The present invention relates to micro-fluid applications. More particularly, it relates to point-of-care and lab-on-a-chip devices having functional modules that enable diagnostic solutions.
Various diagnostic platforms utilize thermal cycling processes which involve heating of reagents at different temperatures to alter certain properties of the reagents. An example application is Polymerase Chain Reaction (PCR) which is a method used to amplify genetic material for detection and analysis. Analysis speed is especially important in diagnostic applications. For example, shorter analysis time would allow faster turnaround time in identifying infectious diseases, or enable the analysis to take place in the time it takes for a physician's appointment.
Thermal cycling methods generally fall under two categories: stationary and continuous flow. Stationary systems conduct thermal cycling by holding a fixed volume of sample fluid and/or reagents stationary in a chamber while varying the temperature of the chamber to alternately heat and cool the reagents. A disadvantage of this kind of thermal cycling is reduced amplification efficiency due to heating and cooling ramping rates associated with varying the chamber temperature during each cycle. Continuous flow systems, on the other hand, conduct thermal cycling by allowing fluid samples to flow through different temperature regions. In particular, each temperature region maintains a distinct temperature and reagents are allowed to pass through the temperature regions for a number of cycles by propelling them, using pumps, to flow through a long channel having sections formed on each temperature region. Delay in inter-temperature transition time can be reduced by controlling the flow rate of fluids within the channel. As a result, continuous flow systems can shorten analysis times compared to stationary thermal cycling.
A number of micro-fluidic approaches to diagnostic applications utilizing continuous flow thermal cycling have been developed for lab-on-a-chip and point-of-care devices. Micro-fluidic devices manipulate microscopic volumes of liquid inside micro-sized structures. As such, it can provide advantages over conventional and non-micro-fluidic based techniques such as smaller sample volumes, greater efficiency of chemical reagents, high speed analysis, high throughput, portability and low production costs per device allowing for disposability.
Micro-fluidic modules can be built by combining several components like channels, connectors, filters, mixers, heaters, sensors, micro-valves, micro-fluidic pumps, and etc. Among these components, it is well known to be difficult to attain micro-fluidic pumps which are ready to be assembled with micro-fluidic devices at low costs. For example, while a range of micro-fluidic devices have been miniaturized to the size of a postage stamp, these devices have often required large external pumping systems for fluid transport through channels. Unfortunately, the inclusion of these external pumps presents added complexity in coupling with fluidic channels, and also often increases the overall size of the micro-fluidic system.
Thus, there is a need for a micro-fluidic system which integrates together functional modules, such as pumps and micro-fluidic structures, to provide reliable and even smaller device footprint for point-of-care diagnostic and lab-on-a-chip applications. Additional benefits and alternatives are also sought when devising solutions.
The above-mentioned and other problems become solved by forming pump modules and fluidic structures monolithically on a substrate to provide a micro-fluidic system on a chip. Example embodiments contemplate diagnostic solutions for polymerase chain reaction (PCR).
In a representative embodiment, a chip having a substrate for amplifying genetic material includes a substrate heater having a plurality of substrate heating resistors. The heating resistors define a first temperature zone for maintaining a first temperature, a second temperature zone for maintaining a second temperature below the first temperature, and a third temperature zone for maintaining a third temperature between the first and second temperatures, on the substrate. A flow path formed on the substrate allows conveying of reactions to the first temperature zone, the third temperature zone, and the second temperature zone so as to undergo denaturing, annealing, and extension, respectively, according to a PCR process, for at least one cycle.
In an example aspect, the flow path is formed by a flow feature layer disposed above the substrate heater. In another example aspect, one or more pumps are disposed along the flow path for compelling the reactions to move along the flow path.
These and other embodiments are set forth in the description below. Their advantages and features will become readily apparent to skilled artisans. The claims set forth particular limitations.
The accompanying drawings incorporated in and forming a part of the specification, illustrate several aspects of the present invention, and together with the description serve to explain the principles of the invention. In the drawings:
In the following detailed description, reference is made to the accompanying drawings where like numerals represent like details. The embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It is to be understood that other embodiments may be utilized and that process, electrical, and mechanical changes, etc., may be made without departing from the scope of the invention. The following detailed description, therefore, is not to be taken in a limiting sense and the scope of the invention is defined only by the appended claims and their equivalents. In accordance with the features of the invention, a micro-fluidic system for thermal cycling integrates pump modules and fluidic structures on a single chip to enable diagnostic solutions. The modules are monolithically fabricated on a substrate using inkjet technology and heater chip fabrication techniques. In the following embodiments, representative diagnostic solutions contemplate a case study for polymerase chain reaction (PCR).
PCR is a process by which genetic material, such as DNA, is amplified exponentially for detection and analysis. PCR relies on cycling a mixture of ingredients including DNA sample, primers, and enzymes used for DNA synthesis, among others, through a series of repeated temperature changes, called cycles, to repeatedly heat and cool the mixture of ingredients. Typically, PCR has three thermal control steps/points for each cycle: denaturing, hybridization/annealing, and extension. During denaturing, a heating temperature above 90° C., such as from about 94° C. to about 98° C., breaks a double-stranded DNA molecule into two complementary single-stranded DNA molecules. In the annealing step, the single-stranded DNA molecules are cooled at a lower temperature from about 50° C. to about 65° C., such as about 60° C., to allow DNA synthesis whereby the single-stranded DNA molecules seek their complementary strands (designed primer) to create incomplete double-stranded DNA molecules. During the extension step, reactions are heated at a heating temperature above 65° C., such as from about 70° C. to about 75° C., so that the incomplete double-stranded DNA molecules are extended with the help of an enzyme called DNA polymerase. The cycle is then repeated a number of times to achieve a desired amount of amplification of the DNA material.
Referring now to
Pumps 60 are disposed along portions of channel 35 to propel fluid to flow the channel. In an example embodiment, each of pumps 60 includes a plurality of resistive heaters 65 (65-1, 65-2, . . . , 65-n) formed on heater layer 20 and along a corresponding channel portion, as shown in
In
The heating elements 70 are in thermal contact with the substrate 15 and the substrate 15 should be thermally conductive to dissipate heat from the heating elements 70. In operation, heat generated by the heater elements 70 travel through the substrate 15 and spreads out to each corresponding temperature region 40. Vertical heat flow from the substrate 15 dominates the temperature of the regions 40 and is used to heat fluids flowing through corresponding channels above the substrate 15. Trenches 45 serve to interrupt the travel of heat between temperature regions 40 to provide thermal stability. Additionally, heat sink 80 helps hold the lateral region to region heat flow to a minimum. In particular, with differing temperatures applied to each temperature region 40, a temperature gradient can be formed between adjacent temperature regions. Heat sink 80 collects heat residue between adjacent temperature regions 40 in order to substantially minimize the temperature gradient between regions.
Referring now to
More particularly, for each temperature region 40, a thermal control system 100 includes a preset temperature reference source 105. Preset temperature reference source 105 can be an 8 bit digital to analog converter (DAC) connected to a serial peripheral interface, for example, that provides a desired temperature set point current input I(set) used to set the target temperature for a corresponding temperature region 40. Thermal control system 100 also includes at least one temperature sensor 110 that senses and provides actual substrate temperature readings in the form of a current input I(sense). Temperature sensor 110 can be an active circuit composed of CMOS transistors and substrate PNP which produces an output current proportional to absolute temperature sensed. In
To provide more accurate temperature coverage of an entire length of a temperature region 40, each temperature region 40 may be divided into a plurality of zones with each zone having an associated temperature sensor. For example, as shown in
Once the temperature sensors 110 are calibrated, the preset temperature reference current input I(set) is used to set the target temperature of each zone Z via a preset temperature sink 120. In particular, current input I(sense) from temperature sensor 110 and current input I(set) from preset temperature sink 120 combine to produce a current output I(diff) which is the difference between the current inputs. Essentially, current output I(diff) represents a difference between the target temperature and the temperature sensed by the temperature sensor 110. A pulse width modulation (PWM) generator 125 receives the current output I(diff) and outputs a pulse width modulated heat pulse PWM(heat) that is proportional to the current output I(diff). An AND gate 130 receives the heat pulse PWM(heat) at its input 130A. The other input 130B of AND gate 130 can be an enable signal for heating.
In an example embodiment, PWM generator 125 can be controlled to provide a set of quantized PWM signals during an initial thermal ramp up to a set point temperature. For example, PWM generator 125 could have a 5 phase quantized PWM signal having pulses with duty cycles of 100%, 75%, 50%, 25%, and 0%, during the initial ramp. The duty cycle is proportional to the current output I(diff) as discussed above. In this way, a smaller delay before reaching the set point temperature can be achieved.
Thermal control system 100 further includes a switch 140 connected to an output 130C of AND gate 130. The gates of switch 140 are driven by drive pulses P(drive) so that it periodically activates a connected heater element 70 to produce heat pulses that are delivered to the substrate 15. Heat then spreads throughout the substrate temperature region. Process then loops until the current I(sense) at each temperature sensor 110 is equal to the desired set current I(set) of the preset temperature sink 120 which corresponds to the required temperature for the temperature region 40. Accordingly, when the current input I(sense) from the temperature sensor 110 substantially equals the current I(set) from the preset temperature sink 120, the region is at its target temperature.
Thermal isolation structures, i.e., trenches 45, and heat sink 80 provide added stability in the thermal control.
CF-PCR device 10 is fabricated on substrate 15. The preferred substrate is silicon, which allows forming logic circuits together with the pumps and micro-fluidic structures. In addition, silicon provides high thermal conductivity to conduct heat from the heaters and heat fluids above it. The heating elements 70 associated with each region 40 and resistive heaters 65 associated with each pump 60 are formed by layers or films of semiconductor and other suitable materials formed or deposited, by using known micro-electronic fabrication techniques, on the substrate 15. For example, such heater elements 70 can be constructed in a similar fashion as the resistive heaters 65 as disclosed in U.S. Pat. No. 8,172,369, the contents of which are hereby incorporated by reference. Logic circuits to control heaters are formed on the substrate 15 by silicon processing. The heaters are then formed with the fluidic structures. A silicon dioxide is grown or deposited as the support material 75 on top of the substrate 15 (and alternatively over the heaters). A photoimageable polymer, for example, SU-8 (MicroChem, Newton, Mass.), is used to form the flow feature layer 25. For the cover layer 30, a photoimageable dry film, for example, VACREL™ (DuPont) is used and applied onto the flow feature by a lamination process. Inlet and outlet ports that align with inlets 50 and outlets 55 can be formed by either deep reactive ion etching (DRIE) or a photolithography process. By DRIE, an inlet port and an outlet port can be formed by etching holes through the substrate. In this case, liquid is fed into inlets 55 and the channel 35 from the backside of the substrate 15. An inlet port and an outlet port can be formed on the top side of the CF-PCR device 10 by patterning the flow feature 25 and cover layer 30. In addition, both DRIE and photolithography processes can be used to make an inlet port on the top side and outlet port on the backside of the CF-PCR device 10. A highly thermal conductive material, such as Al, aluminum alloys, Cu, diamond or composite materials like copper-tungsten, can be used for heat sink 80 beneath substrate 15.
Referring now to
In operation, fluids are propelled by pumps 260 through the looped channel 235 to pass through each of the thermal regions 240 to complete one thermal cycle. Depending on the required heating time, PCR reaction mixtures can be allowed to dwell within wells 237 of a thermal region 240 by deactivating pumps 260. Pumping can be continued to allow PCR reaction mixtures to repeatedly pass through the different thermal regions 240 for a required number of cycles depending on the amount of amplification desired. Pumps 260 can be controlled to pump fluids in a coordinated manner to properly direct fluid flow to desired fluid paths. For example, pumps 260A and 260B can be controlled to push fluids from left to right along channel portions 235A and 235B, respectively, while pump 260C is controlled to push fluids from right to left along a channel portion 235C to compel fluids within well 237 of thermal region 240A to flow towards channel portion 235B. Meanwhile, as pump 260B along channel portion 235B is controlled to push fluids from left to right, pumps 260D and 260E along channel portions 235D and 235E, respectively, can be controlled to push fluids from right to left to prevent fluids from flowing into outlet 255 and instead compel fluids within the wells 237 of thermal region 240B to flow towards channel portion 235F. To allow fluid flow into outlet 255, at least each of pumps 260B, 260D, and 260E can be controlled to push fluid from left to right to compel fluid within wells 237 of thermal region 240B to flow into outlet 255. As will be appreciated, other techniques for controlling the pumps to convey fluids within the channel can be implemented.
Referring now to
Thermal control system 300 includes a temperature set point register 305 for holding a binary value B(set) corresponding to a target temperature. Thermal control system 305 also includes at least one temperature sensor 310 that senses and provides actual substrate temperature readings of a thermal region. Temperature sensor 310 can be an active circuit composed of CMOS transistors and substrate PNP which produces an output current I(sense) proportional to absolute temperature sensed. In
Thermal control system 300 further includes an analog to digital converter (ADC) 315 that receives I(sense) from temperature sensor 310. ADC 315 can be an 8 bit ADC that samples and cycles through each thermal zone, sampling the output current I(sense) of temperature sensor 310 and converting it to an 8-bit binary value B(sense). A subtractor 320, which can be a 2's complement subtractor, receives as inputs the target temperature binary value B(set) from the temperature set point register 305 and the binary value B(sense) from ADC 315, and returns a value B(diff) that corresponds to the difference between the two inputs to a quantizer 325. Essentially, output B(diff) represents a difference between the target temperature and the temperature sensed by the temperature sensor 310. Quantizer 325 converts the difference output B(diff) of substractor 320 to a quantized PWM output P(drive) whose width is proportional to the difference output B(diff). The quantized PWM output P(drive) of quantizer 325 is then used to drive a switch 330 so that it periodically activates a connected heater element 270 to produce heat pulses that are delivered to the substrate 215. Heat spreads through the substrate thermal regions and the process loops until the binary value corresponding to the current I(sense) at temperature sensor 310 is equal to the binary value of the register 305 which corresponds to the target temperature for the thermal region. When B(sense) substantially equals B(set), the thermal region is at its target temperature.
In another embodiment, a micro-fluidic PCR device 500 can have a top-side inlet 515 and bottom-side outlet 520, as shown in
Thus, micro-fluidic devices for point-of-care diagnostic and lab-on-a-chip applications are disclosed. The foregoing illustrates various aspects of the invention. It is not intended to be exhaustive. Rather, it is chosen to provide the best illustration of the principles of the invention and its practical application to enable one of ordinary skill in the art to utilize the invention, including its various modifications that naturally follow. All modifications and variations are contemplated within the scope of the invention as determined by the appended claims. Relatively apparent modifications include combining one or more features of various embodiments with features of other embodiments.
Number | Date | Country | |
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61684599 | Aug 2012 | US |