Music Box Diagnostics
ABSTRACT
Small volume fluid handling in single and multiphase microfluidics provides a promising strategy for efficient bio-chemical assays, low-cost point-of-care diagnostics and new approaches to scientific discoveries. However multiple barriers exist towards low-cost field deployment of programmable microfluidics. Incorporating multiple pumps, mixers and discrete valve based control of nanoliter fluids and droplets in an integrated, programmable manner without additional required external components has remained elusive. Combining the idea of punch card programming with arbitrary fluid control, here we describe a self-contained, hand-crank powered, multiplex and robust programmable microfluidic platform. A paper tape encodes information as a series of punched holes. A mechanical reader/actuator reads these paper tapes and correspondingly executes operations onto a microfluidic chip coupled to the platform in a plug-and-play fashion. Enabled by the complexity of codes that can be represented by a series of holes in punched paper tapes, we demonstrate independent control of 15 on-chip pumps with enhanced mixing, normally-closed valves and a novel on-demand impact-based droplet generator. We demonstrate robustness of operation by encoding a string of characters representing the word “PUNCHCARD MICROFLUIDICS” using the droplet generator. Multiplexing is demonstrated by implementing an example colorimetric water quality assays for pH, ammonia, nitrite and nitrate content in different water samples. With its portable and robust design, low cost and ease-of-use, we envision punch card programmable microfluidics will bring complex control of microfluidic chips into field-based applications in low-resource settings and in the hands of children around the world.
Significance Statement
The capacity to implement complex robust multiplex assays in resource poor settings devoid of skilled personnel, power sources and supportive infrastructure can revolutionize difficult to execute applications in global health, environmental monitoring and forensics, anywhere around the world. Combining microfluidics with programming using paper punch card tapes, here we present a novel integrated general-purpose fluidic platform to address specific challenges for resource-poor settings. Powered manually by a hand-crank, our device incorporates a single-layer microfluidic chip in a plug-and-play fashion and is programmed by a paper tape with punched holes as discrete instructions. In addition to the above-mentioned applications, we aspire to enable children to have access to “programmable chemistry kits” in science education settings globally.
The use of microfluidic technology, where small volumes of fluids are manipulated in carrying out miniaturized laboratory assays, has drawn considerable attention owing to inherent advantages that include minimized reagent consumption, miniaturized reaction volumes and the potential to yield robust and rapid results [1]. Application of microfluidics for robust multiplex diagnostic tests in extremely low-resource settings holds great promise but remains currently unfulfilled due to a variety of challenging factors including absence of electricity, lack of refrigeration for reagent storage, unavailable calibration services for devices over time, challenging operating conditions such as fluctuating temperatures and lack of skilled personnel [2]. There is an especially urgent need for multiplexed tests either to diagnose a disease caused by multiple agents, aid in the differential diagnosis of diseases that clinically present similarly or cases of co-morbidities due to a high disease burden in developing countries[2]. Therefore a successful implementation in these settings requires surmounting the above-mentioned challenges, using a platform that is completely self-contained and modular in nature, coupled with access to stable reagents that can be easily replenished.
CREDIT: Kurt Hickman
The capability for performing robust and inexpensive assays that are easy to replicate has applications beyond medical diagnostics. When coupled to the capacity to easily manipulate fluids in a programmable fashion that is easy to implement and run, one can envision new applications in science education settings worldwide. Hands-on introduction of chemistry and biology for school children can instill a life-long passion for science [3]. Although many current scientists admit to having been inspired by open-ended explorations utilizing chemistry kits widely available several decades ago, safety concerns and expensive reagents have made this exploration currently unavailable. Low-cost self-sufficient microfluidic technologies with enclosed chemicals and small-volume reagent reservoirs could potentially provide a wide-ranging solution to the problems mentioned above.
With the implementation of pneumatic micro-valves, it is now possible to run thousands of assays in parallel on the same microfluidic chip [4, 5]. Although significant progress has been made in development and manufacturing of complex microfluidic chips, current external control systems that are often required remain bulky and expensive [2,6]. A few applications for microfluidic devices in educational settings have been explored before, primarily focused on micro-fabrication techniques [7] while others have focused on applying existing platforms to teach principles of fluid dynamics [8]. However a gap still exists for a robust platform that can carry out complex multiplex assays yet being easy to program and use as desired.
To address some of the challenges brought about by specific constrains in low-resource settings, several novel approaches have been implemented, including a finger-actuated microfluidic pump device [9] and battery-powered implementation of pneumatic valves using solenoids [10]. While promising, such approaches are either limited in range of fluid manipulation or still utilize external solenoid valves that can significantly increase device costs and depend on electrical or battery power-source. Dipsticks and lateral flow assays and in general “paper microfluidics” have found greater success in low-resource point-of-care diagnostics [11–15]. Although often low-cost, portable and easy to use, they have limited capacity to run multiplex, complex or a wide range of protocols and are often not as quantitative as traditional microfluidic assays except when paired with specific external readers [16]. Furthermore, due to inherent design limitations of capillary flow in a porous medium, paper microfluidics often cannot take advantage of droplet-based assays that are highly sensitive due to further reduction in associated fluid volumes and discrete and isolated nature of trapped fluid samples inside droplets. To address all the challenges listed above, the ideal technology would therefore have the capacity to (a) run complex, programmable, multiplex assays while being self-contained, (b) be capable of handling large fluid volumes in applications where the biological sample has few targeted events, (c) operate with both single phase and multiphase microfluidics and (d) would not require specialized training or any other external equipment.
Here we present a programmable multiplex microfluidic system based on punch card programming that is hand-crank powered, low-cost, robust, and can run complex biological and chemical protocols with limited chances of human-error. Moreover, our system is rugged, portable, hand-held (weighing approximately 100 grams and measuring approximately 2 inches in length, 1.5 inches wide and 1 inch high) and is self-contained. The system does not require any external pumps or other supportive equipment to run. Multiple protocols can be run in parallel (multiple assays on the same sample or single assay on multiple samples), manipulating fluids arbitrarily with nanoliter volume precision. Because the program is encoded in punch card tape, the protocols can be easily shared like baseball cards to repeat or modify existing assays.
Our current implementation is inspired by punch card programming as historically applied in a wide range of applications beginning with control of textile looms [17], early computing [18] and music replay [19]. Punch cards enable the use of a single actuating platform to execute multiple programs resulting in implementation of complex instruction sets that can yield radically different outcomes by simply switching the punch card tape. Such a platform offers the flexibility of achieving multiple results without the need to redesign the system for new tasks. We have harnessed this approach and implemented it to manipulate fluids in a low-cost platform.
