Heating system and method

Abstract

A suitable heating system for heating the region of a microfluidic device is an RC circuit with a constant potential V PS It includes a DC power supply and a switch system to provide the heating element. When in use, the heating system alternately heats the capacitors of the RC circuit, basically V in the first polarity. PS For example, at least about 0.98 × V PS Charge it to the point where it is basically V, then the capacitor is basically V with the second polarity opposite to the first polarity. PS Charge until it reaches [a certain point]. During each charging period, the resistor in the RC circuit is basically 0.5 × C × (2 × V). PS ) 2 It consumes the amount of energy. The heating system generates the maximum potential difference (V) generated by the DC power supply. PS ) efficiently converts into thermal energy, i.e., heat.

Description

[Technical Field]

[0001] The present invention relates to a system and method for generating heat for heating an object and / or a composition of substances. [Cross-reference of related applications]

[0002] This application claims the interests and priority of UK Patent Application No. 2303651.0, entitled “Heating System and Method,” filed on 13 March 2023, and incorporates its entirety by reference herein. US Patent Application No. 17 / 860,933 (“Application 933”), entitled “Fluid Control in Microfluidic Devices,” filed on 8 July 2022, is also incorporated in its entirety herein. [Background technology]

[0003] Microfluidic devices, such as those disclosed in the '933 application, e.g., microfluidic strips, may be used to determine the presence and / or quantity of one or more targets in a liquid sample. Typically, such microfluidic devices define an internal microfluidic network having an application zone for introducing a sample and one or more channels and chambers through which the sample moves. The microfluidic network may contain reagents configured to react with one or more targets to facilitate their determination. The microfluidic network may include valves configured to allow or block the sample and / or gas from passing through parts of the microfluidic network. Other components of the microfluidic network may include a gas pressure source configured to move the sample inside.

[0004] In some cases, the reaction between a sample and a reagent, the operation of a valve, or the movement of a sample by gas pressure may be facilitated or achieved by heating a portion of the microfluidic network. For example, raising the temperature of a mixture of a sample and one or more reagents above ambient temperature can facilitate one or more reactions. Valves may contain temperature-sensitive materials that change shape or phase when heated, thereby opening or closing the valve. Sample movement can be induced by increasing the gas pressure acting on the sample by heating a large amount of gas within the chamber of the microfluidic device.

[0005] The operation of such thermally operated microfluidic components and processes would be improved by a heating system capable of supplying known and reproducible energy and / or power to a given location of the microfluidic device associated with the component or process. [Overview of the project]

[0006] In some embodiments, the heating system comprises an electrical circuit having a first circuit lead and a second circuit lead, and resistive and capacitive elements arranged in series between the first and second circuit leads, for example between the first and second circuit leads, and a first supply lead and a second supply lead, with a potential V between the first and second supply leads. PSThe system comprises a power supply configured to supply, for example, generate and maintain current; a switch system having (1) a first position in which a first supply lead is electrically in communication with a first circuit lead and a second supply lead is electrically in communication with a second circuit lead, and (2) a second position in which a first supply lead is electrically in communication with a second circuit lead and a second supply lead is electrically in communication with a first circuit lead; and a switch system controller (controller) configured to alternately switch the switch system between the first and second positions. Heat is generated as the current passes through the resistive element, and this heat may be used to heat an object and / or gas, or a portion of an object and / or gas, that is in thermal communication with the resistive element. For example, the resistive element may be positioned to be in thermal communication with a region of a microfluidic device, such as a reaction chamber, detection chamber, valve, and / or gas chamber of a microfluidic device.

[0007] In any embodiment of the heating system, the power supply may be a DC power supply. Potential V PS The potential V may be constant, i.e., a DC potential. For example, the power supply has a relative potential V between the first supply lead and the second supply lead with a relative variation of less than approximately 10%, less than approximately 5%, less than approximately 2.5%, or less than approximately 1% relative to the average potential. PS The power supply may be configured to supply, for example, generate and maintain a constant potential V between a first supply lead and a second supply lead. PS At potential V PS It may be configured to supply, for example, generate and maintain.

[0008] In any embodiment of the heating system, at least the power supply and the switch system may be implemented as one or more integrated circuits, for example, an integrated circuit including two or more 1 / 2H bridge drivers or at least one H bridge driver. The switch system typically comprises at least one switch, for example, at least a first switch and a second switch. In these embodiments, the controller may also be implemented as an integrated circuit and may include a power supply and / or switch system.

[0009] In some embodiments of the heating system, the resistive element consists of essentially a single resistive element, e.g., a single resistor having a resistance value R. In other embodiments, the resistive element comprises two or more resistive elements, e.g., two or more resistors, arranged to give a total resistance value R. Exemplary resistive elements include carbon ink-based resistive elements, silver ink-based resistive elements, metal oxide resistive elements, e.g., silver oxide, and combinations thereof. The resistive element may be formed using printing techniques such as inkjet printing and screen printing.

[0010] In some embodiments of the heating system, the capacitive element consists of essentially a single capacitive element, e.g., a single capacitor having capacitance C. In other embodiments, the capacitive element comprises two or more capacitive elements, e.g., two or more capacitors, arranged to give a total capacitance C. In any embodiment, the capacitive element may be any of the capacitive elements disclosed herein. For example, the capacitive element may be a nonpolar capacitor having a low temperature coefficient, where the variation in capacitance with respect to the capacitor temperature is small. Exemplary capacitive elements may be formed alone or in combination from polyester, polypropylene, ceramic, and combinations thereof. Other suitable capacitive elements include capacitive elements formed by the printing techniques disclosed herein, e.g., capacitors.

[0011] In any embodiment of the heating system, the resistive element has a total resistance value R, the capacitive element has a total capacitance C, and the electrical circuit has an RC time constant given by the product R×C. The RC time constant is typically from about 1 ms to about 1000 ms, from about 1 ms to about 100 ms, from about 3 ms to 50 ms, from about 5 ms to about 25 ms, or from about 7.5 to about 15 ms. The resistance value R of the RC circuit may be basically determined by the resistance value of the resistive element. For example, the RC circuit may not have other resistance sources that substantially contribute to the total resistance value of the RC circuit. The magnitude of the parasitic resistance of the RC circuit may be small compared to the magnitude of the resistance value R. For example, the ratio of R to the total resistance value of the RC circuit may be at least about 0.9, at least about 0.95, at least about 0.975, or basically 1.0. The capacitance of the RC circuit may be basically determined by the capacitance of the capacitive element. For example, the RC circuit may not have other capacitance sources that substantially contribute to the capacitance of the RC circuit. The magnitude of the parasitic capacitance of the RC circuit may be small compared to the magnitude of the capacitance C. For example, the ratio of C to the total capacitance of the RC circuit may be at least about 0.9, at least about 0.95, at least about 0.975, or basically 1.0.

[0012] In any embodiment of the heating system, the controller is configured to (i) switch the switch system to a first position, maintain the switch system at the first position for a time T 1st and then switch the switch system to a second position, (ii) maintain the switch system at the second position for a time T 2nd and (iii) repeat steps (i) and (ii). T 1st and T 2nd Each duration of is typically from about RC to 20×RC, from about 2×RC to about 10×RC, from about 3×RC to about 7×RC, for example about 4×RC, where RC is the RC time constant of the RC circuit. T 1st and T 2nd The durations of may be basically the same. The controller may be configured to repeat step (iii) a total of N times per second, where N is from about (0.5×RC) -1 to about (40×RC)-1 For example, approximately (8 × RC) -1 In some embodiments, for example, N may be about 5 to 500, about 10 to 200, or about 15 to 100.

[0013] If step (iii) is repeated N times per second, the average power consumed by the resistive element is typically, at the input potential V PS It depends on the square of twice that, i.e., approximately 0.5 × C × (2 × V PS ) 2 / τ P = 2 × C × (V PS ) 2 / τ P And here τ P is period T 1st and T 2nd This is the average. The heating system is the difference between the maximum potential and the minimum potential generated by the power supply (V PS It efficiently converts the resistance R into energy and power consumed by the resistive element. The energy and power consumed are essentially independent of the resistance R.

[0014] In any embodiment of the heating system, the controller (i) provides at least about 0.5 × V PS , at least about 0.80 × V PS , at least about 0.90 × V PS , at least about 0.95 × V PS , or at least about 0.98 × V PS (ii) Position the switch system in the first position for a sufficient amount of time to charge the capacitive element with the first polarity to a potential of (ii) switch the switch system to the second position and discharge the capacitive element, then discharge it to at least about 0.5 × V PS , at least about 0.80 × V PS , at least about 0.90 × V PS , at least about 0.95 × V PS , or at least about 0.98 × V PS(iii) maintain the switch system in the second position for a sufficient time to charge the capacitive element with the second polarity opposite to the first polarity to the potential of (iii) switch the switch system to the first position and discharge the capacitive element, then discharge at least about 0.5 × V PS , at least about 0.80 × V PS , at least about 0.90 × V PS , at least about 0.95 × V PS , or at least about 0.98 × V PS The controller may be configured to maintain the switch system in a first position for a sufficient time to charge the capacitive element with the first polarity to a potential of , and to repeat steps (ii) and (iii). The controller may be configured to repeat step (iv) a total of N times per second, where N is approximately (0.5 × RC) -1 ~Approx.(40×RC) -1 For example, approximately (8 × RC) -1 In some embodiments, for example, N may be about 5 to 500, about 10 to 200, or about 15 to 100.

[0015] In some embodiments, the heating method includes generating heat using one of the heating systems described above. The heat source is, for example, primarily derived from the power consumed by a resistive element in an RC circuit. In the implementation of the heating method, the resistive element is positioned to be in thermal communication with the object and / or gas or region to be heated. For example, the heating method includes heating a region of a microfluidic device, and the resistive element is positioned to be in thermal communication with that region. These regions may include, for example, the reaction chamber, detection chamber, valve, and / or gas chamber of the microfluidic device. In any embodiment of the heating method, the resistive element and / or capacitive element may be configured as any of the resistive elements and / or capacitive elements disclosed herein. The heating method may include any embodiment of the heating system disclosed herein.

[0016] In some embodiments, the heating method includes providing an electrical circuit comprising a first circuit lead and a second circuit lead, and a resistive element and a capacitive element disposed between the first circuit lead and the second circuit lead. Typically, the resistive element and the capacitive element are arranged in series. The method has a first supply lead and a second supply lead, with a potential V between them. PS The method further includes providing a power supply configured to supply, for example, generate and maintain a power source. The method further includes alternating between (1) connecting a first supply lead to a first circuit lead and a second supply lead to a second circuit lead, and (2) connecting a second supply lead to a first circuit lead and a first supply lead to a second circuit lead.

[0017] In any embodiment of the heating method, the power supply may be a DC power supply. Potential V PS The potential can be constant, for example, a DC potential. The method involves a relative variation of the potential V of less than approximately 10%, less than approximately 5%, less than approximately 2.5%, or less than approximately 1% relative to the average potential. PS This may include supplying, for example, generating and maintaining a constant potential V. For example, the method is essentially a constant potential V. PS At potential V PS This may include supplying, for example, generating and maintaining.

[0018] In any embodiment of the heating method, the resistive element may have a resistance value R, the capacitive element may have a capacitance C, and the electrical circuit may have an RC time constant of R × C. The method involves performing step (1) and connecting the T 1st Maintain the connection for the duration of step (2), then perform step (2) and connect to T 2nd This may include maintaining the condition for a certain period and sequentially repeating steps (1) and (2). 1st and T 2nd The durations of each are typically approximately RC ~ 20 × RC, approximately 2 × RC ~ approximately 10 × RC, approximately 3 × RC ~ approximately 7 × RC, for example, approximately 4 × RC, where RC is the RC time constant of the RC circuit. 1st and T 2ndThe duration of each step can be essentially the same. The controller may be configured to repeat each of steps (1) and (2) a total of N times per second. The number N is typically about (5 × RC). -1 ~Approx.(0.5×RC) -1 For example, approximately (2 × RC) -1 In some embodiments, for example, N may be about 10 to 500, about 25 to 250, about 50 to 200, for example, about 70.

[0019] The heating method is carried out by (i) performing step (1) and heating at least about 0.5 × V PS , at least about 0.80 × V PS , at least about 0.90 × V PS , at least about 0.95 × V PS , or at least about 0.98 × V PS (ii) Maintain the connection for a period of time sufficient to charge the capacitive element with the first polarity to a potential of (ii) After performing step (2) and discharging the capacitive element, at least about 0.5 × V PS , at least about 0.80 × V PS , at least about 0.90 × V PS , at least about 0.95 × V PS , or at least about 0.98 × V PS (iii) After performing step (1) and discharging the capacitive element, maintain the connection for a period of time sufficient to charge the capacitive element with a second polarity opposite to the first polarity to a potential of (iii) a potential of at least about 0.5 × V PS , at least about 0.80 × V PS , at least about 0.90 × V PS , at least about 0.95 × V PS , or at least about 0.98 × V PS (iv) This may include maintaining the connection for a period of time sufficient to charge the capacitive element with the first polarity to a potential of , and repeating steps (ii) and (iii).

[0020] In some embodiments, the heating method provides an electrical circuit comprising a first circuit lead and a second circuit lead, and a resistive element and a capacitive element arranged in series between the first circuit lead and the second circuit lead, and having a first supply lead and a second supply lead, with a potential V between them. PS The invention provides a power source that generates a voltage and alternately performs the following steps (1) and (2): (1) Charge a capacitive element to potential V1 with first polarity by (a) passing electrons from a first circuit lead to a first supply lead, and (b) passing electrons from a second supply lead to a second circuit lead, wherein V1 / V PS The ratio of is approximately 0.5 to 1, for example, approximately 0.8 to approximately 1.0, approximately 0.90 to approximately 1.0, approximately 0.95 to approximately 1.0, or approximately 0.98 to approximately 1.0, and (2) (a) electrons are passed from the second supply lead to the first circuit lead, and (b) electrons are passed from the second circuit lead to the first supply lead, thereby charging the capacitive element to a potential V2 with a second polarity opposite to the first polarity, where V2 / V PS The ratio is approximately 0.5 to approximately 1.0, for example, approximately 0.8 to approximately 1.0, approximately 0.90 to approximately 1.0, approximately 0.95 to approximately 1.0, or approximately 0.98 to approximately 1.0. In carrying out the heating method, the resistive element may have a resistance value R, the capacitive element may have a capacitance C, and the electrical circuit may have an RC time constant of R × C. The method involves performing step (1) and controlling the flow of electrons to T 1st Maintain for the duration of T, then perform step (2) and set the electron flow to T 2nd This may include maintaining the condition for a certain period and alternating between steps (1) and (2). 1st and T 2nd The durations of each are typically approximately RC ~ 20 × RC, approximately 2 × RC ~ approximately 10 × RC, approximately 3 × RC ~ approximately 7 × RC, for example, approximately 4 × RC, where RC is the RC time constant of the RC circuit. 1st and T 2nd The duration of each step may be essentially the same. The controller may be configured to repeat steps (1) and (2) a total of N times per second, where N is approximately (0.5 × RC). -1 ~Approx.(40×RC) -1 For example, approximately (8 × RC)-1 In some embodiments, for example, N may be about 5 to 500, about 10 to 200, or about 15 to 100.

[0021] In some embodiments, the heating method provides an electrical circuit comprising a first circuit lead and a second circuit lead, and a resistive element and a capacitive element having capacitance C arranged in series between the first and second circuit leads, and each (i) flows current through the electrical circuit in a first direction to charge the capacitive element to potential V with a first polarity, and (ii) flows current through the electrical circuit in a second direction opposite to the first direction to charge the capacitive element to potential V with a second polarity opposite to the first polarity, thereby generating approximately C × (2 × V) in the resistive element per cycle. 2 This includes performing a repetitive cycle that consumes energy equal to . The difference between the maximum and minimum potentials applied to the first and second leads may be about 1.2 × V or less, about 1.1 × V or less, about 1.05 × V or less, for example, about V. The absolute value of the potentials applied to the first and second circuit leads may vary by about 20% or less, about 15% or less, about 10% or less, about 5% or less, or about 2.5% or less relative to the average potential applied to the first and second leads.

[0022] In some embodiments, the self-contained diagnostic reader may include an embodiment of any of the heating systems described above and be configured to perform an embodiment of any of the heating methods. The self-contained diagnostic reader is configured to actuate a diagnostic device, such as a microfluidic device, e.g., a microfluidic strip or cartridge, and to perform a diagnostic assay on a liquid sample applied to the diagnostic device. The self-contained diagnostic reader includes a resistive element positioned such that the resistive element is in thermal communication with a region of the microfluidic device when the device is placed in the working position relative to the reader. For example, the self-contained diagnostic reader may include a platen incorporating a resistor. The diagnostic device, inserted into the working position relative to the self-contained diagnostic reader, is positioned to be in thermal communication with the platen. During operation, the self-contained diagnostic reader dissipates heat on the resistor, thereby actinguating the heating system to heat a region of the diagnostic device. For example, a region of the diagnostic device may include a reaction zone, a detection zone, a valve, and / or a gas pressure chamber, e.g., a gas pressure chamber configured to move liquid and / or gas within the device. An exemplary valve includes a temperature-sensitive material that changes shape or phase when heated, thereby opening and closing the valve. In a reaction chamber, one or more reactions and / or mixing can be accelerated by selectively raising the temperature of a sample mixture containing one or more reagents above ambient temperature. Heating a large volume of gas in a gas chamber can increase the gas pressure, which may induce the movement of samples or other materials that are in gaseous communication with the gas.

[0023] In some embodiments, the diagnostic system may include an embodiment of any of the heating systems described above and be configured to perform an embodiment of any of the heating methods. The diagnostic system comprises a microfluidic device, such as a microfluidic strip, and a diagnostic reader configured to operate the diagnostic device and perform a diagnostic assay on a liquid sample applied to the diagnostic device. For example, the diagnostic assay may be performed to determine the presence and / or amount of one or more targets present in the liquid sample. The diagnostic reader of the diagnostic system typically comprises a power supply for the heating system, a switch system (including at least one switch, e.g., a first switch and a second switch, and a switch system controller), and a controller. The microfluidic device may comprise resistive elements, such as resistors, and / or capacitive elements, such as capacitors forming an RC circuit as disclosed herein. When the microfluidic device is positioned to operate with the diagnostic reader, the power supply leads are positioned to electrically communicate with the circuit leads of the RC circuit of the microfluidic device as disclosed herein. While the microfluidic device is operating, the power supply, switch system, and controller of the diagnostic reader are operated to heat resistive elements as disclosed herein.

[0024] Diagnostic devices, such as microfluidic strips or cartridges, may include resistive elements. For example, a resistive element may be placed on the surface of the diagnostic device and be in thermal communication with a region to be heated, such as a reaction zone, a valve, or a gas pressure chamber, such as a gas pressure chamber configured to move liquid and / or gas within the device. For example, a resistive element may be bonded to the surface of the diagnostic device and be in thermal communication with the region to be heated. The surface may be an external surface, such as a surface that does not directly contact liquids or other materials operated within the diagnostic device. Such an external surface may be, for example, placed between layers of substrate constituting the microfluidic device. Alternatively, at least a portion, for example, the entire resistive element may be placed within the diagnostic device and be in direct contact with liquids or other materials within the diagnostic device. The resistive element may include an electrical insulating layer, such as a coating, to prevent short circuits in the presence of liquids, other materials, or other electrical elements of the diagnostic device. Exemplary resistive elements suitable for use with diagnostic devices include carbon-based resistive elements, such as carbon ink-based resistive elements, silver ink-based resistive elements, metal oxide resistive elements, such as silver oxide, and combinations thereof. These resistive elements may be printed or otherwise deposited on the diagnostic device, for example. The diagnostic device and diagnostic reader may be configured as microfluidic strips and readers disclosed in the '933 application and may have these features. The area of ​​the diagnostic device to be heated may include, for example, a reaction zone, a detection zone, a valve, and / or a gas pressure chamber, for example, a gas pressure chamber configured to move liquid and / or gas within the device.

[0025] A diagnostic device, such as a microfluidic strip or cartridge, may comprise resistive and capacitive elements. For example, the capacitive elements may be configured as capacitors printable on the surface of the diagnostic device so as to be in electrical communication with the resistive elements to form an RC circuit. The surface may be an external or internal surface of the microfluidic device. In such embodiments, the RC circuit may be entirely located on and / or within the microfluidic device, for example, between layers of substrate constituting the microfluidic device. Circuit leads of such an RC circuit may be formed as contacts arranged to be in electrical communication with the supply leads of a diagnostic reader when the microfluidic device is positioned to be operable with respect to the supply leads of the diagnostic reader. The diagnostic reader comprises a power supply and a switch system.

[0026] The diagnostic method may include any of the heating methods described above, and may utilize, for example, an autonomous diagnostic reader or diagnostic system. The diagnostic method may include placing a liquid sample within the reaction zone and / or detection zone of a microfluidic device, the reaction zone being thermally connected to a resistive element, and performing a heating method to heat the liquid sample within the reaction zone and / or detection zone. The diagnostic method may, or in combination, include heating a thermally operated valve within the microfluidic device to open or close the valve. The diagnostic method may, or in combination, include heating a gas chamber within the microfluidic device and applying driving pressure to the liquid and / or other material within the microfluidic network of the microfluidic device (or all three).

[0027] In some embodiments, the heating method includes heating a material composition, a manufactured product, or a combination thereof using one of the heating systems described above (including a diagnostic reader incorporating these heating systems or a diagnostic system incorporating these heating systems). For example, the heating method may be incorporated into a diagnostic method that includes determining the presence and / or quantity of one or more targets in a sample. The heating method may include, for example, heating a thermally operated valve to open or close the valve, heating a sample (including one or more reagents optionally combined with the sample) to facilitate a reaction or mixing of the sample and / or reagents, and / or heating a large amount of gas to apply driving pressure to a liquid or other material to be moved within the microfluidic network of the diagnostic device.

[0028] In any embodiment of a heating system, heating method, self-contained diagnostic reader, diagnostic reader, or system and method incorporating such heating systems and methods, the power supply may comprise a single potential source applied to the RC circuit of the heating system. Such a system does not include, for example, two or more potential sources used to alternately apply potential to the RC circuit.

[0029] In any of the heating systems, heating methods, and embodiments of diagnostic readers and systems and methods incorporating these heating systems and methods, the potential supplied by the power system, for example, V PS The voltage can be, for example, approximately 5V to approximately 50V, or for example, approximately 12V. [Brief explanation of the drawing]

[0030] [Figure 1] This is a schematic diagram illustrating the heating system of the present invention. [Figure 2] This figure shows the time dependence of the potential applied to the RC circuit of the heating system in Figure 1 during operation, as well as the time dependence of (i) the potential drop across the resistors of the RC circuit and (ii) the potential drop across the capacitors of the RC circuit in response to the applied potential. [Figure 3] This figure shows an example output of a conventional AC power supply that oscillates as a square wave between the maximum potential V and the negative potential -V. [Figure 4] This figure shows an example of how the heating system shown in Figure 1 can be implemented to heat the reaction zone of a microfluidic device. [Figure 5] This figure shows temperature-time plots obtained for each of the two resistors described in the examples using the heating system of the present invention. Each row of the chart represents a temperature difference of 5°C, and each column of the chart represents a time interval of 30 seconds. [Modes for carrying out the invention]

[0031] Referring to Figure 1, the heating system 10 comprises an RC circuit 12, a DC power supply 22, a first switch 28, and a second switch 40. A controller 11 (e.g., an electronic processor) is configured to operate the DC power supply 22 and the first switch 28 and the second switch 40. The controller 11 can communicate directly with the heating system 10 via electrical and / or wireless communication. The RC circuit 12 comprises a resistor 14 and a capacitor 16 arranged in series between a first RC circuit lead 18 and a second RC circuit lead 20. The DC power supply 22 and the first switch 28 and the second switch 40 can be implemented using, for example, an integrated circuit that provides at least two 1 / 2H bridge drivers or at least one H bridge driver. An example integrated circuit is the Texas Instruments DRV8844PWP quad 1 / 2H bridge driver.

[0032] During use, the resistor 14 is positioned to be thermally connected to the heating target location 52. Location 52 may be, for example, a region of the microfluidic network of a microfluidic device, such as a thermal control valve of a microfluidic device, a gas pressure source (e.g., a gas chamber), or a reaction chamber (e.g., a reaction zone). The controller 11 activates the DC power supply 22 and the first switch 28 and the second switch 40, thereby applying a time-dependent potential 200 to the RC circuit 12 (Figure 2). The application of the time-dependent potential 200 causes the capacitor 16 to be repeatedly charged and discharged, and all of its charge and discharge current flows through the resistor 14. As will be described later, the current flowing through the resistor 14 consumes a known amount of energy at a known rate, i.e., a known power, thereby enabling control of the heating of location 52. The heating system 10 can maximize the amount of thermal energy, i.e., the relative amount converted to heat, from the potential difference generated by the power supply 22, and therefore has high heating efficiency.

[0033] The resistor 14 has a resistance value R. In an exemplary embodiment in which the heating system 10 is used to heat a region of the microfluidic network of a microfluidic device, R is, for example, about 25 Ω to about 500 Ω, for example, about 150 Ω. The capacitor 16 has a capacitance F. In such an exemplary embodiment, F is, for example, about 20 μF to about 100 μF, for example, about 50 μF. The RC circuit 12 is typically formed such that, when measured at a frequency of less than 200 Hz, the resistance value R of the resistor 14 accounts for substantially all, for example, basically all, of the resistance value of the circuit 12, and the capacitance F of the capacitor 16 accounts for substantially all, for example, basically all, of the capacitance value of the circuit 12. Thus, the magnitude of the parasitic resistance of the RC circuit is typically small compared to the magnitude of the resistance value R. For example, the ratio of R to the total resistance value of the RC circuit may be at least about 0.9, at least about 0.95, at least about 0.975, or basically 1.0. Furthermore, the parasitic capacitance of an RC circuit is typically small compared to the capacitance C. For example, the ratio of C to the total capacitance of the RC circuit may be at least approximately 0.9, at least approximately 0.95, at least approximately 0.975, or basically 1.0. The resistance R and capacitance C typically determine, at least fundamentally, the RC time constant of the RC circuit 12. For example, when R = 150 Ω and F = 50 μF, RC = 7.5 ms.

[0034] The resistor 14 may be formed as a resistive element placed, for example, attached to the surface of a microfluidic device, such as the outer surface of the microfluidic device or the inner surface of the microfluidic network of the microfluidic device (for example, the inner surface of its channels, valves, or chambers). Exemplary resistive elements include carbon ink-based resistive elements, silver ink-based resistive elements, metal oxide resistive elements, such as silver oxide, and combinations thereof. These resistive elements may be printed or otherwise deposited on a diagnostic device, for example. In some cases, due to the inaccuracy of the manufacturing process, the resistance value of individual resistive elements is unknown unless determined by measurement. However, it has been empirically found that the range of resistance values ​​due to such manufacturing processes falls between an upper and lower limit. Therefore, it can be predicted that any manufactured resistive element will have a resistance value greater than the minimum and less than the maximum.

[0035] Capacitor 16 is typically a nonpolar capacitor with a low temperature coefficient, and its capacitance variation with respect to temperature changes is small. To further reduce the temperature dependence of the capacitance, two or more capacitors may be combined. The first capacitor has a negative dependence on temperature, and the second capacitor has a positive dependence on temperature. By combining them, these capacitors form a capacitive element with a combined capacitance that has reduced temperature dependence. Suitable capacitors may be formed individually or in combination from, for example, polyester, polypropylene, ceramic, or combinations thereof. In this specification, the term capacitive element means an electronic element such as a capacitor or combination of capacitors having suitable capacitance, polarization characteristics (e.g., nonpolar), and a low temperature coefficient.

[0036] The DC power supply 22 includes a first power supply lead 24 and a second power supply lead 26. At position 25, the first power supply lead 24 branches into a first power supply sub-lead 24' (terminated at a first power supply switch contact 42) and a first power supply sub-lead 24'' (terminated at a first power supply switch contact 36). At position 27, the second power supply lead 26 branches into a second power supply sub-lead 26' (terminated at a second power supply switch contact 32) and a second power supply sub-lead 26'' (terminated at a second power supply switch contact 46).

[0037] The first RC circuit lead 18 branches at position 19 into the first RC circuit sub-lead 18' (terminated at the first RC switch contact 44) and the first RC circuit sub-lead 18'' (terminated at the first RC switch contact 48). The second RC circuit lead 20 branches at position 21 into the second RC circuit sub-lead 20' (terminated at the second RC switch contact 30) and the second RC circuit sub-lead 20'' (terminated at the second RC switch contact 34).

[0038] The first switch 28 includes a bridge contact 38. In the first switch position shown in Figure 1, the bridge contact 38 provides an electrical connection between the second RC switch contact 30 of the second RC circuit sub-lead 20' and the second power supply switch contact 32 of the second power supply sub-lead 26'. In the second switch position indicated by arrow 28' in the figure, the bridge contact 38 provides an electrical connection between the second RC switch contact 34 of the second RC circuit sub-lead 20'' and the first power supply switch contact 36 of the first power supply sub-lead 24''. The second switch 40 includes a bridge contact 50. In the first switch position shown in Figure 1, the bridge contact 50 provides an electrical connection between the first RC switch contact 44 of the first RC circuit sub-lead 18' and the first power supply switch contact 42 of the first power supply sub-lead 24'. At the second switch position indicated by arrow 40' in the figure, the bridge contact 50 provides an electrical connection between the first RC switch contact 48 of the first RC circuit sub-lead 18'' and the second power supply switch contact 46 of the second power supply sub-lead 26''.

[0039] The DC power supply 22 is configured to supply a constant potential V between the position 25 of the lead 24 and the position 27 of the lead 26. However, the direction of the potential drop in the RC circuit 12 depends on the positions of the first switch 28 and the second switch 40. Referring also to FIG. 2, the time-dependent potential 200 represents the potential drop of the RC circuit 12 as observed by a voltmeter having a positive contact at the position 19 of the first RC circuit lead 18 and a negative contact at the position 21 of the second RC circuit lead 20. When both the first switch 28 and the second switch 40 are in the first switch position (FIG. 1), the potential drop measured between the first RC circuit lead 18 and the second RC circuit lead 20 of the RC circuit 12 is V PS (FIG. 2, for example, the pulse 200' at times τ1 to τ2). When both the first switch 28 and the second switch 40 are in the second switch position (indicated by the respective arrows 28', 40' in FIG. 1), the potential drop measured between the first RC circuit lead 18 and the second RC circuit lead 20 of the RC circuit 12 is -V<> PS (FIG. 2, for example, the pulse 200'' at times τ3 to τ4). The pulse period τ PS is typically the same for each pulse. Between consecutive pulses, for example, between time τ2 (the end of the pulse 200') and time τ3 (the start of the pulse 200''), both switches 28, 40 are in the open position, and the potential drop of the RC circuit 12 between the first RC circuit lead 18 and the second RC circuit lead 20 becomes 0. However, the length of the open period is typically much shorter compared to the pulse period τ P and thus the open period is not shown in FIG. 2. For example, the ratio of the open period to the pulse period may be about 0.01 or less, about 0.005 or less, or about 0.001 or less. P The first switch 28 and the second switch 40 can reverse the polarity of the potential drop in the RC circuit 12 as shown in FIG. 2, but the output of the DC power supply 22 is constant, i.e., V

[0040] PS ​remains as it is. When the DC power supply 22 is off, that is, when no potential is generated, the output is 0 volts (Figure 2, times τ0 to τ1). Therefore, the difference between the maximum potential and the minimum potential generated by the DC power supply is V PS is. In contrast, as shown in Figure 3, the zero-centered square wave output 200 by an AC power supply (not shown) is not constant and oscillates between the maximum potential V AC and the minimum potential -V AC . The difference between the maximum potential V AC and the minimum potential -V AC for such an AC power supply is 2V AC .

[0041] The heating system 10 can be configured and operated as follows, for example. The resistor 14 is positioned to be in thermal communication with the heating target position 52. As described above, the RC time constant of the RC circuit 12 is 7.5 ms when R = 150 Ω and F = 50 μF. Figure 2 shows, in addition to the time-dependent potential 200 in the RC circuit 12, the time-dependent potential drop 202 in the resistor 14 (e.g., between the position 19 of the first circuit lead 18 and the position 23 between the resistor 14 and the capacitor 16), and the time-dependent charge of the capacitor 16 (e.g., between the position 23 and the position 21 of the second circuit lead 20). Before heating starts, since the DC power supply 22 is off, the potential drop across the RC circuit 12 between the first RC circuit lead 18 and the second RC circuit lead 20 is 0 (time τ0). At time τ1, the controller 11 activates the DC power supply 22 to a voltage V PS (e.g., 12 V DC), positions the switches 28, 40 at the first position (Figure 1), and then maintains the switches at the first position for a pulse period τ P to generate a voltage pulse 200' (Figure 2). The ratio of the pulse period τ P to the RC time constant (τ P :RC) is 4 (τ P = 30 ms).

[0042] During the pulse 200', the potential drop in the resistor 14 (shown by the segment 202' of the time-dependent potential​The voltage of capacitor 16 decreases exponentially from 0V at time τ1 to 0V at time τ2. PS It is charged (shown in segment 204' of time-dependent potential 204). τ P Because the time constant is long relative to RC, at the end of pulse 200' (time τ2), the voltage drop across resistor 14 is basically 0V, and capacitor 16 is basically V PS It is charged to e. For example, the potential drop across resistor 14 is e ^ (-τ P / RC)×V PS = 0.018 × V PS Therefore, the capacitor is [1-e ^ (-τ P / RC)]×V PS = 0.982 × V PS It is charged to the potential of . The amount of energy consumed by resistor 14 during pulse 200' is 0.5 × C × (0.98 × V). PS ) 2 = 3.45 mJ, which is basically 0.5 × C × (V PS ) 2 This is equal to 3.6 mJ.

[0043] At time τ2, the controller 11 switches switches 28 and 40 from the first position to the second position (indicated by arrows 28' and 40' in Figure 1), thereby reversing the polarity of the potential applied to the RC circuit 12. The output of the DC power supply 22 itself is V PS It remains in that state. Subsequently, the controller 11 moves the switch to the second position with a period τ P Maintaining this state, a voltage pulse 200'' is generated, starting at time τ3 and ending at time τ4 (Figure 2). During the transition between pulses 200' and 200'', the switch is temporarily in the open position as described above. At time τ3, the potential drop across resistor 14 (shown in segment 202'' of time-dependent potential 202) is the sum of the potential of the charged capacitor 16 and the potential applied by the DC power supply 22, i.e., basically -2V PS Therefore, during pulse 200'', the potential drop across resistor 14 is basically -2V at time τ3. PSFrom time τ4, it becomes exponentially 0V. Capacitor 16 is basically V at time τ3. PS From there, it passes through 0V at the midpoint of pulse 200'', and towards time τ4, it reaches -V. PS It discharges exponentially until (shown in segment 204'' of time-dependent potential 204). At the end of pulse 200'' (time τ4), the potential drop across resistor 14 is basically 0V, i.e., -e ^ (-τ P / RC)×V PS = -0.018 × V PS Therefore, capacitor 16 is basically -V PS , that is -[1-e ^ (-τ P / RC)]×V PS = -0.982 × V PS It is charged to the potential of . The amount of energy consumed by resistor 14 during pulse 200'' is 0.5 × C × (2 × 0.98 × V PS ) 2 = 13.8 mJ, which is basically 2 × C × (V PS ) 2 = Equivalent to 14.4 mJ. The amount of energy consumed during pulse 200'' is four times (4 ×) the energy consumed during the initial pulse 200''. This is because capacitor 16 is basically V PS This is because, after being charged to a certain level, the potential applied by the DC power supply 22 combines with the potential change that occurs during pulse 200'', resulting in an increase in the potential drop across the resistor 14 and the current flowing through the resistor 14.

[0044] At time τ4, the controller 11 switches switches 28 and 40 from the second position to the first position (Figure 1), thereby reversing the polarity of the potential applied to the RC circuit 12. The output of the DC power supply 22 itself is V PS It remains in that state. Subsequently, the controller 11 moves the switch to the first position with a period τ PMaintaining this state, a voltage pulse 200''' is generated, starting at time τ5 and ending at time τ6 (Figure 2). During the transition between pulses 200'' and 200''', the switch is temporarily in the open position as described above. At time τ4, the potential drop across resistor 14 (shown by segment 202''' of time-dependent potential 202) is the sum of the potential across capacitor 16 and the potential applied by the DC power supply 22, i.e., basically 2V PS Therefore, during pulse 200''', the potential drop across resistor 14 is 2V at time τ5. PS The voltage decreases exponentially towards time τ6, becoming 0V. Capacitor 16 is basically -V at time τ5. PS From there, the pulse passes through 0V at the midpoint of pulse 200''', and then V towards time τ6. PS It discharges exponentially until (shown in segment 204''' of time-dependent potential 204). At the end of pulse 200''' (time τ6), the potential drop across resistor 14 is basically 0V, i.e. ^ (-τ P / RC)×V PS = 0.018 × V PS Therefore, capacitor 16 is basically V, that is, [1-e ^ (-τ P / RC)]×V PS = 0.982 × V PS It is charged to the potential of . The amount of energy consumed by resistor 14 during pulse 200''' is the same as the energy consumed during pulse 200''.

[0045] After pulse 200''', at time τ7, the controller 11 switches switches 28 and 40 from the first position to the second position, thereby reversing the polarity of the potential applied to the RC circuit 12 again. Subsequently, the controller 11 moves the switches back to the second position for a period τ PMaintaining this state, a voltage pulse 200'''' is generated, starting at time τ7 and ending at time τ8 (Figure 2). The potential and energy consumption behavior during pulse 200'''' is the same as during pulse 200''. The process of switching the potential applied to the RC circuit 12 can be repeated as many times as necessary to achieve the desired heating of the object 52. For example, the potential is switched N times per second, where N is approximately (0.5 × RC) -1 ~Approx.(40×RC) -1 For example, approximately (8 × RC) -1 It may be such that, in some embodiments, for example, N may be about 5 to 500, about 10 to 200, or about 15 to 100.

[0046] As described above, the average power consumed by resistor 14 during the initial pulse 200' in which capacitor 16 is first charged depends on the square of the input potential, and is 0.5 × C × (V PS ) 2 / τ P = 0.12W. In contrast, between each subsequent pulse, for example between pulses 200''~200'''' and each subsequent pulse, the charged capacitor contributes to the potential drop across resistor 14. Therefore, the average power consumed by resistor 14 between each subsequent pulse is the input potential V PS It depends on the square of twice the value, and is 0.5 × C × (2 × V PS ) 2 / τ P = 2 × C × (V PS ) 2 / τ P = 0.48W. The heating system 10 is controlled by the difference between the maximum and minimum potential (V) generated by the DC power supply 22. PS The current is efficiently converted into energy and power consumed by the resistor 14. The average power consumed is inversely proportional to the period length of each pulse and the number of pulses generated per second. However, the energy and power consumed do not depend on the resistance value of the resistor 14.

[0047] Referring to Figure 4, a diagnostic reader 112 and a microfluidic device embodied as a microfluidic strip 114 are shown. The diagnostic reader 112 is configured to operate the microfluidic strip 114 to perform a diagnostic assay for a target present in a liquid sample applied to the strip (disclosed, e.g., in the '933 application). The diagnostic strip 114 comprises a microfluidic network 116 having a sample application zone 118 and microchannels leading to a reaction zone 122 (e.g., a detection zone). The microfluidic strip 114 may be configured to include the features of a microfluidic strip disclosed in the '933 application, e.g., reagents, a gas chamber (gas bladder), and an electrical sensing element. The microfluidic strip 114 further comprises a resistive element 124 positioned to be thermally in communication with the reaction zone 122. For example, the resistive element 124 may be formed from a carbon ink-based resistive element, a silver ink-based resistive element, a resistive element of a metal oxide, e.g., silver oxide, and combinations thereof, and may be printed or otherwise deposited on the outer or inner surface of the strip 114. The resistive element 124 is connected to a first terminal 126' via a first lead 126 and to a second terminal 128' via a second lead 128. When the strip 114 is inserted into the receiving slot 113 of the leader 112, terminals 126' and 128' engage with corresponding connectors in the leader 112, providing electrical communication between them. The rest of the heating system 10, such as the DC power supply, capacitor, and switching assembly, is housed within the leader 112. The resistive element 124 of the microfluidic strip 114 and the capacitor in the leader 112 form a series RC circuit as disclosed herein.

[0048] During use, the strip 114 is inserted into the receiving slot 113, and the liquid sample is applied to the application zone 118. The sample flows along the microfluidic network 116 and is manipulated by the leader 112 to move the liquid sample or mix the sample with the reagent. The heating system 10 is activated to heat the reaction zone 122 to promote the desired reaction or state of the liquid sample and the reagent within it. The capacitance of the capacitor in the heating system 10, the DC voltage of the power supply, and other operating conditions (e.g., pulse period and frequency) are selected to produce the desired heating level in the reaction zone 122. In some cases, the manufacturing process of such resistive elements may result in elements with unspecified resistance values. However, the range of resistance values ​​can be determined with, for example, a confidence of 99% or more. Typically, the duration τ of the pulse generated by the heating system 10 P This is determined based on the maximum assumed resistance value of such a resistive element, τ P >It is set to be the RC time constant. For example, τ P The ratio of RC is approximately 3-10, 3-7, 3-6, and for example, 4.

[0049] In any embodiment using a microfluidic device (e.g., a microfluidic strip or cartridge), capacitive elements may be located on or within the microfluidic device. Typically, in such embodiments, both resistive and capacitive elements are electrically connected in series to form an RC circuit on or within the microfluidic device. Such a microfluidic device typically comprises at least one electrical contact corresponding to a first RC circuit lead 18 and at least one electrical contact corresponding to a second RC circuit lead 20. Each of the aforementioned electrical contacts may be configured, for example, as a pair of contacts, i.e., one as the first RC circuit sub-leads 18' and 18'' and the other as the second RC circuit sub-leads 20' and 20''. A diagnostic reader configured to operate such a microfluidic device comprises electrical contacts configured to engage with the electrical contacts of the microfluidic device. The diagnostic reader typically comprises a power supply, a switch system including a first switch and a second switch, and a switch system controller, as disclosed herein, for example.

[0050] Techniques for forming capacitive elements on or within microfluidic devices include, for example, inkjet printing, screen printing, and 3D printing. Exemplary materials for forming such capacitive elements include (i) carbon-based nanomaterials such as activated carbon, carbon black, carbon nanotubes, graphene, reduced graphene oxide, and graphene oxide, and (ii) Ti3C2T XExamples include ternary carbides and nitrides containing one or more transition metal elements, as well as hybrid materials such as (iii) carbon-based nanomaterials and materials containing metal oxides. Examples of capacitive elements (including appropriate materials and manufacturing techniques) that are placed on or inside microfluidic devices (e.g., by printing) include those disclosed in Advanced Materials, Volume 27, Issue 24, June 24, 2015, pgs. 3669-3675; ACS Nano 2019, 13, 1, 54-60; Sci Rep 9, 13324 (2019); and Chem Phys Mater, Vol. 1, Issue 1, January 2022, Pages 17-38. [Examples]

[0051] A heating system was fabricated to evaluate the ability to generate the same amount of heat from multiple resistive elements with different resistance values. The first test RC circuit was fabricated by connecting a 27Ω resistor and a 47μF nonpolar capacitor in series (RC=1.27ms). The second test RC circuit was fabricated by connecting a 150Ω resistor and a 47μF nonpolar capacitor in series (RC=7.05ms). Each resistor was a 1 / 8W carbon film resistor. Each RC circuit had a first circuit lead corresponding to the first circuit lead 18 of RC circuit 12 and a second circuit lead corresponding to the second circuit lead 20 of RC circuit 12. The first circuit lead of each test RC circuit was connected to output 2 of a Texas Instruments DRV8844PWP quad 1 / 2H bridge driver ("driver"), and the second circuit lead of each test RC circuit was connected to output 1 of the driver.

[0052] A constant (DC) power supply was used to input a 12V potential to the driver. A switch system controller (electronic processor) was used to input a control signal to the driver and switch the state of the internal switch. In response to the control signal, the driver simultaneously and alternately switched the polarity of the potential (12V) applied between each lead of each RC circuit in the heating system 10 as described above. Pulse period τ P The time constant was 28.2 ms, which is four times the length of the longest RC time constant of the two test RC circuits. The driver's current and potential capacitance were sufficient to prevent the driver from being overloaded when both RC circuits were operated simultaneously. Approximately 35 pulses per second were applied simultaneously to each circuit. The temperature of each resistor was monitored by its respective thermocouple, which was positioned to communicate thermally with the resistor. The resistors were thermally isolated from each other but exposed to the same ambient environment.

[0053] Referring to the temperature-time chart in Figure 5, the temperature of each resistor rose from ambient temperature (approximately 26°C) to approximately 65°C within approximately 2 minutes. The measured temperatures of each resistor were consistently within approximately 1°C of each other. Similar temperature profiles demonstrate the system's ability to dissipate a constant average power from the resistors, independent of their resistance values. Ripples in the temperature-time curve are thought to be due to airflow generated by the computer cooling fan. After the heating system was switched off, the temperature of each resistor returned to ambient temperature within approximately 2.5 minutes. Each 1 / 8W resistor has a much larger heat capacity than the ink-based resistor elements deposited on the surface of the diagnostic device. Therefore, the resistor elements of such a diagnostic device are expected to heat and cool much faster than the 1 / 8W test resistors used in this embodiment.

[0054] The aspects of this disclosure are defined in the following numbered sections: 1. A method for heating the reaction zone of a microfluidic strip, The method involves positioning a microfluidic strip at an operating position within a diagnostic reader, wherein the microfluidic strip comprises (i) a microfluidic network including a reaction zone, and (ii) a resistor attached to the surface of the microfluidic strip so as to be thermally in communication with the reaction zone, the resistor having a resistance value R. The resistor and capacitor placed within the diagnostic reader of the microfluidic strip are connected in series to form an RC circuit having a first RC circuit lead and a second RC circuit lead, wherein the capacitor has capacitance C and the RC circuit has an RC time constant = τ RC Having, The method involves preparing a reaction mixture within the reaction zone of a microfluidic strip, wherein the reaction mixture comprises a liquid sample and at least one reagent. A constant potential V exists between the first power supply lead and the second power supply lead located within the diagnostic reader. PS To generate and maintain, A constant potential V exists between the first supply lead and the second supply lead. PS While maintaining this, the reaction zone is heated by performing the following steps alternately and repeatedly, thereby passing 2 × C × (V) across the resistor. PS ) 2 / τ P To consume the average power: (1) Connect the first supply lead to the first RC circuit lead, and the second supply lead to the second RC circuit lead, approximately 4 × τ RC time τ P The process of connecting between them, and (2) Connect the second supply lead to the first RC circuit lead, and the first supply lead to the second RC circuit lead, for a time τ P The process of connecting during A method that includes this. 2. The method according to Section 1, comprising the step of heating the reaction zone for a period of approximately 10 seconds to 6000 seconds. 3. The method according to Section 1 or 2, wherein the step of heating the reaction zone includes performing each of the connection steps (1) and (2) about 10 to 50 times per second. 4.V PSThe method described in any one of sections 1 to 3, wherein the voltage is approximately 5 volts to approximately 25 volts, for example, approximately 12 volts. 5. The resistance value of the resistor is approximately 20Ω to approximately 200Ω, as described in any one of sections 1 to 4. 6. The capacitance of the capacitor is approximately 20μF to 75μF, as described in any one of sections 1 to 5. 7. The method described in any one of sections 1 to 6, which includes consuming an average power of approximately 0.2 watts to approximately 1.0 watt across a resistor. 8. The RC time constant is 7.5 ms, τ P =30ms, V PS The method described in any one of sections 1 to 7, wherein the voltage is 12V and the average power consumed is approximately 0.48W. 9. The heating step is the method described in any one of sections 1 to 8, which includes heating the reaction mixture to a temperature of approximately 40°C to approximately 100°C. 10. The method according to any one of sections 1 to 9, wherein the ambient gas temperature surrounding the microfluidic strip is approximately 20°C to approximately 30°C, and the heating step includes heating the reaction mixture to a temperature approximately 20°C to approximately 80°C higher than the ambient temperature. 11. The resistive material is a carbon ink-based resistive material, a silver ink-based resistive material, a metal oxide strip, or a combination thereof, as described in any one of Sections 1 to 10.

[0055] All publications, patents, patent applications, and other documents cited herein are incorporated herein by reference in their entirety, and to the same extent as individual publications, patents, patent applications, or other documents are incorporated herein by reference. Although various specific embodiments have been illustrated and described, the above specifications are not limiting. It will be understood that various modifications are possible without departing from the spirit and scope of this disclosure. Many modifications will be apparent to those skilled in the art who have referenced these specifications.

Claims

1. A method for heating at least one of the reaction zone, valve, or gas chamber of a microfluidic strip, The method involves arranging a microfluidic strip at an operating position within a diagnostic reader, wherein the microfluidic strip comprises (i) a microfluidic network comprising at least one of a reaction zone, a valve containing a thermally responsive material, and a gas chamber configured to move a liquid within the microfluidic network when the gas inside is heated, and (ii) a resistor disposed to communicate thermally with at least one of the at least one reaction zone, valve, or gas chamber, the resistor having a resistance value R. The resistor and a capacitor located on or within the microfluidic strip or within the diagnostic reader are connected in series to form an RC circuit having a first RC circuit lead and a second RC circuit lead, wherein the capacitor has capacitance C and the RC circuit has an RC time constant = τ ＲＣ Having, Heating the at least one reaction zone, valve, or gas chamber that is thermally in communication with the resistor by alternately and repeatedly performing the following steps: ＰＳ This is the potential between the first power supply lead and the second power supply lead located within the diagnostic reader: (1) Connect the first supply lead to the first RC circuit lead and the second supply lead to the second RC circuit lead, approximately 2 to approximately 5 × τ ＲＣ time τ Ｐ１ Connected during the time τ Ｐ１ During this time, the potential between the first supply lead and the second supply lead is set to approximately V ＰＳ The process of maintaining, (2) Connect the second supply lead to the first RC circuit lead, and connect the first supply lead to the second RC circuit lead for a time τ of about 2 to about 5×τ ＲＣ of time τ Ｐ２ and maintain the potential between the first supply lead and the second supply lead at about V Ｐ２ during the time τ ＰＳ ; As a result, approximately 2 × C × (V) is distributed across the resistor. ＰＳ ) ２ / ((τ Ｐ１ +τ Ｐ２ Consuming the average power of ) / 2) A method that includes this.

2. The method according to claim 1, further comprising the step of heating the reaction zone, valve, or gas chamber for a period of about 10 seconds to 6000 seconds.

3. The method according to claim 1 or 2, wherein the step of heating the reaction zone, valve, or gas chamber includes performing each of the connection steps (1) and (2) about 10 to 50 times per second.

4. V ＰＳ The method according to any one of claims 1 to 3, wherein the voltage is approximately 5 volts to approximately 25 volts, for example, approximately 12 volts.

5. The method according to any one of claims 1 to 4, wherein the resistance value R of the resistor is approximately 20 Ω to approximately 200 Ω.

6. The method according to any one of claims 1 to 5, wherein the capacitance C of the capacitor is approximately 20 μF to approximately 75 μF.

7. The method according to any one of claims 1 to 6, comprising consuming an average power of about 0.2 watts to about 1.0 watt across the resistor.

8. The aforementioned RC time constant is approximately 7.5 ms, τ Ｐ１ and τ Ｐ２ Each is approximately 30 ms, V ＰＳ The method according to any one of claims 1 to 7, wherein the voltage is approximately 12V and the average power consumed is approximately 0.48W.

9. The method according to any one of claims 1 to 8, wherein the heating step includes heating the at least one reaction zone, valve, or gas chamber that is thermally in communication with the resistor to a temperature of about 40°C to about 100°C.

10. The method according to any one of claims 1 to 9, wherein the ambient temperature of the gas surrounding the microfluidic strip is about 20°C to about 30°C, and the heating step includes heating the at least one reaction zone, valve, or gas chamber that is thermally in communication with the resistor to a temperature about 20°C to about 80°C higher than the ambient temperature.

11. The method according to any one of claims 1 to 10, wherein the resistor is a carbon ink-based resistor, a silver ink-based resistor, a metal oxide strip, or a combination thereof.

12. The method according to any one of claims 1 to 11, wherein the capacitor is located within the diagnostic reader.

13. The method according to any one of claims 1 to 11, wherein the capacitor is located on or within the microfluidic strip.

14. τ Ｐ１ and τ Ｐ２ The method according to any one of claims 1 to 13 is substantially the same.

15. The method according to any one of claims 1 to 14, wherein the thermally responsive material is a gas.

16. The method according to any one of claims 1 to 14, wherein the thermally responsive material is a wax, an oil, a hydrogel, or a thermally responsive polymer.

17. A system for heating at least one of the reaction zone, valve, or gas chamber of a microfluidic strip, comprising an RC circuit and a constant potential V ＰＳ A system comprising a DC power supply and a switch system operable to supply a DC power supply, and configured to perform the method according to any one of claims 1 to 16.

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