Patent Application
20160047701
The present invention relates to a micron-scale calorimeter and a calorimetry method utilizing the micron-scale calorimeter. In accordance with the invention, there is provided a micron-scale calorimeter comprising a micro-channel string, being restrained at least two longitudinally distanced positions so as to form a free released double clamped string in-between said two longitudinally distanced positions said micro-channel string comprising a microfluidic channel having a closed cross section and extending in the longitudinal direction of the hollow string, acoustical means adapted to oscillate the string at different frequencies by emitting sound waves towards the string, optical means adapted to detect oscillating frequencies of the string, and controlling means controlling the strength and frequency of the sound wave emitted by the acoustical means and receiving a signal from the optical means representing the detected oscillating frequencies of the micro-channel string.
Calorimeters are today used in numerous different ways for different purposes. calorimeters in the micron-sized range, is for example used to estimate an exothermic reaction by mixing two or more chemicals and used to detect an activity of bio cells. Wonhee Lee, Warren Fon, Blake W. Axelrod, and Michael L. Roukes “High-sensitivity microfluidic calorimeters for biological and chemical applications” Proceedings of the National Academy of Sciences, 2009; and Wonhee Lee, Warren Fon, Blake W. Axelrod, and Michael L. Roukes “High-sensitivity microfluidic calorimeters for biological and chemical applications” Proceedings of the National Academy of Sciences, 2009 disclose some details as to known calorimeters.
Current technology employs a design where a void—being sealed to prevent out- and inflow to the void of substance—is used and the substance to be examined is present inside the void. Heat produced in by the substances gives rise to a temperature change in the material surrounding the void. The known design employs a thermopile (made of a material with a temperature dependent resistance) and an electrical heat source, to perform calorimetry at a desired temperature. Thus, by measuring the resistance of the thermopile an indication of e.g. the exothermic reaction or the activity of bio cells can be obtained.
One such example is disclosed in Review of Scientific Instruments 79, 064901 (2008): Real-time thermal characterization of 12 nl fluid samples in a micro channel. This document discloses a sensor having a structure composed of a micro channel and a thin-film strip fabricated on a glass substrate. The thin-film acts as both an electrical heater and an electrical resistance based thermometer and detects the temperature response at a 3w frequency, i.e. the tripled frequency of heating.
Such a system has a number of drawbacks. For instance, for the electrical heating measuring, metal electrodes must be applied close to the site where heat is being generated. Further, the resistance of the metal layer which changes with temperature/heat must be monitored. But at the same time, metal layer also becomes a source to conduct heat away from its origin. Which means that metal electrodes cause both a loss of heat, production of heat and are used to determine resistance (correlated to the thermal properties to be determined), thereby providing error sources into the measurement. Furthermore, as steady state often is not a possibility the transient state or—in general—the unsteady behavior of the system has to be taken into consideration. Such consideration involves handling of heat transfer being different in different materials.
Hence, an improved calorimeter device and method for determining calorimetric properties of samples in the micro or nano volume range would be advantageous, and in particular a more efficient and/or reliable calorimeter device and method would be advantageous.
It is a further object of the present invention to provide an alternative to the prior art.
In particular, it may be seen as an object of the present invention to provide a micron-scale calorimeter that solves the above mentioned problems of the prior art with
In particular, it may be seen as an objective of the present invention to provide a calorimeter, such as a chip calorimeter, which employs a vibrating micro string as a temperature sensor thus avoiding use of a thermopile which also causes a loss of minute amount heat by using conductive metal layers. This helps in solving problems mentioned earlier in the prior art.
Thus, the above described object and several other objects are intended to be obtained in a first aspect of the invention by providing a micron-scale calorimeter comprising:
As there exist a correlation between the oscillating frequency of the string and the heat generated in the micron-scale calorimeter according to the present invention, such calorimeter may be applied for numerous purposes. A micron-scale calorimeter according to the invention may successfully identify different substances based on the detected oscillating frequencies (as these may be seen as a unique finger print for each substance). A micron-scale calorimeter according to the invention may also be used to monitor activities of bio cells due to their production of heat during growth. Additionally chemical reaction by mixing minute amounts (picoliters) of two different chemicals (compatible to the material of the device) can also be monitored by a micron-scale calorimeter according to the present invention.
In the present context, terms are used in a manner being ordinary to a skilled person. However, some the used terms are explained in some details below:
Micron-scale or micro-sized is preferably used to denote element(s) having a size in the micron meter range scale i.e. having dimension in the range of 10−6 m.
Micro-channel string is preferably used to denote string having a longitudinal extension in the micron meter range as well as having cross section in the micron meter range. Further, micro-channel string is preferably used to denote a string having a microfluidic channel having a closed cross section and extending in the longitudinal direction of the hollow string, which channel is tubular shaped in the sense that it is not open to exterior of the string except at inlet(s)/outlet(s) arranged at the distal ends of the channel.
Free released double clamped is preferably used to denote that the string is supported at its two longitudinal distances positions (ends) and hanging (free released) in the middle.
A string is preferably used to mean an elongated member. The elongated member may advantageously be under tensile intrinsic stress, preferably introduced by a thin film of silicon rich silicon nitride (SRN), which means something is pulling it from its both ends. In relation to the present invention, the longitudinal stress on string may be around 200 MPa (Mega Pascal).
Microfludic is preferably used to denote a volume in the micro litre range
Microfluidic channel is preferably used to denote a channel provided inside the micro-channel string having a total volume in the micro litre range.
Nano-scale or nano-sized is preferably used to denote element(s) having a size in the nano meter range scale, i.e. having dimensions in the range of 10−9 m.
Calorimeter is preferably used to mean a device adapted to provide a detectable signal, e.g. a change in resonance frequency, correlated to change of heat in a substance.
Chip calorimeter is preferably used to mean a calorimeter embodied in a small element e.g. a 1 cm×1 cm element. Such a chip calorimeter may preferably be adapted to fit exchangeable into a measuring device and comprise interface mating a corresponding interface of the measuring device, whereby easy integration of the chip calorimeter may be achieved.
A micron scale calorimeter according to the present invention may advantageously be used inter alia to estimate an exothermic reaction by mixing two chemicals. Additionally, it can also be used to detect an activity of bio cells. Generally when bio cells grow they emit heat which can be detected by micron scale calorimeter according to the present invention. A micron scale calorimeter according to the invention can furthermore be used as a chip calorimeter.
The resonance frequency of a string depends inter alia upon the moment of inertia and material properties of a resonating structure. For a sensor, the moment of inertia should advantageously remain constant during a sensing operation. However, material properties may change because of some external or internal effects like temperature and stress. When temperature changes, stress in a string (under a tensile stress) changes which affects stiffness of a structure thus changing the resonance frequency. Thus, while material properties could be more dominant factor during a sensing operation of a sensor, a calorimeter device according to the present invention is typically and preferably designed so that the dimensions of the string are more dominant than the material properties.
Accordingly, the string is preferably made from a material or a selection of materials with a low heat capacity, so that once a heat is generated by some source inside the string, the material of the string would absorb that heat and quickly transfer it to its surroundings. This has more likely to cause an expansion in the material thus a higher change in the resonance frequency.
The present invention relates in a second aspect to a calorimetry method using a micron scale calorimeter according to the first aspect of the invention. The method preferably comprising
The first and second aspect of the present invention may each be combined with any of the other aspects. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
It is noted that a calorimeter according to the present invention may be suitable for any application which would cause heat generation inside the micro fluidic channel of a string.
The present invention and in particular preferred embodiments thereof will now be disclosed in connection with the accompanying drawings. The drawings show ways of implementing the present invention and are not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.
Reference is made to
As indicated on the figure, the micron-scale calorimeter comprises a micro-channel string 3. This micro-channel 3 is shaped as an elongated member as will be described in further details in connection with
The void serves the purpose of containing the substance to be measured by the micron scale calorimeter. At least two modes of use of the calorimeter can be employed; one where the substance is contained in the void and the openings in the void are closed during measurements and another mode where the one of openings is connected to substance reservoir delivering substance and the remaining opening connected to a receiving receptacle. Thereby, a mode may be possible during which the calorimeter is used for e.g. a streaming sample through the micron scale calorimeter, streaming two or more streams through the micro scaled calorimeter which may include mixing the two or more streams prior to entering the micro-channel string or while present in the micro-channel.
The micro-channel 3 is restrained at least two longitudinally distanced positions (typically being the distal ends of the micro string 3) by use of support elements 4. In
A concept behind the present invention is based on that the micro-channel string 3 has a resonance frequency depending on the temperature of the micro-channel string 3 and that the temperature of the micro-channel string 3 is governed—or at least influenced—by exothermic or endothermic reactions in the substance contained inside the micro-channel. This means that the invention resides inter alia in that a correlation between the parameter(s) to be determined and the resonance frequency exist and if the resonance frequency can be determined so can the parameter(s).
In some preferred embodiments of the micron-scale calorimeter, the string is pre-stressed so that the string has a longitudinal tension in between the two longitudinally distanced positions. This may be used to set the resonance frequency of the string within another range than if the string is not pre-stressed.
To strike the resonance frequency of the micro-channel string 3 acoustical means in the form of a loud speaker 1 is applied. In some preferred embodiments, the acoustical means adapted to oscillate the string comprising a piezo actuator. A piezo actuator is easy to use due to its size (typically dimensions are 5 mm×5 mm×2 mm). The loud speaker—or in general the acoustical means adapted to oscillate the string—is connected to a controllable source of alternating current (not shown in
Once the frequency of sound waves matches with the resonance frequency of a micro-channel string 3, its vibrational amplitude increases substantially as compared to a string not being excited by a loud speaker (piezo actuator). The oscillations and in particular the frequency of the oscillations are detected by use of optical detector means 5. A mode of oscillation of the micro-channel string 3 is shown schematically in
A micron-scale calorimeter according to the present invention may further comprise controlling means controlling the strength and frequency of the sound waves emitted by the loud speaker and receiving a signal from the optical means representing the detected oscillating frequencies.
A calorimeter according to the present invention further comprising or makes use of optical means 5 adapted to detect the resonance frequency of the free released double clamped string. Typically and preferably, such optical means 5 comprising a laser Doppler vibrometer (LDV) which detects amplitude as well as frequency of the vibrating micro-channel string 3.
Reference is made to
As shown in
As also disclosed in
Typical and non-limiting dimensions of two designs of micro-channel strings 3 are 30 (all dimensions are in μm):
In the above table, “Symbol” refers the symbols used in
Reference is made to
As shown in
Thus, in use feeding means (not shown) for feeding one or more liquid into the microfluidic channel 19 (
As shown in details in
The requirement imposed on a mixer 11 was to mix two fluids in the form of two different solutions. The mixing aimed at was mixing by diffusive mixing before the fluids enter into the microfluidic channel 19 of the micro-channel string 3. The mixer 11 take up a certain volume (the interior volume of the mixer) and it was found that by reducing volume of a mixing chamber, speed of mixing can be improved but as a result this also decreases Reynolds number thus increasing laminar flow of a liquid. Laminar flow was not desired for mixing, so by increasing flow speed, quick mixing can be achieved.
An embodiment of a mixer 11 is shown in
Another embodiment of a mixer 11 implemented by mixing elements being square shaped protrusion in the sidewall of the mixer 11. Such mixing elements extend the full height of the mixer 11 and are square protrusions (10 μm×10 μm, width×length) which are found to be an efficient source to disturb a laminar flow of samples inside the chamber and thereby provide a mixing. A source for the design of this mixer can be found in S. H. Wong, P. Bryant, M. Ward, and C. Wharton. Investigation of mixing in a cross-shaped micromixer with static mixing elements for reaction kinetics studies. Sensors and Actuators B: Chemical, 95 (1):414{424, 2003.
As also indicated in
A string according to preferred embodiments of the invention is made from a material having a heat capacity lower than 1000 J/kg*K, such as lower than 900 J/kg*K, preferably lower than 800 J/kg*K. Preferably, the string is made from SRN with a heat capacity of around 691 J/kg K. Additionally SRN is transparent to normal light which facilitate a visual inspection of contents in a micro-channel.
Although a micron-scale calorimeter according to the present invention may be used without placing it in an actively controlled atmosphere, it may be advantageously to arranged at least the part of the micro-channel string in-between the two longitudinally distanced positions in vacuum to reduce air damping, or a mass reduced atmosphere.
Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms “comprising” or “comprises” do not exclude other possible elements or steps. Also, the mentioning of references such as “a” or “an” etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.
| Number | Date | Country | Kind |
|---|---|---|---|
| 13162524.6 | Apr 2013 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/DK2014/050080 | 4/4/2014 | WO | 00 |
