Abstract
Microfluidic method and device that can be used for sensing and measurement of properties of liquids, gases, solutions, and particles is proposed, wherein the measurable liquid or gas (with or without particles) flow in at least one channel through a measurement chamber (cell) formed between at least two isolated electrodes is used for electrical impedance measurement. The proposed solution is characterized in that the cross-section of at least one pair of similar spatial electrodes decreases smoothly towards the tiny measurement chamber (cell) in order to increase the sensitivity and accuracy of the measurement. Typically, a device with multiple similar channels is advantageous to use for comparative measurement and differential measurement schemes.
Claims
1. A microfluidic method, comprising: a fluid or a gas under investigation flows in at least one channel, a measurement is performed in between two spatial electrodes insulated from each other, and the measurement is accomplished in a miniature measurement chamber which is formed in between the two spatial electrodes positioned within said channel in a direction of flowing of the liquid or the gas such that the liquid or the gas flows through the two spatial electrodes, and wherein a cross-section of the two spatial electrodes is smoothly decreasing from both sides towards the miniature measurement chamber.
2. The microfluidic method, according to claim 1, wherein electrical impedance is measured between the electrodes.
3. The microfluidic method, according to claim 2, wherein the electrical impedance between the electrodes is measured at multiple frequencies as a spectrum.
4. The microfluidic method, according to claim 2, wherein the fluid or gas under investigation flows in parallel in two or more channels each having at least one pair of electrodes with the aid of which the impedance in the given channel is measured.
5. The microfluidic method, according to claim 4, wherein one fluid or one gas channel is a reference channel for comparing result of at least one other channel.
6. The microfluidic method according to claim 4, wherein differential measurement is used between two or more channels.
7. A microfluidic device comprising at least one liquid or gas channel in dielectric materials and at least one pair of spatial electrodes isolated from each other and positioned within the at least one liquid or gas channel in a direction of flowing of the liquid or the gas such that the liquid or the gas flows through the two spatial electrodes, wherein a cross-section of the at least one pair of spatial electrodes is smoothly decreasing from both sides towards a measurement chamber located in between the spatial electrodes forming the at least one pair.
8. The microfluidic device according to claim 7, wherein the electrodes with decreasing cross-section towards the measurement chamber have a conical shape.
9. The microfluidic device according to claim 7, wherein there are two or more channels containing electrode pairs for measurements.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIG. 1A shows a typical frequency response of a solution impedance magnitude in a measurement chamber (cell).
(2) FIG. 1B shows the frequency response of the complex impedance magnitude of the same solution with a smaller measurement chamber (cell) and smaller electrodes.
(3) FIG. 1C shows the frequency response of the complex impedance magnitude of the solution for a smaller measurement chamber (cell), but with circular conical electrodes with the larger surface area.
(4) FIG. 2A is a cross-sectional front view of the proposed single-channel device with a pair of spatial conical electrodes.
(5) FIGS. 2B, 2C, 2D are top views of the same embodiment of a device with circular, rectangular, and oval cross-sectional of the channel, respectively.
(6) FIG. 3 is a cross-sectional front view of a dual-channel device with electrical connections for each electrode separately.
(7) FIG. 4 is a cross-sectional front view of a dual-channel device in which the electrodes are electrically connected in pairs.
(8) FIG. 5 is a cross-sectional front view of a two-channel device having electrical connections between the electrodes on the upper and lower surfaces of the dielectrics.
(9) FIG. 6A is a front view of a dual-channel device having pairs of electrodes in channels between two dielectric materials.
(10) FIG. 6B is a cross-sectional top view of the same embodiment.
(11) FIG. 7 is a cross-sectional front view of a dual-channel device with divided electrodes.
(12) FIG. 8A is a cross-sectional front view of an embodiment of a three-channel device, and FIGS. 8B and 8C are a side view and cross-sectional side views, respectively.
DETAILED DESCRIPTION OF THE INVENTION
(13) The examples below illustrate the invention.
(14) FIG. 2A depicts a cross-sectional front view of a single channel (01) device with a pair of three-dimensional conical electrodes (02) in which the electrical connections (03) are made in the planes of the third dielectric material (05) between the upper (04) and lower (06) dielectric material. The opening in the dielectric material (05) between the tapered ends of the electrodes forms a measurement chamber (07). Arrows at the ends of the channel indicate the direction of movement of the liquid or gas.
(15) FIGS. 2B, 2C, 2D show the top views of the same device with a circular (01a), rectangular (01b), and oval (01c) channel shape, respectively.
(16) The solution works as follows: the liquid (mixture, gas, particles, etc.) flows in the channel (01), and the AC impedance, or preferably its spectrum, measured in the measurement chamber between the electrodes (02) depends on the composition and properties of said liquid and particles, allowing them to be measured, counted or characterized using the changes of the impedance or its spectrum.
(17) FIG. 3 shows a cross-sectional front view of an embodiment of a dual-channel device in which the electrical connections (33) of each electrode are shown separately. Note: Electrical connections may also be perpendicular to the plane of the drawing. Such a solution allows comparative measurement in two channels, for example, using one channel as a reference channel, for example, with a known liquid, mixture, or the like.
(18) FIG. 4 shows a cross-sectional front view of a dual-channel device in which the electrical connections (43) of the electrodes are connected in pairs inside the device. Note: Electrical connections may also be perpendicular to the plane of the drawing.
(19) FIG. 5 shows a cross-sectional front view of a two-channel device having electrical connections (3) to the electrodes (2) on the upper and lower surfaces of the dielectric (4) and (6).
(20) FIG. 6A shows a front view of a dual-channel device having pairs of electrodes in the channels (21) between the two dielectric materials (24) and (26).
(21) FIG. 6B shows a cross-sectional top view of the same device in a plane of the junction of the dielectrics (24) and (26). The measurement chambers (27) between the pairs of electrodes (22) are optionally formed by the same dielectrics (24) and (26), and the electrodes (22) are optionally convex in shape.
(22) FIG. 7 shows a cross-sectional front view of a two-channel device in which the pairs of electrodes are divided into two to implement a so-called four-electrode impedance measurement scheme.
(23) FIGS. 8A, 8B, and 8C show in more detail a three-channel embodiment example of the device. FIG. 8A is a cross-sectional front view of the device in a plane of the center of electrodes (52). O-ring seals (8) and (9) have been used to seal the channels. The upper (54) and lower (56) dielectric employ printed circuit boards having conical gold plated apertures forming pairs of electrodes (52). Measurement chambers (57) are formed by holes in a dielectric (55) located between the electrodes. FIG. 8B is a top view of the same device with connector plugs (10) and fittings (17) for connecting of fluid hoses. FIG. 8C is a cross-sectional side view of the same device in a plane of the center of one pair of electrodes (52). Electrode connections (53) extend to the connector plugs (10). The fluid reservoir is further formed with dielectric material details (12), (13) and (14) and is provided with a fitting (17) for connecting of hoses. The solution under investigation is entered into the funnel opening (15) and can be directed between the electrodes (52) of the measuring chamber (57) by applying negative pressure through the fitting, but also in the opposite direction, applying excess pressure. By changing the pressure direction, the fluid in the reservoir and between the electrodes can be moved back and forth, for example, for mixing.
