Patent Application
20080041453
The invention relates to a fluid container with microchannels and a testing system comprising such a container for the examination of a fluid.
The examination of small samples in integrated platforms is becoming increasingly important in biology and medicine. Such platforms typically have microchannels which contain and guide fluid components that shall be processed, e.g. transported, reacted or measured. From the U.S. Pat. No. 6,030,581 a testing platform is known that is integrated in a Compact Disc (CD) like device and that comprises different means to manipulate a sample fluid. Said testing platform may particularly comprise valves with metal foils which require an integrated wiring for switching by electrical voltages.
Based on this situation it was an object of the present invention to provide means for the examination of small samples of fluids that are reliable in their use and that can be produced in a cost-effective way.
This object is achieved by a fluid container according to claim 1 and a testing system for fluids according to claim 8. Preferred embodiments are disclosed in the dependent claims.
A fluid container according to the present invention comprises microchannels that contain and guide (gaseous or liquid) fluids which shall be processed and/or examined. The term “microchannels” shall indicate a miniaturization of the fluid container which allows the analysis of tiny samples. The microchannels typically are rectangular with a height ranging from 1 to 1000 μm, preferably from 10 to 100 μm, wherein the width of the channels is a less critical design parameter that may typically range from 1 to 1000 μm. According to the invention, at least one “active element” is disposed in at least one of the microchannels at a fixed place in such a way that it can be reached by a light beam coming from a light source which may be internal or external with respect to the fluid container. The wavelength of the (mono- or polychromatic) light beam typically lies in the range from 350 nm to 850 nm, though other wavelengths (e.g. of infrared) may be applied if useful, too. The active element may by definition be transferred from a non-activated to an activated state by the effect of light, wherein the active element shall assume different shapes in the “non-activated state” and in the “activated state”, respectively. The term “shape” shall refer to both form and dimension here, such that e.g. two spheres of different diameter are considered as having different shape. Different shapes may particularly be associated with a difference of volumes and/or of extensions in at least one direction, said difference preferably being larger than 5%, most preferably larger than 20% (with respect to the smaller volume/extension). Thus the difference is significantly larger than that associated with usual heat expansion that is experienced by every material due to heating. The consistency of the active element as a whole shall be non-liquid in both the activated and non-activated state, such that the active element assumes a more or less defined shape in these states.
A fluid container of the aforementioned kind can be produced rather cost-effective because it does not require any electrical equipment or wiring. Instead, control elements for fluid flow like valves or pumps can simply be realized by active elements of an appropriate material that are accessible to a light beam. The light beam may for example be produced by an optical system similar to the reading/writing devices of Compact Disc players. This has the advantage that many available components can be used and that the fluid container can be controlled without direct mechanical contact. Moreover, the light source can often be used for other purposes, too, e.g. for a optical analysis of the sample.
A variety of different realizations are possible for an active element that changes its shape under the effect of light. According to a preferred embodiment, the active element comprises a material (e.g. a wax) that undergoes a phase transition in a temperature range of about 10° C. to about 80° C., most preferably of about 30° C. to about 40° C., if heat is added to the material or removed from it. In this case a change of volume that is associated with a physical phase transition of a suited material is exploited, and the active element therefore does not need to be structured in a complicated way but may simply be some quantity or mass of material. The phase transitions may for example be one of the transitions between solid, liquid and gaseous phases and/or between different types of solid phases (crystal structures).
In a preferred realization of the invention, the active element comprises a gel, particularly a hydrogel with an upper-critical solution temperature. Such hydrogels dissolve and swell in a solvent, for example in water, at low temperatures, but phase separate at elevated temperatures, i.e. the solvent moves out and the gel collapses. The associated volume changes of such gels may be up to 200% or more. The gel may optionally have a structured design with an enlarged surface area in order to improve the reaction speed and to accelerate diffusion processes.
In a further development of the aforementioned embodiment, the active element comprises a converting material that converts absorbed light into heat. Said converting material may be heterogeneously or homogeneously mixed with or chemically bound to the gel which has the advantage that light is absorbed throughout the whole active element yielding a fast and uniform transition. Alternatively, the converting material may be disposed separately from the gel, optionally even separated from it by an intermediate protection layer, in which case heat generated in the converting material has to be conducted into the gel.
The change of shape of the active element can be used for an efficient control of fluid flow in the fluid container. The active element may for example be disposed in a microchannel such that it blocks said microchannel in its expanded state. Thus, the active element serves as a valve that selectively allows or interrupts fluid flow through a microchannel.
According to another application in flow control, the active element is disposed along at least one wall of a microchannel in such a way that it drives fluid out of said microchannel in its expanded state. The active element may additionally block the microchannel in its expanded state or not. More important is in this case the effect that some amount of fluid is expelled from the volume of the microchannel such that the active element serves as a pump.
The microchannels of the fluid container may at least partially be covered by a transparent material, for example glass or transparent plastics. An active element that is disposed in such a microchannel may then easily be reached by a light beam in order to initiate a desired transition to an activated state.
The invention further relates to a testing system for fluids (particularly for small amounts of fluid with a typical volume in the order of 100 nl to 1000 μl), comprising the following components:
The aforementioned testing system provides a complete arrangement for the manipulation of samples in a fluid container of the kind described above. In this case, the active elements of the fluid container are controlled by light that is generated in the optical system, i.e. externally of the fluid container. Therefore, the fluid container can be kept as simple as possible, e.g. only comprising the microchannels, the active elements and the sample. Of course all special embodiments of the fluid container that were described above may be used in connection with the testing system. Therefore, reference is made to the preceding description for more information on the details, advantages and improvements of the testing system.
In a further development of the testing system, the optical system comprises a controller that is adapted to control location, intensity and/or duration of the light beam according to the desired effects on the active elements. If an active element for example serves as a valve in a microchannel and said valve shall be kept open for a certain time, the light beam must guarantee this and for example deliver enough energy to maintain a phase transition in a hydrogel and to compensate cooling effects of flowing fluids.
Furthermore, the optical system may comprise means for scanning an area inside the fluid container with a focused laser beam. Such means may particularly be derived from the reading and/or writing units of a Compact Disc players. The scanning and focusing of a laser beam has the advantage that only one light source has to be provided for the control of a plurality of active elements. The scanning can normally be done fast enough to switch a large number of active elements practically simultaneously due to the inertia of the thermal processes in the active elements.
According to another embodiment of the invention, the optical system of the testing system may be adapted to perform an optical processing of the sample. It may for example be able to generate and guide a light beam into the sample that can start certain processes there, e.g. chemical reactions or the stimulation of fluorescence. Moreover, the optical system may be adapted to collect (reflected, transmitted, luminescent, . . . ) light emerging from the sample for measurements of optical characteristics of the sample.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.
In the following the invention is described by way of example with the help of the accompanying drawings in which:
The analysis of biological samples on integrated miniaturized fluidic platforms like the fluid container 10 is of increasing importance in medical care and pharmacological development. The success of this technology in practice is however strongly dependent on the reliability, ease of operation and low cost of such devices. Hand-held disposable cartridges inserted in a reader need to carry out a complex sequence of steps for the preparation, mixing, filtering, splitting and measuring of samples and internal standards, etc. depending on the type of biological assay and type of detection. This sequence of steps requires the precise manipulation of liquid volumes in microscopic channels.
There are many approaches which have been proposed for this purpose. A first category of approaches is the so-called passive fluidic devices. Passive devices make use of external mechanical forces, like a push-pin with a membrane, a fluid pump, centrifugal force or compressed air (pneumatic actuation). Passive devices suffer from limited functionality and a vulnerable interface. The mechanical and/or fluidic interface between cartridge and reader in such systems requires high precision and certainly maintenance.
A second category are active devices in which the fluidic actuation is achieved on the cartridge without “mechanical” interface, but rather an electrical interface. The electrical signal and energy is then transformed into a movement of the liquid itself (electrophoresis) or channel walls (like in MEMS devices). Active devices with electro-mechanical actuation require MEMS (Micro-Electromechanical-Systems) technology, based on relatively expensive substrates. Apart from the cost also the reliability and proper functioning of valves and pumps is still an issue (like the requirements of no dead volume, no leakage flow in the off state, etc.).
Various embodiments of a testing system proposed here that are both reliable and cost-effective are shown in the Figures.
Furthermore, “active elements” 1 are disposed in the microchannels 13, 14 that can change their volume under the influence of a light beam 35 and that can thus control the movement of the fluid through the microchannels 13, 14. In the left microchannel 14 of
The active elements 1 may particularly comprise a responsive gel. Polymer gels can respond to a change in the environment by a change in dimensions, as a consequence of a changed solubility in (typically) water. The stimulus from the environment can be the pH, electrical charge or temperature. Gels with an upper-critical solution temperature (UCST) dissolve (and swell) very well in a solvent at low temperature but phase separate at elevated temperatures (cf. C. Yu et al., Anal. Chem. 2003, web ed. http://dx.doi.org/10.1021/ac026455j). The volume change of such gel systems is extremely large (>200%). Furthermore, the US 2004/0050436 A1 describes the use of polymers which can be transformed from a liquid-like state (“sol”) to a solid-like state (“gel”) by heat induced cross-linking, wherein said polymers shall be added as a sol to a sample liquid and selectively transformed to a gel if a microchannel is to be blocked.
Moreover, the active element 1 comprises a “converting material” or dye which absorbs at the wavelength of the laser radiation (e.g. 785 nm, like in CD-R or 650 nm like for DVD-R) and converts absorbed light into heat. The dye may be added (homogeneously) to the hydrogel during preparation.
In the upper part of
While
Moreover, it is of course also possible to use more than one light source (e.g. an array of lasers) in order to irradiate several or even all of the active elements independently and simultaneously.
A central aspect of the proposed system is the use of a focused and actuated laser beam 35 as heat source for the manipulation of liquid on microfluidic platforms. The laser and its manipulation system comprises a set-up which is essential like a pick-up used for optical data storage, like CD-R, with the important difference that the substrate is not rotating but a resting fluid container 10.
During operation of the device shown in
In the following, a concrete example of a testing system will be described in more detail. In this example, poly-NIPAA (N-isopropyl-acrylamide) is used as a hydrogel. The reliable switching of poly-NIPAA in water requires the switching from room temperature to about 40° C., i.e. 20° C. temperature rise. The heat capacity of such a gel is almost equal to that of water, i.e. 4 kJ/kgK. The volume which is addressed depends on the time scale in the case of a stationary beam. In any case the heat penetration should be in the order of the height of the valve in order to achieve a homogeneous temperature distribution. With a heat diffusivity of approximately 2·10−7 a penetration of 50 μm is achieved in 5 ms. The power required to heat 50 μm3 in 5 ms by 20° C. is 2 mW which can easily be absorbed from a diode laser as used in optical storage. As soon as the gel 1 or 2a (
Next to polyNIPAA there are more materials with UCST behavior which can be used. As absorbing dye the standard CD-R dye can be used which is water soluble, but it has to be attached to the gel network to avoid contamination of the biological sample. This can be achieved by attaching a reactive group, like an acrylate group to the dye and copolymerizing it with the gel. In the case of a separate converting or “heating” layer 2b underneath the gel 2a (see
FIGS. 3 to 5 show a top view of a part of a fluid container 20 with microchannels 22-24 in which active elements 3-5 are disposed as valves or pumps, respectively.
In
In summary, the control of the flow in microchannels is an essential part of a miniaturized sensor for analyzing biological and/or chemical samples. The selective detection of for instance proteins in a biological sample requires a sequence of flow-controlled actions and interactions which can only be achieved with the aid of valves. Instead of passive valves which are inflexible and electro-mechanical valves which are expensive to make and less reliable, it is proposed to use thermally activated valves of polymeric gels with an upper-critical solution temperature in water. The thermal activation, i.e. temperature change is achieved by absorption of laser radiation by the inclusion of a dye in the hydrogel. By fast actuation/scanning of the laser with optically controlled positioning multiple valves can be addressed quasi-simultaneously. In this way the fluidic action can be adopted during the execution of a certain analysis. The required laser action can be achieved with a CD-R or DVD-R pick-up. The described system can be implemented readily on all-plastic substrates in combination with a micro-fluidic channel system by photo-lithographic or other structuring technology and in this way enable very low cost cartridges with a robust all optical interface very similar to CD technology.
Finally it is pointed out that in the present application the term “comprising” does not exclude other elements or steps, that “a” or “an” does not exclude a plurality, and that a single processor or other unit may fulfill the functions of several means. Moreover, reference signs in the claims shall not be construed as limiting their scope.
| Number | Date | Country | Kind |
|---|---|---|---|
| 04104900.8 | Oct 2004 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB05/53196 | 9/28/2005 | WO | 4/3/2007 |
