invention have been described for illustrative and not restrictive purposes.

Claim 1:
A system (<NUM>) for evaluating particles of a biological sample obtained from an individual, comprising:
a volumeter assembly (<NUM>) having a conduit adapted to receive a fluid suspension containing the particles therethrough, the conduit defining an axial conduit wall length having a central region of higher electrical resistivity disposed between a first distal region of lower electrical resistivity and a second distal region of lower electrical resistivity;
a first chamber (<NUM>) in fluid communication with a first orifice of the volumeter assembly conduit, the first chamber (<NUM>) adapted to contain at least a first portion of the fluid suspension;
a second chamber (<NUM>) in fluid communication with a second orifice of the volumeter assembly conduit, the second chamber (<NUM>) adapted to contain at least a second portion of the fluid suspension; and
a current source and sensing circuit module (<NUM>, <NUM>) in direct electrical connectivity with the first and second distal regions of the volumeter assembly (<NUM>),
wherein the current source and sensing circuit module (<NUM>, <NUM>) is configured to provide an electrical excitation current to the first and second distal regions to establish a particle-sensitive zone within the conduit, and
wherein the current source and sensing circuit module (<NUM>, <NUM>) is configured to detect current changes occasioned by particles of the biological sample passing through the particle-sensitive zone,
wherein the conduit wall length is provided by a semiconductor wafer which is doped with an electrically active impurity to provide the central region of higher electrical resistivity disposed between the first distal region of lower electrical resistivity and the second distal region of lower electrical resistivity.